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[
"How does a virus, such as chickenpox or HSV, physically damage the skin to cause blisters?"
] |
[
false
] |
[deleted]
|
[
"Usually a virus does not cause direct damage that you can see on a macroscopic level. The sores caused by some herpesviruses such as HSV1 are caused by self-directed immune responses which cause damage to your own body. "
] |
[
"Why at the skin though, does the virus concentrate in skin cells somehow?"
] |
[
"It has been a long time since I have learned about these. From what I remember HSV1 likes to reside latently in the trigeminal ganglia. If i remember correctly it migrates to the area around your lips, which is where cold sores occur due to the immune response against the virus. "
] |
[
"How is a male anglerfish not rejected by the female's immune system?"
] |
[
false
] |
So I know the has a rather unique reproductive strategy, where the male latches onto a female and atrophies until basically he is just his reproductive organs receiving nutrients from the female. As I understand it, at the attachment site their circulatory systems essentially connect. Looking now at humans, if I were to, say, lose a hand and have another person's hand grafted in its place, I would have a host of complications, the biggest being immunorejection of the new hand. Long story short, how are the attached males not rejected by the female anglerfish's immune system? I'm willing to accept that they are so evolutionarily removed from us that comparing our immune systems is apples and oranges (though a little further detail on that would be much appreciated).
|
[
"Hagfish and Lampreys (aka jawless vertebrates) have the most basic type of adaptive immune systems, however they do not have B cells or T cells. Instead, they use VLR (Variable Lymphocyte receptors) cassettes to recognize pathogens. However, plants and invertebrates have \"innate\" immunity that recognizes certain patterns that some pathogens may have. They cannot \"remember\" previous encounters with a pathogen that would initiate a fast immune response. ",
"Jawed vertebrates have a combination of innate and adaptive immune systems that allow us to deal with a large array of pathogens we may encounter ."
] |
[
"Alternate question. What's the most primitive form of animal with an immune system?"
] |
[
"While I am not an authority on vertebrate immunology, I am somewhat familiar with the subject and literature. The adaptive immune systems of all vertebrates have many similarities at the cellular and molecular level, although the organs differ considerably. Fish have T-cell receptors, MHC molecules, cytokines, and immunoglobulins. After doing a search, it appears that no research addressing immune compatibility has been done on genera of anglerfish that reproduce in the way you described. Therefore, we can only speculate as to how they are able to perform this behavior. ",
"But here is more information on their morphology and evolutionary history.",
"The best hypothesis I can give would likely involve limited polymorphism of MHC class I. If the male and female share the same MHC class I allele, their tissues would appear immunologically indistinguishable. This is similar to what is seen in Tasmanian devil facial tumour disease. Bites transfer cancerous cells from one individual to another, however their limited MHC diversity allows the cancer to appear as normal tissue leading to unchecked tumour growth. ",
"Source",
" ",
"Edit: According to ",
"this source",
", the males in some species of anglerfish retain their hearts and gills, suggesting they only rely on the female for nutrition. This calls into question if their vascular systems truly connect or have a type of selective barrier. While pictures of male-parasitized angler fish show considerable degeneration, much of the tissue growth around the female appears superficial. This article: \"Histology of the attachment between the parasitic male and the female in the deep-sea anglerfish Haplophryne mollis\" would help clarify the issue considerably if I had access to it. "
] |
[
"Antarctic Life, how did it get there?"
] |
[
false
] |
As far as I've read, there are only two flowering plants on Antarctica, and a bunch of various lichens and mosses and a handful of vertebrates. What's the theory on how all of this more evolved life (if that's the right term) got there? Like, did Antarctica split off from the other continents, or did animals/plants travel there, or something else? Furthermore, if Antarctica did split off from the other continents, does that mean that many species went extinct as it drifted south? Much thanks. Edit: How are the new plants and animals evolving? Is it too soon to be able to see notable changes yet?
|
[
"Antarctica is thought to have once been connected to both South America and Australia. It was probably populated my marsupials which originated in South America and ended up dominating Australia. As the continent drifted south and ocean currents changed, the climate became much colder and most life died off.",
"Edit: here's a link to an interesting PBS Eons episode about Antarctica: ",
"https://youtu.be/cC4WiBCoVeo"
] |
[
"Antartica used to be part of Gondwanaland along with South America and Australia. ",
"It also wasn't always frozen, in fact in the grand scheme of life on earth, it's only done so twice, first at the end of the Ordovician and again in the current ice age.",
"That isn't to say it hasn't always been cold, more like a modern temperate zone when the Earth was much warmer.",
"In fact, it had dinosaurs",
"Currently most of the life there is migratory, a variety of birds and marine mammals thanks to the nutrient rich water up welling from the deep."
] |
[
"Also to add to this they recently found fossilised remains of rainforest plants under the ice in some places so it almost certainly was not always a frozen desert like we see it today. \nIt would have been much warmer in the past."
] |
[
"Is it possible to determine our birthdate from our bodies through some biological/chemical/physical means?"
] |
[
false
] | null |
[
"The approximate age of a person can be determined a number of ways (prortion of naive T cells, growth plate presence in bone, etc.), but these approximations are all based on average values across many humans, so there isn't a way to get exact birthdate - usually you'd be looking at a 2-5 year window of age."
] |
[
"This is true, however the invasive surgery into the semi-circular canals should be avoided in any living patient."
] |
[
"Otoliths (acceleration-sensitive structures) are located way in the inner ear. In order to get to them, you'd have to do a lot of cutting. That's okay if you're doing an autopsy, but not okay if the subject is still alive."
] |
[
"Why are cats so much more focused on cleanliness than dogs? Is there an evolutionary advantage for cats to remain clean and no such advantage for dogs?"
] |
[
false
] |
I was watching the cat at my work clean herself today, and I realized that dogs only tend to lick themselves when they're wounded. They don't clean themselves the way cats do. If they're both predators I don't understand why it would be more beneficial for cats to remain clean and not for dogs to stay clean.
|
[
"Cats and dogs are predators, but they have very different hunting strategies.",
"Dogs are chasers. When they find prey, they run them down and kill them. Cats are pouncers. They lie in wait and strike when prey is in range.",
"The difference means that it's not very important to a dog if the prey knows there are dogs in the area because the dogs are going to chase the prey down if they run.",
"Cats are very particular about their hygiene and elimination so as not to drive the prey from their territory."
] |
[
"Related?",
"Cats do not like to eat near their water. Cats consider water that is near food to be contaminated. This goes back to the fact that cats are hunters. When they catch prey, things can get messy, leaving nearby water contaminated. While our indoor cats are not usually catching prey, the instinct of the hunter is still strong."
] |
[
"Could this be why many cats drink out of toilets and sinks rather then the water dish that is provided to them that is usually next to their food?"
] |
[
"What's the difference between photoelectric effect and photovoltaic effect?"
] |
[
false
] | null |
[
"The photoelectric effect refers to emission of electrons from one material into another, typically into a vacuum, although air photoemission (into a gas) or internal photoemission (from one solid through a barrier into another solid) also exist. The defining characteristic of photoemission is that the electrons are kicked into an unbound state and they are free to leave the material.",
"In the photovoltaic effect, electrons are excited but they remain in a bound state. These excited electrons do not leave the material but they move around in it until they find a place they can fall back into to release their energy. This can be a hole left in the electronic state of the material by the same or another elevtron after it was excited and moved away, but it can also be a contact with a lower lying energy level. In the later case, the electrons and holes piling up at the contacts generate a voltage and that's the photovoltaic effect."
] |
[
"For materials that can act as a photovoltaic, it depends on how energetic the photon that hits it is. For silicon, the band gap (the minimum energy to excite an electron for photovoltaics), is about 1 electron-Volt, which corresponds to the energy of a near infrared photon.",
"In contrast the work function of silicon for the photoelectric effect is 4.5 eV, which is in the ultraviolet. So everything less energetic than a UV photon, but more energetic than a near IR photon (i.e. visible light) will potentially contribute to a photovoltaic effect. Everything higher energy than UV (x-rays, etc) will be photoelectric."
] |
[
"THANK YOU! All of the other answers were great, but your answer was EXACTLY what I was looking for!"
] |
[
"How do scientists know that the red shift means the universe is expansing and it doesnt mean that other stars are moving away from us through empty space?"
] |
[
false
] |
How is the red shift of stars any diffferent than the red shift i would get if I launched a rocket away from earth wirh a bright light. Both indicate they are moving away from us?
|
[
"Those are both the same thing.",
"Imagine a round inflated party balloon with a bunch of ants crawling on it. If the ants move randomly, every ant tends to see about half the other ants moving away from it and half moving towards it, at various angles. In order for an ant to see ",
" the other ants moving away, one of two things would need to happen: Either (1) all the ants would have to decide to move away from that one ant, or (2) the balloon would have to be continuously inflating. But (1) gives that appearance ",
" to that one particular ant, whereas (2) gives the same appearance to ",
" the ants, so, from the point of view of an arbitrarily selected ant, (2) is scientifically more probable.",
"In the real world, the Universe is like the balloon, and galaxies/planets/etc are like the ants. The reasoning is the same."
] |
[
"The measured redshift increases with distance, which indicates not just that galaxies are moving away from us, but that that further galaxies are moving away ",
". What would cause galaxies to be moving away faster the further away from us they are? The expansion of the universe. "
] |
[
"To elaborate, the observed redshift could, ",
", just be observed because all of the distant galaxies conspired to be moving away from us at a velocity proportional to their distance from us. However, that would mean that there is a special point in the universe---us, right at the center. (At least, the center would be somewhere near our galaxy.) This is in serious odds with the Copernican principle---that is to say, that we are ",
" special, and all places in the universe are more or less the same. But more importantly, we have actually measured the distributions of galaxies and have seen that there is no special place; things really are pretty much uniformly distributed.",
"The choice is then between a huge coincidence: all places look pretty much the same but everything ",
" to be moving away from ",
" which doesn't look special at all; or space itself is uniformly expanding.",
"Besides, an expanding universe is totally generic in general relativity, and Einstein had a hard time making his model of the universe NOT expand. So the expansion of the universe as a simpler explanation for cosmological redshift wins on several counts.",
"Edit: as a couple replies have pointed out, I was slightly too quick with the argument that everything moving radially away implies a special point. Obviously, because we are not a special point and we see everything moving away from us, this is a possible outcome. The key is that there is ",
" for there to be no special point: the velocity of a galaxy must be directly proportional to its distance from us (up to a certain distance over which we can treat things non-relativistically; past that we need to use GR and things get complicated). The fact that Hubble found v proportional to d, and not d",
" or sqrt(d) or anything else, is what makes the expanding universe explanation compelling. (Besides all of the theoretical reasons that we understand in retrospect.)"
] |
[
"Why didn't reindeer herding catch on with the natives of Canada, like it did with the Sámi in Scandinavia?"
] |
[
false
] | null |
[
"The transition from hunter-gatherer to agricultural society is one of the most significant shifts a civilization can undergo. Historically, it seems to happen in warmer climates first, with more temperate climates transitioning later. (Why it happens this way is another question...) There are very few examples of it reaching as far north as sub-arctic climates before the industrial era.",
"North America seems to have lagged Eurasia in this transition, in general. (Again, another question, which ",
" tried to answer, although its conclusions are disputed.) But at any rate, in the western hemisphere, domestication of livestock didn't get much past the 30th parallels (approx. Mexico, Bolivia)."
] |
[
"The Saami were originally hunters, and traces of this such as trap ditches can still be seen. The transition to a cash economy was forced by the northwards expansion of Swedish control in the 18C. As a result of this, they moved towards herding. ",
"The lack of a similar change in North America may be as simple as different skins (e.g. beaver) being in demand for trade. ",
"There was a similar transition to a trade economy in Canada among the Inuit, leading to a change in kayak hunting methods to a more team based approach, with a corresponding change in the design of kayaks. ",
"Sorry this is a bit vague : it's from various snippets and archaeological studies rather than anything coherent. "
] |
[
"No, I was only talking about herding reindeer and accompanying them on their migration, treating them more as property than prey. I'm afraid I haven't read anything on when they came to be used as beasts of burden."
] |
[
"Why are mountains so tall in other planets?"
] |
[
false
] | null |
[
"Mars has lower gravity than earth so mountains can grow higher before the pull of gravity causes issues such as with Mauna Loa which due to its weight pushes down into the planets crust an additional 20K feet below the surface of the ocean."
] |
[
"Another important point about Mars is that it doesn't have plate tectonics. Olympus Mons has been able to grow to the heights it has because it hasn't moved relative to the hotspot underneath it."
] |
[
"Speaking specifically about Mars and other planets without an ocean: they don't have an ocean, and mountains on our planet are generally measured relative to sea level. While Mauna Kea measured from sea floor to peak is still much smaller than Olympus Mons, it is not hard to imagine tectonic or volcanic forces similar to those present on Earth to have created a \"larger Mauna Kea\", as measured from base to peak.",
"But as others have mentioned, the lack of as much erosion is another factor. It is also possible that Mars is no longer tectonically active (assuming that it was in the past, for which we do not have complete proof when last I checked), which could cause a volcanic hot spot to erupt in one place on the surface for a longer period of time - allowing Olympus Mons to grow ever bigger in one spot as opposed to a chain of volcanic islands forming as the tectonic plate moves. Lower gravity can also play a factor. This ",
"Space.com article",
" has links to a lot of sources undergirding these reasons."
] |
[
"If we never would've existed, would every lake in the world have different species of fish?"
] |
[
false
] | null |
[
"No, fish eggs can be transported around by ducks or other water fowl.",
"This happens all the time. Go ask a farmer. They will dig a hole, which turns into a pond after the groundwater fills it. A few years later it will be full of fish.",
"Over longer timescales you will have floods that allow different lake's fish to intermingle."
] |
[
"Are you trying to understand how humans affect the biodiversity of lakes?"
] |
[
"Would Every single lake in the world ever have different species? The odds of this are astronomically low, however, nonzero..."
] |
[
"Is dark matter affected by the gravity of black holes?"
] |
[
false
] |
Astrophysicists always talk on the abundance of dark matter in the Universe, so I started wondering what effect black holes would have on said dark matter. I understand that black holes also fall into the category of dark matter, but I'm talking about the abunant dark matter that allegedly surrounds everything, including galaxies. Would black holes affect dark matter similar to the way it affects matter??
|
[
"Yes. The one thing we know about dark matter is that it interacts gravitationally; that is how we detect it."
] |
[
"Dark matter has never been observed directly. It is a way to explain why measurements don't line up with theory. ",
"In theory, you can measure the light coming from different parts of a galaxy and determine how much stuff is there. Our sun is at least 99.8% of the mass of the solar system, so measuring the number of stars is a good estimate for the amount of stuff there is. If you know how much stuff is there, you can calculate how fast stars should be moving as a function of the radius from the center of the galaxy (it works the same for planets and satellites: GMm/r = 1/2 m v",
" solve for v ). ",
"You can also measure the Doppler shift of the light to determine if the star is coming toward you or moving away from you and about how fast it's moving. Stars are powered by Fusion, and fusion emits a distinctive color of light. The whole galaxy is generally swirling in the same direction. That distinctive fusion light on one side is red shifted because its moving away from you, stuff on the other side is blue shifted because its moving toward you. ",
"This is where things don't line up. With our current understanding of gravity and star life cycles, we expect stars near the middle of the galaxy to be moving very quickly, while stars near the edge are moving more slowly. ",
"What we actually observe is that stars are moving about the same Speed all the way to the edge of the galaxy. ",
"Here's a graph showing the difference.",
"The dotted line A is what we expected to see, based on the amount of stuff we estimate based on the light we see. The solid line B is what we actually see based on the color of the light.",
"So something about our theory isn't correct. The elements of it are: 1) how gravity works. 2) How star life cycles work and 3) The amount of stuff we can see.",
"Scientists are pretty confident they have gravity figured out (though there is some specualtion that things ",
"work differently",
" at the edge of a galaxy where acceleration is very very small.)",
"We've got a lot of stars in our own galaxy to confirm our model for the life cycle of stars, so that's probably not what's wrong with our theory. ",
"That leaves the final piece, maybe measuring the amount of light from a galaxy isn't enough to estimate the mass of that galaxy. Maybe there's stuff which doesn't emit light causing the difference. Lets just change our estimate to make the observation match the theory. How much mass would that take?",
"A whole lot. Something like twice as much as the matter we can observe. Wow. With that much stuff, were would it be!? Wouldn't it block some of the light from the galaxies? Shouldn't we see dark matter \"shadows?\" Also to make the graph from before look right, the matter needs to be in a \"halo\" or a cloud around the outside of the galaxy. That's weird due to how rotating bodies work. ",
"You know those giant funnels where you can put a coin in and watch it spin around and around? Some of them have two ramps to drop coins into them, facing opposite directions. When you drop in a bunch of coins all at once, the coins headed the same direction go a long time without bumping, but the coins coming at each other from different directions collide a lot. ",
"Now imagine those coins are giant hunks of matter. If they're swirling about a galaxy in all directions, forming a cloud or halo, there will be collisions. That's why galaxies and solar systems are more or less all in the same plane (flat like pancakes). If we want to have a WHOLE LOT of matter that we can't see out there in a cloud, it has to behave differently than any other matter we can see, it has to be \"non-self-interacting\" meaning, it can't bump into other matter. ",
"So we have a bunch of matter that doesn't bump into itself, doesn't block light, and hangs out in a big cloud around galaxies. That is not like any matter we have ever observed on earth. That is DARK MATTER. The only way we can detect it (so far as we know) is by seeing weird gravitational effects. ",
"Source: was an undergrad research assistant who worked on the galactic rotation curve problem."
] |
[
"that is how we detect it.",
"Should read: this is how some believe observations should be interpreted."
] |
[
"How can the observable universe be larger than the age of the universe?"
] |
[
false
] |
I was reading the Wikipedia article on the universe and it states two things that seem contradictory to me. The radius of the observable universe is 47 billion light years. The age of the universe is 13.7 billion years. How do we observe things that occurred more than 13.7 billion years ago? Here's the page:
|
[
"The universe is expanding."
] |
[
"The most distant thing we can see is the Cosmic Microwave Background. The light from it traveled 13.7 billion light years to get to us. However, the matter that emitted that light is now 45 billion light years from us. This is because the metric expansion of space can result in the distance between two objects increasing at more than 299,792,458 meters per second."
] |
[
"As the others have said, it's because of the expansion of space itself - a concept that's really hard to grasp if you've never taken a general relativity class (I've taken a class that did GR for the last 3 weeks or so and I don't really understand it)",
"Link that might explain it for you: ",
"http://en.wikipedia.org/wiki/Observable_Universe#Misconceptions"
] |
[
"Does \"slow light\" age?"
] |
[
false
] | null |
[
"The popular picture that photons in a material are constantly absorbed and emitted cannot account for a lot of what happens when light interacts with solids/liquids. If you think about it, how could this essentially random process generate a consistent speed of light in a material, which can be expressed as the refractive index? There are explanations based on interactions of the effective electric field of the atoms inside the bulk material and the electromagneric field of the incident light. Or if you prefer a quantum explanation, photons convert to lattice excitations inside the material which have effective mass and thus travel slower than c. Upon exit the lattice excitation converts back to photons which continue to travel at c."
] |
[
"The popular picture that photons in a material are constantly absorbed and emitted cannot account for a lot of what happens when light interacts with solids/liquids. If you think about it, how could this essentially random process generate a consistent speed of light in a material, which can be expressed as the refractive index? There are explanations based on interactions of the effective electric field of the atoms inside the bulk material and the electromagneric field of the incident light. Or if you prefer a quantum explanation, photons convert to lattice excitations inside the material which have effective mass and thus travel slower than c. Upon exit the lattice excitation converts back to photons which continue to travel at c."
] |
[
"Indeed, which is exactly what I said above, that the photons are absorbed and emitted by atoms and vibrational modes. It's true that the latter plays a larger role, but I was simply trying to answer OPs question and the interaction of electromagnetic fields with solids is extremely complicated"
] |
[
"What are the possible consequences to a baby's immune system who was born into quarantine?"
] |
[
false
] |
Let's say that the baby was born at the hospital, went home the same day and has had contact only with their parents since then. Is it possible (or probable) that this baby will have a compromised immune system compared to babies who go out and see other people if they stay in quarantine for, say, 6 months? One year?
|
[
"Not necessarily, but it will depend on 3 things: If the baby was naturally born, if the mother breastfeeds, and if they vaccinate.",
"Last I checked, it was still being researched, but natural birth introduces some bacteria to the baby that is beneficial (I’d have to do some research, though; Ob-Gyn isn’t my focus).",
"Breast milk, especially the milk produced the first few days after birth, is rich in the mothers antibodies giving the child a limited passive immunity to anything the mother has been exposed to.",
"These are time sensitive, though, since the baby’s immune system isn’t developed yet. The antibodies clear out - and without exposure to the actual pathogen baby won’t produce innate antibodies. This is where the vaccination schedule comes in. Each shot is timed to coincide with when the baby loses it’s passive immunity (e.g. Whooping cough immunity is only 2mo and that’s the first shot. Measles, mumps, and Rubella last a year; and that’s why we give the MMR at 1 yr).",
"Once the baby has an active immune system then it’s time to let the kids get dirty. Play on the mud, play outside, play with puppies. The more natural exposure results in increased natural resistance on top of immunizations (and some immunologists theorize that this will lead to decreased allergies down the road)."
