The h Bar

12:23 AM

0

Q: $L^2$ Hodge decomposition on $\Bbb R^n$

In Majda and Bertozzi, Vorticity and Incompressible Flow on page 32, the orthogonal decomposition of a vector field $v\in L^2(\Bbb R^n)\cap C^\infty(\Bbb R^n)$ is proved, namely $$v=w+\nabla q, \quad w\bot_{L^2} \nabla q,$$ with both $w$ and $\nabla q$ in $L^2\cap C^\infty$. The proof is stated ...

Sir Cumference

12:47 AM

Sigh I keep losing my wallet

Have to look everywhere now

Sigh, never mind, it was in my pocket...

Phase

@SirCumference get a wallet wallet

Keeps all your wallets safe and close to hand

Question: can someone give me an example of a Linear operator that maps a vector space to a different Vector space like $T_1H_1 \to H_2$

0ßelö7

1:24 AM

@Phase is there supposed to be a $:$ there

Phase

Yep

There is

0ßelö7

if so, consider $p:\Bbb R^2\mapsto \Bbb R, (x,y)\mapsto x$.

@Phase does that resolve your doubt

Sir Cumference

I feel like SE should have "subtags" — for example, newtonian-gravity would be a subtag of gravity, so a post tagged with newtonian-gravity would also show up in gravity

That would make things a lot more organized

Phase

Oh

Yeah

How do you prove that things are linear? Just churn through the definitions like f(x+y) = f(x) + f(y) manually?

Or is there a quicker way

0ßelö7

1:46 AM

@Phase yes

just look at it

it's almost always obvious

Giskard42

Gah, my DIY molecular diffusion pump doesn't work. Doesn't pump worth a sausage.

dmckee

@Giskard42 I think I recall hearing that those things are fiddly to build. I trust that you've started with a good enough rough vacuum that it makes sense to expect it to work, yes?

@AlexKChen The Open Source Physics and Physlets projects both provide infrastructure for that kind of thing.

You could use tkinter for the drawing if you were doing it in python, but that is, in some ways, the easy half of the problem. Getting a robust simulation to underlie the graphics is the places with horrifying traps for the unwary.

I think OSP uses a custom java framework with a specialized IDE (and maybe they also support javascript which I thought was weird when I heard it). I forget what physlets is built on.

Secret

2:28 AM

Is physicaloxy.com a scam website, the uni email seemed to be flooded with their emails?

and who is Axel Holmberg?

rob

@Secret Physicaloxy addresses directly and personally each of 420,000 professors, lecturers, researchers and academic managers sending specialised newsletters with job vacancy notifications twice a month.

God, that sounds horrible.

Secret

How on earth did my uni get involved in such annoying thing...

dmckee

@rob Given that we can presume that 420,000 such people didn't ask to be so addressed that is the very exemplar of spam.

rob

@Secret Do you think that the university paid those folks to place ads? Or do you think that the website scraped all the university emails and spams everybody?

0ßelö7

I just inhaled a plume of smoke

dmckee

2:35 AM

In other words they are a blight on the face of the interwebs and no one will cry if their servers burn in a fire (started, of course, by mischance or act of god and certainly not by a misled soul).

rob

Most IT departments have an address (often abuse@) where you can forward persistent spam or phishing attempts or whatnot.

0ßelö7

am I going to die?

dmckee

@0ßelö7 Depends on what kind of smoke we're talking here.

0ßelö7

@dmckee tried to reheat some frozen cookies and burnt them to a crisp

dmckee

Maybe you'll just cough some and maybe you'll demolish a whole jumbo sized bag of double-stuff oreos.

rob

2:37 AM

@dmckee No, he's going to die. However the kind of smoke may or may not determine when he dies.

dmckee

@0ßelö7 I'm afraid that is the just coughing scenario.

@rob Yes, and if he gets the 'Eat entire bag of double stuff oreos' off his bucket list first or not.

rob

@dmckee There are ... there are people who've never done this?

0ßelö7

that seems like a bad idea

although having milk makes it healthy

rob

I suppose everyone has to get their start at some point

Secret

That I am not sure, for one thing, back in UNSW (which interestingly is listed in that website) I never received anything from this website once. So my only suspicion is that somehow either this website somehow spam USyd starting from this year's may (because the earliest one is 15/5/2017), or one of the uni clubs I joined somehow involved with that website.

I think I will forward this to IT and have them figure out what it is

Secret

2:40 AM

On an unrelated note, I almost sent an email to my professor with a very scary typo: Dead instead of dear

:O

@rob what?

@0ßelö7 What what?

Wut wut?

@rob have you eaten a whole bag of oreos in one sitting?

rob

2:53 AM

@0ßelö7 Don't knock it till you've tried it

Giskard42

@dmckee Yeah, I've got down to ~300 microns from just the roughing pump, which is a little high, but acceptable

@dmckee I think it's likely my nozzle - I tried to find an ideal shape with the nasa laval nozzle simulator

But I'm not sure what my boiler pressure is - the pump oil's vapor pressure charts are giving me nonsense values

So I just eyeballed it

I was thinking of using an aerospike, since (afaik), that would partially compensate for any pressure mismatch

Secret

3:54 AM

So, the uni said they have not subscribed to such website. Now to check the clubs I joined...

skullpatrol

Yeah, I smell a scam...

