The h Bar - 2017-08-06 (page 3 of 3)

« first day (2467 days earlier) ← previous day next day → last day (2464 days later) »

2:00 PM

@AccidentalFourierTransform Please take complaining about other users seriously. Either ask them directly to stop what they're doing or flag it; or, if you are not actually feeling harassed as I suspect in this case, don't say anything to that effect at all.

(removed)

(removed)

@BalarkaSen @Blue Why would he have done that in 12th grade?

@ACuriousMind In other news, I got an SSD for my computer and a Gsync monitor. Do you know what that is?

AccidentalFourierTransform

;_;

you guys are mean

-_-

2:03 PM

@0cel because I am in 12th grade and I have it

@AccidentalFourierTransform Did you get kicked?

AccidentalFourierTransform

yes i did

really?

@BalarkaSen That seems highly abnormal and unnecessary.

Who else besides a mathematician would need to know that?

@0celóñe7 Yes. The first is awesome, the second I don't particularly care for because I never had much trouble with screen tearing

2:05 PM

@BalarkaSen If you let me in that room I will contribute effectively. I like @Blue after all.

@ACuriousMind It's a Samsung 960 EVO 500GB M.2

@ACuriousMind As for the monitor..I play games from 144 fps down to 40 fps, and they all run perfectly smoothly. There would definitely be frame tearing otherwise.

Not having to bother with Vsync is pretty great

@AccidentalFourierTransform for how long?

AccidentalFourierTransform

@user685252 I am still suspended

@ACuriousMind ^ He is admitting to circumventing a ban

@BalarkaSen ;_;

AccidentalFourierTransform

if I feel harassed by that comment, should I flag it?

no

stahp challenging everybody

2:11 PM

what an abysmal mess this room is

Abysmal Mess: Return of the ACM

what happened to that comment

AccidentalFourierTransform

I deleted it

doubtful

AccidentalFourierTransform

but true

I smell @Loong

2:11 PM

?

was it you?

@Loong wanna coffee?

This room has turned into a mess..

in The Periodic Table, 34 secs ago, by Chemobot

user image

@Sid has it?

2:13 PM

@user685252 1. What business of yours is that? 2. Kicks proceed in the standard fashion of 1-5-30 mins without any possibility of manual adjustment.

@0celóñe7 Too many messages removed, users fighting... I love it. :P

we are not fighting

@0celóñe7 Eh, I never bothered with vsync, either ;) Guess I got lucky with setups that don't run into much trouble with it

@ACuriousMind Do you have a 120 Hz monitor?

Maybe I'm just not that occupied with graphical fidelity in the end, though...

@0celóñe7 no, 60 Hz (I believe, currently on my laptop)

2:16 PM

@ACuriousMind Wow, most games run at 100 fps on my computer on Ultra, and the frame tearing is horrendous on my old monitor

2:27 PM

@ACuriousMind Is "univalent" for "injective" in the context of algebra some old German word?

@0celóñe7 Not German, it's Latin

@ACuriousMind Of course, but was it standard in German math?

Not in the math I learned - we use "injective", too

Hi, everybody.

Henlo

2:29 PM

hi

Although eindeutig was also used

@ACuriousMind Sounds like one-to-one

Mithrandir24601

Hi

hi

@0celóñe7 Yeah. A bijective map is eineindeutig in old German math speak, also funnily enough some dictionaries also say it can mean merely injective. So in any case it's better to stick to the modern words :P

2:33 PM

@ACuriousMind Hmm. This is the second book by German expats that uses "univalent" for "injective linear map."

Well, it's a possible synonym for injective in German, too. I just don't think it's any more common than it is in English

Although one could observe that "uni-valent" is a part-for-part translation of the actual German "ein-deutig"

What is the Latin root? Probably not valere, pretty sure that has something to do with worth.

@0celóñe7 It is indeed valere, which can mean "to have worth" specifically when applied to money instead of its more common meanings.

