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[
"Is using electronics such as iPads actually better for the environment than using paper?"
] |
[
false
] |
[deleted]
|
[
"I think this only holds if you are talking about using the iPad exclusively as a notebook, which is not how they are typically used. What about if you use it as an e-reader that replaces books, magazines, and newspapers? What about if you use it and e-mail/other electronic messaging services to replace postal mail? Think of it in the \"paperless office\" sense."
] |
[
"I think this only holds if you are talking about using the iPad exclusively as a notebook, which is not how they are typically used. What about if you use it as an e-reader that replaces books, magazines, and newspapers? What about if you use it and e-mail/other electronic messaging services to replace postal mail? Think of it in the \"paperless office\" sense."
] |
[
"No; but it really depends what you mean by better.",
"First: Paper isn't inherently bad for the environment. Unlike wood the majority of paper within a first world country comes from virgin pulp farms, tree farms planted and harvested every 4-5 years specifically for the use of paper. In fact we have more trees when paper usage goes up. Now this isn't universally true, but in a first world country pretty much is in majority of cases. Want more trees? Use more paper. Unlike wood, you don't need huge/old trees for use in making the product. ",
"Second: In reference to point 1, recycling paper may actually be detrimental to the environment more then just making new paper. Some things we recycle we really shouldn't be. The reasoning is collection, sorting, making back into pulp, and the recycling process uses more energy then just getting new trees to make paper. The reasoning is pretty simple if you think about it: Collect treesfrom a single farm/multiple farms and create paper OR collect from hundreds of thousands of locations, transfer it to various location, spend time sorting through types of paper/colour/unusable paper and then redoing the same process. However in some cases in the right way, it may use less energy.",
"http://en.wikipedia.org/wiki/Tree_farm#American_Tree_Farm_System",
"http://fhsarchives.wordpress.com/2011/06/12/american-tree-farm-system-turns-70/",
"http://www.carbon.sref.info/estimating/calculator",
"http://en.wikipedia.org/wiki/Paper_recycling",
"Third: IPads and electronics use a lot of rare earth materials that are pretty bad for the environment during mining procedures and industrial manufacturing. Not only that but also energy use through to environmental impact of where they end up after being disposed of. It is highly suggested we recycle electronics, they are wasted hazardous waste that won't decay readily, while throwing paper in the trash will decay fairly regularly. "
] |
[
"Why are allergies seemingly so much more prevalent today then in previous decades?"
] |
[
false
] |
It seems to me that, say, 20 years ago peanut allergies (for example) weren't nearly as commonplace as they are today. Peanuts were served on airplanes, practically everyone ate peanut butter and jelly sandwiches in elementary school, etc. Now, planes serve pretzels and many schools have banned peanut butter campus wide. Is there an environmental effect here? is it the way we process or breed peanuts? Whats going on here? One thought I had was that they might have been just as prevalent, but now are just more widely acknowledged, but that doesn't seem to match up with what I've observed. Peanuts being just a common example. I know there are plenty of allergies out there. Thanks for your expertise!
|
[
"This is a variation on the on-again off-again \"Clean Baby Hypothesis\" or \"Hygiene Hypothesis\". It is quite controversial, and has been for a long time. I used to work in allergic airway diseases back in the late 90s, early 2000s. This stuff was on the fringe when I started, got popular in the early 2000s, peaked with people importing gut parasites from Africa to take in pill form around 2004/5, and was then discredited towards ~2006/7. It has since gained traction again, and I am quite certain this cycle will continue for quite some time.",
"Personally, I fall into the \"It's a ",
" more complicated than that\" camp. It's not just infection or exposure or where you live or if mommy made you wash your hands too much. For example, it's not \"western society\", it's really more well correlated with being urban. The rule of thumb is farm kids don't get asthma. This may be due to hygiene, it may be DEPs, it may be a lot of things or it may be one factor we don't know about. Hell, it could be exposure to concrete for all I know....it's just unclear. Allergy is like that. ",
"Another complicating factor is the class and timing of exposures. Some exposures are potentially protective, others not so much, others promote allergy if the exposure is timed right, etc etc. ",
"I do think the concept of poor-context exposures plays a role, and I think you'd be hard pressed to find any scientist that would say it plays no role. However, it's far from a settled matter as to how important it is. "
] |
[
"This is a variation on the on-again off-again \"Clean Baby Hypothesis\" or \"Hygiene Hypothesis\". It is quite controversial, and has been for a long time. I used to work in allergic airway diseases back in the late 90s, early 2000s. This stuff was on the fringe when I started, got popular in the early 2000s, peaked with people importing gut parasites from Africa to take in pill form around 2004/5, and was then discredited towards ~2006/7. It has since gained traction again, and I am quite certain this cycle will continue for quite some time.",
"Personally, I fall into the \"It's a ",
" more complicated than that\" camp. It's not just infection or exposure or where you live or if mommy made you wash your hands too much. For example, it's not \"western society\", it's really more well correlated with being urban. The rule of thumb is farm kids don't get asthma. This may be due to hygiene, it may be DEPs, it may be a lot of things or it may be one factor we don't know about. Hell, it could be exposure to concrete for all I know....it's just unclear. Allergy is like that. ",
"Another complicating factor is the class and timing of exposures. Some exposures are potentially protective, others not so much, others promote allergy if the exposure is timed right, etc etc. ",
"I do think the concept of poor-context exposures plays a role, and I think you'd be hard pressed to find any scientist that would say it plays no role. However, it's far from a settled matter as to how important it is. "
] |
[
"Essentially yes. Your immune system is a thing that is continually changing throughout your life.",
"It's quite possible through repeated exposure to an allergen to develop an allergy, this is seen occasionally in bio labs where people pick latex allergies to the latex gloves. It is also quite common to slowly become resistant to an allergen which you are continually exposed to. Peopel with mild cat allergies living with cats are occasionally seen to go either way."
] |
[
"Are all snowflakes really unique?"
] |
[
false
] |
I understand that there are many different formations of snowflakes, but there are also a lot of snowflakes in the world. Thinking about it with respect to the birthday problem en.wikipedia.org/wiki/birthday_problem isn't it almost certain that some snowflakes are the same?
|
[
"They are nearly unique. Think about this - watervapor combines with dust particles to form snowflakes..and the path taken by the watervapor and the dust particles it comes in contact with determines the shape of the snow flake.. Endless combinations are possible"
] |
[
"Right. We need to be careful not fall into a pedantic trap here though.",
"One could extend this to state that essentially no macro structures are identical or that all are unique. There are nearly endless combinations of shape available depending on the level of detail you wish to examine and even regular structures are differentiated if you want to consider atomic scales or temperatures or whatever else you like.",
"The usual treatment of snowflakes as near-endlessly complex and varied is just fine of course though."
] |
[
"Depends, of course, to what degree of accuracy you want to consider 2 to be \"the same\".",
"You will find many that will be \"almost identical\" for any reasonable definition of almost."
] |
[
"How can Fourier expansions be made an integral?"
] |
[
false
] |
I see how a discrete Fourier expansion works by forming a linear combination of orthogonal functions. And when we write such an expansion, we are working in a basis of those orthogonal functions. So when we use the integral Fourier transform, are we working with a continuous distribution of basis functions? If so, are these continuous bases related to infinite dimensional matrices?
|
[
" In all, if you have a function F(x) from some domain D into the complex numbers, you can perform a Fourier Transform of it by comparing it with one of the fundamental functions from D into the unit circle inside the complex plane, which we can call E",
"(x). These functions fundamental functions will be parameterized by y in some other domain D",
" and the Fourier Transform will take F(x), whose domain is D, and output a new function F",
"(y), whose domain is D",
". In this case, F",
"(y) is the dot product of F(x) and E",
"(x), which is either the finite sum, infinite sum or integral of F(x)E",
"(x) over x in the domain D. Repeating this process for functions with domain D",
" will land us back into D.",
"This is quite literally how ",
" Fourier anything works. It goes under the name \"",
"Pontryagin Duality",
"\" and it can be applied to a large swath of mathematical objects, making it ",
" powerful. You can even derive the Riemann Zeta Function (and it's generalizations) from this kind of process over super abstract spaces in Number Theory (called Adeles)."
] |
[
"Instead of thinking of uncountable collections of basis functions, I think it's better to view both of your examples as a special case of what is called a \"Pontryagin dual group\".",
"If G is a locally compact abelian group (such as the real numbers modulo 1) , we call a function chi mapping G to the complex unit circle a character on G if chi(x +y) = chi(x)chi(y) for all x and y. When your group is the real numbers modulo 1, the continuous characters are as follows: we need chi(0) = 1. Unless chi is uniformly equal to 1, it is easily seen that there is a smallest rational number of the form 1/n for which chi(1/n) = 1. This character is the usual basis function e",
" ",
"The point is that the characters form a group under multiplication: In the case of the real numbers mod 1, this group is the group of functions of the form e",
" where n is an integer. This group is called the Pontryagin dual group, which I will call H.",
"The Fourier transform of a complex-valued function f : G-> C chi is a function f",
" defined on the dual group H: f",
" (chi) is given by the integral of f(x) chi(-x) with respect to the Haar measure- in the case of a function defined on a finite interval, the usual measure on the interval.",
"It turns out that if G is the group of real numbers under addition, the Pontryagin dual group consists of all functions of the form e",
" where s is a real number. This is why the Fourier transform of a function defined on the real numbers is another real valued function: the Pontryagin dual group is isomorphic to the real numbers under addition. ",
"So getting back to your question, I don't think it's really useful to view the Fourier characters as \"basis functions\" in the case where the Pontryagin dual group is uncountable. The functions e",
" are not orthogonal and do not form a minimal spanning set for L",
" (R)- in fact, these functions are not even in the space L",
" ! Nonetheless you can still piece together an L",
" function defined on the reals by knowing its correlation with each of the Fourier characters.",
"One difficulty that arises if you try to think of these continuous fourier characters as basis functions is that the Fourier inversion formula has an integral in it- and therefore depends only on the value of f",
" almost everywhere. So if you change the value of f",
" at finitely many locations, you'll end up with the same function f back out.",
"I think it's better to take the perspective that Fourier series and the Fourier transform are both special cases of the Fourier transform on locally compact abelian groups. If your LCA group has a nice, countable Pontryagin dual then you can view the Fourier characters as forming an orthonormal basis, but this perspective is, in my opinion, bad if the dual group is uncountable. "
] |
[
"All Fourier ",
" do the same thing. Take a function and find another function using properties of integrals (and sums) using it.",
"Take, for instance, periodic functions. We can wrap a periodic function around in a circle, so that it becomes just some function from the circle into the real or complex numbers. Now, there are very special function from the circle into the reals, the trig functions. These are special because they act like the fundamental \"nodes\" of vibrations on the circle. If we have some random function from the circle into the reals, we can then ask \"How do they compare to the fundamental functions?\" To do this we find, what amounts to, their dot-product. Just as in a regular dot product, where the vectors (a(1),a(2),a(3)) and (b(1),b(2),b(3)) go to the sum a(1)b(1)+a(2)b(2)+a(3)b(3) (ie the sum of a(n)b(n)), we will \"dot\" f(x) and, say, sin(x/N) by getting the ",
" of f(x)sin(x/n)over all x in the circle. This is the typical integral formula for the corresponding Fourier coefficient. ",
"Now, this isn't the whole story for periodic functions. One thing that is kinda clunky about how Fourier Series are typically introduced is that you have different ones for sine and cosine with special rules for what you're \"supposed to do\" for each. But we can combine the sine and cosine cases into a single case using Euler's Formula e",
"=cos(x)+isin(x). In this way, we combine the fundamental nodes into a function into the complex numbers. The interesting thing about this complex number is that it, too, lies on a circle, the unit circle inside the complex plane. So e",
" is a function from the circle into another circle. That is, e",
" ",
" the circle over itself one whole time. The interesting thing about this is that the Nth fundamental node corresponds to the function e",
" and this wraps up the circle around itself ",
"-times (use -N for a clockwise wrap). In this way, the Nth complex Fourier coefficient of f(x), f",
"(N), which is the integral of f(x)e",
" along the circle and acts like the dot-product, tells us how f(x) compares with the fundamental function that wraps the circle around itself N times. This means that f",
"(N) is the dot product between f(x) and exp",
"(x).",
"The interesting thing that is happening is that we are taking one function, f(x) from the circle into the complex numbers, and getting another function f",
"(N) that takes in ",
" and outputs complex numbers and tells us how f(x) compares with exp",
"(x)=e",
", the fundamental N-node function. So we take a function whose domain is the circle and output a function whose domain is the integers. ",
"What if we have any ol' function g(N) that takes in ",
" and outputs complex numbers? Can we use similar logic to take this integer domain function and get a circle domain function? To do it before, we compared f(x) to the fundamental functions from the circle into the circle. We should just try to do a similar thing here: Compare g(N) to the \"fundamental functions\" from the ",
" into the circle. In this case, the corresponding fundamental function will be the functions that ",
" the integers up evenly around the circle. Imagine we have the number line, with just the integers on it, and we try to wrap it up into a circle while keeping them evenly spaced (the spaces can grow, but they all have to be the same size). So if we always send 0 to the rightmost point (which is e",
"=1+0i) then, since we're keeping everything evenly spaced, we just have to choose one point on the circle to send 1. So if x is an angle between 0 and 2pi, then we can send 1 to e",
", which will mean 2 goes to e",
" and N goes to e",
". This means for every point on the circle, we have a function from the integers into the circle in the complex plane. These are our fundamental functions from the ",
" into the unit circle. Let's label these functions q",
". This means that q",
"(N)=e",
". ",
"If we want to try and get a function, g",
"(x), from the circle into the complex numbers from g(N), which takes in integers and outputs complex numbers, then we should do what we did in the original direction: Use their \"dot product\" to compare it to the functions q",
"(N) which, in this case, is the sum of g(n)q",
"(n) over all integers n. The value we get will depend on which x we choose on the circle for q",
"(N), so we are outputting a function from the circle into the complex numbers, which we can call g",
"(x). So the value of g",
"(x) is the dot product of g(N) and q",
"(N).",
"What is interesting is that the ",
" operation takes a function whose domain is the circle and outputs a function whose domain is the integers, and ",
" operation takes a function whose domain is the integers and outputs a function whose domain is the circle, so it is totally valid to do one and then do the other. In fact doing ",
" to f(x) and then doing ",
" to f",
"(N) will give f(x): (f",
")",
"(x)=f(x). This formula is the statement of the Fourier Series for f(x). Similarly, (g",
")",
"(N)=g(N).",
"This is a little peak of the behind-the-scenes for Fourier Series. Note that the integral for the Nth Fourier coefficient, and the Fourier Series evaluated at x are completely analogous. This is because integrals perform the same function as the familiar sum in the Fourier Series.",
"We then do the ",
" same thing for Fourier Transforms. In this case, instead of having the domain be the circle or the integral, our function's domains are the real line. We then want to compare them to the \"fundamental functions\" from the real line into the circle. This time, if r is any ",
" number, then Exp",
"(x)=e",
" will be a fundamental function. This is pretty much the same idea as with the integers, we're just trying to find all ways to wrap up the entire real line into a circle. The only difference is that because the integers are disconnected, we couldn't tell the difference between wrapping things around once or twice, sending 1 to e",
" and e",
" are exactly the same, for the reals wrapping around once or twice makes it stretch differently. So if f(x) is a function from the real line into the complex numbers, then we can compare f(x) to the rth fundamental function via the \"dot product\" of f(x) and Exp",
"(x) which, in this case, is the integral of f(x)Exp",
"(-x)dx over all the reals. This gives us f",
"(r), the Fourier Transform of r. ",
"The interesting thing about this is that the old domain for f(x) and the new domain for f",
"(r) is the same, whereas it changed in the Fourier Series case. In this case, going in the opposite direction just means finding the the integral of g(r)Exp",
"(r)dr. This is the inverse Fourier Transform, and we have f",
"(x)=f(x). Note that, in this case, the inverse Fourier Transform is completely analogous to the Fourier Series, (f",
")",
"(x)=f(x) just finding the dot product of something that we already took some kind of Fourier Transform of to get back the original function.",
"Finally, we have the Discrete Fourier Transform, which is used in CS a lot. All of the functions we've considered so far have infinite domains, but we generally can't work well with that in applications. So, instead of looking at function from integers, reals or circles into the complex plane, we'll look at functions whose domain is {0,1,2,3,...,N-1}, the first N non-negative integers. That is, these are function H(n) who input an integer between 0 and N-1 and output some complex number. H(n) can be a list of numbers, or a collection of data, or even an image where H(n) is the grayscale output of the n+1th pixel.",
"What are the \"Fundamental Functions\" from {0,1,2,3,...,N-1} into the unit circle in the complex numbers. This works a lot like the integer case, first we send 0 to 1 and then we just need to figure out where 1 goes and keep the rest of them evenly spaced. The only issue is that we only have N of these, so if we send 1 to just some random point, the final point where we send N could be non-evenly spaced. We get around this in the integers, because there is no \"last number\". In particular, these points must be vertexes on the Regular N-gon circumscribed on the unit circle. So we have N choices about where to place 1, e",
", e",
", e",
", e",
",...,e",
". In general, we can send it to e",
" and 2 will then go to e",
" etc. If we set q",
"(n)=e",
", then the functions q",
"(n), q",
"(n),...,q",
"(n) are all the possible fundamental function to compare H(n) with.",
"So, we can then get the \"dot product\" of H(n) and q",
"(n). In this case, it is literally the dot product, because these are both just finite lists of numbers. We then output H",
"(k), which is the dot product of H(n) and q",
"(n), and equals the sum of H(n)e",
" for n=0,...,N-1. ",
"Note that k can only be 0,1,...,N-1, meaning that, like the reals, the new domain is just itself. So the inverse transform for G(k) one will just be G",
"(n), the sum of G(k)e",
" for k=0,...,N-1. In this way, the Discrete Fourier Transform is it's own legitimate Fourier Transform, and not just an approximation of some other case (though, it does that too). The Discrete Fourier Transform is actually used in Number Theory quite a bit."
] |
[
"Is it possible for a beneficial virus to exist?"
] |
[
false
] |
Upon being infected, we become stronger, or increased mental capacity, etc. Does not have to be a virus specifically, could be bacteria or something else that usually is associated with causing sickness.
|
[
"Pretty sure Bacteriophages count",
"http://en.wikipedia.org/wiki/Bacteriophage",
"They are viruses that specifically target bacteria. They have been used as anti-biotic treatments and are also used to help keep food fresh since they kill the bacteria that might make it go bad."
] |
[
"I know of a few interesting examples but not any that perfectly resemble what you are talking about.",
"Retroviruses are viruses that add their DNA to the infected cells. Most of the time this just causes the cell to create new Retroviruses. However these bits of DNA can be passed on and become valuable parts of the infected creatures DNA. ",
"wiki can go over the details better then I can",
"These same kinds of viruses are the perfect tool for humans to use to stick new DNA in to our selves. This is better known as Gene therapy. It's the best hope for people with genetic defects. They did some really interesting things with AIDS to cure cancer in one case. ",
"http://www.jdjournal.com/2012/12/10/reprogrammed-aids-virus-successfully-cures-child-of-leukemia/",
" Not sure that counts as gene therapy but its a similar idea.",
"In the area of bacteria the most known example is all of our gut bacteria. Wiki can explain it better then I can. ",
"Though people can survive without gut flora, the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful, pathogenic bacteria, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats. ",
"Link",
"Finally it's thought that mitochondria were once bacteria that have become permanent parts of cells. Read up on ",
"Endosymbiotic theory",
" for more. "
] |
[
"Wow thanks for all the info. Are there any known retroviruses that are naturally transmitted (air/water/etc.)?"
] |
[
"Why does orange \"A\" taste bitter, but orange \"B\" is sweet?"
] |
[
false
] |
[deleted]
|
[
"Fruits develop and ripen individually regardless of what tree they're on or when they're harvested. In early stages of growth they're bitter/sour to discourage creatures from eating them before they're ready to spread their seeds.",
"In oranges in particular, as they ripen citric acids become diluted, the various bitter compounds are broken down and sugars accumulate. Citrus fruits must remain on the tree to accumulate more sugars and so reach their maximum sugar content (sweetness) at the moment they're picked.",
"So in this case, one of those was simply not ready to be harvested."
] |
[
"So every time I go to buy one, I am rolling the dice as to getting a ripe vs unripe orange? =/"
] |
[
"Pretty much, but they're loaded dice in your favor. Producers do try to get them at the right point of ripeness, but they don't check each fruit - they harvest whole trees, as there's no other way to produce in volume."
] |
[
"Are there any animals that do not feel physical pain? If so, how does this work?"
] |
[
false
] | null |
[
"There is a genetic disorder in which some people are pain insensitive due to a problem producing pain fibers.",
"http://en.wikipedia.org/wiki/Congenital_insensitivity_to_pain_with_anhidrosis"
] |
[
"what about animals?"
] |
[
"In general, we can only judge this behaviorally, so it's hard to tell. We measure pain in terms of response to potentially damaging stimuli. More or less anything you'd want to call living demonstrates averse responses to certain stimuli, so there's a case to be made for calling this pain.",
"One can take this too far in a sense: one might want to think of a single celled organism responding to noxious stimuli as not feeling pain the same way as we are - but it's hard to tell where to draw the line (we're just responding to stimuli too). The experience of an amoeba is probably not as rich as that of a human - we don't really know what it's like to be something radically different from ourselves, so we don't really know how to characterize the experience of nonhumans.",
"A good rule of thumb is this: the more an animal's nervous system has functional traits in common with ours, the more its experience is like our own. The functional system for physical pain in most animals with a nervous system is pretty similar to ours, so there's reason to believe their pain experiences are like ours.",
"Not experiencing pain (or at least reacting to damaging stimulus) is, in general, not an adaptive trait. As whatdc points out, there are people with pain insensitivity - they tend to die quite young, as they destroy their own bodies without noticing."
] |
[
"Are asymptomatic people meaningful vectors of transmission of COVID-19?"
] |
[
false
] |
Two of the main symptoms of the flu are sneezing and coughing. These symptoms also help A LOT in transmitting a respiratory disease. Considering that COVID-19 asymptomatic people don't sneeze or cough, are they really meaningful vectors of transmission?
|
[
"Yes. Numerous studies have shown that the SARS COV 2 virus is aerosolized, which means it is emitted in infectious quantities in normal breathing and talking. No coughing or sneezing is necessary for transmission."
] |
[
"Agreed. This is why Covid-19 is so dangerous. If people were sneezing and coughing they would know to quarantine. In this case they don't and become great spreaders."
] |
[
"Sure. Here's a review paper that has links to multiple studies throughout. ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293495/",
".",
"Another",
"Another",
"Another",
"And here's the October update to the ",
"CDC guidelines",
" where they finally acknowledged aerosolized transmission.",
"Many, many more studies available - Google \"Aerosolized Covid\" for days worth of reading if you're so inclined."
