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[
"Why does pancreatic cancer have such a low survival rate?"
] |
[
false
] |
Automod I do not have cancer, I'm not asking for medical advice so backkkkkkkk offf. Alex Trebek just announced he has stage 4 pancreatic cancer thats why I'm asking.
|
[
"From my very limited knowledge, is that this type of cancer only shows symptoms in late stage. By the time most people search/find it it's to late. A family member had it, it happened to show up in the top corner of a scan while they were looking for something else. 2 other doctors missed it, then one noticed a spot. They caught it early enough that he survived. "
] |
[
"Yes, it causes either no symptoms or very nonspecific ones until it's far too late to do anything about it. The pancreas is also a very...\"internal\" organ, and you can't really look at it unless you're doing specialized scans that aren't done routinely."
] |
[
"The pancreas releases insulin directly into the bloodstream. When symptoms appears it's usually very far along (stage 4) then cancer cells are already breaking off and spreading into other parts of the body. ",
"It's something like 5% survival rate. My old bosses father died of it. He donates $5 million a year into reaseach. Hopefully they are finding new treatments. "
] |
[
"Could the Huygens probe have contaminated Titan?"
] |
[
false
] | null |
[
"Hi demojunky73 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary Sci"
] |
[
"‘Planetary Sci’"
] |
[
"Why are most of the oldest living people in the world female?"
] |
[
false
] |
According to most of the oldest living people in the world are female. Why is that the case?
|
[
"Statistically women tend to live longer than men. This may be due to a number of factors:",
"Up until fairly recently, men tended to work outside the home, while women did not. This put men at greater risk of exposure to work-related injuries and illnesses.",
"Men are more likely to neglect their health and routine checkups than women.",
"Men tend, on average, to develop heart disease about 10 years earlier in life than women.",
"Men tend to take greater risks than women. They are more likely to die in an accident, or to die by suicide, than women. (Now, statistically, women tend to have more car accidents than men, and to attempt suicide more frequently. However, these tend to be minor car accidents, and they are more likely to use less lethal means in a suicide attempt, as well as to attempt in a place where they know they will be found quickly.)"
] |
[
"As ",
"/u/Agnurse",
" mentions, there's a variety of sociological factors that will play a role. But I'd dare to say there's also biological reasons, as the same pattern holds true in most other mammals. For ",
"cats",
", ",
"dogs",
", ",
"monkeys",
", and I could go on.",
"As a general rule of thumb, large animals live longer that small animals. At least one of the reasons for this is, large animals have a larger volume to surface area ratio, so they don't have as much heat loss, and can therefore afford to have a lower heartrate. And if you plot ",
"heartrate as a function of life expectancy",
", you'll see a clear negative correlation, though humans are clear outliers here (yeah, correlation is not causation and all that). In other words, we could expect someone with a lower heartrate to live longer, all else being equal. And as it turns out, ",
"women tend to have a lower heart rate than men",
".",
"So, is that the reason? I don't know, I haven't really studies this. I'd bet it's part of the reason though."
] |
[
"While these would explain why the average woman would live longer than the average man, I would think looking at the just the longest lived list, we're just looking for the outliers. There has to be men that didn't work outside, was conscientious about their health and didn't take risks. No men in the top 50 makes me think there has to be biological component too."
] |
[
"How fast does electricity move?"
] |
[
false
] |
I just saw that gif of the people lined up, and the guy at the end touched the electric fence and it seemed as though they all were instantly zapped at the same time. If the line were a lot longer would it take more time?
|
[
"The electrical energy travels at what is called the ",
"propagation velocity",
" Or ",
"this link",
". Typically between 60 to 90% of the speed of light, depending on the cable used.",
"You can use that information with a device called a ",
"time domain reflectometer",
" to find the distance to a cable fault."
] |
[
"The speed of signal propagation in a metal wire is basically the speed of light divided by (the square root of) some material dielectric permittivity and permeability, which for a metal would be quite close to 1. You can see a table of examples here:",
"https://en.wikipedia.org/wiki/Velocity_factor#Typical_velocity_factors",
"Where, for example, a coaxial cable transmits at about 80% the speed of light."
] |
[
"It almost travels the speed of light so there's no point to try and shock 2 people at different times no matter how far away they are (on earth). It's technically true that they'd be shocked at different times but not practical."
] |
[
"Could the expansion of universe be explained by theory of our universe being inside another as a black hole?"
] |
[
false
] |
[deleted]
|
[
"It's a perfectly reasonable theory. However, your problem is that it doesn't actually predict anything, it just describes something that we already know about in a vague way.",
"If you want your theory to be scientific, you need to do more than that. You need to identify some property of the universe that would be different depending on whether or not your theory is correct, something that we can measure. Not only that, but your prediction needs to be new, you can't 'explain' something we already know about, because that's easy...the only way for your theory to be verified is for it to predict something new to us that is not already predicted by accepted theory. And it has to be a proper prediction with a good grounding in a well constructed framework, otherwise it's no better than saying 'universe gnomes would make the universe look like this, therefore universe gnomes'.",
"Now, if you manage to do that, you've made a good start into creating a valid scientific theory. Full acceptance would come as the model were further developed and made more unique predictions. The more evidence that supports your theory and not others, the more accepted it will become. Or, alternatively, if your theory made predictions that were proven incorrect, your theory would be ignored or abandoned in favour of one that worked better."
] |
[
"It's a hypothesis, sure. It's also a theory, by a standard, normal and historical use of the term. But it's not a ",
" theory.",
"I think that accepting the meanings of words but drawing distinctions where necessary is better than trying to enforce rigid redefinitions that aren't even used in a standard way in science."
] |
[
"It's a hypothesis, sure. It's also a theory, by a standard, normal and historical use of the term. But it's not a ",
" theory.",
"I think that accepting the meanings of words but drawing distinctions where necessary is better than trying to enforce rigid redefinitions that aren't even used in a standard way in science."
] |
[
"Do animals have a sense of time?"
] |
[
false
] |
Do they sense a passage of time or do they know if winter months are coming soon? Is the foraging for food just out of instinct or is it because of a sense of passage of time
|
[
"It's been showcased that orangutans not only plan ahead for the future, but they also communicate it to their peers. It shows evidence that they keep a bit of a schedule for their daily lives.",
"Source",
"If you don't want to read an entire peer reviewed journal on this study, ",
"here",
" is a more streamlined version of it."
] |
[
"They certainly do have a sense of time, but not necessarily in the way you mean.",
"Animals, including humans, almost all have a sense of time that is described in three scales: millisecond timing, which is largely controlled by the cerebellum and mostly concerned with coordinating movement; interval timing, on the scale of seconds to minutes to hours, distributed throughout the brain (and especially the striatum) and concerned with determining the typical duration between two events; and circadian timing, the 24-hour internal clock coordinated by the suprachiasmatic nucleus and adjusted based on solar cues (and, to a lesser extent, cues like eating times).",
"See, for example, the excellent timing review by Buhusi & Meck, 2006: ",
"\"What makes us tick? Functional and neural mechanisms of interval timing\".",
"What you're talking about is circannual timing, meaning the timing of yearly (or thereabout) events. This almost certainly is largely controlled by instinct, or at best by other cues (e.g., shortened days and colder temperatures). Read more in my previous AskScience AMA ",
"here",
". It's sometimes hard to disentangle learning and cognition from instinct, but consider how ",
" most animals would be if they didn't intuitively know what to do as their first winter approached. ",
"How animals subjectively experience time is a very difficult question to answer, but it's just one of many stimuli that govern animal behaviour. Whether they ",
" the future or merely react to things that previously have been associated with what they should plan for is contentious, and I will quote ",
"myself from an earlier question",
":",
"Future anticipation and future-planning in nonhuman animals is a really interesting, difficult-to-measure thing. First, \"future prediction\" mostly isn't necessary - we can usually predict the future pretty well based just on what has worked in the past (i.e., reinforcement learning). This complicates figuring out if an animal is deliberately planning, because you need to study it in circumstances that the animal isn't totally familiar with (or else they'll just respond in ways that have previously worked well), and then that seems a little unfair to expect the animal to cope with. There have, however, been some pretty successful studies of future anticipation in rats and monkeys. I've also found that pigeons start responding on options that currently aren't paying off but will soon (even at the expense of missing out on current food). Whether these are the same as what humans experience (and whether what humans experience is real, or just the way we interpret our decisions!) isn't currently answerable. In short, your dog probably lives mostly in the present and that works for it, but that doesn't stop it from doing things that work in the future (and it might even think about it, but we don't know!). "
] |
[
"So... Does that mean animals also procrastinate?"
] |
[
"If someone listened to the same sound (i.e. a music album) when trying to fall asleep each night over a long period of time would that sound eventually help them fall asleep faster? Conversely would they find it harder to fall asleep if they couldn't listen to it?"
] |
[
false
] | null |
[
"Interesting question. People find that falling asleep to white noise is easy, because it's the same constant sound and no irregularities. This noise allows a person to be able to shut down their brain and fall asleep faster. If a person substituted this with a music album it would depend on what memories are associated with this type of music. Each song, note, lyric instrumental sound would represent a trigger for memories and cause the person to start rehashing such memories while trying to fall asleep, thus making it harder to shut off the constant thinking and get to a restful state... Also the minute they start listening to such music if it were to only be used for sleeping, they are already associating thoughts to particular parts of the song, setting themselves up for the next day when the music comes on remembering they were thinking about this or that when this song came on. White noise is a bland and constant sound that can help a person to just settle down and not associate one specific thought or memory to that sound. "
] |
[
"I've done that very thing for 6 of the last 10 years. Same album , same volume. IMO it absolutely does help me fall asleep. I stopped for a few years and it didn't keep me from falling asleep. But like turning off the lights it does help me fall asleep faster and sleep better."
] |
[
"In terms of classical conditioning, this could more or less work to make you fall asleep faster. This is essentially the same principle used in stimulus control instructions to treat insomnia, but in that case the goal is to associate bed (not music) with sleep. The trick is to avoid associating bed (or music in this case) with wakefulness, so stimulus control instructions stipulate that you should only go to bed when sleepy and get out of bed if unable to sleep. Other instructions include maintaining a consistent wake time 7 days/week and not napping. Use of stimulant and depressant substances should also be limited if not eliminated.",
"Would it make it harder to sleep without it? I can't think of any studies on that offhand, but it stands to reason that it would be harder to sleep without it."
] |
[
"What physical property makes certain materials transparent or translucent?"
] |
[
false
] |
Diamond and graphite are both carbon, yet one is translucent and the other isn't. So are transparency and translucence solely a consequence of molecular structure? Or is there more going on?
|
[
"Take a clear grocery bag, and stretch it. Starts off transparent, becomes translucent.",
"In this case, some of the tangle of polymer chains that make up the bag line up and the result are these microscopic regions with more crystallinity that scatter light. So the bag looks cloudy and translucent -- still lets some light through, but it's not transparent and you can't see through to the other side.",
"I don't understand what you mean by translucent graphite. I normally think of it as opaque...but maybe you have a very thin sample of it or something?",
"Almost all ordinary matter is made of atoms and molecules, so I suppose it follows that everything is a consequence of molecular structure...But here is a different example that is more \"physics-like\": ",
"a critical opalescence video",
". Near the phase transition, the fluctuations become comparable with the wavelengths of visible light and so scattering takes place. The fluctuations are much much larger than the size of the molecules involved."
] |
[
"Oh, I see. In this case, the distinguishing feature is the electronic band gap of the material, and yes, this strongly depends on the arrangement of atoms. In the case of diamond, the band gap is something around 5 or 6 eV. A photon has to have at least 5eV before it will be absorbed by the diamond. Visible light is around 1.5 - 3 eV, nowhere near the size of this band gap. So it will pass through the diamond no problem. For graphite, its electronic structure allows it to absorb the entire visible spectrum (and a lot more) so it looks exceptionally dark."
] |
[
"Here's a great video by Nottingham science: ",
"https://www.youtube.com/watch?v=Omr0JNyDBI0",
"Basically, when a photon hits an opaque material, it uses it's energy to put an electron into it's excited state. By doing that, the photon \"disappears\". When a photon hits a transparent material, it has not enough energy to excite the electron and passes through."
] |
[
"Let's say you are being teleported somewhere - Wouldn't you \"die\"?"
] |
[
false
] | null |
[
"Well, teleportation is magic and you can define your magic to work however you want. If you're talking about quantum teleportation (not magic, a real thing but not what it sounds like) then there is a ",
"theorem",
" that states that you can't create a clone of a quantum state."
] |
[
"I just understood it as that teleportation has worked,",
"Where did you get the idea that teleportation in the sense you describe it, \"has worked\"? (or even been attempted?)"
] |
[
"I just understood it as that teleportation has worked,",
"Where did you get the idea that teleportation in the sense you describe it, \"has worked\"? (or even been attempted?)"
] |
[
"Why is leukemia contagious between cats but not between humans?"
] |
[
false
] | null |
[
"It's a feline virus that causes leukemia in cats, and it's the virus that can be transmitted. Leukemia in humans is hereditary and associated with risk factors like radiation exposure but is not related to a transmittable virus."
] |
[
"As the others have alluded, there are some cancers that can be caused by a virus. In humans the HPV virus can cause cervical cancer. In other animals other viruses may cause other types of cancers.",
"And since viruses are mostly species-specific, the end result is different types of cancer(really cancer-causing viruses) being contangous."
] |
[
"It's typically not hereditary. And there are viruses that cause leukemia in humans."
] |
[
"How is velocity measured in space? What is it measured relative to?"
] |
[
false
] | null |
[
"Usually this is done by the Doppler method. This means that we are measuring the velocity relative to Earth. We then often use models for how Earth and the sun moves to calculate the velocity relative to ",
"local standard of rest",
"."
] |
[
"At a more cosmic level, velocities can be measured relative to the comoving zero dipole anisotropy frame of the cosmic microwave background. ",
"So you might be talking about motion relative to a point on the Earth's surface; but that point on the Earth's surface is moving at up to 0.46 km/s relative to the centre of the Earth (depending on latitude); the centre of the Earth is moving at 0.01km/s relative to the Earth-Moon barycentre; the Earth-Moon barycentre is moving at an average of 29.8km/s (varying by ±0.5km/s) relative to the Sun; The Sun is moving at up to 0.02km/s relative to the Solar System Barycetre; the Solar System is moving at about 20km/s relative to the Local Standard of Rest; the LSR is moving at about 250 km/s in relation to the Milky Way Barycentre (in an elliptical orbit around its centre), the Milky Way is moving at something like 80 km/s in relation to the Local Group Barycentre, the Local Group is moving at about 630 km/s in relation to the comoving CMB zero dipole anisotropy frame, and all points in this ",
"comoving frame",
" are moving away from each other as the universe expands at relative speeds given by the ",
"Hubble Law",
".",
"And all these motions are in different directions. ",
"It's not surprising when people get overwhelmed, but there it all is.",
"Luckily there are no absolute frames of reference in the laws of physics, so unless you really need to track the relative motion of these things, none of it matters at all."
] |
[
"Interesting, thanks! I've always found it really bizarre when I hear \"the space shuttle travels at <x> miles per hour\"... relative to... the Earth? Which is also moving and is orbiting the Sun? Which is also moving? It all gets very confusing."
] |
[
"When an old star begins fusing Iron it begins \"using\" more energy than it produces. Is the \"used\" energy what builds up to produce super-nova?"
] |
[
false
] |
I realize there must be enough mass to begin with. But what exactly happens to tip the balances again and set off the explosion?
|
[
"Iron is the heaviest element a very massive star will produce to gain energy through nuclear fusion so it can withstand the gravitational pull (technically nickel is the heaviest element that still gives off energy in a nuclear fusion process, but for other reasons the star mainly stops at iron). Once the core has turned most of its elements into iron, it stops the nuclear fusion entirely because from here it requires, not produces, energy to fuse heavier elements. When the fusion stops, the radiation pressure no longer resists the gravitational pull. To make a long and rather cumbersome story short, the outer shells basically fall onto the iron core where it bounces off with a huge shockwave and is sent out into space in a ",
". This type of supernova is often referred to as a ",
" because the material collapses and bounces off the iron core, but it's not an explosion as is evident in a ",
". What remains then is a mostly an extremely dense core of iron and either a sphere of neutrons (because electrons and protons were squashed together to form neutrons during the core collapse) called a ",
", or if the star and its iron core was extremely heavy so not even the degeneracy pressure created by the neutrons, which are a type of particles called fermions, can counter the gravitational pull, the core collapses entirely to a singularity known as a ",
"."
] |
[
"You can easily google the fission and fusion terms and see that your definition is wrong.",
"The core collapse is also not because of massiveness of the core but because the pressure inside the core drops significantly which causes the collapse."
] |
[
"You can easily google the fission and fusion terms and see that your definition is wrong.",
"The core collapse is also not because of massiveness of the core but because the pressure inside the core drops significantly which causes the collapse."
] |
[
"When you feel full after eating, is it because your stomach is literally not able to fit more food or is it just your brain telling you to stop eating?"
] |
[
false
] | null |
[
"When you start eating and filling up your stomach, your body produces a hormone called leptin that signals to the brain that you’re getting full, reducing your appetite and giving you the feeling of fullness.",
"As you keep eating and your stomach becomes distended as a result of ",
"eating, your body will continue to produce leptin, but you’ll feel a growing sense of discomfort the more your stomach is stretched beyond its normal capacity."
] |
[
"True! There are other hormones like ghrelin (which stimulates appetite) whose levels decrease during meals, and cholecystokinin (CCK) & glucagon-like-peptide-1 (GLP-1) [which increase after eating] that are also important factors in feeling \"satisfied\" after meals. ",
"Like most functions in our body, even hunger is quite a complex process predicated on the changes of a number of things. Just wanted to keep it simple :)"
] |
[
"Leptin is not the main satiety hormone during meals. It's produced by fat cells and works over long periods of time. Other hormones are much more important in the short term. For example - grhelin drops and cck and glp1 increase after eating while leptin remains relatively stable."
] |
[
"Torque on paramagnetic material in a magnetic field"
] |
[
false
] |
I've come across an equation in a paper about magnetism that isn't derived. I'm trying to figure it out, but haven't found it yet, and it's outside my usual field. It's about how torque is applied by a magnetic field to a paramagnetic fibre. Apparently, the most torque is applied when the fibre is at 45 degrees to the field - the sin(2*theta) term. I'm not sure why that would be, intuitively the torque would be maximum at 90 degrees. Torque=0.5 * mu * V * H * dx * sin(2*theta) where, mu is vacuum permeability V is the volume of the fibre H is the magnetic field intensity dx is the anisotropy of volume susceptibilty theta is the angle between the fibre axis and the magnetic fiield
|
[
"I'd have to see a diagram, but I guess the force varies as cos(θ), the lever arm as sin(θ), so the torque as sin(θ)cos(θ) = sin(2θ)/2"
] |
[
"Ok, I think I got this sussed. Too many years since I did magnetism though.",
"Firstly, your equation for torque is the cross product of magnetic moment and magnetic field.\n",
" (Nm)= ",
" (Am",
" x ",
" (N/Am)",
"Because it's paramagnetic, the susceptibility χ is very small and",
" = μ (1+χ) ",
" ~ μ ",
"The magnetic moment is split into an isotropic part which doesn't cause any torque, and the anisotropic part. The isotropic part is:",
"iso = V χ H, a vector aligned with the field.",
"The anisotropic part we need is:",
"ani = V δχ H cos θ, a vector aligned with the fibre",
"Then you cross B with m ( the iso part vanishes)",
"iso x ",
" = 0",
"ani x ",
" = (V δχ H cos θ) * (μ H) sin θ",
"= 0.5 * μ * V * H",
" * δχ * sin(2*θ)"
] |
[
"That would make sense, not sure what you mean about the lever as sin(theta) though...",
"Here's a diagram",
"(Blue is for reference as an axis, the black line is a fibre in the magnetic field caused by the magnets either side)",
"According to the wiki, torque is a cross product of the field and the magnetic moment, which should be as sin(theta). Could a cos(theta) term come from it being paramagnetic?"