] |
[
"FYI, most pediatricians want you to wait a few weeks/months before taking your baby out in public anyway. They are not vaccinated at birth so they are highly susceptible. So in that respect it's not that different. The baby will already be exposed to the rest of the family members, they are not in isolation so they will still be exposed."
] |
[
"There's also plenty of bacteria in the home; it's not like a house or apartment is perfectly sterile and we only encounter microbes on the street."
] |
[
"When two light beams distructively interfere, where does their energy go?"
] |
[
false
] | null |
[
"when two beams of light destructively interfere, they only do so in ",
" location. There will always be other locations in the optical system where there is constructive interference which contain the seemingly missing energy. The entire system still contains the same amount of energy when you take all interferometer outputs into account.",
"Source: My MS thesis research was all interferometry (i did research related to LIGO)"
] |
[
"If you have two sources of waves, there is only ",
" way that they could destructively interfere - if the sources occupy the same spot. In that case, the system is indistinguishable from not having any waves at all.",
"If you have two spatially separate sources, you will never get destructive interference throughout all space."
] |
[
"not ",
", no. It would be more correct to say that some parts in the optical system experience constructive interference, while corresponding parts experience destructive interference."
] |
[
"Does gut bacteria affect our taste?"
] |
[
false
] |
[deleted]
|
[
"I'm a grad student in the microbiome field and I have never heard of anything like that. Peanut allergies are not (directly, at least) caused by gut bacteria or digestion - they are the result of an immune system reaction to something in the peanuts.",
"I would guess you hate peanuts because you associate them with medical emergencies? Also some people just don't like them, especially non-Americans."
] |
[
"I can't speak to the nature of bacteria enhancing flavor detection, but I believe flavor would be more affected by oral microbiomepopulations more than gut. I just read an NPR article about dog olfaction and it mentioned human sense of smell as mostly connected to flavor/taste via a process of retro-olfaction, I think. ",
"As far as as allergies go, there's a protein (in your instance, in peanuts) that your immune system has identified as a potential threat which then sets off a cascade of steps in the immune response leading to hives, labored breathing, itchiness, swelling, etc. "
] |
[
"Oh right! I believe the protein is what causes an immune response (I can have peanut oil, just not actual peanuts). Thanks for the insight!"
] |
[
"Shouldnt everyone get checked on toxoplasmosis and treated?"
] |
[
false
] | null |
[
"Whether something should or shouldn't be done is a matter of policy and should be addressed to a different sub. Perhaps there is a medical or health policy sub."
] |
[
"This is not a policy question but a risk assesment depending on if my viewpoint is right.",
"I can reformulate it, if you want."
] |
[
"In general, we also do not allow posts asking for medical advice so questions of the form \"should I be screened for X?\" would not pass muster either. Perhaps something along the lines of \"what is the incidence of X\" or \"are cases of X increasing?\" would work"
] |
[
"How do bubbles seem to magically appear in fizzy alcoholic drinks? Why are they generally sourced near the bottom and sides of the glass?"
] |
[
false
] |
My best guess that is the magic bubble appearance is based somewhat on saturation of the internal liquid, but it's worth wondering why the same bubble stream doesn't happen with soft drinks. Assuming it is the saturation, why does it happen at the bottom and sides of the glass, and not all throughout?
|
[
"What you observe is a describe case of a more general effect where bubbles preferentially form at interfaces or rough patches of a given vessel. First of all, consider why bubbles form in the first place. In the beginning carbonated drinks are ",
"supersaturated",
" in CO2, meaning that they have a higher concentration of the gas than is energetically favored. As a result, CO2 molecules have a natural tendency to escape from the solution, but to do so they must first come together (coalesce) to form bubbles, which can then escape.",
"The problem is that the rate of bubble formation is normally rather slow. The reason is that while it may be energetically favorable for the bubbles to form, the initial formation of the bubbles (a process called ",
"nucleation",
") requires an input of energy (the so called activation energy), which can be substantial, ",
"as shown in this diagram",
" (where the gas in solution is the reactant, the bubbles are the product and the initial hump labelled Ea is the activation energy). Because of this activation energy, the process of bubble formation becomes fairly slow. This is why beer doesn't go flat immediately and why glasses of champagne can produce bubbles over the course of more than an hour. ",
"However, nucleation can happen much faster around areas of inhomogeneity in a medium (e.g. near interfaces, kinks, or rough surfaces), in a process called ",
"heterogeneous nucleation",
". The reasons for this are rather complex and case dependent, but the net result is that the activation barrier for nucleation becomes less than what it is in the bulk. Furthermore, once you start forming bubbles, the bubbles perturb the environment in such a way that you increase the rate of nucleation for new bubbles. In other words, bubbles that create other bubbles, which results in a visible stream of bubbles. You see a similar effect when you dip your finger in a carbonated solution as seen ",
"here",
"."
] |
[
"The ",
"etched logos",
" you see at the bottom of some branded pint glasses provide nucleation points, ensuring that their product looks appropriately bubbly and appealing. "
] |
[
"Cool, so my beer would stay carbonated longer in a supersmooth glass? "
] |
[
"What happens to the human body when a person comes in contact with nuclear materials/extreme radiation?"
] |
[
false
] |
[deleted]
|
[
"Wikipedia on radiation poisoning.",
"Wikipedia on NBC suit"
] |
[
"There are a variety of radiation sources, and each acts differently.",
"Gamma radiation and Beta Radiation act similarly to light: They can be fairly easily blocked (Gamma by several feet of concrete, beta by clothing or a thin wall). Both can cause immediate burns as well as cancers by damaging DNA.",
"Alpha radiation and isotopes of compounds can cause heavy metal diseases and cancers by interactions with DNA. Particularly, radioactive iodine can accumulate in the thyroid and cause thyroid cancer.",
"Those suits can't protect from a nuclear blast, but can protect against alpha and isotopic radiation."
] |
[
"Well I can answer your first question. Radiation is just one a list of \"effects\" and compounds that are termed mutagenic. The main idea is that these things generate mutations in your DNA. How it exactly works is probably beyond my scope (I guess it has to do with inducing kinks in the backbone?). But the effects of mutations may or may not be detrimental and they may or may not become readily apparent. It could result in cancer, radiation sickness, or perhaps even genetic diseases (oh so very rarely). "
] |
[
"Wouldn't plants be more efficient at gathering light if their leaves were black?"
] |
[
false
] |
From what I understand the colours we see are the non-absorbed wavelengths of visible light, meaning the green we see is light energy the chloroplasts are not utilising. If plants leaves were black wouldn't they gaining more usable energy?
|
[
"It would be more useful to take advantage of the full spectrum, but apparently evolution seems to have trapped plants in a different solution. ",
"Bacteriorhodopsin",
" is a simpler light harvesting complex found in archaea, and it absorbs in a single broad peak centered in the green region. Archaea that use it are typically extremophiles, so if you ever saw a ",
"salt pond",
" from the air that is why it has a magenta (i.e. red+blue, since green is absorbed) color. ",
"Chlorophyl is tuned to absorb blue and red light, so it works in the space in the spectrum that archaea doesn't use. That has led some propose that eukaryotic cells had to develop photosynthesis after archaea and exploited the light they could find. The hyperphysics page ",
"has some nice spectra",
" to demonstrate this.",
"Eukaryotes do have molecules called carotenoids that can cover ",
"some of the missing spectrum space",
". Some cultivars of Japanese maple have purple leaves that can absorb more of the spectrum thanks to carotenoids. "
] |
[
"No, because not all frequencies are useful for photosynthesis. This would just heat the leaves up and hurt the plant. For example, light in the near infrared is pointless to photosynthesis and therefore plants are very reflective in that range."
] |
[
"Chlorophyll only absorbs energy from blue and red light, not green.",
"Right, but more broadly, the question is \"why didn't plants evolve new kinds of molecules sensitive to other wavelengths\"? After all, there are at least half a dozen different kinds of chlorophyll, each with somewhat different absorption spectra. Not to mention different compounds used by bacteria for the same purpose. And other molecules used for energy transduction of light, for example, those in rods and cones in the retina.",
"So the fact is that there are indeed different molecules sensitive to to different parts of the spectrum that have evolved over time. Why then don't we have black plants, either with new molecules with a wider absorption spectrum, or multiple molecules with overlapping spectra?",
"I think the answer is two fold. One is that none of these molecules is 100% efficient at converting the absorbed heat to chemical energy, and in fact, a lot of absorbed energy simply goes towards heating the leaf. So a black leaf would run very hot, and in most latitudes it would probably shut down during the middle part of the day because it was too hot. That is hardly a net increase of efficiency.",
"The second reason is that we mistakenly assume that light is the limiting factor for photosynthesis, and simply increasing the light energy (or light energy absorbed by photosynthetic molecules) would increase carbohydrate production. This is manifestly not true in all environments. In fact, in many sunny latitudes, the limiting factor is carbon dioxide. This is why increasing the CO2 concentration increases the rate of photosynthesis. This is also why C4 photochemistry developed, to allow plants (specially in warm and dry climates) to increase local CO2 concentration locally inside the leaves. This is why C4 plants often have higher yields.",
"So the range of conditions in which having black leaves would be useful is actually quite narrow, probably limited to high latitudes (where sunlight is low and a pigment that uses more light energy would actually be useful), where other nutrients including CO2 are not a bottleneck for carbohydrate synthesis, etc. And any downsides of having black leaves are not serious enough to exert selection pressure against them.",
"This does not exist so far as we know. At least, not today. Perhaps there were evolutionary experiments along this line in the distant past, but did not prove sufficiently advantageous."
] |
[
"Is there a reason North is associated with 'up' and South with 'down'?"
] |
[
false
] | null |
[
"pure convention; it used to be that in Europe, maps had east at the top - from which we get the verb 'to orient'; which was literally to turn a map so that the east (the orient) was at the top. ",
"http://en.wikipedia.org/wiki/Map#Orientation_of_maps"
] |
[
"It's totally arbitrary but an interesting little sound byte is that the true north pole is actually the magnetic south, as proof I submit to you that like poles repel, correct? Then why would the north needle on the compass point to the north. Mind = Blown"
] |
[
"I was simply stating a that was vaguely relevant to the question that people might have found interesting. Yes, in terms of naming the poles then you are entirely correct. North or south, a name is just a name. But in magnetic terms the core of the earth (as I'm guessing you already know) is a giant ball of molten iron that has a north and a south that can be defined by the direction of travel of the magnetic field (flowing from north to south) and so what we know as the 'magnetic north' is, in actuality the magnetic south. Again though, names are whatever you take them to be so if its called magnetic north then its magnetic north, no more on the subject."
] |
[
"Is it possible to build an electrostatic dust collector? Would it be effective?"
] |
[
false
] |
Every week or two my screens and my furniture are full of dust so I want to know whether it is possible to build an electrostatic dust collector. E.g. an electrostatically charged metallic ball that you can place somewhere in the room which attracts most of the dust so it doesn't get onto your furniture. Would it be effective?
|
[
"\"Air Ionizer\" style devices are essentially what you're proposing. ",
"The problem is that they process very little air, in general. So you need to, generally, put some fan to move air through them to actually pass dust through it. They also produce some amount of Ozone (O3) which is toxic to some degree. So at that point, why not just pass air through a hepa filter?"
] |
[
"Yes, it's possible and it has been done commercially for years. I have a large (size of a 1950s TV set) 25+ years old air purifier that has a large \"cassette\" style electrostatic filter. Essentially it's just a stack of evenly spaced out plates, electrostatically charged to attract dust, and a couple of fans to blow air through the plates. The cassette is pulled out through the side and the accumulated dust is rinsed off with water.",
"Note that this is ",
" an air ionizer! An air ionizer works on the principle that ions in the air will attract dust particles, so that the dust particles \"clump up\" and fall to the floor/other surfaces. This device actively collects the dust on the charged plates. Although it's most likely ionizing the air as a side effect, that is not the primary action. "
] |
[
"Is it effective? Or why did they stop selling it?"
] |
[
"Why do you throw up after swallowing too much of your own blood?"
] |
[
false
] |
Why can't it go through the digestive system?
|
[
"Blood is in essence warm, salty water. Our bodies have safeguards to prevent drinking too much contaminated water such that it would throw off our ability to regulate fluids within our cells. If you were for example to drink more than a pint of similarly salty water I suspect you would experience similar effects."
] |
[
"Ah thank you, that makes sense. Sorry if this is a dumb question, but why are we able to drink a big bowl of warm, salty broth without our bodies reacting the same way?"
] |
[
"Because it isn't as salty as our blood. About 85% of the sodium in the body is present in the blood and lymphatic fluid; it is almost as salty as the ocean! While you can drink a big bowl of broth, I don't expect your tummy would react particularly well to drinking a big bowl of seawater."
] |
[
"How does etching a chunk of silicon with different crystal planes exposed get eaten away with time?"
] |
[
false
] |
I'm aware of how potassium hydroxide etches silicon anisotropically. The 100 planes get eaten the fastest while the 111 planes get eaten the slowest. This is commonly used to form trenches in 100 planes bounded by 111 surfaces. What would happen if you dunked something in KOH? It's hard for me to visualize. There are 110 planes, 111 planes, and 100 planes visible. I know the etch rate of 100 > the etch rate of 110 > the etch rate of 111. But if I placed a hunk of silicon that looked like that in KOH, what would happen?
|
[
"Assuming that chunk of silicon was single crystal, then each set of faces would be a different plane. That means that each face (pair of faces I believe) would etch at a different rate, with the rate being constant throughout the face and the etching direction perpendicular to the face. As the chunk is etched, some faces would etch, and therefore expand (as the face is etched down towards the center of the chunk, the area of that face will expand, ignoring the effect of the other faces), faster. Eventually the fastest etching faces would completely overtake/erase the slower faces and you would end up with a simpler shape that would then slowly shrink in size while maintaining its geometry.",
"Edit: Not my field, but this is what would happen if the rate of etching only depends on the plane. Also, I'm not sure what happens at the edges between planes. I would guess nothing special, but I don't know."
] |
[
"Chemist here, ",
"If you were to dunk the bottow right shape into KOH for \"science,\" imagine if you were to just \"push in\" the <100> planes inwards, maybe 4 atomic planes in, then you \"push in\" the <110> planes in 2 atomic planes in. These \"pushed in\" surfaces would represent what was etched away, while the <111> surfaces would now stick out of the shape, leaving some strange octahedral shape, with the triangular <111> faces sticking out."
] |
[
"imagine it would only etch the 100 planes. then you would first get the shape above it and eventually end up with a cube (if you take away layers of the 100 faces, those get broader while the other faces shrink untill they are gone). now if the other ones etch aswell, but not as fast that whole process will of course take longer because the other faces don't shrink that fast anymore."
] |
[
"Why are laws of physics absolute?"
] |
[
false
] |
I'm only asking this question from a ignorant stand point of view. I usually hear a normal discussion on tv, radio or even in life, and it goes something like this: Person A: "Dude, that new spaceship can travel faster then the speed of light." (Sorry can't think of a great example right now) Person B: "Dude, that goes against the laws of physics/thermodynamics/etc." It's my understanding that the "Laws of Physics" are a conclusion drawn from what we have observed and tested in our little corner of the galaxy. How are we so certain that these laws apply to the whole universe? And why isn't this same principle applied to evolution on our planet? I mean we have so much evidence and date yet it is still called "theory." Why can't it become an absolute fact?
|
[
"We just call it a law because so far, all the evidence we have support them. So, we are not certain that they apply to the whole universe but you can't just make a random claim that is not supported by any evidence or is impossible to test. ",
"As for evolution, a lot of the naming is political, but it does indeed have plenty of evidence backing it up."
] |
[
"That really isn't how \"law\" works in the scientific community. Specifically, laws are relationships and trends in specific sets of data. Most laws enumerated as such are really just relics of an older age and the word doesn't seem to be used as much anymore. This is probably mostly because we know that laws are very often only approximations of the truth. Newton's laws of motion only have an approximately true definition of momentum. Newton's law of gravitation is only approximately true for weak gravitational fields and only works for massive bodies, completely missing gravitation of light. Hooke's law only works for sufficiently small compression/expansion of springs. Ohm's law only really holds so long as the resistor doesn't heat up too much. And so on and so forth. ",
"Theory on the other hand is actually rather more robust than law. Theory takes relationships among data and ties them together in one unifying explanation or framework. Electromagnetic theory takes the relationships one finds about electricity and magnetism and explains them all through the Maxwell-Helmholtz equations of electromagnetism. Even this theory though is a classical approximation of a more fundamentally true theory, Quantum Electrodynamics. ",
"So my takeaway message is this: the words theory and law have... fuzzy meanings in science. I mean, they have specific meanings but sometimes we also mean other things when we use those words. The things we almost ",
" mean are the definitions that non-scientists imply when they use the words. Laws aren't graduated theories after sufficient evidence. Laws aren't universally true. Theory does not mean \"educated speculation.\" Theory can often be an approximation of some more fundamental theory. etc."
] |
[
"There is no strict definition as to what constitutes a Law or a Theory (or a Conjecture or a Principle or a Rule). There is no Grand Council of Science that holds a vote to see if a Theory is ready to be promoted into a Law. There are Theories than are nigh absolute and Laws that are dead wrong.",
"There are some general trends, but mostly, whatever term was attached to an idea when it gained popularity is the one that sticks."
] |
[
"Any chemists on reddit know about a legal liquid/solid..."
] |
[
false
] |
...with a melting point 10-20 degree Celsius above or below room temperature? I need something that can be flexible for a short amount of time then solidify to hold his shape. Any ideas?
|
[
"Gallium."
] |
[
"You could try Polymer Clay, like Fimo or Sculpey. It is stiff at room temperature, and when heated up, it becomes pliable.",
"http://en.wikipedia.org/wiki/Polymer_clay"
] |
[
"You want flexible, or a liquid that you could cast into a shape then freeze? ",
"H20 is quite legal so you can pour it into a mold then freeze it. It freezes roughly 20 degrees below room temperature.",
"However if you want something you can mold then keep it in such shape, why not try making bread or cookies, you can shape it then cook. Obviously this depends on shape you need, as well as strength."
] |
[
"Most cities do not allow wells to be drilled on city lots. Why is this? Doesn’t ground water partially come from rain water? We have been artificially moving water from rivers, etc and converting it to ground water via sprinklers that we could reuse to water our lawns?"
] |
[
false
] | null |
[
"There are a lot of considerations here and my post will surely miss many of them. To start however, it's important to have a clear understanding of groundwater, i.e., ",
"aquifers",
". What you're mostly describing or envisioning, would be an unconfined aquifer which can be recharged through infiltration from surface water. Even though they can be recharged, the infiltration and flow rates within unconfined aquifers are typically slow compared to the rates of extraction. Related to this, the rates of infiltration into unconfined aquifers are typically dramatically reduced in developed areas by building large swaths of impermeable surfaces (e.g., roads, buildings, etc), meaning that more water will runoff and/or evaporate than infiltrate and recharge any shallow, unconfined aquifers (so depending on the details of the area in question, your underlying premise may be mostly wrong). ",
"Many wells however are drawing water from confined aquifers. These are saturated sections of rocks bounded on their top and bottom by less permeable rocks, typically below the water table. What this means is that surface water directly above these aquifers will not recharge them (or will only have small amounts that make it from the surface into these confined aquifers). Some confined aquifers do have recharge zones (i.e., areas where surface water can reach them more easily because the impermeable layer is absent), others do not and the water in them is effectively \"fossilized\" in that it accumulated when there was a recharge zone for this layer that has been sealed off through geological processes. Even with those that have recharge zones, as flow rates from the recharge zone to zones of extraction (i.e., wells) are slow (years to centuries, depending on details and distances), some care needs to be given to how much extraction is allowed and the zones of recharge may be quite far from the zones of extraction (i.e., water falling on the surface above a confined aquifer does virtually nothing in terms of recharging it).",
"As for the reasons to regulate extraction, there are of course questions of conservation, but there are also a variety of relatively serious ",
"issues that can develop from over-extraction",
", e.g., subsidence (sinking of the ground surface) or salt-water intrusion if near a source of salty water in the subsurface. You also very quickly get into lots of thorny legal questions and issues of ",
"water rights",
". The level of complexity of these typically depend on the scarcity of water in the region in question. For some cities, the city (or its residents) may not actually have the water rights to the groundwater beneath it, depending on the details and history of the region. Even if the city does have the water rights to at least part of the groundwater, the city itself may tightly regulate private wells because the city does extract groundwater for municipal use and wants to avoid some of the potential negative outcomes of over extraction. Bound up in this is that there may be a lot of different actors competing for the groundwater beyond simple municipal use, e.g., agriculture and various industries are incredibly water intensive and many prefer groundwater depending on the quality of available surface water."