] |
[
"How do we know that certain animals are colorblind?"
] |
[
false
] |
Any examples of testing animals, as obviously they can't talk?
|
[
"If by this, you mean that the whole species cannot see a certain color, instead of say an abnormal individual: ",
"We have different proteins called opsins found in each type of color-sensitive cone in our eyes that are responsible for us being able to see these colors. These proteins absorb light most effectively at different wavelengths (or colors) of light. In humans, this means, for example, that we have cone opsins that best absorb red, green, and blue light. These 3 types are all we need to see all of the colors that we do, and they are coded for in our DNA by specific genes (rods have a fourth, but they are not involved in color discrimination). ",
"So, in animals there are ways to figure out what colors they are probably able to see based on by comparing their genome to ours, for example. Opsin genes are similar enough that we can figure out if a dog, or a monkey, etc. has a \"red\" opsin or not, for example. Based on the sequences of their opsins, as well as the combination they have, we can determine what colors they are likely to be able to see. ",
"There are also behavioral measures that can be used. One such experiment looks at the optokinetic response. This is basically the tendency for an animal's eye to follow the direction of objects across the visual field. To test this with color discrimination, you can create a \"drum\" (which is just a moving ring that the animal sits inside and takes up its visual field) that has vertical stripes made of 2 colors (of course, controlled for brightness), like red and green if you're testing if the animal can tell the difference between the two. When the drum starts moving, if the animal's eyes \"track\" the movement of the stripes, you know that they can discriminate between the colors. If they do not, then you know they can't tell the difference and cannot see the stripes. ",
"There are other behavioral measures, as well, for testing this. And I'm not sure how many animals this test could be used in. This is just an example of how this could be done. (There was a recent paper with monkeys that uses reward conditioning, instead) I hope this helps! Sorry it's so long. "
] |
[
"Oh thank you for an awesome reply!"
] |
[
"You could look for the opsin genes but I would look for the protein in an actual specimen to prove that it's there and potentially functional. You would fix the animal in paraformaldehyde, get a thin slice of its eye, and then do some immunohistochemistry. You would use a primary antibody to detect the three opsin proteins (green, red, and blue). ",
"http://www.millipore.com/catalogue/item/ab5405",
" To actually see where the protein is in the eye, you would add a secondary antibody with tag and visualize it under a microscope. "
] |
[
"If a male has very high-functioning Aspergers Syndrome (to the point that it isn't even noticeable by others), how much more likely are his children to have an autism spectrum disorder?"
] |
[
false
] | null |
[
"Good question, I'm also interested in the answer. My son has Aspergers and it's pretty apparent, though his is by no means crippling. I'm going to suggest when he's a teen to really consider reproducing though because he also has Neurofibromatosis 1, which is 50% inheritable."
] |
[
"Here's a Wired article",
" about the rising prevalence of Autism-spectrum disorders in Silicon Valley, which some attribute to lots of geeky people (who have some but not all of the traits associated with ASD) having kids with each other. There's probably some relevant information for you in there."
] |
[
"I'm not here to give you medical advice. ",
"But I will tell you what I know about autism inheritance patterns: it's complex and we don't know as much about it as we do for, say, cystic fibrosis. The inheritance pattern isn't all simple mendelian genetics - it's a heterogenous mix of inheritance processes. ",
"Some level of risk of getting autism is determined by the accumulation of certain multiple susceptibility single nucleotide polymorphisms (SNP) in currently identified high risk genes. ",
"This study",
" found that an average sibling risk based on a bunch of data is 3%."
] |
[
"What is the most efficient way to breath while running?"
] |
[
false
] | null |
[
"I ran track through college (sprinter). I generally found that your body is going to tell you what it needs, and you are going to breathe correctly no matter what. One thing you probably already do naturally is breath in rhythm with your stride, and I feel that is important. \nThat being said the other two comments are correct. Biologically speaking, aim to breathe through your nose as much as possible. Once your aerobic threshold is reached/passed, you will start breathing through your mouth pretty fast.\nAs an aside, if you feel like you are not getting enough air, or are using your accessory muscles to breathe harder (chest muscles, not just your diaphragm), you may want to try taking a few quick breaths through pursed lips (like you are blowing out candles). The positive pressure in your lungs can help expand/inflate them a little more, so you can get that little extra bit of air in."
] |
[
"If you breathe in through your mouth you get more air in, but if you breathe in through your nose, the conchae/sinuses etc warm and humidify the air, conditioning it for your lungs. Breathing out doesn't require the same, as it remains conditioned until it leaves your body.",
"Breathing in through your nose will delay that lung burning feeling, so you should breathe in through the nose and out through the mouth for as long as possible.",
"EDIT: I'm not a runner, so I only have a narrow perspective."
] |
[
"Inhale deep through the nose and exhale through the mouth. "
] |
[
"How do you feed someone in a coma?"
] |
[
false
] | null |
[
"Med student here. There are a few options depending on the needs of the patient and how long they are in a coma for.\nMost of the time we will run a tube from the patient’s nose, down their throat and into their stomach. We then run a complete liquid formula through the tube that provides the patient with all the nutrients they need.\nIf the patients in a coma long term then we might do a minor surgery to place a tube directly from the patients abdomen into their stomach through which we will run the same formula.\nIf a patient’s digestive system isn’t working then we do have complete intravenous nutrition which typically gets delivered through a small tube that through one of their veins and delivers the nutrients into the blood near their heart. This isn’t a great option long term though because it comes with a big infection risk!"
] |
[
"The digestive system is basically a mechanism for breaking food down into microscopic nutrients that are so small they can cross into the blood stream in the small intestine. The large intestine's main function is to provide water and salt balance in the blood stream as well as removing waste particles (like dead and broken apart red blood cells) from the system to flush out along with undigested foodstuffs.",
"The blood system then takes these nutrients around the body for immediate use, or through storage processes (here comes the liver!) to be used later."
] |
[
"Wow thank you!",
"I'm betting all of these processes are quite costly...",
"regarding the last option, how is blood getting the nutrients able to support the entire body?"
] |
[
"What in physics is fundamental?"
] |
[
false
] |
Okay so I've had this question for a long time and got a variety of answers. If I were making a list of the fundamental laws of the universe, what equations, constants, and background knowledge would need to be on it? Would it just be Einstein's field equations and the standard model (can you write the standard model in one equation)? Would any equations that explain quantum or newtons laws be necessary or are these derivable from more basic laws? How bout the speed of light? Can everything we know be summed up in one equation like the photo posted? Thanks for any insight you can offer
|
[
"Nothing we know ",
" to be on the list of fundamental laws. The image you posted, by Sean Carroll, is a compact writing of the theories that so far describe just about every observation we've ever made. But this is only an ",
", meaning it only works below some energy scale. That's the meaning of the \"k < Λ\" in the integral at the very beginning of the equation - this is only supposed to work for energies (roughly, k) below some \"cutoff scale\" (Λ) where our laws of physics break down and need to be replaced by something more fundamental. This Λ is probably no larger than the Planck scale, and can potentially be quite a bit smaller. We have, almost by definition, no firm idea of which principles in physics are going to hold at energies far above Λ. It's all open for now, as it should be.",
"But what if we ignore that point, and just ask about the most fundamental physics that we know of? Then the answer, which is meant to be summed up compactly in that equation, includes a few things:",
"The Standard Model can be written in many ways, and the second line of that equation is about as compact a way as you can do it.",
"You should definitely check out Sean Carroll's discussion of that equation, and how it's meant to summarize all of known physics, ",
"here",
"."
] |
[
"From what I can see, that says ",
" equals a whole bunch of other squiggly lines and stuff. What does the ",
" represent?"
] |
[
"As ",
"/u/RobusEtCeleritas",
" said, you'd be hard-pressed to find a better explanation than Carroll's. But that is probably geared at a lower level than physics undergrad, so for that audience, I can add a few things.",
"First, the part labelled \"quantum mechanics,\" as well as the \"W\" on the left-hand side, has to do with the ",
"path integral formulation",
" of quantum mechanics. This is a way of thinking about quantum mechanics that is probably not what you learned in your intro class, but happens to be much better-suited to describing a wider range of physical phenomena. In quantum mechanics, you compute probabilities for various events to occur. You get this probability (roughly) by squaring an ",
", and that's what we're computing, W. This amplitude is, in the path integral formalism, given by an integral (as you'd expect). It's not quite a normal integral, as indicated by the unusual [Dg], [Da], etc., instead of something like dx.",
"The things you're integrating over - in that equation, g, A, ψ, and Φ - are ",
". They're the underlying mathematical objects that give rise to particles and forces. You might be familiar with some of these - for example, A is a vector which represents the electromagnetic field (as well as the fields for the strong and weak nuclear forces). If you've studied Maxwell's equations, you might have heard that the electric and magnetic field can be re-expressed in terms of a scalar and vector potential. If you combine them into a four-component ",
" vector, in order to be compatible with relativity, then you have precisely that vector A. Then we have g, which is a matrix representing the curvature of spacetime - it's the gravitational field. While you won't have learned to think about the gravitational field as a ",
" unless you've taken general relativity, in the Newtonian limit (small speeds and weak gravitational fields), this matrix boils down to a scalar, which is the usual 1/r gravitational potential. Then ψ represents the various matter fields, for things like electrons and quarks, and Φ is the Higgs field, which gives rise to the Higgs boson.",
"Now you'll see that the path integral is of the form W = ∫[D fields] e",
", where S itself is an integral over d",
"x, containing the last term of the first line and all of the second line. This S is an extremely important quantity in physics. It's called the ",
", and you've probably already seen it in several guises, most notably in Lagrangian mechanics. In classical mechanics, you have a Lagrangian for some system, call it L = T - U, the difference of the kinetic and potential energies. You may have learned that if you use the Euler-Lagrange equations to find a path that minimizes L, you recover the laws of classical mechanics. Another way to derive that Euler-Lagrange equation is by integrating the Lagrangian over time, S = ∫L dt. That integral is precisely the action. You can calculate the action for all the various paths a particle can take, and you'll find that the Euler-Lagrange equations pick out the path that extremizes (minimizes or maximizes) S. So the action provides another perspective on Lagrangian mechanics - starting with an action S, you can obtain the equations of motion for a physical system. And, indeed, all this path integral rigamarole serves to generalize that to include quantum mechanics, by allowing you to derive quantum probabilities from S. In nearly all of particle physics and gravitational physics, the action is what defines a theory. When you write a new theory, your starting point is nearly always some action, S.",
"So in this equation we're not actually finding the paths which minimizing our Lagrangian, but instead using the Lagrangian to weight our path integral and then doing path-integral quantum mechanics to determine which paths are most likely quantum mechanically. As you'd guess, the probability is usually highest for paths which minimize the Lagrangian, so this really does generalize our understanding of Lagrangian mechanics to a quantum setting.",
"Now let's look more deeply at the action S in that equation. As a reminder, it's everything in the curly brackets apart from the i. First, notice that it's an integral over d",
"x, rather than over dt as in classical mechanics. This is just to include relativity, which treats space and time on equal footing. Similarly, the sqrt(-g) factor after the integration measure is also there to keep things kosher from a relativistic point of view. You're allowed to change your coordinates freely, since physics doesn't care what coordinate system you use, but if you change coordinates you'll change d",
"x. The sqrt(-g) factor, where g is the determinant of the gravitational field matrix, changes in the opposite way so as to keep the whole thing invariant. You'll have seen this in multivariate calculus - if you're integrating something in Cartesian coordinates in 2D, you'll integrate over dx dy, but if you integrate in polar coordinates, you integrate over r dr dθ. The r in front is nothing other than the 2D version of sqrt(-g).",
"Now we're finally at the meat of things, which is the quantity in the square brackets. This is called the Lagrangian density, or usually just the Lagrangian (though it's not ",
" the Lagrangian L from classical mechanics - you may be able to see why). This contains all of the information about what particles and forces exist, how they evolve, and how they interact. All the stuff we've gotten to before was just setup - telling us that we have quantum mechanics, and setting it up to work in a relativistic context. The Lagrangian is where the actual physics comes in. That we have been able to determine this Lagrangian, describing the Standard Model and general relativity, is one of the greatest intellectual accomplishments in human history.",
"The first term in the Lagrangian, M_P",
"/2 R, is called the Einstein-Hilbert Lagrangian and gives you general relativity. It tells you how the gravitational field, that matrix g which encodes information about the curvature of spacetime, evolves. M_P is called the Planck mass, and it's related to Newton's gravitational constant (as well as hbar and c, which we'll ignore). It sets the strength of gravity. By finding which paths extremize the Einstein-Hilbert action, you obtain Einstein's equations of general relativity, which generalize Newton's law of gravitation. It tells you how spacetime curves in response to matter and energy.",
"The second line, the rest of the Lagrangian, is the Lagrangian for the Standard Model of particle physics, written in an extraordinarily compact notation. The first term, -1/4 F",
" (with a bunch of indices), is the Lagrangians for electromagnetism, the strong force, and the weak force all summed up. For electromagnetism, F is the ",
", which is an object you're likely to run into at some point in an undergrad physics major. It's an antisymmetric 4x4 matrix that contains the electric and magnetic fields. If you find paths that minimize the electromagnetic Lagrangian, which is the trace of the square of that matrix F, you end up with Maxwell's equations.",
"The next two pieces, labelled \"matter\" and \"Higgs,\" are the Lagrangians for the various matter fields and the Higgs field. You'll learn more about these in a quantum field theory course. The equations you get by minimizing the matter Lagrangian tells you how quarks, electrons, etc. behave, including the electromagnetic, weak, and strong forces. These equations are responsible, in wildly complicated ways, for the formation of all the matter that we deal with in our lives, of course. And then finally the Higgs Lagrangian leads to equations of motion which tell you how the Higgs gives particles masses."
] |
[
"telescopes"
] |
[
false
] |
perhaps this is a stupid question, but I don't understand optics very well and I was just curious about this: if you shine a flashlight forward through a telescope, what would happen? And backwards?
|
[
"Less concentrated than at its source though."
] |
[
"if you shine a flashlight forward through a telescope, what would happen?",
"If you hold a flashlight up to the eyepiece of the telescope, its light will be sent up wherever the telescope is pointing.",
"And backwards?",
"If you put a flashlight in front of a telescope's primary mirror/lens, the light will mostly go to the eyepiece (although since the light is really close it will be out of focus and some will be reflected back out of a mirror, or in a refracting (lens-based) telescope will hit the insides of the telescope tube.",
"When trying to point an amateur sized telescope, one technique to tell where the telescope is pointing is to put a green laser pointer up to the eyepiece, and then it will point straight at wherever the telescope is pointing."
] |
[
"will it in any way concentrate the light?"
] |
[
"Is there any REAL difference in retention between audiobooks and hardcopy books?"
] |
[
false
] |
I've searched for evidence and cannot really find anything compelling. I often hear it suggested that reading ebooks results in lower comprehension and retention, but I was not able to find any good studies comparing either modality to audiobooks. I know there are people who are auditory learners vs. others who are visual learners so I would expect that makes the question harder to study. I was hoping some of our psychology friends could chime in! Thanks.
|
[
"What you found is comparing e-journals to print journals, I think OP wants to know if there's a difference between audio and print"
] |
[
"Yep! That’s what I’m looking for and NCBI/Google Scholar searches aren’t coming up with much. "
] |
[
"You haven't found anything very compelling because there's not a ton out there that's conclusive! Part of what needs to be considered is HOW we're measuring those differences. In the body of your question, you talk about comprehension and retention - which are two good metrics for understanding individual differences, for sure.",
"However, inter-individual differences come in to play there. While there isn't much evidence to support the anecdotal auditory-versus-visual-learner distinction (see ",
"this",
" for an overview of that subject), there has been good evidence to suggest that, in general, people remember or retain information somewhat better depending on modality.",
"State-dependent memory or learning is something covered in most basic psychology classes, but more in-depth research has been done on the difference between visual and auditory stimuli in these types of situations. There have been a few studies over the last decade investigating this question, but ",
"here",
" is a good rundown from Nat Geo of some of what's been studied.",
"Personally/anecdotally, I find it a lot harder to sustain attention with audiobooks--it seems much easier to \"zone out\" while listening versus reading, so it takes a lot more attentional effort and concentration for me. ",
"I should also note I'm not a researcher; I'm a clinical psychologist, so I don't presume to be an expert on this research, but hopefully my answer is somewhat helpful!"
] |
[
"Why would an increase in mean free path mean an increase in thermal conductivity?"
] |
[
false
] |
If I'm understanding this correctly, mean free path is the distance an energy carrying molecule must go before a collision, which is when the energy is transferred. If the path is longer, wouldn't that mean energy is transferred less often or efficiently, making it a better insulator?
|
[
"Remember that the units of thermal conductivity are W/m/K. Thermal conductivity measures how quickly heat is allowed to travel across a length of a substance. If energy carriers (electrons and phonons in solids, molecules in fluids) have a large mean free path, that means that they're allowed to travel a long distance before depositing energy elsewhere, which means that the energy gets spread around a larger distance in the same amount of time. "
] |
[
"Here is an approximation-heavy perspective.",
"Suppose quanta of heat jump around the lattice ",
"randomly",
". Thus the distance traveled after a time t is ",
"*sqrt(",
"*",
"), where ",
" is the average jump distance and ",
" is the average jump rate. By analogy (explained on the wikipedia page) ",
", the diffusivity, or ",
", the thermal conductivity, goes as ",
"*",
".",
"In popular usage, the jump distance ",
" is assumed to be the mean free path while the jump rate ",
" is assumed to be approximately constant (actually, it is often assumed to rely on an energy barrier and the temperature but I am skipping this for now). This tends to give a good agreement with experiments, but it implies that the time spent jumping is negligible (so the jump rate does not depend on jump distance).",
"What if we instead assume the jump rate depends on jump distance? Specifically, what if ",
" goes as ",
"/",
" for some average velocity ",
"? For ",
" conductivity",
" that is a perfectly reasonable assumption that also gives good results. We find that ",
" is proportional to ",
" (plus some constants), so after cancellation ",
" conductivity once again scales as ",
". However, this is because there is an external driving force and we find the average velocity by integrating over the distance ",
" assuming we started at a stand still.",
"There is a \"force\" for thermal conductivity (called the thermal driving force, and it is referenced ",
"sometimes",
") but it is a side effect of the thermal gradient so the \"force\" only exists as a statistical effect, not a true force acting on a single particle. Because of this the explanation I gave about electrical conductivity doesn't seem like it should apply here (though the result is correct).",
"Regardless, the fact that the conductivity scales (very roughly) with the mean free path has plenty of experimental evidence. All the models I have discussed are pretty simply approximations and phonon/electron simulations would give much more accurate results."
] |
[
"means that the energy gets spread around a larger distance in the same amount of time.",
"But why is it the same amount of time? Shouldn't it take longer because it's farther to travel? "
] |
[
"Do electrons \"teleport\"?"
] |
[
false
] |
I assume the answer is a resounding "no," so other possible titles: "How do electrons pass through nodes", "How do electrons 'move'", Do electrons "move"? I may be exhibiting a supreme ignorance here, as I know it's all a lot more complicated than I begin to understand, but it's my (flawed, I think) understanding that electrons exist, delocalized, in a probability state (definitely wording that wrong). That meaning that at any given time an electron in a certain orbital has a certain percentage chance of being at any of a number of locations in relation to the nucleus. Now, there are some locations, nodes, that the electron cannot possibly be at - ever. In order to "cross" this node, does the electron not have to move in some way other than "through space" as we know it? Finally, it is also my understanding that that probability curve of the location of the electron at any given orbital is asymptotic. Does this mean that at any given time there is a > 0 probability that an electron in a given atom can be a lightyear (or any distance, really) away? I'm working off of two years of high school chemistry, a year of high school physics and a year of college chemistry and a healthy dose of curiosity and personal research. (Also: I know that if they did "teleport" that would not conform with "nothing can travel faster than the speed of light" which is why I'm thinking I'm flawed somewhere in my "logic." I'm hoping someone can show me where I'm flawed rather than just tell me that I'm flawed.)
|
[
"In order to \"cross\" this node, does the electron not have to move in some way other than \"through space\" as we know it?",
"This is something of an interpretational question. The more common view would be that there's simply no meaning here to the idea that the electron has a definite location. The location-probabilities given by its orbitals (which are the things with nodes) are as close as you can get. ",
"Now, in the Bohm interpretation, these orbitals are statistical ensembles of continuous trajectories, under the influence of a 'quantum force'. But that force (or potential) is ",
". That means that you could say that, rather than having electrons moving in a mysterious, discontinuous, manner in space, you have a mysterious force acting on them in a mysterious, discontinuous manner in space. But this is a minority view, and there are quite a few difficulties with it. (One, which was enough to put Einstein off the idea, is that one of the consequences is that the electron in the ground-state hydrogen atom is actually stationary in space)",
"Does this mean that at any given time there is a > 0 probability that an electron in a given atom can be a lightyear (or any distance, really) away?",
"Yes. But they still can't move faster than the speed of light and violate causality. If the position of the electron is 'measured' and thus known at one point in time, there's a zero probability of finding it outside its light-cone."
] |
[
"It's not the electron is in some particular place, and we just don't happen to know where. The electron is in the entire orbital, and it is literally meaningless to talk about which ",
" of the orbital it's \"actually\" in. There is a probability distribution, but that just describes the locations the electron could be in if you collapse the orbital wavefunction and force the electron to localize. As long as you don't do that, the electron just does not have a meaningful location other than in the orbital.",
"And technically, yes, the probability distribution includes a nonzero value for points a light year away. But it extremely ",
" close to zero, so for every practical and theoretical purpose it is accurate to just say that the electron cannot be a light year away."
] |
[
"I think you are thinking about the electron wave as being like a \"standing wave\". That is a good way to visualize....but there is one fact that you should keep in mind. The \"wave\" is quantized in terms of \"energy\" and not position. So the nodes and anti nodes are in energy and not in positions as such. The shapes of the orbital that you see in the books are not in \"position\" but in \"energy\" (and \"momentum\").",
"I don't do much quantum chemistry, my area is more towards electronic structure and quantum transport in solids. In solids too we get similar forbidden \"bands\" where electrons cannot stay. Principles are the same and these \"nodes\" and \"bands\" can be calculated by solving Schrodinger Equation (view it as quantum version of Newton's Equations of motion).",
"EDIT: I should probably tell you that in introductory mechanics courses the description of objects are typically in position and velocity. The reason is that it is closer to our daily life experience. A little deeper analysis tell us that it is often easier to calculate things in terms of energy and momentum. That is why advanced classical and quantum mechanics is always framed in terms of energy and momentum."
