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user54412
12:41 AM
What's this? A question in the flag queue? That's pretty rare.
 
@ChrisWhite Flagged as spam or hate speech or something like that?
 
user54412
nah just low quality (the smallest possible burning thing)
 
Yeah I just VTC'd that one. Pretty poor question and I think this is the wrong place for it.
 
user54412
I find the answers and comments on this hilarious
 
user54412
2
Q: Can frequency be equal to 0?

chepseskafIs correct to speak about frequency equal to 0 ? $$f= \frac{1}{t} $$ If $t\rightarrow\infty$ can I consider that the frequency is equal to 0 ?

 
user54412
12:49 AM
everyone is so sure of themselves, but everyone has a different response
2
 
user54412
just goes to show the community can diverge in terms of definitions and terminology
 
I think Dimension10's close reason is pretty rude and immature and inappropriate.
2
I think it's a bad question but I couldn't find any reasonable close option that would work for it so I voted to leave it open.
 
user54412
 
user54412
I feel like this has been asked before, but how does Community approve edits?
 
user54412
it can't be anonymous, because you need a certain rep level to approve them
 
3:02 AM
@ChrisWhite if the OP approves it or if one approver uses "edit", iirc
 
 
2 hours later…
4:41 AM
Someone doesn't know that the Laplace equation and Legendre polynomials are used by PHYSICISTS.
 
@Pulsar While I don't use my moderator superpower on that kind of thing, in that question the physics has been done and all that remains is math.
And while there is sometimes an advantage to be had in letting physicists answer if they use different conventions than mathematicians, those standard orthogonal functions have been standardized for so long that we're in agreement on the conventions.
Mind you, I learned them in a physics course. But it was called Mathematical Methods in Physics.
 
5:35 AM
@Pulsar Migration was requested by the OP and one other user. Also, what dmckee said.
 
 
5 hours later…
10:57 AM
Duh, I missed the whole chat session yesterday, because of a weird guest!!! -_-
 
11:11 AM
@Manish @David or @dmckee: You may have seen that "Love is in the air" tweet... I've put my own modification to that, for this valentine's day (I mean, "Physics" as my valentine :P)
I thought of posting in our meta... (probably for fun)
Um, is that okay?
(/me has also thought of writing a poem) :D
 
 
2 hours later…
12:51 PM
0
Q: Asking math questions

JeffDrorI understand that asking pure math questions on the physics site is discouraged and I've seen many questions moved over to math. However, often times such questions are more suited for physicists to answer since they those types of questions more often. Furthermore, they are more likely to answer...

 
 
3 hours later…
4:06 PM
0
Q: What are the rules for pinging someone in comments?

John RennieIn my comments to Can (quantum) angular momentum $L$ be zero? I tried to @PPG, but it won't let me. Presumably the conditions for whether or not I can ping someone are listed somewhere ...

 
@Pulsar bear in mind that "used by physicists" is not the criterion for a question to be on topic for this site.
@Waffle'sCrazyPeanut I'd say put it here in chat. I don't think it's appropriate for meta. (as it's not a question about the site)
 
4:33 PM
@DavidZ Alright... ;-)
 
0
Q: Epic and Legendary badges

John RennieIs there a way to find out how close you are to the Epic and Legendary badges, that is how many times you've hit the daily limit? I've seen clever things done with queries so I'm guess there is a way to calculate this.

 
4:57 PM
@DavidZ @Manisheart So what is this question still doing here???? physics.stackexchange.com/questions/98863/…
 
@Pulsar Because not enough people have voted to migrate and the OP hasn't asked for migration
The mods aren't magic, the community still has to do it's part.
6
 
@Pulsar And it seems it was probably knocked out of the review queue by a few leave-open votes.
 
FWIW I just voted to close it but I was unaware the question existed
 
5:18 PM
@Pulsar I would actually consider that on topic here because it's about units.
 
5:28 PM
@DavidZ That is ridiculous. A solid angle is a purely mathematical concept. If Legendre polynomials are off-topic, then solid angles are most definitely off-topic.
 
@Pulsar ...but the the notion of the angle having units is a physics concept.
 
@Pulsar Then flag to migrate and move on in life. You can express your opinion quite easily without complaining or attacking those who agree or disagree
4
 
@Pulsar So you would also say that length and time are purely mathematical concepts?
And mass? Charge? Current?
 