] |
[
"Air and water are both fluids — why are there no birds that fly like fish swim or fish that swim like birds fly?"
] |
[
false
] | null |
[
"Do you have a source for this?"
] |
[
"https://en.m.wikipedia.org/wiki/Atmosphere_of_Earth",
"Air is a gas"
] |
[
"Air is not a fluid."
] |
[
"Do people with wider set eyes have better depth perception?"
] |
[
false
] |
Calling ophthalmic optricians (optometrists) or biologists. Has there been a study on width between the eyes and a correlation with better/worse vision?
|
[
"Sitting here with me is a device called a stereoscope. This stereoscope contains adjustable mirrors which can be adjusted in such a way that they are effectively setting your line of vision for each eye, outward. As though the eyes are further apart. ",
"There is a point where the brain loses its focus and is unable to handle the signals coming in and you experience a mess of images. The same thing that you experience when you cross your eyes. The interesting thing is what your brain interprets up until that limit. You see the world in 3D. I'm not a professional in the field of anything even related to vision, so I can't explain it in any other term than that. 3D. You perceive depth in a far more pronounced way because your eyes take in more picture information. More parallax. If there is an object on a table in front of you, you see more of its sides and the brain pieces it together just as is done when you watch a 3D movie. In fact I use this stereoscope for 'squeezing' two videos together while actually editing two side by side videos that will later become a 3D video.",
"So from personal experience, yes the depth is far more greatly perceived but again there is a limit to the distance where the brain can't hold its focus. I don't believe that the vision itself is any better or worse.",
"Bonus tidbit. Read about what a pseudoscope is! It's a device that uses mirrors to swap signals from left eye to right eye and vice versa... With surreal results!"
] |
[
"The ",
"Pseudoscope",
" is nauseating even just reading about it, for some reason."
] |
[
"Related: is there a measure of \"depth-perception\"? Would it be related to the standard 20/20 system?"
] |
[
"Microscopy Questions"
] |
[
false
] |
My apologies, as this is not a traditional askscience post, but I feel that I could reach the most interested parties here. I had a question about a microscope purchase I'm planning on making coming up pretty soon and some other redditors I've contacted have suggested making a general post. I'm doing a project that will involve looking at some slides of stained CNS tissue and blood but mostly looking at fecal samples for parasite loads. Since I'm going to be spending a lot of time doing this (around 500-1000 fecal samples), I was thinking about getting an LCD screen scope instead of the traditional binocular scope. Do any of you have LCD screens experience? If so, any company recommendations? If not, could you recommend a scope in the range of 400-600 dollars? This is an example of the kind of thing I was looking at: but I could go more expensive for a LCD I would.
|
[
"Well, I forget what brand of scopes I tend to use (inverted and not). But Traditionally we buy the scope, then buy a camera attachment that attaches to a computer. I have seen scopes with LCD controls, but all scopes I have seen with visual displays have an attachable camera. You can scan SO much faster through the ocular lenses, then switch to camera to take a picture/change exposure, etc. ",
"Unfortunately, the last scope I saw purchased was more in the $500,000 range for the set up. "
] |
[
"Congrats you made me spill my coffee"
] |
[
"Agreed. A good CCD camera on a decent scope will be much more beneficial than having an LCD screen in which you have to scan with. The NIKON COOLSNAP range are pretty decent CCD cameras and a good place to start looking if you are interested."
] |
[
"Why do some fruit juices, take orange juice for example, need to be refrigerated when the orange itself does not need to be?"
] |
[
false
] | null |
[
"Well an orange's skin secretes oils that have anti-fungal and anti-bacterial properties. An orange with an uncompromised skin will last relatively long. However, the juice and pulp contain no such defenses and certain bacteria and fungi will happily grow on/in it. Refrigeration generally slows down growth and activity of most microorganisms"
] |
[
"In addition to the physical barrier the skin provides, the undisturbed cell wall structure of the fruit compartmentalizes the components of the orange that microorganisms would metabolize. Additionally, enzymes that would hasten chemical degradation of the fruit are similarly bound. Once the cell walls are disturbed all of these compounds are more readily available to microorganisms, as well as to oxygen and enzymatic degradation. "
] |
[
"Keep in mind that this is only the case if the container of the juice has opened at some point. Leaving it intact keeps the juice inside mostly-sterile, and it's just about as preserved as an unpeeled orange. This is why compromised containers of fruit juices with no preservatives tend to become unsterile and full of bacteria (",
"Capri Sun, for example.",
") while untampered packages of the same juices are relatively safe to store at room temperature. Of course, no food item is free from contamination, so your orange will eventually succumb to the likes of mold.",
"Side note: Not sure if the whole anti-bacterial oil secretion factoid is true since the oranges sitting in your kitchen are picked."
] |
[
"Are animals' facial expressions representative of their mood or do humans just interpret them that way?"
] |
[
false
] |
If an animal appears to be smiling, is it actually happy or is it's face just doing that? For some types of expression, I imagine the answer is obviously yes. If a tiger is bearing it's teeth at you and hissing, it is pretty clear that it is demonstrating that it is aggressive. But for expressions like happiness, worry, fear, relaxedness and the like, is that actually how the animal is feeling or do humans just assign human emotions to vaguely similar expressions on animals?
|
[
"Most animals do actually show facial expressions to indicate their mood however they’re often different than that of humans, for example smiling is not shared by a large group of creatures as the facial structures for animals vary widely so most need to develop different ways since their faces are so different, a cat can’t move it’s face like an elephant for example and vice versa."
] |
[
"There's been a number of articles around lately claiming that dogs evolved eyebrow muscles to better communicate with humans - apparently we liked the more expressive ones better.",
"Animals have body language, and have some very deep-seated yet basic perception around the body language of other animals - something increasing apparent size or showing teeth is almost universally understood as a warning/threat, which is why cats arch their backs and numerous animals puff up and grimace when they feel threatened. Reducing apparent size is a common expression of fear too.",
"The human smile is a bit of an outlier, very few animals habitually show their teeth when they're happy. Dogs learn it from us, wild ones don't smile.",
"Humans are uniquely able to communicate with each other about our experiences of various animals' more subtle body language cues that might otherwise only be meaningful within a species or group."
] |
[
"It’s important to note too that facial expressions (specially in animal science) are deemed predictive of a general motivation or tendency to engage in a series of actions. Using this approach, it may be easier to understand the facial expressions of nonhumans that are dissimilar in their look."
] |
[
"Conduction heat transfer to surface from temperature field?"
] |
[
false
] | null |
[
"Hello,",
"We don't offer schoolwork help here."
] |
[
"Who said anything about schoolwork? "
] |
[
"The question seems like a homework problem, and you made a brand new account called \"engHelp\" in order to ask it.",
"Is it ",
" schoolwork?"
] |
[
"How would we know if Voyager 1 or 2 crashed into something?"
] |
[
false
] |
I went to JPL's website, but there is nothing there about the possibility of it happening. Did we just chose a course that at the time looked pretty empty to us?
|
[
"We're still in contact with both so if that ceased unexpectedly then we'd at least know something went wrong. More than likely it'd have been some kind of failure on one of the crafts but knowing it had crashed into something would be pretty difficult to figure out. Perhaps if part of a spaceship was hit and the trajectory changed or it went into some kind of tumble then we might be able to deduce that it was hit.",
"In the long term though, space is pretty empty of large things that it could crash into. Or rather, space is so large that the chances of hitting those few things are incredibly slim, which has been discussed in previous questions before. So could it crash into something in the distant future way out there? Sure, it could. However, shutdown of the instruments will be on the timescale of a ",
"decade",
", so we wouldn't be able to tell after that anyway."
] |
[
"Just fyi, traveling at it's current speed it would take Voyager about 76,000 years to reach the nearest star. So they don't have to worry about a trajectory change due to being near a star or black hole. Space really is mind blowingly big!"
] |
[
"Perhaps if part of a spaceship was hit and the trajectory changed or it went into some kind of tumble then we might be able to deduce that it was hit.",
"If we're still talking about the Voyagers here, then it is pretty certain we would never be able to ascertain what happened in the case of a fatal collision unless the spacecraft was active transmitting to Earth at the time. ",
"Once the high gain antenna no longer points at Earth, the craft is uncontrollable and untrackable. If the craft was transmitting when the incident occurred, maybe a Doppler shift anomaly just before final LOS could provide a clue."
] |
[
"Would a relay system of satellites speed up interstellar communication?"
] |
[
false
] |
If we are trying to talk to an object, let's say 100,000 light years away. We are limited to at most the speed of light let's also say. Would having 100 relay satellites spaced out between us and them, would our transmission would go faster at all?
|
[
"You can't improve latency (indeed, adding relays will worsen latency). However you can improve bandwidth; a shorter signal path to a relay will have a better signal-to-noise ratio, so you can send at a higher data rate before it becomes unreadable (with each relay applying error-correction codes to restore the message before retransmitting)"
] |
[
"No. Transmission can't go faster than the speed of light. How would the relays improve on that?"
] |
[
"Speed, in terms of communication, can refer to one of two things: latency, and bandwidth. Latency is how quickly (time-wise) that information is conveyed, while bandwidth measures how much information is able to be transmitted at once (typically measured in megabytes per second). Bandwidth can always be improved by adding more pathways or improving the way information is sent, but latency is fundamentally limited by the speed of light."
] |
[
"So in spacetime and gravity, time dilation happens. Does space dilation happens too?"
] |
[
false
] |
Keeping my fingers crossed that this question sees the light of day. Does this question makes any sense? If it doesn't, why it doesn't? If it does, why it does? If the post gets deleted, it's probably the question is ambiguous or retarded. And I'd understand.
|
[
"Does space dilation happens too?",
"We call this length contraction. If a 1-meter long rod flew past you at 0.99c, it will look about 14 centimeters long. If that rod was made of electrons you'd see a significant magnetic field despite there being none in the rod's reference frame. Gravity will cause space and time contractions and dilations as well, but the specific form will depend on the system and your reference frame."
] |
[
"I think its worth emphasizing to OP that the rod doesn't just ",
" 14 cm long to you, it ",
" 14cm to you. As it flew past you could contain it in a 15cm long box like ",
"this",
". This image is from the wikipedia article on the ",
"ladder paradox",
" which explains the situation well.",
"It probably seems like a silly distinction between ",
" and ",
" 14cm long, but I remember when I first learned relativity it wasn't immediately obvious."
] |
[
"The sphere would contract in its direction of motion, so it would end up being ellipsoidal. "
] |
[
"What is the largest planet we know? How big can a planet get or is there something restricting it from being Enormous?"
] |
[
false
] |
[deleted]
|
[
"Well, they eventually cross over into brown dwarfs. Once they get large enough to begin nuclear fusion, they become stars.",
"Jupiter for, instance, would have to be 80 times more massive than it currently is to initiate hydrogen fusion.",
"Large brown dwarfs can fuse deuterium and tritium, two isotopes of hydrogen, but can not fuse regular elemental hydrogen.",
"When you ask about size, do you mean volume or mass? A brown dwarf 60 times as massive as Jupiter would actually be about the same size as Jupiter, because as an object gets \"heavier,\" its gravitational effect increases and it compacts more.",
"So in terms of outright volume size of planets, Jupiter is close to the upper limit, though there are definitely less dense planets that are a couple times larger than Jupiter out there."
] |
[
"It's more than the star forming leads to hydrogen fusion. Once enough matter collects in a single place, it begins to collapse under its own gravity. This heat and pressure becomes so strong that atoms start fusing. At that point, the outward pressure of the fusion fights against the crushing pressure of the stars own gravity and a sort of equilibrium is reached. A star is little more than an ongoing thermonuclear explosion.",
"Ok, it's a hell of a lot more than that, but that's the extremely quick version.",
"The larger the star, the shorter it's life as it burns its fuel faster. Stars start by fusing hydrogen into helium. Then they start fusing helium then carbon then oxygen and so on until they reach iron. Iron is a death sentence for stars, as iron can not fuse in a star's core. For very large stars, then end can come quite rapidly after iron starts being created in the core. Fusion stops in the core, there is no more radiation pressure to hold back the gravitational collapse. For large stars, this means supernova.",
"In a supernova, the star collapses on itself at resistivistic speeds. The core compresses as much as it physically can. The outer layers of the star slamming into the core \"bounce off,\" and that's what creates the explosion. If the star wasn't super huge, just very huge, a neutron star is what's left. An object only 10 to 20 kilometers across with 3.5 times the mass of our sun, that is for all intents and purposes, one giant atom.",
"If the star is really big, even degeneracy pressure can't hold back the collapse, and what remains is a black hole."
] |
[
"Thoroughly fascinated. I had no effing idea planets can become suns. I thought they were just two different kinds of celestial bodies.",
"Can you explain the hydrogen fusion and how/why that leads to a star forming?"
] |
[
"Why can't you absorb mercury (metal) with a sponge?"
] |
[
false
] |
[deleted]
|
[
"When you pick up water with a sponge, some of the water forms very weak chemical connections with the material of the sponge. We say that the sponge is 'wettable' with water.",
"Mercury doesn't have the same chemical properties as water, and won't make the same connections. If you had a sponge made of say, gold, it would pick up the mercury, but the mercury would also form an amalgam with the gold."
] |
[
"Cohesion is the intermolecular force between molecules that allows molecules of the same substance to adhere to each other, this creates surface tension. Adhesion is the ability of a liquid to stick to other things, like how that last drop of beer at the bottom never quite makes it to your mouth. Mercury, has a very high surface tension, but it does not wet things. That is to say, based on its physical chemistry, it has wicked cohesive strength, but pretty beta-adhesive. If your beer was mercury, you would be able to drink that very last drop.",
"Edit: This is my hypothesis only, and im assuming regular polymer sponge"
] |
[
"I don't know what would happen.",
"I would guess that it's a mix of the sponge staying squished, and some mercury getting forced into the cells and capillaries of the sponge."
] |
[
"Has a gravitational force been observed between massless particles?"
] |
[
false
] |
Light is attracted to mass by gravity (black holes, gravitational lensing). Due to Newton's 3rd law (For every action, there is an equal and opposite reaction) the light will assert a force on the mass via gravity. Extending this, is a gravitational force between photons? And is it large enough to be observed? I understand at high energies, pair production will be a factor, but I was thinking about lower energies than this. Additional question: If you shine two lasers of wavelength X metres in parallel, Y metres apart, how long will it before the beams converge due to gravity. I'm not sure about my logic here. Please correct me if I'm wrong.
|
[
"Extending this, is a gravitational force between photons? ",
"Yes, if they are not perfectly parallel (that also answers your last question).",
"And is it large enough to be observed?",
"Not with today's technology, and not with any planned or even proposed experiment."
] |
[
"An accessible, but somewhat naive, way of motivating the idea is that you can always shift into a reference frame where two parallel beams or photons of light are redshifted arbitrarily close to zero energy. Since spacetime curvature is affected by energy density (and some other factors), then in such reference frames you should expect to see little effect. If the beams are not parallel, then you can't find a reference frame where both beams simultaneously redshift arbitrarily close to zero, so there will be some non-zero energy and momentum density in all reference frames.",
"Another way to think about it is in terms of the rest mass of the system of two photons. In special relativity, E",
" = (mc",
" ) + (pc)",
" . For one photon, the rest mass m = 0, yielding E = pc, and from quantum mechanics we know that the energy of a photon is E = hf (Planck's constant times frequency). For a system consisting of multiple photons, the equation becomes (E_total)",
" = (Mc",
" )",
" + (∑pc)",
" where M represents the mass of the whole system. For photons moving in the same direction, the energy and momentum terms match up and M = 0. But consider two photons are moving in ",
" directions: then ∑p = 0, and the equation reduces to E = Mc",
" – the system has no net momentum, but it clearly possesses energy, and so it also has mass. ",
"These are, of course, largely special relativistic explanations and ignore the finer points of general relativity. They are, nonetheless, reasonable ways to motivate why parallel photons do not gravitate towards each other, even if they aren't the whole story."
] |
[
"Why would there not be a force if they are parallel?"
] |
[
"Is it important for a 14 yr old to study science in school? Why?"
] |
[
false
] | null |
[
"Initially your first question in your subject seems like it can be answered scientifically, or at least with with some kind of data to support either side.",
"You're second question is more of an opinion. Some individuals will claim that everyone is naturally scientist in some way, that we strive to answer the unanswered. Also, the argument can be made that the less we know the better; perhaps less violence, less fear, etc. While the counter-argument would say that we are better off finding out answers, like medical advancements, making life easier, etc."
] |
[
"Is it important for a 14 yr old to study science in school? Why? ",
"The only really objective thing I can say is that obviously not everybody needs to be good at science. Investment bankers don't need to understand vector products and actors don't need to know about meiosis to do their jobs well or lead a fulfilling family life. You can be very successful in many aspects of life without being good at science. ",
"You're probably going to be better off if you do put the effort into learning science, because it gives you a better understanding of the nature of the world around you, but it's not strictly ",
"."
] |
[
"John, you will be delighted to see the non-profit I started - ",
"www.students2science.org"
] |
[
"Are prokaryotes capable of lysing foreign cells?"
] |
[
false
] | null |
[
"Absolutely, usually via exotoxin secretion into medium or injection into target. For example, streptolycin o is an exotoxin secreted into the medium by Streptococci to lyse erythrocytes, by forming pores in the target cell's membrane."
] |
[
"Thank you so much!"
] |
[
"Adding on- lysing cells is one way that bacteria can spread in the body. They will use the cell's favorable conditions to grow their numbers, lyse the cell, then find their way into new cells to repeat the process."
] |
[
"During the experiment conducted by Ernest Rutherford in which the nucleus is discovered, an alpha particle is shot at a thin foil strip. An alpha particle is a helium nucleus, so how did they not know the nucleus existed despite being able to isolate one and fire it?"
] |
[
false
] |
As far as i understand it the gold foil experiment was conducted when the plum pudding model was the accepted theory by the science world, including Rutherford himself. But how can the nucleus not have been discovered before when you consider that the alpha particle is a helium nucleus. How can they not have known what an alpha particle is despite them being able to isolate and ‘fire’ one at the gold foil?
|
[
"They knew that radioactive materials gave off radiation, but they did not know what that radiation consisted of. There were three types of radiation that were observed: one was charged and heavy (can be stopped by paper), one was charged and light (can be stopped by metal), and one was neutral and light (can only be stopped by thick layers of lead). They called these alpha, beta, and gamma. It was later discovered that the alpha particle and the helium nucleus were identical, just like beta particles and cathode rays were identical (now called electrons)."
] |
[
"I actually don't know the historical sequence. Apparently for the beta particle it was 1900. With alpha particles it was Rutherford in 1907. However, it wasn't known that ionization involved removing the electrons to leave the much smaller nucleus, because the atomic structure wasn't known."
] |
[
"Electrons were already known to have existed, did they know electrons were beta particles at the time or did they, like with the alpha particle, only connect them later?"