] |
[
"When betting on the result of a flipped coin, is it always probabilistically advantageous to bet on the opposite of the most recent flip, given that in each iterative flip it's less likely that it will continue to be that same result?"
] |
[
false
] | null |
[
"This is the very ",
" of the gamblers fallacy. "
] |
[
"Granted.",
"So let's use a caveat of the Gambler's Fallacy. Let's say that instead of betting on an individual coin flip result, you're betting on a streak. Let's say you're betting that the coin will land on heads ten times in a row. Or twenty times. Or thirty times.",
"At what point does it become statistically unreasonable to expect the streak to perpetuate? Winning a million dollars on a bet of two heads in a row is a no-brainer, go for it, but three? Four? Five? When does it become ",
" that the cost (whatever it may be) is outweighed by the unlikelihood of it?"
] |
[
"Betting on a series of events is equivalent to betting on the individual events sequentially. This is because of the independent nature of the trials.",
"You are confusing yourself because you are trying to use the probability of the sequence, in place of the probability of the next flip. Specifically letting ",
" be a sequence of events for ",
" coin flips. ",
"Now, the probability of any sequence ",
" occurring is ",
", so yes a string of ",
" heads is practically much impossible. But, if you had witnessed 39 heads straight, you must factor this information into the probability, you want ",
" instead of ",
". Of course, due to the independent nature of the trials, this is equal to ",
".",
"So continuing with the ",
" straight heads example. The probability that ",
" straight heads occur is ",
", but the probability that ",
" straight heads occur given that you have already witnessed ",
" is ",
". This extremely unlikely event has now become more likely given your observations."
] |
[
"Is it possible to build a circuit or electronic device in such a way that it wouldn't matter which way you insert the batteries?"
] |
[
false
] |
I tried googling this answer, but all I got was tutorials for beginner circuitry projects.
|
[
"Note that this also wastes a significant amount of power, as there's a voltage drop over the diodes. Even if you use ideal diodes (circuits that approximate the behavior of a diode with no voltage drop), it still consumes something.",
"Edit: The term \"ideal diode\" seems to make a lot of people upset. It has two definitions:",
"A theoretical circuit element that allows current to pass in one direction but not in the other, with no voltage drop, and no reverse breakdown at any voltage.",
"A real-life circuit which approximates this behavior. Because it's in the real world, it has some loss associated with it.",
"EEs tend to talk about the second definition because they're a thing that we use, you can buy them on Digikey. I guess physicists talk about the first?"
] |
[
"Note that this also wastes a significant amount of power, as there's a voltage drop over the diodes. Even if you use ideal diodes (circuits that approximate the behavior of a diode with no voltage drop), it still consumes something.",
"Edit: The term \"ideal diode\" seems to make a lot of people upset. It has two definitions:",
"A theoretical circuit element that allows current to pass in one direction but not in the other, with no voltage drop, and no reverse breakdown at any voltage.",
"A real-life circuit which approximates this behavior. Because it's in the real world, it has some loss associated with it.",
"EEs tend to talk about the second definition because they're a thing that we use, you can buy them on Digikey. I guess physicists talk about the first?"
] |
[
"Yes, a simple filament bulb doesn't care about polarity. ",
"This circuit",
" functions identically if you flip the cell around. ",
"But more complicated electronic circuits (definitely anything that starts to resemble a computer) will almost certainly contain diodes and other components which require current to flow in one specific direction. "
] |
[
"What happens if you shine a laser while you're at light speed?"
] |
[
false
] | null |
[
"You can't go at light speed. When you fire a laser it will always appear to go the speed of light in your reference frame, unless you fire it through a medium where it travels slower."
] |
[
"Nothing would happen. You would observe the light moving away from you at the speed of light, as per usual. Your velocities wouldn't compound. Space and time will deform in a way that you and the light emitted from your laser will both move at the speed of light."
] |
[
"I'm not certain that the electronic components would function the same way once they are made of energy instead of matter."
] |
[
"For years I have sporadically experienced something that I have called \"blink sleep\" for lack of a more technical term. Can anyone tell me how it works?"
] |
[
false
] |
[deleted]
|
[
"While I agree that staying only in Stage 1/2 NREM would explain the continuation of thought, I wouldn't describe it as a variation of normal, and I'm not sure it explains the other aspects of OP's experience. That said, I don't have a better explanation, other than noting that people have repeatedly been shown to have horrible ability to accurately report experiences during the times in and around sleep."
] |
[
"While I agree that staying only in Stage 1/2 NREM would explain the continuation of thought, I wouldn't describe it as a variation of normal, and I'm not sure it explains the other aspects of OP's experience. That said, I don't have a better explanation, other than noting that people have repeatedly been shown to have horrible ability to accurately report experiences during the times in and around sleep."
] |
[
"It's not very accurate; it goes based on the idea that you're going to move around more depending on your place in the sleep cycle. Actigraphy has been shown to correlate to standard polysomnography, but I'm not sure how well established that is."
] |
[
"Was Tesla really that good?"
] |
[
false
] |
[deleted]
|
[
"I am pretty sure that all of Tesla's discoveries would have been found without him, but his personality brought them into existence. He had some great ideas he also had some very strange ones. The use of alternating current vs direct current for electrification of society certainly is his greatest acknowledged contribution. He never bothered to patent wireless communication he was more interested in the wireless transmission of power. If you build a radio and don't know it does it count?",
"Tesla developed the AC electric motor making everything from blenders to electric locomotives possible. Tesla tweaked all sorts of technology in his day making improvements in numerous devices.",
"Yes Tesla was brilliant. He also failed at translating his genius into a financial success. He died broke and pretty much alone and all but forgotten. "
] |
[
"I'm pretty sure all of every great scientists discoveries would eventually been found without him. Newton's work? Revolutionary, but would've been figured out shortly afterward. Darwin? Someone else had actually figured out his exact same theory at the same time. Watson and Crick? They just got lucky, Linus Pauling probably would've figured it out within a couple years if Watson/Crick didn't once the US government stopped targeting him for being a communist.",
"It's what distinguishes science from art."
] |
[
"Hardly \"all but forgotten\". I still remember the ",
"Tesla coil",
"."
] |
[
"Why do different elements vary in color/properties if they're all made out of electrons, neutrons, and protons?"
] |
[
false
] | null |
[
"Why don't all buildings look the same if they're built out of bricks and girders? Because there are different ways of arranging them. The same applies to atoms.",
"The vast majority of the properties of atoms (including colour) come from the arrangement of their electrons. Atoms are electrically neutral, so they have the same number of protons and electrons. Since an element is defined by the number of protons in its nucleus, then it follows that each atom of a different element has a different number of electrons. Things with different numbers of electrons are going to behave differently - some might want to get rid of a single electron, others might want to gain a single electron, there might be more 'room' for the electrons to be excited in a specific way in some, some might have some sort of isolated electrons that give them magnetic properties."
] |
[
"Going along with this, the different amount of electrons and electron shells affect how the atom absorbs and reemits or reflects photons in the visible light spectrum. Simply put, an atom with many electron shells will affect light of a certain wavelength, whereas an atom with less electrons will affect light of a different wavelength (of course wavelength here would correspond with color.)",
"Source: X-ray tech. Had to take radiation physics and biology, different spectrum of EM radiation, but similar concepts."
] |
[
"So, with materials one way that the properties differ is how the atoms are bonded together. For instance, graphite and diamond are both made solely of carbon atoms. But they ar very different, due to the structure of how the atoms are joined. With graphite the atoms arrange more in a layer structure, meaning they are easier to break apart. But in diamond the atoms are bonded together in a stronger structure, so they can't be broken apart as easy.",
"So the way in which the atoms bond together is one key way in which materials differ :)"
] |
[
"Can someone please explain why escape velocity is necessary?"
] |
[
false
] |
So here's my thought: if I have a rocket (let's pretend for the moment it has infinite, weightless energy with which to move) and I take off at say, 100 kph. If I keep a constant velocity what will prevent me from leaving the planet?
|
[
"If I keep a constant velocity what will prevent me from leaving the planet?",
"Nothing. Escape velocity is the velocity required to leave earth orbit without any further thrust, i.e. it's the velocity you would need to throw a ball with so that it would leave earth orbit (ignoring air resistance). If the ball has a rocket attached to it that is constantly exerting thrust, it can leave orbit at whatever velocity it likes. ",
"Escape velocity is important when, say, traveling to the moon (edit: or more precisely some other planet) because eventually you want to be able to stop your rockets from firing. So, you need to achieve escape velocity before you can shut them off."
] |
[
"Escape velocity is important when, say, traveling to the moon",
"Actually, the Moon is in orbit around the Earth, so in theory you can reach it just with a Hohmann ellipse travelling a bit slower than escape speed. It won't be a lot slower though.",
"Escape velocity is important when travelling out of Earth's sphere of gravitational influence (approx. a million km)."
] |
[
"Escape velocity is the velocity you have to shoot out of the planet (or some other mass) so that the distance grows and the gravitational pull weakens faster than the gravitational pull slows you down i.e. the speed never turns negative because of that gravitational pull (with smaller speeds you would eventually fall back to the mass). It is also the speed an object will get if dropped to the mass from a distance approaching infinity.",
"This is important because we cannot pack the probes we send with huge rocket boosters, they need to get most of their speed on the start of the journey and still get out of the gravity wells in the solar system. "
] |
[
"If I was in a cave 1000 miles below sea level, would I feel heavier, lighter or the same?"
] |
[
false
] |
[deleted]
|
[
"Heavier, but only by a tiny bit.",
"Where you would normally experience ~9.81 m/s",
" acceleration due to gravity on the surface, at 1,000 miles deep, you would experience ~10.0 m/s",
"\nThis is due to the varying density of the Earth. As an example, if you were to be 2,500 miles deep, you would experience the heaviest possible weight, at ~10.7 m/s",
"Here is a ",
"chart",
" denoting gravity at particular depths of the Earth.",
"EDIT: Formatting."
] |
[
"Adding to your point, if the earth's density ",
" constant throughout, gravity would strictly decrease as you got closer. This is because \"if [a] body is a spherically symmetric shell (i.e. a hollow ball), no gravitational force is exerted by the shell on any object inside, regardless of the object's location within the shell\" (",
"Wikipedia",
"). So the spherical shell of everything further from the center than you cancels out its own gravity and you only are affected by the mass closer to the center than you."
] |
[
"It's called the ",
"Preliminary Reference Earth Model"
] |
[
"What does \"cooking\" dynamite into \"grease\" mean?"
] |
[
false
] |
Big fan of Prohibition-era non-fiction and in a memoir I read of a safecracker, he talks of the explosives -- aka "grease" -- he would use to open safes: He doesn't mention anything else about it and I've Googled this from every angle I know how. What does he mean by "cooked"? Literally, in an oven or on the stove? What is all even in that "grease"? Is it soupy or solidified? EDIT: I'm now aware of Nobel having made nitroglycerin safer by inventing dynamite so that's cool.
|
[
"\"shooting\" is blasting slang for detonating. \"A box\" is referring to either the safe or the case of dynamite. \"Grease\" is a reference to nitroglycerin mixed with any number of additives that were used in manufacturing dynamite . Nitroglycerin can be made from saturated fats, so \"grease\" is an apt slang term. Texture wise, it's a viscous, oily liquid. Think about the consistency of liquid hand soap or a little thicker. \"Cooked out\" refers to the impure nitroglycerin that has settled or sweated out of the dynamite. Old processes of manufacturing dynamite allowed the nitroglycerin to settle out and weep through the casing of dynamite. Since the nitroglycerin from dynamite contains additives, it isn't the same viscosity as pure nitroglycerin. The additives also affect the properties of nitroglycerin, potentially changing detonation rate, so you wouldn't know how powerful the detonation would be unless you had \"shot\" this particular brand before. The amount that had weeped out could also change detonation rate since it's no longer impeded by the filler it was soaked into."
] |
[
"Nitroglycerin is also very unstable. A bottle of it could explode if dropped or even jostled too hard. Dynamite was helpful because it was fairly stable - it needed a blasting cap to explode."
] |
[
"I mean, dynamite is essentially a filler to keep the explosives stable, and the reason is: In 1864, Alfred Nobel filed patents for both the blasting cap and his method of synthesizing nitroglycerin, using sulfuric acid, nitric acid and glycerin. On 3 September 1864, while experimenting with nitroglycerin, Emil and several others were killed in an explosion at the factory at Immanuel Nobel's estate at Heleneborg. After this, Alfred founded the company Nitroglycerin Aktiebolaget AB in Vinterviken to continue work in a more isolated area and the following year moved to Germany, where he founded another company, Dynamit Nobel.[1]",
"Despite the invention of the blasting cap, the instability of nitroglycerin rendered it useless as a commercial explosive. To solve this problem, Nobel sought to combine it with another substance that would make it safe for transport and handling but yet would not reduce its effectiveness as an explosive. He tried combinations of cement, coal, and sawdust, but was unsuccessful. Finally, he tried diatomaceous earth, fossilized algae, that he brought from the Elbe River near his factory in Hamburg, which successfully stabilized the nitroglycerin into a portable explosive.[1]"
] |
[
"Are explosions additive or multiplicative?"
] |
[
false
] |
I've always wondered this. Is the explosion caused by 2 sticks of dynamite twice as big as the explosion caused by 1, or does it scale by some factor? As kind of a corollary, if two sticks of dynamite go off in rapid succession (within ms of each other) does that follow the same pattern, or does it act differently?
|
[
"I don't actually know precisely how they scale, but generally, for dimensional reasons, quantities cannot scale multiplicatively unless they are dimensionless."
] |
[
"Not a specialist but I'd say that it's less than additive, the raw energy liberated is twice as much if you take 2 sticks of dynamites. But the energy then spread in 3D, therefore it's only going to be 2",
" more powerfull."
] |
[
"An explosion is a rapid increase in volume and release of energy. ",
"Both are ",
" and are additive for independent, noninteracting subsystems.",
"So yes it's additive, this is why you can get TNT equivalent for big explosion like the one cause by a nuclear bomb. ",
"However, note that in the definition of explosion there is \"rapid\". If two sticks go off in succession, it may appear less violent (it should have less destructive power) than if they go off together."
] |
[
"Why is the air drier in the mountains?"
] |
[
false
] | null |
[
"At higher elevation the vapor pressure is lower, and moisture tends to evaporate quicker. This makes the air seem dryer. In fact, the air at higher elevation will hold less water than at sea level because it is less dense -- it takes less water to reach 100% humidity."
] |
[
"Thanks, makes sense!"
] |
[
"Its not. Mountains usually create a rainshadow effect. Air encountering the mountains on the windward side drops moisture (the Pacific Northwest in the US and canada is largely temperate rainforest and a good example of this). This air is able to top the mountains and proceeds to the leeward side much much drier (the great plains of north america in relation to my previous example.)"
] |
[
"Where do air planes dump their fuel for emergency landings?"
] |
[
false
] |
In the news this morning, a United Airlines flight from Honolulu to SF had to make an emergency landing because the engine was sparking. The plane had to dump it's fuel, so where do they do it? What's the environmental impact, and couldn't the act of dumping the fuel cause more of a chance for an explosion because the engine is sparking? Source;
|
[
"No to mention the fuel all spills out into the environment anyway if the plane crashes because it was too heavy. "
] |
[
"If you have to dump fuel, and an ocean is available, you do it over the ocean. You don't dump it from the engine; you dump it from the fuel tank, which is nowhere near the engine, so it doesn't matter if the engine is sparking. You dump fuel because you can't land with that much weight, not because you think it might explode. ",
"Of course there's an environmental impact, but probably pretty minor compared to all the other fuel that's spilled in the normal course of business around the world every day. And you don't tend to lend much weight to minor environmental concerns when hundreds of lives are at stake. "
] |
[
"Because the mechanical stresses of landing are different from those of takeoff. Most commercial aircraft are engineered to withstand landing stresses at lower weight limits than takeoff stresses, because that's the way 99.99% of your flights will be flown. It's only the emergency situations that arise at takeoff with a transoceanic fuel load that might require landing at near the maximum takeoff weight... and that is what the fuel dump is for.",
"Private aircraft generally do have landing weight limits equal or very near to their takeoff weight limits, since they are small and can be built rigid enough without adding too much weight or cost to the airframe. And you could in principle design a large airplane to land at the same weights that it takes off, but that airplane would be over-engineered, heavier, and less efficient than it needs to be for those 99.99% of its flights. Some aircraft are designed this way, actually, but mainly those that can be refueled in flight, where the assumption that you'll be landing with significantly less fuel than you took off with is less certain."
] |
[
"Is there a name for the point where gravity shifts from Earth to the Moon?"
] |
[
false
] |
There must be some threshold between the Earth and the Moon where an object on one side will gravitate toward Earth, but on the other side of the line is affected more by the Moon's gravitational pull. I have done some Googling, but could not find the answer. Does anyone know if there is a term for this point and/or line? Similarly, is there a general name for this type of line between other celestial bodies, such as Mars and the Sun, etc.?
|
[
"The ",
"Hill sphere",
" is the (approximate) region of space around a body where its gravity dominates that of whatever it orbits. So outside of the moon's Hill sphere, Earth's gravity is dominant, and Earth in turn has a Hill sphere relative to the sun."
] |
[
"L1",
"There are five ",
"Lagrange points",
" where an object can orbit the earth and keep the same position relative the the moon. I know that isn't quite what you asked. You were asking just about gravity, while the Lagrange points also consider the centrifugal force due to movement of the moon."
] |
[
"This and ",
"Sphere of Influence",
" are the most appropriate answer to OP's question, in my opinion."
] |
[
"Is there a material that conducts heats easily, but is highly electrically insulating?"
] |
[
false
] |
It seems like electrical conductivity and heat propagation are often related in materials. I have a project that would benefit from a material that wouldn't conduct electricity easily, but would propagate heat easily. It would be a plus if this material were something that could be cast into a mold as well. (Like a ceramic, cement etc.)
|
[
"Mica",
" is what is typically used when you want to put a heatsink on a transistor with an exposed back. It's a naturally occurring rock that is notable for it's high thermal conductivity and low electrical conductivity. "
] |
[
"If you want a good thermal conductor that is a good electrical insulator the formula is based on a strong covalent bond and a relatively close match in size/mass between the anion and cation, or like diamond a single atom.",
"Some great examples of these materials are diamond, beryllium oxide (careful of toxic dust, I have a few pieces in my collection of materials), aluminum nitride, boron nitride, and to a lesser degree silicon nitride.",
"Now the issue with these materials is the same strong covalent bonds that make them good thermal conductors make them very challenging to process. They generally have to be sintered at high temperature to densify them and some (diamond) cannot be sintered. You can get some of the benefits of these materials by using them in a composite such as aluminum nitride filled epoxy, but it will not perform as well as a dense piece of the same ceramic. THis is a very hot field (pun intended) for electronics packaging, as they want a great electrical insulator, thermal conductor and a low dielectric constant so they can pull heat out of the chips without hurting performance."
] |
[
"Diamond is another material that meets the specified criteria. From Wikipedia, \"diamond has the highest hardness and thermal conductivity of any bulk material\" and \"some blue diamonds are natural semiconductors, in contrast to most diamonds, which are excellent electrical insulators\". ",
"Teflon (Polytetrafluoroethylene (PTFE)) is an excellent electrical insulator, with more thermal conduction than many plastics. It conducts heat well enough to function effectively as a cookware coating. ",
"The same is true of glass and porcelain, along with other dense ceramics. All of these are excellent electrical insulators. They are good conductors of heat, compared to many common materials. The original posting doesn't indicate how good a thermal conductor is needed, nor what other factors are important, such as price, toxicity, etc. ",
"http://en.wikipedia.org/wiki/Diamond#Electrical_conductivity"
] |
[
"One of the many definitions of Joule is defined as the energy required to increase the temperature of 1 kg of water by one degree centigrade is equal to one Joule. Is this definition independent of pressure of the environment?"
] |
[
false
] | null |
[
"That is not the definition of the joule. The joule is defined so that 1 J is exactly equal to 1 kg m",
"/s",
". The joule is a composite SI unit defined in terms of the base units kilogram, meter, and second."
] |
[
"There is no mention of pressure in what I wrote. "
] |
[
"There is no mention of pressure in what I wrote. "
] |
[
"Physically speaking, what is a memory?"
] |
[
false
] |
What physically happens in the brain when it stores memories? How are they stored? Is it like burning a CD? If someone were to replace a piece of my brain with the same piece of someone else's brain, would I be able to experience that person's memories, or would my brain not be able to process it?
|
[
"Moser, MB / Trommald, M / Andersen, P, PNAS, Vol. 91, No. 26, Dec 20 1994, page 12673-12675",
"Moser EI, Krobert KA, Moser M-B & Morris RGM (1998), Impaired spatial learning after saturation of long term potentiation. Science, 281: 2038-2042.",
"Whitlock et al., 2006, Science, 313:1093-97.",
"http://www.sciencedirect.com/science/article/pii/0092867494904006"
] |
[
"There are many different types of memory but the memory people think of is declarative memory. This is processed in the hippocampus and stored there for a short term through LTP. Long-term Potential (LTP) is when a neuron produces a long-lived enhancement in the postsynaptic cells response to a subsequent single-pulse stimuli. Basically if a presynaptic cell and postsynaptic cell are excited together they can later become excited more easily and can grow new synaptic connections. Different neurons become excited more easily to different stimuli causing memory. It has been established that LTP is the process through which memory is formed.\nIf you could somehow change the excitability and the connections of neurons to match someone else's brain I wouldn't see why you wouldn't have their memory. You cannot just cut out a piece of someones brain because neurons go from that regions to all over the brain/body. You would somehow need to take out neurons and replace neurons and reconnect them properly. "
] |
[
"[citation needed]",
"It has been established that LTP is the process through which memory is formed."
] |
[
"How can spacecraft safely enter orbit of other planets?"