] |
[
"Also, urban living and thousands of wells is how you get dysentery and cholera outbreaks. Of course our waste water system is different but doesn't really eliminate it."
] |
[
"Many towns and cities still have a ",
"combined sewer and stormwater system",
", which means that in periods of high rainfall the combined capacity is exceeded and sewage is discharged directly into local rivers, streams, lakes, etc."
] |
[
"If we were to see a black hole up close, would we be able to see everything that fell into it on the event horizon?"
] |
[
false
] |
I remember being told that if you were to watch someone fall into a black hole, at a certain point they would seem frozen in place forever (as light can't escape beyond this point). If a lot of stuff has fallen into a black hole, would we see a jumble of clutter at the event horizon of everything that has ever fallen in? I'm imagining a static version of the win screen of the old solitaire on Windows ( )
|
[
"Yes, but the images of the objects also become increasingly redshifted exponentially fast to the point that they become completely invisible to any kind of detector in a very short time. "
] |
[
"The image would fade away very fast. As for the shape it can stretch or thin or deform depending on the trajectory of the object; moreover in general there are multiple images."
] |
[
"Not just redshifted. There's also fewer photons leaving. The object would only emit finitely many before hitting the event horizon, so only finitely many escape."
] |
[
"How do sprays like Febreze actually work?"
] |
[
false
] | null |
[
"To eliminate odors, a product needs to remove the volatile compounds causing the odor. Hydroxypropyl beta-cyclodextrin works by binding the volatile compounds in its ring. When bound, the compounds causing the odor are no longer volatile, which means they become vapor/gas less readily. Since the compounds aren't vapor, they don't reach your nose, and you no longer smell them."
] |
[
"Wikipedia",
" lists the active ingredient as hydroxypropyl beta-cyclodextrin which is a cylic structure that can trap compounds inside it."
] |
[
"Febreeze is a solution of beta-cyclodextrin, a compound consisting of seven sugar rings grouped as a larger cyclic structure.",
"These sugars twist within the overall ring to orient themselves so that their hydroxyl groups (OH) are pointing outwards and their other functional groups are facing inwards, to the ring's internal cavity. This has the effect of producing very different interactions with molecules of different polarities.",
"The external surface interacts strongly and favourably with polar molecules like water and is referred to as being hydrophilic. The internal cavity is the opposite and avoids interacting with such polar molecules, referred to as being hydrophobic.",
"A significant number of the odour producing molecules you encounter in every day life are non-polar and usually contain long hydrocarbon chains. Because they're not very polar at all, these molecules love to exist within the hydrophobic internal cavity of the cyclodextrins in Febreeze, so they're easily taken in and removed from general circulation and very difficult to remove once they're in there."
] |
[
"Why do phone/laptop/etc batteries hold less and less charge over time?"
] |
[
false
] | null |
[
"The causes of batteries degradation vary by battery type. Modern electronic devices typically use one of several varieties of Lithium-ion battery, which are generally degraded by three things: high temperatures, frequent deep cycling, and high state-of-charge ",
"[1]",
" ",
"[2]",
". (This last one means that keeping the battery fully charged can actually be worse for it than keeping it at a low-to-moderate charge level, which is a bit counter-intuitive for people who are used to older battery technologies that prefer to be fully charged ",
"[3]",
".) Note that the exact effects of these three drivers of degradation are complex, interdependent, and not fully understood. ",
"If you are asking about the internal physical mechanisms of battery degradation, I'll leave that for someone else, but the short answer is that there are various mechanisms including loss of active sites for the electrochemical reaction and buildup of a barrier at the solid-electrolyte interface. "
] |
[
"A problem common to all batteries, re-chargeable or not, is that undesired side-reactions occur. These can lead to the formation of insoluble deposits that cannot participate in the charging cycle. This lowers the capacity of the battery.",
"Basically, irreversible chemical reactions degrade battery life.",
"Source: I read the wiki on Lithium-ion batteries a minute ago. "
] |
[
"I can explain one of the types that reduce battery capacity.",
"When you charge and discharge a li-ion battery, you'be basically moving lithium ions to and from the cathode and anode. Metallic Li deposits can begin to form on the anode that inhibit ion transport. These deposits can end up \"filling\" the carbon (negative electrode) with lithium, causing areas to be unusable resulting in permanent capacity loss. This is called ",
"lithium plating",
". This tends to occur faster in high current applications. Plating can ultimately short the electrodes.",
"Interestingly enough, plating can also occur in low temperature applications. Since chemical reaction rates decrease with temperature, it causes reduced current carrying capacity which makes it more difficult for Li ions to be reinserted into the anode.",
"High temperature applications actually can damage the cell. I don't have a good enough understanding to explain that, however.",
"source: I'm also an electrical engineer."
] |
[
"Happy Pi Day everyone!"
] |
[
false
] |
Today is 3/14/16, a bit of a rounded-up Pi Day! Grab a slice of your favorite Pi Day dessert and come celebrate with us. Our experts are here to answer your questions all about pi. Last year, we had an pi day . Check out the comments below for more and to ask follow-up questions! From all of us at , have a very happy Pi Day!
|
[
"You could determine the value of pi experimentally. Take a small stick (or set of identical sticks) and draw parallel lines on a piece paper with a spacing equal to the length of the stick.",
"Then repeatedly drop the stick from a decent height onto the paper and count the total number of drops and the number of times the stick lands in such a way that it crosses one of the lines. The ratio (#crosses / total #drops) will approach 2 / pi.",
"This approach converges extremely slowly, so be prepared to spend a long time to get any reasonable approximation."
] |
[
"There are plenty of algorithms that are suited for computers related to pi, but which are tractable with pen and paper? Can finding the n'th digit be done on paper reasonably?"
] |
[
"I like how we have a computer simulation of a method to find pi using nothing but a pen (which could be the stick) and paper."
] |
[
"How does quantum annealing work?"
] |
[
false
] |
[deleted]
|
[
"To understand quantum annealing, it's first going to be necessary to understand classical annealing (disclaimer: my knowledge of classical annealing comes from discussions on quantum annealing, so if I mess something up, hopefully someone who knows more can correct me).",
"Here is how classical annealing works. Suppose you have a classical system, at some temperature and energy. We imagine that in the lowest energy state of our classical system (in QM this would be called the global ground state), we have encoded the answer to the problem we wish to solve. How this is done is a bit technical, and not necessary to understand how classical annealing works.",
"So now, to solve our problem, we need to bring our classical system to its lowest energy state. This seems simple enough, all we need to do is slowly lower the temperature (assuming the lowest energy state can be reached before T = 0 Kelvin). However, there is a problem. Let's consider what is called the energy landscape of our system, which basically just describes the allowed energies for our system. We want to bring our system to the global minimum of this energy landscape, but what if it has local minima? If we just slowly lower the temperature, it is possible that we might end up in one of these local minima, and then we'll be trapped, and never reach the global minimum.",
"To avoid this, we occasionally allow for random temperature fluctuations, which would allow our system to escape local energy minimas, and continue towards the global minimum. This is classical annealing.",
"Now quantum annealing is exactly the same idea, using random fluctuations to escape local energy minima. However, in quantum annealing, instead of random temperature fluctuations, we have quantum fluctuations, which allow our system to quantum tunnel out of the local energy minima, and hopefully continue on to the global minimum.",
"The article you linked is talking about the D-wave computer, which isn't using quantum annealing to solve problems. What they claim their computer does is a kind of adiabatic quantum computing, and they hope that quantum annealing like effects will help correct errors that arrise as they run their computer.",
"In brief, an adiabatic quantum computer starts with a quantum system in the ground state of one set of constraints, and slowly (adiabatically) changes the constraints, which hopefully brings you to the ground state for the quantum system under a different set of constraints (which solves your problem). However, sometimes in this process you might accidentally go to a higher energy state, and this is what D-wave hopes quantum annealing can correct."
] |
[
"If you don't mind me adding something, there's a simple but essentially-accurate analogy to be made here for classical annealing: Take a bunch of different-sized objects (rocks perhaps) and throw them randomly into a box. Things 'want' to be in their lowest energy state, which in this case means having the rocks as close to the bottom of the box as possible. But your jumble of rocks most likely isn't like that - there are a bunch of holes where smaller rocks could fall down, but they can't get there because other rocks are in the way. So it's in a 'local minimum' - a lower energy state exists, but it can't get there. ",
"So you simply shake the box a bit (raising the temperature), and the rocks get some kinetic energy, enabling them to move about and eventually find their way around each other to the lowest energy state, settling as densely as possible to the bottom - the global minimum. ",
"With quantum annealing, you could say you're taking advantage of the fact that nothing is ",
" stationary in quantum mechanics, except for the ground-state/global minimum itself. So without raising the temperature, things will find their way there by themselves, if they're left alone and allowed to behave quantum-mechanically. The former being a prerequisite for the latter, and one that's far from being as easy as it sounds, in practice. (And on the opposite end you have the ",
"quantum zeno effect",
" - repeatedly interfering with a system to ",
" it from reaching its quantum-mechanical ground state)"
] |
[
"Thank you, detailed and easy to read."
] |
[
"Change in weight when going below the earth's surface?"
] |
[
false
] |
Intrigued by something I read today, and hope someone can enlighten me! When descending into the earth, your weight will steadily decrease, as there is less mass to provide gravitational force. I'm assuming that at some point the decrease will slow and eventually stop. But at what point might that occur? To clarify my question, let's assume you are standing on a scale atop the planet's surface (the crust). As weight is effected by the gravitational forces at work, you will become lighter as you pass through the crust and mantle and less of the earth's mass is beneath your feet. But at some point as you descend, I assume the mass you will begin to counteract the mass you, and your weight loss will slow and eventually stop. Should you continue through the planet's core in a straight line, I would think the weight measured by the scale would cease to be the weight of your body and become the weight of the scale itself being pulled by gravity. I'm theorizing that the would then begin gaining weight as it is pulled towards the earth's mass and its movement limited by your feet. One unknown here is the relation in density between the earth's layers. I know the inner core is the most dense portion, but does density increase at a relatively stable rate as you progress towards the center (excluding, of course, the widely-varied density of the lithosphere)? Obviously a human could not survive such a descent, so this is a purely theoretical scenario. But I am curious as to how mass, gravity, and measured weight interplay here. Much thanks for any information!
|
[
"The blue curve in this graph",
" shows the interior gravity of the Earth, as best as we can tell from measurements of the density at different layers, which is determined from measuring the speed of different earthquakes. There was a more recent measurement using neutrinos, which is really cool but also not very precise.",
"The non-obvious fact is that gravity actually ",
" the first part of the way down. This is because, as you said, the density is increasing and you are getting closer to a higher-density sphere. In the core, gravity then falls towards zero as the mass \"below\" you approaches zero."
] |
[
"And inside such a homogenous sphere, measured weight would also decrease in linear fashion, correct?"
] |
[
"And inside such a homogenous sphere, measured weight would also decrease in linear fashion, correct?"
] |
[
"Question about the physics involved in \"tube transport\", video inside."
] |
[
false
] | null |
[
"I'm not singularly familiar with the concept, however thinking logically the carriages would almost certainly have pressure sensors on or be hooked into a monitoring system on the network, so if a breach occurred it would be notified and would slow down. If a breach appeared in front of it before it could be warned, braking systems combined with the drag from the air pressure gradient sweeping down the tube would most likely bring it to a safe halt. Difficult to be certain without a lot more information, though."
] |
[
"Thanks for responding!",
"I wonder how long it would take to slow down from 6500 km/h though. Wouldn't going from zero air resistance to instantly hitting air at that speed cause the capsule to be crushed? Especially if the capsules aren't even aerodynamic, like in the video. "
] |
[
"It's a difficult one. You'd assume the capsule would be fairly sturdy (Although as you noted it's a little blunt), but you can only decelerate so fast before you liquify the people inside.",
"I get the impression that's an extremely optimistic peak speed for one that traveled round the world, as that's 1800 metres per second. But at that speed even at a very heavy 5G deceleration you'd need over 30 seconds to stop. So if it impacted a wall of air I doubt things would be pretty, for the capsule, tube, or people inside."
] |
[
"If I hit a baseball with a bat, can the ball go faster than the speed that I'm swinging the bat?"
] |
[
false
] |
I'm thinking of a ball that is stationary, like on a tee. I guess that maybe the question would work better for a golf ball now that I'm thinking about it. If it is a pitched ball, can the ball ever go faster than the combined speed of the bat and the ball? Does it matter what the ball is made of, or how strong the person swinging the bat is?
|
[
"Yes, the ball can. Assuming an elastic collision, both kinetic energy and momentum of the system must be conserved. Focusing on the small period of time surrounding the hit of the ball, obeying these two conservation laws means that the ball can shoot off with a much higher velocity than the bat, because the bat has a much larger mass (and benefits from the mass of the person holding the bat).",
"The material matters because this determines how elastic vs. inelastic the collision (between the bat and the ball) is. More rigid materials will lead to more elastic collisions (meaning less energy is lost to heat) and hence more energy stays as kinetic energy and the ball shoots off faster. Squishier materials lead to more inelastic collisions (meaning more energy is absorbed into deformation of the materials and generating heat) and so the ball will not bounce off as fast."
] |
[
"the ball isn't being accelerated to 2v. it's velocity ",
" by 2v. ( from v to -v). ",
" for a perfectly elastic collision between the ball and bat.",
"maximum separation speed is only v+u. in reality flyout velocity is much lower as the bat continues motion in the same direction as the hit ball (this subtracts from the separation speed limit)."
] |
[
"Note that this is different than throwing a ball. When throwing a ball, the maximum ball speed is the speed that your hand is moving through air."
] |
[
"How does the mold on my bathroom ceiling obtain nutrients?"
] |
[
false
] | null |
[
"Found this:",
"Link"
] |
[
"Fungi are master degraders and can use many diverse sources of nutrients. They can breakdown the wood, the paint, etc. for growth. In addition their growth pattern is by a network of hyphae so the mold you see may not be eating anything it could be a search party looking for richer nutrients with a base in the wood within your ceiling.",
"I've grown fungi on something as simple as deionized water and agar plates. Somehow they can live on the trace amounts of nutrients that provides.",
"In other tests, I found that most types of fungi can grow quite well on used motor oil poured on autoclaved soil. This shows that degrading hydrocarbons for energy is not a problem. Your paint can provide a similar carbon source!"
] |
[
"No, kill them, it's okay! If your paint is safe to bleach, spraying them with a pure bleach solution works best in my experience. Don't feel bad about killing the fungi, they wouldn't mind slowly destroying your house. :) Let them do their work in the forest.",
"Here is a very cool article about what happened before fungi developed the ability to degrade lignin, the tough polymer in wood.",
"http://www.scientificamerican.com/article.cfm?id=mushroom-evolution-breaks-down-lignin-slows-coal-formation",
"The wood just piled up! These piles formed the coal we dig out of the ground today. That must've been a very strange world before the wood could be degraded by fungi."
] |
[
"If an object is moving through interstellar space at a significant fraction of c, does it have a sort of \"wind resistance\" from the interstellar medium?"
] |
[
false
] | null |
[
"Yes, it does. What is more, ",
"lethal radiation",
" would arise from the \"wind resistance\".",
"Using Einstein's special theory of relativity, Edestein—an expert in radiology—concluded that astronauts will die instantly from radiation overload, thanks to the kinetic energy of the atoms surrounding the ship. The hydrogen atoms floating in the empty space would reach 7 teraelectron volts, which is the equivalent of staying at the center of the Large Hadron Collider set at maximum power. Even with a 10-centimeter-thick aluminum hull, 99 per cent of the energy will pass, destroying humans and circuitry inside.",
"His bottom line: \"Hydrogen atoms are unavoidable space mines.\""
] |
[
"Does that mean that all is not relative and there is a way to stay still compared to space?"
] |
[
"No, it simply means that any given matter has some velocity with respect to some other lump of matter. If one accelerates a spaceship up to a velocity close to c ",
" the starting velocity of the ship, then one will find that most of the matter in space that one encounters will have a much lower velocity (closer to the ships starting velocity). However, this still does not mean that there is in any sense a preferred reference frame which we can think of as \"standing still\"."
] |
[
"Run the United States Economy off of Solar Power? Sustainability Student help."
] |
[
false
] | null |
[
"the inefficiency is the most common response i have received so far. Even though solar has come a long way, it just hasn't come far enough. Most people i asked say that once harvesting solar power is more effective it COULD produce enough to run the economy. You are the first one to bring up the point of scarce materials however which is a large blockade to the push for solar energy. Thanks for the input!"
] |
[
"I'll add to this answer in regards to the sheer amount of area of solar panels required to power everything. We're talking about covering an area roughly the size of the Sahara desert to power everything. ",
"If you want further reading, I'd suggest this ",
"online book",
" by a very noteable scientist involved with climate change in the UK Government. The book contains many back of the envelope calculations regarding all manner of renewable technologies and how viable they are for mass implementation."
] |
[
"The biggest inhibitor to changing how all renewable sources interact in our economy is energy storage. If you can solve the storage problem economically, and in a way that can scale then you have a chance."
] |
[
"Has there been a line of related species (documented by fossil evidence) that lost a certain trait, and then gained the same trait after years of evolution?"
] |
[
false
] | null |
[
"Fish have fins. Mammals eventually descended from fish, and the first mammals did not have fins. Eventually, dolphins descended from the first mammals, and dolphins have fins. So fins were lost and re-acquired, so to speak."
] |
[
"Yes, I believe what you're looking for are ",
"atavisms",
", which are the re-appearance of traits that were present earlier in the evolutionary history of an organism but had been lost. They occur because the genes for a trait don't necessarily disappear if the trait. Those genes just aren't expressed, for any number of reasons. Basically, natural selection is acting on the phenotype (observable characteristics) rather than the genotype, and the genotype can either change, be suppressed by other genes, or be activated only at certain times during development. If a dormant gene is suddenly expressed again, a long-vanished trait can pop back up. For example, as that article I linked to discusses, birds have the genetic coding they need ",
"to grow teeth",
". ",
"There are other instances of atavisms:",
"Frogs lost teeth on their lower jaws almost 230 million years ago, but in ",
"one species they've reappeared",
" in the last 20 million years.",
"Gastropods (snails) have lost coiled shells in multiple instances, and it was thought that a coiled shell couldn't re-evolve. However, there are instances in which ",
"coiled shells have re-evolved",
".",
"Stick insects have ",
"lost and re-gained",
" wings several times in their evolution.",
"Dolphins and whales show up every so often with ",
"hind limbs",
". The genes that led to their development are still there, and hind limb buds ",
"show up in developing cetacean embryos",
" before being resorbed.",
"The claws on ",
"hoatzin chicks",
" are likely an atavism.",
"A family of salamanders had lost their larval stage in favor of direct development, but one genus within that family ",
"re-evolved that larval stage",
".",
"Skinks have lost limbs multiple times in their evolution, and ",
"regained them",
" as well."
] |
[
"This is highly improbable. Loss of a trait is due to a long sequence of highly improbable mutations with each step selected for. Given the same environmental/selection factors there is no reason to believe the same end point would arise a second time. ",
"Reversal of a lost trait would require randomly tracing back this highly unlikely path, exactly. The odds against that are astronomical. So, for example, whales have flippers, but flipper are not fins - they are entirely different (though functionally equivalent) appendages which arose from limbs. "
] |
[
"Why are there static and kinetic coefficients of friction? Why isn't there just a single coefficient of friction?"
] |
[
false
] | null |
[
"What I believe is that there are two main cause of friction- Interlocking and inter surface adhesion. Now when the body is at rest, both of these causes are in action, but when the body stars moving, the inter surface adhesion diminishes because it needs some time to form bonds between particles on both the surfaces. Now, since the body is moving, there is no bond formation. Hence when the body is at rest, forces are larger in magnitude leading to a higher coefficient of static friction."
