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5:00 PM
@vzn I have to drive slowly. We have moose on site. ;-)
 
vzn
@TerryBollinger not following this all that closely but arent they based on deuterium fusion? where does tritium show up
 
I think in total I looked at or encountered about half a dozen "Solutions" to the fusion instability issue. Not too surprisingly, all of them failed. I did manage to save one venture capitalist a few million bucks by having him test one approach before he funded it fully.
I felt guilty about the million bucks. He was absolutely delighted about how much he didn't lose!
 
@TerryBollinger Is the waste problem still true for proton-boron fusion? I read those were aneutronic and thus didn't have the radioactivity problems that other fusion methods do.
 
@vzn the deuterium gusion is absolute nonsense. they let people think that so they can go on about infinite energy from seawater. It's complete Balderdash.
@Green it's actually the helium-3 Fusion process that is the most accessible aneutronic Fusion process. it is far too many orders of magnitude more difficult than anything we can do now with tritium. Many Venture capitalists have lost huge amounts of money on that one.
ALL current Fusion research and discussion is based on DT Fusion. They kind of like to skip over that detail.
 
5:08 PM
So correct me if I'm wrong, but we don't have any professors in the chat right?
 
Not me!
 
@SirCumference I'm a profaner. Is that close enough?
 
@JohnRennie always thought you had a cussed streak!
 
@TerryBollinger Thanks for clarifying! I saw a boron-proton project a while ago but it seems to have dropped off the radar. Your explanation is probably why.
 
I am a professor in theoretical phys ed.
 
5:09 PM
@JohnRennie Are you implying you're not a creationist? :O
 
Anonymous
@SirCumference We have @rob
 
@Lozansky Huh, I thought you were a student
@Blue Isn't he a lecturer?
 
Has anyone worked with excimer lasers?
 
Anonymous
@SirCumference Is there a difference? I don't know how the US system works
 
@Blue I guess I should clarify, I was thinking tenure track
 
Anonymous
5:11 PM
Ah, I see
 
Or at least that's the main difference I know between profs and lecturers
 
Anonymous
I don't know whether he is a tenured professor
 
@SirCumference Phys ed ≈ gym class :P
 
@Lozansky Ah, I too spend my time on theoretical exercise
 
Anonymous
@SirCumference There are a lot of confusing titles: "reader", "associate professor", "assistant professor", "senior professor". I don't know the difference between the first three
 
Anonymous
5:15 PM
@Lozansky lol
 
We also had (assistant/associate) research professors that didn't teach. I think that there were only 2 or 3 of those though
 
@Blue Generally speaking, a lecturer is someone who teaches/researches, but won't necessarily get tenure after a few years. Assistant professor is a professor without tenure, but depending on their research they will get tenure after six years (otherwise, they're necessarily fired instead).
 
Anonymous
So how is "lecturer" different from post-doc?
 
Associate, full and distinguished professors are tenured. Those ranks are mostly promotions in terms of salary, which you obtain by putting forth valuable research. Assistant < Associate < Full < Distinguished
@Blue Not really sure
 
hmmm...
 
Anonymous
5:17 PM
@SirCumference That was a nice summary!
 
Anonymous
And any idea what "reader" means?
 
Anonymous
"The title of reader in the United Kingdom and some universities in the Commonwealth of Nations, for example India, Australia and New Zealand, denotes an appointment for a senior academic with a distinguished international reputation in research or scholarship."
 
Anonymous
Are they considered to be equivalent to full professors?
 
Though as stated, full and distinguished are promotions for good research. Some professors stay as associate profs their whole life.
@Blue I was listing the main ones in the US, which are similar but slightly different than those in other countries
This list of academic ranks identifies the hierarchical ranking structure found amongst scholars in academia. The lists below refer specifically to colleges and universities throughout the world, although other institutions of higher learning may follow a similar schema. == Afghanistan == According to Article 34 of Afghanistan's Civil Higher Education Law, academic ranks for the lecturers of higher learning institutions are as follows: A: Assistants 1. Junior teaching Assistant پوهيالی 2. Teaching Assistant - پوهنیار 3. Senior Teaching Assistant - پوهنمل B: Lecturers 1. Assistant Professo...
Here's the list
 
Bye all!
 
