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/sci/ - Science, Technology, Engineering, and Mathematics

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Parabolas in autodesk inventor Anonymous 14/11/04(Tue)17:45 No. 15963 ID: b2989d [Reply]

File 141511955922.png - (2.77KB , 197x256 , parabola.png )

I need to create a parabola in autodesk inventor for a school assignment, and the parabola needs to be shaped like the bottom of a circle (kind of like a lid) what do?

Anonymous 14/11/08(Sat)09:40 No. 15965 ID: 789203

>the parabola needs to be shaped like the bottom of a circle
Well, that's not a parabola then, is it? It's an arc.
arc(x, h, v) = (v / h) * sqrt(h^2 - x^2)
h being the radius of the horizontal elliptical axis, and v the same of the vertical one.

Anonymous 14/10/12(Sun)19:00 No. 15929 ID: b20a90 [Reply]

File 141313325435.png - (193.71KB , 450x450 , BT clients.png )

Hello /sci/!

Does anyone please know of a program that can analyze torrents? What I want it to do is to create a printout of all the files in the torrent. I also want to make comparisions of torrents; to see if two torrents have files with the same name and/or the same hash value.

Anonymous 14/10/16(Thu)11:00 No. 15936 ID: 789203

Yes, dumptorrent.

Hashes are computed per-block, not per-file. Meaning, the hashes a torrent contains will depend not just on its particular contents, but also the particular order in which they appear, and the block size that was used. It's very unlikely that two distinct torrents containing the same file will also share any hashes, even if the block sizes are the same. It's even less likely if the file in question is smaller than twice the block size.

Let n be the absolute offset of the file on the torrent A (given by the sum of all the file sizes that came before), and let m be the same on B, if file_size >= block_size * 2 and n is congruent to m modulo block_size, then there will be at least one duplicate hash between the two torrents. For randomly constructed torrents (a reasonable situation) with a random file_size the probability of the congruency condition being met is of 1/block_size. So for block_size = 4 MiB (a common block size), the probability is lower than four million to 1.

Anonymous 14/10/07(Tue)08:26 No. 15918 ID: 1b02b6 [Reply]

File 141266316925.png - (44.05KB , 993x834 , dfgdfgdfg.png )

2 questions. In photo,

Exhibit 1: A point charge q exerts its electric field over a spherical body. Along the flux lines diverging "radially" away from point charge, there exists 2 points at opposite ends of sphere's surface area (along diameter). The electric field, E, in accordance with Coulomb's law, is stronger towards the charge than away from it, the vector lengths of E indicating this ever dying weakness, and vectors, dA, normal to the area.

Told: That the total electric field on the body is zero, because the cross product of the electric field on both points are "equal" but opposite, cancelling each other out. This applies to all points along surface area of the sphere.

Question: What is wrong in my photo? It seems that they have completely forgotten about Coulomb's law, in that the closer you are to a body, the stronger the electric field. If the point charge was negative, I imagine the electric field vectors to be a lot larger along the sphere's hemisphere closest to the point charge, and smaller on the other hemisphere. Wouldn't all but the tiny difference between the electric field strengths remain after cancellation? Shouldn't the total electric field be in slight favour of the negative charge's force?


Exhibit 2: a. A point, p, inside charged sphere has an electric field, E, of zero.
b. A point, p, exists in the sphere of a charged similar body comprising a sphere with an attached appendage that loops around half the sphere, with same electric field as E in exhibit 2a.

Told: That in all closed surfaces, the net electric field, E, at any point in the closed system is zero.

Message too long. Click here to view the full text.

Anonymous 14/10/07(Tue)09:10 No. 15921 ID: 1b02b6

Also, why are the charges along the surface? Is it just easier to think that way after summing all the negligible point charges together?

Anonymous 14/10/10(Fri)03:15 No. 15926 ID: 789203

1. I don't see how the field strengths on the surface could possibly have opposite directions unless the point charge is inside the sphere.

