-  [WT]  [PS]  [Home] [Manage]

  1.   (new thread)
  2.   Help
  3. (for post and file deletion)
/sci/ - Science, Technology, Engineering, and Mathematics

Join us in IRC!

•This is not /b/ or /halp/. Tech support has its own board.
•If you are not contributing directly to a thread, sage your post.
•Keep the flaming at a minimum.
•Tripcodes⁄Namefags are not only tolerated here, they are encouraged.
•We are here to discuss sci-tech, not pseudoscience. Do not post off-topic.

•♥ Integris


  • Supported file types are: GIF, JPG, PNG, WEBM
  • Maximum file size allowed is 5120 KB.
  • Images greater than 200x200 pixels will be thumbnailed.
  • Currently 399 unique user posts. View catalog

  • Blotter updated: 2018-08-24 Show/Hide Show All

There's a new /777/ up, it's /gardening/ Check it out. Suggest new /777/s here.

Movies & TV 24/7 via Channel7: Web Player, .m3u file. Music via Radio7: Web Player, .m3u file.

WebM is now available sitewide! Please check this thread for more info.

New Textbook/Book Request Thread deadbabies ## Mod ## 13/08/25(Sun)06:03 No. 15270 ID: f34135 [Reply] Stickied
15270

File 137740339172.jpg - (401.45KB , 1680x1050 , titanfalsecolor.jpg )

First off, hello there, I'm deadbabies, and I will be taking over as /sci/ moderator. Rules will remain the same. Please use the report function if you see posts that violate the rules, but also do not abuse it.

I have officially expanded the scope of /sci/ a bit. You may discuss Science, Technology, Engineering, and Mathematics here now. No science is discriminated against as long as it's of the peer-reviewed variety. If someone wants to discuss Anthropology or Social Science, by all means, let them. If you do not like it, just don't post in the thread.

The IRC channel #/sci/ is now (finally) re-registered and I am running as operator on here. Feel free to stop by and say hi. I do leave my computer idling on IRC, so check back or leave me a message if you have any ideas, suggestions, or just want to tell me off. You can get onto #/sci/ by joining the server irc.7chan.org at port 6667. You can also use SSL at port 6697 but you will have to set your client to accept invalid certificates.

ADDITIONALLY and IMPORTANTLY I have had several requests on IRC regarding the old Ebook FTP that we used to have. Unfortunately, the mod who ran it entered the military and no longer runs or maintains it. I have no plans to make another one, but if one of you guys would like to, by all means advertise here.

That being said, I'm just going to leave this link here:

http://ebookee.org/index.php?tag=7

You may find what you seek here.

I will be unstickying the old ebook/source articles thread. Please post any new ebooks/source articles here, and feel free to post any working links from the old thread there; I will eventually be deleting it.
Message too long. Click here to view the full text.


14 posts and 2 images omitted. Click Reply to view.
>>
Solutions Manual to E&M, 3rd Edition by Purcell Anonymous 16/11/19(Sat)00:05 No. 16384 ID: 1ae570
16384

File 147951030462.jpg - (27.55KB , 406x500 , Purcell 3rd Edition.jpg )

Looking for the the solutions manual to Electricity and Magnetism, 3rd edition by Purcell and Morin. The problems are much more difficult and numerous than in the previous two editions, making it one of the best problem books on the subject. Was able to find the solutions to two analogous books in Classical Mechanics:

http://bookzz.org/book/2592413/e67f58

http://bookzz.org/book/2592412/fd6171

Sadly, all my searches for the solutions to the E&M book have been fruitless. It's the last manual that I need to complete my collection.




Binomial Irgendwas Anonymous 18/09/11(Tue)02:39 No. 16694 ID: f54f31 [Reply]
16694

File 153662638063.jpg - (29.41KB , 331x400 , confused1.jpg )

I have a question with regards to what I would call a particular object that enumerates the elements of a binomial coefficient. Let me explain the thing first.

Lets say I have 6 elements and I'd like to choose 4 of the stupid things. The binomial coefficient tells me that there are 15 of these groupings. I.e. these:
{{1,2,3,4},{1,2,3,5},{1,2,3,6},{1,2,4,5},{1,2,4,6},
{1,2,5,6},{1,3,4,5},{1,3,4,6},{1,3,5,6},{1,4,5,6},
{2,3,4,5},{2,3,4,6},{2,3,5,6},{2,4,5,6},{3,4,5,6}}
I would like to enumerate over these groupings; and I have an object that does.

My question then is, what would I call the thing that enumerates over those groupings?
Binomial Enumerator?