] |
[
"[Physics] How does dew form? And also, what exactly does the dew point mean?"
] |
[
false
] |
I was up early this morning and was looking around my yard. And also looking at the dew, and wondering how it formed, and what the dew point has to do with it. My best idea is that condensation comes down overnight and makes dew stick to everything? At least until the sun comes and "melts it off"?
|
[
"Air always contains some small amount of water vapor. We generally refer to the amount of water in the air as \"humidity\", generally given as a %. At 100% humidity, by definition, the air is fully saturated and can't hold any more water.",
"It turns out that the colder air is, the less water it can hold. So for a constant amount of water in the air, the humidity % will go up as the temperature goes down. The \"dew point\" is the temperature at which humidity will reach 100%, given how much water is currently in the air.",
"Overnight, things get cold. If it gets below the dew point temperature, the air has 100% humidity, plus extra water, which ends up condensing as water droplets on colder surfaces. When the sun comes out and it gets hot again, humidity goes down and the water evaporates back into the air.",
"Side notes/minor details: hotter surfaces (the ground itself, tree trunks, animals) will keep the nearby air warm such that it doesn't reach the dew point and no condensation happens. On the other hand, colder objects (the coke can you just took out of the fridge) will cool down nearby air below the dew point and form \"dew\" on the surface, even when it's much warmer than the dew point outside."
] |
[
"Air can only hold so much moisture given its temperature, we call this relative humidity. As the temperature drops overnight, the air can no longer hold all that moisture and it condenses on surfaces it touches and it turns to water droplets. There's more science behind it but that's the gist, I work in the humidity industry."
] |
[
"Thank you for a very detailed answer. \n🇬🇧👍🏻🇬🇧"
] |
[
"If I cuy myself in vacuum, what colour would my blood be?"
] |
[
false
] |
[deleted]
|
[
"Normal blood is red: oxygenated blood is brighter red, deoxygenated blood is dark red.",
"So the answer would be red."
] |
[
"I don't think \"blue-ish\" is an accurate description of ",
" blood. Venous blood is not blue."
] |
[
"Red."
] |
[
"Why is Voltage directly and inversely Proportional to the Current?"
] |
[
false
] |
V=IR therefore I=V/R. Thus a greater voltage = greater current. However, P=IV therefore I=P/V. This means a greater voltage=smaller current. Why?
|
[
"Voltage is directly proportional to current when resistance is constant and they're inversely proportional when power is constant. Typically in a circuit voltage will be fairly constant and changing the resistance will change the current causing power to change."
] |
[
"Your question has more to do with math than physics.",
"Say you have a function (in this case I) of two independent variables, and you want to see how it \"reacts\" when you change one of them (say V) . This is ",
" defined if you specify which other variable remains constant (in this case either P or R).",
"For example say you want to see how the current will change when you leave the same resistance, but connect a battery with more voltage.",
"Both expressions (I=V/R and I=P/V) are valid, but the first one is clearly more useful, because R is a constant for this experiment. If you use the second one, you have to take in account that P is not a constant, and when you replace P using the equation",
"P=V",
" /R you arrive to the same result."
] |
[
"In your second equation, greater voltage means smaller current if you keep the power the same.",
"If you increase the voltage and want to keep the power the same, you need to do something to drop the current, which means more resistance."
] |
[
"In fusion reactors, how do they use magnets to control the heat?"
] |
[
false
] | null |
[
"In a magnetic confinement reactor the magnets are used to confine the plasma. You can use magnetic fields to confine charged particles to some region of space, for example using ",
"magnetic mirrors",
".",
"The reactors are designed with particular geometries and field configurations to trap the hot plasma inside."
] |
[
"There is stuff like solar and wind which do turn energy directly into DC electricity. However, they're still a small percentage of the overall generation capacity. There is a way to turn heat directly into electricity but it's not as efficient yet and I have no idea if or when it will be better. If it gets to 40% or better and can work in extreme conditions and temperatures while being comparable price wise, or even if it costs more but lasts a lot longer without maintenance, then it will replace current technology."
] |
[
"It should be stated plainly, the magnetic fields created by the superconductive electromagnets do not control the heat, they confine the plasma so it doesn't get too close to the inner surface of the walls which in turn do receive a lot of heat through the vacuum of the chamber, just like we receive heat from the sun through the vacuum of space, but it is managed with additional cooling that transfers said heat to produce steam which in term drives a steam turbine connected to a generator, thus making electricity. Just like fission reactors, fusion reactors are a fancy way of boiling water."
] |
[
"How long would it take for the positions of the stars to appear different from earth?"
] |
[
false
] |
We are orbiting the sun, and the sun is orbiting the center of the Milky Way along with all of the other stars that we can see from Earth. From my understanding, the constellations/postions of stars that we see on earth have remained the same for thousands of years because the galaxy is so enormous that our point of view really hasn’t changed much. Is my understanding correct? How long would it take for the sun to move far enough that the stars would be in different positions in the night sky? Side question: Is the sun moving quickly or slowly compared to the other stars of the Milky Way?
|
[
"The Sun seems to be going maybe 10% faster than average, but there's generally a scatter of 10s of km/s between stars on the same rough orbit, so that's not unusual.",
"What you're getting at here is called \"proper motion\". This is the speed in degrees/year that a star appears to move across the sky. Due to parallax, nearby stars appear to move a lot faster than distant stars - their speed in km/s is the same, but in degrees/year it's very different.",
"The stars with the highest proper motions are moving at about 1 degree every few hundred to few thousand years. The Moon is about half a degree across, as a baseline. But most stars move much much slower than that.",
"The more significant effect (from the Earth's perspective) is the precession of the Earth's axis. The Earth's tilt gradually wobbles in a circle over thousands of years. This causes ",
" the stars to appear in different places in the sky, and is why the sky is oriented differently than it was during e.g. Ancient Greece. This explains some weird stuff, like constellations that are quite far south having Ancient Greek and Latin names, and also why the signs of the Zodiac no longer actually line up with which constellation the Sun is actually in. It's a much quicker effect than the Sun's motion relative to nearby stars."
] |
[
"The next north star will be Gamma Cephei in about 4000 AD. Vega won't be the north star until about 13000 AD, and it won't be very precise. Actually Polaris about now is as good as it gets for the north star.",
"https://en.m.wikipedia.org/wiki/Axial_precession",
" has some nice charts."
] |
[
"Fantastic answer. Thank you very much."
] |
[
"Does curvature of the universe require an extra dimension to \"curve into\"?"
] |
[
false
] |
I've been having a Reddit argument with sirbruce in the comments section of some article in , and it's going nowhere ( , and it feels like it's going in circles). Could you guys help out? As far as I can tell, his claim is that it's impossible for the universe to be curved without a dimension to "curve into". My claim is that the extra dimension is either outright unfalsifiable, or its existence is at the very least not proven beyond a reasonable doubt. Can any of you shed some light on this?
|
[
"I doubt it will get you anywhere — from a quick skim of that exchange, it looks like you're dealing with someone who thinks he has only answers and no questions — but you might consider pointing out that Gravity Probe B parallel-transported a vector around a closed curve and measured a deflection, conclusively proving that spacetime really is intrinsically curved.",
"But really, it's a bit pointless. Nash's embedding theorem tells us that any intrinsically curved manifold can be embedded in a flat space of sufficiently large dimensionality, so the fact that we've definitely measured intrinsic curvature won't be sufficient to rule out the \"there are higher dimensions\" thing for a person with little experience with the subject.",
"You could just fall back on the old inverse-square law — it only works in exactly three spatial dimensions — but honestly, I'm not sure that'll convince him either. Once someone has become convinced that he knows the truth, there's little to be gained by arguing with him about it."
] |
[
"Yeah, sirbruce is completely wrong. It's perfectly possible to have curvature without needing to embed your surface in a higher dimension. Think of a sheet of grid paper lying flat on a table. You then warp the grid lines somehow. The grid is now curved without being embedded in a higher dimension. This is intrinsic curvature (the wiki page sirbruce linked to actually discusses this).",
"We have pretty good evidence that if there are other spatial dimensions, then they must be pretty small. Smaller, in fact, than the curvature of space that we measure. So, we must be seeing intrinsically curved space.",
"I wouldn't worry about arguing with sirbruce - they've made up their mind about the definition of these things, that only extrinsic curvature is \"real\". To be honest, I found about half of their statements to be either semantically empty or just incomprehensible."
] |
[
"That video is rubbish. The book it was created to promote is so fundamentally ",
" that one can't help but wonder if it's not just a big joke. The author is not a physicist, nor a mathematician, nor a person with any particular authority on the subject. He's a musician, and a notorious looney."
] |
[
"Does strength and muscle growth increase more rapidly if you're regrowing muscle to an amount you previously had?"
] |
[
false
] |
If I had been lifting weights and had increased my lean body mass, but then stopped lifting and my body mass decreased, would I be able to get back to the lean body mass I was at more quickly than the first time? Same with strength.
|
[
"Um...what?",
"http://en.wikipedia.org/wiki/Myosatellite_cell",
"http://www.nature.com/stemcells/2008/0801/080131/full/stemcells.2008.29.html",
"http://www.unm.edu/~lkravitz/Article%20folder/musclesgrowLK.html",
"http://www.ncbi.nlm.nih.gov/pubmed/18436694",
"From that last study:",
"\"These findings strongly suggest myonuclear addition via SC [satellite cell] recruitment may be required to achieve substantial myofiber hypertrophy in humans. Individuals with a greater basal presence of SCs demonstrated, with training, a remarkable ability to expand the SC pool, incorporate new nuclei, and achieve robust growth.\"",
"I'll be sure to let the researchers know that satellite cells don't exist in muscle tissue...lol.",
"I'm not sure what your background is, anatomyguy, but given that the subject of this thread is \"strength and muscle growth,\" yes, we're talking about skeletal muscle fibers. Based on you being unaware that satellite cells exist in muscle tissue, I am going to hazard a guess that you don't have any particular background in anything kinesiology or exercise physiology related.",
"Either way, you're completely wrong about this. There is quite a bit of research looking at the role of satellite cells in the process of muscle growth going back > 10 years, and everything I posted above is correct. As I said, the size POTENTIAL of muscle fibers is intimately linked with the number of nuclei they contain. Satellite cells get activated (via IGF-1) following mechanical strain to muscle tissue, like the sort you'd experience during resistance training (with an especially important role for eccentric contractions), differentiate, and then fuse with muscle fibers to help repair them, and as part of this, some donate their nuclei.",
"As such, there's a plausible mechanism by which strength/muscle could be more rapidly regained than gained the first time, and there are no shortage of anecdotes of people doing this after long layoffs from regular weight training."
] |
[
"First, your question is VERY vague. If you are 60 and looking to regaing the strength of your 20's, no.",
"Even if you are young, I do not think muscle builds itself any faster just because you \"were that buff\" previously. I remember being a soccer player/cross country runner in high school. Each year, the first day of training would hurt like HELL for the next 3 days, didn't matter how good of shape I was in. Each year, I would increase my ability. BUT, I did NOT start with the same ability. Despite a lazy offseason, I was better to start with. Thus I didn't really \"improve\" any faster, I just started off in better shape.",
"If you spend 5 years fat and lazy, then 2 years getting buff, and 5 more years devoted to getting as fat and lazy as you were in the first place..... I'd bet it would take you just as long, and as much effort, if not MORE, to get back to the same level of \"buff\".",
"This isn't scientific. I've never seen a study anything like what you are asking, maybe a PMT doctor (physical medicine/therapy) could offer more insight."
] |
[
"This is patently false. Muscle cell nuclei might decrease, over time. But they NEVER increase via \"satelite cells\". There are no cells in muscle tissue called \"satelite cells\". ",
"Muscle cells, if you mean skeletal muscle cells, or cardiac muscle cells, do in fact have multiple nuclei. Smooth muscle cells are individual cells with one nuclei.",
"But assuming we are talking about skeletal muscles, cells can be as long as 10 cm or so long. This is because as a fetus, the skeletal muscle cells fuse together to form very long skinny cells. And each cell that fused leaves its nucleus in the mature cell. They do not multiply, they do not divide, and the number of nuclei in muscle cells is not any sort of indication of the health or size of that muscle cell."
] |
[
"How exactly do antimicrobrial copper alloy surfaces work to kill germs?"
] |
[
false
] | null |
[
"Ions of copper and zinc have antimicrobial properties. Copper ions specifically disrupts protein structure, and such a lot of membrane proteins and enzymes have their function eliminated. They can also bind lipids causing cells to leak. Copper and zinc also form complexes that can inactivate viruses.",
"Wiki",
"PubMed"
] |
[
"Awesome, thank you for your explanation. "
] |
[
"Interesting read. If copper is so efficient, why not make all water pipes copper?"
] |
[
"As cosmic rays are so powerful, where does the energy go when they hit earth?"
] |
[
false
] |
[deleted]
|
[
"When a cosmic ray strikes the atmosphere, it creates a shower of new particles. Its energy is converted to the mass and and kinetic energy of all of these particles. Some of these particles hit the ground and are absorbed by the ground. Some of these particles are unstable and decay into other particles. Scientists who study cosmic rays detect the shower of particles on or near the ground and then trace them back mathematically to learn about the cosmic ray that created them. The particles can also trigger nuclear reactions in atmospheric atoms. For instance, cosmic rays cause nitrogen in the air to become radioactive, which is a good thing for scientists who rely on radiocarbon dating. The effects of cosmic rays are considered part of the natural background radiation."
] |
[
"Here's the incident they were referring to:",
"http://en.wikipedia.org/wiki/Oh-My-God_particle",
"It is an extraordinary amount of energy for such small particles, but on a human scale it's relatively low energy; the Oh My God particle had the kinetic energy of a baseball at 60 mph. But as Chrisbaird mentioned, we are still able to detect the effects of these particles and the side-effects from them."
] |
[
"A few other points that may be helpful to you:",
"Cosmic rays have a wide range of energies. The super-energetic cosmic rays are much rarer than the low-energy rays.",
"Cosmic ray impacts are very common. The lower-energy rays strike each square meter of Earth's atmosphere thousands of times per second. The very-high-energy rays are more like one per century per km.",
"Despite cosmic ray impacts being common, they are such small particles that they carry very little total energy."
] |
[
"Objects fall into black holes, but an observer falling in would see time slow near infinitely (?) as they approach the horizon. Is this a paradox? Do the two times sync up somehow?"
] |
[
false
] |
If from the observers view they never fall in, and perhaps that is an incorrect statement, how do the two views of the event match up?
|
[
"The visible light you are observing coming from the man as he approaches the event horizon would get stretched out into longer and longer wavelengths, first going through infrared and then into the other non-visible wavelengths beyond, by the intense gravity of the black hole. This continues until none of it is left in the visible spectrum."
] |
[
"For the one falling, time wouldn't change except the rest of the universe would move in time faster and faster.",
"For someone on Earth, the man falling into the black hole would go slower until, on the event Horizon, he would stop and fade away redshifting"
] |
[
"\"Fade away redshifting\"?"
] |
[
"In western countries, life expectancy is around 80 years. I'm 25, so on average, I have 55 years to go. But in the past 50 years life expectancy has gone up 10 years. Assuming it will do so for the next 50 years as well, what is my life expectancy?"
] |
[
false
] | null |
[
"Cannot tell if this is a trick question or not? ",
"Your new life expectancy is 91... right?"
] |
[
"It's what I would guess. But I got a weird feeling that the math is trickier than that. I'm assuming that 80 is the age people die on average ",
". ",
"So mine would be 90, as you pointed out. But is it really? Or am I missing something?"
] |
[
"The math does get \"trickier\" but it also gets trivial.",
"In 50 years the life expectancy will be 90, you will be 75. In 15 years after that, life expectancy will be 93, you will be 90. In the 3 years after that, the life expectancy will be 93 + 3/5. Etc. Just a case of diminishing returns.",
"Also this is pure math, not relevant to the real world."
] |
[
"Could there theoretically be an infinite number of elements?"
] |
[
false
] |
Since an element is determined by the number of protons it has, could you theoretically just keep adding protons and forming new elements infinitely?
|
[
"I've answered this ",
"once before",
"The answer is no.",
"\"could you theoretically just keep adding protons and forming new elements infinitely?\"",
"No, not forever.",
"What causes a nucleus to continue existing is its stability. There are certain shapes such as the 4 nucleons of Helium that are particularly stable, and a C12 nucleus can be thought of as being similar to three He nuclei fused together.",
"With very large atoms such as U 238, their nucleus tends to be unstable. As you get to larger and larger artificial elements that you see being added to the bottom right of the periodic table, then you will find that they are very unstable and some half a half life of seconds or less. ",
"Making heavier and heavier atoms increases instability in an analogous way that piling building blocks to make a taller and taller tower would also increase instability.",
"There must be a limit, and yes there will be a point where it becomes impossible to make them.",
"If you want to know what the limit is, ",
"according to this paper",
" it is element number 154, and acccording to ",
"this paper",
" it as at element 155.",
"But of course, another point to consider is that in the same way that some buildings structures are more stable than others, certain nucleon structures would be more stable than others. Some elements in the current periodic table are radioactive while others are not, and this is due to the stability of the nuclei. All of the elements near the limit of 154 would be radioactive, but some would have longer half lives than others.",
"Hope this is helpful. :)",
"Edit: - I've just found another paper arguing that the limit is at ",
"element number 155",
" not 154. There may be debate within the scientific community as to where this limit is, but there is not debate that such a limit exists. The overall answer to the question 'Can elements go on forever?' is no. "
] |
[
"No, 155 is the largest possible.",
"But your basic point of some elements being more stable than others is correct. It has been theorised that there are so called '",
"islands of stability",
"' of element numbers where elements will be less unstable. There's a ",
"cool picture here"
] |
[
"Is it possible that there would be a gap making structures like 155, 156, 157 etc. impossible, but the structure for 1037 would be stable enough to exist, or is it a steady decrease in stability?",
"(Atomic numbers just an example, not sure if 1037 is significant)"
] |
[
"How deep into the ocean will the impacts of a hurricane be felt?"
] |
[
false
] |
I was watching the forecast of Florence and though about how deep a submarine would need to be to not be effected.
|
[
"Three times the effective wave height.",
"The magnitude of water movement underneath a wave tails of quite rapidly with depth. Once you are about three times the wave height (trough to crest) below the surface, the movement is barely noticeable.",
"\"Effective wave height\" is the average height of the biggest third of all waves. Once you're three times deeper than that, the effects are negligible.",
"Typical maximum wave heights in a hurricane are rarely exceed 15m, so once you're 50m deep, you're not going to get much effect.",
"This also means that hurricanes cause remarkably little damage in the ocean. It's only when they get into waters less than about 15m deep that the devastation happens.",
"As another puzzle, we have no idea how air-breathing marine life weathers a hurricane. How to dolphins survive? We simply din't know."
] |
[
"We're gonna need a rag-tag group of young marine biologists, a small fishing boat, and a Vice reporter."
] |
[
"Very interesting, thank you!"
] |
[
"Are light and other small wavelength electromagnetic waves simply caused by the drop in energy levels by an individual electron? If yes, how are ~2 km wavelength radio waves made?"
] |
[
false
] |
[deleted]
|
[
"Good answer. Just wanted to add that other wavelengths of light, even visible and x-rays, can be created by similar methods (accelerating electrons). This is how synchrotrons produce light for experimental research."