6:05 PM
@Blue there's a dedicated UK list with a slightly better explanation
It isn't synonymous to Professor - any institution in the UK that hands out the title Reader will also hand out the title Professor, and the latter is always more senior
as to whether it is "equivalent" or not - it depends on what you mean by 'equivalent' ;-)
 
seems like doing many generations of tpot doesn't help with this dataset
apparently it learns as best as it can in only 1 generation
roughly
 
Anonymous
@EmilioPisanty Thanks for the link. I mean is "Reader">"Associate Professor"? It doesn't seem to be clearly written in the Wiki article. Or is there no such hierarchical order in the first place?
 
@Blue I don't think you can rigidly rank the two
not all institutions offer both, and where they do, the ranking might differ
I suspect few institutions have both figures
 
Anonymous
I see, interesting
 
Anonymous
BTW, about this:
 
Anonymous
6:10 PM
@whurley I was thinking more in terms of something like this, which is a straight rotation, though now that I see it, it probably needs a designer to work a bit more carefully on the angles on the ends of the C to make it work to its fullest potential. I liked v1 a bit better than the current v2, though. — Emilio Pisanty 20 hours ago
 
Anonymous
I didn't understand what exactly you meant by "work a bit more carefully on the angles..."
 
Anonymous
I mean, do you want the ends of it (the C) to be straight? Or curved?
 
Anonymous
 
Anonymous
By straight I mean ^
 
Anonymous
 
Anonymous
6:12 PM
This is the one with a curve ^
 
making the ending of the lower leg of the C fully vertical, for example
making it look like a properly-typeset C, basically
 
Anonymous
@EmilioPisanty But that makes it look a tad asymmetrical I guess? (I'm referring to the white C superimposed on the grey Q)
 
so?
logos don't need to be symmetrical to look symmetrical
 
Anonymous
Well, maybe it's just that I find it a little less visually appealing :P
 
Anonymous
6:22 PM
@EmilioPisanty Umm, that has some merit. I see your point now
 
@Blue but it needs a designer to get it right
 
Anonymous
They do have a graphic designer I think. But I guess it is necessary to convey the point to them thoroughly :) I'm not sure whurley understood what you were trying to say (and neither did I, until now)
 
I'm proud of myself, I posted 2 answers today
I really try to post answers, but it costs me a lot more than posting questions
not sure I ever answered 2 questions within a day before. and I've been a member since years
so I'm damn proud ^^
 
Anonymous
It's an addiction, beware ;)
 
visited the website over 1000 days
im here all day long
 
6:29 PM
and here I am damning the fact that I'm probably going to almost-but-not-quite make the rep cap today
@user54826 congratulations
 
even got the message from the server "we noticed a strange behavior from your site, we want to make sure you're human" and offered me a captcha
 
@user54826 indeed it does. Keep it up - it gets easier.
@user54826 did you have the question open for a long time?
 
thanks ^^ or should I say, grazie mille
uh which?
 
the one you were answering
 
no
 
6:31 PM
@user54826 I'm not Italian, despite what my name might suggest.
 
just saw it a bit earlier today, found it interesting and answered it now
 
¯\ _(ツ)_/¯
 
oh really?!
ah I confused with Walter Moretti or something like that then sorry :D
 
Anonymous
Haven't met many Italians here
 
Anonymous
Language barrier probably
 
Anonymous
6:34 PM
...and also small population
 
60 M people ? :)
not that small
 
Anonymous
There are tons of people from France though
 
Anonymous
And quite a few from Spain
 
Anonymous
Among the European countries
 
I am located in France ^^
 
Anonymous
6:35 PM
Lol
 
like Slereah
Samuel The Reah
 
Anonymous
Where do you study?
 
don't want to reveal too much on me :/ sorry. especially since the chat is logged forever
google can return our messages
 
Anonymous
Ah, okaies
 
Anonymous
You are anonymous anyway so it wouldn't matter. But I can understand :)
 
6:37 PM
a bit anonymous. I guess I am not for the server and some admin(s) since they have my IP :)
they can get my geographical location pinpointed I believe
 
Anonymous
So, umm, is the average Frenchman fairly conversant in English?
 
