The h Bar - 2014-11-14

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12:11 AM

@AndréNeves So the answer to that question -- once the tap is opened, a shock wave forms in the pipe as the air rushes into the vacuum. You are exactly correct in the harmonic oscillator part. As the shock passes rapidly, it overshoots the pressure (but the sensor is not fast enough to pick up the shock wave -- the diameter of the sensor hole is probably bigger than the shock width, plus the time sampling is too low to pick it up so it averages in both space and time and "misses" the peak)

Once the shock passes into the chamber and the chamber fills with air, you'll have a pressure wave reflecting off the right surface of the chamber and moving back upstream

Some of that wave will enter the pipe, some will reflect off the left edge of the chamber

So there will be compression waves followed by rarefaction waves due to the acoustic interactions off the chamber walls from the initial shock wave

Which will lead to oscillations about the final pressure. Since air is not very viscous, it will take awhile to damp down all the oscillations

So you're spot on with the under-damped harmonic oscillator features. But we can't just go out and tell OP that answer. At least not right away. In a few weeks, when we are reasonably convinced the assignment has been turned in and there's no impropriety involved, we can post a real answer

@tpg2114: Are you sure the person you are talking to can hear you?

@ACuriousMind I was pretty sure you could tag any user in chat, but it won't auto-complete their name unless they've been in chat recently

I could be wrong though

It only pings them if they were in the room the last two days or so

I thought that's what was needed for auto-complete the name but it pinged anybody any time if you typed the name correctly. If not, oh well. I can't alert that person on the comment threads without also letting OP know the answer is sitting in chat :)

@tpg2114 Apparently not, pings are indeed only applied to users active within the last 2 days.

12:27 AM

Lame. Oh well. I did my civic duty by not posting the answer on the question while also feeling better about getting it out of my head

So still a victory for me!

Heh, talking to oneself sometimes has its uses :)

Talking to people who know the answers to the questions I have is better than asking myself those questions sometimes though

2 hours later…

2:33 AM

@ManishEarth @DavidZ @dmckee Alright mod team, this one is above my pay grade: redacted

I'm tapping out of that thread

@tpg2114 $1 says Clemson wins by more than 14

@KyleKanos If you Clemson folks were smart enough to answer any of my questions, I'd bet a nice bounty that GT will win ;)

What questions do you have?

I dunno, there's 11 I've asked on Phys.SE

Right now I have some questions about characteristic boundary conditions... they are kicking my ass man

On another note, somebody is getting feisty and threatening people: physics.stackexchange.com/questions/146668/…

3:05 AM

@tpg2114 Good call for tapping out, and I've done something about it. I've also edited your chat comment just to keep things on the QT. I hope that this does not offend.

3:33 AM

@dmckee Such censorship! I actually don't mind, but you should also redact my previous comment just before you sent me this

Brandon Enright

4:21 AM

@Qmechanic heads up I created the shape-dynamics tag. It seems like we should have one but of course I'd like to run it by you too.

3 hours later…

7:26 AM

@BrandonEnright : It seems that the machs-principle tag could cover shape dynamics.

Brandon Enright

7:50 AM

@Qmechanic Ah interesting and good point. I'd suggest shape-dynamics be a tag synonym for machs-principle but I never did figure out the tag voting system.

4 hours later…

11:30 AM

@BrandonEnright : Done.

2 hours later…

1:07 PM

For those who care about mathematicians: Grothendieck died yesterday :(

1:17 PM

@Danu I heard :(

1:30 PM

Damnit, I may have to change my username, that one's been here before me

@Danu I thought he'd become some sort of hermit - who informedus of his death?

@ACuriousMind He must have had friends, just not ones that publicized it

Hm, possible. I still suspect he didn't want his death to be known

2:38 PM

sigh.....I brought the wrong power cord for my laptop to work

Guess I'll be spending time learning about GR and Stochastic Calculus when the battery dies

@KyleKanos: Oh, stochastic calculus? Which text are you using?

Handbook of Stochastic Methods is pretty good

@JamalS Jacobs, Stochastic Processes for Physicists

@Danu : Grothendieck, eccentric maths genius, dies in France.

4

2:59 PM

Answer of the day!

@New_new_newbie Well played.