] |
[
"How are they ",
" made?",
"When humans make them, we do it by taking a big long metal wire and making the electrons jiggle back and forth. The change in the electric field only moves at the speed of light, so we make different wavelengths by jiggling the electrons faster for shorter wavelengths and slower for longer wavelengths.",
"They can be created in nature by any process that involves the movement of electric or manetic fields, but that's how we do it.",
"As for electron transitions, I'm not going to pretend I know more than anybody else here about quantum stuff. Sorry."
] |
[
"The simple answer is that it means that charged particles interact with photons. Photons are electromagnetic waves (oscillating electric and magnetic fields)."
] |
[
"How do we know pi is never-ending and non-repeating if we're still in the middle of calculating it?"
] |
[
false
] |
Note: Pointing out that we're not literally in the middle of calculating pi shows not your understanding of the concept of infinity, but your enthusiasm for pedantry.
|
[
"I've posted this ",
"earlier",
" to a similar question about why is pi irrational.",
"Why is pi irrational? Its not the easiest thing to prove but is has been done. A simpler proof is why sqrt(2) ~ 1.414 ... is irrational. First, you assume sqrt(2) rational. That means there is some fraction sqrt(2) = x/y where x and y are integers and share no common factors (that is the fraction x/y is fully reduced like 40/30 gets reduced to 4/3 cause they share the common factor 10). So if sqrt(2) = x/y and you square both sides of the equation you get, 2 = x",
" /y",
" or 2y",
" = x",
" That means that x must be an even number (remember y is an integer and 2y",
" is an even number if y is an integer). Hence you can rewrite x = 2z, where z is an integer. Then you have the equation 2y",
" = (2z)",
" or y",
" = 2z",
" By the same argument, we just used we know y must be an even number. Hence, we just showed that x and y are both even numbers. That means the fraction x/y isn't fully reduced, but that's what we assumed at the start. All rational numbers have some fully reduced fractional form; hence sqrt(2) is not a rational number.\nSimilar proofs have been done for pi.",
"Now, you may say well how do we know that an irrational number (one that can't be written as a fraction of integers) never ends. Well if it had an end (say it was just 3.14) then it would be possible to write it as a rational fraction (314/100). Similarly if it repeated decimal there are ways to write it as a rational ",
"fraction",
"."
] |
[
"This is correct. The answer is that pi is irrational, so it cannot be written as a ratio of integers, i.e. p/q for some integers p and q. If pi's decimal expansion terminated or repeated, then it would necessarily be a ratio of integers.",
"There is one minor thing I'd like to point out about your answer though, which is this statement:",
"Similar proofs have been done for pi.",
"This isn't true as far as I know. There are many proofs that pi is irrational (e.g. see ",
"here",
"), but they aren't similar to the proof that the square root of 2 is irrational. It is more complicated to show that pi is irrational."
] |
[
"This is why Physicists and Mathematicians never remain friends for long."
] |
[
"What causes sufferers of dyslexia to perceive words as jumbled up?"
] |
[
false
] | null |
[
"They don't see words \"jumbled up\". People with this kind of dyslexia can't supress the mechanism which normally alows us to see objects as the same regardless of their orientation. As the result, some letters look almost identical to each other, such as n vs u, m vs w or b/p/q/d. Specially designed fonts where the shapes of these letters are all clearly different usually solves the problem and allows them to read normally."
] |
[
"Do dyslexics exist in places where the alphabet has no such sets of congruent letters?"
] |
[
"However, there is something called ",
"visual stress",
", which isn't recognised as a disorder, but is being studied, where words can appear distorted and jumbled. "
] |
[
"If atoms are 99% 'empty space', how big would the universe be if we compressed every atom down to it's most space efficient arrangement, essentially leaving no space between particles?"
] |
[
false
] |
Or our observable universe, whatever is easy to speculate on... My thoughts were that perhaps the universe would become small enough to resemble what was present before the big bang, and the expansion between everything has just taken a very slow and long time (the rate at which our universe is expanding now?) and appears to have "exploded", hence the Big Bang...
|
[
"The \"atoms are 99% empty space\" thing is a big misconception. Particles do not have \"size\" as we typically think of it. An electron in an atom is a \"wave of probability\" and does not have a specific \"size\" or \"location\", these properties don't make much sense quantum mechanically. In fact ",
"these heat maps",
" are what the electrons look like in the atom. Most of that space is not empty. Each of those is a different \"orbital\", the energy and angular momentum of an electron determines the shape of the electron and that's what we refer to as \"orbits\". It's not that electrons are whirring around at different speeds, they just have different shapes around the nucleus.",
"What we can do is take electrons, shoot things at them and look at the scatter pattern. The things we shoot are also wave of probability, but based on the scatter pattern we can get a good idea of the sphere of influence of the electron. This gives us a notion of the \"size\" of the electron, though it's not good to think of electrons as hard spheres of stuff floating around since they're waves of probability in different configurations. ",
"If you want to compress things, though, you can look at ",
"Neutron Stars",
" this is a star that is so dense that atoms cannot exist. They're like a dense plasma of nucleons held together by gravity. This is similar to what happened near the beginning of the big bang, the particles were too energetic and compressed to form atoms. In fact is was too energetic for even protons and neutrons to form, and was basically a plasma of quarks and gluons. The ",
"wikipedia article has a good timeline",
". Like Neutron Stars, a kind of star that is like this has been conjectured called a ",
"Quark Star",
" that is supposed to look like the very beginning of the universe in it's core."
] |
[
"Quantum Mechanics never fails to blow my mind over and over again. Thanks for the reply."
] |
[
"So density is mass/volume or volume = mass/density. Our mass is 10",
" and our density is 8x10",
" if we divide 10",
" by neutron density, we get a volume of 1.25x10",
" m",
"Taking the cube root, we get a box with side length 500 million kilometers, or about 3 times the distance between the earth and the sun. "
] |
[
"Is noise a way to release energy?"
] |
[
false
] |
Let's take a car accident. When those two cars crash, the energy is released via crumpling the car, breaking headlights and being metal. Talking about energy, what part is lost by noise in a car crash? Does noise take up energy? I hope this is clear. And if it does take energy to make crashing noises, then is it possible to have crash crashes release the entire energy via noise?
|
[
"Noise (sound) is actually pressure waves and pressure waves are moving air. The air that is moving after the crash (the sound waves) was not moving before the crash so some of the energy was definitely spent on making the sound you hear. I can't imagine any way to direct all of that energy to moving only the air though. However, cars do tend to crumple/collapse in a very specific way. That is no accident (no pun intended). A lot of engineering goes into directing this sort of reaction to areas not occupied by passengers. I mention this only because I think this sort of deliberate distribution of energy is where you were going with this question, right?",
"Edit: words."
] |
[
"Yes, you're on point. I was wondering more along the lines of whether it's possible to have two objects collide with each other, but instead of damaging the two items, the sound created through the collision is enough to dispel the force. But that's very likely... impossible."
] |
[
"Well, if we imagine a car that is infinitely rigid and impervious to damage, most of the energy probably ",
" be dissipated as sound. But, I think you actually want the car to crumple, or at least \"spring\" a little (or, maybe, a lot) so that you, the passenger, gradually decelerate. If you're inside a car moving at 70 miles per hour and then stop instantly, it's going to be a very bad day."
] |
[
"Do we know the \"universal common ancestor\"?"
] |
[
false
] |
So we were learning about phylogeny trees and wanted to know if we traced waaaaay back, if we could find a common ancestor. My Bio prof said yes but he didnt know what it is or if it has been done.
|
[
"so have we pretty much ruled out that its possible life could have sprung up independently of one another in different parts of the Earth, and therefore two branches could not share a common ancestor at all? "
] |
[
"so have we pretty much ruled out that its possible life could have sprung up independently of one another in different parts of the Earth, and therefore two branches could not share a common ancestor at all? "
] |
[
"Not entirely correct. Viruses depend on cells (prokaryote & eukaryote) to replicate. So viruses are most likely younger than the first cell. Even in evolution 'simpler' isn't always 'older'.",
"Viruses could be escaped transposons, for instance."
] |
[
"Is there objective evidence for our mind's \"inner world\" of experiences?"
] |
[
false
] |
Aside from our own individual, personal, experiences, do we have any scientific evidence for the existence of conscious experience? I know we can tell if someone is conscious by looking at their brain with various tools, but do we have anything, other than anecdotal evidence, to suggest that such brain signals correspond to an inner, subjective experience? I feel sure there must be something as it's such a basic thing to know about, but can't think what.
|
[
"No, there is no way to infer or measure consciousness.",
"An EEG will show you electrical activity in the brain. An fMRI will show you blood flow in the brain. A PET will show you sugar metabolism.",
"In all of these modalities, there are ",
" of consciousness - patterns which are associated with consciousness. But we don't know if they actually ",
" consciousness. So we can't tell if somebody is conscious or not.",
"In fact, people under general anesthesia may be conscious. They don't remember anything, because anesthetics cause amnesia (they block NMDA receptors). Anesthesia may just be a lapse of memory, rather than a lapse of consciousness."
] |
[
"As well you should. We don't even have even good ",
" as to how brain circuitry creates conscious experience. ",
"For more, but from the philosophy of mind side of the story, look into the mind body problem, David Chalmers and the Hard Problem of consciousness, etc."
] |
[
"Thankyou very much for this reply. I find this gap in our knowledge and/or ability astounding."
] |
[
"What mutualistic organisms could I pair with a bonsai tree?"
] |
[
false
] |
I've just recently bought a bonsai tree and wondered if I could have some kinda fungus growing around it or even some insect of some sort. Such as moss.
|
[
"Micorrhiza Fungi is great for bonsai trees. HOWEVER: spores are species specific, your bonsai will probably 'find' its species specific fungus on its own. You're better off ensuring the soil is good, and adding trace elements to it. \n",
"http://bonsaistudygroup.com/general-discussion/myconox-mycorrhizal-fungi/",
"\n",
"http://torontobonsai.org/Archives/horticulture/mycorrhizae.htm",
"EDIT: Mycophilia by Eugenia Bone is a brilliant read. Fungi are more crucial than you could possibly imagine. \n",
"http://www.amazon.com/gp/product/1605294071?ie=UTF8&force-full-site=1&ref_=aw_bottom_links"
] |
[
"Don't know why the down vote.... ",
" regularly appears in flowerpots, and small mushrooms growing with a bonsai tree look very artistic.",
"http://www.mushroomexpert.com/leucocoprinus_birnbaumii.html"
] |
[
"Don't know why the down vote.... ",
" regularly appears in flowerpots, and small mushrooms growing with a bonsai tree look very artistic.",
"http://www.mushroomexpert.com/leucocoprinus_birnbaumii.html"
] |
[
"Will a heavier object absorb more momentum than a light one? Or is there no difference at all?"
] |
[
false
] |
[deleted]
|
[
"no. both energy and momentum must be conserved. if you take the equations for those and apply them to a 2 body system, you can show a proof of the variable transfer of energy mathematically ",
"here",
"to summarize, a small object hits a big object, it gets bounced away, keeping some of its initial energy.",
"an object hits an object of the same mass, it will stop, imparting all of its energy.",
"a large object hits a small object, it will continue to move forward after the hit, keeping some of its initial energy"
] |
[
"thanks a lot!",
"Then what I need to know is just how much of that kinetic energy that is transfered, and what factors that determines it.",
"EDIT: Very nice explanation, it's just as I hypothesized. :)"
] |
[
"thanks a lot!",
"Then what I need to know is just how much of that kinetic energy that is transfered, and what factors that determines it.",
"EDIT: Very nice explanation, it's just as I hypothesized. :)"
] |
[
"Is it true you should put both feet together and hop away from a downed power line?"
] |
[
false
] |
I was once told that if a power line falls down near you, you should put your feet together and hop away, rather than walking. Something about how the way the power spreads out as it goes into the ground, if you walked, there would be enough voltage difference between your back foot and your front foot to electrocute you. Is this true or BS? Anyone care to estimate what kind of voltage differential there could be between your feet in that situation?
|
[
"To electrocute you a current would need to flow through your body. If the voltage difference is between your feet the current would need to flow up one leg and down the other, but if there is \"electricity\" in the ground already why would it bother to flow through you in the first place? If the ground is already saturated with current you are effectively infinitely resistive by comparison. Moreover the current has already earthed, there is no need for it to pass through you to reach a point of lower potential, it can only face a higher potential in passing up your leg.",
"Sometimes its better to reason qualitatively before we start calculating.",
"So hopping is probably not necessary and if you are worried, just wear, you know, shoes...."
] |
[
"Electricity always follows the shortest path",
"No, it follows the path of least resistance.",
"Well, technically, the current flowing through each path is dependent on each path's resistance - a lower resistance path with have a proportionally higher current flowing through that path."
] |
[
"The reason is to prevent current from going higher up into your body. Electricity always follows the shortest path (ok, it is actually more complicated than that, but as a simplification...). If it has the option to travel up one foot, through your ankles, into the other foot, and back down, it will do that rather than travel up through your legs abdomen. This is a very good thing, because electricity will do more damage to your internal organs (located in your abdomen) than it will to your lower legs and feet. That being said, it is still better to avoid downed power lines. ",
"The voltage difference across your feet would not really be affected by this, just the path the current travels."
] |
[
"Is Adenovirus \"escape\" from the lysosome into the cytosol species specific?"
] |
[
false
] |
[deleted]
|
[
"Apparently I didn't do a good job explaining the hypothetical scenario, both people who responded misunderstood what I meant lol"
] |
[
"Apparently I didn't do a good job explaining the hypothetical scenario, both people who responded misunderstood what I meant lol"
] |
[
"Here's a better scenario. If you enclosed adenovirus into an artificial membrane vesicle that you produced in a lab, then acidified the vesicle, would it fuse to the vesicle membrane and release its naked DNA into the outside solution?"
] |
[
"If there are 11 dimensions, is the magnitude of the \"eleven-velocity\" still c?"
] |
[
false
] |
As I understand it, the magnitude of the spacetime four-velocity is constant, c. If there are additional dimensions, do they extend the concept of four-velocity, and is the magnitude of the resulting "n-velocity" still c? If so, if an observer were to have a large velocity in one of the higher dimensions, could he or she experience time-dilation while still remaining stationary in regular space?
|
[
"Yes, it's exactly the same (with the same value of c) but the Lorentz indices go from 0 to 10 instead of 0 to 3. And yes, I believe it would mean that. The problem is you can't just accelerate in the transverse dimensions because of momentum conservation. Moreover, because the extra dimensions must be compactified, the momentum in the extra dimensions must be quantised (it's like a quantum particle in a box), which means the smallest amount of non-zero transverse momentum you can have may have to be really really big."
] |
[
"is it possible (but unlikely) that we're all traveling at a non-zero velocity around one of the compact dimensions?",
"To answer this question, you need to specify an additional piece of information: relative to ",
"? There are no absolute velocities, so any non-zero velocity must be in reference to some other object (real or imagined).",
"To be clear, in some reference frames you'll have zero velocity and in another reference frame you'll have non-zero velocity, and both reference frames are correct in their description of whether you are moving or not.",
"Also, just because momentum is quantized doesn't mean you ",
" be moving, nor does it mean that your actual momentum ",
" take on a multiple of a specific value. It means that ",
" in momentum must be in a multiple of a specific value.",
"It actually resembles the phenomenon of spin. Spin is quantized in multiples of Planck units (h-bar), but you still have particles which are spin-1/2, spin-3/2, etc. This is allowed because spin only needs to ",
" by whole units, but it could (in principle) take any value unless it's restricted for some other reason (which spin actually is, though momentum is not). So a particle with spin +1/2 can only change to -1/2, it can never have a spin of 0. But, a particle with spin +1 could, though it could never take on a half-integer value.",
"Likewise with momentum -- you can describe the system in any reference frame, and thus give yourself any velocity you want. But if momentum is quantized, then you must ",
" your velocity only in specific increments.",
"If so, what would the consequences be if one could stop (barring the quantization problem)?",
"There would be none, since you are ",
" at rest in your own reference frame, and nothing special happens.",
"Hope that helps!"
] |
[
"Thanks! I hadn't considered the momentum being quantized due to the compactness of the extra dimensions.",
"Along these lines, is it possible (but unlikely) that we're all traveling at a non-zero velocity around one of the compact dimensions? If so, what would the consequences be if one could stop (barring the quantization problem)? "
] |
[
"If you entangle 2 particles, then put one in a black hole, then look at the other one : information coming out of a black hole?"
] |
[
false
] | null |
[
"The general understanding of entanglement has nothing at all to do with particles \"communicating\" information between them",
". In the interpretations of quantum mechanics where they ",
" communicate, it's faster than light communication anyway, so there's no real reason to believe a black hole would hinder that.",
"Edit, for more detail: Suppose a spin-zero decays into two spin-1/2 particles. You know, by conservation of momentum, that the daughter particles have equal and opposite momenta. But you don't know which is which. Now if you send me a daughter particle and keep one for yourself, how do we \"talk\" using them? What we do is that you can rotate your particle along x or y or flip it or do nothing to it. Then you measure yours and tell me, after you rotate it, whether you measured spin \"up\" or \"down\". You tell me what your measurement is, and I measure my particle, and through some maths and physics, I can tell how you rotated your particle, if you did.",
"The \"message\" I receive is, in fact, your rotation. That's how you encode your \"bit.\" (in this case you actually can encode 2 bits of info total). But it still requires you to message me what your measurement was in order for my measurement to mean anything.",
"Now, if you fell into a black hole... how am I going to receive your message about what your measurement is/was? It doesn't matter how you rotate the particle, you can never tell me what you measure it to be. So therefore, the \"messaging\" capacity of entanglement is destroyed."
] |
[
"I have two marbles; one red and one blue, and I tell you their colors.",
"I give you a red marble but I never actually show you the blue one. But, from the information that you derive from the red marble, you can make reasonable assumptions about the other one. For instance, if the one you have in your hand is red, then the other must be blue.",
"If I go into another room and smash my blue marble, then you wouldn't know it unless you saw it for yourself. Quantum entanglement isn't transmission of information, it's derivation of information based on what you already know. What happens to my blue marble doesn't matter, all you know is that it can never be a red marble."
] |
[
"the results of my measurement. You need to know if I measure \"spin up\" or \"spin down\" for example. If we both agree ahead of time what we're measuring, then we send no information at all.",
"Let's be more specific. I prepare two entangled spin 1/2 particles. We both agree on what our x,y,z axes are, and we agree that our measurement will be whether the spin is aligned positive z or negative z. ",
"But I am free to rotate my particle before I measure it. I can rotate it to x or y or flip it or do nothing. Then I make my measurement along z and tell you the result, say \"spin up\". You measure your particle along z and, combined with \"spin up\", you know whether I rotated or flipped it or did nothing. And that's my message to you. We agree ahead of time maybe that doing nothing is '00', flip is '01', x is '10' and y is '11.' You get 2 bits of information out of the overall experiment. We repeat it over and over again, and we can send bank account information really securely."
] |
[
"Is it possible to accurately predict the magnitude of an earthquake by measuring the waves in backyard pools?"
] |
[
false
] | null |
[
"In Medieval times, especially in Asia, pots of water were buried near walls and checked for ripples, not for earthquakes, but to detect if someone was trying to tunnel under the wall. They could even triangulate where the tunneler was using 2 or more pots.",
"What you're asking is possible, but not feasible. You'd need multiple pools, they'd have to be in quiet areas (no trucks rumbling by) and they'd likely have to be indoors to prevent interference from the wind. Using 2 pools and recording cameras you could triangulate the epicenter. If the pools were identical in diameter and volume it would make calculations about the magnitude easier."
