@ACuriousMind aren't you bored? You are alone in the room.
@ACuriousMind I would go to sleep too, but I have a problem with Emilio that instead of being in bed at this hour, made an editing of an answer of mine, and I don't know what to do, because there is no field there that allows me to approve its editing.
@Sofia The edit was automatically applied to your post already - edits from users with more than 2.000 reputation are always applied without waiting for approval
@ACuriousMind : don't spend nights being awake, you will regret later on. I am having terrible problems because I got used to be awake by nights. That destroys my mornings.
@ACuriousMind well whenever you'll decide to go to sleep, sweet dreams!
While trying to find something in my browser history, I somehow, after highlighting "Last Month", managed to make the browser open all of the web pages I visited the last 30 days.
I've been using Ruby to write scripts for research, but I want to get into some heavier stuff that Ruby is just too slow for. I noticed there are a few things written in C and C++, but there is an oddly large proportion of software used in computational chemistry that is written in FORTRAN (which...
@tpg2114 I've been a member of chemistry.se for a month or so now, and I find the frequency of questions asked very dismal in comparison to Physics. I know it's still in beta, but it's been so how long? About six months or so?
Surprisingly, sites like bicycle.se ( yes, there is such a site) have already progressed from beta before chem.se has. Any idea what the reason may be?
As a matter of pure opinion, as a developer who has developed in perhaps a dozen languages, there is no reason I would recommend FORTRAN for any developer for any task unless there is a legacy FORTRAN codebase to interface with. People are simply not learning the language anymore, meaning you will have to maintain any code you write forever. It will be hard to hand off to anybody. — Cort Ammon8 hours ago
@KyleKanos I noticed that as well. I put together some puzzle pieces that I won't elaborate on in open chat. But I don't think that was the first account associated with that person. He asked for his previous account to be deleted because of some (arguably) mean/disrespectful things that went down on Meta before.
So out of respect for privacy, I won't explain any more. But it's regrettable that he left again. Although this time I don't know that things were actually as offensive as last time
He seemed pretty upset about my rubber duck physics comment in chat. I don't know why it was thought to be demeaning, it's a legitimate thing to do.
In other news, GT messed up yet again and sent my W-2 to the wrong address. Right about the time that happened, somebody used my SSN to change my mailing address with my bank and ordered a new debit card that was activated this morning
Never got any notifications about changes. Only found out because my card was declined and I called to find out why.
@Gaurav I wouldn't attribute it to any single source. There are multiple reasons evident from the discussions here and on Meta. None of it was helpful.
Sometimes, specifically with sorting/clustering algorithms, it would be nice to be able to provide a gif to illustrate a point. Does anyone else think this could be a good feature?
I suppose SVG would be even more awesome (well, it has limited uses but for illustrating concepts and plotting you probably want vector graphics, anyway)
GIF isn't very efficient at compression, though, and as you mentioned does have a restricted colorspace. I mean, depends on the contents of course, but I guess that much of the new GIF use could well be replaced by webm (and some GIF sites allow both formats to be uploaded).
Size is the real problem, the animations can get gigantic
But the colorspace is actually a good thing. I try to explain to people that most scientific visualization shouldn't have more than 16-32 colors anyway
Otherwise you lose a lot of information about the fields
Yeah... it depends on the audience. To demonstrate technical data, limited color spaces are generally much clearer. For showy presentations to non-technical project managers, the Colorful Fluid Dynamics approach can be better
Side note, I'm super picky about data visualization and am trying hard not to get on a soapbox :)
At one point I kind of developed a fetish for vector graphics, meaning that I wanted all my figures (in publications as well as presentations) to be scalable.
I did several posters with beamer as well. It works surprisingly well. Although from what I remember, I did have to manually throw in the coordinates which was a bit of a pain (well, I did do one with automatic boxes, but that results in a bit of a boring presentation)
Yeah, I've used impress.js. D3.js is more for the visuals, plots and stuff.
I used impress.js, or rather jmpress.js (with jQuery) once. I wouldn't recommend it though: The Prezi-style presentation might seem cool, but I think a traditional one is more efficient.
I made a poster with it. But used that as a talk, so the slides would be like different parts of the poster, kind of. I think it wasn't bad per se, but wouldn't do it again.
At least I had fun making it.
Here's someone's more or less technical presentation with impress.js
The good thing about that is that if the presentation is as nice as that one, it can sort of make an interesting website.
@alarge Since you were asking whether animations can be used in answers on se, a recent high-voted answer had a pretty neat animation: physics.stackexchange.com/questions/161406/…
Well, I meant for the end user. As in if you want to download the presentation there, there in principle is no single file for you to download, you'd have to download several. Furthermore, you might also have problems running the presentation locally (so you might have to install a dummy webserver).
Back when we sorted out the book recommendation and resource recommendation requests, we made it so there was a permanent banner instructing those answering to abide by our policies regarding the questions.
Since we get so many homework questions, can (or should) we have a similar banner for th...
