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12:23 AM
Q: $L^2$ Hodge decomposition on $\Bbb R^n$

0ßelö7In 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 ...

12:47 AM
Sigh I keep losing my wallet
Have to look everywhere now
Sigh, never mind, it was in my pocket...
@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 $T_1H_1 \to H_2$
1:24 AM
@Phase is there supposed to be a $:$ there
There is
if so, consider $p:\Bbb R^2\mapsto \Bbb R, (x,y)\mapsto x$.
@Phase does that resolve your doubt
I feel like SE should have "subtags" — for example, would be a subtag of , so a post tagged with would also show up in
That would make things a lot more organized
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
1:46 AM
@Phase yes
just look at it
it's almost always obvious
Gah, my DIY molecular diffusion pump doesn't work. Doesn't pump worth a sausage.
@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.
2:28 AM
Is physicaloxy.com a scam website, the uni email seemed to be flooded with their emails?
and who is Axel Holmberg?
How on earth did my uni get involved in such annoying thing...
@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.
@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?
I just inhaled a plume of smoke
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).
Most IT departments have an address (often abuse@) where you can forward persistent spam or phishing attempts or whatnot.
am I going to die?
@0ßelö7 Depends on what kind of smoke we're talking here.
@dmckee tried to reheat some frozen cookies and burnt them to a crisp
Maybe you'll just cough some and maybe you'll demolish a whole jumbo sized bag of double-stuff oreos.
2:37 AM
@dmckee No, he's going to die. However the kind of smoke may or may not determine when he dies.
@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.
@dmckee There are ... there are people who've never done this?
that seems like a bad idea
although having milk makes it healthy
I suppose everyone has to get their start at some point
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
2:40 AM
On an unrelated note, I almost sent an email to my professor with a very scary typo: Dead instead of dear
@rob what?
@0ßelö7 What what?
Wut wut?
@rob have you eaten a whole bag of oreos in one sitting?
2:53 AM
@0ßelö7 Don't knock it till you've tried it
@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
3:54 AM
So, the uni said they have not subscribed to such website. Now to check the clubs I joined...
Yeah, I smell a scam...
4:53 AM
Q: How (if at all) can the neutron-proton ratio of stable atoms be explained under the nuclear shell model?

user2996957To 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...

An interesting question that is not GR, not QFT, QM, not condensed matter, not astrophysics
2 hours later…
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 ?
"kick-muted" sounds like an act of violence
No, exactly that was done. Read a couple of transcript of me and Mego after this
Hmmm, I see.
I've been "kick-muted" so many times, pal :-)
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.
The durations increase.
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
@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 :-(
@AlexKChen Something like that, it depends on the severity of the offences and, of course, the mods.
Good morning @JohnRennie :-)
God mourning @JohnRennie :)
mourning? :-)
6:46 AM
Mourning could be "good"
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.
Yeah, the automatic one does top out at 30 minutes, as far as I know.
@AlexKChen shouldn't it be:
from visual import *
How long can the room owner kick out someone?
Don't use *. It will pollute the namespace and make it hard to troubleshoot program errors
6:52 AM
@skullpatrol 30 minutes
What's the min?
@JohnRennie Why visual, not vpython ?
1 min, I think.
6:54 AM
A: A guide to moderating chat

bluefeetWhat 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...

(Anyway, I have posted about that here. If you have any insights on how to fix the issue, please answer/comment)
@AlexKChen I don't know, but if I Google for vpython example code it seems to import from visual.
@JohnRennie `Error: No module named 'visual'', as expected
@JohnRennie thanks for that post.
7:12 AM
@AlexKChen Ah
I think vpython uses an internal HTML server to display the graphics.
Try running:
from vpython import *
When I run that IE pops up and displays the box.
So what you describe is completely normal
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 :)
Thanks a lot @JohnRennie. You made my day today.
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 *
No it now works perfectly.
8:08 AM
Hey @DanielSank, have you ever seen this paper? I'm finding it quite interesting.
Hey @EmilioPisanty have you seen this computer? Now that's my kind of computer :P
8:51 AM
Is there a kelvin scale with Farhenheits
9:40 AM
@ACuriousMind (& other mods / 10k'ers) does this one really need the protection?
Q: The Planck constant $\hbar$, the angular momentum, and the action