@DavidZ Your own words: " 'used by physicists' is not a criterion".
 
Yes, so?
 
5:36 PM
In other news, I may end up with 7" of snow by tomorrow morning. I can't wait until it's 100+ degrees in May
 
lol
 
@tpg2114 Yeah, the kids are awfully excited about it
After Little Miss takes a nap, we're gonna go out and play in the snow
 
I'm glad the ice-line shifted south. I'd take 7" of snow over 1.5" of ice like was originally forecast
And I feel bad for the people south of the city that will get over an inch of ice. That sounds absolutely miserable
 
Ugh, ice does suck
 
6:07 PM
I have a really tough time reading weather maps. They need to pick colorblind-friendly colormaps
 
user54412
@tpg2114 and even for us with full color vision, the standard scheme is too... haphazard
 
@ChrisWhite Yeah, it's almost like they want to use a categorical scheme with ordered data
 
user54412
I can only conclude it was devised by a random walk in color space
 
Like why is < 0.1" of ice this slightly pale blue while 1+" of ice is white?
With pink and purple in the middle
I can really only tell apart the purple from the rest. None of the others really make sense...
 
6:34 PM
@Pulsar 3 votes to close on it. It may get there. "Why is this around" isn't an argument to keep something else, especially when the other post is new and hasn't had time to go through the system yet.
We're trying not to apply too many mod binding votes either.
@Pulsar Did you not hear me when I said that the OP requested migration? If a post is on topic on two sites, the OP can request migration and we usually honor it.
And fwiw the solid angle question is about dimensionality.
That's not a math concept.
 
7:19 PM
@ManishEarth Huh?
The curse of dimensionality refers to various phenomena that arise when analyzing and organizing data in high-dimensional spaces (often with hundreds or thousands of dimensions) that do not occur in low-dimensional settings such as the three-dimensional physical space of everyday experience. There are multiple phenomena referred to by this name in domains such as numerical analysis, sampling, combinatorics, machine learning, data mining and databases. The common theme of these problems is that when the dimensionality increases, the volume of the space increases so fast that the available d...
 
@GlenTheUdderboat not that dimensionality
The one from units and dimensional analysis
 
@GlenTheUdderboat :p not that one
units. physical units.
The question is about the units of the solid angle, basically
 
Well, that's 1.
 
@GlenTheUdderboat Nope. The steradian
Which is actually rather confusing
 
7:27 PM
@ManishEarth "The radian and steradian are special names for the number one that may be used to convey information about the quantity concerned. In practice the symbols rad and sr are used where appropriate, but the symbol for the derived unit one is generally omitted in specifying the values of dimensionless quantities."
PDF (p. 118). Or trust me.
 
7:46 PM
@GlenTheUdderboat nice, always thought that to be the case but didn't know it was an official thing
still, the steradian and all are used in physics. Mathematicians won't care:p
 
And here comes the downpour of sleet...
 
@tpg2114 I had to look up 'sleet'. Apparently, I must know where you're from, in order to understand it.
Sleet is a regionally-variant term that refers to two distinct forms of precipitation: *Rain and snow mixed, snow that partially melts as it falls (UK, Ireland, and most British Commonwealth countries) *Ice pellets, one of three forms of precipitation in a "wintry mix", the other two being snow and freezing rain (United States and Canada) See also *Freezing rain *Graupel *Ice storm *Snow *Hail
 
It's the ice pellets
Precipitation that starts as snow, falls through a layer of warm air and melts, then falls into a thick enough layer of cold air to refreeze into pellets
Freezing rain starts as snow, falls through warm air and melts, then back into cold air but not a thick enough layer to refreeze
So it then freezes on contact with cold surfaces making a layer of ice
 
are Langley Calibration questions on topic here?
 
@Amaterasu Without seeing the exact question it's hard to say
But some data analysis methods are allowed when the physics underlying them is important
But implementation of analysis should be somewhere else, probably SciComp, and math questions related to statistical things should be on Stats.SE
So depending on what your question is it may or may not be on topic here
 
7:58 PM
How is the Langley calibration performed on devices that have a large FWHM (10nm)?
 