So in some ways, the banner is more to alert people answering a question to the policies, rather than OP (because if the question was against policy, it would be closed). But we can use it to gently remind OP also
I disagree. Somebody could show a problem, explain why they are stuck and ask for the physical explanation. That's well posed. But somebody could come along and answer it by saying "Here's the concept where you got stuck. And by the way, the answer is 10"
@ACuriousMind what's your opinion to change "some day" that vampire-style picture? You frighten people. There are all sort of eccentric picture but your one is on top.
@ACuriousMind You current avatar is freaky enough to approach awesome.
@tpg2114 Being bothered by a suggestion that is widely applied in all kinds of detail-oriented creative enterprises is not something that I can easily understand. Telling it to the duck is a tool for bringing to the surface things you already know.
Can someone help me on a formula related to the Young-Laplace equation on a pdf ? I'm new to those, and there's one coefficient which's formula I don't get.
@alarge PDF is way more portable and reliable. To the point that many particle physics types will actually grumble aloud if a presenter uses powerpoint, because we don't feel confident we can display it right on our machines.
I had two classmates give a presentation in a seminar recently. They used Powerpoint. Font: Comic sans. Half the room audibly groaned when the first slide came up :D
@Hippalectryon I think it is homework-like and doesn't ask a conceptual question, so I'd advise against asking it. I know nothing about what you are doing there, though, so I don't know the answer, either.
No problem. I'll leave it to you to derive the Young-Laplace equation (from what I remember the derivation for the general curved surface is painful; sphere is obvious though, so you might convince yourself using that as an example and just "generalize").
@EmilioPisanty Did I miss something while I was gone?
@KyleKanos I would deny them too if I left because I was (in my mind) being bullied etc.. There's just way too many coincidences for it to be somebody different
@dmckee I didn't understand being upset either, nor do I feel bad about it now. I'm just saying it seemed to be upsetting. No idea why
Which is why I refrained from bringing it up before, and I will not discuss details in public now
Oh man, so in extra fun bonus day -- not only was my debit card jacked up, but GA rejected my income tax return as one of the batch of returns from TurboTax that is fraudulent!
@ManishEarth Hey, there's a new user's answer that isn't an answer but really deserves to be made a comment as it's a referenced correction to the question. Flag for mod attention or do the usual not an answer thing anyway?
hmmm... question is 9 months old. Probably isn't worth the effort
On a completely unrelated note, I love the sound bug zappers make. That bzzt lets me know how much it's working. Now, I know it's not possible, but wouldn't it be great to have that kind of thing for protected questions? A little counter or something that indicated each time it prevented a new answer to an old question from a random google searcher. For instance, don't you wonder how many answers the protection on this question has prevented?
I'd just feel so soothed to hear that little bzzt everytime some young kid is prevented from posting his own theory of what gravity is. Alas, too bad it will never be possible
@Jim use the standard "not an answer" flag for that sort of thing
@Hippalectryon I actually think that would have been a fine question. To my mind, "Where does [factor] in [formula] come from?" is unlikely to be the bad kind of homework-like, and is the sort of thing I see this site as being for.
I suppose the paper is talking about the field outside of the magnet, in which case you'd have to look up the formula for the magnetic field of a dipole of magnitude $\mathbf{m}$ and compare that to the paper's formula.
($\mathbf{m}$ is the magnetic dipole moment, right?)
@DavidZ That gives me $H=\dfrac{r(m\cdot r)M}{r^2}-\dfrac{M}3$, which doesn't look like the expression in the paper (I know that we're considering a centered sphere here while it's not centered in the article, but the formulas do not even seem similar)
@Hippalectryon In cylindrical coords r is the projection to the plane. In the equation you posted above (wiki?), you're indeed dealing with spherical coords
Is there a standard method of estimating the probability of a stochastic path? Suppose I have some stochastic process that I sample at regular intervals; What's the density kernel? I suppose I could use e.g. Parzen windows (or just discretize the state space) assuming that the process is Markovian, but that's not particularly elegant.
@alarge In the wiki's formula (image above), $m$ and $r$ are vector right ? If so, how do I turn $r$ in spherical coords to $r$ in cylindrical coords ? $\sqrt{r^2+z^2}$ is not a vector.
@Hippalectryon Yes, $\mathbf{r}$ and $\mathbf{m}$ are vectors. Do you remember how to change basis? Basically you want to figure out how to write out the spherical unit vector $\hat{\mathbf{r}}$ in terms of the cylindrical $\hat{\mathbf{R}}$ and $\hat{\mathbf{z}}$.
It is. I think Wikipedia probably has the formulas somewhere, but it's useful enough that you should try to figure it out at least once if you have time.