] |
[
"The reason you have two coefficients is due to the fact that the kind of interactions you have when two bodies are resting together or sliding one on another are indeed very different.",
"But let's start from the beginning with the usual example of the mass on a slope. Let's also assume that we can change the incline of the slope.",
"I assume that the only force acting on the system is the gravitational pull.\nAt first we take the slope to be horizontal. The body is at rest obviously. This means that the vincular force (or reaction force) from the surface of the slope cancels the gravity force acting on the mass.",
"If we now start changing the inclination of the slope the vincular reaction no longer cancels the gravity. A component of the gravity is indeed parallel to the slope now and so, if the body is still at rest, we need some force to cancel exactly this parallel active force. This kind of reaction is due to static friction (i.e. to the different kind of interactions that happen between the two surfaces - which vary a lot with the kind of materials you consider but that are essentially electromagnetic in nature). As you can see this is simply a way to express these various interactions.",
"But what about the specific coefficient? \nWell, let's keep making the slope steeper. For a while the mass will stay stuck to the surface which means that the reaction due to static friction is growing as to balance exactly the parallel component of the gravitational force. At a certain point though the body statrts sliding. This tells us that the parallel gravity exceedes what the static friction can cancel.",
"So, what do we choose to describe this static friction? The maximum force that it can cancel; and since this force is roughly proportional to the normal component of the gravity, we choose our coefficient as to satisfy F par max = static friction coeff. * F nor",
"Why can't we pick another relation for the coefficient? Well, we simply would not be able to pick one if we did not consider the biggest inclination possible for the slope.",
"Notice now that the parallel reaction is in general less than this maximum force (otherwise the body would absurdely start to climb up the slope being subjected to a reaction bigger than the active gravity force!).",
"This way you see that the static friction is a maximum friction.",
"As the body starts sliding it is indeed still subjected to friction; now kinetic friction. You can still describe it as proportional to the normal force but now you no longer have a maximum force involved since the body is moving and the parallel reaction is no longer compensating exactly the parallel component of gravity.",
"If you write this relation as F par = kin friction coeff * F nor you can also see that the kinetic friction coefficient needs be smaller than the static one otherwise the body would experience a bigger reaction just as it starts moving and thus would be expected to stop immediately.",
"If we go a little deeper we actually find out that these coefficents we used to parmetryze the system are strongly dependent from the conditions in which we choose to study our system. For example the kinetic friction will change with temperature or with the medium you put the bodies in (the friction of copper on steel is not the same in dry air or water or lubricant oil obviously) and thus could even become stronger than the static one.",
"If you consider these situations though, you see that two coefficients are not enough and you end up needing running coefficients as functions of more parameters. ",
"So, in short: you need at least two different coefficients because you are parametryzing (in the simplest way you can) two different kind of interactions."
] |
[
"Imagine a box on a rough floor. It takes more force to start moving the box, this is the static coefficient. Once the box is already moving you don't need the same amount of force to overcome the sliding or kinetic friction."
] |
[
"In your opinion, is this a scam or a honest request from a very bad doctor?"
] |
[
false
] |
I got at my work. As a scientist, I sometimes get collaboration offers, so it could make sense. But I also get emails from Nigerian widows. This letter has a lot of scientific words, but they're in sentences that don't make any sense to me, almost as if a randomizer has been used to write it. At least, let's say that this person would have a very unusual understanding of cancer! Does anybody know if this is a well-known scam I haven't heard of before? Or is it simply a doctor with very weird ideas? A quick Google search showed me that there is indeed a doctor with this name in Romania, although I can't read the language.
|
[
"Crackpots often come up with theories at home and then try to shop them around to professors at universities, whose names they find via google. Most Math departments have a collection of such letters and they pull them out from time to time when they need a giggle. ",
"Most of these people are a little crazy and any response will probably encourage them to keep writing you. Just trash it and go about your day."
] |
[
"Well, the second guy had a point. Think about all the chicks gravitating around race cars."
] |
[
"I was also going for the crazy person theory. Good to know it's not unusual. I'm starting my collection today!"
] |
[
"In what order did the kingdoms become multicellular? And, are symbionts ubiquitous?"
] |
[
false
] |
I'm writing an essay and I've come up with some questions I'm having a hard time answering. Maybe it's because I don't know how to Google very well, or because whoever asked this question first didn't put it up on the web for the Google to find, but I can't seem to find concrete answers to these questions. From my understanding the first evidence for multicellular life is a fossil of red algae that dates to ~1.2 bya. Is it commonly accepted that the first instances of multicellular eukaryotic life were marine plants? What's up with the Francevillian Group Fossils? They legit? What kingdom do they belong to? After the emergence of multicellular plants, what was the next kingdom to evolve multicellularity? (fungi ftw?) What protist group did fungi come from? What is the first evidence of unicellular symbionts living with a multicellular eukaryotic host? Are there any multicellular eukaryotes in any kingdom that don't have some sort of unicellular symbiont living on and/or within them?/Are unicellular symbionts ubiquitous to multicellular organisms? Any answer to any part of these questions would be awesome. Heck, any advice that leads me to the answers would be appreciated.
|
[
"Multicellularity has evolved several times, independently in plants and animals for sure, and perhaps more than once within the fungi. A key point is that all true multicellular organisms are made fron eukaryotic cells (as opposed to prokaryotes), and eukaryotes evolved only once (i.e. all eukaryotes can be traced back to a single common ancestor that was most likely a symbiont between an archaon and a bacterium). This is the endosymbiosis theory originally from Lyn Margulis, but its now widely accepted that mitochondria and cholorplasts (and perhaps other organelles) had a bacterial origin.",
"Nick Lane has argued quite convincingly that the key to becoming multicellular is having mitochondria so that we can do respiration internally rather than across our plasma membrane (like bacteria do). This allows us to maintain control over much larger membrane areas over which we do respiration (I'm talking about Peter Mitchell and chemiosmosis here). Bacteria, no matter how much they evolve, simply can't get big and complex in the way that eukaryotes have done, because they are constrained by surface area:volume ratio as they have been unable to 'internalise' their respiration.",
"Since eukaryotes have done this with mitochondria, they were able to become bigger and more predatory (to eat other things - phagocytosis), and this put them on the road to complexity and ultimately multicellularity. Bacteria don't do this because it would break their outer membrane and disrupt their respiration. It is definitely worth noting that ALL modern eukaryotes either have or once had mitochondria. The origin of the eukaryotic cell may have been indistinguishable from the unity between two prokaryotes that eventually gave rise to mitochondria in larger cells.",
"Hopefully that answers some of your questions"
] |
[
"Some of this is simply unknown. Precise phylogeny of these groups of organisms is ",
" difficult. In the first place, fossil remains of soft-bodied organisms are rare, making radiometric dating difficult at best. In the second, there has been such a long time of divergent evolution that in most common sequences, the rate of mutations even in unchanged proteins has reached saturation (that is, so many mutations have taken place that most locations along the amino acid change have either not changed at all or have changed more than once), which makes molecular phylogenetic techniques extremely difficult.",
"One thing that is known is that fungi and animals are more closely related to each other than to plants, and are furthermore the only other major kingdoms that later diverged. So, after plants, both fungi and animals evolved ",
" - there was one common ancestor and its lineage essentially split into two, so both groups were born simultaneously and are equally distant, evolutionarily, from plants.",
"The rest of your questions are pretty far afield from my knowledge base, and I don't have the opportunity at the moment to go grind the research stone."
] |
[
"So, after plants, both fungi and animals evolved at the same time - there was one common ancestor and its lineage essentially split into two, so both groups were born simultaneously and are equally distant, evolutionarily, from plants.",
"Was this common ancestor unicellular or multicellular?\nAm I right in understanding that multicellularity evolved independently multiple times?"
] |
[
"How exactly does a shock wave from an explosion kills you (assuming that you don't die due to heat and objects flying around)?"
] |
[
false
] | null |
[
"A shock wave is a region where the pressure changes instantaneously on one side to the other. The region where the jump in pressure occurs is called the shock front.",
"",
"A shock wave that's large enough to kill you has to be quite powerful, with a significant pressure change across the shock front. The moment the shock front passes through you, half of your body is at one pressure, while the other half is at a much higher pressure. You can imagine what this means without the shock wave: what would happen to your body if one half of it was being squeezed really hard and the other wasn't?",
"",
"A large enough pressure differential of this fashion can rupture organs and otherwise damage your body structures, resulting in death."
] |
[
"During grenade training, they told us to never, under any circumstance block your nose if you sneeze while in the grenade hut. Holding your breath while a grenade goes off nearby could result in a ruptured blood vessel or pop a lung."
] |
[
"The same way that sound can pass through walls. The pressure at the boundary has to be equal on either side of the boundary, so the pressure in the air and the pressure in your body when it reaches you are equal (some energy might get lost through absorption or reflection, but for a shock wave big enough to kill you these losses are minimal). The shock wave can enter your body pretty easily, and now you are the medium in which it travels, so all of your organs and what not compress and expand as rapidly as it the wave can pass through you."
] |
[
"Is it impossible to reach Absolute Zero?"
] |
[
false
] |
This idea starts with m=E/c which most of us know states that mass is primarily a function of a body's energy. That being said, Absolute Zero (0 K) as I understand is the total absence of energy (assuming the body in question has no potential energy) in non-organic compounds. So if a body was to reach Absolute Zero, then its mass would be so minute (or absent all together) that it would no longer be matter. If you can follow my benny-addict like logic, is this true?
|
[
"Absolute Zero (0",
" K) as I understand is the total absence of energy ",
"It's not, and it's never been defined that way either. I don't know where your understanding comes from, but it's incorrect. (Also, temperature is not defined any differently for organic and non-organic compounds. The definition has nothing to do with chemistry. And 0",
" is an undefined thing, mathematically) ",
"A system is completely in its energetic ground state at 0 K. That is not the same thing as not having energy, nor does it mean that lower-energy states can't exist. They only need to be adiabatically inaccessible, meaning the energy cannot get lower without first adding energy. ",
"It is impossible to reach absolute zero for other reasons, namely the ",
"Third Law of Thermodynamics"
] |
[
"This is correct, but I think by 0",
" K OP meant \"zero degrees Kelvin,\" which is incorrect terminology (you don't say \"degrees,\" you simply say \"zero Kelvin\"), but it's a common mistake."
] |
[
"An important point is that temperature is a measure of average kinetic energy not the total energy. Zero Kelvin means all particle motion has stopped but the mass energy still exists along with the zero point energy of the system and hence we dont lose mass as we cool atoms down. ",
"Edit: to actually answer your question, my lab readily can produce atoms at 10 nano kelvin however I dont believe anyone has got any closer than that. There was one case of atoms having negative temperature but I believe that was based on a technicality rather than actual measurements."
] |
[
"How does a frisbee fly?"
] |
[
false
] |
So since frisbees only fly well when they are spinning, I imagine it has something to do with that. Does the rotation induce some sort of lift as it flies through the air?
|
[
"The rotation doesn't cause lift, but it keeps the disc stable as it flies. When a frisbee is flying straight without wobbling or flipping, it acts like a wing, but if it isn't spinning, it will go out of control almost immediately."
] |
[
"So, the aforementioned \"wing\" comment is correct, although I'd like to tangentially add that throwing a disc \"flat\" will not actually end up allowing you to throw it further. You actually want to try throwing it \"hyzer\" or \"inside-out\" (that being with the leading edge tilted opposite to the direction of spin) and slightly up. ",
"The latter is just to do with countering gravity. Much like aeroplanes tilt their wings slightly up to achieve take-off, a disc needs to do much the same. In this plane, the disc will self-correct to flat, but with a certain leading edge up angle (haven't done the maths), will get a greater amount of additional height to counter gravity than it will lose distance due to the greater drag area.",
"The reason for throwing the disc in hyzer/inside-out is to counter skin friction due to the spin. A disc will naturally attempt to correct itself in its aiflow to align with the flow of air around it. Due to skin friction that self-correction will be slightly down in the direction of spin at the leading edge. ",
"eg:",
"Looking 90 degs at the front of the disc:",
"\\ \\",
"If the disc is correcting to that, that means the front of the disc is spinning \"down\". As such, to prevent this, the disc needs to be thrown:",
"/ /",
"meaning the front of the disc is now spinning \"up\". This effect is more notable when throwing up-wind, whereby you can start with the spin at the front of the disc being \"up\" and it flips over to being \"down\". This is because the effect of skin friction in stronger winds is greater due to the increased relative velocity of disc and wind. ",
"(NB: In terms of throwing technique, start throwing with the edge of the disc furthest from you pointing at the ground)"
] |
[
"this is correct. look at the profiles of a couple disc golf disks:",
"https://michaelfonta858.files.wordpress.com/2013/04/photo.gif",
"They look a lot like wings! But as we know, wings only work at relatively small angle from their direction of travel, else they stall. So we have to get the frisbee to stay flat. Have you ever tried pushing a frisbee flat without spinning it? doesn't work! it's like a knuckleball. but as was said, when you spin it, it acts like a top or gyroscope and conservation of angular momentum keeps it rotating about the same axis.",
"Keep the disc flat, it fly far."
] |
[
"Why is it when tap water is cold, it appears to be clear but as it gets warmer it appears to become tinted and cloudy?"
] |
[
false
] |
I noticed this after I filled a water bottle back up with tap water. I have a well if that makes any difference.
|
[
"It's difficult to say as you are asking about your own individual situation which we don't have definitive information on (and there could be health ramifications).",
"In general the cloudiness is tiny gas bubbles. They are dissolved in the water (when under pressure in the pipe) and come out of solution when exiting at the faucet. Hot water forces more gas out than cold. It could also be that the hot water is more prone to grab particles from the pipe or hot water heater."
] |
[
"I am on city water and have a tankless water heater. If I turn a faucet on 'hot', I can hear and see a difference in the water once the water switches from cold to hot. "
] |
[
"I know what OP is talking about, and it's just water vapor trapped in tiny bubbles so small it looks cloudy, they will float to the top and the water will clear up in about a minute for a standard sink."
] |
[
"How different is sublingual absorption of drugs compared to gastric?"
] |
[
false
] |
[deleted]
|
[
"I notice that people have written at length about why we use sublingual rather than oral administration at times, going into details of the hepato-portal circulation and metabolism in the liver.",
"However, nobody has answered your specific question about how the rate of absorption differs between the two routes.",
"The answer is that ",
", there is not much difference between the two routes.",
"For example, ",
"this study",
" compares the pharmacokinetics of clonidine via these two routes. They found that the peak plasma concentration, time to peak, and area under the curve were the same for both oral and sublingual administration. So the two routes are equivalent, and either can be used without adjusting the dosage.",
"This study",
" compared the pharmacokinetics of lorazepam via sublingual and oral. They used two different sublingual formulations. One was the same as the regular oral form, but it was held sublingually instead of being swallowed. The second was a special formulation which was designed to more rapidly dissolve in the saliva.",
"The found that the time to peak for oral/sublingual/special-sublingual were 2.37, 2.35 and 2.25 hours, and that the absorption half-lives were 32.5, 28.5 and 28.7 minutes. So sublingual was very slightly faster, but not enough to make any practical difference. If you want ",
", you have to go with IV or IM administration.",
"So in general, for drugs which are readily dissolved in saliva, both sublingual and oral routes are equivalent for all practical purposes. Of course, the caveats that other people mentioned about degradation in the stomach or changes in the liver still apply."
] |
[
"The main reason for sublingual administration of drugs is because some drugs such as nitro glycerin are degraded in the small intestine. To get the effects of the drug it has to enter the circulatory system in a different route "
] |
[
"To expand on this for broader understanding (as this answer is completely correct), the stomach and most of the intestines drain into a venous system that leads to the liver instead of the systemic circulation. This means that blood and anything absorbed into it via the intestinal and gastric mucosa goes through the liver before it goes to the rest of the body. The liver modifies and eliminates some substances very quickly and others more slowly. ",
"The nitric oxide that is the active byproduct of nitroglycerin, for example, is very quickly and thoroughly broken down by the liver meaning very little active nitric oxide actually enters the systemic circulation and is able to reach systemic vessel walls where it has a strong dilatory effect. As this is the goal of nitroglycerine (and therefore nitric oxide) administration in cases of angina and myocardial infarction, a swallowed pill form is mostly worthless.",
"The drainage of the oral mucosa (and, therefore, anything absorbed sublingually) instead immediately enters systemic circulation. This is not only faster in terms of absolute digestive transit time but avoids the liver modifying and eliminating substances that enter the bloodstream here before it can effect receptors and tissues throughout the body. Chemicals absorbed here will eventually pass through the liver as the liver does receive blood from the systemic circulation as well. As such, the liver will get a shot at most everything, but it gets a shot at things absorbed in the stomach and intestines much earlier. Hence the idea behind \"first-pass metabolism\".",
"Other drugs such as anti-emetics (anti-vomiting) agents (i.e. ondansetron) are administered sublingually because they are given to patients at risk of vomiting and if they are swallowed we are to assume they will just be rejected by the stomach before they can be absorbed at all.",
"TL;DR - The liver destroys some many substances that enter via the stomach and intestines before they can work; putting stuff under the tongue bypasses/delays this."
] |
[
"Why is a Planck time defined the way it is?"
] |
[
false
] |
defines the Planck time as t(p)=sqrt((hG)/c )). Since a planck time is the time it takes light to travel a Planck length, why is it not simply defined as t(p)=h/c? Since G is involved, I assume it has something to do with general relativity? The c really threw me for a loop though... Any help would be appreciated.
|
[
"The way it is defined is the unique way (up to a constant factor) to combine h,G and c to get something with the units of time. It ",
" also equivalent to the time it takes light to travel a planck length. h is not the Planck length, it's the Planck constant (and it has units of angular momentum) - very different! If you look at the Wikipedia for Planck length, you'll find it = sqrt(hG/c",
" )."
] |
[
"It's a pretty simple proof. The basic units are Mass (M), Length (L), and Time (T). G has units of L",
" M",
" T",
" . c has units of L T",
" . h has units of M L",
" T",
" So if you write [T] = G",
" c",
" h",
" then this becomes a 3x3 matrix problem for x,y, and z. You can use standard techniques to show the matrix problem has a unique solution."
] |
[
"No; it's a popular misconception that the Planck length (say) is the minimum possible length, or things like that, but we don't know enough about quantum gravity to know if any of that is true. It's just a way of combining constants to figure out where we know we need quantum gravity by."
] |
[
"What, exactly, makes an orbit stable or unstable?"
] |
[
false
] |
[deleted]
|
[
"from pure mechanical point of view, you can get unstable orbit only in relativistic mechanics and only very close to the center of gravity (close to the event horizon).",
"in newtonian gravity, you always get some kind of orbit. the sum of potential and kinetic energy is constant. if you have more potential energy than kinetic energy, you get eliptical orbit. if you have more kinetic energy than potential energy, you can fly to infinity over hyperbolic orbit (i.e. even if you move to infinity, you still have some kinetic energy left). parabolic orbit is what you get when the potential energy is exactly equal to kinetic.",
"in newton mechanics you cannot crash to a mass point that you are orbiting unless you go straight down on it. that is because the gravitational potential goes to infinity as you get close. so when you come closer, your speed increases and in the end you start going further. the resulting behaviour is as described above.",
"in relativistic mechanics you can only write something that's called \"effective potential\" (google it up, add \"relativistic\" for more info). and that potential looks quite similar to the classical newton potential when you are far enough, but it is very different when you are close. under certain radius you simply cannot have any value of potential energy to stay in orbit. you either don't have enough kinetic energy and move towards gravitational center until you go under event horizon, where the time and radial coordinates swap and going forward in time means going towards center, or you can have enough kinetic energy just above the event horizont and at the same time move away from the center and escape to infinity."
] |
[
"In reality, there are always external forces that act on orbiting bodies.",
"For the second question, in the ideal mathematical case, the moon's orbit should be stable and constant. In reality, it's not, as we know it's orbit is expanding. I understand this is caused due to the moon's effect of slowing down the Earth's rotation. That transfers energy from the moon's orbit to the Earth momentum. If this eventually results in Earth being tide-locked with the moon, at which time, that transfer would stop."
] |
[
"I'm familiar with the basic, super simple model of orbit with Kepler's laws and Newtonian gravity. In that context, everything either orbits, crashes, or flies away.",
"This is only true in the context of a two body system. When more than 2 bodies are present, the system becomes chaotic and eventually unstable. So it isn't a question of stable vs. unstable, it is a question of stable ",
" to stick around for a stellar lifetime.",
"Orbits are stable until they are not. Mars's moon Phobos, for example, has an \"unstable\" orbit around Mars. Due to tidal friction, it is slowly getting closer to Mars, and will eventually be ripped apart to form ring system. But that won't happen for another 8 million years...for now, the orbit is \"stable\"."
] |
[
"Could a bullet made of frozen blood really be more effective than a bullet made of water?"
] |
[
false
] | null |
[
"First of all, blood is ~80% water, so the same general problems with ice bullets still apply. In addition to that, blood has a whole bunch of stuff dissolved in it that disrupts the formation of ice crystals and mechanically weakens the frozen phase. So, a bullet made from frozen blood would actually be worse than an ice bullet!"
] |
[
"I don't know if it constitutes an authority as per the side bar, but Mythbusters had an episode dealing with frozen water / meat / gelatin bullets, ",
"'Magic Bullet'",
". ",
"But blood bullets could potentially have higher lethality than ice bullets. The trick would be to keep from infecting yourself with the HIV / ebola / whatever blood-borne disease that'd be contaminating your weapon and be misted out whenever you fired."