I think so. the younger generation at least
for sure much better than say 2 decades ago
thanks to Internet
 
Anonymous
Cool, makes sense. Similar here
 
which country/language/
?
 
Anonymous
@user54826 India
 
6:41 PM
@Blue You're never really anonymous online :P
 
ah India yeah.
 
Anonymous
@SirCumference Heh. Well, practically anonymous since I don't think hackers would waste time on me ;)
 
I think Ed. Snowden might be able to be anonymous for some time. and security experts... but I don't know enough of that to give an accurate answer. but for sure, it's difficult
(or impossible)
 
Anonymous
@SirCumference But if I become something like this, SE might give out my IP :P
 
Anonymous
 
6:59 PM
@gateprep People here are generally more willing to answer conceptual and general questions, not specific problems (and especially not homework ones). That said, this is only a group of people with a shared interest in physics. No one is obligated or being paid to answer your questions, and you must remember that when you ask for their time.
 
Some people put a whole lot of efforts to answer homework problems
they literally spend hours on a single problem, making drafts on several sheet of papers
and eventually scan their detailed solutions with lots of insights
the perfect example of this is Farcher. Poor guy, honestly. many times he has 0 vote for his answer, but you can see how he demolishes the homework problem and give a very valuable answer, for absolutely no reward at all
I don't know how he has the stamina to continue to do that, but yet he does
 
Anonymous
@user54826 They are usually those who regularly teach younger students. Answering hw questions help them to brush their skills. I don't think Farcher even cares about votes/rep at this point.
 
Anonymous
When you start taking votes and imaginary rep points a little less lightly, life becomes a lot easier
 
@Semiclassical Hmm is $V(\mathbf{r}) = \dfrac{1}{4\pi \epsilon_0} \int \dfrac{dq(\mathbf{r}')}{R}$ essentially meaningless when the charge density extends infinitely?
 
Anonymous
On the other hand, they might also be retired people who have a lot of free time
 
7:07 PM
@Blue he certainly cared not too long ago. he created a meta post on this
 
Anonymous
For example, JR helps a lot of students in the "JEE prep" room
 
JR?
 
Anonymous
John Rennie
 
ah
John Rennie
ok
I see. wow. man that man, I don't know how he has the time to be number 1 of PSE and answer so many JEE prep questions
also I'm kinda proud . I've seen the rise of V.F.
 
Anonymous
Well, he's a retired millionaire. What else do you expect him to do to prevent his brain from atrophying? :P
 
7:09 PM
when he had a few hundreds points, I saw his high quality answers. in a few months he became the top guy of PSE
(earning more points than anyone else in that period)
 
Anonymous
V.F. does have a lot of good answers, yes
 
yeah ^^
then 2 other special dudes are my2cts and freecharly. they both answer in very very short but extremely concise and deep answers. but on different topics
they're very similar!
 
Anonymous
Floris also writes a lot of insightful answers in the basic/general physics category
 
i don't see him often nowadays, but yeah. many of his answers are day-long thoughts ones
 
@Lozansky pretty much, yeah.
 
7:16 PM
So typically you'd need the electric field first to compute the potential :>
 
Yep
Luckily the two principal cases of such are an infinite wire and an infinite plate of charge, where the field can be computed using Gauss’s law
 
so if you have an infinite volume charge like mentioned, you could just call it any constant value everywhere, right?
(it being the potential)
 
Ehhh. That case is sufficiently non-physical that I wouldn’t draw a conclusion
 
Yeah that's kind of the direction I'm heading while trying to think about an infinite volume charge
 
Another route is to somehow truncate an infinite charge distribution at some length scale. Then you can indeed compute the electric potential using Coulomb’s law
 
7:21 PM
But hey who needs physical situations anyway?
 
