The h Bar

Anonymous

6:00 PM

@Sid lol :P I'll get something like that I guess

Anonymous

My languages weren't very good. Maths and sciences were fair.

Sid

Yeah, I got 97 in Physics and 95 each in Maths and CHemistry.

Anonymous

Congrats :) Anyhow, I'm least bothered about board exam results now :D

Anonymous

I'm waiting for 11th June :P

Sid

So am I. WHo cares about those? The 11th is always that matters now..

Anonymous

6:04 PM

I started learning multivariable calculus and linear algebra meanwhile. It's interesting :)

Anonymous

Oh, and I'm going to watch Sachin's movie tomorrow! Yeah :D

Sid

Sachin's got a movie?

Anonymous

@Sid You don't know? :O

Sid

facepalm - Just googled it. Apparently, it's a new movie.

Anonymous

This?

Anonymous

6:06 PM

Yup

Sid

I don't really watch movies nor am I a big fan of them..

Anonymous

Ow, on the other hand I'm a movie buff :P

Sid

I have just been reading about international conflicts..

Anonymous

I watch almost every new Hindi and English movie that releases :)

Anonymous

@Sid Which?

Sid

6:08 PM

They are so much covered in shades of grey that you could probably make tons of movies on them and yet show no side as superior over the other.

Usually controversial international conflicts..

Territorial disputes, etc.

Anonymous

Heh. Yeah, in wars usually there is no good/innocent side.

Sid

Yep. that is what makes them interesting.

Anonymous

I don't like those type of movies. I prefer happy movies. Not the cynical ones. :P

Sid

Those "happily ever after" movies don't give a reflection of true life. True life is covered in shades of grey not in pure black and white terms.

But, that is my own opinion.

Anonymous

Exactly. I don't want to watch movies based on true life.

Anonymous

6:13 PM

I like fairy tale like movies in a world of fantasy :D

Anonymous

"Happies Endings"

Sid

Happy endings don't exist in real life, I guess.

Meh, I am being too dark here..

Swapnil Das

Hi

@blue Could you tell me who's better. Mohit Tyagi or MC sir?

Anonymous

If the ending isn't happy then it isn't the ending. :) (My philosophy :P)

Anonymous

@SwapnilDas Both are very very good. It depends on who suits you better.

Swapnil Das

6:19 PM

I mean I don't find anything new in Tyagi.

Anonymous

MC Sir suited me more

Avantgarde

Hey people

Anonymous

He also gave the solutions to all the exercises and past papers.

Anonymous

So MC Sir covers more questions while MT sir teaches the concepts in greater depth.

Anonymous

I recommend learning the concepts from MT sir and solving the problem sets by MC sir

Swapnil Das

6:21 PM

Ic.

Anonymous

@Avantgarde Helloa!

Swapnil Das

What book did you use for maths?

Anonymous

@SwapnilDas No book.

Swapnil Das

Topper!

Avantgarde

Hey @blue

Swapnil Das

6:22 PM

Hi @Avantgarde

I use Cengage.

Avantgarde

Hey Swapnil

Swapnil Das

I take 5 mins for each hard problem :(

Sid

If you limit yourself to book in Maths, you are not doing justice to the beauty of the subject.

Swapnil Das

No I don't.

Anonymous

@SwapnilDas If you solve MC Sir's problem sets you don't need to solve any other book

Swapnil Das

6:23 PM

But a standard textbook seems necessary.

Anonymous

I used to use 5 books in class 11 and none in class 12. Hehe

Swapnil Das

lol.

Anonymous

I wish I didn't spend my time on so many books in 11

Swapnil Das

Cengage has better probs than MC sir's

Anonymous

@SwapnilDas You need to solve relevant problems and not tougher problems.

Sid

6:24 PM

I used to solve from TMH..

Swapnil Das

@Sid That's nice too.

Anonymous

After 2 years you won't remember any of the tricks used to solve the tougher problems

Anonymous

But you will remember the concepts

Swapnil Das

Yes. I apply the principle on me.

@blue Account block warning. I logged out.

Anonymous

What I recommend is learning the whole 11+12 maths from MC sir and MT sir. And in 12 solve as many full papers on maths as you can. That complete syllabus practice is the only thing that matters. Not the ultra tough problems that you solved from Arihant or Cengage.

Avantgarde

6:27 PM

MC sir?

Anonymous

@Avantgarde Manoj Chauhan :P

Avantgarde

I'm guessing this is IITJEE book discussion?

Anonymous

@SwapnilDas ? :O What happened

Swapnil Das

Multi Access detected.