] |
[
"Thanks!"
] |
[
"Are there any “holes” in the periodic table that could be filled with undiscovered elements?"
] |
[
false
] | null |
[
"Nope, just any elements with Z > 118."
] |
[
"Would discovering new ones create holes?"
] |
[
"It could. For example, if 120 were to be discovered before 119."
] |
[
"What is the largest (and/or most massive) known solid/liquid body?"
] |
[
false
] |
As far as I understand, and and are designated including their atmosphere, which accounts for most of their mass and volume. If we ignore the atmosphere, what would be the largest solid and/or liquid body known to us in the universe? In particular, I'm interested in bodies that are kept solid not by extreme pressure, but because of their composition (i.e. that would have been solid even without the pressure).
|
[
"Check out the ",
"Sloan Great Wall",
". It's 1.37 billion light years in size, or about 1/60 of the size of the Universe. ",
"Though that may not quantify as the largest 'body', it is indeed the largest known system."
] |
[
"I should have said ",
" not ",
". Sorry about that. VY Canis Majoris has only a mass between 30 and 40 solar masses."
] |
[
"How is 'structure' being defined there, exactly? It's an impressive record."
] |
[
"Not trolling, just seemed like the right place to ask. Will I get cancer if I stick my testicles in the microwave?"
] |
[
false
] | null |
[
"No, but you will eventually boil the water in the exposed cells. It won't be fun."
] |
[
"How are you going to close the door on those bad boys? "
] |
[
"I realize this is old, but ",
"/r/shittyaskscience"
] |
[
"why aren't semis shaped like a bullet train?"
] |
[
false
] |
[deleted]
|
[
"Most semis are designed they way they are because they require a large amount of air flow to help the radiator to cool the engine more efficiently.\nA flat front end, decreases aerodynamics but increases the air flow to the radiator.\n",
"How radiators work"
] |
[
"There have been attempts to improve aerodynamics of semis: if you see a semi that has plastic vanes hanging underneath the trailer, those are placed to improve airflow.",
"Many of the newer semis also have better aerodynamics in their body shape, however semis last ",
" longer than your average car does - so the older blocky models are still seen on the road quite a bit."
] |
[
"A vehicles drag coefficient is affected by the frontal area, therefore a semi truck is always at a disadvantage. Bullet trains' aerodynamic nose shape is actually very long, adapting it to a semi truck front would increase its length so much I assume road maneuverability would be terrible.",
"However, the semi trucks' long cubic trailer creates a strong negative pressure zone immediately behind it. Several truck companies have shown \"slip on\" teardrop or cone shapes for the back end of semi trailers, to minimize the negative pressure zone. They have never been accepted, I don't know why other than to guess cost and awkwardness to fit and remove to load / unload.",
"In their own very small way incremental aerodynamic design of semi cabs have improved with flowing wheel wells, mildly conic steep angled front hoods, integrated cab top air dams, and the under trailer air skirts Amadameus first mentions."
] |
[
"If I fired a conductive chain from the ground up into the clouds during a thunderstorm, would lightning 'follow' along the chain?"
] |
[
false
] |
When I was a kid, I wanted to create a lightning machine, and this was the best idea I had at the time. Since air is not very conductive but it still ionizes to allow energy to travel along it during a thunderstorm, would helping it along cause a predictable lightning strike?
|
[
"Yes, this would work. In fact, ",
"it is already done on a regular basis",
" by lightning researchers, launching rockets into thunderstorms which trail a thin copper wire behind them attached to the ground. These ",
"lightning rockets",
" are apparently effective at inducing lightning when the right conditions are present, but for the life of me I can't find any solid data on just ",
" effective they are. Every study I read omits the number of successful vs unsuccessful launches, and the parameters that determine launches. So, sadly, I can't give you a better answer than \"it can work some of the time\"."
] |
[
"hypothetically, could this be done with something on the order of a model rocket?",
"hypothetically"
] |
[
"Yes, but probably not very reliably. The higher your rocket gets, the more likely lightning will hit it though. Also your surroundings will also play a role. ",
"Storm clouds",
" can be much higher than most model rockets 10,000-20,000 ft vs 1,500 ft so I would guess that this would not induce lightning but instead attract lightning was planning on hitting something within 2,000 feet of you anyway."
] |
[
"Are there alternatives to randomized double blind trials when such trials would be unethical?"
] |
[
false
] |
Hello all, so this has come from an interesting debate, but I need to explain it first with an analogy. First, imagine a person who wanted to test the theory that removing a malignant tumor would be helpful to a cancer patient. Following a double blind trial, they then ask a surgeon to remove only half of the tumors from a group of cancer patients and not tell them which got the "placebo treatment" of just a surgical scar. You can see how such a study would never make it past the IRB. However, this is a very real issue in studies of my condition. I'm transgender and at last report we had a which is greatly elevated over the national average, so it's safe to say that our condition is life threatening. However, the standard treatment for gender dysphoria is transition, and while there is a large body of work suggesting that transition is beneficial to trans people, there remain calls for . However, the statistics suggest and I can personally attest that gender dysphoria is extremely unpleasant to the point of being life threatening and trans people will be quite miserable when denied transitional care to the point of it being dangerous to the control group. Also the effects of hormone therapy are rather obvious and difficult to mimic with a placebo (growth of breasts and facial hair are obvious). Thus we have a conundrum. How do you test the effectiveness if the standard controls are functionally difficult and unethical?
|
[
"There are two parts to your question.",
"Part 1: when placebo is unethical, what do you do in your control group?",
"The answer to this is that you never define your study in terms of \"control group gets placebo\". Instead, you always define your study in terms of \"control group gets best currently available treatment\". If there is currently no treatment, that means that control group gets placebo. But if there is currently available treatment, ultimately you a. don't care about whether new treatment is better than the placebo, but whether it's better than existing treatment anyway and b. dodge the ethical bullet by making sure that everyone gets some treatment — either current best known treatment, or experimental treatment.",
"A brief sidebar: sham surgery (in which an incision is made and then sutured, but no other surgical interventions are performed) has actually been done as part of a trials in the past. You can get that past an IRB in some cases — basically, when there is doubt about whether the existing surgical treatment is effective, then comparing it to placebo surgery is not necessarily unethical.",
"Part 2: when blinding is impractical, how do you control for confirmation bias?",
"The answer to this is that you don't. Or you get really clever. For example, people have come up with some really clever ways to perform placebo acupuncture, but it took a lot of work and some clever engineering.",
"As you can imagine, sometimes there is nothing you can do. There is no placebo for almost all gender-realignment therapy. ",
"In such cases all can do is acknowledge that your studies are potentially vulnerable to bias, and move on with your life."
] |
[
"This basically covers it. I would just add that in some extreme cases, I believe clinical trials may be halted if the new treatment performs drastically better or worse than the \"best currently available\" control. This would be done when it is considered unethical to continue with treating patients in the two groups differently, because of drasticaly different outcomes."
] |
[
"If I recall, an example of when halting was done was with the study on low dose aspirin for reducing the risk of heart attack. "
] |
[
"When they announce discovery of a new breed of bird or fish or whatever, are they always meaning \"Never before discovered\" or does it sometimes mean a new crossbread from previous breeds/types?"
] |
[
false
] | null |
[
"It depends on the type of animal (wild v. domestic) but the majority of the time they mean never before discovered. But discovered can mean different things, maybe it a species that we've never seen before or maybe it's an animal that we misclassified. An example of this is the platypus, after genetic testing it is though that there are two subspecies not one species as originally thought."
] |
[
"Yes, but the emphasis is on \"different\", not on \"producing offspring.\" In case of subspecies, unless they found a lone individual specimen, it would be trivial to note the population can produce ",
" (offspring are not sterile) offspring.",
"So what makes them sufficiently different? In many cases (especially among fish, but present in most groups of animals), the subspecies, and sometimes even species from different genuses can still hybridize and produce viable offspring, if given the chance. So while inability to breed across subspecies is usually sufficient (I think it is always sufficient, afaik), as I just explained by example, not necessary for defining a subspecies.",
"Two populations of a species begin to drift apart when there is a geographical barrier between them, be it a desert, a forest they can't live in, etc, or if they spread far enough across a space that a species on one extreme does not normally have the opportunity to breed with species on the other side (Google \"ring species\" for extra fun--both groups on both sides might eventually be unable to breed with each other, buy can both breed with the guys in the middle!)... Well, then they have an opportunity to genetically drift, as the populations are separated. Eventually, they drift to an extent where it becomes \"noticeable\" by a taxonomist, they then genetically test the two populations to determine whether certain mutations are uniform within each population, and if \"enough\" are, then we consider them to be subspecies. What is \"noticeable,\" and what is \"enough\" are constantly bickered about in taxonomic circles."
] |
[
"So does that mean two different animals successfully produced offspring?"
] |
[
"I understand the need for a standardized order of operations, but is there a reason behind the specific order? Or is it arbitrary like the order of the alphabet?"
] |
[
false
] | null |
[
"It’s just a shared language so that people can understand one another’s equations.",
"For what it’s worth, when people to whom math is important write equations out, they write them in a way that is pretty clear even if you’re not familiar with the standard order of operations. The “lol 6 x 7 ÷ (4-1)” Facebook riddle stuff is not used."
] |
[
"It's more like grammar rules. Standardized grammar rules is an attempt to capture how people speak and write, in order to teach them to students. Standardized order of operations is an attempt to capture how mathematicians usually write and interpret their algebraic expressions (which had been gradually developed for a few centuries), in order to teach them to students. Neither are perfectly correct description of how people actually speak/write, but close enough. With the modern development of computer and calculator which requires unambiguous rules, they are likely to stay with little changes, I guess.",
"How much of it is arbitrary? The fact that multiplication and division have priority over addition and subtraction, or that exponentiation have even more priority, is probably not arbitrary. Various mathematicians in history had been using different conventions, yet they all naturally agree on the idea that multiplication and division should have priority. It makes polynomials much easier to write, for example. Same goes for exponentiation over multiplication and division. There is a very natural hierarchy there."
] |
[
"Order of operations is only relevant to how we ",
" equations. Using PEMDAS we would say 1 + 3 * 5 = 16, but if we all agreed to instead use PEASMD (just made that up) we could say 1 + 3 * 5 = 20. There's nothing objectively incorrect about using the second system, it's just not convention and you'll confuse everyone if you do. But if we all agreed to switch to a new order of operations, math wouldn't break, we'd just need to convert all of our existing equations."
] |
[
"Why don't we use capacitor as normal battery? Would it charge faster?"
] |
[
false
] |
well, all is in the title
|
[
"While you can make capacitors behave like a battery by using a ",
"sepic",
" converter, capacitors are far behind batteries in energy density. From ",
"wikipedia",
", \"Conventional capacitors provide less than 360 joules per kilogram of energy density, whereas a conventional alkaline battery has a density of 590 kJ/kg.\"",
"Ultra capacitors",
" (or super capacitors) have higher energy density but are both very expensive and still beat by conventional batteries.",
"To answer your specific question, the reason why we don't use capacitors in place of normal batteries is primarily an economics reason. While you could, it's not going to last as long as a standard battery of similar size, and it will cost a lot more. Yes, you can charge a capacitor much faster than a normal battery."
] |
[
"And in fact, ultracapacitors ",
" used instead of normal batteries where it makes sense. For example, some Solid State Drives (SSDs) use an ultracapacitor so that if the power is interrupted, the SSD can still work for a very short time. This allows the SSD to write data that was in temporary storage to the flash memory chips so that it isn't lost. Or in some \"secure\" SSDs, it gives the controller time to issue an erase command and wipe the drive. "
] |
[
"That's not the reason we don't use capacitors. They ",
" dump all of their energy very quickly if you short circuit them, but any reasonably-designed circuit will work just fine. The problem with capacitors, as aleenaelyn said, is that they simply don't hold very much energy compared to batteries."
] |
[
"Many bacteria seem to have developed a highly symbiotic relationship with humans to the extent without either side, the death of both organisms would result. Does this situation ever occur with viruses?"
] |
[
false
] | null |
[
"I don't have a link at hand, but I remember listening to a lecture on the subject. It seems our DNA in fact contains several pieces of used-to-be vira that has been integrated into our DNA. Not exactly the same, but still fascinating. "
] |
[
"I've heard this before too. I wonder if viruses aren't responsible in part for genetic mutations that allow for evolution of the species."
] |
[
"No. The reason for this is that bacteria are metabolically active, with numerous organelles performing various functions. They break down substances and bio transform others -they're quite the little workhorses. These same functions are often beneficial to other organisms. Viruses, however, are simply packets of protein that exist solely to replicate themselves. They are metabolically and otherwise totally inert. Therefore they don't break down or produce/transform anything. They invade cellular machinery, some inserting themselves into DNA and then using that machinery to make copies of themselves, in the process damaging/killing the cell."
] |
[
"Coconut oil health uses."
] |
[
false
] |
I hope this goes here- just used coconut oil on my son's diaper rash because of the anti fungal, antibacterial, antiviral and yeast killing properties. What other health benefits are there for the little known super food?
|
[
"Was it applied in their diapers?"
] |
[
"Not that I'm aware of, usually mice prefer to eat it. You did only ask about coconut oil and health, not just diapers. ",
"Coconut oil's beneficial properties in regards to diaper rashes more stem form it's ability to create an impermeable membrane and promotes the restoration of the intrinsic immune system of the skin than anything else. In theory you could do the same with lard, although a lard-covered baby might draw some glances.",
"Edit: incomplete sentence structure."
] |
[
"Thank you- I appreciate the info and dealing with my late(for mommy) night mommy humor. I've read about the ups and downs of the oil before but have never seen anything definitive. "
] |
[
"How do the lungs heal after a smoker quits?"
] |
[
false
] |
I'm a biochemistry major who just quit smoking and I'm curious about the processes (e.g. chemical reactions, replacement of cells, removal of debris) that are taking place within my lungs. When I go on the internet, I get a very broad sense of what is going on, but I'm more interested in the details and science. Could anyone answer this question? Please do not be afraid to use scientific vernacular. Thank you.
|
[
"A little bit to get people started. ",
"\"The British doctors study showed that those who stopped smoking before they reached 30 years of age lived almost as long as those who never smoked.\" ",
"Wikipedia",
"/",
"Cancer.org",
" ",
"Histopathological Changes from the ",
"Surgeon General",
" (PDF warning) ",
"Pg. 103 - \"The occurence of unciliated atypical cells, the most severe change before invasive carcinoma, was similar among ex-smokers and never smokers but considerably greater among current smokers. When current smokers were matched with fromer smokers of the same age at time of cessation, former smokers showed fewer lesion, suggesting that the number of lesions decreased rather than merely failed to increase after cessation of smoking\" ",
"104 - \"Several reports have described levels of DNA adducts formed by the combination of chemical carcinogens or their metabolites with DNA in the tissue of never, former, and current smokers. Decline of DNA adduct levels in human lungs after smoking cessation... whose who had not smoked for 5 years or more had adduct levels similar to non-smokers\" ",
"301/7/33 - Cessation may lead to: recovery of epithelial integrity, increased tracheal mucous velocities, return of normal immune state of the lung, improvement of FEV1 in people who quit early."
] |
[
"Great references in the second half. I despise the first half (which we often see in a timeline format) since it groups together all smokers - those who some maybe a cigarette a day with those who go through 2 packs a day. Is there any research that defines averages of consumption?"
] |
[
"I expect he means to say that the total damage vs number of cigarettes curve looks logarithmic. That doesn't seem entirely counter intuitive to me."
] |
[
"Motionless Water Doesn't Freeze?"
] |
[
false
] | null |
[
"You just happened to make supercooled water! This happens if you cool water gently enough without disturbing it. Its temperature is below freezing, but yet, is still a liquid. It will turn to a solid at the slightest provocation.",
"A nucleation site is needed for the ice to form -- basically a rough spot or turbulence somewhere. Your handling of the bottle is enough to do this. This trick with supercooled water will heavily favour containers that are relatively smooth.",
"Is this helpful?"
] |
[
"The process is called ",
"supercooling",
"."
] |
[
"I think this is the same (but obviously opposite) reaction type as super heating water in the microwave. If you heat water in a very very smooth container and there is no break in surface tension the water will actually super heat without boiling. Then when you break the tension by moving the glass the water actually explodes. "
] |
[
"Why is it that whenever I stir orange sherbert quickly with a spoon to make it soft the outside of my cup freezes over?"
] |
[
false
] | null |
[
"It could be caused by increased heat transfer due to convection caused by stirring. Normally, with no stirring, the outside of the sherbert will be warmer than the center after it is taken out of the freezer and some time passes (because the room temperature warms the glass which warms the outside layer of the sherbert, it would take more time for that heat to conduct to the center).",
"However, if you stir it, the colder sherbert at the center will mix with the warmer outer layer, decreasing the temperature of that, and then the glass, causing increased condensation to form on the glass. "
] |
[
"The cup of sherbert is going to rob its surroundings of heat, BUT it's very viscous so no convection currents will form to distribute the heat that it is absorbing. So it absorbs some heat, and melts a thin layer of sherbert that then acts as an insulator to the rest of the cup, slowing the process of absorbing even more heat. When you vigerously stir the sherbert you're artificially creating convection currents, distributing the absorbed heat more evenly and removing this insulating effect, it can then absorb much more ambient heat much more rapidly. In this way it absorbs enough heat from the immediate ambient air to condense and then freeze the moisture in the surrounding air."
] |
[
"The cup of sherbert is going to rob its surroundings of heat, BUT it's very viscous so no convection currents will form to distribute the heat that it is absorbing. So it absorbs some heat, and melts a thin layer of sherbert that then acts as an insulator to the rest of the cup, slowing the process of absorbing even more heat. When you vigerously stir the sherbert you're artificially creating convection currents, distributing the absorbed heat more evenly and removing this insulating effect, it can then absorb much more ambient heat much more rapidly. In this way it absorbs enough heat from the immediate ambient air to condense and then freeze the moisture in the surrounding air."
] |
[
"Why don't all clouds form at the same elevation?"
] |
[
false
] |
[deleted]
|
[
"Most clouds form at the same height, at least the cloud base does. This is due to the temperature of the air at that point reaching the dew point (the temperature at which a certain amount of water vapor is 100% saturated) and the clouds will start to condense around Cloud Condensation Nuclei. ",
"This elevation is generally the same height for all clouds in a given area, making their bottoms (cloud base) the same. The tops, however, can differ vastly and that is due to convective forces in the air. More turbulent air produces higher clouds, with cumulonimbus stretching over 5 km vertically. ",
"Clouds form at different heights also due to inversions. Inversions are layers in the air where the temperature stops dropping and instead rises back again. If the gradient of temperature is not negative, clouds can not pass through it (because then it goes back over the dew point and water vaporizes again). Above the inversion, cloud formation can happen again if there is enough water vapor in the air."
] |
[
"The below comment is specifically for cumulus clouds:",
"Cumulus clouds usually form at what is referred to as the lifted condensation level (LCL). However, the LCL isn't exactly where the temperature is equal to the dewpoint, it is were the temperature of a surface parcel, if lifted, would cool to the surface dewpoint.",
"You can think of a surface parcel as a bubble (like the bubbles in the bottom of a boiling pot). If this bubble were to rise, whether it because it is warmer than the surrounding air (and thus less dense), or if it were forced by terrain or a cold front or dry line (which act kind of like terrain due to higher density), this bubble will cool at approximately 10 degrees celsius per km as it expands. If this rising bubble becomes cooler than the environmental temperature before it cools to it's dewpoint, it stops rising and no clouds form. This is why you rarely see cumulus (small puffy clouds) before around solar noon. This is because the bubble is either too cool to start rising, or too cool to keep rising. However, later in the day, the surface warms, and these bubbles can rise until the cloud forms. ",
"While at the most basic, you can assume when the temperature of the parcel equals the dewpoint a cloud will form, it's actually a little more complicated. If there are no cloud condensation nuclei (CCN; dust, smoke, sulfates, sea salt etc.) then the water vapor in the air must condense spontaneously through a process known as homogeneous nucleation. Homogeneous nucleation requires relative humidity above 100% such that the dewpoint would be above the actual temperature of this parcel. With that said, CCN almost always is present where clouds form.",
"While, the LCL can be found on atmospheric soundings, it's altitude is dependent on the surface temperature and dewpoint. Because, on any day, these change within relatively short distances, the cloud base altitude will also change. There are also dynamical (as opposed to thermodynamical) issues that come into play to change cumulus altitude, but I will explain those in a second reply."