2. I agree with you, it seems counter-intuitive. I could easily construct a closed fractal shape that has infinite surface area on one side of the charge and is nearly spherical on the other. I'm not in physics, so I don't know what to tell you. See if this link helps:

Anonymous 14/10/10(Fri)19:00 No. 15928 ID: 1b02b6

I worded it poorly. E isn't opposite on both ends, dA is (normal to the surface on opposite ends). I was just trying to say that the field dies off the farther you are away from charge.

Meteorite Anonymous 14/08/18(Mon)20:37 No. 15827 ID: 040c46 [Reply]

File 140838707141.jpg - (104.25KB , 960x741 , Lunar Meteorite.jpg )

Kickstarter campaign to purchase Lunar Meteorite


Anonymous 14/09/19(Fri)15:01 No. 15879 ID: c4882d


Anonymous 14/09/20(Sat)15:50 No. 15886 ID: 15121f

You can grab your plain ol' honest-to-goodness meteorites from your gutter using a strong magnet. You'll get little chips that have bounced off your roof and collected there.

I thought I found a sizable meteor in my backyard, turns out it was industrial waste, slag, probably from WWII when my area was involved in war production and waste of this kind would be common.
It's an easy material to confuse for spacerock :)

Anonymous 14/09/08(Mon)10:07 No. 15872 ID: 84146f [Reply]

File 141016364114.jpg - (21.14KB , 521x161 , slui.jpg )

I need a product key activator for Windows 7 Ultimate SP1 ASAP. I tried activating it manually, but I receive this error message.

sage Dumb_Nigger 14/09/08(Mon)11:24 No. 15873 ID: b2bc2a

try google, faggot

Anonymous 14/09/16(Tue)14:44 No. 15876 ID: a29f36

Buy a real Windows 7 Ult key faggot

Anonymous 14/04/24(Thu)21:56 No. 15638 ID: cf7d56 [Reply]

File 139836940417.jpg - (32.02KB , 599x399 , image.jpg )

Faggotry is hormonal imbalance. It has to be. What else could it be besides environmental trauma?

22 posts omitted. Click Reply to view.
Anonymous 14/09/08(Mon)08:10 No. 15871 ID: 789203

>For example, being intelligent and/or social on its own doesn't provide much advantages as to being able to adapt to an unstable environment. Going down the list of most intelligent animals (excepting for the moment humans) is like taking a trip down the endangered species list.
Well, being smart isn't going to give you many advantages if you're going up against something smarter and more powerful than yourself. You can't outthink a bulldozer tearing through your home, or a gun shooting you in the face.
Being smart can help you figure out safer ways to get food. We devote over 1/5 of our energy expenditure to brain upkeep. Compare to around 1/20 for most other vertebrates. Having such large brains would put us at a significant disadvantage if they weren't able to compensate by providing more food and generally being better able to the body safe.

>Meanwhile, species like ants and bacteria that don't even have brains as we think of them thrive in every environment on Earth.
Just imagine how terrifying they'd be if they were smarter than us!

>The only reason human intelligence and cooperative power has provided an evolutionary edge is because it (after a few hundred-thousand years of doing nothing in particular) suddenly and exponentially enabled them to alter the environment to suit their needs. However, the same technology that gives humans long, (re)productive lives as medical care, perfect food, and air conditioning has also lead to global warming, which might be the thing that kills us all.
And? If that was our ultimate fate, it would just show that evolution is a sub-optimal algorithm, not that intelligence doesn't make sense evolutionarily.

Anonymous 14/09/10(Wed)03:54 No. 15874 ID: 00718f

>hormonal imbalance
I believe not in full grown people but in the womb enough testosterone was present for Y chromosomes etc but not enough to fully convert the brain leaving a more feminine physios

Matchbox Prince 14/09/11(Thu)10:04 No. 15875 ID: 2f260d


It's a myth that homosexuals have less testosterone; they actually tend to have more. Also, while the brains of homosexual men work more like heterosexual women in certain ways when looked at with PET or fMRI scans, the statistical difference is so insignificant (differences between individuals are far larger than the differences between the groups) that it's really irrelevant. Any association of homosexual men with feminine traits is culturally generated and exclusive to the modern, Western world.

