The h Bar

@Ramanujan it is reversible

if you feed mechanical energy to a dynamo, it will produce electrical energy

if you feed in electrical energy, it will produce mechanical energy

they are inter convertible

motors and generators are the same thing

Ramanujan

@YashasSamaga, magnet in a dynamo is movable, isn't it?

All I can say: Don't try to reverse engineer the problem to get to the answer. I am a little busy now. Will go through that problem later.

Little Rookie

5:03 PM

The Prof. of the course said that it is the midpoint of the duct.

Fawad

:( @ACuriousMind you are bad guy

:O what did ACM do?

@Fawad He isn't a guy. He is an AI. :D

People have started worshipping ACuriousMind. :O

ACuriousMind, you got fans!

@ACMisbadguy Oh, using a sockpuppet to circumvent a suspension? Bad move.

ArtOfCode

5:11 PM

@ACuriousMind and I was literally about to ping you :)

…

Hehe. This was funny. :D

The name is too good :P

@Slereah wat

Are you looking in the weird corners of the internet again? :P

Koolman

Can anybody help me in this

5:17 PM

@Koolman You know, you always just throw an exercise in here and ask if anyone can help you. How about you tell us your thoughts, and what exactly you're unsure about instead for a change, instead of expecting someone to just give the solution to you?

3

Koolman

In that if we rotate coil there would be change in flux because of which there woud be more current induced . Now how can we find deflection from this

5:34 PM

@Koolman Deflection is w.r.t $+{7^0}$. It goes to $-7^{0}$. So deflection is $14^{0}$.

Not a well framed question.

Koolman

@anonymous oh i see

Thanks

vzn

5:54 PM

in theory salon, 2 hours ago, by vzn

saw this last nite on appletv, awesome flick, recommend it CERN documentary / Geyrhalter

@ACuriousMind hmm, how about a new homework policy for the chat?

@Mostafa Uh don't do that. People here anyway guide the users to show their effort. Why create unnecessary friction?

@ACuriousMind Is is supposed to be obvious that $\langle a,b|aba^{-1}b\rangle$ contains a subgroup isomorphic to $D_4$?

@YashasSamaga Are you done with Salt Analysis ?

three years ago

6:05 PM

@0celo7 It's not obvious to me

practical or theory? @anonymous

@YashasSamaga Theory for advanced

@ACuriousMind My alg. top. prof is a group theorist...

Qualtitive Analysis

I need to revise chem

From where did you do it? Which book ?

6:06 PM

J.D. Lee

Hmm, I need to do the cations

Concise Inorganic Chemistry

They are so difficult to remember :P

@YashasSamaga J. Lee is a popular name

It has too many things outside the syllabus but it is awesome

6:07 PM

I am making color charts and hanging them on my room's walls

you should never be learning to finish off the syllabus

Yeah. I am doing it slowly. One cation each day

Anions I have completed

@0celo7 is that the fundamental group of the Klein bottle?

JD Lee has too much details I think

yes it does

but it is interesting

you won't doze off

6:09 PM

My memory is weak. Even if I find it interesting I will surely forget it unless I revise everyday

Okay thanks

You are supposed to study Q.Analysis, Metallurgy, block chemistry, etc. in the last few weeks

and take tests

@ACuriousMind Yes.

I am well versed with the blocks :)

And metallurgy

@0celo7 I'm thinking it is "obvious" if you present the Klein bottle as a square with its sides glued in a particular manner. Then you can use the symmetry of the square - the dihedral group of order 4 - on a contractible loop (one of the diagonals, I think) to get a bunch of non-contractible loops due to the different ways the sides are glued. I haven't checked that, though.

@ACuriousMind That's how we computed the fundamental group

But I had no clue what he was talking about after he started talking about $D_4$

I wasn't sure how the generators of the fundamental group were supposed to correspond to the symmetries

6:28 PM

Hey @0celo7

hi

Ordered Haag, Jost and Reichenbach

Reichenbach?

amazon.in/Philosophy-Space-Dover-Books-Physics/dp/0486604438

@0celo7 This I guess ^

700+ Indian money?