] |
[
false
] |
After reading the question about New Horizons and Pluto, I was curious about aerobraking around planets that have atmospheres. The cheapest way to land on Mars or Venus, I assume, is to use their atmospheres to slow your craft down. But how well do we really understand the physical characteristics of their atmospheres, and how? Can we tell the altitude-density relationship using ground-based optical telescopes? Can aerobraking be done "conservatively", so that e.g. the craft has a 95% chance of entering some orbit, which can be tuned with further aerobraking? Lastly, before we flew close by them, how could we tell the mass of Mercury and Venus, that have no moons? Was it just a guess based on volume? Can magnetic fields (implying iron content) be observed from a distance?
|
[
"The cheapest way to land on Mars or Venus, I assume, is to use their atmospheres to slow your craft down.",
"Absolutely! But as you imply, it's not quite as simple as it sounds.",
"Firstly, as you're probably aware, there is a critical angle for aerobraking - below which the spacecraft will 'skim' the atmosphere and end up on an escape trajectory and above which the spacecraft will plummet to the ground too quickly to lose all that kinetic energy safely. Interestingly, the first problem can become part of the solution - it's possible to successively 'skim' a spacecraft several times to slow it down enough to aerobrake safely.",
"This angle is dependent on the density of the atmosphere. On Venus it's easy to aerobrake, because the atmosphere is so thick, but it's also easier to get it wrong and 'skim'. On Mars, where the atmosphere is thin, it's harder to skim off (though still possible) but easier to not aerobrake enough.",
"It's also important to separate out the aerobraking from the 'controlled descent' phase, which can also utilise the atmosphere. For example, you don't use a parachute for aerobraking - the spacecraft will be moving much too fast and other mechanisms are used, such as ablative heatshields. However, a parachute could be used (and most often is at some stage of the descent) in the controlled descent.",
"But how well do we really understand the physical characteristics of their atmospheres, and how?",
"This is a very important point. And the answer is - we do a weather forecast. Both atmospheres are very dynamic. For example, Mars' atmosphere varies by a few hundred % annually and by several tens of % daily during storm events. So to know exactly how dense the atmosphere is, we have to combine observations with models in exactly the same way as terrestrial weather forecasts to predict atmospheric conditions. My supervisor was one of the people doing the 'forecast' for the descent of Curiosity. ",
"This is important for several reasons. Firstly, and this applies more to Mars, you need enough atmosphere to slow you down. If the atmosphere is 'thinner' than expected, the extra few metres or hundreds of metres of descent the spacecraft doesn't get could mean the difference between it surviving and ending up in a junk heap. But it's also important for the controls that mean that should be avoided. The descent systems on all landers will have automatic sensors and controls to tell the spacecraft how far above the surface it is. In some cases, it can use this to slow down more (e.g. with an active rocket descent system) or tell it when to deploy or release parachutes.",
"These forecasts are still important for spacecraft that aren't landing, as the amount of aerobraking depends on the atmospheric density, but to a much lower degree. As you ask, it's very common to use fairly conservative aerobraking, though planetary 'capture' is all or nothing essentially (must be completed in one manoeuvre), but successive aerobraking can be use to circularise an orbit after capture. For example, the Trace Gas Orbiter will successively aerobrake for nearly a year before it reaches its final orbit."
] |
[
"Just a small detail to add, which you probably omitted because it is a bit obvious but clarifying does no harm:",
"Aerobraking",
" is the technique of using atmospheric drag to decrease the speed and migrate to lower orbits, possibly through several successive atmospheric \"scraps\". This has already been performed a few times.",
"Aerocapture",
" means using atmospheric drag to migrate from an interplanetary trajectory to a closed orbit. The main difference is that in this case the spacecraft is initially ",
" and it has to slow down to a bit lower than this number in a single attempt. Failure to achieve enough speed loss will send the spacecraft back into interplanetary space. AFAIK this has been theorized long ago but not attempted yet."
] |
[
"I can't answer all your questions but here is a few:",
"But how well do we really understand the physical characteristics of their atmospheres, and how? Can we tell the altitude-density relationship using ground-based optical telescopes?",
"There is several techniques to see what the atmosphere of a planet is made of. For Venus we can use its transit in front of the sun and look at the spectrum of the sunlight going through the atmosphere. This gives us density and composition. I believe that you can also do that with stars and Mars.",
"A simple spectrum of the light reflected by Mars can also provide you with hints of the composition of the upper atmosphere.",
"Lastly before we even got into orbit of any of these planets there was some fly-by missions (Mariner program in the US)",
"Lastly, before we flew close by them, how could we tell the mass of Mercury and Venus, that have no moons? Was it just a guess based on volume? ",
"Nope you can actually calculate the mass of those planets by looking at the gravitational influence of other planets of known mass on them."
] |
[
"Is it possible to use light to transmit a voice over a fiber cable without using a speaker, microphone, etc?"
] |
[
false
] |
Using simple objects that I'd probably have lying around or could easily get, is it possible using a battery, etc? I want to be able to speak into one end and have my voice be sent to the other end using light sent down a fiber cable.
|
[
"So what could be used in lieu of a traditional microphone? "
] |
[
"What do you mean no microphone? I've seen audio transmitted via a laser to a speaker. It isn't a \"simple object\" set up though."
] |
[
"Well, not a commercial microphone, is what I mean."
] |
[
"Why is there a breathalizer test for alcohol levels but there isnt one for any other drugs? Do other drugs not escape through the lungs like alcohol, and why does alcohol exit the lungs?"
] |
[
false
] | null |
[
"Breathalyzer tests detect the presence of acetaldehydes that are the result of alcohol being metabolized and are passed easily out through the lungs. Other drugs just don't result in the same sort of molecules. The metabolites of THC are present in urine for weeks and that's what the tests look for. "
] |
[
"The answer is obvious: they ",
" arrest people for having detectable THC metabolites in their blood or urine, despite not being presently intoxicated (e.g. they smoked earlier, but are not intoxicated at present). It's a controversial issue in states that have legalized recreational use.",
"Source:",
"http://www.washingtondui.com/blog/I502-washington-marijuana-dui-law-changes"
] |
[
"No, that's what an oral swab is for. That can tell if you've smoked recently."
] |
[
"How can we see galaxies that were formed shortly after the big bang if matter cannot travel at the speed of light?"
] |
[
false
] |
I just read a article about a galaxy that shouldn't exist. And mabey I don't understand the big bang enough but how did we get ahead of the light to see a galaxy that was formed 3 billion years after the big bang? Edit :
|
[
"because matter can travel away from other matter at speeds close to but still slower than the speed of light.",
"In fact, cosmological expansion can result in recession velocities that ",
" the speed of light.",
"Link the article. What do you mean shouldn't exist?",
"The article is ",
"this one",
". Hubble found a grand-design spiral galaxy at a distance where normally one wouldn't expect to see such structures (given the amount of time they would have had to form). The paper discusses a plausible reason for the existence of the structure that time.",
"As usual, pop-sci sources around the net are embellishing; it's being reported as a galaxy that \"shouldn't exist\"."
] |
[
"Yes. The most remote galaxy we can see is ",
"UDFj-39546284",
". The light we're seeing from it right now was emitted about 460 million years after the big bang.",
"The surface of last scattering was the moment/event where the universe became transparent. For the first 370 thousand or so years, the universe was opaque. Then it became transparent and light was able to travel."
] |
[
"At the surface of last scattering, light was emitted from ",
". It continued to be emitted from any light-emitting source after that. About 3 billion years after last scattering, this galaxy was sufficiently far away that light emitted at that time took about 10.6 billion years to reach us."
] |
[
"How is our sense of touch able to differentiate between things such as wet and dry or hot and cold?"
] |
[
false
] |
I would highly appreciate an answer that describes the exact interaction between molecule and nerve-ending when for example when a finger touches something wet/dry/hot/cold down to what happens on an atomic scale and describes the way this information goes up my arm to the brain to be interpreted as accurately as possible.
|
[
"Not really, as there is very little evidence for direct chemoreceptors in the skin, as that would require an exposed neuron that is not capped by the epidermis, or protected by mucus secretions, and thus would be subject to abrasion and dessication from the outside environment. ",
"Also, think about something like a sensory deprivation tank, where the humidity is high (no evaporative cooling), and the water you float in is set to the same temperature as the skin. This gives most of your skin the sensation that you are floating, but not the sensation that you are wet. Conversely, when you wash your hands and then \"dry\" them with a towel, the cracked and flaky outer surface of the skin and the spaces between your fingerprints will retain some of that water for a while even though your hands are \"dry\". This is because the small amount of water trapped in these places is heated up to skin temperature, and isn't interacting with the higher sections of skin that interact with other solid surfaces, and thus does not give off the temperature and pressure profile of \"wet\" even though it technically is.",
"Ultimately, its not simply pressure and temperature, but the intricate pattern of pressure and temperature that gives away the unique signature of wet/dry, smooth/ruff/fuzzy. You have to realize that hard or dry surfaces may only activate sensors on the peaks of the skin surface, and progress along the skin surface as a defined boundary. A liquid from a wet surface will activate thermoreceptors on the top of the skin as well as down in the nooks and crannies, and will progress along the skin via both the flow of the bulk droplets (a semi defined boundary) as well as capillary flow through these small nooks and crannies. Because the film thickness will be variable, as well as the heat transfer characteristics of the liquid, the temperature profile of the liquid on the skin as it moves across and is heated by the body (combined with the minute pressure sensations of this movement) will be very different from a large, solid, dry object moving along the skin. I think this intricate difference in pressure and temperature paints a picture of wet or dry. It's kind of like being able to tell the difference between a flat paint surface and a satin paint surface, you arent necessarily aware of all the extra irregularities on the flat surface, but your body is, and interprets that intricate pattern of signals into your conscious mind as \"smooth\" or \"rough\". "
] |
[
"I don't think it is an atomic interaction that governs differentiation between these characteristics, but a combination of different sensory input and the prior experience to tell the subtle differences.",
"For instance, there are several different types of skin touch sensors. Their differences include the placement (both location on the body and depth in the skin), response frequency (low to high vibration, or static loading), and duration of action potential (long or short). ",
"So between these different sensor cells, you can get a sense of general shape and edges (long response time, static load response), surface characteristics like smooth or fuzzy or rough (short response time, high vibration frequency response as fingers are moved over surface), and a good sense of frictional characteristics using data on force applied and skin stretch while dragging a finger over the surface.",
"This data is then compared to what you have learned over the years. This is the reason that you sometimes can't tell when something is wet or dry or if it's just cool and/or a good conductor of heat (like cool metal against bare skin) until you have some extra time to gather more sensory input. ",
"TLDR - It's more a combination of pressure sensing and temperature sensing. "
] |
[
"Not really, as there is very little evidence for direct chemoreceptors in the skin, as that would require an exposed neuron that is not capped by the epidermis, or protected by mucus secretions, and thus would be subject to abrasion and dessication from the outside environment. ",
"Also, think about something like a sensory deprivation tank, where the humidity is high (no evaporative cooling), and the water you float in is set to the same temperature as the skin. This gives most of your skin the sensation that you are floating, but not the sensation that you are wet. Conversely, when you wash your hands and then \"dry\" them with a towel, the cracked and flaky outer surface of the skin and the spaces between your fingerprints will retain some of that water for a while even though your hands are \"dry\". This is because the small amount of water trapped in these places is heated up to skin temperature, and isn't interacting with the higher sections of skin that interact with other solid surfaces, and thus does not give off the temperature and pressure profile of \"wet\" even though it technically is.",
"Ultimately, its not simply pressure and temperature, but the intricate pattern of pressure and temperature that gives away the unique signature of wet/dry, smooth/ruff/fuzzy. You have to realize that hard or dry surfaces may only activate sensors on the peaks of the skin surface, and progress along the skin surface as a defined boundary. A liquid from a wet surface will activate thermoreceptors on the top of the skin as well as down in the nooks and crannies, and will progress along the skin via both the flow of the bulk droplets (a semi defined boundary) as well as capillary flow through these small nooks and crannies. Because the film thickness will be variable, as well as the heat transfer characteristics of the liquid, the temperature profile of the liquid on the skin as it moves across and is heated by the body (combined with the minute pressure sensations of this movement) will be very different from a large, solid, dry object moving along the skin. I think this intricate difference in pressure and temperature paints a picture of wet or dry. It's kind of like being able to tell the difference between a flat paint surface and a satin paint surface, you arent necessarily aware of all the extra irregularities on the flat surface, but your body is, and interprets that intricate pattern of signals into your conscious mind as \"smooth\" or \"rough\". "
] |
[
"An experienced runner and someone who is very out of shape run a mile. Do they burn the same amount of calories?"
] |
[
false
] |
If we assume their weight and the circumstances of the run are the same, and the experienced runner runs slow enough for the inexperienced one to keep up, so the question comes down to: is there a difference in how efficient calories are used?
|
[
"Several factors indicate the out of shape runner will burn more calories:",
"Two factors contribute to the fit runner burning more calories:",
"Overall, the first two unfit factor can result in large amounts of extra calories burned, while the other factors are weight dependent or only impact BSM. So the unfit runner is going to expend more calories."
] |
[
"I have run a few marathons.",
"\nThe inexperienced runner will burn more energy, because:",
"The inexperienced runner almost certainly has bad running form, which would waste more energy. ",
"The experienced runner has better muscle energy efficiency, the efficiency is defined as output_mechanical_energy/consumed_energy, long training runs will improve this efficiency of your running muscles, that's why we runners are always so obsessed with our weekly/monthly training mileage. "
] |
[
"Note that while caloric expenditure correlates with heart rate, it does so negatively with VO2Max, which might strike your first point."
] |
[
"Why do so many chemical compounds manifest as clear, colorless liquids or white powders?"
] |
[
false
] |
[deleted]
|
[
"Color is based off the absorption of radiation in the ultraviolet-visible region (200-800ish nm wavelength). Since this is a sliver in the wavelength spectra, not many compounds have the necessary \"chromophores\". The most common are conjugated double bond systems, though metals of certain oxidation states absorb in this region. "
] |
[
"it's not even inexplicable - if our eyes had rods and cones that responded to different frequencies of light, we would indeed see things as coloured that we see as colourless now (and vice versa)."
] |
[
"They already do. Sometimes you have to add external input like a specific wavelength light. UV light, for example, can assist one in telling different white paints.",
"Some counterfeit goods can be detected via UV because their plastics are of different composition than original plastics.",
"To add to the lights, blue light can be used to spot blood. Often used by hunters to track prey."
] |
[
"What is the commonest cause of death in common laboratory mice?"
] |
[
false
] |
I'm primarily interested in the commonest cause of death in mice in life-long studies in which mice are left to live out their lives without major interventions. For example, common lab mice, say a C57BL/6 strain, are placed on a normal diet and monitored until they die, what is the most likely cause of death? I think neoplasia may be the most common cause of mortality, but I'm having trouble finding sources clarifying the details. Can anyone help?
|
[
"Here's a relevant manuscript ",
"http://vet.sagepub.com/content/early/2013/09/06/0300985813501334.full",
" with an excerpt below. Cancer is common in older mice and kills a percentage of them. But other degenerative organ changes can also occur and lead to death such as cardiovascular problems and kidney problems. The commonest cause of death varies by mouse strain as some strains are very tumor prone and others aren't. In C57BL/6 mice about 40% of mice had tumors when examined at death, while the remaining 60% did not.",
"We identified the cause of death (COD) for 1236 mice; in 37 mice, the cause of death was not unequivocally identified. The cause of death was generally attributed to a single disease in the case of neoplasms. Chronic degenerative nonneoplastic lesions were considered the COD if a single disease was observed and the impact of that lesion was evident. Aging mice usually showed a complex set of lesions that contributed to death. The causes of nonneoplastic lesions remain unknown in most cases. However, Helicobacter infection should be taken into consideration in cases of rectal prolapses and lymphocytic infiltration in liver sinusoids, necrosis of hepatocytes, fibrosis, and cytomegaly in liver."
] |
[
"This paper discussed mouse deaths at upenn. Most frequent cause cited was spontaneous death of unknown origin.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3838613/"
] |
[
"Very helpful, thanks!"
] |
[
"What exactly happens when you fire ceramics?"
] |
[
false
] |
As in, what happens to the clay particles in high heat that makes them harder and waterproof? Is fired clay chemically different than unfired clay? And if not, is it theoretically possible to un-fire ceramics?
|
[
"Yes, it is chemically different.",
" Fully fired clay takes the particles, drives off the chemically bonded water, and takes the aluminum and silicates of each particle and binds them into a continuous whole. The finished ceramic is chemically changed from the beginning clay.",
"As such, it is impossible to \"un-fire\"."
] |
[
"Not to my understanding. Ground up ceramics are called \"grog\" and used to provide structure in larger ceramic sculpture. It's still ceramics, just ground finely.",
"Purely physical changes, like grinding, aren't going to affect chemical changes. The process described in the link I posted also lists other things, like organics, carbon, and sulfur, that are burned off during the process. Those don't come back,either; it's non-reversible. And you can't chemically re-add water, sulfur, carbon, etc. without turning into such a molecular soup it couldn't really be called clay or ceramic at all anymore; you'd be better off starting with fresh clay again or even pure chemicals rather than trying to rehydrate aluminum silicate."
] |
[
"If I understand correctly what you say, if you theoretically ground up ceramics really thinly and somehow chemically bond water to it, wouldn't it be \"un-fired\"?"
] |
[
"What makes some clouds have a flat underside while the rest of the cloud is puffy?"
] |
[
false
] | null |
[
"As air rises, warmed up by the ground, the temperature falls by adiabatic effect (fall in pressure) to an average rate of 0.65 C per 100 m of altitude.",
"At 15 C (the average temperature worldwide) a cubic meter of air can contain 14 grams of water. No more.",
"As the rising air cools down, it has less and less place for water vapour and soon the temperature reaches what is called the dew point, i.e. when the air is 100% saturated and cannot cools any further without condensing in droplets; the cloud.",
"The base of the cumulus is flat because it is exactly the place where the air reaches the dew point.",
"But once 'in the cloud' the air cools down at a lower rate because the condensation of water creates energy released as heat. Because of that, the air inside the cloud continues to rise until, eventually the temperature becomes even with the surrounding temperature and the convective rise stops.",
"The reason the top of the cumulus is cauliflower shaped is that, each 'bump' is in fact the top of one cell of warm air that has been rising.",
"Such cells, often called thermic cells are what glider pilots are looking for because they use it to circle in and climb. You will also see birds like seagulls and eagles taking those 'elevators' to gain altitude without effort. ",
"credit"
] |
[
"The base of the cumulus is flat because it is exactly the place where the air reaches the dew point.",
"So the altitude of where the clouds begin is a function of relative humidity. Never thought of it that way. Interesting."
] |
[
"In reference to the dew point and the formation of clouds there are also other factors involved such as the amount of cloud condensation nuclei (CCN) which are basically particles like dust. It is actually very difficult for water vapour to \"spontaneously\" change state to liquid water in the atmosphere; a relative humidity of around 400% if i recall correctly. When they have a surface to coalesce around it requires much lower vapour pressures. So while cloud formation is a function of relative humidity in real life formations of clouds other factors may be limiting where the cloud forms.\nI'm not well informed on the structure of clouds but the explanation of the shape due to convective processes and the bottom limit making it flat makes sense to me."
] |
[
"Could those advanced scanners that view the \"layers\" in very old paintings be used on certain scratch-off lottery tickets?"
] |
[
false
] |
I am referring to the scratch tickets that have multiple choices.
|
[
"I have access to all the tools, XRF, XRD, Auger, TOF-SIMs, FIB, Raman, environmental-SEM, you name it. If anyone here on Reddit can propose an experiment, I will review and maybe carry it out for you."
] |
[
"While interesting, this link provides no assistance in answering OP's question. Just a reminder to all that top-level comments should help in the scientific discussion related to answering OP's question. All the best!"
] |
[
"I remember back in the late 80's where a few people who worked in a hospital or something in the US were using the x-ray machine to see the correct boxes to scratch. They got caught and scratch tickets went through a technology change to address the problem. I'd search for the original story but I'm such a lazy."
] |
[
"Increasing displacement is velocity. Increasing velocity is acceleration. So what is increasing acceleration? Does it go even further?"
] |
[
false
] | null |
[
"First, a technical point: velocity is the ",
" of position, and acceleration is the ",
" of velocity. These can act to ",
" as well as ",
" (when you hit the breaks, you're accelerating in the direction opposite your direction of motion).",
"To your question, the rate of change of acceleration is called ",
"jerk (or jolt, surge, or lurch)",
".",
"Then you have ",
"jounce",
" for the rate of change of jerk, though this is also sometimes called snap, which leads to the idea of calling the next two crackle and pop.",
"But, really, there's no standard name for these things."
] |
[
"But, really, there's no standard name for these things.",
"Sure there is! d",
" x/dt",
" "
] |
[
"It's called \"jerk\"."
] |
[
"If the Moon is moving away from Earth, will it eventually escape Earth gravity?"
] |
[
false
] | null |
[
"Warning! Back of the envelope calculations below.",
"Every billion years, the moon will be 1x10",
" * 3.8x10",
" = 38,000 km farther away from us. When the sun turns into a red giant and engulfs the inner solar system, the moon will be 4 x 38000 = 152,000 km farther away. Currently it's 384,400 km out so when the sun asplodes it will be approx 536,400 km away, which is still within earth's gravity's influence."
] |
[
"No. The Moon is gaining orbital velocity (and as such a higher orbit) at the expense of Earth's rotational energy. Eventually the Earth and Moon will become tidally locked and the orbit will stabilize."
] |
[
"The only reason I'm aware of for why the Moon is moving away from Earth is because of the differences between the rotation of the Earth and Moon, which are slowly becoming more and more similar. Eventually the Moon and Earth will become 'synced'. The time it takes for the Earth to rotate once (one day) will equal the time it takes for the moon to rotate around the Earth. At this point, the Moon will have stopped moving away from the Earth (as far as I'm aware), and I believe it would actually start to slowly move in toward the Earth due to the (very) slight drag around Earth.",
"Regardless, as you point out, the time scales for this will be longer than the sun will be around, so it's certainly nothing to worry about."
] |
[
"If someone was partially submerged in water and otherwise unable to drink, would they absorb the water through their skin?"
] |
[
false
] |
Assuming it is fresh water.
|
[
"I remember this was asked more recently, but this is the most recent version I found:\n",
"http://www.reddit.com/r/askscience/comments/k4szf/if_someone_were_sitting_in_a_bathtub_full_of/"
] |
[
"There is absolutely no mechanism that I know of to allow this. While there are some vitamins and such that we can absorb through our pores, they absolutely cannot absorb water for the purpose of hydration."
] |
[
"A person can be floating in water, and die of thirst, so ... no.",
"People afloat in the ocean, after a boat sinking, often know better than to drink salt water, so there have been recorded cases where a person surrounded by water, immersed in water, can die of thirst, or become very dehydrated."
] |
[
"Why (or how) does gravity bend light?"
] |
[
false
] |
Light moving near a massive object causes light to bend around the object (or in the case of black holes into it,) my question is since a photon is a massless particle how is it bent? Is it space time curving which causes this and the photon "thinks" it is going in a straight line? Or are any of my assumptions incorrect? Any elaboration on this would be much appreciated.
|
[
"Is it space time curving which causes this and the photon \"thinks\" it is going in a straight line?",
"I think you have it."
] |
[
"Yeah. Objects follow paths called geodesics, and the shape of a geodesic is influenced gravitationally by massive objects."
] |
[
"It's actually not too big of a feat to travel 0 distance instantly in a timeframe. I just did it right now."
] |
[
"Do any animals show signs of actual homosexuality?"