Anonymous

I need to change password again

Anonymous

6:30 PM

@SwapnilDas Check your mail.

Swapnil Das

Nah, I won't use your account.

They have screened the software.

They might block mine too, so sorry about that

Anonymous

@SwapnilDas Screened? What?

Swapnil Das

Yes, they have used software screening.

Anonymous

So you can't access it any longer?

Anonymous

I changed the password just now

Swapnil Das

6:33 PM

No, that's a risk. I won't take it.

Anonymous

So you are planning to buy it yourself?

Swapnil Das

No,

I'm fine.

Anonymous

Okay, all the best!

Swapnil Das

I've learned from experience that being an abstract subject, mathematics can't be taught

I need to work hard and rest will do.

Anonymous

Depends on how you define "taught" :)

Swapnil Das

6:35 PM

Hmm. I mean getting lectured.

Anonymous

Learning mathematics is like learning how to play football :P

Anonymous

Sure, no one can teach you how to play but someone can obviously guide you. Experience matters.

Swapnil Das

yes!

true, my FIITJEE teacher can help out, I hope.

Anonymous

@SwapnilDas You joined FIITJEE?

Swapnil Das

ofc.

i'm from 10th

Anonymous

6:41 PM

Heh. Then why do you need so many books? :P Their books are enough :D

Swapnil Das

no!

they are nonsense.

Anonymous

I meant for the problem sets

Sid

I think it would be a better idea to switch the discussion to the room where it belongs..

Anonymous

The theory is not good.

Anonymous

Ah well, I'm off now. Ttyl about this

Anonymous

6:43 PM

Goodnight

Swapnil Das

night.

Emilio Pisanty

7:03 PM

> I'm looking at page 21 of the paper (arxiv.org/abs/1208.4074.pdf)...

no, you're not

that's not a url that you can just copy off your browser

peterh

7:25 PM

@EmilioPisanty It shows to me only the length of the suggested edit queue, but it may behave differently for 10k+ accounts. I've seen, how a 10k+ screen looks! Thanks :-)

AccidentalFourierTransform

@peterh out of curiosity, why did you vote to reopen here: physics.stackexchange.com/review/reopen/176603

its a terrible question

if you vote to reopen every question by default, and never pause and think if its actually a good question, people wont take you seriously in the future

2

dmckee

@EmilioPisanty ::chuckles::

AccidentalFourierTransform

@EmilioPisanty my bad, sorry :-P

Emilio Pisanty

7:45 PM

@peterh The number it shows is pretty meaningless.

20

Q: Please dim the color of the review task counter when there are no actionable tasks

I am glad to notice that the massively annoying refusal of the 10k flag counter to disappear when I'm not needed has been appropriately dealt with via the extreme decapitation method of simply eliminating the 10k flag queue. As of a few days ago, the orange-ish counter on the top bar now links to...

It is vaguely related to the total number of review tasks in all the queues, even if you can't access them or you've already reviewed them.

Is that stupid and counter-productive and can only lead to a de-sensitization w.r.t. the counter, with the result that people will just ignore it?

quite possibly, yes

Sha Vuklia

Guys, is there a quick way to calculate for instance:
$$
\frac{1}{2}\int_0^a x\psi_1^2(x)\,dx.
$$
I’m guessing I should write out:
$$
\psi_1^2(x)=\frac{2}{a}\sin^2(\pi x/a)
$$
But then I will have to use trigonometric identities and integration by parts, and the whole computation is going to take a while. Same for the third term in the integrand. I was wondering if there was some trick to see the answer quicker?

Emilio Pisanty

@ShaVuklia sure, what 'bout'em?

@ShaVuklia not particularly

AccidentalFourierTransform

^

Sha Vuklia

@Emilio that means I have to do it all by hand?

AccidentalFourierTransform

the trick is to use Mathematica

Sha Vuklia

7:48 PM

LOL geee

Emilio Pisanty

^^

Sha Vuklia

okay well good to know

I don't want to be wasting my time on the test, if there was a quicker way

Emilio Pisanty

you can try differentiating from out of the integral sign

i.e. the Feynman trick

but no guarantees it'll be simpler than just doing it by hand

Sha Vuklia

hm right, thanks

Mithrandir24601

8:01 PM

@ShaVuklia What's $\psi_2\left( x\right)$ in this case?

Sha Vuklia

well the same as $\psi_1$, but then the argument in the sine is doubled @Mithrandir

Mostafa

8:23 PM

Hi @AccidentalFourierTransform; welcome to PhysicsSE. Please note that we prefer descriptive and comprehensive answers that are useful for potential future viewers, even if the question is not well posed. Therefore, if possible, please expand your answer, or leave a comment instead.

