Recent comments in /f/askscience
zowie54 t1_j4t26ae wrote
Reply to comment by UpperCardiologist523 in If nuclear fission in U-235 causes the atom to be split into 2 smaller atoms (such as Kr-92 and Ba-141) then how is it that U-236 is produced as waste since the U-235 was just split into smaller peices? by Ian98766
Think about it like breaking a cookie. It will break slightly differently each time you break it, and produces two major pieces (not necessarily equally sized), and some crumbs. While it is easy to break a cookie, exactly how it will break will be determined by lots of variables, so many, that measuring the statistical frequency is usually how outcomes are predicted. Some reactions require certain minimum energy thresholds to be overcome, and the energy of an incoming particle can determine how likely certain types of decay are. That being said, a neutron is actually absorbed by the 235, which becomes unstable and breaks apart. U-235 fission produces an average of 2.41 neutrons per fission, the neutrons being analogous with a seed or something in a cookie that cannot break apart easily, and so either is in one half or the other, or in neither as a crumb.
autoantinatalist t1_j4t0wm0 wrote
Reply to What makes a fiber or fabric absorbent, wicking, breathable, or cooling? by DisenchantedAuD
Weave can factor into this some. A satin weave is worse for breathability because the threads are very close together and tightly packed to create the smooth surface satin is known for. There are various kinds of twills that are less tightly packed and more open, that are better for preventing the fabric from trapping heat.
Prestigious_Carpet29 t1_j4t0cjk wrote
Reply to What exactly is the process when someone "trains" an AI to learn or do something? by kindofaboveaverage
"AI" and "machine learning" tend to be used interchangeably, especially in mass-media articles. In theory "AI" is more "intelligent" but ... well.
Anyway in a previous job I worked on a "machine learning" project which used a "binary classifier" (a relatively simple machine-learning method) to determine whether a short sound recording was "baby" or "not baby".
To train it, we had a whole load of sound recordings (.wav files), of domestic "non-baby" sounds, like hand-washing dishes, washing machine, vacuum cleaner, TV etc. And a load of "baby" sounds, which included babies babbling as well as crying. The "training" comprised getting the program to analyse those sounds (from the two labelled categories) and "learn" how to classify them. Set the computer-program running, and wait for an hour or two...
As with much audio-processing (including speech recognition), the sounds were analysed in short pieces lasting a few 10's milliseconds each, each characterised with about 20-30 parameters relating to the frequency-content and rate-of-change with time. In this case the "training" was essentially fitting a plane through a 20-30 dimensional graph of those parameters, splitting the set into "baby" on one side and "non-baby" on the other. Once trained, you could then give the algorithm new recordings that it hadn't "heard" before, and it would classify them accordingly.
A problem (symptomatic of many machine learning methods) was that if you presented it with a recording of a baby but with some other sound in the background - even just a cooker-hood fan, that it hadn't been trained for - it would fail to recognise the baby.
There is an ever-present danger with AI/ML systems that if you haven't included all possible confounding factors in the training data, they may completely and unexpectedly fail to work properly when that factor pops up in the real world.
[deleted] t1_j4t00ts wrote
Reply to comment by full_hammer in What happens to the energy of sound in space? by full_hammer
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[deleted] t1_j4szn4k wrote
Reply to comment by Saidear in What happens to the energy of sound in space? by full_hammer
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UpperCardiologist523 t1_j4sx3h2 wrote
Reply to comment by echawkes in If nuclear fission in U-235 causes the atom to be split into 2 smaller atoms (such as Kr-92 and Ba-141) then how is it that U-236 is produced as waste since the U-235 was just split into smaller peices? by Ian98766
Wow, thanks for a great answer. I've always thought (probably because i misunderstood or remember wrong) while watching videos about Thorium-Salt reactors, how they were better than the breeder reactors we've currently on, and that current reactors were breeders, because of how inexspensive they were to build. I better go back and watch those videos one more time.
I knew about Hanford, which is a breeder.
Anyways. Thanks a lot for answers.
Saidear t1_j4sww6h wrote
Reply to comment by [deleted] in What happens to the energy of sound in space? by full_hammer
That would imply continuously increasing energy in the fork. While the initial vibration might be faster, and it will fall off slower.. the energy will be decreasing and thus, any material fatigue minimum
[deleted] t1_j4swaiu wrote
Reply to comment by wastedintime in What happens to the energy of sound in space? by full_hammer
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[deleted] t1_j4sul0m wrote
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BNeutral t1_j4styf0 wrote
Nowhere, things are just more efficient. Or less efficient. Depends on how you want to look at it.
Yelling is a very bad example for your question thought because the mechanics are a bit harder to follow? On earth, if you hit something, the molecules of that move around, and eventually some of them at the borders push on the air and sound is created. In a vacuum, the molecules of what you hit don't push any air, and either more of that is converted to heat, or the molecules oscillate longer as the wave propagates through them, or more kinetic energy ends up propelling what you hit, or some combination of all of this.