6:36 PM

Yeah. Different Currency. :)

Rupee.

I thought that's what it's called

But I had a suspicion I was confusing India with Hyrule.

Hyrule?

Video game ? :P

Haha

Only the second most famous of all time.

That book is referenced in Geroch

And it was like 3€

So I thought I'd give it a look

lol

@ACuriousMind May we know who "ACM is a bad guy" was a sockpuppet for ?

6:41 PM

Fawad

What did Fawad do?

4

Q: Can I use chat?

Stack exchange has feature to chat with other learners/teachers available at chat . So is it haram to chat? Because I think mahrams and non mahrams will be there.

Also, wow

"sin-or-not" is a tag??

Q: Is it sin to listen to Quran recitation in the bathroom?

It is on the islam wiki

1

Is it sin to listen to quran recitation on phone in bathroom and toilet? I know it is makrooh (disliked) but is it forbidden in Quran or Hadith? Can you show with evidence?

quran sin-or-not

important

@0celo7 Actually it should be changed to "haram or not" :)

Anyway I don't want to express any religious opinion.

Haram is an Islamic concept.

Meh. If someone said "is it OK to chat with black people" we'd denounce them. I think that question is similarly disgusting.

@Slereah xD

Do you understand the question? (mahrams and non mahrams)

6:44 PM

@0celo7 No comments XD

@anonymous It's not even a comment on religion.

@Mostafa (en.wikipedia.org/wiki/Mahram)

Q: What does Judaism think of math?

21

Is it permissible according to halacha to do math? If so, are all kinds of math OK? This question and its answers are Purim Torah and are not intended to be taken completely seriously. See the Purim Torah policy.

purim-torah-in-jest

Q: Is masturbation permissible for a man during an extended period of unmarried life?

@0celo7 There are hundreds of similar questions on Islam SE. I find this a bit funny (islam.stackexchange.com/questions/3004/…)

10

I see that Islam has given very good options for people to remain sexually fit. My question is that nowadays usually people have only one marriage and even that at an age of 25-37 (my own observation, which may be very wrong). Now there is a whole lot of time in between which is spent without hav...

sharia halal-haram masturbation

Those people are not well.

> Whilst the Torah clearly tells you not to add or subtract, it does tell you to be fruitful and multiply

So group theory is OK, but ring theory is off-limits.

6:49 PM

Well, only additive groups

@Slereah Addition in an abelian group is just multiplication in disguise.

Maybe, but

one is permitted, the other isn't!

So you can only do noncommutative group theory

Analysis is off-limits too

GR

summation convention is anti-Semitic!!!

What is the best math religion

Is it scientology

Atheism :^)

6:53 PM

I feel most Jews don't follow those rules. How can one learn math without doing addition and subtraction ?

Goes over my head :')

set theory

Maybe that's why Asaf is a logician

You might have noticed the giant note that said "THIS IS A JOKE"

@Slereah I read that. It doesn't say it's a joke.

@Slereah Where?

It doesn't seem to be a joke..

"This question and its answers are Purim Torah and are not intended to be taken completely seriously. See the Purim Torah policy."

cf en.wikipedia.org/wiki/Purim_Torah

6:56 PM

@Slereah Oh I didn't know that :)

Sigh!

It's too bad Physics SE is pretty tight assed about fun posts

@Slereah We have Yahoo answers for that ;)

Too many fun posts on serious questions

@Slereah I am reorganizing my books. Will you actually he reading Jost?

@0celo7 I'm reading it a bit on the side

I am kind of doing too many things at once

Sanya

7:01 PM

@heather hey =) yeah, sorry, there's quite a bit of everyday trouble these days, so I'm kinda out of time ... hope that changes soonish

I have last learned that a local minimum/maximum means $f' = 0$

v. hard

@Slereah It could be an inflection point too? Isn't it ? $f'(x)=0$

I said that it implies that

Not that it was equivalent

Oh okay

@Slereah mean value theorem, no?

