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1:36 AM
 
 
2 hours later…
3:44 AM
 
 
2 hours later…
5:34 AM
@ACuriousMind How are you downloading them? All of mine have names like "1210.1910v1.pdf" which is not very informative, but at least the format tells me where I got it and when to go for better metadata.
 
@ACuriousMind It is not the arxiv default name. The name looks like md5sum hash, so it may be your downloader problem to rename it like this.
 
5:50 AM
Hey guys and guyettes (if that exists), I posted an answer to this question on my tab : http://physics.stackexchange.com/questions/153797/does-irregular-reflection-form-images

For some reason, the images got placed around in the answer hapazardly, easily qualifying for the prize "Most poorly formatted answer" . What san I do to correct this ? (Thought I'll post it as a question on meta, but not sure it'll be well received)
 
6:39 AM
@Simha: What works for me when that happens is to insert the same image, but instead use paint or some other photo editor to make a rectangular white image with the image in the center, the same width as for SE answers. That way, the alignment works.
 
7:04 AM
@JamalS Thanks !
:)
 
 
3 hours later…
10:32 AM
What is the safe range for ultrasonic sound waves for pets...?
2
 
 
1 hour later…
11:32 AM
^lol
@ChrisWhite Lol Kip Thorne
 
12:30 PM
Under an infinitesimal transformation, the stress-energy tensor of a CFT with central charge $c$ behaves as, $\delta_\epsilon T(z) = 2 \partial \epsilon(z) T(z) + \epsilon(z) \partial T(z) + \frac{c}{12}\partial^3 \epsilon(z)$. What would be the easiest way to obtain the finite form of the transformation from this?
 
@deostroll If memory serves me right, the pain threshold level for dogs is approx. 32k hertz frequency-wise, although a more practical answer would be justin beiber's voice, which holds for all animals.
 
@Simha lol
 
So what do you do, @Gowtham ?
 
masters in Material science 2nd year ongoing now
now back at home(India) for break
 
2-year course ?
 
12:46 PM
yes , but most complete thesis by 5th or 6th semester i think . since getting funding is pretty difficult
 
Ah. Within asia ? Indian parents normally don't prefer sending their sons too far. Most of those who do go out, never come back. (Not generalising, but by and large)
 
i came for a short while. I am doing masters at Pennstate , USA . yeah people usually dont come back till finishing , but i came for some personal reasons . last year indian graduate students just going to usa increased by 15%(or something close) i think :P
 
:-) I've heard that German universities give generous scholarships to foreign students over those in other countries, increasing foreign student inflow by a staggering amount (I'm not sure how much tho)
In addition to that, most of them have removed German as a compulsory medium of instruction, replacing with english, dutch, etc.
 
1:03 PM
German universities usually dont fund masters , but they dont have a Tuition fee or very minimal like 500 euros per semester. FOr PhD there are more scholarships from DAAD i think and also from universities itself. I actually did an internship at Stuttgart :) but i felt that learning german is going to be impossible for me :/ and without knowing german getting a job there is next to impossible.
Also doing PhD in german is also very difficult , i dont think many universities offer PhD in german (i maybe wrong here)
i mean english not german hehe . i have this habit of actually trying to mean something and writing/speaking the opposite :P
 
In the US, I've heard it's the other way. While you have to get a score above 1000 in the SAT for any scholarship, scholarships are given for moderate GRE scores...
 
what about you @Simha ? what are you studying
nah , for International students scholarships are very minimal , and its usually funding in the form of TA/RA/GA but only provided after 1 or 2 semesters .
 
I'm a freshman doing statistics at IITM
 
@JamalS what do you think of my attempt to interpret the LSZ reduction formula: physics.stackexchange.com/questions/152967/…
 
*They call UG as freshman here..
 
1:12 PM
esp for masters they dont fund students right away during admission atleast for average or above average students. only for really good profiles like (high CGPA , high GRE , 2 or more publications etc ) i think , but this is just from my experience.
 