What are the more common meanings?

What does it have to do with maps?

@0celóñe7 "to be in good health", for one, or "to have power"

2:40 PM

Ah yeah, a healthy map :P

@0celóñe7 Ah, well: worth ~ value, and an injective maps is "one-valued" for every element of the source.

@ACuriousMind Oh, of course

Truth has worth, as in a true map.

@ACuriousMind This seems like a really random observation. Is it not obvious that a multivariable polynomial has a finite number of zeros?

Or, is it even true that it has finitely many zeros?

@0celóñe7 Does the polynomial $x+y$ have finitely many zeroes in your opinion?

2:45 PM

@ACuriousMind Yes.

:P

Then discovering that $\mathbb{R}$ is finite should earn you either a prize or the scorn of every mathematician :P

@ACuriousMind Apparently, it is finite a.e. :D

I think in terms of Lebesgue measure, of course

Sometimes, I don't get why incomplete answers get more votes. For example, the most highly voted answer here only answered 1 out of the 2 questions thrown out by OP (while the second answerer have addressed the 2nd question, but not as much the 1st one)

0

Q: Are the frequencies of a photon real motions if so is this motion limited by the speed of light?

In Newtonian language a photon oscillates to get his frequency. In the quantum field theory the photon is an excitation of the electromagnetic field. But are these excitations also limited by the speed of light giving the frequency of a photon a maximum?

photons frequency

(Although tbh, it probably does not matter much since some users are going to read all answers as long there are small enough number of them, I guess)

(and it is really the highly negatively voted ones that are the bad answers)

@BalarkaSen That is a good question. Is there an obvious Hamel basis of $C(R)$?

Fourier will only work for $L^p$.

I don't really care about a Hamel basis for C(R).

I am aware

2:56 PM

Then you have to put a topology on it...I don't think there's a good one.

There are analytic subtleties in the notion of basis in the context of Fourier theory that I am thinking of. But I would not talk about those to anyone I am teaching linear algebra, primarily because I don't know it :p

In mathematics, a Schauder basis or countable basis is similar to the usual (Hamel) basis of a vector space; the difference is that Hamel bases use linear combinations that are finite sums, while for Schauder bases they may be infinite sums. This makes Schauder bases more suitable for the analysis of infinite-dimensional topological vector spaces including Banach spaces. Schauder bases were described by Juliusz Schauder in 1927, although such bases were discussed earlier. For example, the Haar basis was given in 1909, and G. Faber discussed in 1910 a basis for continuous functions on an interval...

@0celóñe7 It should be parsable in L2 somehow.

Like, difference between a function and the orthogonal projection to the span of {cos(nt), sin(nt)}_{n = 1}^N has smaller and smaller norm.

Isn't a hamel basis for any infinite dimensional vector space must be uncountable?

@Secret I thought it was so for Banach spaces.

Maybe all infinite dimensional ones, not sure.

@BalarkaSen The Fourier basis proof that I know uses compactness, so only works on the n-torus.

There might be a more general proof.

@BalarkaSen Hermite polynomials from quantum mechanics

Very relevant for Blue

they are, modulo a Gaussian damping, the eigenstates of the harmonic oscillator

Anonymous

3:31 PM

@0celóñe7 I'm flattered =P

Anonymous

(＠_＠;)

Anonymous

3:53 PM

@Yashas Our brain probably just calculates the relative location of the sound w.r.t the two ears. That's the reason we have two ears and not one. It should just be due to difference in intensity of sound. Reflected sound must have lower intensity than the direct sound. Also remember that when you make a sound behind one of your ear then the sound intensity will be lower than when you make a sound in front of your ear.

Anonymous

Sound localization

Sound localization refers to a listener's ability to identify the location or origin of a detected sound in direction and distance. It may also refer to the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space (see binaural recording, wave field synthesis). The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system uses several cues for sound source localization, including time- and level-differences (or intensity-difference) between both ears, spectral information, timing analysis, correlation...