] |
[
false
] |
Ive been told that humans are not the only species with homosexuals but no one has ever shown me proof.
|
[
"Homosexual behavior in animals wikipedia page."
] |
[
"2003 Ig Nobel Prize in Biology",
"Film: (",
"http://www.improbable.com/2009/10/08/minimovie-homosexual-necrophiliac-duck/",
")",
"About the award winner: (",
"http://improbable.com/about/people/KeesMoeliker.html",
")",
"Edit: award winner not author"
] |
[
"Maaaaybe. There are some animals that will definitely do things that look homosexual, but it's complicated by the fact that with a purely behavioral observation it's very difficult to tell the difference between a cis-gendered gay duck, a transgendered straight duck, and a duck that for some reason just can't tell the difference between males and females."
] |
[
"How do S-Waves react upon non-newtonian substances?"
] |
[
false
] |
If shear waves have a difficulty traveling through liquids, and non-Newtonian fluids solidify upon application of pressure, what happens when the two meet? Do the shear waves travel through undisturbed? Does the wave make it some way without failing? Or does it just not cause enough stress for the fluid to solidify in the first place?
|
[
"Just saying 'non-Newtonian' is really too broad of a term, as there are many different behaviors that fluids can have in response to shear that are not Newtonian. When you say 'non-Newtonian fluids solidify on application of pressure', that actually doesn't really make sense. Whether a fluid is non-Newtonian or not depends upon its response to the application of ",
", not pressure. Since liquids are all essentially incompressible, applying static pressure to a container of fluid won't tell you anything about its rheology.",
"As explained in the ",
"wikipedia article",
", there are 7 different classes of behaviors that a fluid can have when stress is applied, only one of those is a Newtonian behavior.",
"If you are referring to a shear-thickening or dilatant fluid, then application of s-waves would most likely cause the fluid to increase its viscosity, causing weird effects like ",
"this",
"."
] |
[
"Hmm, that's a good question. I would guess the induced shear from an earthquake might cause it to harden to some extent, but I don't think you would see the weird patterns like in the video I linked to earlier. The frequencies in an earthquake are much much longer than what a loudspeaker is producing, and it is the difference in induced shear at the location of nodes and antinodes that causes the strange flowing behavior on the speaker.",
"However earthquakes can also cause another non-Newtonian behavior, ",
"soil liquification",
"."
] |
[
"Sorry about the incorrect wording in the post. I'm not the best at understanding science. ",
"Is the effect that appears in the video you posted the same effect you would observe from a collection of cornstarch during a 6.0-7.0 magnitude earthquake? Just out of personal curiosity."
] |
[
"What is the difference between an inner monologue and auditory halucinations from disorders like schizophrenia?"
] |
[
false
] | null |
[
"The major difference between internal dialogue and 'schizophrenic dialogue' is the parts of the brain active when the 'messages' are interpreted. A brain scan showing internal dialogue in a mentally healthy person will depict relatively active areas in the prefrontal cortex, areas associated with logic and reason. In a person with schizophrenia, experiencing a schizophrenic episode, the brain scan will depict highly active areas all over the brain, an unordered mess. Most notably, excessive increases in activity can be detected in the occipital (vision-hallucinations) and auditory (auditorial-hearing) regions of the brain - which would explain the perceived experience of hearing very clearly auditory anomalies and other visual anomalies. ",
"People with schizophrenia generally experience their thoughts on the 'outside' as a result. This can be grueling and mentally exhausting, given the extreme difficulty in distinguishing between actual and internalized stimuli that are triggering the areas in the brain associated with conscious observation.",
"source"
] |
[
"That seems more like 'intrusive thoughts'. A condition where an otherwise normal person is experiencing thoughts they don't want to. ",
"http://en.wikipedia.org/wiki/Intrusive_thoughts"
] |
[
"Wait, so voices that are experienced as being internal but more or less uncontrollable wouldn't be a symptom of schizophrenia?"
] |
[
"At what point do you think that humans will be unable to comprehend their own theories and models about the universe?"
] |
[
false
] |
As our models of reality become more and more mathematical and complicated, fewer and fewer people are able to understand them. As time goes by, more and more previous knowledge and understanding is needed for us to have access to the limits of human knowledge. Do you think there will be a point at which very few people are capable of pushing the boundaries? Will we design computers capable of using the scientific method and trying countless possibilities, effectively carrying our original research that may be beyond us? Vague, amateurish questions I know, but I would like to know what some of the very smart and thoughtful people here think. Thanks! Added: Do you think that understanding the mathematics behind something (complex numbers, for instance) amounts to understanding the concept itself? I guess we are also limited by language itself.
|
[
"In my opinion (and I'd say that of almost all mathematicians of physicists) the regrettably-named \"imaginary\" numbers are no more or less imaginary than real ones. In itself, i * i = -1 is not more abstract than 2*4 = 8. Both can be visualized fairly easily and used to represent many ordinary things. It's just that people are seldom well-versed enough in using complex numbers to fully understand how they work and apply them to an imaginable situation.",
"To do so: An integer can be visualized as a row of objects. Multiplication then, could be visualized as a rectangular field of objects, with a row of n objects and a column of m objects for n*m. Doing the same for complex numbers, a complex number can be viewed as describing where a point is relative a pole in the ground. Multiplication with a real number moves the point farther out by that factor, multiplication with an imaginary number rotates the point around the pole. (where ",
" is 90 degrees, multiplying with i twice is 180 degrees, which is the same thing as moving the point to the opposite side of the pole, which is the same thing as multiplying it with the real number -1)",
"Not that visualizing or having an \"intuitive\" understanding of something is required to truly understand it, or should be. Plenty of unintuitive things are true, and plenty of intuitive assumptions are false. The whole point of magic and optical illusions is to play with incorrect intuition. It still seems weird, even though you know for a fact it's a trick. But I wouldn't say we're \"unable to comprehend\" illusions. We understand quite well how they work. It's just that understanding something isn't the same thing as intuitively expecting it."
] |
[
"I understand what you're saying, kind of. And I'd say we are already there.",
"Look at the wavefunction of a quanton, Psi (x,t) for example. Most of the time, these functions involve complex numbers and mathematical ideas that humans just don't have the ability to comprehend. ",
"Quantum mechanics is already at a point where our description of existence and matter is becoming outdated, but we can only describe them mathematically. "
] |
[
"Do you think there will be a point at which very few people are capable of pushing the boundaries?",
"Advances at the edge of physics and technology ",
" a level of creativity and skill that very few people can master. But that is true in any skilled profession. ",
"If you were to talk about composing music the same thing is true. The best-of-the-best composers have skills that mere hard work is not enough to achieve. You need the skills honed by years of practicing your profession ",
" a spark of creative invention that no one knows how to teach and that has always been associated with high intelligence.",
"Most people can't be an Einstein. But most people can't be a Mozart or a Shakespeare, either."
] |
[
"Why are there Valence electrons? Why don't electrons just keep creating new shells around an atom?"
] |
[
false
] | null |
[
"As you add electrons to an atom, the Pauli exclusion principle forces them to pile into higher and higher shells. All electrons in the outermost shell are called \"valence\" electrons. So I'm not sure I understand the question."
] |
[
"I'm asking why there is an outermost shell. Why can't there be another shell formed after the last electron shell is filled? Do the protons stop attracting electrons past where the valence shell is? "
] |
[
"A nucleus with Z protons will only be able to grab onto Z electrons (forgetting about negative ions). Wherever the outermost ones lie is the valence shell."
] |
[
"Where can I get cheap/used lab supplies?"
] |
[
false
] |
So, first of all, I'm not cooking meth or anything illegal. Just curious. I work in a lab, and so often I think to myself how useful some of the glassware and things could be at home. Example: I found a 2L erlenmeyer flask at a goodwill, and I now use it as a goldfish tank. Example 2: I want a grad. cylinder to put a rose in as a table centerpiece when cook dinner for my also-nerd girlfriend. I know what stuff usually comes in contact with labware, and if I were to get anything used you have to assume the worst re: chemical residues, but there are plently of safe uses for those who know how to deal with this stuff. Does anybody know where/how I could get anything like this?
|
[
"Ebay. You can get any of the glassware you mentioned and more super cheap. Not just common stuff either, I bought a soxhlet setup for almost nothing."
] |
[
"Interesting... As I understand it, the soxhlet extractor could be used for example to extract oils from something like plant matter, correct? It looks like an incredibly simple apparatus to accomplish such a useful task. I suppose once you extracted the oils you'd just need a method of separating it from the solvent."
] |
[
"Yep, it continuously extracts for as long as you run it. For separation I use isopropyl alcohol which evaporates. I use it to make plant extracts like kava kava as well as marijuana hash oil."
] |
[
"Can single-celled organisms become cancerous?"
] |
[
false
] |
[deleted]
|
[
"No, they can't",
". Basically, cell division in a unicellular organism is just reproduction, and they don't have any real internal reason to regulate it (external reasons include things like resource availability). Multicellular organisms, on the other hand, need to regulate just how many of each type of cell they have. This lead to the evolution of regulatory genes that control just when the cells can divide. Cancer is essentially a breakdown of these regulatory pathways, pathways that unicellular organism don't have."
] |
[
"Except the human is external to the bicycle; the bicycle didn't break down, the human did. The bicycle is fine and will work fine again when the human starts pedaling again."
] |
[
"not even all vertebrates or mammals afaik are susceptible to cancers.",
"All multicellular life is susceptible to cancer, though some have more defenses against it than others.",
"I suppose that single-celled eukaryotes could technically get something akin to 'cancer' if a mitochondrion or a plastid began reproducing out of control."
] |
[
"Is it actually possible for a camel to go through the eye of a needle if it goes fast enough, or do I just not understand relativity?"
] |
[
false
] |
Because of length contraction under special relativity, if we accelerate a camel at a high enough speed, shouldn't we be able to make it go through the eye of a needle (theoretically)?
|
[
"But is the contraction still real?",
"It's very real.",
"Let's say there's a train longer than a tunnel. If the train goes fast enough, is it possible for all the passengers of the train to be under the shade of the tunnel at the same time?",
"You need to specify reference frames. Let me see if I understand the proposed setup and question:",
"Start with a train at rest and a tunnel. In this reference frame, the train is longer than the tunnel. Now, keeping the tunnel at rest and having the train travel at sufficiently high speeds, is it possible for the entire train to be inside the tunnel at once? The answer to that question is absolutely yes. On the other hand, to the people inside the train, it is the train that's at rest and the tunnel that's moving, so the train is still longer than the tunnel and they will see that there are always some people not inside the tunnel. Both points of view are correct.",
"The problem here is one of simultaneity. Let's say the train is moving at just the right speed that, to a person standing beside the tunnel, the train appears to be precisely the same length as the tunnel. Then to that observer, the event \"the front of the train is under the far end of the tunnel\" and the event \"the back of the train is under the near end of the tunnel\" are simultaneous. But to the people on the train, these events are ",
" simultaneous—the front of the train passes the far end of the tunnel ",
" the rear of the train reaches the near end."
] |
[
"Length contraction happens in the direction of travel only. A high-velocity camel going past you forwards would be observed not to be very long from nose to tail, but just as wide and as tall as the more common nearly-stationary camels."
] |
[
"In other words, a 10 meter long train could fit within a 5 meter barn if it was going fast enough, but the barn would still have to be as tall and wide as the train."
] |
[
"When a person feels \"run down\", what systems or internal processes are creating that feeling?"
] |
[
false
] |
[deleted]
|
[
"I am far from an expert on this but there is a class of molecules called cytokines that are likely the culprits. These are signaling molecules within the body that serve a variety of functions; however, four in particular (interleukin-1, interleukin-6, tumor necrosis factor-alpha, and interferon-gamma) are responsible for much of the body’s inflammatory response and also have effects on the brain. ",
"Here",
" is an article that goes into a little more depth on the mechanisms of how these molecules act on the brain, but I didn’t want to get too far into the weeds here. If you scroll down in the article to Box 1 you will find more info on this topic :)",
"Edit: not sure whether the paper was open access so I pasted the relevant bit below. ",
"“During the activation of the immune system, immune cells produce cytokines that coordinate the immune response. In addition to their peripheral actions, cytokines are able to signal to the CNS. Several such immune-to-brain communication pathways have been described, including a neuronal and a humoral pathway. The former refers to the fact that cytokines can activate the vagus nerve at the periphery, which then modulates functions of the brain targets of vagal afferents (38). Cytokines can also activate brain immune cells (microglia) that are located alongside brain vessels where the blood–brain barrier is weaker (e.g., in the circumventricular organs) (39). These cells then produce cytokines locally. The cytokine signal propagates in the brain via diffusion, microglial activation, and neuronal projections (37).",
"A crucial mechanism by which cytokines modulate neuronal functions is through modifications of monoaminergic neurotransmission, specifically by activating enzymes interfering with dopamine and serotonin biosynthesis. One of these enzymes is the GTP-cyclohydrolase 1 (GTP-CH1), which is involved in the production of neopterin. The production of neopterin happens at the expense of the production of tetrahydrobiopterin (BH4), which is an essential cofactor for the biosynthesis of dopamine and serotonin (40, 41). In addition, cytokines activate the indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme degrading tryptophan along the kynurenine pathway (7, 42). The degradation of tryptophan reduces its availability for serotonin biosynthesis. By activating GTP-CH1 and IDO, cytokines thus reduce the synthesis of dopamine and serotonin. Cytokines also modulate dopamine- and serotonin-transporter activity, reducing their synaptic availability (43, 44). In addition to neurotransmitter systems, cytokines modulate neuroendocrine systems, such as the hypothalamic–pituitary–adrenal axis, activating the release of corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol (45, 46).",
"Although cytokines induce a large array of behavioral changes, including changes in mood and cognitive functions, fatigue is, interestingly, one of the first and most common symptoms associated with an activated immune system (47). This has been demonstrated in patients suffering from cancer or hepatitis C, who undergo immunotherapy with the pro-inflammatory cytokine interferon-α, which activates the immune system and has neuropsychiatric side effects (48–50). Among these, fatigue develops very rapidly after instauration of the treatment in a large proportion (up to 80%) of patients, while other behavioral alterations, such as depressed mood and cognitive dysfunction, appear later and only in a subpopulation (30–60%) of patients (49, 51). This suggests that fatigue is very sensitive to the effects of cytokines, and underscores the biological connection between fatigue and inflammation.”"
] |
[
"Burning through your neurotransmitters that need good sleep to replenish, micro-tears in muscles, a general lack of down time where the vagus nerve does its thing and you digest food and heal. ",
"Humans evolved for a hunter gatherer lifestyle, that's low stress socialising that can be done while gathering and high octane excitement hunting for a few hours, that's why people, especially men enjoy action movies. We're fantastic at high stress impacts followed by support, free loving and moving on, not constant background crap.",
"The grind isn't what we evolved for."
] |
[
"connection between fatigue and inflammation ",
"I occasionally wonder if my autoimmune disease (Crohn’s) is somehow linked to all the severe mental stress and fatigue I went through in college. It surfaced not long after."
] |
[
"If I tied a bag around my head, how many plants would I need to put in the bag for me to be able to breathe comfortably?"
] |
[
false
] |
[deleted]
|
[
"might be better phrased if you were in a sealed room as I think it would have to be a mighty big bag."
] |
[
"According to ",
"this TED talk",
", you'll need at least 4 areca palms, 6-8 mother-in-law tongues, and 1 (maybe more? he didn't specify) money plant per person."
] |
[
"It did conjure up a pretty funny image, though."
] |
[
"If a fish's gills can extract oxygen from water, why can they not extract oxygen from the air?"
] |
[
false
] | null |
[
"It's not just about extracting oxygen, but also about releasing carbon dioxide.",
"So, when a fish is out of water, its gills are wet with a film of water that quickly gets saturated with carbon dioxide, and the gas exchange between the water and the air isn't sufficient/fast enough for the fish to survive.",
"Also, over time the water evaporates, and so ANY gas exchange is reduced. Fish don't have a way to re-wet their gills on their own, like land animals do."
] |
[
"An essential step in the process is the gills excreting ammonia into the seawater. This lowers the pH of the blood. ",
"The decreased pH changes the distribution of electric charges on hemoglobin molecules in the blood. This physically changes the shape of hemoglobin and allows it bind or unbind oxygen",
"A simple analogy for how this works is a plate with a round depression in the middle that is just the right size and shape to hold an O2, and a lever underneath that can extend or retract to push the oxygen molecule out.",
"Changing the pH of the blood changes the shape of hemoglobin, thereby retracting the lever and allowing oxygen from seawater to bind to the active site in hemoglobin in blood cells.",
"When the blood travels to the fish's muscles and tissues, it's cells emit ammonia into the blood as a waste product. This increases the pH of the blood, thereby extending the level arm of hemoglobin and ejecting the bound oxygen molecules, so they can be absorbed by cells.",
"Ammonia is highly water soluble, but under most conditions, only evaporates slowly into the air.",
"So a fish out of water can't give off ammonia from it's gills, and this prevents hemoglobin from absorbing enough oxygen. Note that since most fish are cold blooded, they can generally survive longer without oxygen than warm blooded humans can, due to their slow metabolism. ",
"A similar process in land animals occurs with carbon dioxide. "
] |
[
"Last time this question was asked the top answer was that they can breath the air just fine but their gills collapse because they don't have the water to help keep them up.",
"So which is it"
] |
[
"Why do the lights dim sometimes when large appliances come on?"
] |
[
false
] |
I noticed that when the air conditioning comes on in my house, I can see the lights dim a little bit, for maybe half a second. What causes this? All I can find on Google is that the appliances "pull" a lot of current- I remember enough from college physics that this is way too vague for me, but not enough that I can come up with any more satisfying answers myself. Is there some part of the power supply process where the voltage is being reduced because the current is too high? Is this some alternating-current shenanigans I am not familiar with?
|
[
"Former AC technician here. What you're witnessing is the effect of the motor in the appliance drawing ",
"\"locked rotor\" current",
". As others have already pointed out, when the motor first comes on in your AC unit (actually there are two in the condensing unit outside -- a fan motor and a compressor motor -- and one in the indoor air blower section), it draws a very high current until it comes up to speed. In the AC unit, the compressor motor draws most of the current. After a fraction of a second, it's up to speed and drawing much less current.",
"The lights in your house dimming briefly is normal and anticipated in the design of the electrical system. ",
"Fun fact: Circuit breakers or fuses for AC/refrigeration units have to be of a time-delay type to allow for this momentary high current draw. Otherwise they would trip or blow immediately when the unit came on. "
] |
[
"I suspect it is more that many devices draw more current when they are first turned on. Motors coming up to speed would be an example."
] |
[
"Well I install tile and I know when we use the drill and wet saw at the same time but staggered you notice a dip in power for both. I think it's the fraction of time it takes for the power in the house to level out from the extra load the circuit received. It can totally handle it, it just takes a bit out of the rest to ensure it didn't have too much power in the circuit at once"
] |
[
"What is the optimal amount of degrees to throw something?"
] |
[
false
] | null |
[
"Is this a homework question?"
] |
[
"Nah man im just wondering"
] |
[
"Neglecting drag, the best angle is 45 degrees from the horizontal.",
"Including drag, the problem becomes a lot more complicated."
] |
[
"If I was in a completely airtight room by myself, how many trees/plants would I need to never run out of oxygen?"
] |
[
false
] | null |
[
"This guy, ",
"Kamal Meattle",
" from India, has been studying precisely that for past past couple of decades. They have been using combinations of ",
"areca palm",
"(Dypsis lutescens) for producing oxygen during daylight hours, ",
"snake plant or mother in law's tongue",
"(Sansevieria trifasciata) for producing oxygen during nighttime hours, and ",
"money plant",
"(Epipremnum aureum) as an air filter/conditioner. The current numbers given are 4 areca palms, 6-8 mother in law's tongue, and a money plant, though I haven't been able to find any actual supporting studies anywhere. That said, these guys are the most prominent group I have been able to find in many years of searching for studies on this topic."
] |
[
"Not only that, but if it were actually sealed, you'd have a hard time getting other stuff like nutrients for yourself and your new-found plant buddies. Look no further than the ",
"Biosphere 2 closure experiments",
" for a prime example of our biggest attempts (and failures) at creating a completely sealed-off, and self-sustainable environment.",
"But still, Meattle's experiments are so very useful for simply creating clean air around your home environment. The difference in air quality you can achieve by having a nice mix of these plants in and around your home is quite nice."
] |
[
"Not only that, but if it were actually sealed, you'd have a hard time getting other stuff like nutrients for yourself and your new-found plant buddies. Look no further than the ",
"Biosphere 2 closure experiments",
" for a prime example of our biggest attempts (and failures) at creating a completely sealed-off, and self-sustainable environment.",
"But still, Meattle's experiments are so very useful for simply creating clean air around your home environment. The difference in air quality you can achieve by having a nice mix of these plants in and around your home is quite nice."
] |
[
"A box is heated from the inside to 600 deg. C. If it’s made of aluminium, the inside is starting to melt. If it’s made of lead, the outside is starting to melt. Why the difference?"
] |
[
false
] | null |
[
"His wording is poor, or at least a bit terse. Pb melts at much lower temperatures (327°C) than Al (660°C), and the outside of the box is always cooler than the inside. 600 C is nearing the melting point of Al, so the inside would be getting gooey but the outside wouldn't get to that temperature very quickly (perhaps never) due to radiation and convection of heat away from the surface. Since Pb has a lower melting point, both inside and outside would likely be melting. "
] |
[
"My impression is that the reader thought (if my reading of \"Why the difference\" is correct) \"if it's lead, it's melting on the outside\" implicitly means it is not melting on the inside, and thus behaving in a different fashion than the aluminum. A simple enough misunderstanding."
] |
[
"Me too, but I blame the writer, not the reader. The wording simply wasn't that explicit. "
] |
[
"Is there such thing as a seismographic camera?"