IsaacIs 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?

one bad answer over five years seems like an acceptable rate
2 hours later…
11:39 AM
@EmilioPisanty probably not
12:24 PM
So I sat in on an Honors Diff Eq class. It's heavily proof based and seems pretty hard. Is that some mindset people adapt over time?
What mindset?
One to immediately know how to prove something
The mindset that things should be proven? Yeah, it's called being a mathematician ;)
@SirCumference Not "immediately". Learned mathematicians produce these proofs often seeemingly effortlessly because they have seen them dozens, if not hundreds, of times in various disguises. Proving things is something you can train by doing it just like any other skill
12:29 PM
@ACuriousMind diff eq is usually the first class americans take in college
those kids are likely fresh out of high school
@SirCumference just needs to git gud
I'll never understand American education :P
@ACuriousMind I'm confused too, I don't see the point in having a first course on diff eq be proof based
just like I think having a first course on calculus being analysis is silly
@ACuriousMind did you see my hodge question on MSE?
@0ßelö7 Yes.
How did the poster presentation go?
@skullpatrol very well modulo one hiccup
12:33 PM
Did you wear a suit and tie?
no tie
it was too hot for that
and I would have been overdressed
What was the hiccup?
@skullpatrol I asked for the math credentials of a Very Important Tenured Professor (I had never heard of her before)
I was polite
dunno what the issue was
+ you can always take a tie off
she said she was in the PDE group. I wanted to say that I've never seen her at the seminars, but that would have ended badly
12:37 PM
@ACuriousMind What's up about your PhD?
don' ask him that
@ııııııııııııııııııııııı Nothing I'd like to share.
@0ßelö7 Uh, not here. Generally people start with Calc II
@SirCumference honestly unless you went to a garbage high school there's no reason to take calc 2 in college
I think you're just the exception
12:39 PM
and I'm talking trash high school
@0ßelö7 But I did go to a garbage high school
my high school calc teacher didn't know what a Laplace transform is and still got most everyone a 5 on the BC calc test
@0ßelö7 You think that's bad? My calc teacher hadn't taken calc in ten years
She couldn't answer any questions I had
@SirCumference What? Most people haven't taken calculus in a decade
@0ßelö7 Well apparently she forgot it all
12:40 PM
@SirCumference No, lots of people get a 5 on the AP test
Most of the class was just sitting around
Maybe an occasional Khan Academy video
@SirCumference How does that work? What was actually happening in the lesson?
I can't imagine a class room full of teenagers and everyone just sitting around doing nothing
@ACuriousMind Sometimes she'd do nothing and just give us the same "differentiate this" problems. At one point she jumped to partial differentiations before we even finished regular diffs
The entire class was confused because the lesson involved multivariable calc
That doesn't sound like "sitting around", that sounds like a bad lesson.
12:42 PM
Not to mention, she "taught" integration before differentiation, for some bizarre reason
your testimony is tainted by hatred
@ACuriousMind Well it's not a lesson if we aren't learning
@ACuriousMind Anyways, I think it would be really a waste if someone like you doesn't do a PhD....*please* stay in academia
@ııııııııııııııııııııııı What?
Just imagine the good that someone like @ACuriousMind could do in the real world
12:43 PM
@0ßelö7 I've only seen a couple of freshmen in my Diff Eq class
@SirCumference Of course it is. A tree that falls in the forest still makes a sound.
Though not many people take Diff Eq to begin with
@0ßelö7 That's the sound you make, not the tree
@0ßelö7 Isn't academia real world?
12:44 PM
@ııııııııııııııııııııııı Not in the slightest
@ACuriousMind A teacher without any topics isn't teaching tho
Not theoretical physics adademia at least