Anonymous

And yeah, as somebody had linked

@Blue what

Hey all, new member here. I don't have enough rep to ask on meta, so I would like to post this question here: are questions asking for feedback on improving home experiments allowed on Physics.SE? I'm specifically asking for advice on how to more accurately measure the actuation force of small buttons using a home setup.

Anonymous

@0celóñe7 "I like @Blue after all." =]

Anonymous

4:00 PM

@chesnutcase I think : yes. Describe your attempt to solve the problem in detail and your observation and inferences

Anonymous

Also, some experiments might be more suitable for some other site like Engineering SE etc..

I worry about it being closed for being irrelevant as I don't think there's much theoretical physics involved in pushing a button.... but I might be wrong

Anonymous

571

Q: Cooling a cup of coffee with help of a spoon

During the breakfast with my colleagues, a question popped into my head: What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon? A qualitative answer would be nice, but if we could find a mathematical model or even better make the experiment (we don't h...

thermodynamics experimental-physics home-experiment popular-science

Woah I didnt know there was an Engineering SE, I'll take a look at it first. Thanks!

@chesnutcase yes those sorts of questions are on topic, though we get very few of them as we seem to have few members doing experimental physics. However make it very clear your question is about experimental technique/protocol as people are a little prone to jump to the conclusion that you're asking about engineering.

2

Anonymous

4:02 PM

This is an example of a good experimental physics question ^

@Blue hmmm but that question involves quite "physics"-ish topics like thermal dynamics... I'm just pushing a button here haha.

And it's a somewhat casual home experiment, no crazy lab equipment available

Anonymous

@JohnRennie Yeah, we need more experimental physicists. Too many mathematicians here :'D.

3

Anonymous

@chesnutcase Just ask, man/woman. :P Doesn't matter if it gets closed. You'll learn to improve. You could try asking it here also.

@JohnRennie just to clarify, what makes a question a "physics" question and what makes a question an "engineering" question?

31

Q: Experimental Physics & Engineering

I know that most of us are "paper theorists," but I think we need to remember that experimental physics is physics too! We have several tags for experimental physics (with tag excerpts): experimental-technology Use this tag for questions pertaining to the limits, management, and operation ...

discussion scope close-reasons

4:08 PM

@Blue why is that face supposed to be though

Convince Balarka to let me in the room pls

@chesnutcase it's not a clear cut divide. If you're just going to be asking how to measure the force needed to push a button this does sound like engineering i.e. you don't need any knowledge of physics to do it.

Anonymous

@0celóñe7 Just a smiley

@Blue I've come to the conclusion that experimental physicists are too busy to bother with online chats

Anonymous

@0celóñe7 He is the owner :P Ask him

@0celóñe7 Daniel Sank might disagree

4:09 PM

@KyleKanos he's doing something wrong

Probably, but that's the nature of experimental physics: keep doing it wrong until you do it right.

@JohnRennie yeah I doubt pushing a button requires knowledge of any major theoretical physics topic. Off to engineering I go then, I'll be back if they chase me out lol

Mithrandir24601

@KyleKanos Surely you mean keep doing it wrong until you do it slightly less wrong? :P

@Mithrandir24601 Mostly equivalent

@BalarkaSen do you troll on r/socialism?

4:16 PM

Oh, Balarka has a secret room? Is he planning to overthrow the mods?:P

Anonymous

Nah. He is teaching me linear algebra so that I can overthrow the mathematicians XD

@0celóñe7 socialism is worth trolling though. :P

@Blue did you have the linear algebra chat? If so how did it go?

Anonymous

♦ $Mathematics$ the no-normie zone

no normies allowed

Anonymous

Here ^ :)

4:23 PM

Thanks, though I was mainly interested to hear your reaction after your first exposure to LA.

I must admit I sometimes find it hard to see the point when I'm introduced to maths like that.