] |
[
"What about from multiple pools around the affected area?"
] |
[
"I mean, maybe with a lot of effort? At the simplest level, if you replace pools with ",
"seismometers",
", this is basically what we do to locate and measure the magnitude of earthquakes in the first place. For the use of pools, to get in the right ball park, you would need to know a variety of things. You would definitely need a network of pools to pool (pun intended) the observations and correct for distance from the epicenter. For all the pools, you would need to know details of their dimensions, i.e. the period of the standing waves (seiches) that develop because of shaking are controlled by the ",
"dimensions of the water body as this sets the resonance of the water body",
". You would then need some sort of set of calibration experiments for each type of pool, i.e. for this level of surface shaking as measured by something like ",
"peak ground acceleration",
" how does the pool react or the relation between ",
"surface waves",
" and the waves that develop in each type of pool. Then you would need to know about the ",
"seismic site effects",
" of each area housing each pool and how this would be expected to influence surface shaking. From there, if you have well calibrated pools, knowledge of the site effects, and a way to record both the details of the waves in the pools along with the timing of the waves, with a sufficiently broad network of pools you could try to work out the location and magnitude of an earthquake. Since at this point you're basically using a pool as a (pretty poor) substitute for a seismometer, you'd probably be served with an affordable consumer grade seismometer like a ",
"raspberry shake",
"."
] |
[
"Is there currently a widely accepted theory in Biology that describes how prokaryotic cells became eukaryotic cells?"
] |
[
false
] |
Bacteria seem to be able to adapt to their environments so well that that there doesn't seem to be any adaptive advantage to complexity, and there doesn't appear to be much in the way of proto-eukaryotic intermediaries that you would expect if natural selection were at work. So what gives? Is there an established theory in biology that explains this?
|
[
"Yes - it is called the ",
"Endosymbiotic theory",
". Essentially the belief is that a prokaryotic cell engulfed another prokaryotic cell (Theories differ exactly on what these cells were but I believe generally the cell that was engulfed was particularly good at energy production) and that this turned into a symbiotic relationship.Thus the organelle was born.Significant evidence supports this in modern eukaryotes - most notably the presence of double membranes on some organelles (presumed to be residual from the orginally engulfed prokaryote) and the presence of organelle genomes e.g. mtDNA or mitochondrial DNA."
] |
[
"Piggybacking this. One of the main reasons this is well-accepted is that a cell's mitochondria has completely separate different DNA than the cell's nucleus. In human sexual reproduction, DNA is taking from nuclei of both parents and not the mitochondria. As a result, you actually have the same mitochondrial DNA as your biological mother. And yes, some diseases are only passed through mitochondrial DNA, which can be confusing for young students learning about punnett squares and trying to derive genotypes off of phenotypes. "
] |
[
"Prokaryote is a general term that describes any organism without a nucleus (or other membrane-bound organelles), so whether or not it was identical with any living prokaryote, there must have been a prokaryote (or two) that gave rise to all eukaryotes by endosymbiosis with mitochondria and/or the development of a nuclear membrane. Whether the endosymbiotic event (as opposed to the horizontal gene transfer that follows it much later) should even be considered \"evolutionary\" in our modern genetic sense is another question."
] |
[
"Do babies that are born via C-section have a lower immune system versus babies that are born vaginally?"
] |
[
false
] |
From what I understand is babies born vaginally have bacterial flora introduced into their system when travelling down the vaginal canal. Because babies born via C-section are not exposed to this bacteria does it mean that they start out with an immune system that is not as strong? If so are there treatments that babies undergo to give them a boost?
|
[
"Yes.",
"C-section increaes the risk of developing type 1 diabetes by 20%.",
"It also increases the risk of asthma by the same amount.",
"It is possible (although unproven) that this is due to the lack of exposure to maternal commensal bacteria. The above studies are meta-analyses so are relatively more trustworthy, but there are individual studies which suggest that ",
"babies born by CS have a disturbed microflora in the beginning of life compared to vaginally delivered babies.",
"The role of our commensal flora is a fairly recent and rapidly growing field which we still have a lot to learn about. "
] |
[
"I'm not sure what point you think I was making? I don't know what the mechanism is, but I don't see how it's a stretch to consider it possible that diabetes has a link to microbiotic exposure at birth. The researchers in the diabetes meta-analysis mentioned that their results couldn't be explained by known confounders. "
] |
[
"There is some ",
" data",
" on this practice, colloquially known as \"seeding\". I would not recommend it without much more evidence, the potential for contamination from things like faecal matter and normal vaginal infections would be a huge risk factor in this sort of thing. "
] |
[
"Brazilian president suggested that someone should start working on a way to storage the wind, as we do to the water, for later use to generate energy. It's possible ?"
] |
[
false
] | null |
[
"It's possible. There is a utility down south that put aircompressors on their towers and corked a cave to store the compressed air. Then they added an airturbine to the front of one of their steam turbines and use the compressed air to drive the generator when there is enough wind. When there isn't they use the boiler to run the steam turbine. Pretty slick. We could do the same thing with depleted oil and gas domes most places."
] |
[
"You can also use the energy generated to pump water to an uphill reservoir and then use it later to turn a turbine, or spin up a large low-friction flywheel. Hydrogen and normal batteries also work."
] |
[
"It's called ",
"compressed air energy storage",
" and it is awesome.",
"Even when not dealing with somewhat unpredictable sources such as wind or solar, there's this problem where it takes several minutes to turn on a big natural gas turbine to keep up with everyone deciding to turn on the lights at once. Having a megawatt-range and nearly instant-on source makes life easier for a utility.",
"The downside is that it is optimistically about 70% efficient so you don't get back all the power you put in. On the other hand it is many times cheaper than warehouses full of batteries, which aren't perfectly efficient either."
] |
[
"Is there any wind on the moon?, even a negligible amount"
] |
[
false
] |
So, The moon has an atmosphere nothing like the one on earth obviously, but a thin layer of gases that are “attached” to the moon through gravity barring any space weather, impacts and the like. My question is with the extreme temperature changes between the light and dark side of the moon would it not generate wind? I’m not talking about let’s build a windmill wind more something detectable with modern instruments, even theoretically. Or is the density/pressure just too low for the effect to take place?
|
[
"The “atmosphere” of the moon is a surface boundary exosphere. This means molecules are ejected from the surface (by various processes), fly on a ballistic arc, then hit the surface again with almost no chance of encountering another molecule on the way.",
"Without interaction between molecules, the atmosphere does not behave as a fluid and cannot form winds.",
"Any object with enough gravity that ejected molecules have a decent chance of falling back, but no denser atmosphere, will form a surface boundary exosphere."
] |
[
"I don’t believe there is a high enough density of molecules in the “air” on the moon to produce the same thing we call wind on earth. Sure, they’re going to move around a bit, but they’re unlikely to collide with each other often enough to create a detectable trend of common movement, aka wind."
] |
[
"Thanks, I thought this might be case. But just could rule out a small boundary layer that moves very very slightly. We'll explained my good man"
] |
[
"Question about an imgur photo of a torn pectoral."
] |
[
false
] |
Some of you may have seen image of a torn pectoral on imgur. What is the reason for the regular patterning of the bruise?
|
[
"To me it looked like he had bandages on it while the bruise formed. I can't answer your question, but when I had seriously major bruising you could see lines from my bandages, ice packs, tape and clothing. I guess I should add that you could only see those imprints in the very shallow bruising; all deep bruises pretty much came no matter what"
] |
[
"This.",
"The recommended treatment for muscle tears is ",
"ice and light compression",
" to minimize swelling (bleeding into the muscle and surrounding tissue. ",
"Taping perpendicular to the grain",
" is also recommended."
] |
[
"This is not a full answer to your question, but it might be worth noticing that the pectoralis major is not a continuous, flat muscle, rather it connects in bands, as can be seen in these photos:",
"anatomy - edit: look at mc2222's link, mine didn't work apparently",
"body builder"
] |
[
"What are itches, and why do they occur?"
] |
[
false
] |
My arm itches... but why?
|
[
"Some foreign body (an antigen) is activating cells on your skin (IgE antibodies probably) to cause your mast cells to degranulate releasing histamine, causing inflammation and release of bradykinins which cause pain and itching"
] |
[
"Are there not other causes? I've heard of menopausal women having the feeling of bugs crawling on there skin. ",
"I personally have chronic exzema, and I wonder, other then the raw irritated skin, why I itch. I know part of it has to do with antihistamines, but there has to be more to it."
] |
[
"I am not sure about menopausal women and the cause. However, I know that methamphetamine addicts itch their skin to a bleeding rubble because it 'itches.' This is due to the deposition of crystal pyproducts (and other chemicals) of meth into the dermal layers and sweat gland pores - which many people say is because they hallucinate that bugs are crawling in their skin. Which may be true, but they probably initiate the hallucination because of the deposition of crystal byproducts. The skin develops the characteristics scabs or lesions from the itching, but also the increased vasoconstriction and hypoxia in the body. ",
"Source",
"SOURCE"
] |
[
"How random are genetic mutations?"
] |
[
false
] |
I know that when an offspring appears (for let's say ... a mammal species), it's genes are a random combination of it's parent's genes. Q1: Do we know what determines which genes will be active or inactive? Q2: Is the process following a limited set of rules? Q3: What factors influence the process?
|
[
"I wouldn't say mutations are 100% random. There are certainly several specific defined mechanisms for mutations that will have a bias for certain sequences or locations or mutation type. For instance, damage from UV radiation occurs when you have adjacent thymine bases, spontaneous mutations have a couple of common mechanisms like deamination or depurination that are more likely to happen to specific bases, and certain regions are more likely to be mutated, such as regions with repetitive sequences that are more likely to cause insertions, duplications, and deletions because of misalignment during recombination, as well as genes that are on or near transposable elements. Certain regions in DNA are recombination or mutation hotspots where there is a much higher rate of mutations occurring at those locations.",
"Some mutation processes are guided and intentional, such as somatic hypermutation in your immune cells that affect the variable regions of immunoglobulin (antibody) genes, allowing for a a large amount of diversity in antibodies.",
"One example I know of of a non-random mutation is a highly prevalent chromosomal mutation (a translocation) that is found in a type of cancer called CML, where the translocation mutation creates a new fusion gene that subsequently causes leukemia. Here's the ",
"wiki page on it for anyone curious",
"."
] |
[
"I talked about actual genetic mutations in my reply to another comment, but I figured I'd try to address your specific questions.",
"1) We have some idea, but the process is incredibly complicated. There are a ton of regulatory processes that control gene expression (whether or not genes are active) ranging from things like the presence of specific transcription factors which are proteins that bind to regulatory elements in genes and promote or inhibit their expression, to epigenetic factors that alter the way the DNA itself is packed into the cell by modifying chromatin structure, where in a gross oversimplification it can be thought as if genes that are not very active are more likely to become tightly packed in dense regions where they are not easily accessed by transcription factors and enzymes, and active genes are found in more open regions of DNA with greater access to such factors. The study of gene expression by itself constitutes an enormous field that fills numerous entire courses, and there is tons of information out there if you are curious.",
"2) There are a variety of mechanisms we have identified that underlie certain mutation processes, so while I wouldn't exactly call these \"rules,\" it's not like all mutations are just something that happens and we don't understand what affects it.",
"3) I talked about some of the factors in my other post, but I'm sure if you looked on the ",
"wiki page",
" you'd find a better summary."
] |
[
"Unfortunately not true for translocations and rearrangements. They're highly biased and we're just beginning to learn why."
] |
[
"Spending even a short amount of time in complete silence of the Anechoic Chamber at Orefield Labs causes people to experience a good deal of emotional discomfort. Why don't deaf people experience this same discomfort?"
] |
[
false
] | null |
[
"According to this article:",
"http://www.dailymail.co.uk/sciencetech/article-2124581/The-worlds-quietest-place-chamber-Orfield-Laboratories.html",
"It's not so much the silence that makes people uncomfortable, but that when you're in such a quiet room your ears begin to adapt to the silence and start becoming very sensitive, allowing you to hear noises you are unlikely to be accustomed to. These noises include the sound of your heartbeat, the subtle noises your lungs and stomach make, and even the sound your throat makes every time you kind of swallow your own saliva, you begin to hear that and only that in complete isolation and detail. You can even apparently begin to hear the pulsing of blood through your veins. Listening to that for 20-40 minutes likely makes you very self conscious and an overall unpleasant experience.",
"Here is another except on the phenomenon:",
"http://books.google.ca/books?id=5aY1nrVTAZIC&pg=PA18&lpg=PA18&dq=Anechoic+chamber+discomfort&source=bl&ots=LGTBWRBtsf&sig=r7gmOF4aXz5vcKb0IIq87giTyCI&hl=en&sa=X&ei=gFCUUYu1OMXprAGVvYGQBQ&ved=0CDYQ6AEwAg#v=onepage&q=Anechoic%20chamber%20discomfort&f=false"
] |
[
"Hi! I can answer this, as I have one at my place of work and used one extensively at university. ",
"Many people don't like the sensation because the lack of near and far field reflections almost tricks your brain into thinking everything is in close proximity. ",
"Being in an anechoic room with another person is quite strange, as the lack of reinforcement of their voice by reflections causes them to \"appear\" quieter when in fact the level of direct sound is very similar to a free field (out door) environment! ",
"Source: I'm an acoustic engineer. "
] |
[
"Can anyone explain why this is such an unnerving and unpleasant experience in practice? I read this description and I think it would be incredible to hear my body working with that level of acuity."
] |
[
"A doctor told me once you attempt suicide, the same meds (SSRIs/SNRIs) don't work as effectively - why?"
] |
[
false
] |
As far as I understand it, SNRIs and SSRIs just tell the brain the produce more serotonin, or rather, they delay the nerve that says "Hey, stop making serotonin!". Obviously in the case of SNRIs that's also norepinephrine. So, why would the brain react differently post-suicide attempt? Even if the neural pathways change, it should still be the same nerve that controls serotonin, right? TO CLARIFY: I am not asking what happens with the drug if you tried to kill yourself by overdosing on an SSRI, but by other means. The doctor I was speaking to mentioned that after every suicide attempt, the efficiency of the same dosage of an anti-depressant is no longer as effective, and often medicines have to be switched.
|
[
"What exactly did the doctor say?",
"My guess is he meant to say that a suicide attempt is a sign they aren't working effectively, or is a side effect that would be contraindicative.",
"Also, if this is about ",
" treatment, please consult a professional, and not the internet, for your medical advice."
] |
[
"Edit: There was some confusion about what OP was actually asking, and my original answer (which I've left below) was answering the question as though OP was asking if an overdose on SSRI/SNRI would have an effect on the medication. As for the actual question ",
"that after every suicide attempt, the efficiency of the same dosage of an anti-depressant is no longer as effective, and often medicines have to be switched.",
"There is no truth to that.",
"Original Answer:There is actually some truth to this. As your brain gets used to the changes in neurochemistry produced by the medications, it actually starts to change it's functioning by increasing or decreasing the quantity and function of some of the receptors in your brain; we call this up-regulation or down-regulation. When taken in high supratherapeutic doses, some medications can cause drastic up/down-regulation that can then alter the way in which that medication would work. Typically this is not permanent, however there is research being done to better understand what happens with supratherapeutic doses, with some research suggesting that it could cause permanent changes in the up/downregulation, however at this point it is still believed to be rather temporary. With SNRI's/SSRI's the effect is pretty minimal, but in the first several days/weeks after an overdose I would agree that the medication's efficacy could be diminished. "
] |
[
"It's not a nerve but an enzyme. Anyway, yes, they should work the same. I have not heard anything like that before, and I have used SSRIs."
] |
[
"A question about black holes, and I promise I'm not high."
] |
[
false
] |
I realize that this will probably sound like wallbanger moon logic, but here goes anyway: As I understand it, the distance from the event horizon to the center of a black hole is greater than the diameter of the event horizon itself, and this distortion is created by the superdensity of the matter of whatever initially created the black hole. The actual matter of a black hole exists in a kind of spatial asymptote. My question is this: Would it be possible for a chunk of matter to have sufficient density to hide itself in a spatial distortion crossing over the threshold into planet-eating singularity territory? In other words, could an object's density create a spatial bubble exactly equal to the physical volume of the hypothetical object without creating the discontinuity of an asymptote? I fully accept that the only dense thing here might be me, and that the very nature of this question might well belie a vast and embarrassing misunderstanding of singularities, gravity, or even basic arithmetic. I promise that the reasoning underlying the question was not induced by recreational chemicals. In my defense, questions about black holes and spatial distortions will, by their very nature, tend to sound drug-induced.
|
[
"Its ok...we all want a ...Tardis..."
] |
[
"General Relativity has at its heart the \"Einstein Field Equations\". Essentially: the curvature of space-time is equal to the stress energy tensor; curvature equals stuff making curvature. Now usually, we start with the stress-energy tensor, maybe throw in the information about a star, and see what curvature results. ",
" it's an equation, so, in principle, we should be able to start on the other side of the equation, the curvature, and figure out what configuration of stress-energy we'll need to make that curvature.",
"Well we've tried this previously with things like wormholes or warp drives, and the necessary stress-energy tensor doesn't obey the laws of physics. So, eyeballing the rough properties of what you'd need to make this happen, particularly something that curves space negatively, we run into the same problems with negatively curved requirements of wormholes and warp drives."
] |
[
"Are you asking if it's possible for an object to be (at least marginally) bigger on the inside?"
] |
[
"Is it possible that not only space is expanding, but time as well?"
] |
[
false
] |
Could you provide reasons or sources, if you think just space is expanding and time is unable to? Related questions:
|
[
"Similar questions have come up previously. ",
"Here is a link to one such post",
" and ",
"here is a link to one of my several responses",
". I offer a response that shows you some of the math behind the question, and the top response by ",
"/u/adamsolomon",
" offers a less mathy explanation. Take your pick, depending on your background.",
"The ultimate gist is the same: coordinates (or how we measure time and space) are rather arbitrary. In my response, I discuss at least three different ways of defining time and space in cosmology.",
"The standard \"co-moving\" coordinate system in which time just marches on as normal and only the spatial universe expands.",
"A \"conformal\" coordinate system in which both time and space are expanding, and at the same rate.",
"A \"proper\" coordinate system which captures a more intuitive notion of how to measure distances, but which mixes time and space together in a rather odd way. Neither is really expanding, and there is both a frame dragging effect and a horizon.",
"Whether you understand all of the math is irrelevant, as long as you know this:",
"General Relativity allows us to pick whatever coordinates we want, it is a sort of freedom we have called general covariance.",
"Because the coordinates themselves don't necessarily have any physical meaning, we ",
" say unambiguously that space expands but time does not (or anything similar). The question \"does time expand as well?\" is ultimately a meaningless question."
] |
[
" here I was going to give a reply, and you go ahead and just link to me making the same reply someplace else! :P"
] |
[
"Proper coordinates consists of proper spatial coordinates to measure distance and so-called cosmological time to measure time. The proper distance between two galaxies at a given time is the distance measured between those galaxies using rulers ",
" and you always use the same rulers. So as space expands, you need more and more rulers to measure the distance between the same two galaxies. The definition of cosmological time is a bit technical, but, in short, it's the time on the clock of so-called ",
", a special class of observers that see the CMB as isotropic.",
"If you read any pop-sci article on universal expansion or cosmology, the author is almost certainly describing the universe in proper coordinates. When we talk about space expanding, we mean exactly that the proper distance between galaxies is increasing over time."