Hey @DavidZ is there a way to cancel an edit to a post? I edited the title of the "Why do most formulas in physics have rational exponents?" but it was actually perfect the way it was
@alarge Isn't it just $\hat{r'}=\cos\theta\hat{z}+\sin\theta\hat{r}$ ? $(\hat{r},\hat{\theta},\hat{z})$ is cylindrical, $(\hat{r'},\hat{\theta'},\hat{\phi'})$ is spherical
@alarge I get $\hat{H}=\dfrac{R^3}{r^5}C\sin\theta\hat{r}+\dfrac{R^3}{r^5}C\cos\theta\hat{z}-\dfrac{R^3}{3r^3}\hat{M},C=\hat{M}\cdot(\hat{r}\sin\theta+\hat{z}\cos\theta)$
The system is axisymmetric, so I thought I could choose any $\theta$ I want... but we see above that it leads us, for $\theta=0$, to no $\hat{H}$ towards $\hat{r}$...
@pentane you can revert an edit, which gets recorded as a new edit that undoes the previous one (though there is no way to erase the evidence that the edit ever happened)
You have like $r = r'\cos\theta$, $z = r'\sin\theta$, though, right?
So, the first term, for example, should be $\frac{\mathbf{r}'(\mathbf{M}\cdot \mathbf{r}')}{r'^5} = \frac{(r\hat{\mathbf{r}} + z\hat{\mathbf{z}})(M\hat{\mathbf{z}}\cdot (r\hat{\mathbf{r}} + z\hat{\mathbf{z}}))}{(r^2+z^2)^{5/2}}$
So if you multiply what I have above by $R^3$ (the radius of the actual sphere), you'll get the $\hat{\mathbf{r}}$ component (the other term is in z-direction, so there's no contribution)
@DavidZ : Why some questions are restricted only to the pleasure of people who have > 10K? I saw a question to which I am forbidden to answer because I have less, and though, I have an answer.
@Sofia because those questions are deleted. You (or anyone else) shouldn't be answering them. (and I'm not sure what you think pleasure has to do with it)
@Hippalectryon By definition, see your figures. Anyway, we have to pick some direction for the magnetic moment, and we might as well align our coordinates with it (as we don't expect it to be moving).
And m should really be replaced by 4/3 pi R^3 M z, right.
@Sofia yes, well, it's the nature of the community here that you don't get to simply answer whatever you want. 99% of the time, sure, you can, but there are some cases where people are prohibited from answering questions; always for a particular reason.
@alarge Ok I'm still missing one last step. I got $\hat{H}=\dfrac{rzR^3M}{(r^2+z^2)^{5/2}}\hat{r}+\left(\dfrac{z^2R^3M}{(r^2+z^2)^{5/2}}-\dfrac{R^3M}{3r^3}\right)\hat{z}$
The first factor (before $\hat{r}$) is good
But the coefficients of the last one do not match the paper's formula
The paper's formula would be $$\hat{H}=\dfrac{rzR^3M}{(r^2+z^2)^{5/2}}\hat{r}+\dfrac{1}3\left(\dfrac{2z^2R^3M}{(r^2+z^2)^{5/2}}-\dfrac{R^3M}{(r^2+z^2)^{5/2}}\right)\hat{z}$$
@DavidZ : why is the Copenhagen interpretation the most accepted? And I, that work exactly in the domain of fundaments of QM for long, long years, and I have a chance to answer well, because I know the other interpretations - I can't answer. I don't want to argue with you, of course not. But it's very bad. At least I should be able to see such questions.
@Sofia I believe it is more fair to say that "Shut up and calculate" is the most accepted interpretation. Most physicists I know emit a pained groan as soon as someone wants to talk to them about "interpretations". Also, >10k people can only see these questions - they cannot answer them, either.
@Hippalectryon You have a mistake in your denominator in the formula you derived. Fixing that and making the denominator the same, you get... almost the same formula as in the book.
Ok thanks a lot for the help. I just have one last general question on notations.
Where I come from (France), I have only seen the $\vec{e_r}$ etc .. notation for vectors. What's the meaning of the notation $\hat{h},H^*$ ? Do we use them in different cases ? The paper seems to use $^*$ all the time for non units vectors.
Yeah, so I think the * probably refer to some coordinate transform. As in, the non* ones for h might have a different definition for 0, say, so h* = c - h (for example).
This just came up again:
homework is not acceptable if the asker has made no effort whatsoever
I'm developing a bit of an involuntary twitch that manifests itself when I encounter the word "effort" on Stack Overflow these days.
Don't get me wrong — effort is good. At least, productive eff...
@DavidZ That is an interesting thread, and certainly a long one. It's always interesting to see how other sites deal with the same kinds of things that crop up here -- our problems really are not all that unique.
Sometimes, specifically with sorting/clustering algorithms, it would be nice to be able to provide a gif to illustrate a point. Does anyone else think this could be a good feature?
Back when we sorted out the book recommendation and resource recommendation requests, we made it so there was a permanent banner instructing those answering to abide by our policies regarding the questions.
Since we get so many homework questions, can (or should) we have a similar banner for th...
This just came up again:
homework is not acceptable if the asker has made no effort whatsoever
I'm developing a bit of an involuntary twitch that manifests itself when I encounter the word "effort" on Stack Overflow these days.
Don't get me wrong — effort is good. At least, productive eff...