@Danu: Reading the addendum now.
 
do you mean IIT , Madras ? O.o
 
@Danu: Well, I certainly like the last words :)
 
@JamalS I wonder whether there is some kind of change of picture that one can perform to achieve a simplification
...what about the rest? :P
 
@Gowtham I'm a touch and go ranker, so it's not so great.. :-)
 
1:15 PM
@Danu: Although it's hand wavy, I think you've done a good job of ascribing a physical interpretation to the operators.
@Danu: Do you have any suggestions for my CFT question in chat?
 
@Simha what do you mean by touch and go ranker ? 1 or 2 rank below the topper ? and also do you study at IIT , Madras or does IITM mean something else ?
 
@JamalS Link?
 
Actually, I was really interested in the BS program at IISc, but couldn't clear the KVPY in the first two attempts. And unfortunately, I can't write it again because I' m a B.mat student..
My real interest is astrophysics
@Gowtham
 
@Simha thats unfortunate, i actually did my B.Tech in Metallurgy and Material science from NIT Trichy :)
also my inherent interest was to go into aerospace or astrophysics too :P i couldnt attend an interview at NISER Bhubaneshwar due to floods at that time . so there went my dream .
@Simha since parents were skeptical about sending me to Punjab university which is the only good university(apart from IITs and MIT,chennai) that offered Aerospace. i had to just bury my dreams and go for MME at NIT , life goes on , but i stay connected to physics through things like SE :)
 
1:30 PM
If possible, I'm changing to physics BS at IITM itself.. statistics is really not my cup of tea.. and too boring.. I don't know if the change is possible yet, however. My proffessors are gonna blast me ! :)
About the physics.se part, me too
:)
 
0
Q: iOS app cannot render a particular question

FlorisI frequently use the iOS app on both an iPhone 5s and 6 plus, and find it convenient. But there is one question that keeps crashing the app: Does Newton's third law apply to momentum or to forces? Every time somebody comments and I want to see what happens, I find that the app quits. There must...

 
Panjab University got all that rep simply because the Bose of 'bos'on once worked there
 
@Simha haha , yeah the system here in india is not flexible which is the most frustrating thing, i wished i could study atleast mechanical at NIT , but apparently quotas and state quotas means if i dont get a good rank i cant pursue my course of liking :/
 
And talking about quotas, the previous gov regime was gonna apply it to private sector businesses as well.. So, yeah, you can say it's pretty screwed up..
 
@Simha i actually heard about Punjab as i was going through Kalpana Chawla's history. i dreamt of becoming an astronaut but having 80% vision in one eye is a very good source of discouragement :/
 
1:37 PM
So, you gonna stay on and pursue Ph.D ?
astronaut at ISRO or NASA ? ;-)
 
Should be good: High performance computing & numerical modeling, Sass-Fee lecture notes by Volker Springel
 
@Simha i actually dont know as of now , maybe i will go for a job . but PhD as of now is 80-20 chance . lets see how this 1 year is gonna change my mindset :P
 
(Sorry for my late reply; I was watching a lecture video and didn't hear the SE beep.)
 
Okay @Gowtham, nice talking with you.. I GTG.. classes.. :)
 
@Simha haha having 80% vision in one eye has huge implications :P so i gave up on it when i knew about my problem , catch you later :)
 
2:06 PM
@JamalS wasn't there a question on exactly this on that website of joshphysics'?
how to get finite transformations from infinitesimal ones
 
@dmckee @hwlau: Ahhh, I see how it happened, but you misunderstood - though I dislike the arXiv pdf names, the ones I posted are not arXiv files
 
 
1 hour later…
3:17 PM
sigh I was about to answer this question (10k+ rep needed) when OP deleted it. Basic failure to read the problem was his problem
 
3:33 PM
@KyleKanos : The (deleted) question seems off-topic anyway.
 
@Qmechanic Also true
But I was going to answer it in the comments
 
@KyleKanos : Ah.
 
user54412
3:45 PM
@Simha How do you want the post to look?
 
user54412
The formatting works best if you place images in "paragraphs" of their own: blank lines above and below the ![description][#] line
 
user54412
see if the following code formats like you want it:
 
user54412
Simply because two light rays intersect at a point it does mean that an image is formed. You need *millions* of light rays to intersect at a point to form an image.