@SirCumference But she had topics, even gave you exercises about it. I'm not saying she wasn't a bad teacher, but pointless exaggeration isn't helpful
Funnily enough, I saw my last calc prof in that honors class (he was subbing for the Diff Eq prof). I asked if it was gonna be harder than our last class, he said "Oh, that? Yeah, this is going to be WAY harder"
I just blankly stared
@ACuriousMind Regardless, the misleading way she taught some things actually made calculus more difficult when I got to college
@0ßelö7 hmmm now that I think about it, I think ACM can't do much good in the real world. He can be much more productive in the imaginary world of theoretical physics
12:47 PM
@ACuriousMind So the class was actually worse than pointless
We seriously need more table top accelerators
Don't say that ııııııııııııııııııııııı
@Secret I'm sure you have a CRT monitor laying around, no?
@SirCumference Now that's a much more useful statement than what you said before
@Giskard42 CRT monitor? What year is it?
@Secret we urgently need to know what's going on at the center of a black hole
12:48 PM
@Giskard42 O sorry, I forgot to be specific: A table top accelerator that can produce at least some heavy hadrons
@ACuriousMind But no less exaggerated :P
@Secret Fine, a CRT monitor and a 100kv power supply.
Point away from face.
probably the CRT will be fried first....
@Secret Why would you need such a thing?
In seriousness, I dunno if the honors is worth it. It seems too time consuming especially since I have a lot of classes this semester
12:49 PM
@Secret That's just an engineering problem.
@ACuriousMind Well, if high energy particle physics can be made at benchtop, perhaps it will greatly put the progress of particle phenomenology in line with the development in theoretical particle physics, as currently the theory is mostly ahead and the currently strongest accelerators are still far from the required power and sophistication to test the models
There are some table top accelerate examples out there, but they have yet to reach that level
@Secret But we don't need more particle accelerators. If anything, we need more powerful ones. Why does their size matter?
Also, who doesn't want a desktop particle accelerator!
@ııııııııııııııııııııııı I don't think ACM is in academia
Oh wow, didn't realize he was a student...
@SirCumference ...
12:53 PM
Regular sized instruments is probably easier to manage in terms of engineering. Just recall what happens back last year when that squrrel bit off a wire in the LHC
I'm not sure what the deeper context of this discussion is and there may be something I missed, but I came here to see what's going on and this is what it looks like at first glance to an outsider: A huge boasting competition with some people trying to show how much smarter than the educational system they are. I'm sure that wasn't directly the intention, but it looks pretentious. I know you, but maybe scale it back, guys, if you don't want to give people that don't the wrong impression
Are you high?
Where the hell have you been these past years
@0ßelö7 I couldn't sleep much, first day back is rough...
@ACuriousMind I thought you were in industry all this time...
@Secret probably, and I'd bet having thousands more people working on even low-energy stuff could figure new stuff out
Don't ask me why
12:55 PM
@Secret And...you want that sort of disastrous power concentrated into a thing that fits on your table?
@ACuriousMind You wouldn't?
Well, of course, just like all dangerous devices, usual lab safety applies. So if we can increase power while downsizing them, it will help cost down the cost dramatically on the maintainence
@Jim Which part of the different discussion threads are you talking about, exactly?
and.....@0ßelö7 dominates the starboard again
@SirCumference It has said I'm a student in Heidelberg on my profile all this time.
12:56 PM
@ACuriousMind Yeah but I haven't individually looked at everyone's profile...
It was all directed at high school