7:05 PM

Same chapter as that, yes

I bought the paper book so that I can read it on the can

Gross

Please

I learned many things on the toilet

10

That's where I learned about dimensional regularization

@ACuriousMind physics.stackexchange.com/review/first-posts/163463

A good installment for toilet readers :'D

Toilet is in the same room as the tub so I don't really keep books there

7:10 PM

My gosh....I can't stop laughing now!

lol @anonymous

Don't want water on me books

@Slereah Use the water gun wisely and you're done XD

Would be funnier if it was hentai @anonymous

@0celo7 I hate that.

7:11 PM

Hate what?

Hentai I guess

hen***

He only reads the finest mangas

That's an awfully strong reaction. Sounds like you're in denial lol

It's ok to have a waifu

Oh please. I love anime and stuff. But hentai is plain gross.

Q: Origins of איל משולש and Vilna Ga'on's bathroom math

7:14 PM

@Slereah related:

11

There is a well-known fact that the Vilna Ga'on studied math while in the bathroom since Torah was out of the question in an unclean place. It is also somewhat well-known that he produced the material for a book on geometry/הנדסה(?) during his time in the bathroom called איל משולש. There is (or ...

history rabbis books-generally bathroom mathematics

I only watch high quality stuff :D

A wise man

So you say it's gross, not that you hate it

Unfortunately I can't follow the example of another wise man for math

I'm keeping an eye on you

7:14 PM

Since amphetamines are illegal

I hear amphetamine is really great for math

@0celo7 I feel weird if I watch it. That's all.

t. Paul Erdős

Implying you have watched it. At least multiple times

Not something I'd be admitting in chat if I were you

@anonymous I'm trying to troll you without getting banned

It's hard with a subject like this

IIRC there's a website devoted to analyze the blackboards in the background of porn

@0celo7 In grade 6 or something. 5 years back. After that, never. I feel very weird and I don't know why.

7:17 PM

Most of them have very poor math

You know what had great science boards?

Black Mesa

Including some wormhole physics whiteboards

Good stuff

:35527185 Yeah I will feel less weird watching that.

@Slereah who writes GR that neatly

The fine scientists at Black Mesa, apparently

Dr. Klein has very neat handwriting

Also why does that energy momentum tensor have a dotted index?

which one

7:22 PM

the matrix

Might just be a stray mark

hard to tell at that resolution

This one has Krasnikov tubes :

although that's not what the metric says

I take it back this game sucks

8:17 PM

@YashasSamaga

This is pretty interesting problem

You could try it :)

I used self energies of the shells and got wrong answer initially

Then I solved by direct integration

Do tell me how you would approach the problem!

8:29 PM

Okay, I solved it using self energy method also. Yay ! I forgot to take the potential energy of pair of shells.

@YashasSamaga

8:55 PM

Hi, everybody.

hello @DanielSank

Wait

Does aqft have the hamiltonian and momentum

I think it does because it has automorphisms related to the Poincare group

But those are probably fine because they are not members of the C* algebra, I guess?

No weird issue with products of distributions

9:14 PM

@heather Yo

i've been writing tag wikis

Uh... fun?

kind of, actually.

k

9:29 PM

hmm, that's annoying

$\oiint$ doesn't work with mathjax.

Too bad.

i'm trying to replace a picture with mathjax, and now i don't know how to do that.

@heather Link?

Q: Divergence theorem with a hemisphere

-2

State the divergence theorem. Describe the regions over which the integrations are carried out and the quantities that are being integrated. Consider the vector field $$\mathbf{V}=\frac{3y\mathbf{i}+2xz\mathbf{j}-z\mathbf{k}}{\sqrt{x^2+y^2+z^2}}.$$ Find the outward flux across the ...

homework-and-exercises electromagnetism vector-fields calculus

Also, heather, I invite you to join in here.

9:33 PM

i edited already for the stuff I could do.

@heather You can use Unicode directly...for double closed integral

@anonymous, oh? How?