Anonymous

Hehe. Most of it was going over my head initially. Balarka is a good teacher though :D

Anonymous

Actually the concepts don't seem very complicated. The notations confuse me

Anonymous

It's sometimes waayyyy too formal

It's one of the things on my todo list to learn LA properly. But it's a long list and lots of other things are nearer the top :-(

Anonymous

Well, you can learn from Balarka's lectures =P I must admit that at his age I didn't even know 1/10 th of the maths he does. He is a year younger than me!

4:38 PM

@0celóñe7 Sure, I meant that for periodic function on a compact interval

@Blue JR probably knows all the linear algebra he needs to know. I doubt he needs the abstract terminological basics I rambled on about

Anonymous

Well, he doesn't need any physics or math anyway. He is a computer nerd nowadays. :D

i can't computer

Anonymous

@BalarkaSen Actually you should try out the Project Euler programming problems. They are mostly based on math (esp number theory). You'll like them. You can pick up the syntax and stuff on the way. Mathematics and Computing is a hot field nowadays

I've heard of those

Proj Euler is fun, but it's more math than programming

Anonymous

4:47 PM

@KyleKanos Exactly. That's why it is suitable for @BalarkaSen

I used to know number theory one point in my life

I don't anymore

Maybe the first 30-40 you could say are programming based, but even then it's still loads of math exercises

@BalarkaSen I have a complete proof written up if you want it.

@0celóñe7 Maybe some other day. You can still link it up and I'll save it on my computer

Too brain dead for analysis today

@ACuriousMind gyazo.com/1efe79f988d045cb7f469f02c8384da2

5:00 PM

cute cat

is that skyscraper made specifically for newton to sit on

or was he called einstein

i forget

Einstein

@BalarkaSen he can look out to the yard and street

very nice

@user400188 fyi what is not yet widely realized/ "appreciated" is that there seem to be some classical systems that have nearly the same math formalism as QM, contrary to some of the ideas/ assertions/ intuitions of the founders of the theory... (have been working halfheartedly to show that there are some that match exactly...) this correspondence is too much to be a mere coincidence if you ask me.

@BalarkaSen I am struggling with TeXstudio

cant help with that

5:13 PM

oh, now the pdf showed up

@BalarkaSen drive.google.com/a/utk.edu/file/d/0B04gbnTMKWUvc2ItUTFXQUt5X1E/…

@BalarkaSen No epsilons

very clean analysis

Can anyone actually open that link

@0celóñe7 it's asking for access

damn commies

Hey guys, an hour ago I showed up here asking if I could post a question on physics.SE about feedback for a home experiment regarding actuation force, I posted it on Engineering.SE instead here (engineering.stackexchange.com/questions/16641/…), please take a look if you are free, I would appreciate the feedback from all the bright minds here :)

drive.google.com/file/d/0B04gbnTMKWUvc2ItUTFXQUt5X1E/…

@BalarkaSen there

@chesnutcase That seems like a interesting question to ponder over

5:28 PM

@0celóñe7 Thanks!

Hmm. I think I used to know another proof of this.

By approximations to identity something something. It's similar to the proof of Stone Weierstrass

blah i need to get work done

@chesnutcase how bout using a spring balance? Slowly dropping the weight on the button till it presses it?

you can set up a stand for it for better control over the spring

Anonymous

The spring will probably slack in such an arrangement...

I can't really visualize that as I've never used spring balances before...

@Blue hence the need for a stand

use the coins instead of the weight

And I don't have have a spring balance in possession, but I can look to acquire one if the plan is solid I guess.

Anonymous

5:37 PM

@PhyMan What type of "stand" ?

@Blue filteration stand? the spring is hung from the loop, which can be moved along the vertical axis

seems like a proper jugaad

another advantange is that you can get an accurate reading

@chesnutcase did you understand my idea?

I understand now. But the important catch is I need the weights/coins to be only touching one button at a time. The coins are so large that it covers the entire D-Pad when centered...

Unless I cover the entire D-Pad anyway and divide the resultant weight by 4. Does it work like that?