And study how the potential behaves in the limit where that length scale goes to infinity
Lol
 
@danielunderwood infinite volume charges don't work.
@Semiclassical it depends on where you put the center of those finite distributions.
hence it doesn't work.
unfortunately.
 
Point
 
charge
 
field
 
7:23 PM
I mostly have in mind how the electric potential of a rod is related to that of an infinite wire
Though the electric potential of an infinite wire is goofy no matter how you slice it
 
@Semiclassical it's a great way to learn to let go
about where the zero of the potential should be
 
In order for it to be well-defined, you need a scale at which the potential vanishes. But said scale is arbitrary in the problem as written
@EmilioPisanty p much
 
19
A: Is there a limitation on Gauss' law?

Emilio PisantyGauss's law is always fine. It is one of the tenets of electromagnetism, as one of Maxwell's equations, and as far as we can tell they always agree with experiment. The problem you've uncovered is simply that "a uniform charge density of infinite extent" is not actually physically possible, and ...

17
Q: Paradox with Gauss' law when space is uniformly charged everywhere

RevoConsider that space is uniformly charged everywhere, i.e., filled with a uniform charge distribution, $\rho$, everywhere. By symmetry, the electric field is zero everywhere. (If I take any point in space and try to find the electric field at this point, there will always be equal contributions f...

it's crazy how old answers are these weird echoes inside my brain. "did I write something about this at some point?" "maybe?" "but where?"
and that one's not even that old
 
One way to look at the issue is that an infinite sphere of charge is an inherently contradictory object. On the one hand, as a sphere it has to have rotational symmetry. But since it’s infinite, there’s no meaningful center to it
 
It doesn't really matter what shape it is if it extends out to infinity, does it?
 
7:37 PM
As such this question has a “garbage in, garbage out” feel to it
 
Ahh the good old GIGO queue
 
@danielunderwood nah, but a spherical shape makes it easy to see what’s going on
 
↑ cuts a liiiiiitle too close to the bone, dunnit?
 
Lol
My favorite SMBC to quote is the “know your linguistic philosophies” one
It applies to so many subjects beyond linguistics
 
7:41 PM
@Semiclassical was it you that linked the Schrödinger vs Newton one?
 
Probably, that’s a fun one
 
Isn't new theme just a copied version of Math.SE's new theme??
 
probably should reread up on decision trees...
 
Feb 14 at 14:22, by Semiclassical
I'm always fond of this one:
heh
 
7:43 PM
Jul 19 at 18:41, by Semiclassical
can't help be reminded of this old SMBC: https://www.smbc-comics.com/comic/2009-05-18
ah, there we are
@Abcd you did see the whole "we're re-theming all the sites to make all the themes more similar so that they're easier to update" bit, right?
 
@EmilioPisanty No.
 
@Abcd well, there you have it
 
Well, there you go
 
141
Q: Ch-ch-ch-changes: Left nav, responsive design, & themes

Joe Friend Thanks everyone for your feedback. The team has responded to feedback in the post Left nav, responsive design, and theming next steps . Check it out. Ch-ch-ch-changes are coming. As you've hopefully read in our various posts on Teams, we are in the midst of some major work. We're introduci...

84
Q: Left nav, responsive design, and theming next steps

Joe Friend Those interested can now opt-in to beta testing new themes across the network. More details in Opt in to beta testing new themes In the post entitled Ch-ch-ch-changes: Left nav, responsive design, & themes, I described a number of changes that are coming with the introduction of the left nav...

> Every Q&A site has its own theme. But there is great inequality in the level of theming that we support. A few (~10) get Cadillac treatment, some (<50) are more like a Honda, while most (~100) are a Yugo. The reality is we created a theming system that we didn't have the design resources to fully support, thus the inequity. In addition, as currently defined, our theming gets in the way of releasing new features on the sites.
> In order to deliver the left nav, responsive design and future improvements to all sites we've created a more standardized way to support theming. This will reduce the burden of supporting designs as we make Q&A improvements. The result is that most sites will see an improvement in the level of theming that they can get. While some sites will see a reduction. All of Q&A (Enterprise, Teams, etc) will standardize on this new theming scheme.
particularly this bit:
> The result is that most sites will see an improvement in the level of theming that they can get. While some sites will see a reduction.
they forgot
> Some sites that see a reduction will attempt a user revolt and try to boycott SE.
 