Secret

4:53 AM

0

Q: How (if at all) can the neutron-proton ratio of stable atoms be explained under the nuclear shell model?

To begin where I did with this question, I was originally wondering about why the neutron-proton ratio is close to 1 for stable nuclei. The answer to my original question (as far as I understand it) is that, due to the exclusion principle, not all of the protons or neutrons can be in the ground e...

nuclear-physics

An interesting question that is not GR, not QFT, QM, not condensed matter, not astrophysics

Alex K Chen

6:27 AM

@vzn So you're suggesting I should ask that in that chatroom ? I remember I was probably kick-muted for few minutes for asking vpython simulation questions in the PPCG chatroom (Mego told me it's "spam and noise"), so not sure if same will happen in that chatroom.

@NeuroFuzzy Any ideas on this ? vzn told you might be helpful.

@vzn Also, what should I see for more info ? The source codes ?

skullpatrol

"kick-muted" sounds like an act of violence

Alex K Chen

No, exactly that was done. Read a couple of transcript of me and Mego after this

skullpatrol

Hmmm, I see.

I've been "kick-muted" so many times, pal :-)

Alex K Chen

Oh I thought after some kick mutes you get permamently chat banned :)

Also, the guys at PPCG is a bit weird, to say the least.

skullpatrol

The durations increase.

Alex K Chen

6:38 AM

Like,.. 1 m, 2m, 4m, 15m, 30m, 1hour, and you're dead after that ?

Why the hell typing "from vpython import *" keeps redirecting to "http://localhost:50484/" in IDLE

John Rennie

@AlexKChen you can ask pretty anything here. If you keep repeatedly posting after you've been asked to stop you might earn a kickmute, but not otherwise.

However I can't help with vpython - sorry :-(

skullpatrol

@AlexKChen Something like that, it depends on the severity of the offences and, of course, the mods.

Good morning @JohnRennie :-)

Alex K Chen

God mourning @JohnRennie :)

John Rennie

mourning? :-)

Alex K Chen

lol

skullpatrol

6:46 AM

Mourning could be "good"

John Rennie

I don't think repeated kickmuting leads to an automatic ban. But the third kickmute attracts the mods attention and they may decide to impose a suspension. As far as I know the kickmute penalty tops out at a 30 minute suspension.

skullpatrol

Yeah, the automatic one does top out at 30 minutes, as far as I know.

John Rennie

@AlexKChen shouldn't it be:

from visual import *

skullpatrol

How long can the room owner kick out someone?

Secret

Don't use *. It will pollute the namespace and make it hard to troubleshoot program errors

John Rennie

6:52 AM

@skullpatrol 30 minutes

Max?

Max

What's the min?

@JohnRennie Why visual, not vpython ?

skullpatrol

1 min, I think.

John Rennie

6:54 AM

73

A: A guide to moderating chat

What tools are available to room owners? Room owners are users that have some elevated permissions in a chatroom. Typically, they will be the first line of defense when it comes to inappropriate content or behavior in a room. Users will look to the room owners to guide the room. The room owners...

Alex K Chen

(Anyway, I have posted about that here. If you have any insights on how to fix the issue, please answer/comment)

John Rennie

@AlexKChen I don't know, but if I Google for vpython example code it seems to import from visual.

Alex K Chen

@JohnRennie `Error: No module named 'visual'', as expected

skullpatrol

@JohnRennie thanks for that post.

John Rennie

7:12 AM

@AlexKChen Ah

I think vpython uses an internal HTML server to display the graphics.

Try running:
from vpython import *
box()

When I run that IE pops up and displays the box.

So what you describe is completely normal

Alex K Chen

7:45 AM

@JohnRennie 1. Make a list of the dumbest guys you know 2. Cut of the first guy's name, and insert my name there... What the hell, I was closing IE every single time instantly it opened, thinking it was an error ;(... It works perfectly now, of course :)

John Rennie

:-)

Alex K Chen

Thanks a lot @JohnRennie. You made my day today.

John Rennie

I've been Googling for vpyhton example code but there must be an old version of vpython. The example code I've found doesn't run.

And it uses from visual import *

Alex K Chen

No it now works perfectly.

Emilio Pisanty

8:08 AM

Hey @DanielSank, have you ever seen this paper? I'm finding it quite interesting.

skullpatrol

Hey @EmilioPisanty have you seen this computer? Now that's my kind of computer :P

Slereah

8:51 AM

Is there a kelvin scale with Farhenheits

skullpatrol

Rankin?

*e

Emilio Pisanty

9:40 AM

@ACuriousMind (& other mods / 10k'ers) does this one really need the protection?

11

Q: The Planck constant $\hbar$, the angular momentum, and the action

Is there anything interesting to say about the fact that the Planck constant $\hbar$, the angular momentum, and the action have the same units or is it a pure coincidence?

quantum-mechanics angular-momentum uncertainty-principle dimensional-analysis action

one bad answer over five years seems like an acceptable rate

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