>>
Anonymous 18/09/11(Tue)18:27 No. 16695 ID: be6f8f

The technical term for each of those "groupings" as you call them is "combination". The action of picking combinations is usually called "choosing" (e.g. 6C4 is read "6 choose 4").
So you could call the enumerator "combination enumerator", "combinator", or "chooser". I think those are all acceptable names.




invite acidburn 18/08/28(Tue)00:03 No. 16693 ID: ada4d2 [Reply]
16693

File 153540739798.jpg - (253.94KB , 800x1088 , 75d4f1bc580ca84f84f1056cf3d48bab5779bedd6069298424.jpg )

e z c a p e c h a t .com/rooms/a n i m a m u n d i
n o s p a c e s

psychonautics x void




Atmospheric absorption/scattering of sunlight Anonymous 18/07/27(Fri)04:35 No. 16685 ID: 953c1f [Reply]
16685

File 153265890490.png - (96.72KB , 620x359 , solar-panels-australia.png )

Hey, /sci/. I'm running a simulation of solar panel efficiency and I need some way to calculate energy production from the sun's position in the sky. For example, assuming a panel that is always pointer at the sun, when the sun is closer to the horizon the panel will generate less energy than when it's high in the sky.

I'm looking for something like f(x radians) = y W/m^2.

Thanks.


>>
Anonymous 18/07/27(Fri)04:50 No. 16686 ID: 953c1f
16686

File 15326598517.png - (21.74KB , 1115x717 , theta.png )

Here's part of what I'm doing. Assuming a panel can rotate side to side and track the sun, but cannot rotate up and down, these are the angles of inclination of the panel for a given latitude that will yield the maximum energy production throughout the year. The problem is that this assumes that as long as you point the panel directly at the sun, you will generate the same amount of power at noon as you would just before dusk. So for example at the equator the optimal angle is predicted to be 42°, rather than something flatter. At the same time, energy production is predicted to be higher in Antarctica (99% efficiency) than at the equator (92%), which is nonsense.




Anonymous 18/06/28(Thu)13:01 No. 16668 ID: c6e9b2 [Reply]
16668

File 153018367186.jpg - (15.82KB , 500x500 , 3bfc065f.jpg )

Yay /sci/!

Does anyone please know of a way to determine if there's any local max and min *within a set range of X-coordinates*?

As we can see, there's a local max somwhere around -1 and a local min somwhere around 3 and none whatsoever in the range 1-2.

But how do I prove that there's no local max nor min in that range?


>>
Anonymous 18/07/01(Sun)09:09 No. 16670 ID: af0184

First, what class are you taking? What level mathematics are you looking at?
Then, what is the f(x)?

Hopefully, calculus I. Take the derivative; set f(x)'=0, solve for all x values. That proves the only time slope=0 can be at those specific points (watch out for those pesky imaginary numbers).

We could also do a differential equation, i think. It looks like we have enough information from the graph to knock one out. However, its been awhile since I did one. Id need to review some notes.


>>
Anonymous 18/07/25(Wed)08:59 No. 16682 ID: c6e9b2

>>16670
Not taking any class and don't know my level.

And what if it's f(x)=(sin 10X)+X ?

That will be a constantly increasing sin-wave with no global maximum and a lot of local maximums.


>>
Anonymous 18/07/25(Wed)21:33 No. 16684 ID: be6f8f

>>16682
Given a closed interval of the domain, any continuous function *necessarily* has both a global maximum and a global minimum[1], since the closed edges of the interval are candidates to being global maximum and minimum. For example f(x) = x^2 in the interval [-1; 2] has a global minimum at x = 0 and a global maximum at x = 2. However, it has no global maximum in the intervals [-1; 2) and (-1; 2). On the other hand, f(x) = 1/x has no maximum or minimum in any of those intervals.

Discontinuous functions may not have any extrema even in closed intervals. For example, f(x) = x/x + x, interval [-1; 0].

There's no general algorithm to prove that a given function has no extrema in a given range. As >>16670 mentioned, the zeroes of the derivative is a good place to start, but it doesn't end there. Some functions have extrema and are continuous but nowhere differentiable[2]. Some have extrema and are nowhere continuous[3].


As for your example of f(x) = sin(10 * x) + x:

Definition:
acos: [0, pi] -> Reals
acos(y) = the value of x such that cos(x) = y

f'(x) = 0
Message too long. Click here to view the full text.




Deductive, inductive or abductive? Anonymous 18/07/24(Tue)12:27 No. 16679 ID: c6e9b2 [Reply]
16679

File 153242807199.png - (799.65KB , 1770x2328 , thinker.png )

Hello /sci/!

Yesterday when I took a walk, I saw a bunch of huge plastic containers by the roadside in a shallow natural pit.

I considered it to be a trash dump.

What kind of reasoning did I use. Deductive, inductive or abductive?

And if I used the other two kinds of reasoning, would I reach the same conclusion? And how would I use them?