@KyleKanos: Played?

Slightly sarcastic statement in regards to the linked answer. See this Urban Dictionary definition of the phrase

@KyleKanos - Haha! Yes. (Assuming I got it correctly now...)

Phew. This got deleted quickly. (Just noticed that my -1 got restored.)

But this fast deletion sometimes robs (rep-poor) people of fun.

Waffle's Crazy Peanut

Yeah, yeah... Silly me, I'm late!

3:15 PM

@New_new_newbie Well, when you hit 10k, you can still see them!

Waffle's Crazy Peanut

@KyleKanos Now you're just showing off! :P

These people keep saying it, but I don't get it (obviously, since I don't know what that esteemed "create a human female" question really was). But regarding the above delete-worthy answer, it is really silly to crave for 10k just to read this answer!

@KyleKanos Yeah. In about 5 years :(

@Waffle'sCrazyPeanut Am not...just point out a fact of the SE system

@New_new_newbie It took me about 1.25 years to get it. It also took ACuriousMind about 8 months to get it

Or maybe I don't have to wait for that long.

I could just hack your account!

But again, to read that!

I could take a screenshot for you....

3:19 PM

Pleaseee :)

Waffle's Crazy Peanut

@New_new_newbie I guess it'd still be fun to read deleted answers. Pop into any question and a funny answer will be there waiting for you! :D

@Waffle'sCrazyPeanut Exactly. Mods are killjoys, they delete all the fun.

deleted...

Huh, wrong one

teasing ?

No, I just clicked the wrong one

...deleted so Danu can't see!

2

There it is

But let me know when you read it, because I'm in with Chris on teasing Danu about it

Waffle's Crazy Peanut

3:22 PM

@KyleKanos I can still see that! Ah, look... A plot gallery! :P

And I need to delete that message before too long

Haha

Waffle's Crazy Peanut

@KyleKanos You can always delete it... We can still see that! :D

@KyleKanos Haha.

Yeah I saw it.

And it changed the link!

Poor @Danu. Hahahaha ...

Waffle's Crazy Peanut

3:25 PM

For a long time, I had this question, "Is it just me, or everyone who lives out in the internet world have dozens of tabs, which they switch often?"

@KyleKanos - if only I could give you a bounty for that screenshot :P

Lol

Waffle's Crazy Peanut

@KyleKanos LOL! That's funny... Thanks for the screenshot! ;-)

No problem

But: you guys can't talk about it's contents to Danu

2

:D

And Danu will feel robbed when he gets to see the transcript of this session.

3:27 PM

Yep

That he will

Waffle's Crazy Peanut

Heh, he'll surely ping me! :)

Hahaha... What a happy note to sign out on!

Bye guys :)

See ya!

Waffle's Crazy Peanut

@New_new_newbie C'ya around later...

"See ya" guys too. Bye :)

Waffle's Crazy Peanut

3:29 PM

@KyleKanos: Now, back to the plot gallery... What are those? "rey... rey... rey..." ?

I can quite get "SN1006" but not the others...

In order (top row, L->R, then bottom row): a folder, Lord Blackett, 2 radial profiles of a Type II SNR, a 2D map of a Type II SNR, the outer shell of SN 1006 in optical (via HST), the magnetohydrodynamic (MHD) equations, my presentation on SN 1006, a radio image of SN 1006, 2 polarization images of SN 1006, 6 images of SN 1006 in different wavebands (x-ray, gamma-ray, optical, radio, 2x X-ray), another radio image of SN 1006, and I forget

If you want more details about any of them, let me know and I can expand on it

Waffle's Crazy Peanut

@KyleKanos Now, I'm curious. Why Blackett?

We do something called "5 Fun Facts about a Famous Dead Physicist" in our Local Group (LG) meetings--a weekly seminar for our astro group

I chose Blackett that week because he was quoted as saying, "Electromagnetism is difficult, hydrodynamics is very difficult, but magnetohydrodynamics is damn difficult"

Waffle's Crazy Peanut

Nice! So, that's one of your assignments...