That might be better at astronomy.SE
But without the exact wording I can't say anything about it really
Plus I know nothing about the topic
 
it is for irradiance measurements, the Langley calibration determines the extraterrestrial irradiance
 
user54412
@Amaterasu I could believe that's on topic here
 
Right -- so you might have better luck at astronomy.SE since your question seems to be more on how to do it rather than the physical justification. But anything that's on-topic on astronomy.SE is also on topic here
Technically at least
 
I know how to do the Langley calibration, I am wondering about the implications of having a wide FWHM - 10nm as opposed to 2nm used in most instruments
 
user54412
8:03 PM
well solar physics is a rather niche part of astronomy - if the astro.SE community is the same as it was when I last checked (mostly hobbyists), I doubt you'll find many solar observers there
 
user54412
not that I can point to too many here, mind you
 
hmmm probably not a good one, eh?
 
user54412
I think the question could very well be a good one (technical, answerable, etc.)
 
user54412
probably not a hot network question though - I doubt all those coders are doing Langley calibrations in their spare time :P
 
heathens !!
 
8:09 PM
@Amaterasu Does this (PDF) help?
 
thank you for that,I have this one - however, my question is, as in the UV, the FWHM is 2nm, my instrument has a FWHM of 10nm
 
@Amaterasu Well, go ask.
 
8:28 PM
Okay so I added a question just now but then I deleted it when I realized the flaw in my reasoning
So now I'm wondering, is it true that in general, if you find the trajectory of a particle in one frame, it's hard to find the trajectory in another frame?
 
@Amaterasu What did Beer die of at 38? (Just wondering.)
 
not sure, to be honest
@ChrisWhite it be done
oh well, off to work!
 
@BrianBi How do you define "hard"?
 
It seems like it requires solving an equation (and in general equations are hard to solve)
 
If you know the trajectory of a particle with respect to one set of basis vectors, it's not hard to change to another vector space that defines your other frame.
So "hard" depends on how complicated your frames are
 
8:42 PM
It's special relativity, inertial frames
I think I'm just doing it wrong
 
I don't do relativity so I can't really help you. But I will say that if you know your two basis vector sets and the map from one to the other, then changing frames is just math
And it may or may not be "hard" depending on how complicated the map is
 
@BrianBi then finding the trajectory isn't that hard. You just substitute the transformed coordinates and that's it
 
If x' = f(t') then
gamma(x - vt) = f(gamma(t - vx/c^2))
It seems hard to solve this for x in terms of t
 
Depending on what f() looks like
 
@BrianBi Oh, you want to get closed form solutions for x
not always possible
 
8:45 PM
If f(x) = x
Then it's easy
 
when you say "trajectory" it doesn't have to be a closed form solution
@tpg2114 gamma is the Lorentz factor
 
Fixed... like I said, I don't do this
 
So I guess this means that if you want to get a closed form solution for a particle's trajectory
The approach of boosting to a frame where the dynamics are easier to analyze, solving for the trajectory there, and then using that to get the trajectory in the original frame
might not work sometimes?
 
No, that would always work
if you do it correctly, of course
 
I mean at the end, if f is a complicated function, it might be too hard to solve the equation
 
9:00 PM
@DavidZ he wants a solution of the form x'=f(t'); not always possible
 
Well there might not always be a symbolic expression for it, but the solution does always exist
 
Okay, that's what I wanted to know
Lemme ask my prof whether he needs a closed form solution
 
I once got into some argument about whether an algorithm (a bunch of nested summations and products and indicator functions) would count as a closed form solution. I couldn't see the distinction. But apparently the distinction is made.
 
The particular problem here is to find the motion of a relativistic charged particle in constant, uniform, perpendicular electric and magnetic fields
 
user54412
"closed form" isn't well defined by physicists - they usually mean "has a nice look to it"
 
9:09 PM
The TA told us to boost into a frame where the field is pure electric or pure magnetic, and I have the trajectory in that frame, but I can't solve for x in terms of t in the original frame
 
user54412
@GlenTheUdderboat I would count any convergent series as closed form
 
@ChrisWhite Aren't numerical discretizations convergent series? :)
 
@ChrisWhite There weren't any infinities involved. Just that my 'closed form' solution amounted to brute force.
 
user54412
@BrianBi while in principle solving for x(t) might be difficult, this sounds like the type of problem where that won't be the case
 
user54412
at least I would hope
 
9:13 PM
All right, I'm not going to post any more lest I be accused of cheating, but I'll think about it some more
 

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