] |
[
"If you are referring to why clouds form at different altitudes (i.e., stratocumulus vs altocumulus vs cirrus) each cloud type actually has a different formation mechanism. The formation mechanism for cumulus is explained in my other comment. Cirrus (the thin wispy clouds) actually form in a variety of ways. The important thing to note with cirrus is their altitude: very high (10-18km) and very cold (cloud top temperature below -37C; e.g., Campbell, J. R., et al. 2016 in J. of Applied Meteorology and Climatology). Thus, these clouds do not form directly from the parcels suggested in my other comment.",
"One mechanism for cirrus formation is anvil blow-off. Sometimes, when the environment is very cold compared to near surface, the cumulus become cumulonimbus (thunder storms). These storms reach to the top of the troposphere in a region referred to as the tropopause. In the stratosphere (directly above the troposphere) the temperature actually increases, and all surface based parcels become stable (stop rising). When the air hits this barrier, it spreads out laterally and forms the anvil (named because it looks like a blacksmith's anvil). The winds at this altitude are very strong, sometimes reaching 200mph! Thus, the ice particles forming in this anvil can get blown away from the parent thunderstorm causing the thin wispy clouds.",
"Cirrus can also form through homogeneous nucleation (explained in the other comment). This often happens due to waves in the atmosphere. The atmosphere acts just like a fluid (just like the ocean!). The thunderstorms explained above can actually push through the tropopause into the troposphere because the momentum of the air pushes it upward. This is called an overshooting top (see ",
"link",
" for both anvil and overshooting top). When this occurs, it causes waves. These waves can actually lift upper tropospheric air, causing cirrus to form. Other large scale upper atmospheric waves cause cirrus this same way.",
"Thus, different cloud types typically form at different altitudes because they are formed through different mechanisms."
] |
[
"How do ants survive long drops?"
] |
[
false
] |
[deleted]
|
[
"Because surface area is squared, and volume is cubed.",
"Therefore when something gets bigger, its volume starts to increase more and more away from it's area.",
"So relatively speaking, ant has huge surface area relative to its volume.",
"Mouse has large surface area relative to its volume.",
"Human has low surface area relative to its volume.",
"Horse has very very low surface area relative to its volume.",
"There's a famous quote from Haldane about this problem \"To the mouse and any smaller animal it presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes.\""
] |
[
"Correct me if I'm wrong, but it would stand to reason that the less mass something has, the less force is exerted when it falls. At a very low mass, that force would be very small."
] |
[
"The force of gravity on a lower mass object is indeed smaller, but the acceleration due to gravity is the same on all objects because it scales with force/mass. In a vacuum all objects fall at the same speed. A feather and brick and an elephant will all fall exactly the same speed and hit the ground at the same velocity. However this all changes when you add air friction. Air friction exerts an upward force that counteracts gravity. So when the object is low mass (like an ant) the force due to air friction is similar in magnitude to the force of gravity at low speed. For a low mass object, the speed at which the forces balance (the terminal velocity) is low, so the ant hits the ground at a gentle low speed whatever the height it dropped from. For an elephant, the two forces don't balance until very high (terminal) velocity because the force due to gravity is large (thus it takes a very high speed for air friction to balance it)."
] |
[
"Will global cooling over the next two years from this Tonga volcanic explosion be bad enough to interfere with crop production? What should we really expect?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"thread",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I want to know what the current answer is if the volcano had stopped after that particular explosion."
] |
[
"Again, this is not known yet. We do not have numbers of the amount of material added to the atmosphere, only estimations from preliminary satellite data (and the event is clearly ongoing as there have been subsequent smaller eruptions since the large blast yesterday). The question remains unanswerable."
] |
[
"Do women have digestive systems that are significantly different from that of a man?"
] |
[
false
] |
I always hear that women have more sensitive stomachs. There seems to be a lot of products on the market that are aimed towards improving the digestive systems for women. Is that all just marketing, or is there some truth behind it?
|
[
"It's just marketing. Individual variation is more than the variation between the sexes.",
"That being said, my girlfriend assures me that the only waste products produced by females are rose petals accompanied by the sound of childrens laughter."
] |
[
"No, they don't. Bacterial gut flora vary between people based on region, diet, day to day changes, medicines, hormones... There is a lot that alters the microflora that makes up a GI tract, but not gender. There is a lot of marketing schemes that people use, and this is one of them. Nothing about being a woman or man makes a person inherently different in their digestive tract. "
] |
[
"I thought there had been a few human microbiota studies that did indeed show differences between men and women? I know this exists, obviously, for the uro-genital tract. My recollection of the larger studies though with multiple collection sites on the body is a bit hazy. Am I misremembering?"
] |
[
"Do any animals have Fresnel eye lenses instead of biconvex ones?"
] |
[
false
] |
Eye lenses seems to have evolved independently numerous times but did the evolutionary process ever give rise to a crystalline lens shaped like a ?
|
[
"You are correct that reduced image quality is a drawback of Fresnel lenses. But it is conceivable that the compactness advantage of a Fresnel lens could outweigh the image quality loss in an animal's eye, just as as it does in some human-designed imaging applications.",
"Edit: I should also mention that Fresnel lenses can, in fact, be used to focus light."
] |
[
"You are correct that reduced image quality is a drawback of Fresnel lenses. But it is conceivable that the compactness advantage of a Fresnel lens could outweigh the image quality loss in an animal's eye, just as as it does in some human-designed imaging applications.",
"Edit: I should also mention that Fresnel lenses can, in fact, be used to focus light."
] |
[
"No, this has never happened.",
"However, one of Richard Dawkins' favorite examples of cool/multiple eye evolution is the brownsnout spookfish, ",
"http://en.wikipedia.org/wiki/Brownsnout_spookfish",
".",
"This fish has evolved a 'typical' biconvex eye and a separate eye that uses a reflector made of guanine crystals to focus the image onto a point. And they both evolved in the same creature."
] |
[
"Would a wooden chair, a paper book or a computer survive in a sealed untouched room for billions of years?"
] |
[
false
] | null |
[
"Iron preserved in vacuum, therefore not in contact with electrolytes, should as far as I am aware survive. At least it will not deteriorate due to oxidation. Minerals, (in the form of a stone table?) could survive.",
"Glass actually behaves sort of like a ",
"liquid",
" over time. It might only exist as 'melted' remains.",
"Radiation in space might also have an impact. High energy particles will penetrate your device with ease.\nPerhaps if the spacecraft were to have some sort of artificially created powerful magnetosphere radiation might to some degree be avoided.\nThe best way to avoid the radiation might be to place the spaceship on a planet (without an atmosphere that might fuck shit up). But the plate tectonics which is a result of the liquid core (which in turns generate the magnetic field you need) will eventually destroy your ship.",
"If you are writing fantasy perhaps you could just invent some sort of interstellar vacuum-chamber made of a tungsten-adamantium-unobtanium alloy which generates a magnetosphere as powerful as that of Canis Majoris? I admire your strive for realism, though :)"
] |
[
"The notion that glass behaves as a liquid over time is a ",
"common misconception",
"."
] |
[
"Hard drives need to be spun up every few months to keep them from going bad, so a computer with a mechanical hard disk most likely would not survive. Assuming that the room that these things are in is shielded from radiation, I see no reason why a chair or a book wouldn't survive, as long as the room is properly preserved."
] |
[
"Does the atomspheric pressure increase when more co2 is produced?"
] |
[
false
] | null |
[
"Very slightly, yes.",
"Although scientists generally prefer the metric system, it can be very useful to think of pressure in terms of imperial units. When we say the pressure at sea level is \"14.7 pounds per square inch\", that literally means for every square inch of the surface, there's an extremely tall skinny column of air pushing down on that square with 14.7 pounds of weight.",
"That also means that if you add mass to the atmosphere, the weight will increase and thus so will the pressure.",
"For most of the excess CO",
" we've created in the past 150 years, it involved digging up carbon compounds, burning them, and releasing the exhaust into the air. That means most CO",
" molecules we create first had to find an O",
" molecule to bond with...so while we're removing oxygen molecules, we're adding carbon dioxide molecules.",
"Since CO",
" has a molecular weight of 44 while O",
" has a molecular weight of 32, we're essentially increasing the weight of those molecules by 44/32 - 1 = 37.5%, which in turn means we've increased the pressure.",
"Bear in mind, though, we're only talking about a tiny fraction of the total atmosphere here. In the past 150 years, we've gone from 280 ppm to 410 ppm CO",
". That means we've replaced 130 ppm = 0.013% of the molecules in our atmosphere with one that's 37.5% heavier.",
"If the average molecular weight of the air was roughly...",
"78.082% N",
" + 20.96% O",
" + 0.93% Ar + 0.028% CO",
"= 0.78082 * 28 + 0.2096 * 32 + 0.0093 * 40 + 0.00028 * 44",
"= 28.9545",
"...and it's now...",
"78.082% N",
" + 20.947% O",
" + 0.93% Ar + 0.041% CO",
"= 0.78082 * 28 + 0.20947 * 32 + 0.0093 * 40 + 0.00041 * 44",
"= 28.9560",
"...which means that the pressure has increased by about 28.9560 / 28.9545 - 1 = 0.005%.",
": Yes, by about 0.005% in the past 150 years."
] |
[
"Scientists typically speaking about pressure in bar or atmospheres. Those are hard to conceptualize. Pounds per square inch is easy. You can conceptualize a 20 lb dumbbell or rock sitting on top of your head to resemble the air pressure. ",
"It was just to help people understand what atmospheric pressure ",
"."
] |
[
"Co2 is measured in ppm. By the time the co2 level raised to the point increased atmospheric pressure was an issue, the chemical effects of raised co2 would have changed the atmosphere in ways that were much less favourable than increased pressure."
] |
[
"What are the benefits from discovering only a few atoms of elements like 118 (Oganesson) and others that were created in an accelerator?"
] |
[
false
] |
Certain man-made elements like Tennessine (117) or Oganesson (118) have been created in a particle accelerator but only a few atoms detected at a time. If we cant physically do anything with these new elements, what are the other benefits from creating/discovering them? And whats the importance of synthesizing others like element 120?
|
[
"It allows us to test and constrain theories in nuclear physics. They don't have any practical use, but they are very useful and important to people who study nuclear physics and nuclear chemistry."
] |
[
"Testing nuclear models with isotopes we can produce also helps to predict the properties of isotopes we cannot produce, like very neutron-rich isotopes that play an important role in the production of all heavier elements. You see where a model fails if you test it for the most extreme cases you can make."
] |
[
"I figured since scientists theorize new elements they would have to synthesize them to prove if theyre calculations and everything were right, i just wasnt sure of what comes next. Like Ok so we were right....we synthesized what we theorized, now what? It makes sense they could just use the answers and info they get, not the actual physical elements, to continue with their theories. Thanks for the response!"
] |
[
"Is there a reason why bacteriophages are not widely used?"
] |
[
false
] |
[deleted]
|
[
"I'm not a biologist, but I was a science journalist and wrote an article about this about 12 years back. I talked to the most active Western researchers in the area; they were hopeful about progress what with the research from Tbilisi finally making its way into English but nothing much seems to have happened.",
"The main problem with bacteriophages is that they're very specific in the bacteria they attack. You have to find out exactly what sort of strep or staph or whatever before pulling the correct bacteriophage out of storage and if it's something new, as it often is, you're out of luck. ",
"A second problem, as I recall, is that your immune system will fight the bactiophage while it's trying to work so it's a lot less effective in the body than it is in the petri dish.",
"Beyond that, it still has the stink of Soviet science on it which means that the decades of research done in Tbilisi all need to be reproduced in the West before it's trusted even if anyone's willing to give it a chance after its failure in the pre-antibiotic era. (Modern researchers say that early work failed because they couldn't type the bacteria well enough to find the right bacteriophage to apply.)"
] |
[
"You got it spot on. My colleague (who did a bunch of projects on it) also mentioned that the immune responses are the main problems: essentially meaning you can give this treatment exactly just once."
] |
[
"I haven't really been keeping up but ",
"this",
" 2005 article says that they're still using phage therapy in Georgia. ",
"As for my article, I wrote it while I was still in journalism school. That means a) it's not so good and b) it was never published. I dug around, but I don't think I've still got a copy."
] |
[
"Let's say you have a very long rope, about as long as the circumference of the Earth."
] |
[
false
] |
So here's the thought: Let's say the rope is 1m long: You and your friend are facing each other, each holding on to a different end of the rope. When you are 1m away from eachother, the rope is taut, and no part of it touches the ground. Let's say that the rope is 40m long: Your friend stays where they are, but you walk backwards 39m, and the rope is taut again - no part of it touches the ground. Now let's say the rope is ~40,000km long (the circumference of the Earth). Your friend remains where they are, you walk backwards ~40,000km, until your back bumps into your friend. You're both pulling on the rope, and it's taut. Can you just tie the two ends together, and have the rope hold itself up, or will the rope fall to the ground? Why? This has been bothering me for a while, I hope you can help, .
|
[
"The rope would create a tangent to the curve of the earth at a certain point (an intersecting point with the ground) between you two after a certain length depending on the height of the two people.",
"So, no, it touches the ground in the middle at some probably easy to determine length value based on height."
] |
[
"Here, I illustrated it for you OP (not to scale): ",
"http://i.imgur.com/WNsdG.jpg"
] |
[
"I think the actual question you had in mind was hamstrung by your hypothetical. Allow me to posit another hypothetical that may more accurately represent your question:",
"Say you built a single large support and from it you and a friend began constructing a bridge in opposite directions which paralleled the curvature of the earth, and continued constructing it until the ends joined; what would happen if its sole support were removed? Would the bridge stay suspended above the earth?"
] |
[
"When animals yawn, is it contagious to members of their own species like it is in humans?"
] |
[
false
] | null |
[
"It has been reported in a couple of species, like ",
"gelada baboons",
", and has also been demonstrated to work in response to video images of a conspecific yawning in ",
"macaques",
". I think both articles discuss previous research as well, mostly in ",
"chimps",
".",
"I'm not aware of any evidence of it occurring in non-primates, but this could be because contagious yawning is a by-product of the ability to mimic actions. This of course is a complex behavior, and even humans don't learn contagious yawning until around 4 years of age - and people with learning disorders like autism, who have difficulties with mimicry, may never learn it. There's an interesting paper on the development of the yawn contagion here: ",
"Contagious Yawning in Autistic and Typical Development",
". ",
"I think it has been speculated that mirror neurons might play a vital role in contagious yawning, which could rule out animals who lack this feature of the brain, but I'm not sure of any hard evidence on that issue. It's also been noted that there is a possible link between the capability of ",
"empathy and contagious yawning",
", where we find that the more emotional investment there is in the model yawner, the more likely it is that the receiver will respond with a yawn. So we're most likely to engage in contagious yawning with family, and then friends, then acquaintances, and then strangers. If this is so, it could be a problem for research looking into non-human contagious yawning as we'd have to ensure that the subjects aren't all \"strangers\"."
] |
[
"Definitely not in all animals; there was actually an Ig Nobel given out for ",
"this",
" where the authors found that red-footed tortoises show no evidence of contagious yawning."
] |
[
"I went to a seminar where the lecturer discussed empathy in other animals, citing yawning a a basic example (possibly) of empathy between animals. I don't remember the more lower-level-intelligence animals that yawned after another to show empathy, but I can tell you that chimps have been shown definitively to do just that."
] |
[
"Do older people vaccinated for Covid have a “good” immune response from it?"
] |
[
false
] |
My otherwise very healthy and independent 94yo grandmother received her first Covid vaccine 5 days ago. I asked her if her arm was as sore as mine and she said it doesn’t hurt at all. I was wondering if the immune response in the older population has been studied much. I’m just curious if her complete lack of side effects is an indication that her body did not get a strong immune response.
|
[
"Just as everyone has a different reaction to COVID infection, ranging from being asymptomatic to dying in full organ failure, everyone seems to have a different reaction to the vaccine. The strength of the reaction doesn’t correlate to the strength of the immune response. My partner hardly noticed his, but one of his colleagues was laid up for a day with dizziness and aches. They’ve both titered as immune, though. ",
"All the various manufacturers’ vaccine trials included people age 70+ and the ones being distributed were shown to be safe and effective across all age ranges. A quick Google of the particular kind you received will let you read the trial results for yourself for a better idea of how many elderly subjects were tested and what the reported side effects were.",
"Wishing you and your grandmother a happy, healthy future!"
] |
[
"The studies for moderna showed 86% immunity after 1 dose for those over 65 I believe, so it actually proved very efficacious for elderly patients. Pfizer was closer to 50%.",
"As far as side effects it’s different for anyone. The lack of side effects will not tell you one way or another on its efficacy, everyone reacts differently- just like when some people get a cold it’s much worse than for others- ",
"I got the first shot of Pfizer and felt fine. Even the soreness wasn’t too bad"
] |
[
"Something to note that hasn’t been mentioned is that even if a vaccine is safe, pain levels can vary widely depending on how high/low it gets injected, and how whether whoever is doing it went a little too deep, not deep enough, etc. ",
"There are many reasons besides the ingredients, these things can happen."
] |
[
"Why does the c in e = mc^2 equal the speed of light?"
] |
[
false
] |
I’ve been thinking about it for a while and I can’t seem to figure it out. Why does the speed of light have anything to do with this equation. Ofc it’s not a coincidence and I just don’t understand how mass and energy have anything todo with the speed of light.
|
[
"When we have an object in special relativity, we assign it 4 numbers for its location in time, x, y, and z. Think of this like an address. The President of the United States lives at 1600 Pennsylvania Avenue, Washington D.C and our object lives at,",
"Great! The only problem though is that time doesn't have the same units as length. We need to convert time to have the same units. In special relativity, the universal speed is the speed of light, this number is the same for everyone, regardless of how someone is moving. So we'll use that.",
"Even better. It is important to make the units the same because in special relativity, when we move from one reference frame to another, time and space get all mixed up. Now can we define how that object is moving? Sure, take the time derivative. But whose time? Our time or their time? Let's use the object's time (big T), but convert it into our time (little t).",
"So our velocity is simply change is position over change in time, but we had to include this (dt/dT) because the change in time for the object might be different than the change in time we measure. It turns out that this factor is,",
"We understand v",
" to just be v_x",
"+v_y",
"+v_z",
". You can also see the zeroth component of the velocity is just \"c\" multiplied by this factor because dt/dt is just 1. It is cool to note that if the object isn't moving, not every part of its velocity is zero. The \"time\" or zeroth component of velocity is just \"c\". This kinda makes sense, when you're sitting still in your room, you're still moving in time. Specifically you're going the speed of light. Basically, our unit conversion is following us. Now we define the momentum of our particle. In Newtonian dynamics, we know momentum is given by p=mv. So let's just do that.",
"Interesting. Our zeroth component is just mass times the speed of light times this (dt/dT) factor. How do we connect energy to momentum in special relativity? Well, you can read about it here:",
"https://www.reddit.com/r/askscience/comments/aqfmcd/why_is_it_not_e12m_c2_like_ke12m_v2_did_einstein/egfs2hu/",
"Anyway, the important thing is that when an object is moving slowly, we notice that the zeroth component of P is related to the kinetic energy from Newton plus an extra piece related to the mass. So let's just call it the total energy E. So now we get,",
"If the object isn't moving, dt/dT is just 1. Thus,",
"The speed of light is just a unit conversion between \"length in time\" and length. Many physicists just get rid of it by setting c=1 and making mass and energy have the same units, therefore,"
] |
[
"essentially it's stating that to create energy, you would have to accelerate a mass (of any magnitude) to the speed of light squared.",
"No, that's not what the equation says, not even remotely. You can't accelerate anything to the speed of light, let alone its square.",
"Of course the speed of light is the speed limit of the known universe, so creating energy is impossible. If you solve for mass instead (m=e/c2), it states that you cannot create mass.",
"The equation isn't about creation of energy, the equation is an equivalence between energy and mass. It states that, if you have an amount of mass, you also have a certain amount of energy (i.e. mass is a form of energy). The conversion rate between the two units is c",
"."
] |
[
"essentially it's stating that to create energy, you would have to accelerate a mass (of any magnitude) to the speed of light squared.",
"No, that's not what the equation says, not even remotely. You can't accelerate anything to the speed of light, let alone its square.",
"Of course the speed of light is the speed limit of the known universe, so creating energy is impossible. If you solve for mass instead (m=e/c2), it states that you cannot create mass.",
"The equation isn't about creation of energy, the equation is an equivalence between energy and mass. It states that, if you have an amount of mass, you also have a certain amount of energy (i.e. mass is a form of energy). The conversion rate between the two units is c",
"."
] |
[
"1 in 100 persons are immun to HIV. Would evolution do it's thing if we would not use condoms?"