Anonymous 14/09/05(Fri)02:34 No. 15861 ID: 9db7e9 [Reply]

File 140987727820.jpg - (233.09KB , 1240x1754 , 981.jpg )

I plan on doing a reductive amination (ketone + nitromethane) in the next few weeks, using Al + Ga metals.
Does anyone have any useful tips on this reaction?
(Reference: "Reductions in Organic Chemistry", Milos Hudlicky, Prof. Chem., Virginia Polytech. + state university).

Anonymous 14/02/23(Sun)14:05 No. 15550 ID: c4b814 [Reply]

File 13931607112.jpg - (17.06KB , 500x390 , 10768_273185959499082_1150917839_n.jpg )

is .999...=1?

41 posts and 4 images omitted. Click Reply to view.
Anonymous 14/08/15(Fri)06:46 No. 15824 ID: c85029

File 140807800432.gif - (286.60KB , 609x862 , 1407771571818.gif )

But like, man, what if it's just how our puny human minds THINK the numbers work; but they don't actually work that way at all. There's probably like, aliens out there that say like, 1+5=blargnip. We could have it all wrong, man. There's absolutely no way to tell if our math is the right math because we're humans man.
Alien math could be like way different. Like, triangles with seven sides or something I don't know. There's just no such thing as a concept that exists independent of opinion and culture.

You guys should take some liberal arts courses, it'll open your eyes.

Anonymous 14/08/15(Fri)07:50 No. 15825 ID: c1bebf


Numbers are based initially on the observation that you can count objects. Any alien entity so divorced from our frame of existence that they don't relate to solid objects in the same way we do will never observe us or be able to communicate with us in any way, so it's a moot point. In other words, you wrong, dude. Any alien being we could be able to encounter will be dealing with the same physical universe we do, and will necessarily be able to relate to concepts based on that physical world, like if you have a gooblatz with BINGBINGBING gobblefertzis growing on it, and BING falls off, there are still be BINGBING left.

Anonymous 14/08/15(Fri)12:39 No. 15826 ID: 789203

And, more abstract mathematical objects (e.g. an infinite sum of increasingly small elements) are based entirely on axiomatizations of those initial intuitions. If the aliens axiomatize their perceptions the same way we do, they'll necessarily arrive at the same conclusions. If they don't, then their conclusions are not relatable to our own, in the same way that you can't use Pythagoras's theorem to prove or disprove the infiniteness of prime numbers.

Why competition? Anonymous 14/08/22(Fri)10:34 No. 15829 ID: 080683 [Reply]

File 140869646585.jpg - (151.24KB , 600x781 , Discworld_Death_by_RobAnybodyFeegle.jpg )

This is most probably from complete lack of commonly accessible hard knowledge, but here's the question:
(1) If genes spanning individuals and species really do compete for survival as units of evolution,
(2) do the levels of competition seen in the natural world really benefit their survival?

They say, there's 1% genetic difference between humans and chimpansees, whatever that precisely means. Is intense competition between and within species not too counterproductive for genes' survival? May there be other, overriding controlling processes that steer genetic evolution from its optimal, maybe more cooperative behaviour?

Also, stupid philosophical crap for your amusement, because I have a psychological need to dump it somewhere: http://whitefielde.wordpress.com/

2 posts and 1 image omitted. Click Reply to view.
Anonymous 14/08/23(Sat)14:17 No. 15841 ID: 080683

The function should evaluate not probability of individual passing genes, but gene pool's resulting survival.

Anonymous 14/08/23(Sat)14:32 No. 15842 ID: e3000c

Of separate note is the fact (apparently) that competition is by no means the goal of evolution. The "goal" appears to be simply replication, and competition makes sense only when different genetic forces use same limited resources.