Anonymous

Then the spring should have to be in compressed state. Otherwise it will give wrong readings

@chesnutcase cut out a small cardboard circle and stick it on the bottom of the coins

@Blue I think a spring balance does all that work for you, doesn't it?

Would I have to factor in the weight of the cardboard circle and the restoring force of the spring?

5:42 PM

@chesnutcase yes, you can measure the initial weight using the spring balance tself

my method doesn't care what you use as the weights

@Blue I didn't get you. What do you mean it will give wrong reading?

$W-N=$reading on balance

I feel like I would need to follow some kind of schematic or drawing or I would screw it up...

Anonymous

Basically either you'll get $N=kx+mg$(when contracted) or $N+kx=mg$ (when extended). The spring balance measure $kx$.

@chesnutcase Yeah wait ill make one

Anonymous

$mg$ is the weight of the coins...or whatever...

@chesnutcase sketch.io/render/sk-6e1ecf7f43b3048be3d648777f8c095f.jpeg

5:56 PM

@BalarkaSen Einstein in his ivory tower? ;)

@BalarkaSen Is that you in the top? atmschools.org/2017/atmw/dg/selected-applicants

Anonymous

@PhyMan Obviously

Thats quite awesome

I was suprised to see the name at the top

How was the program?

Anonymous

6:16 PM

Jul 30 at 5:41, by Balarka Sen

It was very nice, yup. I don't regret going there.

7:50 PM

@ACuriousMind how do you know it's Einstein

@0celóñe7 He looks much like the ball of fur in your earlier pictures :P

Also I dunno why I addressed that message to Balarka and not you...

Einstein was crazy. He would probably look different everyday

@ACuriousMind maybe because we're both brown?

AccidentalFourierTransform

8:24 PM

silly question: is $\frac{\partial}{\partial x}\frac{\delta}{\delta f(x)}=\frac{\delta}{\delta f'(x)}$?

What the hell is that

AccidentalFourierTransform

Functional derivative

In the calculus of variations, a field of mathematical analysis, the functional derivative (or variational derivative) relates a change in a functional to a change in a function on which the functional depends. In the calculus of variations, functionals are usually expressed in terms of an integral of functions, their arguments, and their derivatives. In an integral L of a functional, if a function f is varied by adding to it another function δf that is arbitrarily small, and the resulting integrand is expanded in powers of δf, the coefficient of δf in the first order term is called the functional...

AccidentalFourierTransform

8:49 PM

:-(

9:01 PM

@AccidentalFourierTransform I don't think "$\delta/\delta f'(x)$" is a meaningful object :P

AccidentalFourierTransform

neither do I, but if I write $\delta/\delta f'(x)$, would it be more or less clear that I mean $\partial/\partial x\delta/\delta f(x)$?

It wouldn't be clear at all to me

AccidentalFourierTransform

;_;

it looks so much better

%%%ck the reader

$\delta/\delta f'(x)$ it is

@AccidentalFourierTransform Consider that there might be a product rule involved if you apply two derivatives in succession like that - notating it by a single differential is rather misleading

AccidentalFourierTransform

I guess so

it makes me sad anyway

actually, any functional of $f$ can be written as a functional of $f'$, right?

as in, using $f(x)=f(1)+\int_1^xf'(\cdot)\,\mathrm d\cdot$

so $\delta/\delta f'(x)$ might be well-defined

9:07 PM

@AccidentalFourierTransform You're missing a $+f(1)$ there.

AccidentalFourierTransform

no im not

@0celóñe7 now I use $\int f(x)\,\mathrm dx$ instead of $\int\mathrm dx\ f(x)$

@AccidentalFourierTransform So, that's obviously not writing $f(x)$ as a functional of $f'$.

AccidentalFourierTransform

@JaimeGallego new picture?

you look better in this one - in the previous one you looked like a kid

@ACuriousMind oh no

That $f(1)$ spoils it.