I think there is an unicode character for that

Need to search a bit

@heather Honestly, just leave the silly circle thingy out.

It's totally unnecessary.

it is?

not necessary mathematically?

9:34 PM

Whether or not the thing over which you're integrating is compact/closed/whatever is clear from the set itself. Putting a loop in the integral symbol is notationally redundant.

Q: How do you render a closed surface double integral?

6

In other words, this: According to Wikipedia, the code is \oiint, but it doesn't seem to work on this site.

support mathjax

@heather IMHO, it's redundant.

See the first answer

i never, ever use the circle in my own notes. Ever.

They have the unicode character

anyway as daniel says, it is indeed unnecessary

$$\bigcirc\kern-1.4em\iint_Sf(x,y)\mathrm d\ xy$$

9:36 PM

i ended up using the second answer

where the circle is put in manually.

Yeah, that is a detour

Doesn't look very nice though :P

But okay for normal use !

eh, well. better than nothing. i'd rather stick with the notation the OP used.

the unicode would've looked funky next to the mathjax.

10:01 PM

Are there any outlets to get old papers like this one for free?

I've made a chat room in which to discuss a featured post each week. It's like a little journal club for stuff I find interesting.

5

Please join if interested.

PearlSek

Hi there

there's something I don't get

If we have $E=mc^2$

and we define $c$ to be the basis of speed

it becomes $E=m$

where is the problem in my thinking

@PearlSek Why do you think there's a problem?

You have to be a bit careful what you mean by "basis of speed" and how exactly the equation becomes $E=m$, but thus far you haven't presented any problem.

@PearlSek what is wrong with $E=m$?

looks right to me

@ACuriousMind This camera angle added so much to my playing experience...

@ACuriousMind I don't remember Miranda being quite this bad.

@ACuriousMind Yeah, definitely not like this.

10:24 PM

@0celo7 Do you really need to post those screenshots everytime? I get the idea :P Miranda wasn't as bad, but for a game supposedly focused on story and characters, it was bad enough.

10:35 PM

hello,is there anybody?

No, only nobody is here

in a book on nuclear electronics under the section on detection methods, what would a "detection medium" be?

if necessary i can quote the full sentence.

I have big problem and I thought I try here to ask first,I am trying to learn about turning gases into plasma by alternating MAGNETIC field.... I have very big problem becose no matter what i type into google it will always bring up studies about ELECTRIC gas breakdown or ELECTRO-MAGNETIC ( photons )..... this electric and magnetic is so mixed that alternating magnetic field plasma,laser plasma or high voltage electrode current are all described as electro-magnetic thing,its confusing!

An overlap integral is defined as the measure of how much $\psi (r_1)$ overlaps $\psi (r_2)$. But the word overlap here implies non-interactive contact. So then when I think about the overlap, should I also think that this same overlap causes changes to the two wave functions?

I am trying to learn 2. things..... why when they want to turn gases into plasma they use high freqency like 13 mega hertz and not 60hz? 60hz is much cheaper and simpler.... and what gas at atmosferic pressure is easiest to turn into plasma? Is it xenon with its high magnetic susceptibility,or maybe neon-argon penning mixture?

10:45 PM

@loltospoon What do you mean by "contact"? A wavefunction is not a physical object, it doesn't "touch" things in a meaningful way. The overlap is just the projection of one wavefunction onto the other - exactly like you can project two vectors onto each other.

In fact, the wavefunctions are vectors in a (Hilbert) space of functions, and you are literally computing a projection.

@ACuriousMind I'm trying to understand the definition of the overlap integral. Is there any way to visualize it or is it purely abstract?

alarge

@DanielSank Looking at stochastic processes again (still?) ? Commented on an answer of mine from almost two years ago so I was just curious.

@heather I would guess it is some sort of medium that reacts when the stuff you want to detect moves through it - e.g. by emitting light.

hmm... okay @ACuriousMind

alarge

@DanielSank Well, the usual outlets? en.wikipedia.org/wiki/Sci-Hub etc

10:48 PM

@heather That could be anything; typically a counting gas, a scintillator, or a semiconductor.