@EmilioPisanty Oh, is any site doing that?
Like Science Fiction had a great theme.
 
7:47 PM
41
A: TeX new site theme is live

MicoBoycott this site until and unless the old look is restored! If it's not restored, let's say goodbye and good luck to this site entirely. Why do I say this? It's because I suspect that the only way that the powers that be will ever respect and listen to our views is if we -- and especially the m...

 
Are they revolting?
@EmilioPisanty Who else is revolting?
 
... or threatening to, in any case
 
any other site except tex.se?
 
@Abcd not to my knowledge
 
Here’s a fact for which I only know a tedious proof: if I entangle two spin-s particles in a singlet state, then every allowed value of $S_{1z}$ is equally probable
 
7:54 PM
Is there anything similar that happened before? I've noticed a handful of PSE accounts that say that they're no longer on the site
 
hmmmmmmm
 
Anonymous
@danielunderwood I don't remember anything of this scale happening before
 
Anonymous
But some guys made a new site - Physics Overflow
 
@Semiclassical what do you mean by singlet for spin s?
 
Anonymous
Since they didn't like the moderator atmosphere here. Also it served as a replacement for Theoretical Physics SE
 
7:56 PM
That's just more technical isn't it?
 
Anonymous
@danielunderwood Yeah. But I think you're allowed to be rude there :P
 
Anonymous
Unlike here
 
@Blue that's... a simplistic view.
 
I need to spend some time figuring out if I want to spend a lot of time optimizing this model
 
7:58 PM
@EmilioPisanty total spin 0. Since I’m combining two particles of equal spin, there will be states with total spin 0,1,...,2s.
 
Though I suppose it depends on what exactly the time and optimization is. When you say that, I think a week for a 0.1% improvement lol
 
Anonymous
@EmilioPisanty Well, there are already tons of meta posts about this. Didn't want to elaborate much...especially on the "tensions" between the two sites
 
And exactly one of those states (up to the usual boring phase factor) will have total spin zero
 
@Semiclassical is there only one singlet irrep?
 
Yeah. It’ll be $s\otimes s=0\oplus 1\oplus \cdots \oplus 2s$ in the notation of Shankar
 
8:02 PM
88
Q: Who are the package maintainers here?

Loop SpaceQuick links: LaTeX Packages A-M, N-Z ❧ LaTeX Classes ❧ ConTeXt Modules ❧ Generic Packages ❧ Support Scripts ❧ Biblatex Styles A fair few users here have written or maintain packages on CTAN, some even in the TeX Live distribution, or at the least have some official involvement with a pac...

damn
@Semiclassical so what's the singlet state?
is it just $\sum_{m=-s}^s |m⟩|{-m}⟩$?
 
not quite: in fact there’s a coefficient $(-1)^{s-m}/\sqrt{2s+1}$
 
hmmmmm
 
Ie the states alternate in sign and there’s an overall normalization
 
ah
I'm tempted to say "just use the rotational invariance of the state"
but I'm not sure you can get it to work
 
Yeah
Best I could come up with is that the total raising operator should annihilate the singlet, since you can’t increase m=0
 
8:07 PM
presumably the property is not true if you have, say four spin-s particles?
 
No idea. That many spin-s particles was too much for me
 
@Semiclassical $\mathbf J=0$ as a vector operator on any singlet state
 
Right
 
$J_+=J_x+iJ_y=0$ then follows directly from that
 
Yep
But $J_+=J_{1+}+J_{2+}$
So that amounts to the claim that $J_{1+}=-J_{2+}$ when acting on the singlet
 
8:10 PM
maybe it's possible to say something useful about the commutator of $J_+$ and $|{J_{1z}=m}⟩⟨{J_{1z}=m}|\otimes 1$?
 
