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2:53 AM

While solving a question on heat transfer

The question was as follows a bucket full of ice is kept in a room and the temperature variation versus time graph is given

Here while solving my teacher assume the heat transfer rate to be constant but *how can we"?

Prateek Mourya

3:16 AM

...................................................................................

2 hours later…

satan 29

5:17 AM

@PrateekMourya this is better suited for the problem solving room

2 hours later…

123

7:29 AM

Hi All.

1 hour later…

JingleBells

8:34 AM

In programming (e.g React.js) is it better (faster?) to do import React from 'react' and then React.useState() or import { useState } from 'react' and then useState()?

ACuriousMind

9:32 AM

@JingleBells I'm not 100% sure for JS but in most languages these different forms of inputs have no different runtime characteristics

the question is whether you just want useState in your namespace or if you want React and call some other methods on it, too

JingleBells

10:02 AM

@ACuriousMind reactjs.org/blog/2020/09/22/… :P

3 hours later…

Emilio Pisanty

12:57 PM

Take the $R^2$s over log-linear and log-log transformed data with a *massive* grain of salt. The usual tools for linear regression assume that any noise in your data is (1) gaussian and (2) uniform over the data set. However, a linear-to-log transformation will magnify the noise in places where the signal is smaller. (To see why, plot the error bars on the log scale. What happens to the error bar of $\log(x)$ if $\Delta x$ is bigger than $|x|$?) There are specific ways to deal with this in the statistics (via nonlinear model fits, or non-uniform noise profiles)... — Emilio Pisanty 1 min ago

hmmmmmmmmmmmm

that's unusual

shouldn't "massive" be rendered in italics?

Faded Giant

1:21 PM

@EmilioPisanty not in comments

chemistry.meta.stackexchange.com/…

Emilio Pisanty

1:42 PM

it does work in comments, no? — Emilio Pisanty 14 secs ago

ACuriousMind

2:18 PM

Huh, I'd never have suspected that fridge magnets are anything more complicated than just a simple magnet with paint/stickers on it

skullpatrol

@EmilioPisanty I believe, it requires your comment to have no line-breaks in it.

The same happens in chat

skullpatrol

2:47 PM

hmmmmmmmmmmmm

I've seen it; but, can't reproduce it :-/

Jack Rod

3:42 PM

@ACuriousMind nice dp

what it is about?

ACuriousMind

3:53 PM

@JackRod it's Six from the game Heaven's Vault

Jack Rod

hmm!

skullpatrol

its got a bit of a skull look to it :P

ACuriousMind

4:10 PM

I already had a literal flaming skull once (Morte from Planescape Torment) :P

Emilio Pisanty

It does work in comments, no? Even if the comment is really really really really really really really really really long and it breaks into multiple lines. — Emilio Pisanty 18 secs ago

skullpatrol

4:29 PM

@EmilioPisanty I could be misremembering

Nihar Karve

is the density matrix the imaginary part of the propagator?

From the top answer to this question

Emilio Pisanty

Mind-Blowing Magic Magnets - Smarter Every Day 153

►

there's some pretty fancy stuff out there

@NiharKarve in general: no.

The density matrix is independent of the hamiltonian.

> The reason is that all physical observables are measured with respect to the density matrix $\rho(E)=-2\Im G(E+i0_+)$, which is the imaginary part of the propagator.

I don't understand the context there well enough to tell if that is correct or not. If it is, then it's taking about physical observables in some constrained context, which are measured with respect to that particular density matrix.

Ratman

4:54 PM

hi all,

Nihar Karve

5:09 PM

Thanks Emilio.

Ratman

5:36 PM

i have just spent 30 minutes to write a question about entropy, and just at the end realised the mistake ahahaah

still useful though

Emilio Pisanty

6:04 PM

@Ratman then post it and post an answer

it won't gather a huge score, but if it is suitably discoverable then it could well help out others eventually

and it's always good writing practice.

123

Hi All..

Ratman

6:25 PM

@EmilioPisanty I don't think it was such a big deal, the "mistake" it was quite stupid instead. Mainly I was trying to understand why the following facts aren't contradictory. that 1) entropy is not a property of system ( in non equilibrium) but rather of our knwoledge of the system. 2) yet at the microscopic level entropy is conserved in time (thanks to some special ipothesis on the system).

yet I could write the question and answer to see if what i think is actually true

i think I will do it, maybe as soon as I am able to complete the proof that entropy is indeed conserved

2 hours later…

Emilio Pisanty

8:01 PM

🤔🤔🤔🤔🤔

Q: How should we think about Spherical Harmonics?

Studying Quantum Mechanics I only thought about Spherical Harmonics $Y_{l,m}(\theta , \phi)$: $$Y_{l,m}(\theta , \phi)=N_{l,m}P_{l,m}(\theta)e^{im\phi}$$ as the simultaneous eigenfunctions of $L_z$ and $L^2$. But then I stumbled on these two statements: The Spherical Harmonics are a complete ort...

race all y'all to the HNQ list 😛

2 hours later…

Physics Meta

10:08 PM

-1

Q: Meta Question closed as Opinion Based

I do not like it that my meta question Why has my question from October 16, 2019 been downvoted? has also been closed as Opinion Based. It is not fair for the community because I asked a Meta Question about my own question. Why is my Meta Question closed.