] |
[
"Is it possible that life could exist in currently inhabitable places in space? (details inside)"
] |
[
false
] |
Scientists make predictions on the probability of life relative to what homo sapiens and other animals that survive on Earth need to survive. Is it possible that other life, if present, could survive using different techniques such as using elements that are abundantly available to them instead of oxygen to respire and provide energy to themselves (if they require it)? Would something be able to adapt to their surroundings if it were extremely dark and cold and instead of oxygen, use something that was more abundant in their position in the universe?
|
[
"Yes this is completely possible. NASA has considered Arsenic-based life. ",
"Also search \"Extremophiles\" on Google."
] |
[
"There are lots of examples of bacteria and archeae that have extremely diverse ways of gaining energy.",
"There are examples of bacteria that don't need oxygen or light for energy gain. Some bacteria such as ",
"Acidothiobacillus",
" gain their energy from redox reactions using metal ores in rocks. There are thermal vents under the sea which also provide sulphur compounds which bacteria can use for energy. These fuel an entire ",
"ecosystem",
". ",
"As for cold adaptations there are ",
"extreme psychrophiles",
" that can grow at -12 degrees celcius.",
"There are also microbes that can live extremes of nearly any environment such as ",
"acidophiles",
", ",
"alkaliphiles",
" and ",
"halophiles",
". Then you get something like ",
"this",
" which live just about anywhere. A lecturer once told us it can happily grow at 100,000 times the radiation dose that kills humans. If you look around there are pretty much bacteria everywhere which is why they NASA are looking for signs of them in space.",
"The only problem with regards to oxygen is that although some bacteria are poisoned by oxygen gas, oxygen is present in every known life form in compounds such as amino acids and nucelotides so if oxygen was not present somewhere the life there could not be based on the same structures as ours.",
"There is an extraordinary range of life in seemingly uninhabitable places on Earth so it does seem completely plausible to have life in space somewhere based on what we know already. It could also just develope in an entirely different way to life on Earth that we might not even recognise."
] |
[
"First problem, \"life\" and \"consciousness\" are currently not defined. We don't understand what consciousness is, and we haven't yet agreed on what is alive and what is not alive. ",
"A computer program can pass tests used to define 'life' and can pass self-awareness tests of Artificial Natural Intelligence research, but what does that mean?",
"Scientists make predictions on the probability of life relative to what homo sapiens and other animals that survive on Earth need to survive.",
"Correct, because we know about them and are able to study them (and have agreed they are alive, whatever \"life\" means).",
"Is it possible that other life, if present, could survive using different techniques such as using elements that are abundantly available to them instead of oxygen",
"Yes, we can't rule out the possibility. However, it is hard to study them because we don't know what to look for. Silicon is a popular substitute for carbon in sci-fi as it has similar atomic bonding options.",
"When looking for life in space, it makes more sense to look at Earth-like stuff rather than stare at a bunch of rocks and wonder if it is alive. Or conscious.",
"Whatever life and consciousness are."
] |
[
"Why do the electrons in the double-slit experiment behave differently when observed?"
] |
[
false
] |
Doesn't seem to make sense but there has to be a reason for everything. For those who don't know these may give more information: Electron is observed: No wave pattern Electron isn't observed: Creates wave pattern By the way what is the definition of a particle and a wave?
|
[
"figure that out and the next Nobel Prize is yours"
] |
[
"This also leads to my friend's favourite quantum algorithm: to factorize N, pick some random numbers. If numbers are correct, return the result. Otherwise, destroy the universe"
] |
[
"Observation is not important. Interacting with any other particle is what prevents interference patterns. Loosely speaking, if the photon can go along the left slit and hit the back plate or go via the right slit and hit the back plate in the same place ",
" then we get interference patterns. If the photon tweaks any particle along the way then no more interference pattern. And of course you can't \"observe\" which slit it goes through without some sensitive thing that changes its state if the particle goes through a particular slit. Here's more detail ",
"http://lesswrong.com/lw/r5/the_quantum_physics_sequence/"
] |
[
"Physiologically speaking, how do animals like the arctic fox and arctic hare change their fur color?"
] |
[
false
] |
It is well known that some mammals change their fur color over the course of a year due to seasonal variation. What is the physiological mechanism that allows them to do so? Is it light dependent? Temperature dependent? Edit: Added more specificity to the question.
|
[
"Hi and thanks,",
"I am actually referring to how they adjust their camouflage scheme and fur colors relative to seasonal variation. That is, how is it that an arctic fox can produce white fur during the winter when there is snow on the ground and produce brown/tan fur during the summer?"
] |
[
"Hi and thanks,",
"I am actually referring to how they adjust their camouflage scheme and fur colors relative to seasonal variation. That is, how is it that an arctic fox can produce white fur during the winter when there is snow on the ground and produce brown/tan fur during the summer?"
] |
[
"Ammount of daylight dependent.",
"Many mammals change the outer layer of fur seasonaly. Mostly to adapt thermally and sometimes, like you point out, to change the camo. You can see that even cats are more fluffy during winter. ",
"In most cases this is due to hormonal change triggered by the pineal gland based on the ammount of daylight. Similarly the pineal gland is responsible for other seasonal effects like mating, hybernation. The gland itself is a very old part and the complete function is not well known but it mostly has to do with 24-hour and seasonal cycles.",
"I think in some cases, it might be a little temperature dependent, but I can't find any source for that and I am not sure, maybe someone knows."
] |
[
"Why do neutrons tend to interact more readily with light nuclei rather than heavy ones (i.e., why is water a better neutron shield than lead)?"
] |
[
false
] | null |
[
"It's not because they necessarily \"interact more readily\", it's just that the kinematics is more favorable when they do interact.",
"If you want to slow something down, you want to take as much kinetic energy away from it as possible with each collision, and simple kinematics shows that the optimal way to do that is for the neutron to collide with a nucleus of roughly the same mass, so ideally a proton.",
"That's why hydrogen, and hydrogen-containing compounds are very good neutron moderators. The lighter the nucleus the better."
] |
[
"Surprisingly, water is 14x denser than liquid hydrogen. The bonding angle of the H-O-H makes the O slightly positive and the H slightly negative which then tends to attract another H from the other H-O-H and holds it closer (surface tension). Even at cryogenic level water will have more H than liquid H."
] |
[
"Liquid hydrogen is awkward to work with and water has a higher density of hydrogen atoms."
] |
[
"How do governments tell the difference between nuclear launches and peaceful space missions?"
] |
[
false
] |
This has two parts: 1) Governments monitor the launch of nuclear missiles. But there are rockets being shot into space all the time. How do they know that those rockets aren't carrying nuclear weapons. 2) Satellites are shot into space regularly. How do we know that they aren't hiding nuclear weapons?
|
[
"A computer glitch back in the 80s ",
"nearly started World War III",
", which was only prevented when a Soviet officer remembered exactly this. A Russian early warning system reported an American missile launch. The official policy was that any such warning had to be immediately reported up the chain of command, presumably ending with a retaliatory Russian missile launch. But the Russian officer, ",
"Stanislav Petrov",
" reasoned that the Americans wouldn't ever launch just a single missile, and determined that the warning was probably an error. Fortunately for everyone, he didn't report the alleged launch.",
"Edit: fixed link."
] |
[
"You would think that telemetry would tell you soon enough. Barring that, it makes almost no sense for a nuclear power to start an attack with a single missile. You should start worrying when you see hundreds of 'satellites' being launched at once."
] |
[
"Well it depends where. If you're launching by a commercial provider, SpaceX, Arianespace or something like that, then it's unlikely you could do this \"illegaly\", because of all the tests payloads have to take. Everything is measured, so you can't really smuggle anything apart from what's in the specs (even change in mass distribution, or resonance frequency would be noticed).",
"But if it's for example US or China launching a classified military payload (like a spy satellite) then there is no way for anyone \"outside\" to know what exactly is being launched. But obviously \"someone will know\", starting with people who built it.",
"If you launch something really radioactive then maybe you'd trigger some sensors, but it's not so likely."
] |
[
"Why when we get vaccinated our children don't inherit the immunity?"
] |
[
false
] | null |
[
"The genetics provide the blueprint for the immune system, but you get vaccinated against things you're not naturally immune to. ",
"A vaccination teaches your body how to respond and fight off an illness, but it doesn't alter your DNA. "
] |
[
"When you talk about genetically modifying humans you get into a very messy area of ethics, whatever the reason. It intertwines the ethics of biology, sociology, and philosophy.",
"Aside from that, we can't get everyone to agree on GMO vegetables. GMO humans aren't anywhere close to being a serious talking point. "
] |
[
"By next step I assume you mean \"step we've achieved but haven't legalized for obvious reasons\"."
] |
[
"Are oceans caustic and not acidic? Does the pH level ever go below 7.0?"
] |
[
false
] |
Some say elevated levels of carbon dioxide strive to cause seawater to be acidic, is this true?
|
[
"The pre-industrial pH of the ocean ",
"was 8.179 (see the chart)",
" so the ",
"process of acidification",
" (or see the ",
"NOAA",
" for an even simpler take on the process) is moving the average ocean pH closer to a neutral pH as opposed to crossing into being truly acidic. The current average pH is ~8, representing around a 30% increase in hydrogen ion concentration (remember that the pH scale is logarithmic). As laid out in either the wiki article or the NOAA page, the cause of this reduction in pH is the increase in the concentration of atmospheric CO2 (and thus an increase in the amount of CO2 uptake by the ocean). Projections for the pH of the ocean (which obviously are dependent on projections for the amount of CO2 in the atmosphere, among other factors) do not indicate that the pH would ever be go below neutral (at least not in the next ~80 years).",
"In the geologic past, I'm not aware of any arguments suggesting that the ocean was ever truly acidic. Even during one of the most extreme ocean acidification events (which was related to and in part responsible for the ",
"largest extinction event in earth history",
"), estimates of the ocean's pH bottom out around 7.2, e.g. ",
"Clarkson et al, 2015",
", so still slightly basic (however, proxies for pH require a lot of assumptions). In general, ocean acidification events in the past are typically associated with mass extinctions, including the Permian-Triassic (as mentioned before) and the Triassic-Jurassic boundary, e.g. ",
"Greene et al, 2012",
"."
] |
[
"As ",
"/u/CrustalTrudger",
" says, ocean acidification simply refers to the reduction in ocean pH as opposed to the pH falling below 7. It's important to understand that the pH does not have to fall below 7 to have major consequences for marine life. For calcifying organisms, for example, the key parameter is the ",
"calcite or aragonite saturation state",
" which is related, but not equivalent, to pH. For corals, when the saturation state falls ",
"below around 3",
", it starts to have very significant effects on a coral's ability to calcify and indeed, by the end of the century most of the ocean may be under this threshold (e.g. ",
"Figure 2.4 here",
"), despite the pH being well over 7. It's also interesting to note that the aragonite saturation state is lowest at high latitudes, which demonstrates ",
"the \"pincer\" threat facing our reefs",
" because they're being threatened by heating at low latitudes, and acidification at higher latitudes."
] |
[
"To be clear, in your last sentence, did you mean: CO2 emissions are beneficial ",
", rather than harmful?"
] |
[
"Is it possible for a planet to have a breathable atmosphere without organic life feeding it?"
] |
[
false
] |
For example, here on earth the atmosphere, as I understand, is partially sustained by plants that take in CO² and emit O². When I used to play Spore (I understand its a game), you would have to place plants and animals in order to sustain the "terrascore" of the planet. Does this have truth in real life, or could there possibly be a planet that we could live on that is completely barren?
|
[
"Oxygen can also be generated from water by ionizing radiation. The term \"ionizing\" says it all: it can excite electrons causing them to escape their orbits and leave an ion behind. If this happens to an electron participating in a chemical bond, the molecule may be broken into free radicals or even lone atoms. So H",
"O can become H and OH.",
"We actually have an example of this in the Solar System. Jupiter's powerful trapped radiation is constantly ionizing the surface ice on Europa. This moon has a very low gravity, so it's not capable of holding a thick atmosphere, but it does retain some of the oxygen that is generated this way. (Hydrogen escapes much more easily as it's so light).",
"For the \"we could live\" part it's a bit more complicated and probably even speculative. Obviously the atmosphere that is generated this way should be thick enough so that very little radiation reaches the surface. This is definitely not the case on Europa, you would die from radiation poisoning after a few days."
] |
[
"Oxygen is very reactive. I would imagine it would burn faster than it can be produced by ions."
] |
[
"You're right, but that only happens if there is something on the surface it can react with. On an icy surface like Europa, it just can't.",
"Fun fact: the external surfaces of spacecraft are usually aluminium or glass fiber (beta cloth) to avoid reacting with the atomic oxygen of Low Earth Orbit. They can resist because both of them are oxides (at least on the outer few microns). Atomic oxygen is much more reactive than molecular oxygen, and it's kind of relevant because it's produced by the Sun's UV radiation acting on the upper atmosphere."
] |
[
"How much genetic variation is there in a single person?"
] |
[
false
] |
Among a single person, comparing 2 random cells, how much variation can you expect in their genomes? Over time mutations and such are bound to happen, but I’m not finding any results for how frequently there may be variation. edit: I’ve time-> Over time
|
[
"That is all true in theory. But in practice, there is always mutation. Always. The replication machinery is not even close to perfect, error rates are as high as 1 per 100 nucleotides (the A, T, C, G). With ~3 billion nucleotides in the genome you can expect up to 30 million errors (mutations) per replication. That said, there is a ton of cellular machinery with the purpose of fixing those mistakes.",
"Most mutations that aren't repaired have no material effect and will be ignored. Of those that do have an effect on the new cell, most will cause the cell to die. Those that remain can be neutral, good (fish learns to breathe air), or bad (cancer).",
"But to actually answer your question, they will be almost identical in the coding regions of the genome (part of DNA that codes for proteins) but likely not exact. These variations are called Single Nucleotide Polymorphisms (SNPs) and exist about 1 per 1,000 nucleotides. Therefore any two cells are about 99.9% identical on average."
] |
[
"Great question! Your DNA is broadly divided into exons, introns, and intergenic regions. Exons code for proteins. That is, the DNA will at some point be transcribed into messenger RNA and that mRNA will be translated into proteins that \"do stuff\". This is the classical purpose of DNA as the generic code. But that makes up about 1% of all your DNA. The rest of it is regulatory, or structural, or we don't even know yet. Lots of SNPs happen here as well."
] |
[
"All the cells in a human body have identical genomes with the same DNA combination. Each cell has all the information to reproduce the entire organism.",
"Two sets (alleles) of each gene is required to express a character. One half comes from the mother, the egg, (secondary oocyte) and the other set, sperm, from the father. During fertilization these two fuse and are copied exactly billions of time to produce the entire organism, muscles cells are different from kidney cells because although they have the same information, differentiation causes the expression of only the muscleness of muscles cells and not the other information. ",
"In essence there are two types of cells gametes (sex cells) which have half the genetic material (n) and somatic cells (non-reproductive cells) which have the full complement (2n)",
"Caution: I am unsure of your level of Biology and may have used unfamiliar terms."
] |
[
"Is there any publicly available database that has collected a lot of raw data but no one put the effort to analyze or summarize the result?"
] |
[
false
] | null |
[
"Hi, this is a better question for our sister subreddit ",
"/r/AskScienceDiscussion",
". Our panelists have flair there, too, but the conversation is more open-ended. Also, the short answer is that yes, there are tons of databases out there, and some have lots of unanalyzed data. Feel free to post over on ",
"/r/AskScienceDiscussion",
" and folks can mention some of the databases they're familiar with."
] |
[
"Thanks for the recommendation, I will post it there : )"
] |
[
"Cool, you're all set."
] |
[
"Can stars/sky in a photograph give us the location from where the photograph was taken? If so, how does it work?"
] |
[
false
] |
I've seen this happen in movies/TV many times. Also someone was talking about it(confused celestial coordinates with coordinates on earth) in today. Feel free to go deep about it in your answers if you want. Edit: A lot of you were confused...Assume that the photographs have timestamps and the angle of the photo with respect to the horizon. Thanks!!
|
[
"3) what time it was (hence the importance of clocks that stay accurate on a moving ship).",
"Interestingly, this importance is what lead to the first determination of the speed of light.",
"When Jupiter's moons were discovered, they were found to keep very stable orbits, and it was suggested that their transit times could be used as an accurate clock to measure longitude on board a ship without having to worry about imprecise pendulums swinging onboard. However, it was soon discovered that the tables of predicted times of moon transits ranged over 17 minutes depending on where Jupiter was in the sky.",
"Folks figured out that when Earth was on the same side of the Sun, transits were coming up to 8.5 minutes early, while on the opposite side of the Sun they came up to 8.5 minutes late. This was entirely due to the extra transit time required for light to travel the extra distance, and was both confirmation of light's finite speed as well as the first determination of that speed."
] |
[
"Generally speaking, it's not possible to do that from just a photograph of the sky, though I might be misunderstanding the question. (Maybe link the ",
"/r/space",
" discussion?) The issue here is that astronomical objects are really far away, so everyone on Earth is essentially seeing them from the same angle relative to each other -- therefore, the relative positions of stars on the sky don't tell you about your location on Earth in a useful way.*",
"However, this changes if you have two additional pieces of information: the exact time the photo was taken, and/or the position of the photo in the sky when it was taken (i.e., the angle of the photo with respect to the horizon and cardinal points). You can calculate the position from these additional pieces of information because...",
"1) the positions of stars generally don't move relative to each other (at least not very quickly as seen from Earth), so we can effectively create a fixed map of all the stars in the night sky (from straight above the north pole, to straight over the equator, to straight over the south pole) that just rotates around us in a simple way as the Earth revolves;",
"2) any photo of the sky that includes 3 or more stars can almost certainly be uniquely identified to a position on this map based on the relative positions and brightnesses of the stars (by matching with a catalog of stars that can be seen from Earth);",
"2) the part of this map you can see at a given angle from your reference horizon only depends on where you are on Earth and what time it is (ok, I'm assuming no clouds or ceilings).",
"This is basically how ancient mariners, etc., figured out where they were using the stars... they needed 1) to know where on the \"star map\" they were looking (hence maps of constellations), 2) where the star they were seeing was above the horizon (hence sextants), and 3) what time it was (hence the importance of clocks that stay accurate on a moving ship).",
"http://en.wikipedia.org/wiki/Marine_chronometer",
"\n",
"http://en.wikipedia.org/wiki/Sextant",
"(* Big caveat here: if you move a ",
" big distance, you ",
" actually see stars move relative to each other (in that the positions of nearby stars move with respect to more distant stars). This is called stellar parallax, and it's actually the most fundamental way we calculate distances to nearby stars, using the fact that the Earth moves a very large distance (2 AU) in its orbit every 6 months. *)",
"http://en.wikipedia.org/wiki/Stellar_parallax"
] |
[
"They don't directly; instead, by consulting a table of them which was previously calculated, you could (if the speed of light were infinite) use them to determine what time it was precisely. An accurate time reference relative to another location is what gives you your longitude.",
"For example, suppose a star is due south at midnight on April 17 from Greenwich. Obviously, it won't be due south for everyone on the planet simultaneously, but will be at some time every day. Let's say you find that this star is due south of you at 2 AM instead of midnight on April 17. This tells you that are some distance west of Greenwich, and in fact tells you that you are 1/12 the way around Earth from Greenwich (30 degrees of longitude). As long as you have a clock which accurately tells you what time it is in Greenwich, you can tell how far east or west of Greenwich you are by looking at the times different celestial events occur."
] |
[
"Wouldn't it make sense for airplane manufacturers to make the wheels spin either with a motor or the wind before a landing to preserve tires?"