![Your case][1]

![concave mirror][2]

The reason is that the intensity of light emerging from a two-ray intersection is too less for any human eye to detect. For an image formed due to a concave mirror, however, the intensity is clearly much more, allowing the eye to detect the image:

![enter image description here][3]


  [1]: i.stack.imgur.com/6gEvq.png
 
user54412
You can also put the first two images on the same line: ![Your case][1] ![concave mirror][2]
 
@ChrisWhite Ah, thanks Chris for taking the time to dig up all that ! I appreciate ! :-)
 
3:48 PM
Note also that two spaces and then carriage return will result in subsequent newlines
 
user54412
@KyleKanos Really? So markdown encourages use of trailing whitespace?
 
@ChrisWhite Seems that way
 
I couldn't find time to edit it. So, I thought of waiting for tommorow. Why did you take all that trouble, Chris ? Thanks !
 
user54412
2 deleted characters and 8 inserted newlines isn't much trouble ;)
 
user54412
My general suggestion for markdown (and latex) is to make full use of blank lines -- they are syntactically meaningful in both languages, and semantically the locations where they are needed make sense
 
4:07 PM
Nevertheless, you point a pyrometer at the clear night sky it will give you a temperature reading as a summation over a wide band of IR and optical. Also, 2K73 is just an electronics engineering way of writing the decimal point with the unit in question. For example, 2.73 Ohms is more often written as 2R73, or 2.73 kilo-Ohms as 2K73. Or, 2.73 Volts becomes 2V73 — Dirk Bruere 7 hours ago
o.O
 
@KyleKanos Is...that true?
And I thought physics notation was sometimes bad...
 
I don't know
But if it is true, that's kinda mind-boggling
I mean, how many ways can you #$%^ things up doing that?
 
That would then be another satellite crashing, I guess
And what's the benefit? Is it so hard to just write X.YZ UNIT?
 
Yeah, I'm not sure
 
Especially since it becomes obvious in his very comment that 2K73 could be any kilo-prefixed unit
 
4:11 PM
Can you imagine the first guy that thought to do that?
And how everyone else would be like, "WTF does that mean!?"
And somehow that was accepted?
That's just weird
 
Yeah, it is strange.
 
Well, I've gone ahead and fixed it
 
4:32 PM
@KyleKanos How did you know he didn't mean 2.73 kilo-Ohm ;)
 
@ACuriousMind Hmm, I hadn't considered that.
:D
Fun fact: despite getting most of my hats on Physics, I'm ranked #21 site-wide
 
@KyleKanos Yet, you lead physics.SE by a wide margin
 
That's because no one's competing with me
Or even trying to get any
 
4:51 PM
do you know how you got the chameleon hat?
that's really hard to get
 
What?
That's the easiest to get
Actually, probably the 2nd easiest of the secret hats
 
it's suprising how I am 12th place, didn't expect that... It doesn't seem that many people participate... I thought more people would have 10-20 hats...
 
Last year was fairly competitive
 
@KyleKanos but isn't it still a mystery on how to get it?
 
@TAbraham AFAIK, no it's not
 
4:53 PM
so how do you get it?
 
By following directions
 
That's the only hat I can't find info on how to get...
 
....
Where have you looked?
 
According to this:
254
Q: Winter Bash 2014 Secret Hats

KevinSo far, I've unlocked one of the secret hats. I'm wondering what other secret hats are out there and how to earn them?

"Chameleon is tricky. It is currently unknown exactly what the trigger for it is, but it includes editing your profile."
 
So did you do that?
 
4:55 PM
I already edited my profile, the about me section...
I don't need to really edit any thing else..
 
Superfluous edits for the win
 
but there are things you just can't really edit.. such as the email address..
and I also don't have a website..
 
none.com works just fine
 
ok..
plus I don't want to put my age...
anyway, I will play around and try...
thanks...
 
5:35 PM
@KyleKanos "superfluous" ? Which part of your profile is superfluously written ?
 