] |
[
false
] |
Found this in TIL So let's say we were not as smart to use rubbers, would over time all those non-imune people die and hiv be cured by survival of the fittest? Is it our scientific knowledge that hinders evolution to take care of hiv?
|
[
"Layman here.",
"Aside from the obvious ethical problems, yes, but in a fairly slow way. So would things like glasses, vaccines and boiled water, btw, so don't jump into conclusions.",
"Even if we assume we're 'primitive' people with no ways to treat the sick, the actual effect on survival would not be very big. First the incidence rate of HIV infection is not that big. Second, HIV will be spread mainly sexually, which means that most people affected by AIDS will be well past the beginning of their reproduction age. You would have had some children before you manage to die of AIDS."
] |
[
"True, but then you would likely have children infected with HIV, in which case they probably wouldn't survive to reproductive age without any intervention. Anti-retroviral therapy significantly reduces rate of transmission of HIV from mother to child...but to follow the hypothetical notion of the question, we'd have to pretend that these drugs don't exist either."
] |
[
"Given the low incidence, you would have had some healthy children already before getting infected by HIV. True, your next children will have a higher risk of infection, but your genes would have already been passed on in other individuals."
] |
[
"(Physics)Can a wave produce a wave without acting on anything?"
] |
[
false
] | null |
[
"There is more than one way to think about waves, but you may be describing something along the lines of the ",
"Huygens-Fresnel principle",
", which essentially says that one way of describing the overall shape of a wave as it propagates, is to assume that every point along a wave is constantly producing new waves that radiate spherically outwards, and that the total shape of the wave you see is the sum over all of the waves that are constantly being produced."
] |
[
"So.. Say you have a wave, and then you look at one point on that wave. That point is also producing a wave. Are points on that wave also producing waves and so on?"
] |
[
"Yes"
] |
[
"December 21st was the shortest day of the year. Does each day get longer by an equal amount?"
] |
[
false
] |
I know that there is the least amount of sunlight on the 21st and the most sometime in June, but does it increase an equal amount each day? 10 seconds more today, 10 seconds more tomorrow etc., If not, is it on some kind of scale that can be measured or is it relatively random?
|
[
"No. If each day got longer by an equal amount, then the day before would be even shorter. When you deal with smooth functions, then the difference from the minimum or maximum is usually proportional to the square of the distance as long as you're close by. That applies here. So if the next day is x units longer, then the day after would be around 2",
"x = 4x units longer, then 3",
"x = 9x units longer, then 4",
"x = 16 units longer, etc. Also, that's assuming that winter solstice happens at precisely noon. If not, then you could think of the days as being off by a non-integer amount. If you want a more precise measurement, then it's approximately a sine wave."
] |
[
"Would it be appropriate to think of the year in sunlight as the same as about a wave of light? Thinking of the traditional picture. Something akin to this \n",
"http://www.lehighsla.com/images_level3/Student_YourProg/JB_1213/Gr4Light/BlueRedSm.jpg",
" \nWith the lowest Valley and highest peak being roughly the 21st of December and the 21st of June respectively? "
] |
[
"Like I said, it's approximately a sine wave. That's what those pictures are. Waves of light are not restricted to being sine waves. They're just generally decomposed into sine waves because it makes the math easier."
] |
[
"Why doesn't the water produced from combustion extinguish the flame/ combustion?"
] |
[
false
] |
[deleted]
|
[
"When wood burns, due to ",
"pyrolisis",
" it releases flammable gases. Those are responsible for the visible flame when they burn.",
"As soon as you pour water on the coals they cool down, not only because water itself is cold but also because it absorbs heat when it evaporates (you hear the \"psssshhhh\" as water boils and it stops when temperature drops too low). If they're not hot enough to release flammable gases then the flames are killed (note that moderate amounts of water may be enough to kill the flames but not stop combustion in the coals, so it may still be burning and ignite flames again at a later time).",
"Water released during combustion is hot, it's in gaseous form, it moves upward due to the heat, but most importantly, it ",
" heat when it forms rather than absorbing it."
] |
[
"In general, there are two ways to stop combustion. One is by reducing the amount of energy available to propagate the combustion reaction. This happens when cold water absorbs heat, thereby reducing the available energy. Less energy means slower kinetics and if enough energy is taken away, the reaction will stop.",
"The other way is via wall termination. If you introduce enough molecules into the combustion system that do not participate, the reactions will slow until they cease.",
"Water produced by combustion can not absorb sufficient amount of heat to mess with the kinetics, nor can it be produced at large enough quantities that it will displace the fuel/oxygen."
] |
[
"What combustion are you talking about? The space shuttle engines would be my guess and the answer is simple, the water produced from the reaction is already at or near the temperature of the combustion itself. It has to be, considering it WAS the combustion milliseconds ago. Also because of the heat, this water is in the gaseous state.",
"Normally water puts out a flame for two reasons, it cuts off the heat or it cuts off the oxygen. Most of its heat-cutting ability comes from the energy it takes to make water go from liquid to gas. In the rockets case the water is already gas and its already hot so it will not cut off the heat. Also in the rockets case, oxygen is being supplied by the engines not the air so the water cannot cut off the oxygen either. This leaves no method for the water to stop the combustion."
] |
[
"How far from a black hole are particles typically close enough to transmit sound waves?"
] |
[
false
] |
Please correct me if I'm wrong, but sound does typically not travel through space due to the lack of molecules to transmit the sound. As atoms get caught in the event horizon, is there some distance that they become close enough, as they race toward the singularity, such that sound can be transmitted?
|
[
"sound propagates in any environment that is dense enough. even in very sparse interstellar clouds there is concept of propagation of \"something like sound wave\".",
"in general, accretion discs around black holes are dense enough environment for sounds to propagate... e.g. so called ",
"quasi-periodic oscillations",
" are believed to be (at least by some people) basically just resonant sound waves in the accretion discs (and since resonance frequency might depend on size and discs probably scale with size of the central BH, this might be useful indicator of its mass)"
] |
[
"Can you articulate your question a little better? It's a bit confusing particularly the sound wave part."
] |
[
"What do you mean by that?"
] |
[
"Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Why isn't graphene getting more love? Indeed I get a lot of skepticism and nay saying about graphene?",
"Furtherance of my understanding of this will be greatly appreciated!"
] |
[
"Linguistics question, is there a word, phrase, or logical fallacy that describes this situation:",
"Person Y and Person Z are debating online. Y holds a position on a topic that Z disagrees with. Z searches online and actively looks for someone saying something incredibly stupid/insensitive/deplorable who supports Y's argument. Z uses his results from some rando's twitter or facebook to prove they are correct or to attempt to shame Y into agreement along the lines of \"See this stupid person saying this stupid thing in regards to our topic of debate? You aren't stupid like them are you?\".",
"I see this playing out online everyday and it's incredibly aggravating as there is no lack of people saying stupid things online for any side of any topic."
] |
[
"I thought straw man needed to be a made up character, not an actual person that exists?"
] |
[
"Do hurricanes affect aquatic life?"
] |
[
false
] |
Their damage to land and its lifeforms is uh.... well very obvious to say the least. But does a category 5 hurricane have dramatic effects on the aquatic life underneath it? In regards to shallow coast lines as well as while it is out in the open ocean? Thanks!
|
[
"Not dramatic effects, but there is an effect. First, it will tend to aid in mixing from deeper regions and surface regions, which is beneficial in terms of spreading the nutrient love around. For another, fish will tend to swim a bit deeper to avoid any turbulence.",
"It is pretty dramatic for us humans, but for ocean life, it's nothing special really."
] |
[
"Wow, I mean, I expected as much but it’s still crazy to think about haha"
] |
[
"There actually is a significant effect, although it's mostly confined to shallow water.",
"Sessile species (ones that are attached to the ocean floor and don't move, like corals) can be buried by dirt and mud churned up by the storm. We see this all the time when studying marine fossils. It can also bury species which burrow, like clams.",
"Filter feeders in general have a hard time of it. The mud and dirt tends to clog up their filtering systems.",
"Most pelagic species (swimming species) can swim away to deeper water, so they aren't as adversely affected. Storms affect mainly just the top few tens of meters.",
"Species with limited mobility (like sea urchins or jellyfish) have to hunker down or else be bashed upon the shore. This usually isn't catastrophic, enough survive to carry on.",
"Depending on the time of year, an entire generation of a species can be lost when their eggs are washed away. For example things like sea turtles that lay their eggs on sandy beaches will have their eggs washed away when the beach is washed away.",
"On the plus side, it does tend to stir up the water, which leads to more oxygen and more nutrients being circulated through the water column. These effects can go quite deep.",
"Entire reefs have been lost to storms. Reefs regenerate only slowly, and are a prime ecosystem for a great variety of oceanic life, so once they're gone there is a major impact that lasts for years, decades even."
] |
[
"What is the safest way to jump from an airplane without a parachute and survive?"
] |
[
false
] | null |
[
"Spread out, controlled dive, with very slight forward velocity, relax, roll on impact.",
"...and land on something that will break your fall. And hope whatever it is doesn't spear you to death."
] |
[
"First, look for something soft to land on. If you fall out of a commercial aircraft at cruising altitude, you will be about five miles up, but keep checking below you for a place to aim.",
"Spread out. You want to make as much surface area as you can and decrease your terminal velocity. ",
"If you see smoke or a storm cloud below you, aim for it. There will be rising air in both. It may not slow you a lot, but there was a recorded incident of a person falling from great height who fell into a storm and slowed enough to survive. ",
"If you still don't see something soft to land in, find a slope. Aim for a down slope so you hit the ground and roll. ",
"The only thing to land on is hard concrete? Relax, and yell out loud to clear your head and get some oxygen in your lungs. ",
"About 200 feet above the ground, ball your hands up into loosely curled fists and hold them in front of your face. Keep your elbows bent at about chest height and close in. Bend your knees slightly. Point your toes to the ground. ",
"Look out at the horizon. When you feel your feet hit the ground, you want to land on the balls of your feet. You then roll in the direction of your fall so the next thing to hit is your calf. Then you quickly roll to your thigh and next your buttock. Finally, you come to rest on your ribs just below your armpit.",
"This method has been reported to work by Air Force pilots who have fallen from great distances and survived. "
] |
[
"It'd be great if they could roll out one of those inflatable slides while they're at it."
] |
[
"Nuclear reactor meltdown"
] |
[
false
] |
I've read and I am familiar with Chernobyl, but I am unclear as to what, exactly, a nuclear reactor meltdown means. So, a nuclear bomb is based on the idea of a fissile material having an uncontrolled reaction. That is, as I understand it, at any given instant, each nuclei could be struck by a neutron. This could, then, cause a fission of that nucleus into multiple components, including some number of neutrons, which go on to possibly create the fission of one or more other nuclei, etc. This creates an exponential release of energy. Given enough material, then, this could create a nuclear explosion. A nuclear reactor meltdown, as I understand it, is different in some aspects. The reactor itself would typically have some sort of material inserted that prevents the majority of the fission reaction by absorbing neutrons. However, these control rods are not meshed with the molecules of the fissile material's rods (I believe they are each separated in this way). In that case, each individual rod continues to have a fission reaction mostly or totally independent of the other fissile rods. My lack of understanding, then, is what does it mean for one rod of fissile material to "melt down," and what does it mean for an entire reactor to "melt down?" Is the latter Chernobyl, or Hiroshima? Is the former Three Mile Island?
|
[
"xoites here isn't correct; Three Mile Island (TMI) ",
" have a meltdown (and it says so right under the picture of TMI in the link), but only a ",
" meltdown.",
"But to back up. The nuclear fission reaction in power plants gives off neutrons. Those neutrons cause further nuclear decays, and you have a chain reaction. But for that to occur, the neutrons have to slowed down (somewhat akin to how a bullet moving very fast will be more likely ricochet off an object rather than get stuck). Most of the reactors in use today use ordinary water as their moderator, and also for cooling and extracting energy as heat. Other designs include heavy-water moderated reactors and graphite-moderated reactors. Fukushima is a light-water boiling-water reactor. (moderated and cooled with ordinary water) Chernobyl was a graphite-moderated, water cooled reactor. ",
"The fissile material is in fuel rods in the reactor core, and in between them you have the moderator, and control rods. The control rods are used to control the reaction rate. They consist of neutron absorbing material, such as boron, which breaks the reaction.",
"Since the thing is a self-promoting kind of reaction, there is a risk of a runaway reaction generating uncontrollable amounts of heat. That would lead to the reactor core melting, and possibly breaching the containment of the building. That's a \"meltdown\" in the worst sense and essentially the worst-case scenario for a nuclear reactor. They cannot explode like an atomic bomb, because the concentration of fissile material isn't high enough. You don't have have the 'critical mass' required for that. A nuclear weapon requires fuel that's more enriched than that in a power plant. ",
"To stop a reactor in an emergency you perform a SCRAM (safety-control-rod-axe-man, so called because in Enrico Fermi's original pile, they supposedly had a guy with a fire axe, ready to cut the ropes holding the control rods as they were pulled out). This is designed to be very failsafe; e.g. by holding the rods with electromagnets, such that it it will SCRAM if the circuit is broken. One of the many things that went wrong at Chernobyl was that the control rods did ",
" make it fully back into the reactor.",
"With TMI and now Fukushima, the reactors were successfully SCRAMed. But this does not ",
" the reactions. It merely starts a ",
" of the reactions. It takes days before the thing has stopped completely. During that time, they have to continue to cool the core.",
"If you don't, you still risk a meltdown. But obviously this is a different kind of meltdown; because the reactor was slowing down. I guess you say it's the difference between a runaway freight train whose engine is still running at increasing speeds, and a runaway freight train who's engine has been cut.",
"Okay, so besides the fact that the reactor has been SCRAMed, there are a few other safety factors worth knowing about. As I mentioned, Chernobyl was graphite-moderated and had what's called a \"positive void coefficient\". This meant that when water in the reactor core turned to steam, the loss of water density (bubbles) helped promote the reaction. In modern reactors, and all reactors outside the old Communist bloc, we don't allow them to be built that way; the reactors we use have a negative void coefficient. This means the loss of water from the reactor causes the reaction to slow down. So this also contributes to making this kind of situation less dangerous.",
"So, if the cooling system fails, you start getting steam building up. You have to get rid of that before it causes an explosion. It was a steam explosion that ripped open the reactor at Chernobyl. Since it did not have any secondary containment (just the thin shell of the building) outside that, the reactor was directly exposed to the outside world, and caught fire as well (burning uranium and graphite and stuff), spreading huge amounts of radioactive crap everywhere.",
"So you have to vent the steam (which is vented to the inside of the reactor building, if they can). The steam itself is radioactive, but not so horribly dangerous compared to the contents of the fuel. It seems a hydrogen gas explosion occurred now, which probably happened there (and not inside the reactor). ",
"Back to the meltdown thing. Once the water level gets low enough the reactor core will start to melt. The question is then if the containment will hold. It should, since it's engineered to be able to withstand this kind of situation. Roughly, you have the reactor vessel, which is thick specialty steel, and outside that you have a thick concrete, and outside that the building itself (and bedrock below). ",
"Three Mile Island appears to me to be somewhat similar situation, even though Fukushima is a boiling-water reactor and TMI was a pressure-water reactor. In both cases the reactors were SCRAMed in combination with a cooling system failure. In both cases they've been forced to vent steam. ",
"At Three Mile Island, the reactor core was exposed and melted. But it did not breach the reactor vessel, much less the secondary containment. It was a huge media event at the time (partly fueled by the fact the movie \"The China Syndrome\", about a meltdown situation, was playing in theaters at the time). But the radiation leaks from TMI were perhaps similar to the somewhat less-known Windscale disaster, and far less than Chernobyl and the also far-less-known disaster at Kyshtym.",
"I believe a TMI scale meltdown is the worst-case scenario for Fukushima from what I can tell at the moment. It's certainly not likely to be a Chernobyl. But it's not going to be clear for some time. In the case of TMI, the scale of the damage to the reactor was not known until years later."
] |
[
"His source is clearly vodka and orange juice!"
] |
[
"To add to you discussion of chernobyl, the rods not only failed to insert, but their design created additional positive reactivity in the core, I.e., the tips of the rods had the opposite effect that a control rod should."
] |
[
"Pain is obviously the way of the body telling us something is wrong, but why can it get so severe that it cripples us?"
] |
[
false
] |
[deleted]
|
[
"Does your question basically boil down to 'why does the body not work perfectly'? There are plenty of examples of healthy physiologic processes that can become harmful when taken to an extreme. For example, the ability of your blood to clot is a great help to keep from bleeding out, but when clots form in bad locations you can get heart attacks, strokes, or pulmonary embolisms. Similarly, the body's immune system is so vital in not only protecting us from invasive pathogens but also from cancers and other cellular disorders, but when it can also go overboard and cause anaphylaxis or an autoimmune disease like lupus or arthritis. Just as there isn't some magic switch that turns off the coagulation cascade or stops inflammatory cytokine, there isn't some magic switch that knows when pain sensation is 'crippling' and shuts it down. ",
"Edit to add: I'll also add a note of caution against many explanations that are basically '",
"just-so stories",
"' that inevitably pop up in these sorts of posts. If there's any evidence suggesting that (for example) pain leads to resting which is good for healing, great. But don't simply think that it 'makes sense' that we evolved this way, and ",
"thus it must be so",
"."
] |
[
"I'll reiterate my last paragraph:",
"I'll also add a note of caution against many explanations that are basically '",
"just-so stories",
"' that inevitably pop up in these sorts of posts. If there's any evidence suggesting that (for example) pain leads to resting which is good for healing, great. But don't simply think that it 'makes sense' that we evolved this way, and ",
"thus it must be so",
".",
"Unless there's any evidence supporting your claim, I see no reason to think that 'crippling pain' is anything more than excessive stimulation of normal pain pathways. "
] |
[
"Under normal circumstances, such as a cut or small wound, the body tells us that there is indeed an injury. Or doing something anatomically inappropriate, sticking your finger in boiling water, or touching something sharp for example is a defensive mechanism from your body that tells your brain \"Don't do that again.\" Most of the time, these types of insults to the body are not crippling. When an injury occurs to the body that is beyond this normal realm, it tends to be a crippling pain. Such as an amputation of a leg, broken bone, or large wound. Before modern medicine, these would have likely killed the individual. Things that elicit crippling pain tend to be very severe in nature and life threatening. Once a pain threshold is met, many people typically loose consciousness anyways, another defensive mechanism."
] |
[
"How much does our skull change how we actually hear our voice?"
] |
[
false
] |
According to : But when we hear our voice when we're actually speaking, we hear it in two different ways - externally and internally. First, you hear the sound that comes out of your mouth ( the one that other people hear), and at the same time you hear that which is coming from vibrations produced by our vocal chords, which travel through our head. The bones in our skulls tend to enhance the lower-frequency vibrations, and that's why our voice sounds lower to us than it really is. But I wasn't able to find any numbers anywhere. How much lower does our voice actually sound? If I change the frequency or pitch of my recording, could I change the recorded voice to what I hear in my head?
|
[
"Your skull does not change the pitch, only the frequency spectrum. (equalization) ",
"You can do your own experiments easily:",
"Record a friend, and play it back. Does this sound like the original voice? If so, your recording and playback system is sufficient. You can go over the top with high end microphones and headphones, but a phone recording played on a decent headphone sounds quite good nowadays. ",
"If your friend sounds like your friend, record yourself - this is how you sound to others. ",
"Then try an equalizer on the recording and compare it to what you hear when you speak . If you manage to match the two, you can play to others how you hear yourself."
] |
[
"The idea was to create one myself. A software where one could adjust the settings of the voice and finally let other people hear how the voice in our head sounds. But to make this I need to know how I need to change the voice.\nI will start trying with frequencies and see if I get to any results"
] |
[
"Could you recommend an app or software for this?"
] |
[
"How direct is the correlation between psychological and physiological changes in the brain?"
] |
[
false
] |
For example, If I were to change the way I feel about a certain idea, lets say abortion (for lack of a better example right now), what would the corresponding physiological change be? Would certain neurons/parts of the brain undergo change? and if so what would these changes be?
|
[
"The mind is the product of the brain. Everything in our mind is contained in the brain. Any change in the mind is going to be reflected in some way in the brain. This could be changes in the biology (new synapses, change in firing, change in neurotransmitters, etc).",
"We don't know what the specific changes are that are involved in something as complex as a change in opinion, but it's all in the brain somewhere."
] |
[
"The entire enterprise of psychology and neuroscience is based on the premise that psychological experience is based ",
" brain activity (which is, of course, influenced by the environment, genes yadda yadda yadda). I don't mean this in any way to be insulting to anyone, but this premise is in ",
" contradiction to the existence of a soul that has influence on behavior. Many people who engage in psychological/neuro research don't follow this premise to its logical conclusion or they have adopted some sort of compatibilist alternative way of looking at things, but the premise is THE foundation of psychological science and is absolutely necessary for understanding human thought and behavior. ",
"I say this because you will see disagreement about ",
"/u/stjep",
"'s response within the academic communities of neuroscience and psychology, which leads to gross misunderstandings of the meaning of our findings and, ultimately, stifles our progress. Listen to ",
"/u/stjep",
" on this one and you'll be equipped to grasp psychology much more quickly and easily. "
] |
[
"What you are thinking of is called an \"engram\". It's a theoretical pathway of linked neurons which is where a particular memory is stored. No one has found one yet, but it is a great theory. You know when you have those 'lightbulb' moments? That is the instant your neurons have made a new connection. You now have a new memory in your head that was not there previously.",
"There are many more examples of a connection between physiological and psychological changes in the brain. ",
"One more would be when neurons in your prefrontal cortex migrate into their final positions. The migration takes decades not finishing until the brain is around it's mid '20s. The psychological implications of this are obvious. This is why young people have poor judgement until their brain is fully developed."