] |
[
false
] | null |
[
"Not worth the extra weight and complexity. Tires are relatively cheap and have to be replaced regularly anyways.",
"There were some tests done with an Airbus airliner a few years back where they put electric motors in some of the wheels so the jet could taxi using just using its APU providing electric power. The idea behind it was to save fuel when taxiing by not having to have the engines running (and burning fuel), especially at busy airports where you might have to wait in line for takeoff."
] |
[
"There were some tests done with an Airbus airliner a few years back where they put electric motors in some of the wheels so the jet could taxi using just using its APU providing electric power. The idea behind it was to save fuel when taxiing by not having to have the engines running (and burning fuel), especially at busy airports where you might have to wait in line for takeoff.",
"And?"
] |
[
"It was done by L-3 partnering with Lufthansa, they provided the aircraft. The system worked, it was not flight tested and so after the tests it was removed and jet was returned to regular service.",
"If you do some searching, Honeywell and Safran are planning on testing a flight-worthy electric taxi prototype on an A320 in 2013 and want to have something in production in 2016. We'll see."
] |
[
"Are humans the only animals that cry?"
] |
[
false
] |
(And by cry, I mean shed tears when you get upset.) Anyway, what a maudlin question! But I am a bit curious about it nonetheless! The topic came up in a discussion with my girlfriend, where she claimed that dogs don't cry. Now since she's a vet I'm inclined to believe her, but that brings up a bigger question: What animals besides humans cry? After thinking about it for a bit, I can't really come up with any examples -- but maybe I just don't know enough. So : What is the deal? Are there other animals that cry or not?
|
[
"Crocodiles cry, but it's a way of getting rid of excess salt. "
] |
[
"Elephants cry, but I think that's it. No one knows exactly why humans cry, so we've no idea why other animals don't. It ",
" have something to do with being able to use tears on bare skin to signal distress to others. Or it may not. "
] |
[
"While evolution can be a good explanation for things it's important not to just jump to the most convenient explanation."
] |
[
"Why and how does inbreeding create genetic defects?"
] |
[
false
] | null |
[
"Inbreeding doesn't create genetic defects, it increases the [frequency of homozygosity] within a population.",
"You have a whole heck of a lot of genes, and you have two copies of nearly all of those. One copy is from your mother and one from your father (except in the case of mitochondrial DNA, which is always from your mother). Your mother and father each had two copies from their parents, and gave you one randomly selected copy. If your \"maternal\" (mother-derived) and \"paternal\" (father-derived) copy of a particular gene are different, you are ",
" for that gene. If your paternal and maternal copies of a gene are identical, you are ",
".",
"What's the difference between these paternal and maternal copies? Usually not a whole lot. Sometimes, a whole lot. Differences between genes are one of the major reasons people aren't identical to one another - the typical examples of genetic factors are eye and hair colour, height, etc. These characteristics can sometimes be linked to a single gene, but usually they are the result of a bunch of different genes with interacting effects.",
"So, back to the point. Inbreeding populations don't shuffle around their genes enough. Your mother and father are more likely to have the same copy of a gene if they share a grandparent. A lot of genetic disorders are the result of a homozygous gene; a single copy of \"the bad gene\" does no harm to a heterozygous individual but two copies are enough to cause a disease state.",
"Check out the wikipedia page on ",
"Zygosity",
" and especially the page on ",
"Heterozygous advantage"
] |
[
"In simplest terms, nasty genetic traits are pretty much always recessive (a dominant trait that causes serious defects would just die out). In a suitably diverse population, it is rare for people with the same recessive gene to meet and produce offspring.",
"When close relations breed, they are more likely to share some of these recessive traits and bad combinations become more likely."
] |
[
"Say your grandfather had mutation in a gene (XXm). It's no problem, happens all the time and goes unnoticed for generations because you only have one mutated gene (Xm) and the other normal gene (X) still functions perfectly. Goes unnoticed that is until that fateful day when a baby is born with the same mutation in both his genes (XmXm).\nWhat are the chances you say? Why did this tragedy happen to me and my family?\nWell, if your wife is also your cousin and got parts of her genome from your grandfather chances are much higher than they would be from a totally unrelated person.",
"This is inbreeding. Not more mutations, but the chance that mutations double down in the same spot."
] |
[
"Why would some peppers evolve to be difficult to eat?"
] |
[
false
] |
Doesn't that defeat the purpose of fruit style seed dispersion?
|
[
"Peppers want birds to eat their seeds (since they don't digest them, and just defecate them at some distance), and not mammals (who would digest them.)",
"That's why some peppers produce capsaicin, which is an irritant for mammals, but not for birds."
] |
[
"\"Difficult to eat\" meaning \"spicy\"? ",
"Capsaicin ... is the active component of chili peppers, which are plants belonging to the genus ",
" [peppers]. It is an irritant for mammals, including humans ...",
"http://en.wikipedia.org/wiki/Capsaicin",
"The situation is entirely different for birds. While mammals will avoid food containing as little as 100-1000 parts per million (ppm) of capsaicin, birds will readily consume up to at least 20,000 ppm (mind, we're talking food that's 2% pure capsaicin here). ",
"The difference seems to be that bird receptor cells are largely insensitive to capsaicin.",
"http://www.straightdope.com/columns/read/1857/are-birds-immune-to-hot-pepper-enabling-them-to-eat-vast-amounts-and-spread-the-seeds",
" ",
"The seeds of ",
" plants are predominantly dispersed by birds. ",
"The TRPV1 channel to which capsaicin binds does not respond to capsaicin and related chemicals in birds (avian vs mammalian TRPV1 show functional diversity and selective sensitivity). ",
"Chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, but mammals have molar teeth, which destroy seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it reproduce. ",
"In addition, there is evidence that capsaicin evolved as an anti-fungal agent. The fungal pathogen, ",
", is known to infect wild chilies which reduces seed viability. Capsaicin deters the fungus, and in doing so limits this form of predispersal seed mortality.",
"http://en.wikipedia.org/wiki/Capsaicin",
" "
] |
[
"I would like to hope that you posted that link as a way to say that this is an easy question to answer by a simple Google search, but all it really does is make you look like an ass."
] |
[
"Is there any difference between getting your vitamins from a multivitamin rather than a food source?"
] |
[
false
] | null |
[
"To clarify, there are two types, water soluble and fat soluble. Excess of water soluble vitamins will just pass through the body, but excess of fat soluble vitamins will be absorbed from the body and may cause issues. That's why those ridiculous 1000% DV Vitamin C tablets don't hurt you... 900% DV of vitamin C ends up in the toilet."
] |
[
"This is correct, but in my opinion what OP wanted to know is, Are vitamins from food \"healthier\" than \"synthetic, unnatural\" multivitamins as a lot of people think, and the answer is no, they are chemically the same, but vitamin supplements have disadvantages such as hypervitaminosis and some vitamins work better or get absorbed better along with some other nutrients present in the food."
] |
[
"yes, you can overdose vitamins if you take them from multivitamin etc, or taking it in pure form.\nAlso some vitamins work better if other ingredients are present."
] |
[
"Does science acknowledge a limit to what we as a species can mentally comprehend ?"
] |
[
false
] |
Is there a theory, idea, or acknowledgment that the human brain has limits on just how complex, complicated, etc... of an idea it can comprehend, and work with ? I'm kind of wondering as we continue to advance at such a fast pace into advanced physics like string theory, quantum physics, and all that stuff if we will eventually hit a wall simply because our brains have physical limitations on what they're able to process, and effectively work with.
|
[
"The catch with string theory and/or quantum physics is not that we can't describe or articulate and thus understand it on a language basis.",
"That quantum objects are at multiple places both vibrating and resting at the same time just contradicts the logic we as a lifeform have been trained over the centuries.",
"That banana isn't at multiple places and still is one banana.",
"Switching to the unfiting software/hardware analogy it's a software problem.",
"Also we're increasingly able to use computers to offload a lot of our brute force tasks/calculations",
"That we can compress information pushes the limit we might have far away. So I don't think complexity is the limiting factor here."
] |
[
"There's an interesting idea called \"cognitive closure\" that you might find illuminating. It posits that there are certain things that cannot possibly be understood by the mind because of the intrinsic way the mind works."
] |
[
"Well there are limits to working memory: ",
"http://en.wikipedia.org/wiki/Working_memory#Capacity",
" ... we can hold something like 7 items in our conscious mind at one time, and can't work on tasks that require more than that.",
"However we are able to split tasks up into sub-tasks to a large extent to keep things under that \"limit.\" This is why advanced math/physics is so abstracted and obtuse: a lot of stuff is going on \"behind the scenes\" that is abstracted away/assumed when working with the high-level concepts.",
"Also we're increasingly able to use computers to offload a lot of our brute force tasks/calculations.",
"None of this says there isn't going to be some limit eg what someone can learn and work with in their lifetime."
] |
[
"How does an electron absorb energy from a photon in a solar cell?"
] |
[
false
] |
When an electron and a photon interact to raise the energy level of the electron, what happens? How is energy transfered from the photon to an electron? Is this some passing of quarks?
|
[
"Quarks are not involved. Atoms are made of electrically charged particles (nucleus and electrons), so they interact with external electromagnetic fields.",
"A photon is an excitation of the electromagnetic field. An atom and the EM field can exchange energy, momentum, angular momentum, etc. by creating or destroying photons. But the internal state of the atom must also transition accordingly so that conservation laws are satisfied.",
"For example, you can shoot a high energy photon at an atom, the photon can be destroyed, and a bound electron can be freed with some kinetic energy equal to the difference between the photon energy and the energy it took to free the electron. This is called the photoelectric effect."
] |
[
"A solar cell is a semiconductor diode. The light may excite an electron in the covalent bonds to the conduction band (this is the internal photoelectric effect), leaving a hole in the valence band. If this happens near the junction between p- and n-type semiconductor, the electron and the hole are pulled apart by the strong electric field there. If there is a closed circuit, both the electron and the hole contribute to a current."
] |
[
"It is related to the ",
"photoelectric effect",
" (for which Einstein was granted his Nobel prize) and is related to the particle like nature of light. Basically a photon comes along and \"bounces\" an electron out of its orbit. A photon is pure energy, so all that energy is absorbed directly by the electron, allowing it to roam more freely in the crystal structure of a solar cell. One of the keys to showing that it truly is a collision is that there is no electricity produced at long wavelengths. If you shine a heat lamp or an extreme case, a radio signal on a photocell, they do not produce a weak current, even after a long time. Only when there is enough energy in a single photon to truly \"knock\" the electron out of its bound shell/orbit will electricity be produced.",
"Often you will hear of photovoltaics--the difference is only in the photoelectric effect, the electron is released to a vacuum, while photovoltaics, the electron stays in the material, but in a more loosely bound state (it becomes more of an electronic carrier--either the electron itself, or the hole it leaves behind--a positive carrier or both). ",
"If you are unfamiliar with electronic conduction in matierials, generally only the most loosely bound electrons contribute to conducting electricity. By creating more of those loosely bound electrons you increase your conduction. That is why \"bouncing\" electrons/holes into upper loosely bound levels changes the matierals conductivity."
] |
[
"What is happening when I zip a file?"
] |
[
false
] |
I would imagine it depends on the type of information being compressed, but I'm not sure.
|
[
"Here's a good example of lossless compression.",
"http://en.wikipedia.org/wiki/Huffman_coding",
"In this case what happens is that you analyze the uncompressed file and essentially create an encoding scheme such that from a smaller file you can recreate the original given instructions, which can be read at the header.",
"As an extremely rudimentary example of this type of thing, let's say you have a file that contains 1000000 iterations of the number \"0\", nothing else. One could compress this file by turning it into something that says \"when uncompressed, construct a file with 1000000 of the number \"0\" \". This compressed file would clearly be shorter because it doesn't have to store 1000000 characters.",
"The reason we don't just keep everything compressed in a .zip file or something has to do with the fact that compressed files might not be as easily manipulated. For example, it would be easier to have MS Word open a .doc file than have it extract a .doc file from a .zip file."
] |
[
"You use lossy encoding in \"analog\" files (for lack of a better word—obviously they're still stored digitally) like audio, video, and photos, because the lossy compression algorithm can lead to much smaller file sizes by stripping away near-imperceptible content in these types of media.",
"For example, an .mp3 file is an example of lossy compression of an audio file. The algorithm removes some information/\"sounds\" from the native/uncompressed file that are near-undiscernible by the human ear.",
"Lossless encoding, on the other hand, is used in scenarios like data files, where permanently losing any information would corrupt the file. ",
"So for an image, a compression algorithm could say, \"well, this small block of color looks a lot like this other block, so just store one copy of the block and draw it in both places.\" You lose information this way (the blocks may have some small differences), but you get a much smaller file size, especially in cases like video.",
"But for a Word document, as a high-level explanation, you couldn't say, \"well part of this sentence has mostly the same words as a part of this other sentence, just store one version and copy-paste it into both places,\" because the document wouldn't make sense. So we use lossless compression, which works with the logic, \"this part of this sentence is exactly the same as a part of this other sentence, so we'll store the words once and then copy-paste them into position as needed.\" It takes a lot less space to store a piece of information once along with all the places it appears than it does to fully store the information each time.",
"In compression, the \"words\" in my analogy represent the actual bits of the file. So say we had the following chunk of a file:",
"00101000 00101000 00101001",
"A lossless algorithm would say, \"write the sequence 00101000 twice, and then 00101001,\" or it would even say \"write 0010100\" three times, then add \"0,0,1\" at the end of each placement.\"",
"A lossy algorithm would say, \"well, 00101000 looks a lot like 00101001, so just write 00101000 three times.\" This would save more space (more compression, smaller file size), but you end up losing information that you can't rebuild from the compressed file.",
"Here's another example. You have a horizontal gradient going from black to gray to white in a 512x512 image. ",
"An uncompressed file would store the shade of every single pixel. A lossless algorithm would store the pixel shades in one row (1x512) and then tell the image viewer to redraw this row 512 times to perfectly reconstruct the final image. A lossy algorithm might say, well, this group of adjacent pixels are almost the same shade, so we'll just store their average value and draw them all as the same color when viewing the image. And you end up with a smaller image size than even the lossless compression method, but with blocky compression artifacts when you look at it closely.",
"Keep in mind that this is all a high-level analogy of how lossless and lossy compression works, but I hope it paints a good picture of how the schemes work on the actual stored data in a file."
] |
[
"For example, it would be easier to have MS Word open a .doc file than have it extract a .doc file from a .zip file.",
"Actually, newer MS Office applications use OpenXML file format, represented by extensions ending with \"x\" (docx, xlsx, etc), which are in fact just zipped XML files."
] |
[
"When I look at, for example, the north star, how many photons are hitting my retina every second?"
] |
[
false
] | null |
[
"First you would need to find the factor that the sun's apparent magnitude is brighter than Polaris given by the equation (x=mf-mb) and (v=2.512",
" Which will get you 2.99x10",
"Now here comes the tricky part of your question. The sun produces billions upon billions (sagans) of photons which are spread out across the whole EM spectrum, not just the visible part which you can see. However, I used an average wavelength for the wave and used e=hv using the wattage of the sun as well as factoring in the size of the eye(pupil) and how far away Earth is and how much the radiation would be dispersed. ",
"For my final answer I got 443,341.8 photons per second from Polaris (North Star). Keep in mind that this is a very very rough estimate. It would have been easier if I could have found a source that told me how many photons of the sun reach the retina every second."
] |
[
"443,341.8 photons per second",
"Maybe relevant: I think I recall that the human eye can detect as few as 5 photons per second, but I can't find a source anymore. Can a specialist drop in and clarify?"
] |
[
"It depends - if you mean the maximum sensitivity of our photodetector cells in the eye, then rod photoreceptors are capable of detecting individual photons no worries. If you mean how many until we ",
" that we have detected light, then it's around 9 in less than 100 ms. This difference is due to filtering by the brain to get rid of noise inherent in any biological system. I could link the original papers, but ",
"this",
" site gives a great description."
] |
[
"What exactly does a blast cap do?"
] |
[
false
] |
From what I hear large explosions can be pretty difficult to detonate (such as C4). I hear physical force, raising temperature and a flame doesn't set it off (although I may have heard wrong). What does a blasting cap do to make something detonate?
|
[
"Most military (safe to carry) explosives are very hard to actually get to explode. This makes them safe to carry and store. A blasting cap is a small explosive device (won't be devastating if it goes off) kept separate until it's placed with the primary explosive, like C4. ",
"That way there's almost no risk of a catastrophic failure until the explosive has been placed where it needs to go off. The blasting cap will explode into the secondary (main, big one) explosive, which creates enough energy to set off the secondary explosive.",
"*changed what primary and secondary was. Thanks ",
"/r/sardano"
] |
[
"The blasting cap is a primary explosive, the stable explosive is a secondary."
] |
[
"A blasting cap is a small sensitive primary explosive device generally used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive.",
"Blasting caps come in a variety of types, including non-electric caps, electric caps, and fuse caps",
"From the wiki",
"Basically there are lots of different kinds but they all provide a (relatively) large amount of energy to get the reaction started. C4 and other explosive are call secondary explosives. They have a high activation energy. They need a primary explosive to set them off. That's the gist of it. The wiki will have more info if you are interested."
] |
[
"Can k (the curvature of spacetime) be complex?"
] |
[
false
] |
So in our cosmology lectures we've looked at k from a basic "if it's positive, it does this, if it's zero it does that, if it's negative it does this other thing" point-of-view,with the lecturer saying that a full General Relativity treatment of k will be left till the fourth year. So I'm wondering; can k be complex/imaginary? Is that a thing which can happen, perhaps when doing the full GR treatment of it? If so, what would the physical meaning of such a value be?
|
[
"The parameter k shows up only in maximally symmetric spaces, but the curvature is always real-valued in GR. General Relativity is basically differencial geometry in a space with a lorentzian metric. The metric only has real-valued entries and thus the Riemannian curvature tensor also is real-valued (it can be constructed from the derivatives of the metric). "
] |
[
"No. k cannot be complex because of how k is defined. The spatial curvature parameter comes about because the \"boundedness\" of an object can be described using a coordinate system that has too many variables--in that not every variable can be treated and independently varying. Take the cartesian equation for a sphere, ",
"x^2+y^2+z^2=p^2 \n",
"Obviously I can't freely pick any (x,y,z) point. For p=1, (0,0,0) or (10,0,0) both are legitimate coordinate points which ",
" on my sphere, they violate the sphere surface condition. What k in essence is telling us, are the variables we're using free to take on any value, or is there a restriction on what values they can take. It is then no miracle that flat space, or k=0 has no restrictions on what coordinate points we can explore! ",
"Let's consider a four dimensional hypersphere, (x,y,z,w), ",
"x^2+y^2+z^2+w^2=R^2 \n",
"We know that from the previous equation that the first three terms represent a bounded 3-sphere, ",
"p^2+w^2=R^2 \n",
"Let's take the differential, ",
"pdp+wdw=0 \n",
"So, ",
"dw^2=p^2*dp^2/w^2 \ndw^2=p^2*dp^2/(R^2-p^2) \n",
"Let's now write out the line element for our 4-sphere,",
" ",
"dl^2=dp^2+p^2*dp^2/(R^2-p^2) + angle term\ndl^2=dp^2/(1-(p/R)^2) + angle term\n",
"And here we are. We have some quantity 1-(p/R)",
" This is our spatial curvature, which you can see explicitly as it depends on the 3-sphere parameter p in our 4-dimension geometry. This is why k is ",
" curvature and ",
" spacetime curvature. If you want to explore spacetime curvature, you'll need to explore the Riemann curvature tensor.",
"Now we're going to answer your question. Let's call r=Real[p/R]. The FLRW geometry",
" still works if p/R is complex! If it's complex, then I need to do complex conjugate product, but it's a simple modification. If p/R is imaginary, then line element has the denominator 1+r",
" this is negative spatial k=-1 curvature! If p/R is real, then the line element has 1-r",
" which is positive spatial k=+1 curvature! As mentioned, zero is flat, which is the easy case, there is no inter-coordinate dependence. I can easily rewrite the denominator as 1-kr",
" now which is what you should be familiar with when looking at FLRW.",
"So finally, we now know why k has to be 1, -1 or 0. We've already taken into account imaginary values in our geometry, k simply reflects the sign of the absolute value squared of p/R--or our spatial geometrical restrictions.",
"http://www2.warwick.ac.uk/fac/sci/physics/current/teach/module_home/px436/notes/lecture20.pdf",
" Technically a ",
" not line element, hence dl",
" not ds",
" we're doing slices of constant time. It doesn't change the argument, just makes the math easier and look the same for either 4-hyperspace or 4-spacetime. ",
" The r I defined isn't comoving r which you normally see. I just wanted to take care of the more general case if R is complex which it is usually assumed to not be.",
"Edit: Grammar/typos. Changed the definition of r to yield the traditional comoving coordinates."