[deleted] t1_j4sttot wrote
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[deleted] t1_j4st5at wrote
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[deleted] t1_j4st3y9 wrote
Reply to comment by ellipsis31 in What happens to the energy of sound in space? by full_hammer
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[deleted] t1_j4sszif wrote
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devinmacd t1_j4sp4gg wrote
Reply to Do teeth already have ridges before erupting? How do teeth fit in so nicely after erupting? by Lancerinmud
What do you mean by ridges? Grooves and cusps? They have those before erupting, yes. Crowns are fully shaped before erupting, though they can be worn down over time, ideally they would not be.
Fit together how? Within the arch how they fit against their neighbours? or the occlusion between arches? In absence of malocclusions ("bad bites", which are relatively common), teeth fit together well- i.e. cusp and fossa relationship between top and bottom teeth, presumably by some evolutionary process? Though in an individuals mouth as they erupt they tend to move into place until they are stopped by neighbours and adjacent teeth on the opposite arch.
The goal of braces in fixing a bite is generally to put the teeth, as they are formed before erupting, into their ideal positions to fit together well.
echawkes t1_j4snn8g wrote
Reply to comment by UpperCardiologist523 in If nuclear fission in U-235 causes the atom to be split into 2 smaller atoms (such as Kr-92 and Ba-141) then how is it that U-236 is produced as waste since the U-235 was just split into smaller peices? by Ian98766
>Does the level of energy the neutron hit with, decide what new atoms and therefore how many neutrons are left over?
The kinetic energy of the incoming neutron can affect which pairs of atoms are produced. Higher energies generally result in more neutrons being released, which means that different fission products must result.
>Does this mean that when they enrich uranium/plutonium, reactors are run on lower energy?
Enrichment isn't done in a nuclear reactor. Typically, something like a centrifuge is used to separate the isotopes of uranium. U-235 is a little lighter than U-238, so the centrifuge can be used to get two output streams in which one has more U-235 than the input (higher enrichment) and the other has less U-235 (lower enrichment).
I think you might be asking about something like a breeder reactor, which can produce Pu-239 from U-238, or U-233 from Th-232. There have been very few of these, because some of the neutrons are used up in transmuting one element into another (by absorption without fission), which is a technical challenge. The usual technique is to use a fast reactor (high energy neutrons), so that there are more neutrons produced per fission.
There haven't been many breeder reactors because they are more complicated and expensive to build and operate than normal reactors. Uranium is pretty common and not that expensive, so we usually just mine it and use that. The uranium in power reactors is usually enriched a little. Natural uranium is 0.7% of the uranium you would find in the ground, and it is usually (but not always) enriched as high as 5% in nuclear power plants.
Shufflepants t1_j4sn6to wrote
Reply to comment by d0meson in Why does the existence of magnetic monopoles imply quantized electric charges? by Speterius
>*in a classical universe; not sure whether GR or QFT impact this statement.
Yeah, I would assume that the permeating presence of the electromagnetic field as represented in QFT would alleviate the need for there to be a magnetic monopole.
Chemomechanics t1_j4sm8iq wrote
Reply to comment by wastedintime in What happens to the energy of sound in space? by full_hammer
A while, but not forever. Even elastic deformation dissipates a little heat (termed internal friction or sometimes mechanical hysteresis).
BobGeneric t1_j4slwpb wrote
Reply to comment by rededelk in Does anybody have any good examples or uses of negative derivatives of displacement, such as absement, absity, and so on? Though it is easy to calculate, it’s hard to find use for it. by LunarSolar1234
A pure PID control is more of a calculation than an "if this than that" algorithm. There are different implementations, but at the end it's like output=errorKp + Kdd(error)/dt + Ki*integral(error)dt, where Kp, Kd and Ki are constants tuned to the system to be controled. This output is applied to an actuator that changes the system, and the objective is to zero the error. The PID control was originally a full analog circuit, done with operational amplifiers, so, no if/elses...
Prestigious_Carpet29 t1_j4slp11 wrote
Also note that far more things "are known to cause cancer in California" than anywhere else!
For various interesting/historic reasons, California has exceptionally tight environmental restrictions (for pollutants etc), and one of the lowest thresholds for labeling products as "suspected" or "known" to cause cancer.
I'm in no position to judge whether California is "reasonable" or "over cautious", but for people who want to stir up panic, they'll always cite contamination levels (e.g. in water) compared to California's limits!
Prestigious_Carpet29 t1_j4t28de wrote
Reply to comment by Lord_Gadget in If the left side of your brain controls the right side of your body and vice versa, then what does that mean about people who are left handed? by Reflector368
This question is about the left side of your brain controls the right side of your body and vice versa - which I believe is evidenced from cases where people have brain-injury on one side, and lose control of the other side of their body.
This is completely different to the bogus concept of "right-brained and left-brained people" where one dominant side is supposedly more creative and the other more analytical - which at best is just a lazy psychological metaphor.