@KyleKanos Hey, I took only five months :P

Waffle's Crazy Peanut

3:37 PM

@KyleKanos :P

@ACuriousMind Order of magnitude

@ACuriousMind: Somehow this answer was denied deletion via my flag, despite it being a clear case of Link-only

Then everyone gets it in O(1 year), right? :D

(though it was later converted to a comment by Qmechanic)

And apparently the whole thing was deleted....interesting

@KyleKanos It was denied deletion because Brandon and John saved it by voting "Looks OK".

@ACuriousMind Which makes zero sense to me. If that wasn't a Link-only what the #$% is?

3:41 PM

I have no clue - you gotta ask them, as you can see, I recommended deletion, too

I know

On an unrelated note, my code spent 10,000 seconds on two lines (total run time of in the range of 3.5-4 hrs)

The two lines: r=0; l=0

Zeroing out two 3D arrays :/

4:17 PM

@KyleKanos How big are they?

1 hour later…

5:43 PM

@ACuriousMind 5,5,2

(Sorry for late response, I was in class)

But those 2 arrays are zeroed out nx*ny*nz times each dt for lots and lots of dt's.

Ah...I was just going to say that that looks a bit small to spend 10k seconds on

Fortunately, I think I can fix that

The two variables stem from the Jacobian matrix in hydrodynamics

Those zero's are always zeros for each i, j, k index

So if I zero them out before it's called nx*ny*nz times, I won't need to zero them out in the subroutine

Because only the non-zero values are changed in that subroutine

Sounds legit

6:28 PM

Damn @KyleKanos always having exactly 1000 rep more than me

Stop being an asymptote!

That is rather impressive

Congrats on breaking 10k!

don't change the subject

Have you seen this yet?

i have not

Chris showed me that when I hit 10k

6:30 PM

hahaha!

He said that he was teasing Danu about the contents (since it takes 10k to see it)

that's a hilarious post

I wish I could see what answers it would accrue

Love how he included the character traits of her too... as if our technology is so advanced that we could say "Oh, yes, let me just order that for you. Where do you want it shipped?"

I would have said, "No. But I could suggest lowering your standards a little bit. You never know what you might find out (about yourself and someone else)"

Item #2 is more bizarre for the latter quantifier

and without it?

it seems like his standards are pretty low

and I agree

Really?

6:33 PM

yeah, does that mean she never stops?

I'm curious why #4 is necessary

perhaps that explains the need for the end of #2

That is an interesting point

(the link between #4 and #2, I mean)

His standards are not the issue. His treatment of human beings purely as a means to achieve personal satisfaction is.

yes, that's it

that said, I wouldn't be surprised if there was a non-insignificant population of women that fulfill these criteria

except the last part of #2

or all of #2

@Jim I think the last part of #2 is fulfilled by any woman that can achieve orgasm through masturbation, isn't it?

I said standards because he said that none are perfect enough for him

6:37 PM

@ACuriousMind I'd think so, but maybe he literally means 100% of the time

@Jim Yeah, but then there's the part about them liking him, too

redacted

@KyleKanos and yet he didn't actually include things normally considered standards (except point #1)

I'm gonna delete that last comment

That was mean

People, we might have a tough time finding someone that satisfies #3

6:40 PM

I'll find out in 3 hours if my adjustment was right

why 3 hours?

Code is running and says 2.5 hours until completion

(cf. this comment and subsequent conversation)

what language could you possibly be using that takes 3 hours to initialize a 3d array to zeros

?

It's a full-scale simulation I'm doing

I'm doing a timing analysis to see where hot-spots are in the code

See what I can do to speed them up

@KyleKanos That works as a joke only with people you know very well, the internet usually is not such a place. But as you deleted it yourself, no harm done.

6:42 PM

ah ok, I thought this was another 10000 seconds for r=0

@Jim Fortran, obviously ;D

@Jim I'm getting $dt\sim0.00234$ seconds from $t=0$ until $t=30$, so about 13k re-initializations instead of $13\times10^3\cdot300^2\sim1.25\cdot10^9$

@ACuriousMind Fortran is fast. In 3 hours you can solve a 3d non-linear system of 20 PDEs with a small step size and value-dependent ending criteria

@Jim I said that because Kyle often talks about how he mostly uses Fortran, and how fast it is ;)

and how extensive its math library is

@KyleKanos You know when he asks "built with physics" I thought he was going to suggest atom-by-atom. Not a cloning lab

6:47 PM

@Jim Did you recognize the image that he linked?

oh good lord

I hadn't even looked at it

I'm embarrassed to say I recognize it

Don't be embarrassed!