@Simha He said "I don't need to really edit anything else" as if there were things that needed editing and that nothing else was worth editing
I said "Superfluous edits" to suggest that editing something just to get the hat is possible
 
@KyleKanos concerning the origin of that tortured notation. I'll lay long odds it originated on the Nixie tube display of some (now antique) instrument, and was never meant for use in a written context.
 
@dmckee Hmm, that could be the case. Wonder if that's worth signing onto EE and asking ;)
 
Of course, some programmer probably saw it as a space saving feature and perpetuated it.
 
I'd hate to be that guy who perpetuated such a thing
Like the guy that decided date storage with 2 digits for years was okay
Definitely not forward thinking enough
Should have reserved at least 5 digits for year
 
5:53 PM
I don't believe the gamers don't know how their titles look in the HNQ sidebar, and I fall for them every time: I imprisoned my wife: if I exile her, will we be still married? - sounds very weird until you find out it's just a question about a game mechanics in Crusader Kings.
 
Those ones catch me all the time
 
@ACuriousMind LOL
did you see the four options
execute her
exile her
release her
do nothing , i saw those when i first opened the page LOL
 
6:33 PM
0
Q: Questioning Einstein's view on gravity

user209347Oke, so my mind is blown by Einsteins view on gravity, at least as far as I understand the basics and principles he based his views on. One of the first things that struck me was that most of his equations were based on the fact the photons had no mass, something which is virtually impossible to...

@KyleKanos @Qmechanic thoughts about this one ?
 
@Gowtham It's a duplicate
It's basically asking the same thing as this one:
60
Q: Why would spacetime curvature cause gravity?

user1648764It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it "appears" to be experiencing gravitational acceleration. Do we also say along with it, that the object fly...

 
ah ok
 
user54412
6:55 PM
Oh no not again
 
user54412
-2
Q: How can magic be explained with Physics?

Margaret RosaAssuming that, hypothetically, and for this example only, "magic" means things like magical powers. In movies, games, etc. we witness magic; however, it's never explained how it works with regards to the likeness world in which they take place in to ours. My wonderng is, how can magic be explai...

 
user54412
If we all pile on downvotes silently with no comments it might go away
 
Too late
I commented via custom close
Sorry
I'll not reply though
@ChrisWhite: It got an answer....
 
user54412
well in other news, I'm utterly confused by my research
 
user54412
I seem to be creating magnetic monopoles by changing coordinates
 
7:00 PM
So pick a new topic :D
Aren't magnetic monopoles real though?
 
user54412
@KyleKanos Does this mean my research leads to a Nobel? Oh wait til I tell my adviser the good news :P
 
Do they give out Nobel's for computational work?
 
user54412
no... :( but this is special -- this is groundbreaking, flawed computational work
 
user54412
I also proved it analytically, in plain SR
 
Well, you can win the White award for Faulty Research
 
user54412
7:04 PM
clearly I need to go back to freshman physics and relearn E&M
 
Yeah, maybe your code forgot to do some divergence cleaning?
 
user54412
the thing is, we use a staggered mesh and CT integration -- there is no divergence cleaning to be done
 
user54412
my problem is 1D Riemann problems require the normal component of B to be continuous (equivalent to div(B) = 0 in 1D)
 
Right, f(Bx) = 0d0
Are you at least checking (periodically) about divergences?
 
user54412
but discontinuities in the other B components and/or velocity induce discontinuity in the normal B component if you transform to a different frame -- for example any Lorentz boost not orthogonal to the interface is likely to do it
 
user54412
7:08 PM
this isn't a code problem -- it's a theory problem that prevents me from completing even one timestep
 
user54412
I must be doing something stupid, because certainly I should be able to arbitrarily Lorentz-boost a Riemann problem, solve it, and then Lorentz-boost back, right?
 