Anonymous 14/08/24(Sun)01:07 No. 15843 ID: 789203

>Thanks, that makes sense, although it is a behaviour observed in short-running, low count computer based genetic algorithms, no?
>This short-sightedness might not still be in effect in a superhuge pool like Earth's biosphere for very common and long-running traits, as there might be plenty of opportunity for evolution to go outside local maxima because of sheer number of attempts.
Depending on the maximum possible Hamming distance (given two bit strings, for each bit that's different to the counterpart bit in the same position, add 1 to the distance) between two generations of the algorithm after mutation and the slope of the function, it's possible to prove that some algorithms will never escape some peaks after reaching it.
In other words, if mutations are too conservative and selective pressures are too high, it's possible that once some peaks are reached, the only way out is extinction.
It's similar to the prisoner's dilemma. If just one player will cooperate, they'll get screwed. Either everyone cooperates or the one that does cooperate is much more powerful than all the other players combined.
A possible way out is by ignoring DNA. For example, the optimal thing for us humans to do would be to disregard any suffering that we may cause lab animals and just do whatever. Because of ethics, we don't do that.

>The function should evaluate not probability of individual passing genes, but gene pool's resulting survival.
That may kind of be what it does. What I was getting at is that the range of possible solutions that optimize individual success is a subdomain of the range of possible solutions that optimize general success (and average individual success as a side-effect).

Anonymous 14/05/16(Fri)14:05 No. 15669 ID: 1ac70f [Reply]

File 140024190235.jpg - (10.83KB , 480x360 , hqdefault.jpg )

Any mathematical biologists here? I came across this post about mate choice and I'm not sure if it's a work of near-genius or complete stupidity. Are the arguments right?

The basic claim I'm making is that men have evolved to prefer young virgin girls because they have the greatest long term reproductive potential. You have argued that an adolescent girl would make a poor mate choice since she wouldn't be in her mating prime. I'm going to try to show to you that your position is wrong with a bit of mathematical reasoning.

The first thing I want to show you is that girls who started reproducing in their teens were reproductively more successful than those who started later in their 20s or 30s. It's going to take a bit of mathematical thought so get ready.

Let's imagine there was some ideal age, X, for the females in a species to start reproducing. Females who start reproducing at about this age leave behind the most surviving offspring. Females who start reproducing significantly later that age X leave behind fewer surviving offspring on account of having a shorter reproductive lifespan (since they started reproducing later) and those who start reproducing significantly earlier than age X also leave behind fewer surviving offspring due to them suffering more pregnancy complications and the like. The details don't actually matter that much. It's the principle that reproductive success is dependant on age of first reproduction and forms some kind of peaked distribution centred on the ideal age X that counts. Something like this:


So, what's going to happen under these conditions? If you think about it, it's really simple. Females who start reproducing later or earlier than age X will leave behind a suboptimal number of offspring and over time become a minority in the population. While females who start reproducing at about age X will leave behind the most surviving offspring and therefore come to dominate in the population. The typical age that the females start reproducing will automatically stabilise around age X, since, by definition, females who start reproducing at age X are the reproductively most successful! In a species that is adapted to its environment, the average age and the optimal age of first reproduction will be the same thing.


Message too long. Click here to view the full text.

24 posts and 2 images omitted. Click Reply to view.
Anonymous 14/08/21(Thu)13:04 No. 15828 ID: 597595

File 140861905068.jpg - (51.96KB , 983x549 , VR0pR.jpg )

Matchbox Prince 14/08/22(Fri)23:26 No. 15835 ID: 2f260d


1. Source?
2. Doesn't take into account that the only people stupid enough to google-search for childporn are preteens, themselves.

Anonymous 14/08/23(Sat)03:10 No. 15838 ID: 597595


1. The book "One Billion Wicked Thoughts".
2. I think young boys generally prefer older women, at least I did when I was young.

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