2

@Loong okay.

@loltospoon As I said, it is literally the projection of one function onto another, nothing "physical" about it - but rather visual, just think of ordinary vectors as arrows and project one onto the other. The integral computes the length of the projected vector.

Who here is comfortable diagnosing skin diseases?

I think I have leprosy

PLEASE no pics

^

10:50 PM

lol JK

omg lol

:35529549 a bit strong language. would you have said that if you knew i'm a middle school student? =P

I appologize

not a problem, just letting you know that sort of thing is generally frowned upon here, since there's a permanent transcript, and of course the Be Nice policy.

Shouldn't the Be Nice policy exist everywhere?

10:51 PM

it does

Nah

anyway, could someone check if i'm getting the right picture here? the sentence is "Nearly all detection methods, the Cerenkov detector being a notable exception, make use of the ionization or excitation produced in a detection medium as a result of the absorption of all or part of the energy of the nuclear particle."

When you live as long as I have you realize "a world of nice people" is a hopeful dream

@loltospoon To expand what I'm saying: For n-dimensional complex vectors $v,w$ you have the inner product $\sum_{i=1}^n v^\ast_i w_i$, for functions you have the inner product $\int fg^\ast$. It's exactly the same, just in infinite dimensions.

my image is a medium, such as a gas or liquid, absorbing a particle's energy, and sort of "vibrating" or emitting something at the spot of the particle due to the gain in energy from the particle. then that vibration or emission is detected thereby telling you the location of the particle.

10:53 PM

@loltospoon She took "everywhere" to mean "everywhere on the SE network". That we can't (and don't want to) police the entire world should be evident :P

of course, i suppose this could be electrical charge difference, or really anything gained from the particle, not just emission or movement.

@heather Yes, pretty much, expect that you're not necessarily aiming to detect the position of the particle. Just think of a Geiger counter, it just detects it was there, not where it was

ah, okay.

@ACuriousMind haha I kid, I kid. Anyway, yes so the projection concept is something I'm used to, so that makes sense. Now, what question would I be answering by finding the result of an overlap integral?

one sentence down =P

hmm... so a scintillation detector, for instance, emits light to show that a particle has been detected?

10:55 PM

@loltospoon Do you know any quantum mechanics at all? For instance, the Born rule?

@ACuriousMind Taking the second part of a year-long intro to QM class right now, first exam next Thursday.

does anybody know why they use RF freqency instead of mains 60hz for induction coupled plasma?

@heather yes

ok

If you really want to see the location of the particles, you could use nuclear track detectors.

10:58 PM

@Sweeper I'm not a man...

0celo7 Nice...

@heather it's not in an inappropriate area

There are appropriate areas for leprosy?!

11:13 PM

Lol I don't think that's what he meant

dmckee

@heather A lot of experimental nuclear and particle physics is about trading cost off against what you need to know. For many purposes six or eight very rough position measurements will give you enough track information for what you need to know. Then maybe you just use hodoscope (paddle of solid scintilator backed by PMTs) arrays.

For other cases you need more precise tracking information, then you also employ drift chamber, but maybe only build cheep ones.

For other cases you need high precision information and then you use very dense drift chamber or segmented solid state detectors. But this costs real money.

You can also get tracking data from Ring Imaging C(h)erenkov detectors and time projection chambers (a kind specialized drift chamber)

@alarge yep, still interested in stochastic processes.

11:46 PM

I'm trying to understand how this graph is supposed to tell me that bonding does occur. The system is composed of an electron and 2 protons ($H_2^+$) and we are trying to find out if the system binds at all. We took a hydrogen atom in its ground state and brought in the other proton from infinity.

The author of the book simply says "look at that, the graph goes below $-1$, so bonding is possible". I'm lost as to how he concludes this by looking at the shape of the graph. This is from Griffiths, Introduction to Quantum Mechanics, 2nd. Ed., pg 308.