>>
Anonymous 18/07/24(Tue)16:32 No. 16680 ID: be6f8f

Any reasoning about the world external to your mind of the form "I see X therefore Y is true" is necessarily not deductive, not just because you can't prove that your senses are perceiving reality as it is, but also because even if they are, you are only perceiving a small fraction of reality, and thus you can never know when you have *all* the facts relevant to a particular conclusion. If you were to exercise pure deduction in your daily life you'd be paralized from being unable to make any decisions.

I'd say it's a form of inductive reasoning. The premise you're failing to mention is that (I assume) you've seen things that you knew were trash dumps and looked mostly similar to this thing that you saw in this instance. That's inductive reasoning.
* P(A)
* P(B)
* P(C)
Therefore P(x) for all x that are similar to all three of A, B, and C.

For abductive reasoning, you'd need to consider all the things that could possibly look like a bunch of huge plastic containers by the roadside in a shallow natural pit (from now on, "Bunch"), weight their relative probabilities of this Bunch being that, and conclude that this Bunch must be that thing with the highest probability. E.g.:
Knowing that there's a Bunch here, there is:
* A 70% probability that it's a trash dump.
* A 5% probability that it's a plastic container storage site
* A 25% probability that it's something else I'm failing to consider.
Therefore this Bunch is a trash dump.


>>
Anonymous 18/07/25(Wed)08:49 No. 16681 ID: c6e9b2

>>16680
I see.

But just because there's no pure deductive reasoning, it's still valid?

And wouldn't inductive reasoning be to explore the entire roadside and see what artifacts lay there? Because a lot of the stuff could've been explained by it blowing off from pickup trucks. But plastic containers blowing off and landing in the same area, not so much.


>>
Anonymous 18/07/25(Wed)18:01 No. 16683 ID: be6f8f

> But just because there's no pure deductive reasoning, it's still valid?

No, logically speaking only deductive reasoning is valid. That's not to say you can't fairly reliably arrive at a correct conclusion using non-deductive reasoning. Just that you have no way to verify that you're not making a mistake prior to testing your conclusion with reality. The point of a valid reasoning is that as long as your premises as correct you can be sure that your conclusion will be correct.

> And wouldn't inductive reasoning be to explore the entire roadside and see what artifacts lay there? Because a lot of the stuff could've been explained by it blowing off from pickup trucks. But plastic containers blowing off and landing in the same area, not so much.

Let me clarify my previous explanation. When I said "you've seen things that you knew were trash dumps" I didn't mean "along the same road", or "in that general area at that time". I meant that you've seen them in your life. You've seen things that you were told were trash dumps and you learned the general appearance of a trash dump.
But to answer your question, exploring the entire roadside would be gathering data (premises). It's what you do with that data that counts as one form of reasoning or another.




Starting Math Major soon, how to approach? RedRobin9688 18/07/14(Sat)11:25 No. 16675 ID: 241c58 [Reply]
16675

File 153156031540.jpg - (132.79KB , 757x502 , 1510097214290.jpg )

I move in 8/5/18 and intend to Major in Mathematics, there are four options (Pure, Applied, Applied Stats, Actuarial) which should I formally choose to actually succeed? Should I double major? and if so what in? I'd appreciate the help, I don't want to move in with the parents after school.


>>
Anonymous 18/07/17(Tue)22:07 No. 16677 ID: 953c1f

Applied if you want a real job. Pure if you want to do research. I don't know much about the other two, though.


>>
Anonymous 18/07/20(Fri)20:31 No. 16678 ID: 48d322

Acturial is like accounting sort of. I don't know how to descrive.




Anonymous 18/07/03(Tue)12:20 No. 16671 ID: 91195d [Reply]
16671

File 153061325760.png - (23.51KB , 375x368 , Blood types.png )

I’m a high school science teacher, and about 15 years ago I spent a year teaching science in Bogotá, Colombia at a private school. Rich kids, raised in Spanish and English. Great kids, in fact.

I was teaching genetics with one group and we were looking at blood types. Unlike North America, identification in Colombia includes blood type (seriously, this is a great idea for emergency situations, no idea why it isn’t here) so it’s common for people to know the blood types of their entire family. We did blood tests in class and the students were able to see that it matched up with their ID info. We then used this info with their family’s blood types to look at pedigrees.

One of the girls in the class came up to me after class with a concern. I don’t remember the exact blood types, but her parents blood types didn’t fit. Basically, there was no way her dad was her dad. I fumbled through some bullshit possibility of a mutation, but I learned my lesson - never again will I have students do blood type pedigrees with their families.


>>
Anonymous 18/07/03(Tue)20:32 No. 16672 ID: be6f8f

All that test can tell you is that the person is not the child of *BOTH* of those two people. You can only use it to disprove one out of four possibilities:
1. Both parents are biologically related to the child.
2. The father is not biologically related to the child.
3. The mother is not biologically related to the child.
4. Neither parent is biologically related to the child.