] |
[
"If current tests to date have shown that matter and anti-matter interact with light the same way (i.e. anti-hydrogen photon emission spectrum is the same as hydrogen), how can we assume that the universe is made up of an abundance of regular matter, and not isolated clusters of each type of matter?"
] |
[
false
] | null |
[
"It's because there'd have to be some region of space where the anti-matter and matter parts are in contact, and that spot would look VERY unusual. ",
"Galaxies can be very isolated, it's true, but not so isolated that it wouldn't be observable."
] |
[
"There would still be a region where that antimatter comes into contact with a matter area"
] |
[
"In the distant past everything was closer together. Far enough back, at the time the CMBR was formed, everything was a continuous plasma cloud filling the universe. If it consisted of regions of matter and antimatter, the borders between regions would be violent places and it would have left a major imprint on the CMBR."
] |
[
"What is happening when I push my stomach out to make myself appear fatter/bigger. What is happening when I suck my stomach in. (where does all the size go?)"
] |
[
false
] | null |
[
"My surgeon friend told me that organs move around a lot. Once doctors get inside it's not like the diagrams. They usually identify the target organ by the relation to other organs, not where it sits in the body cavity.",
"gross."
] |
[
"You're pushing your diaphragm (the muscle below your lungs/above the abdominal cavity) down and relaxing your abdominal wall. Since your organs don't have anywhere else to go they \"push out\" giving the appearance of a beer belly. The reverse is also true. You're just sucking the stomach and liver up into the space normally used by your lungs."
] |
[
"While it might make more sense initially to securely anchor abdominal organs, if they were anchored they couldn't move to conform to spaces when the shape of the abdominal cavity changes- i.e. during pregnancy, when you bend over, as you grow, gain weight, etc."
] |
[
"Does holding a glass to the wall/floor really help you hear what is going on in the next room?"
] |
[
false
] |
[deleted]
|
[
"Yes it does. ",
"When sound from the inside of the room hits the wall it causes the atoms in the wall to begin to vibrate in accordance with the frequency of the sound wave. When you press the glass against the wall on the other side, the glass begins to vibrate in this manner as well. Although sound travels faster through denser mediums the sound wave loses much of its intensity. By pressing the cup against the wall you are allowing sound to travel on the outside of the wall through a much smaller area, increasing the intensity.",
"In addition to this the sound waves inside the glass reflect off the inside of the glass wall creating a well known resonance effect, with nodes and antinodes of the sound wave being created throughout the length of the glass. Because of this, there would be some ideal length of the glass which would allow you to hear the sounds more clearly. This ideal length depends on the frequency of the sound wave."
] |
[
"I think this is a good answer! Carrying out experiments is half the fun of science and should be encouraged! Especially for quick easy things like this. OP will then know the answer to their question and can think about asking ",
"this happens."
] |
[
"How about you conduct a ten second experiment and find out yourself."
] |
[
"Why does Nuclear Power Need Cooling? Could they not convert the hot water back to steam?"
] |
[
false
] |
[deleted]
|
[
"This isn't specific to nuclear power. This occurs in all power sources where you convert heat to electrical energy.",
"Turbine output needs cooling because the turbine can't remove 100% of the energy from the water. If you had a closed cycle between the reactor and the turbine, and the turbine didn't remove all the energy, you would be building energy within your system. This would increase heat in the reactor until a meltdown occurred. The water goes through secondary cooling to get these last bits of energy out so that the reactor receives a constant input temperature. ",
"It is easier to extract energy from hot water if the water is extremely hot. The turbine extracts all the easily usable energy. There are some applications now that use waste heat to power heating/cooling systems, but in general this energy is difficult to find an application for. Imagine trying to find a cost effective way to bring heated \"nuclear\" water to people's houses."
] |
[
"Thanks for clarifying that. My point was two-fold, although I didn't explain it well. The first issue is that it would be difficult to bring hot water from a NPP to homes, just because of the distances involved. The second issue is that, even though they are completely separate systems as you pointed out, most people would be scared of \"nuclear\" water. And if they weren't, I'm sure Greenpeace would mention it (as baseless as any fear would be)."
] |
[
"Repost: I completely misundestood your question earlier, here is the amended answer, sorry!",
"The water needs to be cooled down before pumping it back over the fuel due to the ",
"second law of thermodynamics",
" which states that that any closed-loop cycle can only convert a fraction of the heat produced during combustion into mechanical work. The rest of the heat, called \"waste heat\", must be released into a cooler environment during the return portion of the cycle. ",
"This \"waste heat\" need not be wasted! It can be used for home heating systems in a process known as \"cogeneration\". However in nuclear power plants are usually located far from population centres which makes it impractical to transfer the hot water over those distances. ",
"A nuclear power plant with cogeneration was planned in the 1970's in Midlands, Michigan, but the plan was scrapped and a fossil fuel power plant was built instead."
] |
[
"Does a baby's crying wake a person more readily that other noises?"
] |
[
false
] |
I'm interested to know if there has ever been any sort of scientific study to learn whether or not humans are more predisposed (through evolution or any other process) to wake up when they hear a baby crying as opposed to other noises such as an alarm clock for example.
|
[
"It sounds like you are talking about ",
"signal detection theory",
"means to quantify the ability to discern between information-bearing energy patterns (called stimulus in humans, signal in machines) and random energy patterns that distract from the information (called noise, consisting of background stimuli and random activity of the detection machine and of the nervous system of the operator)."
] |
[
"If I'm a close relative or a friend who has spent a relatively large ammount of time with the baby then? I'm guessing our brains doesn't discriminate there, or atleast our sense of helping a crying baby/child"
] |
[
"yes, but ",
" is the question."
] |
[
"Why don't electric vehicles come with 5, 6, or 7 speed transmissions?"
] |
[
false
] |
I know the first generation Tesla Roadster had a 2-speed, but why is it that most electric vehicles out there don't have standard transmissions? I know it has something to do with the way that electric motors produce torque/power, but what is the actual explanation?
|
[
"Electric motors have a far wider range of speeds at which they can produce useful work than do gasoline engines. ",
"A gasoline engine works by pumping air through a cylinder. It has a fairly low maximum torque it can provide. Too slow, and it won't even provide that. Too fast, and drag forces start to eat at the power it provides -- and mechanical linkages (like the piston connecting rod) start to become pretty highly stressed. As an example, an undersquare motorcycle engine running at 6000 RPM (100 Hz) might accelerate each piston from a standstill into motion, and stop again 200 times per second over a stroke of 6cm. It's easy to calculate the acceleration -- d = 1/2 a t",
" so a = 2d/t",
" , or (2)(0.03m)/(0.0025 sec)",
" -- nearly 1,000 G's of acceleration. If the piston itself masses a quarter kilogram, the connecting rod has to hold 2500N (the equivalent force to supporting 250kg at 1G), while whirling around at those 100Hz. It also has to supporting itself on top of that piston load, as well as carrying the actual desired forces for working the engine and delivering power to the crankshaft - it's not long before you start to exceed the ultimate breaking strength of high strength alloys.",
"Electric motors have high torque at low RPM so they can run slower than gasoline motors and still deliver useful energy, reducing the need for low gears; and the rotors are single, compact, rotating assemblies rather than complicated reciprocating air pumps, reducing the need for high gears. "
] |
[
"Fountain pens are more fun than ballpoints because you can fill them with ink, wipe them down when you're done, complain about your inkstained hands, and argue about which nib is better. ",
"For that matter, slide rules are more fun than calculators because you can keep track of exponents in your head and get an intuitive feel for the numbers; hand-cranked ice cream makers are far more fun than buying Ben & Jerry's; LPs are more fun than MP3s, because you can clean the grooves and tweak the needle's performance; gas lights are more fun than electric since you can muck about with wick position and even choose different mantles for the good ones; and everyone should build his own Linux system because it's more fun to muck around with the individual packages than to install some monolithic ",
" or a proprietary OS.",
"Hmmm, this needs more thought.",
"I guess your friend has a point - manually changing gears can be fun, and if you're driving your car occasionally for fun that is a Good Thing. But if you're driving your car to get around, a \"go faster\" pedal with fully automatic transmission (as in the Prius) is a cleaner user interface by far. "
] |
[
"One reason is that transmissions connected to electric motors have to be extremely strong. Tesla tried to make a 2 speed transmission for the Roadster but it kept shredding itself. Don't know the specifics but an electric motor produces full torque at anything considered turning (>0RPM).\nThe main reason is that there really is not a \"power band\" with an electric motor. Torque is horizontally linear until frictional and stressing forces start to cancel out the force of the rotor turning. This means that torque is even all over the rev range with an EV. The horsepower however increases linearly as RPM's increase."
] |
[
"Do cancers have their own 'fingerprints'? How can you tell a cancer is metastatic instead of a new local occurrence?"
] |
[
false
] | null |
[
"Yes they do - as a cancer grows it acquired hundreds to thousands of genetic mutations. Some of these mutations are common among all cancers such as the Ras or Raf genes. A lot of these mutations happen just by chance. By genotyping the tumors you can tell if it has the same chance mutations as the original tumor or if it has different ones. This used to be achieved by karyotyping, but can now be achieved through faster methods such as sequencing."
] |
[
"Hi there! This is what I do ",
"! I'm a pathology resident and mod over at ",
"/r/pathology",
". Not only do cancers have fingerprints, we can often tell where they're from even if we never saw the primary. While cancers almost by definition carry mutations, rearrangements, or some sort of dysorganization of the genome, they still tend to behave like their cells of origin. The trained eye can often figure this out just looking at it, but we have lots of other tricks too.",
"As ",
"/u/tiger_researcher",
" mentioned, we can use karyotyping and sequencing. Far more commonly, however, we use immunohistochemistry: antibodies that bind very specifically to a protein of interest, in fact, a particular ",
" of the protein. So a prostate cancer will usually express androgen receptor, and we have antibodies that label this protein. Small cell lung cancer, on the other hand, wouldn't generally need much androgen receptor (girls have lungs too, right?).",
"Elsewhere, ",
"/u/Furbs1985",
" brought up the EMT pathway. This is one of many pathways a cancer can get \"addicted\" to. This more general thought of \"oncogene addiction\" is that the mutated cells stumble upon some gene that is part of a highly replicative or highly survival-focused pathway, often in the embryonic development pathways. Other pathways involve Wnt signaling (planar cell polarity, apoptosis, etc). There are many others.",
"This, however, only gets us so far. We want to talk about the genome of not just prostate cancer, but ",
" prostate cancer. But, see, the process of mutagenesis (the development or suppression of mutations) itself eventually, sometimes constitutively, becomes dysregulated in cancer. So we see, over a cancer's lifetime, different clones derived from the same ancestor surviving on different pathways, with genetic differences. Maybe one still needs EMT signals, while another is totally on Wnt canonical signalling. It's like a huge, evil family tree. Here's a ",
"good presentation",
" I saw last year by Dr Bejar at UCSD. It's pretty dense, but he used ",
"this very intuitive illustration (Figure 2A) from Walter's 2013 paper in the New England Journal of Medicine",
"."
] |
[
"Sure: karyotyping is done by capturing images of cells in the metaphase stage of mitosis where you can see the individual chromosomes. They are stained so some bands are light and some bands are dark. You can then identify which are chromosome 1 (the longest) which are 2 (next longest) which are 3 etc. Then you can look for ones that don't match up and those are going to be either X and Y or translocations. If you've got one 11, one 8, and a couple funny-looking ones, then you probably have an 8;11 translocation.",
"Sequencing is a lot for a reddit post. Look up Sanger sequencing, then check out the videos on the Illumina website."
] |
[
"When scientists \"map\" the human genome, what are they actually doing?"
] |
[
false
] |
I know they're writing out the code that makes us human, but how exactly are they doing it? And along those lines, how do they map the genome of an entire species? Shouldn't genetic variability across our species make the job essentially impossible?
|
[
"Genetic mapping is different from DNA sequencing.",
"DNA sequencing is the process of determining the exact sequence of nucleotides in an organism's DNA. We have had the technology for about 40 years, but it was such a painfully slow process that we've only done whole genomes in the last 15 years. ",
"The Sanger Method",
" was the first really common protocol for sequencing DNA. I think that link explains it well. But organisms (especially complex ones like us) have a lot of DNA, so we have developed faster techniques. The ",
"Wikipedia article on sequencing",
" isn't great, but the one on ",
"pyrosequencing",
" (one of the newer techniques) is a little better. The first human genome sequence, completed in 2003, took 15 years and roughly $3 billion. Now we can do it in 3-4 days for $5000. I don't think your average citizen realizes how much the field of molecular biology has changed in the last decade - the ramifications of this will be ",
". Anyway, I'm glossing over DNA sequencing because you asked about genetic mapping, which is different.",
"A genetic map is made when we determine the order of genes on a piece of DNA. Genes are stretches of DNA that perform a function (usually coding for a protein). On a long molecule of DNA, genes are laid out end-to-end with a little space between them. Genetic mapping techniques determine the order in which these genes are arranged on the chromosome.",
"Here's an example of how it works. You, as a human, have two copies of every chromosome: one from your mom and one from your dad. This means that you have two copies of every gene. These copies are often a little different from each other. For example (and I am simplifying a little) you will have a gene for \"eye color\" from each parent. Maybe your mom gave you a green copy and your dad gave you a brown copy. These are two ",
" of the same gene.",
"Now let's pretend that the hair color gene is on the same chromosome. On the chromosome from your mom is the blonde allele and on the chromosome from your dad is the black allele.",
"So on the chromosome from your mom you have EyeColor=green and HairColor=blonde. On the chromosome from your dad you have EyeColor=brown and HairColor=black. When you reproduce you will pass on to your offspring either your mother's chromosome or your father's chromosome. If your child gets your mother's chromosome it will have both the EyeColor=green and HairColor=blonde alleles. If your child gets your father's chromosome it will have both the EyeColor=brown and HairColor=black alleles. ",
" in an event called a ",
"chromosomal crossover",
" and your mother's eyes gene end up with your father's hair gene! The closer together the genes are on a chromosome, the less likely it is that they will get scrambled like this. So if we make you have lots of kids (this is easier and more ethical with fruit flies...) we can see how often chromosomal crossovers occur and can estimate how far apart two genes are. Do this for every gene and you can figure out their arrangement on the chromosome.",
"tl;dr: science is easier on CSI"
] |
[
"For many of the genes, we have had a good explanation of how they affect let's say hair color. For example, a gene may encode for melanin protein that specifically localizes to the hair, making it darker. ",
"Each gene has a promoter associated with it, which can be regulated by other proteins (which are deemed transcription factors). Many other genes than the actual encoding gene are simply involved in upregulating or downregulating the expression of certain proteins, which may contribute to the shade of your hair for example. Finally, there are many other ways the body regulates production of a protein (feed forward loops, degradation rates, etc.), which require many other genes that make up a regulatory network. So in short, we have some idea of how many genes influence a complex phenotype like hair color, but we're still far short from modeling how the system might interact and predicting a person's hair color from a set of genes. Keep in mind these also change over time as the body develops and ages, making for a very complex puzzle as expression levels change over time.",
"If you're asking about approximately what % of the genes in the human genome we have a known function for, then I'm not sure."
] |
[
"I heard an amazing lecture on the radio last night about synthetic life:",
"http://www.cbc.ca/ideas/episodes/2012/01/04/synthetic-life-1/",
"Essentially, they have been looking at what individual pieces do inside bacteria genomes. So, for example, they know this is the gene for creating blue pigments, and this one lets you metabolize sugar (I made the two examples up as I still haven't finished my coffee, but he gives good examples in the lecture). They have a list about six million of these things, and they can put them together like lego blocks to build new species of bacteria. Let me say that again since it is a bit mind blowing to me. They take a bunch of chemicals, put them in a given sequence that they use a computer to determine (he equates it to using a compiler to create an executable out of some code), then they inject that into an \"empty\" cell, and a few hours later the new genome has taken over the cell and rebuilds it to do whatever they want. "
] |
[
"Why is the stomach affected when you get nervous?"
] |
[
false
] |
It's seems to vary from cramps, to the feeling of needing to go to the toilet, to feeling sick. Scientifically, why is the stomach that takes so much abuse from nervousness? Surely, increased heart rate, sweaty palms and stuff, is more than enough.
|
[
"When you get nervous or scared, your body reacts with a ",
"fight-or-flight response",
". This involves, among other things, diverting blood away from your digestive system to your muscles and brain, in the anticipation that you'll either have to fight something or run like mad. This is why under stress, people feel 'butterflies in the stomach' (this is your stomach quivering, as the muscles holding it together having to relax) and sometimes, loss of bladder/bowel control."
] |
[
"I was away working 7 days a week for a couple months under high stress and I found that my stomach/bowels, bladder, respiratory system were all effected by the nervousness and stress. I am also curious why."
] |
[
"If you smell like shit and piss threats are less likely to eat you / beat you up"
] |
[
"Why can we walk perfectly fine on the edge of a sidewalk but not the edge of a cliff?"
] |
[
false
] | null |
[
"Hi Benstrosity thank you for submitting to ",
"/r/Askscience",
".",
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"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
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[
"Human Body"
] |
[
"Neuroscience"
] |
[
"If you can determine what elements are in a star by the black lines on its spectrum. Can you find even more elements in the invisible spectrum?"
] |
[
false
] | null |
[
"[I'm reading \"invisible spectrum\" as \"the part of the EM spectrum outside of the range visible to the human eye\" (after all, we have instruments that can see them just fine :D).]",
"The energy levels of electrons in the elements/molecules are what determines the wavelength of the light that's absorbed (or emitted). So there ",
" plenty of lines in other parts of the EM spectrum that carry lots of extra information, yes, though they aren't generally different elements. One broadly different class of lines that usually becomes very important in the infrared, microwave, and radio bands is molecular bands. These wavelengths show relatively low energy transitions in a molecule, either in the vibrational mode or rotational mode of the molecule (these are also discrete values, just like energy levels, thanks to quantum mechanics). Think of it as the molecule stretching in and out like a spring and changing the rate of oscillations, or a molecule spinning around and changing the rate of its spin. Molecular bonds in general can't withstand high temperatures on the surface of a star, so these are better tracers of cold or warm gas, as around star forming regions. There are a few exceptions which can survive on the surface of the coolest stars and have absorption bands in the optical, but break down well before a star reaches the temperature of the sun. Examples that spring to mind are TiO and CN, with which one you see depending on whether the star has more carbon or oxygen in it (the great majority have more oxygen, carbon stars are fairly rare, but pop up enough to throw people off who should know better.)",
"The other type of thing that you can see by moving to different wavelengths is different ionization states of elements, which generally appear as emission lines where electrons are falling back into place, emitting a photon (so bright stripes instead of dark). When an atom loses an electron, it changes the allowed energies of the remaining electrons. Seeing lines that are only allowed by high ionization states of an element tells you something about what the environment is like, in terms of temperature and density. For example, seeing lots of ionized helium (He II) around means there has to be some way to excite the electrons above 54 eV, or the helium would be neutral. Usually that's because there are a lot of UV photons around, but sometimes it's because very fast material is slamming into cold material nearby creating a very hot shock region.",
"Moving up to X-ray wavelengths, a lot of black hole binaries will show highly ionized iron emission lines in their X-ray spectrum as the accretion disk around the black hole is irradiated by high energy photons generated closer to the event horizon. (Some people have tried to extract information about the spin of the black hole by modeling these line profiles, but there's still some skepticism about how good the models are and if the results of their fits can really be believed since they are model-dependent.)",
"The point at which you stop getting information about electron energy levels is around a few hundred keV when you enter the gamma-ray regime. At this point, atoms are stripped of electrons and the changes you see relate to allowed nuclear energy levels. By the time you get up to GeV and TeV, you're at the energies of the LHC and discrete emission relates to whole particles winking in or out. Detection of electron/positron annihilation at 511 keV has been claimed by some groups. As far as I know, emission lines have never been observed from astronomical sources above an MeV, probably because the energy resolution, spatial resolution, and collecting area of the instruments isn't good enough to do it. I'm not a gamma-ray person, though, so someone might step in to correct me here. "
] |
[
"Thank you!"
] |
[
"Hi AndyKansas thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
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