Sha Vuklia

lol welcome to Physics SE @Accidental

anyhow

there is a "trick" to see the integral

I found a different solution online, and they said you can get the answer by inspection, since $\sin^2$ is symmetric about the midpoint of the well

AccidentalFourierTransform

@Mostafa lol, it was kind of a joke answer

I didnt expect it to get any upvote :-P

._.

Mostafa

@AccidentalFourierTransform anyways, $+1$ .

AccidentalFourierTransform

ಠ_ಠ

Mostafa

Have a good night everyone.

AccidentalFourierTransform

8:28 PM

gnite

user314159

cu

AccidentalFourierTransform

nt

Sha Vuklia

@Accidental you have to become more serious.

AccidentalFourierTransform

why?

Sha Vuklia

lol i dunno just random

Anonymous

8:32 PM

Eh, no. Serious is brrooooorrrrriiiiinngggg.

AccidentalFourierTransform

SeRiOuS Is BoRiNg

user314159

WOW!!! kids these days

Anonymous

@user314159 Oye! I suffer from acute inferiority complex.

Sha Vuklia

lol same @blue

why am I even studying

user314159

For fun.

Sha Vuklia

8:34 PM

and torture tho

sorry that got too dark :P

user314159

np

AccidentalFourierTransform

user314159

@blue “I remember when I first offered to pay her a small wage to work on her research from one of my grants,” he wrote. “She refused, saying she was not sure if it was right to be paid for thinking about math.”

Anonymous

@user314159 heart melts o_O

Anonymous

I would have grabbed any money anyone offered :'D

user314159

8:41 PM

:-)

Anonymous

I'm broke anyway :P

user314159

People who are in it for the money are in it for the wrong reason.

Anonymous

Heh. Everyone is in for money. But money may not be the primary reason.

Anonymous

If you don't want to be paid for your job then either 1)You are acting or 2)You are too rich or 3)You are stupid. I don't know how/why not wanting money is equated to nobleness.

user314159

So you think she's acting?

Anonymous

8:48 PM

@user314159 Either that. Or she doesn't need money at the moment. Her parents earn on her behalf.

user314159

perhaps

Mithrandir24601

Arran Fernandez

Arran Fernandez (born June 1995, England) is a mathematician who in June 2013 became Senior Wrangler at Cambridge University, aged 18 years and 0 months. He is probably the youngest Senior Wrangler ever. In October 2010, when he began studying the Cambridge Mathematics Tripos aged 15 years and 3 months, he was the youngest Cambridge University undergraduate since William Pitt the Younger in 1773. Prior to university, he was educated at home, and in 2001 he broke the age record for gaining a General Certificate of Secondary Education (GCSE), the English academic qualification usually taken at age...

Emilio Pisanty

is $\frac{\mathrm d}{\mathrm dx}\sin x=\sin$? — AccidentalFourierTransform 24 mins ago

fantastic

AccidentalFourierTransform

deadly sin indeed

user314159

@Mithrandir24601 interesting how old the previous record was.

Jaime Gallego

9:04 PM

Any LaTeX magician here?

I'm getting errors on latexmk with biblatex references

LaTeX Warning: Citation 'lambertcali' on page 7 undefined on input line 212

Ugh

David Z

Seems pretty straightforward, on line 212 of your LaTeX input file you use \cite{lambertcali} and there is no corresponding entry (with key lambertcali) in the Bibtex database

At least, that's how it seems

Jaime Gallego

But I do have a .bib file with that entry!

One sec

user314159

Hi @DavidZ

Jaime Gallego

David Z

@vzn I assume you mean the chat session slot? That's fine with me

@JaimeGallego Are you actually using that file from the LaTeX document?

@user314159 hi

Jaime Gallego

9:12 PM

I have an \addbibresource with that file on the preamble, yes

\addbibresource{georef.bib} with georef.bib being the file on the same directory

David Z

Hm, well then. Can you make a stripped-down version of the LaTeX file with almost nothing in the document but the citation in question, and see if it also causes the same error?

vzn

@DavidZ awesome thx! @BernardoMeurer you are officially cleared for takeoff! :) plz write a meta post in next wk or so announcing your session. jun13 1600Z hbar chat room. ps can also cc/ advertise this elsewhere this time due to the part-CS-angle! looking fwd to it! :)

Jaime Gallego

@DavidZ I searched through the logs and found biber was mysteriously not installed. I reinstalled it and it works fine now.