Hmm
Worth a try
 
there's probably a fair number of ways to express that commutator as an operator function of $J_{1z}$
if you do get a useful commutator, then your property probably follows with very little effort
 
The argument I do have relies on the observation that $\langle m+1|J_+|m\rangle =\langle -m |J_+|-m-1\rangle$ for any set of spin-s states
Which is true but seems no more obvious than what I started with
 
8:35 PM
@Semiclassical bash out the state, show that $\mathbf J |\psi⟩=0$, you're done.
never mind how you got it
 
I guess
 
that's probably the minimal-ink route
 
What’s hilarious is that Lifshitz takes it for granted that the singlet has equiprobable outcomes
No proof, just a passing statement that “it’s singlet so equiprobable”
Thx a lot
 
Lifshitz? or L&L?
I mean, you know the saying
> not a word of Landau and not a thought of Lifshitz
 
Lol
L&L I think it was
Right. This page: books.google.com/…
The second complete sentence after the sum for psi0
 
8:45 PM
yeah
that's the kind of curveball that sets L&L strictly on the No Beginners lane
or at least, not for the faint of heart
maybe it was obvious to Landau
but if so, it's not obvious to me
I suspect that it wasn't obvious to Lifshitz but he didn't want to argue so he just left it like that but with no explanation coz he didn't have time to ask
Landau was already five pages ahead
 
hmmmm
replacing a question with another makes the predictions much worse...even though the two questions had similar correlation with the target
wonder why that is...
 
@EmilioPisanty sounds right
I mean, I can show it
But it’s such a simple claim that it seems as if it should have an equally simple reason
 
 
2 hours later…
10:59 PM
 
It's really fun the first time you try to integrate $x^n e^{-x}$
 
not sure my plan to use a genetic algorithm for finding root causes of low NPS is really working lol...
 
11:23 PM
@danielunderwood that's a rookie example. $\int \sin(x) e^{x} dx$ is way more interesting.
 
limits of integration please
 
WA tells me the answer and I think it's some sort of wizardry
 
it's less mysterious when you use Euler's formula
 
oh wow that isn't even much trickery. It's just algebra in adding the integral back to the other side of the equation
I feel dumb now
I seriously have $\int \sin(x) e^x dx = ... -\int \sin (x) e^x dx$ on the back of an envelope -_-
 
11:40 PM
hmmmm
 
I think the multi-processing in tpot is broken
setting n_jobs to -1 throws a ton of errors for me
unfortunate..
slows down progress by probably a factor of 10 or so
 
There's a thing on the wiki about setting something. I still had some problems with it though. I think some of the classifiers are already set up to use multiple processes, so it may end up using all cores even if you set it up to 2 processes or something. I also had an issue with occasional classifiers hanging
hold up
 
multiprocessing is hard :P
 
or at least I've never seen it before. The page above is about n_jobs though
 
11:44 PM
I dunno what dask is
meh w/e the data set isn't that big anyways
 
Yeah looks like it was only merged in 5 days ago
It's some sort of multiprocessing library geared towards data? I've heard about it before, but never messed with it. Part of pydata, so it must be legit
 
hmmm
 
I actually have it on my todo list that's way too long
Don't know how much work is associated with setting it up to use dask though
Evidently dask is made to be used with clusters, which is neat
 
I don't have a cluster
just a single CPU and GPU
 
cluster = dask.LocalCluster()
client = dask.Client(cluster)

looks like it'll handle it locally
Meanwhile I can make a makeshift cluster for my use!
 
11:52 PM
I'm a total noob at parallel computing lol
 
It can be delicate to say the least
Although most people today use a pipeline rather than multithreading, which seems to be a lot less error-prone
It looks like using dask with tpot is just a matter of TPOTClassifier(...,use_dask=True) though I have no idea how it actually gets the client and their sample uses TPOTEstimator
And you'd have to upgrade the version of tpot you have installed. Just poke it and see if it drowns you in errors!
 
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