] |
[
false
] |
I want to know if there is a camera that can detect seismographic activity in the ground? If so, how does it accommodate for the base, user, or instrument holding it? Is it an algorithm that differentiates between the movement of the base, user, or instrument and the ground? And how does it build this predictive modeling to accommodate for this?
|
[
"Ok, so if the question is very specifically, \"Is there a type of camera that we can point at the ground that can record details of passing seismic waves in the same way as a seismometer?\" then the answer is no, and we're done (and the follow up questions become irrelevant because the hypothetical device/method does not exist). ",
"If we instead pose a much broader form of the question, such as, \"Are there 'optical' methods, broadly defined, that allow us to study details of earthquakes?\" then the answer is yes. Probably the example closest to what OP is asking about is through the use of ",
", or COSI-Corr (e.g., ",
"Leprince et al., 2007a",
", ",
"Leprince et al., 2007b",
"). The basic idea behind this is you (1) have an image of the land surface from before an earthquake, (2) get an image of the land surface after the earthquake, (3) use details of the camera positions and camera properties of both images to precisely co-register the two images, and (4) use the offset of individual pixels to estimate a displacement field that resulted from the earthquake. For a more technical treatment, Leprince et al., 2007a goes through the details and the ",
"COSI-Corr",
" site has more technical details, software, etc. COSI-Corr can work on either satellite based or aerial (plane, drone, etc) based images and typically provides estimates of the horizontal component of displacement.",
"If we start to get a bit more flexible in our definition of optical and start to consider \"images\" that are produced with wavelengths of EM radiation other than visible light, we find another commonly applied \"optical\" method for exploring earthquake deformation, specifically ",
" or InSAR. ",
"InSAR",
" is used for a lot of applications, but it features prominently in understanding deformation related to individual earthquakes. In short, for InSAR, we use differences in the phase of radar waves bounced off the surface, usually from a satellite platform, between repeated \"images\" of the same area. In terms of earthquakes, what this requires is an InSAR \"image\" before and after the earthquake. Since InSAR is based on phase differences (which can be converted, or \"unwrapped\", into displacements), the displacements you estimate from InSAR will be in the \"look\" direction of the satellite with respect to the surface. Usually this means you're getting something closer to the vertical component (but would only be truly vertical if the satellite was looking straight down at the area of interest). In terms of technical details, the linked wiki page isn't a bad spot to start, but given the prevalence of this technique, there are ",
" of discussions of the way this data is acquired and processed, along with challenges (e.g., atmospheric effects, etc).",
"Finally, if we get real flexible in our definition of \"optical\" and consider basically anything that uses EM radiation to measure details of earthquakes, and in this case, specifically seismic waves like the original question focused on, we could consider ",
". This is a pretty new method but basically exploits existing large-scale fiber optic networks and turns them into arrays of strain sensors (which can thus detect seismic waves). There are a variety of technical treatments and considerations of applications of this emerging method (e.g., ",
"Lindsey & Martin, 2021",
")."
] |
[
"InSAR can be (and is) used to measure changes in the ground surface regardless of the cause. In detail, we use InSAR to measure ground deformation related to earthquakes, interseismic strain accumulation between earthquakes, movement of magma within volcanic systems, movement of groundwater, etc. There are limits on resolution, but in ideal conditions and depending on details of the ",
"radar band being used, size of the receiver, etc.",
", it's not unusual to be able to measure ground deformations on the order of a few mm to a few cm between InSAR acquisitions."
] |
[
"InSAR is primarily useful for short term changes to surface elevtions, so wouldn't have too many applications in this regard."
] |
[
"How long can footprints stay on the moon?"
] |
[
false
] |
Since there is no wind on the moon and very little atmosphere, how long can something (such as footprints) remain on the moon? The link below is a footprint on the moon: [ ]
|
[
"Given the absence of any significant atmosphere to cause traditional weathering, a food print could last dare I say indefinitely.",
"So let's look at what could affect footprints.\nFirst would be lunar dust accumulation acting in the same manner as snow covering footprints here on earth. You would have to ask NASA for the rate of new particle deposits, should it be known.\nSecond would be vibrations leveling out the dust. The moons core is inactive so that leaves impacts from asteroids.\nThirdly is physical removal, be that asteroids again or a person/robot/alien."
] |
[
"Second would be vibrations leveling out the dust. The moons core is inactive so that leaves impacts from asteroids.",
"there is actually seismic activity on the moon independent of asteroid collisions, the most powerful recorded moonquake was 5.5 on the Richter scale."
] |
[
"Do you have a reference? I'd like to learn more about how moonquakes are detected & measured, you've piqued my curiosity."
] |
[
"It's my understanding that the vast majority of the energy humans produce ultimately ends up as heat, does that heat have a measurable effect on the planet?"
] |
[
false
] | null |
[
"A disc with the same radius, provided it is perpendicular to incident sunlight, will absorb the same energy that a sphere does. That's why the oversimplification of treating Earth like a disc was ok for this comparison.",
"The difference is how that energy is distributed. On a disc it will be uniform (in W/m",
" ), but a sphere has a much larger surface area and different incident angles, so as you get closer to the poles the power per area goes down."
] |
[
"The world's energy consumption in 2008 was 143,851 TWh",
". This number may have changed today but not much. A simple calculation shows that this is equivalent to less than 1 hour of sunlight on Earth's surface. Our heat is really minuscule.",
"The greenhouse effect is another story. That one's big enough to get us worried about what we can do to the planet."
] |
[
"So around 1/100th of a percent, that's quite a bit less than I thought it would be. Awesome, thanks for the reply. I couldn't find any information on how much solar energy is absorbed by the Earth and its atmosphere in a given time period."
] |
[
"Why is caffeine, a polar molecule, soluble in supercritical carbon dioxide?"
] |
[
false
] |
I am under the impression that caffeine wouldn't be very soluble in super critical carbon dioxide due to the difference in polarity, yet it a ver popular method for extracting caffeine from coffee beans. Is this something special about supercritical fluids?
|
[
"Caffeine is actually pretty soluble in a lot of nonpolar solvents - another common method for extracting caffeine is to use dichloromethane, a nonpolar solvent that doesn’t mix with water. I would reason that since caffeine lacks significant hydrogen bonding, it doesn’t interact with itself strongly enough to prevent nonpolar solvents from solvating it. ",
"Also, apparently supercritical fluids are able to penetrate more deeply into the solid coffee beans, so that helps the efficiency of using CO2. But in terms of caffeine solubility, a whole bunch of organic solvents will work just fine.",
"Edit - wow, thank you for my first ever reddit gold!"
] |
[
"Yeah, it’s not something you wanna have in your food and drink. CO2 is nontoxic (relatively) and any leftover would just evaporate away when it’s returned to normal pressure."
] |
[
"Supercritical fluids, namely CO2 (the most used SF), are not static solvents with a constant polarity. ",
"If you take Hansen/Hildebrand solubilities, you'll see that organic solvents have solubility parameters that are function of temperature, and that SC-CO2 has a solubility parameter that is a function of pressure and temperature.",
"This means that you can adjust the solubility parameter, and typically you can increase it if you increase pressure (or decrease temperature). Any increase of pressure will lead to an increase of density. Then, what happens is that although CO2 is deemed non-polar, it has a large quadrupole that allows it to interact with polar compounds. This interaction is greater if you have a denser medium (more molecules in contact in a given volume).",
"On the other hand, and focusing now on caffeine side, any increase of temperature will enhance the solubility of this compounds in a solvent. While for organic solvents the maximum enhancement of solubility is typically limited by the boiling temperature of the solvent, under SC-CO2 there is margin to use a wider range of temperature to boost the solubility of caffeine. Of course, there is also a chance of deterioration of the compound if it is a labile one.",
"Finally, in the case of coffee decaffeination using SC-CO2, it is also important to bear in mind that, historically, the process has been carried out in wet green coffee beans, and that water plays a role in the process. In fact, the solubility of caffeine in water is about 20 g/L at 20ºC, while, for comparison, the palmitic acid (very well solubilized in SC-CO2) has a solubility in water of only 0.04 mg/L."
] |
[
"Why do Tyrosine Kinase Receptors come in pairs?"
] |
[
false
] |
I'm a Junior in molecular-cellular biology, and I am currently learning about endocrinology. In every diagram I have seen of the receptor and its mechanism (basic diagram ) It shows them, after binding with the desired signal, aggregating before actually phosphorylating proteins, but in none of my books/ lectures I remember explain why it does this. Is there an added benefit to combining/ can it not function as a single unit? Any enlightenment is appreciated.
|
[
"The intracellular kinase domains of single RTK monomers are not catalytically active. Binding of ligand to the extracellular domains of these monomers causes a conformational change that induces dimerization of two monomers. This dimer then undergoes subsequent autophosphorylation of tyrosine residues in its intracellular kinase domain(s) (the subunits phosphorylate each other). This dimerization and autophosphorylation of RTK monomers activates/stabilizes the intracellular kinase domain of the receptor which can now phosphorylate its substrates inside the cell",
"1",
"2",
"Note: This is true for most RTKs. One exception is the insulin receptor which technically exists as a dimer/tetramer. "
] |
[
"English translation (not being sarcastic, this is just in case any nonspecialists want to follow this nice answer):",
"The part of the receptor that sticks into the cell normally can't do anything. But when a hormone molecule floats by and binds to the part that sticks outside the cell, this causes the receptor to change shape in such a way that it now can stick to another (identical) receptor. Then, they each put phosphate groups on each other, on the parts that stick inside the cell. The phosphate groups activate and stabilize the parts inside the cell, so that now, the receptors (both of them, still stuck together) can put phosphate groups onto certain other molecules that are floating around inside the cell. ",
"The insulin receptor is different; each insulin receptors has two subunits. Then when the hormone arrives, two receptors stick together (so, four subunits total).",
"(end translation)"
] |
[
"Thank you!"
] |
[
"How did early composers know to put low frequency notes \"under\" other notes on the scale, if they didn't know about frequency and sound waves?"
] |
[
false
] | null |
[
"I'm going to point out that the choice of frequency rather than period (that is, cycles per second rather than seconds per cycle) is equally arbitrary. That is, 440 Hz could be called 2.27ms, in which case higher numbers represent lower frequencies. "
] |
[
"Well, this is essentially a question of etymology.",
"When singing, the resonance space for low pitches (chest) sits below the resonance space for higher notes (oral cavity, sinuses). This may give a physical reason for calling them \"lower\" and \"higher\", respectively.",
"I wonder what the literal meaning of pitch qualities is in languages other than English."
] |
[
"But translating energy levels to a direction ",
" completely arbitrary. There's no reason \"higher energy\" has to correspond with \"up\" - when we sort a list, we usually put higher numbers at the bottom.",
"Since everyone so far is already speculating, I'd guess it's as simple as \"your adam's apple moves up when you sing a high note and down when you sing a low note.\""
] |
[
"Lets say we find aliens, and we somehow speak the same language (or have some sort of translation available)"
] |
[
false
] |
How could we communicate something as simple as a unit of time to them? If our time system is based upon our distance from the sun, then wouldn't their definition of a "second" or a minute (never mind days and years) be completely different than ours? Does this mean that time is relative to where you originate? IE a person from the planet Omicron Persei 8 could have calculated their second to be equal to 1.5 of our seconds, who's "right"? Is there some sort of standard unit of time that is simply based on something other than the sun? Wikipedia says a second is: the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. Not sure what that means, and an explanation would be cool too. But what I'm really wondering is how we got to that number, 9 billion some odd periods of radiation seems like such an arbitrary figure. Sorry if these questions seem dumb, its just something that hit me out of nowhere that I couldn't think of an answer to
|
[
"All units are arbitrary. There aren't any special magical units of anything.",
"If you wanted to tell someone how to measure a second, you'd just describe the method for doing so. Same way you'd have to describe the definition of any other unit you might care to imagine. (Except the kilogram. \"It's a lump of metal in France\" isn't going to help anyone.)"
] |
[
"Yes but it would be useless as a time unit because it's incomprehensibly short."
] |
[
"In SI all scientific units are ",
" based on universally observable experiments. For example the second is defined as ",
"which is something you could describe to an alien over the phone. The other units are similar excluding the kilogram which is currently being worked on.",
"With this it's trivial to agree on conversion factors between our system of measurement and theirs."
] |
[
"What drives the movements of tectonic plates?"
] |
[
false
] | null |
[
"There are three main drivers of plate motion, listed in approximate order of importance/strength they are (1) slab pull, (2) ridge push, and (3) basal traction. Slab pull is the force imparted from the negative buoyancy of the edges of oceanic lithosphere/plates which have started to sink into the mantle at ",
"subduction zones",
" as they have reached a state (through cooling and thickening) where they are denser than the asthenosphere below (imagine a rug floating on a pool of water and then you clip some weights to one edge of the rug, that edge of the rug will sink and drag the rest of the rug down with it). Ridge push is largely from positive buoyancy, i.e. new oceanic lithosphere is created at ",
"mid-ocean ridges",
" and this lithosphere is very warm and less dense than the lithosphere adjacent to it (away from the ridge) and so is sitting higher than the adjacent lithosphere, this translates to some force pushing away from the ridge. Basal traction is essentially a drag force imparted to the base of the plates from motion of the mantle driven by convection currents and other movements and it can be a driving or resisting force depending on the orientation of the basal traction with respect to other forces. We can further resolve other forces that both drive and resist plate motion, e.g. ",
"diagrams like these",
", but these are the three major drivers. From the early days of plate tectonics, we've known that under most normal circumstances slab pull dominates plate motion (e.g. ",
"Forsyth & Uyeda, 1975",
"), but there continue to be discussions about just how important (or not important) the other forces are and a lot of the details of slab pull and what influences it, e.g. ",
"Schellart, 2004",
" as one example. But at the basic level, saying that plate motion is fundamentally tied to the life cycle (i.e. creation at a mid-ocean ridge and destruction at a subduction zone) of oceanic portions of plates (e.g. ",
"Crameri et al, 2019",
") and mostly driven by the sinking of subducted slabs would be correct.",
" For all the people replying or commenting elsewhere, the relationship between mantle convection and plate motion is complicated, but ",
". The common, simplistic view of plates passively moving along on top of convection currents in the mantle (a model referred to as the \"passive plate model\") is demonstrably false. A better way to think about this is the plates forming a part of the convective system, but not one driven by heating from below but rather more by cooling from above, where the driving forces end up being the edge forces on plates (primarily slab pull) and plate motion and the geometry of mantle convection are both dominated by the behavior of these subducted slabs (e.g. ",
"Crameri et al, 2019",
"). The nuanced relationship between plate motion and convection is expounded upon in a variety of papers (e.g. ",
"Bercovivi, 2003",
" or ",
"Foley & Becker, 2009",
"), but critically, the dynamics are much more complicated than just saying \"plate motion is driven by convection\" as, for example, the dynamics of the subducted slab and interactions with the overriding plate are critical in explaining many important aspects of plate motion, e.g. ",
"Becker & Faccena, 2009",
"."
] |
[
"If you don't mind I would like to ask several additional questions. 1. Why doesnt the Cascadia subduction zone create a trench I thought all subduction zones made trenches. 2. Which countries are likely to get hit by M9 earthquakes in the foreseeable future. 3. If california is moving west why isn't is a subduction zone and will it become one at any point in the future."
] |
[
"Just wanted to comment as well a cool fact that the Juan de Fuca plate off the north west of america is actually the last remnant of an ancient plate known as the Farallon Plate which has completely subducted underneath the north american plate. ",
"In fact it has been over run so deep by the NA plate that it's mid-ocean ridge itself lies beneath the NA plate in certain areas. It's is suspected to be one of the primary drivers of western american geology over the last 100 Million years and even now that plate is theroized to be related to the formation of the colorado plateau(grand canyon), yellowstone supervolcano, and most of the basin and range geology and topography."
] |
[
"if i used a relatively cheap telescope that can be store bought and if i use it to look at alpha centauri. would i be able to see the star move relative to other stars every 6 months?"
] |
[
false
] | null |
[
"Not by eye. If you made really precise measurements of the stars' angular position over long periods of time, you may be able to measure the parallax. Alpha Centauri's parallax is like a 4000th of a degree."
] |
[
"Apparently Bessel used a 6.2 inch diameter heliometer that looked like ",
"this",
" to measure 61 Cygni's parallax. Pretty impressive."
] |
[
"Bessel was able to do it in 1836 but I don't know what kind of telescope he had. Looking through his original letter, it says he used magnitude 11 stars as reference, so maybe that can be used to figure out the size of telescope required."
] |
[
"If I scramble my dogs medicine with eggs, is it possible the heat will alter the compound and make it ineffective or even dangerous?"
] |
[
false
] | null |
[
"We do not offer any sort of medical, safety, nutritional or really any sort of advice on this sub. Please see the guidelines. If you have a concern, please speak with a physician."
] |
[
"im not really asking for advice, but rather if heat of the temperature range provided by a stovetop applied to a compound will/could materially change the compound"
] |
[
"The answer to that general question is yes -- that's cooking. We can't answer a specific question about your dog's medicine / advise about safety."
] |
[
"Can cameras be built with extended color range? Are any currently available?"
] |
[
false
] | null |
[
"https://en.m.wikipedia.org/wiki/Full-spectrum_photography"
] |
[
"Yes there are infrared and uv cameras"
] |
[
"Misses my point. I don't want an IR camera or a UV camera. I want a camera that converts IR to red and UV to blue, so an 800-300nm spectrum could be converted to traditional RGB colorspace."
] |
[
"Did all trees that have thorns come from a common ancestor or did trees in different regions across the world with thorns all develop them on their own naturally through evolution?"
] |
[
false
] |
I hope I'm wording this right.
|
[
"What we commonly call thorns encompasses a lot of different structures with different origins. Proper thorns are derived from side branches, like for example in Gymnosporia species. The thorns on roses, on the other hand, are properly called prickles, they are derived from the epidermis. And then there's spines, which are derived from leaves, for example in cacti.",
"So, overall, thornlike structures evolved many times independently."
] |
[
"This answer is correct, but massively understates things. Thorns, spines, and prickles are different things that evolved differently, but let's take a look at proper thorns. Did proper thorns evolve once, or many times?",
"The ",
"wikipedia page for thorns",
" lists three plants with proper thorns. Let's look at the first and last.",
"https://en.wikipedia.org/wiki/Citrus",
"https://en.wikipedia.org/wiki/Carissa_bispinosa",
"Now, let's look at the smallest clade containing these two plants: ",
"https://en.wikipedia.org/wiki/Eudicots",
"To quote from that page: \"Some common and familiar eudicots include members of the ",
"sunflower family",
" such as the common ",
"dandelion",
", the ",
"forget-me-not",
", ",
"cabbage",
" and other members of ",
"its family",
", ",
"apple",
", ",
"buttercup",
", ",
"maple",
", and ",
"macadamia",
".\"",
"Obviously not all of these plants have thorns. So while it's possible that the common ancestor of all of them have thorns, and a bunch of members lost them, the fact that thornlike structures have evolved at least three times (as thorns, spines, and prickles) makes it more likely that it evolved independently.",
"Another thing that looking at this evolutionary structure hints at is that not even all ",
" share a common ancestor; a maple tree and a buttercup are closer related than a maple tree and a spruce tree."
] |
[
"Awesome answer. Thank you so much ;)"
] |
[
"How does Quantum Field Theory explain things like Rayleigh Scattering?"
] |
[
false
] | null |
[
"What level of depth are you looking for in an answer, and what kind of background do you have?"
] |
[
"I have a little more than a foundation understanding, I'm aware of bosons and fermions, and the excitation of various quantum fields with which ",
" particles may react while others react to different fields.",
"My understanding is that light hits the atom and subatomics with the atom react to the energy they gain by immediately getting rid of it as another photon (or by any of the steps that can be shown on a Feynman diagram), but as I'm reading now on QED I'm struggling to see how the energy level of the photon causes it to be re-emitted at differing angles.",
"Thanks."
] |
[
"The coupling between the photon fields and the charged particle fields allows excitations of the fields to exchange energy and momentum with each other. Because momentum is a vector quantity, whenever momentum is exchanged, the particles involved will generally change direction."
] |
[
"Are chemicals produced within the body carcinogenic, and to what degree? Does the body use common Organic carcinogens (for instance formaldehyde) as part of its molecular machinery?"
] |
[
false
] | null |
[
"The main carcinogenic byproduct of chemical reactions in our body are oxygen free radicals (superoxide, hydrogen peroxide, etc.). Fortunately, we are well equipped to deal with those under normal circumstances. We have enzymes like superoxide dismutase and coenzymes like glutathione to turn those free radicals into harmless water and CO2, which we then excrete. Most of our cells also have peroxisomes to detoxify H2O2 via similar mechanisms. Antioxidants advertised in commercials refer to preventing free radical damage for the same reason. The strongest antioxidant in our body in Vitamin E, as it is a final acceptor for the negative charge without propagating it down the line.",
"As far as their level of carcinogenicity, it varies, but in general they are highly mutagenic. Free radicals have a negative charge that seeks out and binds to positively charged DNA and proteins. They also tend to self-propagate when left unchecked, leading to a massive capacity to cause mutations in a cell. Carcinogenicity depends on where those mutations end up, which is related to random chance more than anything else. If it mutates certain genes (p53, retinoblastoma, etc.), then the cell will proliferate despite the damage, leading to neoplastic transformation. If apoptotic genes remain intact, then it's more likely that the cell will just commit suicide to protect the organism. It's the last line of defense against mutations proceeding down the line to cancer.",
"So in short, the free radicals are produced by our bodies in many reactions, but we have ways of combatting them. They are mutagenic if they get by our defenses, and those mutations may proceed to malignant transformation if certain genes are involved."
] |
[
"An excellent answer, and I have only one question to ask as a matter of clarification. I was wondering about the reactions between oxygen free-radicals and DNA. Since the assumptions made during PCR include that DNA is negatively charged due to its sugar-phosphate backbone, it makes sense that a oxygen free-radical would react with the nitrogenous bases themselves. Do you have a link to those reactions? It seems like they would be very interesting!"
] |
[
"You are absolutely right about reactions occurring with the bases themselves. The most common examples are pyrimidine dimers (cytosine) associated with free radicals from UV light that lead to melanoma, though there are many others as well. ",
"Wikipedia",
" has a decent summary of pyrimidine dimers, though it only mentions that they are caused by UV light. Digging deeper into the ",
"UV article",
" describes free radicals as the cause. Sorry I don't have more formal links; most of what I know is from the texts I've accumulated over the years. Let me know if I can help you further!"
] |
[
"Have cancer rates gone up? Or has the technology to detect cancer gotten much more advanced?"
] |
[
false
] |
I feel like it's most lily a bit of both... Search 'cancer' on wolfram alpha and you will see where I am coming from.
|
[
"Multiple things here\n1) Yes - detection is much better\n2) People live longer, so other things that killed people - infections, trauma,etc - aren't bringing down the average age of death. So since people are living longer, we are seeing that people are dying of cancer (at a much older age) and at an increased incidence."
] |
[
"so do you feel the toxins that we are putting into our bodies increase cancer rates. for example there was a company out there (sponsored by ciggaret companies) proving that smoking was not bad for you, and finding the positive sides. Point 2, oldest woman that lived to date smoked 2 cigs a day! Does the sun really cause increase cancer rates? chemical etc. what can we do about it?"
] |
[
"Cigarette smoke has repeatedly been linked with increased risk of cancer both in human epidemiological studies and animal model experiments. Anecdotes shouldn't be confused with scientific evidence, saying that cigarettes don't cause disease because she didn't die of cancer is like saying all people should live to be her age because she was able to."
] |
[
"Aren't we technically still in an ice age?"