Are you using any other codes for reference?
 
user54412
If only -- I'm not aware of any other code that both would have these transformations (needed only for non-diagonal metrics like Kerr) and uses a staggered mesh
 
Hmm
It might be hard with Athena's framework, but could you try using something like Toth's FluxCT? That requires cell-centered values
 
7:29 PM
@KyleKanos They did give out the Nobel prize in Chemistry to Karplus et al. for QM/MM & MD simulations last year. I can't seem to remember anything else on computational work, though.
 
8:02 PM
this is what happens when people don't care about formatting their answers, have a look at this mess...
 
XD well suited picture :D
 
8:19 PM
@DanielSank nice answer on that recent quantum information post, very interesting. I'm personally so fascinated by applications of quantum information in QKD e.g., and lately by learning more about quantum computation and possible schemes, just tooooo much fun...I envy you for working in a related field.
 
I guess I should post on -meta but... is there a way to make tiny little grammar edits that don't bump questions to the front page? I feel sheepish whenever this happens
 
Gaw...misread that post. We should be able to do that.
@pentane No, every edit bumps questions to front page
 
That's kinda unfortunate I guess there's no way around it though
 
 
1 hour later…
10:08 PM
@KyleKanos : Hm, it seems the exclamation mark is not implemented yet. Good idea, though.
 
@Qmechanic Yeah, I noticed that immediately, then saw the post says it's just suggested :(
 
I have lost track of the number of times I've edited a crappy title like "Interacting Hamiltonian" to something which actually reflects the content of the post, such as "Can interacting Hamiltonians always be written in second quantized form?"
There was a meta post about this: meta.physics.stackexchange.com/questions/1000/…
That meta post more or less suggested editing bad titles and trying to make good ones ourselves.
But I kind of wonder whether terrible meaningless titles should be a reason to hold a question, you know, to encourage people to take the two seconds required to make the titles meaningful.
I'll make a meta post about this soon, but I wanted to gauge people's thoughts first.
 
@KyleKanos: can you help? Sometimes I post a comment for a person and I begin the comment with @ and the name of the person. But after I send the comment, I see that the @ with the name of the fellow, disappeared. So, he won't be able to see that I answered him. How to overcome this problem?
 
@Sofia: That happens if the thing you're commenting on was written by that person.
In those cases they get a notification automatically anyway, so there's no need for the @.
For example, if I post a question and you then comment on it, I get a notification automatically.
If then someone else posts a comment and they put @Sofia, both you and I get a notification.
 
@DanielSank: Hi, Daniel. But it happens to me that after different other comments I post a comment, e.g. @alanx, and the @alanx in the beginning of my comment disappears.
@DanielSank: By the way, I got so stuck with other things, that I wasn't able actually even to read the article you sent to me. I don't know how to apologize.
 
10:21 PM
@Sofia: Regarding the article, don't apologize. You are the one who wants to understand it so it's up to you as to when to read it :)
@Sofia: Regarding the comments, can you link me an example?
 
 
@Sofia: It looks like your @ symbols are there. Which ones are missing?
 
@DanielSank: no, I don't find the example. What I find is examples in which I posted a comment after an answer, and the symbol @ with the name of the person, disappeared. So, what I did was to write there "to" and after that the @ symbol with the name, in which case I am no more sure that he will get my comment.
 
@Sofia: I don't understand what you're saying. All the @ symbols in those comments make sense to me. You also say in the comments there that one of your comments disappeared. It's possible that it was either moved to a chat room or removed for some other reason by the moderators. I don't know. But trust me, there's nothing wrong with the site.
 
@DanielSank: Aaa! So, you say that even if I write the @ with the name of the fellow in the middle of the comment, not in the beginning, he will get the message?
 
11:03 PM
@DanielSank I don't think it's a good idea to put a question on hold when such a trivial edit can fix it. Experience suggests that putting questions with a certain characteristic on hold is only somewhat effective at preventing new users from posting questions with that characteristic.
 
@DavidZ: Ok.
@DavidZ: No sense in adding rules that don't help :)
In your opinion, does it make more sense to edit the title or down vote for lack of quality?
I have a pretty strong bias against down voting anything...
 
IMO it makes more sense to edit
 
@DanielSank I would encourage you to get rid of that bias
 
and just expect folks to learn by example?
 