#4 can't be disproven with this test, since obviously strangers can coincidentally have the same blood type. You could have told her that maybe she was adopted.

Honestly, I don't think you should stop teaching this. I didn't even know it was possible to disprove blood relation through blood type. This is useful information to have, ESPECIALLY if it uncovers infidelities and adoptions.


>>
Anonymous 18/07/03(Tue)20:51 No. 16673 ID: aace8a

wincest?


>>
Anonymous 18/07/15(Sun)11:35 No. 16676 ID: 83c873

I've had something along these lines happen! Super awkward!

Was looking after a 16 year girl who needed surgery. She asked if I knew her blood type, and I explained that the blood test was being processed and we'd know in an hour or so. She asked if I could let her know, because both Mum and Dad know theirs. They both proudly add they are O+. I explain that in that case she'll either be O+ or O-, because that's genetics.

An hour later her blood group comes back as A+. I tell her this, and then the three of them proceed to ask how that's possible given what I said earlier. I avoid mentioning infidelity, and weakly suggest perhaps her parents were mistaken about their own. Turns out they weren't, and Dad storms out after calling Mum a whore. Mum follows him, and I'm left with the daughter. So... about that appendix...




Excited AcidBlast 18/07/11(Wed)13:49 No. 16674 ID: 708d53 [Reply]
16674

File 153130974673.png - (482.35KB , 720x1280 , Screenshot_20180711-070004.png )

Recently, I was accepted into the biochemistry program at my university. Are there any recommendations on what I should read or study before my classes start? I already have an undergrad degree.




Homosexuality, could it be an anomaly in brain developement? Dr. Nick Riviera 15/02/05(Thu)04:59 No. 16039 ID: 8ec688 [Reply]
16039

File 14231087868.png - (64.35KB , 320x307 , Dr__Riviera.png )

Hi guys, to begin I just want to make a couple of things clear.

- This thread is NOT about discrimination of homosexuals.
- This thread is NOT about considering homosexuality as disease.
- This thread is for pure scientific discussion.

Well, let me begin by telling you that I'm a med student and a embriology assistant at my university and I'm not a native english speaker, so you may encounter some grammatical errors in the text, but you'll get the point.
This whole dilemma began two weeks ago, when my brother told my family that he is gay. It was quite a shock, not because of the fact of him being gay but because he doesn't fit the gay man stereotype. He's a big dude, loves sports, bearded, the true definition of what some call "manly man". We accepted him, of course, and I have to say I've never seen him happier.
But after a few days I began to think, was he always gay? Did he decided to be gay? Why now? These questions started lingering in my mind. So I went to talk with my him about it.
He told me that he always has been, for as long as he remembers. Nothing has changed about him, except for his sexuality (for us, not for him haha). So that got me even MORE questions. Why are some gay men that are like extremely feminine? Why are some gay women extremely masculine? Why are gay guys like my brother who don't appear to be gay? Why do some gay people feel like they are traped inside the other genders body and need to get medical treatment (sex change surgery, hormone therapy) and why others don't?And why are there women like that too? Why many species, whose main goal is to survive (actually this is every species main goal, it's literally in our DNA), has certain individuals who are the contrary to this?
So I decided to tackle all these matters from a scientific point of view? What if during the development of the lymbic system (the part of the brain which controles emotions, memory, sexual desire, etc.) something doesn't go as it should?
So after I thought of this I told myself I couldn't be the first one to ask myself these questions. And of course I wasn't in a world with 7 billion people so thanks to the magical power of the internet I managed to get a cool text about the subject. I took some paragraphs which I thought were the most interesting, still I'm leaving the link (please don't take the text as discriminatory, it's merely scientific, it refers to homosexuality as an anomaly in brain developement because seen from a medical point of view it is, still doesn't mean it's moraly wrong).

"..the body and the brain first become sexually differentiated at about the third fetal month. Prior to this age, although genetically male or female, the fetus is physically/sexually-neutral. With the formation of the testes, and the secretion of testicular androgen, target ti Message too long. Click here to view the full text.


27 posts and 1 image omitted. Click Reply to view.
>>
Anonymous 18/06/05(Tue)13:17 No. 16655 ID: ac4165

>>16274
it cant be 100% genetic if you get sets of identical twins where only one is gay.


>>
Anonymous 18/06/25(Mon)02:20 No. 16664 ID: a521d4

For the longest time, people have been saying yes. Kids ignore them because their foster parents (school, country, media) claim otherwise. Only corrupt dreamers think otherwise.


>>
Anonymous 18/06/28(Thu)13:24 No. 16669 ID: c6e9b2

>>16652
Who cares? Homophobes causes much more problems than the opposite.




Delete post []
Password  
Report post
Reason