] |
[
false
] |
e.g. over Earth's history, having permanent ice at the poles is an anomaly, not the norm (receding from it's peak where ice reached as far south as Ohio at the height of this ice age). From my understanding, we are technically at the tail end of the last ice/glacial age. Losing ice at the poles is inevitable, is it not? The Earth has had ice free poles over the majority of history that life has existed, true? Am I missing something?
|
[
"Hopefully this will help with some of the professional jargon. We are currently in an interglacial, as opposed to an ice age or glacial time. The somewhat informal term in the literature for an ice free Earth is a \"Hot House\" period. This is contrasted to periods with stable polar ice referred to as an \"Ice House\" Earth. The example I'm most familiar with is that throughout the Cenozoic (past 65 million years) the Earth has gradually cooled, transitioning from the Paleocene & Eocene hot house to the ice house of the Oligocene and more recent Earth. Stable antarctic ice sheets developed at the E-O transition and stable arctic ice developed in the Late Miocene (~10 Ma). The terms 'Ice Age', 'glacial', & 'interglacial' are used primarily in the context of only the past 3-5 million years; mostly referring to more recent times as the pattern of expansion and not-total-retreat of northern hemisphere ice sheets became established.",
"tl:dr We are living in an 'Ice House' world during an 'interglacial' period of time. And I'm not using the geologic chronology definition of 'period'."
] |
[
"The Earths glacial - interglacial periods follow closely to the Milankovitch Cycles which in a general sense act on 26000, 41000 and 100000 cycles which effect the global ocean temperature, global surface temperature and sea level which in turn drive the glacial cycles. These cycles will keep occurring, but the effect they have on the earth will not be the same as the past if current climate change continues. Effectively we will still see a change in global temperature etc in the coming thousands of years but the Glacial (colder) periods will be warmer than they would be without current climate change and the Interglacial periods will reach higher temperatures than they normally would on a natural scale. ",
"TL;DR Natural glacial cycles (\"ice ages\") will continue but the effects will be changed due to current anthropogenic climate change. Glacials will be warmer and have a slower onset, Inter glacials will reach new global temperature highs."
] |
[
"This is the scary part of the future as we're moving into uncharted territory with anthropogenic ejection of greenhouse gases into the atmosphere. ",
"Bad things may happen sooner rather than later. We have presage to guide us in making recommendations to governments, but as of right now most governments are ignoring to a large extent the urgency of this matter. ",
"What you've illustrated may be detrimental to the survival of the human race as a whole. We may be adaptive to change, but again this is ",
" for us. Here's to hoping governments implement the necessary changes with haste to avoid any adversity. "
] |
[
"Is there an increase in the average IQ of people born after the worldwide ban of leaded gasoline?"
] |
[
false
] |
We know lead hinders brain development, and makes us a little bit slower. Some have argued that leaded gasoline was responsible for reducing the iq of generations of people. It has now been a while since leaded gasoline has been banned worldwide. Do we see any non-negligible difference in levels of intelligence in people before and after the lead ban? (I know IQ is an imperfect measure of intelligence it is just one data point. And I use it for a lack of a better metric)
|
[
"Lead exposure is directly linked to developmental issues and lower IQ:",
"- ",
"https://today.duke.edu/2017/03/lead-exposure-childhood-linked-lower-iq-lower-status",
"We also know for a fact that levels of lead in blood decreased significantly following the phase out:",
"- ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5810431/",
"- ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3620025/",
"- ",
"https://www.journals.uchicago.edu/doi/abs/10.1086/691686",
"There's pretty good evidence that lead exposure from fuel is linked to an increase in crime:",
"- ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3829390/",
"- ",
"https://www.sciencedirect.com/science/article/abs/pii/S0014498316300109"
] |
[
"It's not a case of IQ going up so much as fewer children were suffering developmental and cognitive issues. So it's like asking \"are we running faster now that we've stopped putting landmines everywhere and blowing off legs?\"",
"\"children with blood lead levels of 10 micrograms of lead per deciliter of blood (μg/dL) score four points lower on IQ tests than children with blood lead levels of 2 µg/dL.\"",
"Although since so many children were affected it may result in an overall average increase over the decades of high exposure :",
"`The findings lend credence to an estimate that, in the U.S. over the last 40 years, interventions to reduce lead exposure may have \"raised the mean IQ in adults by as much as 4.5 points.\"` -- David Bellinger, a neuropsychologist and environmental epidemiologist with Boston Children's Hospital and Harvard Medical School and a longtime researcher of lead's effects.",
"-- ",
"https://pubmed.ncbi.nlm.nih.gov/24853978/",
"",
"Other results put the number higher at 6 IQ points:",
"\"Dr. Philip J. Landrigan, who found that since the removal of lead from gasoline in 1976, there's been an 80% drop in blood lead levels, and in that same period a six-point gain in children's IQs.\""
] |
[
"IQ relative to previous generations has also increased due to iodized salt (iodine deficiency used to be very common). So there are several factors at play here, not just leaded gasoline."
] |
[
"What is the relation between electrons, photons and electromagnetism?"
] |
[
false
] |
First of all, English is not my first language and it has been a while since I actually had education in that area of physics so the following is what I udnerstand and is only partially correct. As far as I understood, photons are the particles that "spread" the force in electromagentism, as electromagnetic waves. I also know that electrons have electric charge and moving electrons cause a magnetic field. Does that not mean that electrons are also an "electromagnetic" particle? Following up, does the wave particle simultanity principle hold for electrons as it does for photons? Does that mean electrons are also "electromagnetic waves"? Additionally, why do we call "light" or photons "electromagnetic waves"? Are all photons electromagnetic waves or does it depend on wavelength/energy or the source? Thank you for any corrections and clarifications of my thoughts.
|
[
"Electrons are particles. We think they are fundamental particles, which means they aren't made up of any smaller particles.",
"Electrons have electric charge, which means that they interact with each other (and with other charged particles) through the electromagnetic field. This is a field that fills up all of space and tells charged particles how to move. Here's how it works: particles with charge shape the electromagnetic field, depending on how much charge they have, where they're located, and how they're moving. Then these same charged particles will move in reaction to the electromagnetic field, which is the same as saying they respond to the other charges in the Universe.",
"If you wiggle a charged particle like an electron around, that will create ripples or waves in the electromagnetic field. Those waves are light. But we know that because of quantum mechanics, these waves can also be seen as particles. Those particles are photons, and it's often sensible to talk about light ",
"either as a wave or as a particle",
"."
] |
[
"A good way to think of these fields, starting from the sort of formal setting and working our way down...",
"A field is a function f(x,y,z,t) that has either a vector or scalar associated with every point. A good example of the former is the wind velocity on Earth, where each point on the globe has a vector representing where and how fast the wind is blowing; an example of a scalar field would be the temperatures across the earth's surface. Fields are defined at EVERY point in the area of interest (in the case of the wind we are dealing with the entire earth'a surface, in the case of the EM field we are dealing with entire universe) even if they have a value of zero at some of the points they still exist there.",
"Vector fields are associated with forces like EM because they tell us how a particle subject to those forces will behave. The vectors of the electric field for example tell us in what direction and with what magnitude a positive test charge would feel the electric force (with negative charges feeling the equal yet opposite charge).",
"Breaking physical reality here a little you can imagine a tiny mass along the wind field showing the same behavior as it would ride along the vectors of the field.",
"This post was for OP, you're post was spot on and I'm confident you knew all that, Mr Cosmologist. Just thought OP might want to know more about fields."
] |
[
"Electrons—and all other particles—exhibit ",
"wave particle duality",
" and can be described as waves as well as particles."
] |
[
"can anyone answer this, has the amount of water on earth been constant from when it was created till now? or has it grew or got less?"
] |
[
false
] | null |
[
"The prevailing geologic theory is that the vast majority of water on Earth was deposited here by asteroids and ",
"planetecimals",
". From that point, the amount of water on Earth has been relatively constant with only a few losses. Atmosphere, including water vapor, is occasionally vented to space, losing some water. Humans used it for fuel to escape the atmosphere. (The shuttle uses liquid oxygen and liquid hydrogen for fuel.) Most of these are fairly small changes to the global amount of water, however.",
"TL;DR It's about the same. We lose a small amount, but it's not really noticeable."
] |
[
"Comets",
" have water in them. Every time one hits the Earth, it adds to the amount of water on the planet. Multiply by billions of years, and a lot of water has been added."
] |
[
"I have a question about this theory. Did water not exist on earth while it was solidifying? If, theoretically, no comets or asteroids hit earth whatsoever, would there be no water on earth?",
"Also, how many water containing comets would be needed to have striken earth, so that three quarts of our planet is covered with water?"
] |
[
"Is a collapsing EM wave function capable of producing only a finite number of photons? If so, is the distribution manipulable?"
] |
[
false
] |
I read and because I was trying to figure out how an "observer" (e.g. my car radio) of an EM signal might affect the strength of that signal for a nearby "observer." I sort of understand that it's not just photon bullets shooting out at some initial density per square centimeter that dilutes as radius increases. So I started thinking about how or if we could see strange behavior of this wave function collapse due to interaction with a physical object. Let's say that there's a star out in intergalactic space that is not terribly bright/energetic. Its light is interacting with physical objects which are uniformly but sparsely distributed in a sphere around it at an extreme distance but still energetic enough to barely excite the atoms it hits on those objects. There's only empty space between the star and these objects. If we came from outside this distance limit and started placing more objects only on one portion of the spherical limit, would it affect the way the light on the other sides of the star interacted with the other objects? If we moved our artificially-placed objects closer to the star than any of the other objects, would that affect the way the light interacted? Probably meaningless background on what made me think of this: I was driving through a pretty sparsely populated area and noticed that as I approached hills the radio signal I received from the town toward which I was driving would drop off. Obviously the hill was getting in the way and absorbing some of the radio signal. While in the car and before I had looked up much on this to learn about wave function collapse I was thinking about how the "radio photons" were probably randomly energizing bits of rock and dirt and worms in the hill instead of my radio antenna. That got me thinking about if we could "cheat" on "focusing" light from a long way away by using the things we know about how weird photons act during e.g. the . Like setting up a double slit or finding one in space and then placing antennas at the "constructive interference" points to get a boosted signal we wouldn't otherwise be able to sense. And now I'm here thinking about lonely stars.
|
[
"The thing about \"wave-particle duality\" is that the limit where a quantum objects acts as a particle is very different from the limit where it acts as a wave. I use \"wave-particle duality\" in scare-quotes because the real description is a purely quantum one which does not act exactly like classical particles or classical waves, but there are two very different limits where the quantum description either looks like classical particles or classical waves, and when you are in the wave-like limit, it is very hard to interpret the system in terms of the \"classical particle\" description and vice-versa. (This paragraph is basically a statement of Bohr's complementarity principle.)",
"In any case, what you are doing is thinking about light which is very close to the wave-like limit and trying to interpret it in terms of particles, which is possible but very awkward. If you try to write down wave-like light in terms of photons, you get what are called ",
"coherent states",
" which are superpositions of different numbers of photons. So the state looks like ",
"k1 |no photons> + k2 |1 photon> + k3 |2 photons> + ....",
"and so on with more and more photons. The coefficients k1, k2, k3 have different weights, and when you read the answers on Stack Exchange referring to certain stars having an enormous number of photons, they are referring to these weights being much larger around some average number of photons, but there is a spread in the \"photon number\" basis because the number of photons is indefinite. This is what I mean by the particle description being awkward. In turn, if you prepare a state with a definite number of photons, the average electromagnetic field is zero, with quantum fluctuations about zero (this is very much not similar to the classical wave description of light).",
"In turn, the low-energy interactions you describe with other objects are also not well-described in terms of photons. Photons were first proposed (by Einstein) to describe the photoelectric effect, where energies are high enough that the particle-like nature of the wave is important in describing interactions with electrons in a material. However, at low energies where the interaction can be described by classical physics, we get normal ",
"Thomson scattering",
". These interactions do not \"collapse\" the quantum state into a particle-like wave function; the final state will still look like the \"classical wave-like\" coherent state described above."
] |
[
"Are you referring to definite photon states or coherent states? Either way, presumably the best resources are quantum optics textbooks which I'm not really familiar with (though I have an electronic copy of Glauber's). I mostly learned about these states while taking and teaching various quantum courses; quantized electromagnetic fields should be developed in a grad QM 2 course (or even introduced to undergrads), so you should find some discussion in your favorite grad-level QM book. ",
"The \"main idea\" is that the Hamiltonian for the vacuum Maxwell equations is just a sum over independent harmonic oscillators which represent different momenta and a momentum-dependent frequency. So for E&M fields with a definite momentum/frequency, the relevant Hamiltonian is literally just a harmonic oscillator with frequency ck, which you can write in terms of creation/annihilation operators. Now the interesting part comes from the relation between the electric and magnetic field operators and the creation/annihilation operators, which then connects everything you know about the harmonic oscillator to light. Coherent states arise already in the 1D harmonic oscillator (Schrödinger already pointed them out a few months after his first paper as a classical limit).",
"Here are some notes I like on coherent states.",
" Some googling found ",
"these notes",
" on quantizing EM fields which look pretty nice at a first glance."
] |
[
"what you are doing is thinking about light which is very close to the wave-like limit",
"What pops into my head when I read this is a \"massive army charging\" scene from a movie. The horn is sounded, everyone starts charging ",
", and from afar the camera just sees a wave of humanity rushing forward. Then as the charging wave of humans gets to a certain point, you're able to pick out this individual human or that one breaking away.",
"Is it fair to say that the quantum physical description of EM energy doesn't really have a \"wave\" or \"particle\" for light?",
"What phenomena would occur to the sensors (or whatever) we installed at the \"wave-like limit?\" Would they heat up/gain energy from the lonely star? If so, would it look uniformly distributed to scientists monitoring the energy levels of the sensors?",
"Would that energy look like an \"individual\" photon's worth of energy? Something less?",
"I really appreciate your answer although it makes me almost certain I know even less about light/quantum physics than I thought (which wasn't very much at all)."
] |
[
"The sun appears to move faster during sunrise or sunset. Why?"
] |
[
false
] | null |
[
"It's an optical illusion based on you being able to scale it against objects on the horizon. When it's in the air, you can't judge its movement nearly as well. If you photograph it every few minutes, you'll see it go across the sky at even intervals."
] |
[
"You are seeing the projection of the sun’s rays refracted through the layers of atmosphere. It amplifies the visual size so that gives the illusion it is traveling faster. (it also appears bigger when it also appears faster, right?)",
"Someone else can probably explain it better than me. Is there an ",
"/r/Astrophysics",
"? X post"
] |
[
"Im not very familiar with any scientific reason this would happen but throughout the day we see the sun move across the sky over a blue medium. When the sun is setting you can still see the sky ex. but your also able to see the sun progressively getting smaller and smaller as the horizon cuts it off. Sunrises and sunsets give us another visual cue which could lead it appear to move faster."
] |
[
"Approximately what magnitude earthquake would it require to destroy the Hoover Dam?"
] |
[
false
] |
In the trailer for the movie San Andreas they show the Hoover Dam collapsing as a result of a super earthquake. Has there ever been an earthquake in history that would have been capable of destroying a structure like the Hoover Dam? What would the absolute minimum magnitude on the Richter scale be for a quake that could cause destruction such as that, assuming it happened as close to the dam as possible? Edit: here's an that kind of covers the premise, but seems to cover the question in terms of what could realistically happen. I guess I'm more wondering what could happen.
|
[
"Buried ",
"deep within this pdf of a powerpoint presentation",
" on the Hoover Dam are a few statements about the dam design with respect to ground motion from earthquakes. It was designed to withstand horizontal ground acceleration up to 0.1g. ",
"Correlating ",
"peak ground acceleration",
" to a scale of earthquake intensity, like the ",
"Mercalli scale",
", is reasonably straight forward and the maximum ground acceleration for the Hoover Dam of 0.1g corresponds to a Mercalli intensity of VI, with strong shaking but light damage. ",
"Now, correlating ground acceleration or an intensity of shaking at a point with an earthquake magnitude (the correct term is the ",
"moment magnitude scale",
", the richter scale has not been used since the 1930's) is not straight forward as it depends on a lot of factors. As mentioned in the article you linked to, seismic waves attenuate as they travel, so the ground acceleration at a location will depend on the distance from that location to the earthquake hypocenter (actual point on fault of failure) and epicenter (projection of hypocenter location to surface of earth). A bigger factor is actually the material in the location of interest. \"Stiffer\" material, like intact igneous or metamorphic bedrock will transfer seismic waves more efficiently, allowing for further propagation of strong shaking (distance wise). Seismic waves will attenuate quicker in less consolidated material (sediment) or very fractured rocks, but especially in unconsolidated sediment, seismic waves will often reverberate and can actually increase the peak ground acceleration through constructive interference. If you look at that page on peak ground acceleration and scroll down to the bottom, you can see just how variable this can be, for example the magnitude 6.0 2011 Christchurch earthquake had a PGA of 1.0g whereas the 1964 Great Alaska earthquake that was 9.2 magnitude had a PGA of 0.18g, despite those differences in magnitude being equivalent to the Alaska earthquake releasing ~63,000 times more energy than the New Zealand 6.0. This difference in PGA can be attributed to different depths for the hypocenters and very different materials through which the seismic waves traveled.",
"This is ultimately why developing detailed seismic hazard maps required lots of geological data, not just locations of faults, but the histories of earthquakes on those faults and the geology of the region in question. ",
"Take a look at this ",
"seismic hazard map from the USGS of Nevada",
". This is presented in terms of a 2% chance in the next 50 years of a given region experiencing a particular peak ground acceleration. The color code is the PGA in percent of 1g, so the Hoover Dam was engineered for a 10 on this scale, and you can see that the location of the dam is in the 14-20, meaning that there is a 2% chance in the next 50 years of an earthquake happening that could cause PGA above the engineering tolerances of the Hoover Dam. Whether this would actually cause failure of the dam is a question for an engineer.",
" - To directly answer your question, yes, there have been many many earthquake that have occurred that could destroy the Hoover Dam, mainly because the Hoover Dam was not engineered to withstand ground acceleration over 0.1g, but Tom Rockwell was right in that article you linked, an earthquake on the San Andreas is not going to cause this because of the distances involved. This more generally accentuates the importance of understanding the seismic hazard of a particular area when building critical structures, i.e. the peak ground acceleration you need to plan for depends entirely on where you are building."
] |
[
"Some citations are always helpful for instances where someone \"cannot be true\". ",
"There are several papers documenting ground peak ground acceleration for the Great Alaska quake and they're all significantly lower than what you might expect. A lot of them are unfortunately not easily found online, for example: ",
"Hanson, R. D. (1973). Behavior of liquid-storage tanks, in The Great Alaska earthquake of 1964: Engineering, National\nAcademy of Science, Washington D.C., 331-339.",
"Housner, G. W., and P. C. Jennings (1973). Reconstituted earthquake ground motion at Anchorage, in The Great Alaska\nearthquake of 1964: Engineering, National Academy of Science, Washington D.C., 43-48.",
"Modeling studies reconstructing ground accelerations for this earthquake, come in around 0.3g ",
"e.g. this reference",
".",
"As for what the damn was engineered for, this paper, ",
"Seismic Evaluation of Hoover Dam Powerplant",
", confirms that the original engineering documents considered it capable of withstanding 0.1g of horizontal motion, but this later finite element modeling of the dam structure suggests this is likely closer to 0.4g."
] |
[
"0.1g is too low. I was about to say that in Greece dams are more robust, but I came across a rather small dam (but with gold mining waste), whose study uses arbitrary PGAs per section, starting with a very reasonable 0.85 and falling until 0.19g, which is too small for a dam on the hanging wall of a normal fault 3 miles away which produced a Ms 7 earthquake in the instrumental era. So I guess that Hoover Dam is adequately designed for its tectonic environment... or not?",
"The 0.18g you mention about the 1964 earthquake cannot be true: at the time there were fewer accelerometers. Even if a typical subduction zone earthquake, its epicenter was officially on land, and we know of a splay fault with 12ft surface displacement on land, plus extensive landslides. These do not sound like anything less than 1.0g. You are, however, true that PGA may hit high values even in rather moderate earthquakes.",
"On the other hand, in the case of dams and especially massive designs (I think Hoover is an arch-gravity dam, not a classic massive gravity dam) the duration of shaking is especially important because it may produce slides of the dam material. Dams can usually tolerate significant deformations and an over-the-design-limit earthquake does not mean that it will produce a catastrophic failure (just like an under-the-limit earthquake may produce some repairable or sustainable damage).",
"Otherwise I agree with the above answer. However I am not familiar with the geology of the region. Even though the main San Andreas fault is far away and it cannot produce respectable PGAs at the Hoover site even in the case it hits Mw 8, there must be other parallel faults a lot closer, as ",
"/u/lindypenguin",
" said."
] |
[
"How do new stars form out of the dust from older exploded stars that were out of fuel?"
] |
[
false
] | null |
[
"When these older stars go supernova (or, in the case of less massive stars, just expel their outer bits in a non-explosive kinda way), they enrich the interstellar medium with the metals they produced. Basically there's a lot of gas between stars, and these explosions add to that gas, giving it more heavy elements than it had before. For one of several reasons, a part of that cloud might be denser than its surroundings. If it's dense enough, its gravitational force (pulling all its matter in) will overcome the pressure which balances it out, causing that bit of the cloud to collapse. This begins the process of star formation."
] |
[
"To add to this explanation, if necessary: the interstellar medium is full of hydrogen, and the enrichment by heavy elements is relatively. So the newly formed star has plenty fuel again.",
"Also, slightly off-topic, when astrophysicists say metal, they mean anything heavier than He. So, carbon is a metal to, in this sense. It's inconsistent with earthly definitions, but historic. Astrophysicists are traditionalists :). "
] |
[
"Astrophysicists are traditionalists :)",
"That explains so much."
] |
[
"Ligo gravitational observatory and nuclear bombs?"
] |
[
false
] |
Could a nuclear bomb trigger ligo? Would we know what it was?
|
[
"Yes it would trigger ligo but they back check all their data with siesmologists because nuclear explosions will read on the richter scale like an earthquake. ",
"And fun fact even large trucks can set off ligo which is one reason they constantly check with each other to eliminate the possibility of false positives."
] |
[
"Even ocean waves hitting the Louisiana coast line more than 100Km away have to be accounted for in their noise calibrations."
] |
[
"LIGO detects gravity waves, but it detects them using EXTREMELY sensitive equipment. The detector sends out laser beams and then measures if there is an interference pattern in the lasers. The distances measured are a ",
" of a proton (I believe, talking from memory). There are even signs at the facilities to drive slow as the beam/measurements are in place. They have to eliminate some artificial noise, but they are able to. Incredible actually!"
] |
[
"Would a mirror reflect radiation from a nuclear disaster?"