David Z

Weird. You'd think that would be the sort of thing that would make a very obvious error message... anyway, good thing it works.

Jaime Gallego

9:28 PM

Thanks anyway @DavidZ

David Z

No problem

vzn

@Mithrandir24601 / @EmilioPisanty next session guest slot is july 11th would either of you be available for it? :)

@DavidZ so youre in the US now? are you at a university? just wondering/ hope youre comfortable or doing well np if its TMI right now

David Z

9:48 PM

@vzn yes and no respectively

Bernardo Meurer

@vzn Sweet! I'll get cralacking right away

vzn

@DavidZ ok hope to hear what youre up to these days outside of cyberspace when you feel like it :) ... china sure is in the news a lot these days it seems like esp wrt STEM. hope you can be guest speaker someday & relate on your experience wrt it etc :)

Bernardo Meurer

@vzn Remember to add me to the schedule thing on the main post

vzn

@BernardoMeurer we tend to update the "main meta post" (listing all the sessions) after the session although it could also be used for upcoming sessions. @DanielSank may update it after you have your meta post ready. DZ can put pin a link to the upcoming talk on some pages eg chat or site main pg, he may do that :)

Bernardo Meurer

10:51 PM

@vzn physics.meta.stackexchange.com/questions/9898/…

2

Physics Meta

2

Q: June 13th Ask Me Anything feat. Bernardo Meurer

I'm Bernardo and I've been invited as the next guest for the Physics Stack Exchange AMA. The session will take place on the h Bar, on June 13th at 16:00 UTC. If you, much like me, gets awfully confused by timezones, just click here. Post questions you'd like answered below The AMA is always inf...

discussion

Mithrandir24601

@BernardoMeurer You got Linux running on a toaster‽ Nice

Bernardo Meurer

@Mithrandir24601 Yeah, but not natively because I couldn't find an IoT toaster back in Brazil. So what I did was that I hooked up the toaster controls to a raspberry pi that lived inside it

Mithrandir24601

@BernardoMeurer That's cheating :P

Bernardo Meurer

@Mithrandir24601 Well, I also managed to get to the shell on my Kindle

And then I made it say "Suck it amazon"

The picture is here somewhere

Mithrandir24601

11:02 PM

@BernardoMeurer Haha! OK, I'll give you that one

@BernardoMeurer Yup - chat.stackexchange.com/transcript/71?m=29602024#29602024

Bernardo Meurer

hehehe

Good times

Shing

11:18 PM

I wonder how much time a Native English speaker will put into preparing himself for GRE?

David Z

11:30 PM

@Shing speaking for myself, none

Then again physics grad schools generally don't care about the verbal portion of the GRE score (as long as it's not outright terrible)

Shing

@DavidZ lol, thanks. then I would study GRE only for English's sake, not for exam. It is a bit embarrassing to acknowledge that I have just learn the word "to agitate" today.

David Z

Yeah, don't worry too much about your score on that exam

unless you're applying somewhere that needs it

Sha Vuklia

Guys, why isn’t it: $d\psi_0/dx=\sqrt{m\omega/\hbar}d\psi_0/d\xi$? Because I would think that $d\xi/dx=\sqrt{m\omega/\hbar}$.

David Z

@Shing Do keep in mind that most native English speakers would not be able to get a high score on the language parts of the GRE without studying.

@ShaVuklia hm, what you're saying seems right to me.

Sha Vuklia

oh okay @David thanks for the confirmation

David Z

11:41 PM

No problem

Jaime Gallego

I created a banner for the AMAs to replace the old one. How does it look?

5

Bernardo Meurer

@JaimeGallego That's really nice!

@DavidZ What do you think?

Sha Vuklia

11:56 PM

Guys, Ehrenfest’s theorem states that
$$
\frac{d\langle p\rangle}{dt}=-\left\langle\frac{\partial V(x)}{\partial x}\right\rangle.
$$
However, I was wondering if we can say the following:
$$
\left\langle\frac{\partial V(x)}{\partial x}\right\rangle=\frac{d}{dx}\langle V(x)\rangle.
$$

Because the way I interpret Ehrenfest's theorem, is that we can use the laws from classical physics when dealing with the expectation values, so since $dp/dt=-dV/dx$, I was thinking we might as well write $d\langle p\rangle/dt=d/dx\langle V\rangle$

I would kind of like to know what the subtleties are, so that I know what I can and cannot do with Ehrenfest's theorem. I'm guessing my main problem is taking derivatives.

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