AccidentalFourierTransform

what if $f(x)=\int_{-\infty}^x\cdots$

and we assume $f\in C_0$

the boundary conditions are included in $\delta/\delta f(x)$

9:11 PM

Are your $C_0$ functions of compact support?

AccidentalFourierTransform

they could be

Then that might work.

AccidentalFourierTransform

yes, let's say they are

Im just playing around

I can make my functions do whatever I want them too

assuming it works, the next thing to do is to check whether $\delta/\delta f'(x)$ agrees with $\partial_x\delta/\delta f(x)$

also, I offered a couple of bounties and the questions got a couple of answers. They've been around for a couple of days and they didnt get any upvotes nor comments

and Im not sure they are correct myself

pls give them a look - I dont want to award a bounty to a wrong answer, nor not to award it to a correct one

physics.stackexchange.com/questions/47504/… and physics.stackexchange.com/questions/306868/…

@AccidentalFourierTransform Consider the Dirac delta. You have $(\delta/\delta f'(x)) \int^0_{-\infty} f'(x') = \int^0_{-\infty} \delta(x'-x) = \theta(x)$ and $(\delta/\delta f(x)) f(0) = \delta(x)$

AccidentalFourierTransform

9:26 PM

;_;

so close yet so far

So at least in that case, the roles seem reversed: $\partial_x \delta/\delta f'(x) = \delta/\delta f$, which looks suspiciously like the E-L equation.

AccidentalFourierTransform

lol it does

wanna write a joint paper about it?

Do it.

AccidentalFourierTransform

you want to participate too?

lets go full italian: a paper by 25 people

@AccidentalFourierTransform ...maybe?

9:30 PM

@AccidentalFourierTransform Italian?

AccidentalFourierTransform

;-P

My group has at least that many coauthors on stuff.

AccidentalFourierTransform

I was joking - but they do tend to publish in large groups, even when the paper is short

@AccidentalFourierTransform Better check whether that holds for anything but the $\delta$ first, though :D

AccidentalFourierTransform

$\delta$ is dense somewhere. QED

9:37 PM

@AccidentalFourierTransform nice

Maybe there's a functional of functionals $\mathscr{F}\{F[f]\}$ with a meta-functional derivative $\mathscr{D}/\mathscr{D} F = \delta/\delta f - \partial_x \delta / \delta f'(x)$ for "higher actions"...

Damn physicists

AccidentalFourierTransform

$$\mathscr F\{S\}\equiv \int \mathrm e^{iS[f]}\mathrm df$$

I was actually thinking about "distributionals" the other day

Nice, a higher path integral :P

AccidentalFourierTransform

a linear map from the space of functionals to $\mathbb R$

9:39 PM

What topology do you put on the space of functional

@0celóñe7 the physics topology

AccidentalFourierTransform

you could take $\delta_f$ as the distributional that gives $\delta_f\{F\}=F[f]$

You need to specify what space of functions the functional act on

@ACuriousMind is that a joke?

@AccidentalFourierTransform You mean $F[0]$, where $0$ is the constant zero function.

Ah, I see what you did, nvm

@0celóñe7 Possibly

AccidentalFourierTransform

you could then define $Z[j]\equiv\int \mathrm e^{iS[f]+if\cdot j}\mathrm df\equiv \mathrm e^{iS[\delta_j]}\delta_j$

there you go: a mathematically well-defined path integral

I want my prize now, please

9:41 PM

@AccidentalFourierTransform Dostribtuons are continuous wrt the inductive limit topology on D or S

You need a topology on your functional space

AccidentalFourierTransform

k

« first day (2467 days earlier) ← previous day next day → last day (2464 days later) »

Transcript for

Aug '176

The h Bar

General chat for Physics SE (physics.stackexchange.com). For M...

join this room
about this room

00:00

06:00

12:00

18:00

all times are UTC

site design / logo © 2024 Stack Exchange Inc; legal

mobile