There are some research groups working on certain table top accelerators such as laser plasma and wakefield accelerators, and their results are quite encouraging despite slow
@Secret "usual lab safety applies." Though I don't think eye wash stations help against vaporization.
@ACuriousMind maybe he figured you're like those profs who haven't updated their pages since 2007
12:57 PM
Yeah, a particle accelerator lab probably need more stringent regulations given the power
That would be the most badass way to go, though. "Mr. So-And-So was disintegrated peacefully by a particle beam of his own design on Friday night."
So wait, is anyone here actually a professor?
This is a list of inventors whose deaths were in some manner caused by or related to a product, process, procedure, or other innovation that they invented or designed. == Direct casualties == === Automotive === Sylvester H. Roper, inventor of the eponymous steam-powered bicycle, died of a heart attack or subsequent crash during a public speed trial in 1896. It is unknown whether the crash caused the heart attack or vice versa. William Nelson (c. 1879−1903), a General Electric employee, invented a new way to motorize bicycles. He then fell off his prototype bike during a test run. Franc...
Actually dmckee is if I recall
@Jim everybody complaining about the level below them not being adequate is normal :-)
1:01 PM
@ııııııııııııııııııııııı en.wikipedia.org/wiki/Anatoli_Bugorski
@Secret The energy in these accelerators is several orders of magnitudes higher than anything you have in an ordinary lab, "usual lab safety" doesn't help you one bit. The idea you can build small accelerators that probe at the energies the large ones do sounds pretty misguided to me
@SirCumference Of the regulars, I think only dmckee is
@ACuriousMind I think he's saying progress would still be made even with many low-energy accelerators, just due to more manpower
@Giskard42 But it wouldn't.
As I said, we don't need more accelerators, we need more powerful ones.
@ACuriousMind I can think of a thousand things I'd want to try with a moderately powerful accelerator
@SirCumference I run a couple lab courses and teach the practical physics component to students. I suppose I'm a third of the way to being classified as a prof
1:03 PM
@ACuriousMind Is it too dangerous or probably infesible?
@Giskard42 Sure, but that wouldn't advance particle physics, which is what Secret was talking about. It might certainly advance other fields.
@Secret Both.
@ACuriousMind True.
@Secret Everyone dies at some point, might as well die in a helium quench.
@Jim Then we'd only have two profs. That's kind of surprising
one and a third
How much do researchers count for?
1:06 PM
@Giskard42 A moderately powerful accelerator may be able to produce heavy hadrons at a faster rate than LHC. While the particles are not new physics particles, given the intense progress in the physics of hadrons, such accelerators might help accelerate it by producing more hadrons at relatively lower cost for analysing the strong force
what's more surprising is that I focus on teaching experimental physics when my background is theoretical cosmology; probably the farthest physics from experimental
@skullpatrol pdf?
A particle accelerator more powerful than LHC may be needed to produce new physics particles, but a particle accelerator of similar power or slightly less than LHC may help on hadron physics
a half. You got the PhD and you work at a university doing research. You need to teach courses to get the other half
@Secret Yeah, I think the benefits of having civilian access to cutting-edge scientific equipment are usually pretty substantial.
1:09 PM
I'd say 49%
@Secret How exactly will having a bunch of hadrons help me "analysing the strong force"?
Particle physics doesn't just take a bunch of particles and looks at them.
If the technology can allow downsizing to that degree be possible, then production of heavy hadrons and jets will become routine enough to accumulate a lot of data in shorter time.