11:08 PM
Yeah, it's reasonable to expect people who actually post here to learn for next time they post. It might be useful to accompany your edit with a comment saying something like "your title was terrible so I fixed it" (perhaps not in those exact words :-P)
Of course such a comment is never required
 
@DavidZ: In my view, down voting and editing are strongly at odds with one another. If I see a crappy question I usually ignore it or edit it. If I were to down vote, I would feel responsible for coming back and up voting if it were edited for improvement.
@DavidZ: Indeed, I have some times been making such comments. I will try to be more consistent about it.
 
I wasn't talking about downvoting and editing in combination. Sure, if you have the option to downvote or edit, then it's better to make the edit. But when something is just bad, you should downvote it. The problem is really when people hold some moral objection to downvoting, saying it's not nice or some such thing.
Incidentally there are some cases where you edit a question and even after editing, the question is still deserving of a downvote.
(same goes for answers, sometimes)
 
Nah, it's not a moral thing for me. I just wouldn't want to leave a down vote on a question which might be edited to be better later. See what I mean?
I think the real issue here, which I've mentioned before in the meta, is how much benefit of the doubt to give to askers.
If I assume they have a good question in mind, I can almost always edit a crappy question into a good one.
 
86
Q: Eeeeek - what happened to my @ salutation?

Mark HendersonI just posted a comment beginning with @username, and my @username part of the comment disappeared (it was the first word in the comment). Is there a lolcat inside the Stack Exchange database nomming on notifications? May I suggest you feed it? P.S. I'm guessing this is a brand spanking new f...

@DanielSank my very strong recommendation is to always vote based on a post's current state. If you think the post might be improved later (but you can't improve it yourself), make a note to come back to it later and check whether your vote needs to be changed.
The exception (if it really is an exception) is when you have an edit to make; in that case, make your edit and the vote based on the state of the post after your edit.
 
so many fundamental questions being asked about QM lately, e.g. 1 or 2, wonder what's causing it :pp
 
11:16 PM
@Sofia more generally see this:
314
Q: How do comment @replies work?

Gnome How do I respond to a specific user when entering my comment? Will they be notified? What do people mean when they talk about "pinging" another user? Related: How do I view my recent replies? Return to the FAQ index

 
@DavidZ:
> make a note to come back to it later and check whether your vote needs to be changed.
Now you're giving me _too much_ benefit of the doubt :)
 
Hello...
 
@Phonon: It's interesting and everyone explains it wrong. That's my guess.
 
@DanielSank yes there are unfortunately a lot of weird/wrong answers...
 
@Phonon: Yes. I've posted about this at length on reddit.com/r/askscience, but not really here.
 
11:19 PM
@DanielSank well I guess my objection is to giving askers the benefit of the doubt. I mean, if someone asks a bad question, then it makes sense to give them a downvote. If their question later becomes good, then at that time it makes sense not to give them a downvote. It doesn't make sense not to give a downvote based on the potential for the question to be good.
If the question has the potential to be good, then I will give the potential to not downvote it ;-)
 
@DanielSank would definitely be nice if you also shared them here on SE
 
@DavidZ: Right, but you see my conundrum, yes? A down vote is forever. The state of a question is not.
@Phonon: Yeah but how?
As an answer to one of these questions?
@Phonon: I started getting into it here: physics.stackexchange.com/questions/153729/…
 
Who here wants to talk about time travel?
 
gotta go. Will think about writing up a nice point of view from an experimentalist on quantum fundamentals.
@TAbraham: Ooooh me me! ...but I have to go. dang!
 
@DanielSank no, downvotes are not forever. You can change them and should do so when appropriate.
 
11:22 PM
@DanielSank yes why not, worst case, do one of those self-question and answer posts
 
@DanielSank Oh... Sorry to miss you...
 
@DanielSank these kinds of fundamental discussions are very valuable imo
@DanielSank I mean it would be already nice to have some of your criticisms commented on some of these dodgy answers, so the readers are more cautious on what they should retain and not
 
anybody else?
is anybody available?
 

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