] |
[
"The short answer is that the curvature is real-valued in general relativity.",
"In more details, the curvature \"k\" used in cosmology is directly related to what is called the \"Ricci tensor\" in general relativity, which is a local measure of how strongly curved spacetime is.\nThe Ricci tensor is itself obtained from derivatives of the metric, the functions which tell you how distances and time are measured in a given spacetime - and the metric is real-valued.",
"Most textbooks on general relativity will give you the mathematical definition of the Ricci tensor. For a version which is freely available online, you can for example look at ",
"Sean Caroll's lecture notes",
", in the section relating to curvature (more exactly, Eq. 3.90). But you'll need some knowledge of differential geometry to go through those notes.\nSection 8 of the same notes, which discuss cosmology, gives the mathematical relation between \"k\" and the Ricci tensor (e.g. equations 8.2 and 8.3)."
] |
[
"What are common applications of usage of the world's most powerful supercomputers?"
] |
[
false
] | null |
[
"There are dozens of applications that really require computing at these scales. I know that protein modelling is one of the heaviest applications but I'm sure someone else here can explain that better. Hopefully someone familiar with geodynamics can chip in too, because those models have to execute some extremely intricate mathematics. ",
"I myself am familiar with two applications:",
"Agent-based epidemiological models - these are probabilistic computer programs that create hundreds of thousands to millions of virtual people, all of whom have a house, job, family and friends and make these people go through their daily lives. The goal, as these digital people move around their digital cities, is to register how people interact and how diseases are consequently spread.",
"General Ocean Circulation Models - this is pretty straight forward, global or large-scale simulations of the Ocean-s currents. These not only solve equations in fluid dynamics coupled with thermodynamics, but they also have several smaller scale processes parameterized into them to better model how energy flows throughout the world's seas. Sometimes these models are coupled with atmospheric programs to predict future weather scenarios and things like sea-level rise. "
] |
[
"I would imagine you're asking what they're used for, as opposed to specific software names. But weather forecasting, quantum computing, simulations on things like weapons testing, black holes, medical simulations on protein folding etc. If you want specific software you can see a sampling here: ",
"https://www.osc.edu/vocabulary/service/software"
] |
[
"Wow, that's extremely interesting. Can you give me anymore information about the epidemiological models?"
] |
[
"Does the casimir effect become weaker over time?"
] |
[
false
] | null |
[
"No"
] |
[
"Then stonger? Or is it a constant?"
] |
[
"The pressure depends exclusively on the separation between the plates, nothing more."
] |
[
"The retina is \"inside-out,\" at least in humans. Are there any species in which this is not true?"
] |
[
false
] |
The human retina is considered "inside-out", with the photoreceptors positioned behind the bipolar and retinal ganglion cells. Is this feature conserved across all species with eyes, or are there any known species in which this is not true?
|
[
"It is not true in octopus. I think that applies for all cephalopod molluscs, but I'm not sure..."
] |
[
"Octopus",
"."
] |
[
"This \"insideoutness\" is what causes animals to have blind spots.",
"Cephalopod eyes are the right way around; no blind spot.",
"Here's a vid which explains it, as well as teaching you a neat thing to do with your eye"
] |
[
"Can a household fan function as a generator?"
] |
[
false
] |
If I put my fan in a breezy window and plug it in, can it generate a few milliwatts? Should I sign up for net metering?
|
[
"Your fan is most likely using an induction motor, according to ",
"wikipedia",
" these need to be spun quite fast in order to generate electricity (that page gives 1800 rpm as a typical speed). Given this requirement, you're not going to get electricity generated with any reasonable wind."
] |
[
"However, if the fan was wired up to it's own circuit (separate from the utilities) and you don't specifically need 60 Hz alternating current, the fan would still provide a current but at a lower frequency if the fan was turning slower."
] |
[
"Most generators are this way. The wind turbines actually have transmissions that turn the relatively slowly rotating blades, into high rpm rotation for the generator. "
] |
[
"Are all nuclei arranged the same way?"
] |
[
false
] |
I understand that neutrons help hold protons together because they have the strong force and exert no electromagnetic repulsion, but it seems to me that would mean there's an optimal packing arrangement of the neutrons in relation to the protons (if you had two protons and a neutron, it would make more sense to put the neutron in the middle rather than the outside). So if I was looking at 10 atoms of carbon, would the arrangement of protons and neutrons be the same in each nucleus? I know that some unstable atoms can have multiple decay modes; is this caused by the nucleus occasionally being "packed" a different way?
|
[
"Thinking about protons and neutrons like little balls will only get you so far, the reality is more complicated. You can consider the proton and neutron wavefunctions (similar to how electron wavefunctions are considered in atomic physics), and the energy levels that are occupied by particles (the way that atomic orbitals can be occupied by electrons).",
"Most nuclei will have the protons and neutrons occupying the lowest possible energy states and building up to higher energies as they get full due to Pauli exclusion. Sometimes a neutron will turn into a proton or vice versa if there are too many of one, because that allows it to fall to a lower energy state (this makes up the symmetry term of the ",
"liquid drop model",
").",
"Within a given stable isotope, however, you can have something called a nuclear isomer, where the nucleus is arranged to have some of the particles in a higher energy state, and eventually these decay to the ground state through gamma emission. In some cases however these isomers can be quite long lived. Holmium-166 for example has an isomer that lasts thousands of years."
] |
[
"This is a great explanation."
] |
[
"This is a complicated problem, but two nuclei with the same number of protons and neutrons in the same quantum state (i.e. the ground state, or an isomer, or any of the excited states) will have the nucleons arranged in exactly the same way (by which I mean they will have the same many body wave functions). You can tell they are indistinguishable by e.g. scattering 12-C off other 12-C nuclei and observing the interference pattern. They show a characteristic pattern coming from the fact that you cannot tell WHICH of the identical initial particles ends up as which final particle. If you switch to 13-C scattering of 12-C the pattern then changes dramatically, because now you can. See Fig. 2 in ",
"this",
" document. "
] |
[
"Why do unhealthy foods taste so much better?"
] |
[
false
] | null |
[
"In the natural world there wasn't any food with the kind of densities of salt sugar and fats that you get in a big mac. So if we found something that was calorie dense/salty/sweet etc. it would be a rare treat and good for our system (as they are rare). As a result we learned to like these the most.",
"Now commercial companies have exploited this idea and give us food that is overly shit for us but is stuffed with all the things that was 'good' when it was rare.",
"Healthier foods were plentiful and were the mainstay of our diet (hence why they're so important, we used to be almost entirely reliant on them) so making them taste amazing was less important as we would definitely be eating them."
] |
[
"our problem is too much of a good thing"
] |
[
"\"bad for you\" foods are usually energy-dense. In the natural world, energy-dense foods are rare, and you need all the energy you can get, so it makes sense for you to really like eating energy-dense food.",
"Nowadays, energy-dense food is everywhere, and we don't exercise as much, so your body stores that unused energy away for later as fat. however, since evolution takes a loooong time to catch up with changes that aren't imminently fitness-affecting, we still instinctually want lots and lots of energy-dense food."
] |
[
"How true is Ohm's law?"
] |
[
false
] |
I've almost never got a perfect straight line while plotting a V/I graph even under lab conditions.
|
[
"Ohm's Law is not a law derivable from Maxwell's equations, but rather just a description of how many materials behave, derived directly from experiment only. (There is some justification for it though from an atomic perspective.) All materials will disobey Ohm's Law past their dielectric breakpoint. There are also materials that just simply don't obey Ohm's Law even under a weak electric field (e.g., semiconductors), and they are said to be ",
".",
"Also note that if you are measuring resistance in a lab and not controlling for joule heating, you will find that ",
" is not a linear function of ",
" simply because the resistance (say, of a bulb) increases with temperature, which itself increases with current. Hence ",
" = ",
"*",
"(",
"), with ",
" a strictly increasing function of ",
" (i.e., not constant). This is not necessarily a violation of Ohm's Law though, because the full statement of Ohm's Law has the caveat that it applies to a circuit element ",
", in particular, at constant temperature. ",
" Some clarification is needed here since many of the comments are getting some things wrong, ",
" contradicting me, or just outright contradicting me.",
"In many physical systems, we have some set of equations that hold no matter what (e.g., Maxwell's equations in classical electrodynamics, or Navier-Stokes equation in fluid dynamics, or Vlasov-Maxwell equations in plasma physics). Often our set of equations is not ",
", which roughly means we have more variables than equations. The problem of closure is particularly notorious in plasma physics. So we need to supplement our equations with what are called ",
". These are equations that hold only for a specific material and only under certain conditions or approximations. They allow us to add enough equations to our system of equations to make it solvable.",
"For instance, in fluid dynamics we may use the approximation that the fluid is Newtonian, which gives us a constitutive relation for the Cauchy stress tensor, the viscosity tensor, and the velocity field. (We may even ",
" approximate the fluid as homogeneous and/or isotropic, which gives us a further constitutive relation that simplifies the form of the viscosity tensor.) There would still be the issue possibly of closing the equations with a proper constitutive relation for the pressure.",
"In electrodynamics, one such constitutive relation we can impose is Ohm's Law, which is ",
" = σ",
", where σ is a ",
" number. This is a fine enough approximation for a wide variety of media. Of course, if you want to be more accurate or if you are investigating a regime in which Ohm's Law is not true for a material for which it usually is, we may write that ",
" = ",
".",
". Here ",
" is a rank-2 tensor, and this is a more general constitutive relation. (See ",
"/u/RobusEtCeleritas",
"'s ",
"post below",
" for some more details.)",
"Of course, we can always make up whatever constitutive relation we want. But if it gives us nonsense results or results that very badly approximate our problem, it won't get used much, if at all. Ohm's Law is a good approximation for many media, in particular, many simple circuit elements for which the temperature (and other state parameters) do not vary too much. So Ohm's Law gets used quite a bit. ",
"Some of the confusion in the other comments I think lies in treating (or mistreating) Ohm's Law as a ",
". For instance, we ",
" a Newtonian fluid to be a fluid such that ",
" = ",
".(",
"), where ",
" is a ",
" rank-4 tensor. But it's just a constitutive relation and we know that not all fluids will obey this equation. Similarly, we ",
" an ohmic medium to be a medium such that ",
" = σ",
", but it doesn't hold for all media. In that sense, Ohm's Law is absolutely true always because it's just a definition. Anything that violates Ohm's Law is just a non-ohmic medium. ",
"Finally, note that the electrical resistance ",
" of a circuit element is ",
" as the ratio of the voltage ",
" and current ",
" through that same element. Of course, there is no reason to believe that ",
" is constant or even independent of either ",
" or ",
". So in that sense the equation V = IR is ",
" true no matter what. But that equation is ",
" Ohm's Law. Ohm's Law is ",
" the statement that ",
" is independent of both ",
" and ",
" (but may still depend on other state parameters such as temperature and strain), i.e., that V and I are ",
". And so Ohm's Law is emphatically not always true.",
"The same exact phenomenon occurs in elastics. We can ",
" a Hookean body to be a body such that ",
" = -",
".",
", where ",
" is a ",
" rank-4 tensor (here ",
" is the stress tensor and ",
" is the strain tensor). In one dimension, this reduces to F = -kx, where ",
" is a constant. This is just the usual ",
" you learn in high school physics. But no one in their right mind is going to say something like \"Hooke's Law holds for all elastic bodies\". That's just absurd. It's only a constitutive relation between the stress and strain that just so happens to be a good approximation for a wide range of materials.",
"Ohm's Law ",
" different to a lot of people because, frankly, I think they forget that the equation V = IR on its own is a definition of ",
" and ",
" Ohm's Law. (Note that Hooke's Law F = -kx is not used as the definition of anything, since ",
" and ",
" can and are defined completely independently of springs. Electrical resistance, on the other hand, needs to be defined in terms of circuit elements.)"
] |
[
"That helps. Thank you."
] |
[
"Remember that real world materials almost never behave 'perfectly', there are manufacturing tolerances as well as all the other effects such as inductance, capacitance, temperature induced changes,etc,etc.",
"Things like Ohms law are totally correct for ideal components, and are close enough to be useful as long as certain factors aren't in play. For example, wires can be treated as having zero resistance unless you have massive currents or very low voltages. Wire wound resistors can be treated as pure resistors as long as you don't have or don't care about AC frequency responses, etc.",
"Learning where these things matter and where they don't is a good chunk of learning to be an electronics engineer, but in my experience it isn't taught explicitly, you just pick up a feeling for it as you go."
] |
[
"Why did the black death just stop?"
] |
[
false
] |
I know there are still a handful of cases that happen each year, but for the most part the plague just seemed to disappear. Why hasn't this also happened with other diseases like the common cold?
|
[
"Improved hygiene and sanitation conditions probably helped out immensely with reducing disease spread. Moreover not everyone would die of the plague, ",
"especially those with mutation that makes them immune against HIV (a very small population)",
".",
"The cold virus also mutates at a much faster rate than the plague which is why we can't vaccinate against all the strains that are possibly generated. ",
"\"Pandemics of plague have ravaged human populations throughout recorded history (1–6). Fortunately, improved sanitation and public health surveillance, coupled with effective therapeutics and a better understanding of transmissibility, greatly reduce the likelihood of a natural, modern day pandemic. Nevertheless, isolated plague outbreaks continue to this day (6–8). Moreover, Yersinia pestis, the etiologic agent of plague, displays natural genetic plasticity (9, 10), can acquire antibiotic resistance (11–14), and has been weaponized (15–17). Thus, plague has considerable potential to re-emerge as infectious disease threat during the 21st century.\""
] |
[
"Just to be pedantic, the plack plague, ",
", is actually a bacterium.\nCCR5 is present in several immune cells and ",
" presumably uses it as help to enter macrophages, but it is not perfectly understood."
] |
[
"This doesn't answer the question at all. Antibiotics were discovered som 600 years after the black plague ended."
] |
[
"To what degree are increases in cancer and terminal illness related to living longer?"
] |
[
false
] | null |
[
"Too a large degree:",
"\"The total number of cancers is projected to increase by 45% from 2010 to 2030, driven largely by the growing number of older adults. By 2030, an estimated 70% of all cancers will occur among adults aged ≥65 years.\"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4544764/",
"Cancer rates when corrected for age are more or less stable, and survival rates are going up. So it's really aging that is the major driving force."
] |
[
"The longer you live, the more time you have to accumulate damage to your DNA that will eventually lead to cancer. A study in 2015 reported that a large portion of cancers can potentially be attributed to \"bad luck\", they found a very linear relationship between cancer type and stem cell division for that cell type. This may potentially be because as stem cells divide more often, they have more opportunities to develop a spontaneous mutation in their genome. Divide enough times, get more mutations, and boom cancer.",
"http://science.sciencemag.org/content/347/6217/12"
] |
[
"There's a direct correlation; most cancers are a disease of age due to the time it takes to acquire the mutations necessary for transformation. This can be influenced by environmental factors, genetic factors and just plain bad luck also. Indeed the mean age of diagnosis varies for different cancers, however you can see ",
"here",
" that age is a factor. "
] |
[
"During Polymerase Chain Reaction, Why does Taq polymerase only extend the primer-DNA hybrid upto 1.5 kilo base pairs and not beyond that?"
] |
[
false
] | null |
[
"Processivity has to do with the likelihood of the polymerase falling off the DNA. In cells there is a protein called the clamp which literally clamps around the DNA and anchors the polymerase to the DNA. This increases processivity enormously. Its not included in the PCR design because its an extra step that is hard to control by temperature alone and requires ATP to reload the clamp every time. For most gene lengths it turns out to not be necessary in a PCR."
] |
[
"PCR can also extend far beyond 1.5 KBP, it depends on the specific enzymes and reaction conditions but 1.5 KBP sounds like a limit placed by extension step timing on the thermocycler. We usually quote a 1 kbp/min line, but it can vary pretty heavily just based on something like GC content of the desired product."
] |
[
"Thanks"
] |
[
"I understand how visible light images are captured with a lens and 2D array of sensors, but not sure how radio telescopes create images. Is it just a single radiowave-sensitive sensor that is scanned across the sky to form a 2D image?"
] |
[
false
] | null |
[
"Typically, yes, a radio telescope has just one \"pixel\" which it needs to scan across the sky to get an image. There's no fundamental reason you couldn't have more than one pixel though - just shove more of those radio sensitive receivers into the focal plane. The trick is that those radio sensitive pixels can be physically big, expensive, maybe require cryogenic cooling, and the focal plane may not be a nice flat plane. Therefore it's an engineering question of whether it makes sense to add more pixels, or to just move the telescope more. Multi pixel radio receivers do exist (eg. ALFA 7 pixel array: ",
"http://www.naic.edu/alfa/",
"), though they are in the minority."
] |
[
"Radio interferometry. Imagine you have multiple radio telescopes, 1000 kilometers away. Depending on where the signal is coming from, it will reach one of the telescopes a bit earlier. You can use the time difference to work out the angle from which the signal is coming from.",
"Now, using complicated math you can scale it up to multiple telescopes across the world. You have to use incredibly precise clocks to keep everything synchronized.",
"https://en.wikipedia.org/wiki/Very-long-baseline_interferometry",
"https://en.wikipedia.org/wiki/Very_Large_Array"
] |
[
"In most cases yes. I don't know of any single radio telescope (as opposed to arrays) that can take a \"snapshot\" image.",
"For good efficiency the receiving element of the antenna - the wire that connects to the receiver circuitry - needs to be comparable in size to the wavelength. For typical radio astronomy bands this is somewhere between a few centimetres and tens of metres. If you tried to have a multiple \"pixel\" sensor with each pixel being that size, well, that's not very practical.",
"Even if you did try to build a multi-pixel radio receiver, the adjacent receiving elements would interfere with each other. When a radio wave hits a wire it induces a current and that current ",
" more radio waves. That's not a problem that exists with a CCD sensor for light. This is actually exploited in many antenna designs such as the Yagi; passive elements, just wires or rods not electrically connected to anything, will re-radiate incoming signals in such a way that signals from some directions constructively interfere and from other directions destructively, creating a directional antenna."
] |
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