But I guess, my major argument is the reduce in cost due to downsizing, and funding is one important factor in experimental particle physics
Why don't you go into nuclear physics? @ACuriousMind
Suppose one can go from trillions of cost to around $10000 to operate and maintain an accelerator, then it should help in accelerating the research, I think...
ACM could build bombs
1:13 PM
@Secret Only if you think there's a lot of data worth gathering that we haven't gathered due to cost
@Secret "accelerating the research" nice one
@ACuriousMind But is that the reality? (I am not sure about that one, though)
However, the accelerators already produce millions and millions of data points. I don't really see why you think scaling that up to (say, these numbers are just illustrative) a billion data points will qualitatively change something.
Is the math too hairy?
Like, point out a single experiment that one could do with a particular accelerator if it were cheaper that has a plausible chance of finding out something new about particle physics.
1:16 PM
@skullpatrol I don't think @ACuriousMind is scared of math
uh, because some decay process are rare enough that it takes a lot more data to see them. Having said that, I am not sure what's the best ballpark number for a "routine production"?
Sobolev spaces...perhaps
hmm... I only have double beta decays in mind atm
@0ßelö7 No, math is scared of ACM :-)
I forgot the name of some other important decay channels that are of intense interest
and only involve known hadrons
1:17 PM
@Secret Oh, so that's a long shot - sure, that possibility always exists, that some decay is so rare it hasn't become significant yet.
That is one reason I am quite excited about the research progress on table top accelerators and also some progress in hadron physics
@ACuriousMind proton decay
@0ßelö7 Hm? How's an accelerator gonna help you with that?
@ACuriousMind gotta make some protons
World doesn't have enough protons
1:28 PM
and hadron jets are too messy to isolate protons from it
@ACuriousMind how does one get an arxiv feed?
when I went to CERN last year on a trip they had a pretty cool 'anti-matter factory' sorta thing goin' on...
@SirCumference you just need one and some luck
@CooperCape How long beforehand did you need to schedule to get in?
@0ßelö7 Or lots of free time to wait
1:29 PM
@0ßelö7 What do you mean? The daily mails about what's new? There are instructions on the arXiv site, search for "subscription"
I dunno it was with school...
@CooperCape ah, okay.
Tried booking a tour last year and there was a waiting list of like a year or so
Oh wow that's an insanely long time...
@CooperCape Well, y'know, it is pretty popular :>
Unsurprisingly so... :p
1:33 PM
@CooperCape And I'd imagine there's only so many people they want to take in at a time, since with larger groups accidents would be more common -
@ACuriousMind imma go ahead and unprotect it
like the thing a little while ago where a journalist almost put his backpack into an emergency-off switch
oh really? That would be a big ol' oopsie...
Does anyone else hate how contradictory mathematical notations can be?
@0ßelö7 also look into arXitics and SciRate
1:37 PM
@SirCumference No.
@EmilioPisanty what's that
(because I have no idea what you mean)
@ACuriousMind Example: does $\ln{x}^2$ mean $(\ln{x})^2$ or $\ln{\ln{x}}$?
1:39 PM
How about how $\tan^{-1}$ can mean arctan?
@SirCumference 1. It clearly means $\ln(x^2)$ :P 2. That's not contradictory, that's ambiguous.
@SirCumference ^ that.
@SirCumference And everything about trig is just historical baggage :P
@EmilioPisanty I don't know what that means
@ACuriousMind Yeah, all this talk about "sin", very archaic
1:41 PM
@0ßelö7 you see the blue text? click and/or tap it
@Giskard42 My point exactly!
@EmilioPisanty goes to a blank site
@ACuriousMind Fine, how ambiguous it is. Like if I say "Point p is on (3,2)". Does that mean p is on the open interval "(3,2)", or that its coordinates are "(3,2)"?
These notations overlap a lot
1:42 PM
@SirCumference so?
language is ambiguous
deal with it
if you want unambiguous mathematical notation, write in Coq input format
@SirCumference Well, there's plenty of ways to make things unambiguous if you really need it. I don't see hwo this is a fault of "mathematical notation" and not people having bad communication skills :P
The worst is how the second derivative has $dx^2$ in the denominator instead of $d^2x^2$
@SirCumference you say the strangest things
@EmilioPisanty I don't get it. What about them?
@0ßelö7 you wanted an arXiv feed, right?
I can't see the starboard but I must be on a roll
1:47 PM
@0ßelö7 ba dum tss
Was that a pun
well, since a pun is, by definition, intended by the author, I guess not
I don't even see the pun
"on a roll" is an idiom, but if taken literally and applied to nautical aviation, a roll might prevent you from seeing the starboard horizon
1:52 PM
@Jim your undergrad degree is showing
::Jim blushes and covers himself::
@0ßelö7 Don't give him the third degree about it
(sorry, I'm sorry)
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