] |
[
false
] | null |
[
"Wouldn't that mean that the mirror is not reflecting the radiation then? Since it did not wipe the film."
] |
[
"Right on! Thank you! "
] |
[
"That's exactly what he said.. but thanks. "
] |
[
"Virtual pair production at the event horizon is often used to explain the mechanism behind Hawking radiation. This is usually accompanied with a disclaimer that it is not representative of the actual math that describes the phenomenon - so what is?"
] |
[
false
] | null |
[
"You can have a look at Hawking's ",
"original paper",
" to read some of his thoughts on this issue. In particular, he describes the way that one can picture the black hole radiation with a pair of virtual particles coming into existence, and says:",
"It should be emphasized that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally. ",
"(...)",
"The real justification of the thermal emission is the mathematical derivation given in Section (2) for the case of an uncharged non-rotating black hole.",
"The virtual particle pair creation explanation is usually the one used because it's relatively simple to understand and more satisfying than just saying \"it is like that because the maths says so\".",
"But, well... it is like that because the maths says so."
] |
[
"Hawking radiation is not unique to black holes (the more general concept is called ",
"Unruh radiation",
", and is just a result of quantum field theory), and so it is naturally misleading to couch a description of it in terms of black holes. It's really just required for consistency of looking at particle decay processes in different reference frames. For example if you accelerate a proton, it can decay (even though it is normally stable) or it can emit bremsstrahlung (even though in its own reference frame it cannot). This is a normal consequence of quantum field theory; the proton can borrow energy from the accelerating agent in order to decay or bremsstrahlung. But without Unruh radiation there is a logical contradiction if you look at the situation from the proton's accelerated reference frame where the proton is stationary. The proton sees Unruh radiation pop out of the vacuum and interact with it. So Hawking radiation isn't some mysterious thing having to do with black holes, it is a subtle \"pseudo-force\"-like effect (like the Coriolis force) that is seen only in non-inertial reference frames. ",
": you don't see Hawking radiation if you are falling into a black hole. You only see it if you accelerate in order to try to hover above the black hole. "
] |
[
"Its also my understanding that the simple virtual pair explanation cannot be right because it would lose the information stored at the event horizon of the black hole.",
"Moreover there is the issue that we have never actually observed a blackhole dissipate, and so experimentally we cannot say this has happened only that theoretically it should happen."
] |
[
"How did we make the first generation of precision tools before precision tools existed?"
] |
[
false
] |
In order to make something precise you need to use tools capable of making stuff with a high degree of precision which themselves need to be precise. So how did we overcome that leap before we had high precision tools to make the first set of tools capable of making things to a high degree of precision? A very simple example is needing a ruler to make a ruler but really it applies to manufacturing equipment and machine tools just as well.
|
[
"One example of how precision tools work is simple gearing. If you can produce an accurate worm gear to turn a screw to move a cutting tool, then you can count how many turns of the first gear are needed to move the tool one centimetre, and you can then easily apply a scale to the first gear to work out how to move one hundredth of a centimetre."
] |
[
"It may sound self-evident, but precision tools evolved to support industries that required manufactured parts that had close tolerances and were interchangeable to a degree. One such industry was watch making. ",
"Britain was the early volume leader in the manufacture and export of watches. British watches were made in a cottage industry where each part was custom-fit to each watch. The Swiss overtook Britain as leading producer of watches in part through greater use of precision machinery and precision tools.",
"The evolutionary path from general tools to precision tools goes roughly like this. First, there was the development of hard machine steel that had dimensional stability and wear resistance. Next was the development of fine files using hard steel. This was especially important in cutting standard gears. Flat gears were used in combination with powered lathes to produce precision screws, worm gears, and drill bits. With these components and either manual or powered drives, it became possible to machine tools with greater and greater precision.",
"The best illustration of this principle is the micrometer, which uses a fine screw to convert relatively large rotational movements into very small and precise linear movement -- shrinking or growing the space between the calipers.",
"Finally, the movement toward mass production required interchangeable parts, which promoted the use of standards of measure with great precision.",
"Sources:\n",
"Manufacturing Time: Global Competition in the Watch Industry, 1795-2000, p 98 - 104",
"Interchangeable parts",
"Machine tools"
] |
[
"You don't need a ruler to make a ruler, the first ruler you make is the one that defines the unit. (most modern units are defined by physical properties, though)",
"You don't need high precision manufacturing to create precision tools. Tools and machinery can be calibrated and reach a higher precision than the tools used to make them. "
] |
[
"Is there a sensible theoretical design for a DIY Ecosphere?"
] |
[
false
] |
Without having to perform an experiment myself, is there data regarding the correct balance limits for a long term sustainable self-contained ecosystem? Most designs I've heard of begin simply with shrimp of one species or another (cherry or Hawaiian), algae (unknown species), and a certain amount of normal atmosphere. However some sources claim this is really a slowly collapsing system, with the shrimp slowly starving to death over the course of years. Light is the only energy source into the system. If anyone has any data suggesting the best structure and size for such a thing, I'd really love to know. (Side-topic: Would it be better to structure an ecosystem first, or just mix stuff together and let the ecosystem try to balance itself? Is there a tipping point or healthy ecosystem range in which a system naturally balances itself out? Is more species better or worse?)
|
[
"If I had the spacetime for it, I'd be setting up dozens of little DIY ecospheres and figuring out how to make them work long-term. ",
"Any fully closed ecosystem will slowly collapse, it's just the nature of entropy. The lifespan of one will depend on size and how it's put together (and what you define as \"collapse\"). I've got no idea whether it's better to structure or just mix stuff in...I do know it will probably have an effect though, many ecosystems are sensitive to the order things were added to them. ",
"Sycosys has good advice. I'd definitely go with freshwater or terrestrial, use animals like shrimp, snails, or if making a land-based one maybe isopods. Also don't neglect tiny aquatic crustaceans like daphnia. Little pools of water are your friend here. Experiment a lot. Perhaps try and let it stabilize with the top open before you seal it off completely (if you want to seal it off completely). ",
"And experiment. If I was going to get around to doing this, I'd make several jars, let them last a good while, and then seed new jars from the ones that did best. Selective ecosystem breeding! ....someday..."
] |
[
"Why boil the wood?"
] |
[
"hey thanks for the positive feedback on my idea. :D",
"if i count them up it looks like i have spent the last ~18 years of my life (since 10) running various aquariums, terrariums, paludariums, etc. ",
"Currently have a beautiful 3 year old Red Slider i got as a hatchling (still had her egg tooth) "
] |
[
"Is Climate Change a Hoax?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/askscience",
"Also consider looking at ",
"our FAQ",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I directed you to do a bit of searching on this sub, but here's a few more resources to check out as well:",
"\n",
"https://www.reddit.com/r/AskScienceDiscussion/comments/2f45iy/so_i_have_two_questionswhen_it_comes_to_global/ck5rzhm",
" ",
"In short, climate change is real and it is most likely driven by human activity. Specifically you asked about the \"global warming haitus,\" more info here: ",
"https://en.wikipedia.org/wiki/Global_warming_hiatus",
"And the most current research on the topic, ",
"http://sciences.blogs.liberation.fr/files/noaa-science-pas-de-hiatus.pdf"
] |
[
"Thank you for the information. I'll do more researching "
] |
[
"What is the effect of diet on LDL levels?"
] |
[
false
] |
So, what I was taught in my Nutrition class some years back, was that dietary cholesterol doesn't really affect LDL levels, but fat intake, especially saturated fat intake, is the main culprit in elevated LDL levels. However, I was reading the faq, and it claims that saturated fat intake does not increase LDL levels. So what's current consensus on the causes of elevated LDLs?
|
[
"Saturated fatty acids as well as trans fatty acids increase LDL levels by downregulating hepatic LDL receptor activity. The ",
"hepatic LDL receptor",
" is important for regulating the serum levels of ",
"cholesterols by reuptake",
"."
] |
[
"In addition to saturated fatty acids, diets high in fructose can promote higher de novo lipogenisis from the liver and promote higher LDL production. This combined with the decreased LDL receptor activity of the liver mentioned above can promote higher circulating LDL if other tissues are unable to compensate for uptake."
] |
[
"Saturated fats in general DO increases LDL cholesterol, however not all saturated fats increase cholesterol to the same degree. The worst types of saturated fat are the short-chains such as the C12 found in palm and palm kernal oil. These short chains fats are preferentially converted to cholesterol and raise LDL levels.",
"Longer chain fatty acids, such as stearic acid, which are a large component of meat fats, tend to be fairly neutral in terms of cholesterol.",
"And yes it is true that fats raise cholesterol much more than cholesterol itself. "
] |
[
"Is it theoretically possible to create a sound so loud that its waves could be physically dangerous, or even lethal, to a person?"
] |
[
false
] | null |
[
"Absolutely. I mean, there are always the warnings against listening to music that's too loud because it can damage your ears, but really any shockwave is fundamentally the same as a sound wave. Explosives produce these kinds of shockwaves, but a significant portion of the force is outside of human hearing range."
] |
[
"Every object has a frequency that it vibrates most powerfully with, called its resonant frequency. It's the reason why standing next to a speaker that plays a sound with no bass hardly makes you vibrate at all, but a sound with heavy bass makes your insides feel like they're churning. The sound with more bass is closer to the resonant frequency of your body. A more familiar example might be opera singers hitting a very high pitch note and shattering a glass, since glass's resonant frequency is very high. ",
"We could get more specific. If you wanted to make a person have issues seeing, you could play a sound that is at the resonant frequency of the human eye, around 19 Hertz, then it will make it very hard to see because your eye will be vibrating as its trying to create a sharp image, causing strange gray shapes. ",
"Vision problems aren't lethal, so let's get more deadly. The diaphragm, the muscle that controls your lungs, has a resonant frequency similar to that of the eye (for the rest of this post, I'll just assume that the frequency is 19 Hertz, as the human body doesn't change enough to significantly alter its resonant frequency, so 19 Hertz should get you close enough). If you were to make a sound louder, measured in Decibels, then it has a larger force that it could potentially exert. By my calculations, a little under 180 Decibels (slightly louder than a shotgun next to your ear, although this frequency is below your hearing range so it would actually be silent) would be enough to vibrate your diaphragm enough to make it very difficult to breathe. Essentially, your body would be trying to breathe 19 times per second, which is enough hyperventilation to cause someone to pass out fairly quickly due to lack of oxygen. ",
"If you wanted to be more theatrical, then you could do something like being to vibrate the person's body until it began to shake itself apart. Injuries like limbs becoming dislocated, internal organs rupturing, or even someone's skull exploding, begin to occur in the 200-250 Decibel range. ",
"Well, this got morbid. Umm, hope that answers your question. "
] |
[
"Great answer! Thanks! "
] |
[
"Do animals get/have mental disorders?"
] |
[
false
] |
I know some animals can experience PTSD from traumatic events, but things like OCD/Bipolar/Autism etc...
|
[
"OCD, bipolar disorder and autism are all complex disorders (heterogeneous causes, heterogeneous presentation), but there absolutely are animal models for these as well as other mental disorders. Most of the work is done in genetically modified mice examined within a laboratory setting as a way to better understand these conditions, but variation within these genes&traits and/or spontaneous mutation exists in natural populations. There are some elements of mental disorders that do not phenocopy well due to human's relative mental complexity, and some elements that we are simply unable to explore (is a mouse having obsessive ideation? Is it suicidal? Does it see things that aren't there? How does it perceive what it's experiencing?), but existence of disordered mental states is undeniable.",
"For an animal to model a human disease, you want to satisfy three major criteria [from ",
"Silverman, et al. (2010) Nature Reviews Neuroscience",
"]:",
"endophenotypes",
"Diagnosing a mouse with ",
" involves observing altered/impaired social function, altered/increased repetitive grooming, changes in vocalization (another measure of normal social interactions in mice), etc. See (as above): ",
"Silverman et al., (2010) \"Behavioural phenotyping assays for mouse models of autism\" Nature Reviews Neuroscience",
". 38 distinct mouse models of autism have been described in the research literature, involving 28 unique genes ",
"according to Mouse Genome Informatics",
".",
"Mouse models of ",
" exhibit hyperactivity and impaired memory storage. Ref. ",
"Tarantino and Bucan (2000) \"Dissection of behavior and psychiatric disorders using the mouse as a model\" Human Molecular Genetics",
"Mouse or rat models of ",
" exhibit perseveration, indecision, increased grooming and increased marble burying. Ref ",
"Albelda and Joel (2012) \"Animal models of obsessive-compulsive disorder: Exploring pharmacology and neural substrates\" Neuroscience & Biobehavioral Reviews"
] |
[
"I study primates, and I know that things like depression (see Harlow's horrifying work from the 1950's) can be induced. Captivity can also cause stereotopies and self injurious behaviour, including things like \"floating limb syndrome\" and reacting to things that aren't there (captivity is truely, truely awful). In humans we can use language to ask why someone is doing those things (and they can confirm they are having hallucinations, etc.) but in non-humans all we see is abnormal behaviour - and we definitely see that. Also some chimps seem to be murderous (see Goodall's reports of Pom and Passion) and cannibals, without it being a 'regular' behaviour. "
] |
[
"Mostly lab primates (usually macaques) suffer the most (where the goal is to just use them, not provide for them). In studies of self injurious behaviour (things like biting themselves, picking, etc.) it was found that rates didn't go down just because cage size increased (ie they weren't acting out because of lack of space) but they dropped dramatically when given just an inch x inch space to be able to reach through and touch others. Primates are extremely social, and worse (in my mind) than physical torture is social deprivation. They don't even have to be living together (which is ideal) but just given auditory, visual, and tactile access to one another.",
"However, having a large enclosure doesn't guarantee mental stimulation. There needs to be enrichment (food puzzles, textures, climbing structures, toys, magazines, etc.) and social interactions. I've worked at a couple different captive primate places and a HUGE part of the job is to put out new, different, exciting, unique enrichment ",
" times a day, and it often goes completely untouched because often what they want is someone to ",
" with them ",
" the object. They do flip through the magazines or put on clothes or hats, and food puzzles are good, but the stuffed animals, art supplies, plastic rings, balls, etc. generally aren't used solo. ",
"But even with enrichment and space, sometimes it's just really really bad to be captive. Think about it... imagine if human prisoners were put on display as an example of human behaviour, and research was then based off of this abnormal way of living. Have you ever seen an animal at the zoo that has a routine (where I used to live it was a bear that would take 13 steps along the back of his habitat, swing his head, take some more steps, swing it twice, and so on and so on over and over) and it becomes clear that they clearly have a psychosis? [note: I know this is an anecdote, but I'm just using it to illustrate a point that science backs up]",
"So... yeah... all captivity is not good, but obviously there's a gradient dependent on space, social partners, environment, enrichment, etc.",
"I like talking about primates. :)"
] |
[
"How are the Covid19 vaccines progressing at the moment?"
] |
[
false
] |
Have any/many failed and been dropped already? If so, was that due to side effects of lack of efficacy? How many are looking promising still? And what are the best estimates as to global public roll out?
|
[
"They're all progressing steadily - no major failures have been reported yet, but this will take time. Best estimates are initial/topline data by year end, with a potential approval shortly after. Global roll out to public is unlikely till around June or so next year (due to a combination of manufacturing times, approvals etc.)The problem is that to prove a vaccine works is fundamentally different from a therapeutic. With a therapeutic, you can give the therapsutic/drug to x people, placebo to x people, and in a relatively short time ( weeks to months) you can find out who's getting better, and prove efficacy.With vaccines, you need time most importantly. You can give the vaccine to x people, and placebo to x people - and then you need to wait certain time - long enough to compare infection rates between placebo and vaccine group. For e.g. there's 3 possible outcomes",
"To reduce the likelihood of option 3, the approach is to test in large numbers of patients, over a significant amount of time ( 6 mo or so) , so that they can have data on the placebo side to compare. That's why this will take time.",
"Also the reason why anyone saying they'll have \"great results\" for a phase 3 trial that started in June/July by Oct/Nov is either unaware of the level of data needed, or is bowing to non-scientific pressure.",
"That said, you could have preliminary data (from a part of the tested population etc.) sooner than year end, but usually that's not enough to approve drugs unless in extreme circumstances. Additionally, a longer follow up is required for safety, which we may not have by then. So we could see promising candidates start to show up soon, but not ready for global prime time till mid next year",
"Source: Ph.D. in Vaccine Immunology.",
"Edit: Fixed typo.",
"Edit: Thanks for the gold!!!!",
"Edit 3: Wow. Thanks for all the awards. Now I have to figure out what they actually do! I'm reading the replies and am trying to answer them as best as I can.",
"Edit 4: To clarify my timeline estimate further, I was referring to June as the expectation for the general public, i.e. all of us. The vaccines will most likely be rolled out in stages, with front line workers or high risk populations first. Depending on if EUA is granted, we could see a conditional or emergency approval by early next year meaning those groups could get this by March or so. And then it'll be available to the rest by June.",
" My best post ever, and the day I post AZ halts their trial - smh. This halt is not a failure. It's proof that the system is working as it was designed to, with the clinicians observing an AE they didn't expect, and so the trial is paused till they understand it better. ",
" The most frequent qn below is why not test the vaccine by infecting them with the virus. I've answered below, but briefly its ethics. Informed Consent is a key part of trials, and even more important in these cases to communicate the risks involved. We still don't know all the potential long term consequences, so how do you convince someone to risk their life by purposely giving them a potentially fatal virus? Offering money etc, would also be unethical. It's a complex topic - not unlikely but very complex."
] |
[
"Like I said above, the statement from the CDC is generally not agreed upon by the scientific community including Pharma companies, who stand to lose a lot more (trust, brand value) by rushing a vaccine to market. It's unclear to the reason behind the CDC's communications on this, but from a rigorous scientific perspective, this is highly unlikely."
] |
[
"Why has the CDC said something about distribution by October or November? Is this just political pressure to get a false statement out? If so, won’t the ramifications be bad when nothing happens in October/November or if a bad vaccine is approved? ",
"Is there any possibility at all that we could get a good vaccine out before the end of the year?"
] |
[
"How is a drug made ?"
] |
[
false
] | null |
[
"Hi Averysweetpotato 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, ",
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", 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.",
" ",
" "
] |
[
"'Chemistry', 'Biology', 'Engineering'"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Why do Males have 10% more water content than Females?"
] |
[
false
] |
[deleted]
|
[
"It's not about what males have more of, it's that females have a higher fat content than males do. I'm sure someone can give you a more detailed answer, but as far as medical school is concerned, that's as much detail as we were given.",
"Interestingly we didn't learn the body water compartment ratios are different (ie extracellular vs intracellular, etcetera), so I'm unsure of if they're actually similar, or the MD teaching us just considered that superfluous (they consider a lot of stuff superfluous) so I'm not much more help than the base answer. I would hazard a guess that they're actually similar since fat is primarily stored in its own cell types, but this again loops back to someone else being able to give more details. "
] |
[
"It's the added piss and vinegar. (j/k) But I suppose why would one expect them to be exactly the same. They have different distributions and quantities of different tissues types. Different types of tissues hold water at different concentrations."
] |
[
"It's the added piss and vinegar. (j/k) But I suppose why would one expect them to be exactly the same. They have different distributions and quantities of different tissues types. Different types of tissues hold water at different concentrations."
] |
[
"How can we be sure that the laws of physics hold throughout the entire universe?"
] |
[
false
] |
Let me clarify. I was talking to my dad last night about why x-men are an impossibility, due to conservation of energy etc. and he asked how we can be sure that CoE holds everywhere? Well that sorta got me thinking. I understand that by definition, the laws of physics hold in any inertial frame of reference, but with how friggin enormous the universe is, are we absolutely sure? If so, how do we know we're right?
|
[
"So there are a couple aspects to this.",
"First, ",
" (I'm capitalizing them so you know they are important) are the way the universe really works. By definition they must hold everywhere and every time, or else they wouldn't be ",
". That doesn't mean everything must behave the same everywhere. For example, maybe ",
" allow for the electric field to be stronger in some places and weaker in others, just within a framework that is rigidly obeyed (",
").",
"We are not given ",
". What we have are the \"laws\" of physics, which are what we mere mortals have, through the process of science, determined to be what we think ",
" are, or at least are close to. Right now as far as we know the electric field strength is the same everywhere, but being aware that we do not yet know ",
", we can try to come up with experiments to check this. If the field were stronger then the emission lines of atoms would be different, so we can use telescopes to look at emission lines all around the observable universe and check if they are different. So far no difference has been convincingly found, but it's possible that there is a difference either too far away for us to see, or to subtle for us to detect as yet.",
"There are theories (candidates for ",
") that allow certain properties to be different in different regions of space. For example different sets of particles could exist, and forces of different strengths. Both the properties of our region of the universe and theirs would obey ",
".",
"So, if we ever get a theory that seems to describe everything we know of in perfect accuracy, that may be as close as we can get to knowing ",
". Perhaps that theory is ",
", and could tell us what is and is not allowed for distant parts of the universe. We sure aren't there yet though.",
"Now about the law of conservation of energy, which you specifically cited. Under the classical \"laws\", it simply is the case that energy is conserved: it is a consequence of those equations. But thanks to ",
"Noether's theorem",
" we now have a better appreciation for where conservation laws come from. Her theorem tells us that, for example, ",
" the laws of physics do not change with time, then energy must be conserved. This is Mathematical Truth, dependent on that \"if\"."
] |
[
", by definition, are complete and inviolate. That doesn't mean they have to be deterministic, however. There is nothing wrong, in principle, with randomness as in quantum mechanics. That randomness is still constrained by ",
".",
"If some of our \"laws\" fail in certain situations, that is just an indication that they are not ",
", but perhaps an approximation. Science will hopefully take us closer to the truth."
] |
[
"Yeah many of the rules, like conservation of energy-momentum hold from Noether's theorem and we would expect to be universally true. But other things, like the strengths of interactions and such are free parameters. The best we can say is that our best measurements have indicated these parameters have had the same value throughout all the universe we can see, so we extrapolate that notion to them having the same value throughout all the universe. We can't know for certain... but it's a reasonable assumption."
] |
[
"I feel the consensus is that poor dental hygiene is extremely conspicuous when dealing with people. Did people, before the advent of good toothpaste, just have to accept that everyone had bad breath, or was it somehow less noticeable?"
] |
[
false
] |
I do realize there are things that help in similar ways to toothpaste that people might have used, but was that really ever as widespread as toothpaste is now?
|
[
"I think this goes some way towards an answer: \"Until [Listerine began to be marketed], bad breath was not conventionally considered such a catastrophe.\"",
"http://en.wikipedia.org/wiki/Listerine#History"
] |
[
"Before the advent of refined foods, our teeth were significantly healthier than they are now."
] |
[
"Thank you! Best answer yet."
] |
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