That tells me quite a bit about this guy

I had 2 PSX memory cards that had about 8 saves from different runs that had more than 60 hours put into that game

I had almost 60 hours from just 1 save

6:50 PM

@Jim Where does it come from? I've wondered for quite a time now

Final Fantasy 7

FF7

Ah. And my lack of JRPG knowledge shows again :D

Considered one of the greatest video games ever

(Often beat out by the glitch-heavy Ocarina of Time)

(and rightly so)

6:51 PM

Given how glitchy OoT is, I'm not so sure

It can be beaten in less than 20 minutes....

Even with the PC glitched version of FF7, it still takes about 3 hours to beat it

Just because it's short doesn't mean it's not better

But Zelda games always garnered more interest in the populous than the JRPGs

Enjoyed by a broader audience

Still, I wouldn't choose either for best game of all time

@Jim Only for the fact that Zelda & Mario games came packaged with Nintendo systems, FF games never enjoyed that

@Jim So, what would you choose?

6:54 PM

No idea

I can just think of other games I also wouldn't choose that are better

img2.wikia.nocookie.net/__cb20110831172139/pokemon/images/thumb/…Pokémon-I_Choose_You.png/180px-IL001-_Pokémon-_I_Choose_You.webp

Damn that didn't work as well as I thought it would

error 404

I'd personally choose Final Fantasy Tactics

@Jim Obviously, given the link, it was supposed to be Pokemon stuff

what about the phrase "of all time" means "only games at least 10 years old"?

Nothing

6:56 PM

Yay

I've watched TheClaude play FFT many times.

4 hour streams on Twitch

FTW

Of course, right now I'm listening to XeroKynos do a 100% run of FF7

Which he says will be followed by a 100% run of FF8

I like many new games...but when it comes to the best, those I have played so often I have them almost memorized, those are invariably the older ones

In that case, if you can think of anything wrong with Portal other than its having the most annoying fans on the planet, then it's not the best. Otherwise, give it some thought

Portal (both parts) are really great.

Portal was enjoyable, but once you solved the puzzles it quickly became mundane

That is to say its replay value was awful

6:59 PM

Alright, without user mods and the multiplayer aspect of #2, I have to concede that it lacks in the replay department

you win

Never played 2, so I can't rightly judge

I've seen some guys run it on AGDQ

Does that count?

Still, that's a great review if the top negative aspect is that you can't play it again and again

and no, it doesn't count

Damn

0

Q: Q&A: What is the inertia tensor of a hexadron/hexagon extrusion?

I looked around for a long time for the inertia tensor of an extruded hexagon, and thought after a while that I would probably have already solved it by then. I don't want anyone to reinvent the wheel like I did, so here is the answer to reward the skilful Googler: Answer $$[I]=\begin{pmatrix} ...

classical-mechanics moment-of-inertia inertia

Um...what?

So the guy seems to have asked and answered the question in the question box....

And a homework question at that...

indeed

7:05 PM

What do we do with self-answered questions that are off-topic?!

close them as off-topic. Their having an answer is irrelevant

There's no point in closing them, because they already have the answer closing is intended to block

Or rather, people can earn just as much rep with closed off-topic self-answered questions as they can with non-closed ones

closing them also keeps them off the site and deters others from posting similar things

I still voted to close it

It is really a weird situation

But yeah, VTC doesn't do harm

7:09 PM

@KyleKanos You've done an amazing job of changing the subject from you being a complete and utter asymptote (and I'm not being hyperbolic)

I didn't even notice until now

Well, we all have a limit, no?

Yay, nerd puns

Well, let's just hope we don't diverge into such a subject

ya, no. I'm all out of them

Well gravity can pull you back into the swing of things

7:13 PM

I really don't know whether the sound I just made was a groan or a chuckle

it was a gruckle

Haha, glad I can make people do something

A classmate gave a presentation on disk gaps in T Tauri stars (often thought to be a young planet clearing its orbit). One slide had a plot from some guy's paper that apparently put a data point actually on the x-axis.

I said to my advisor, sitting next to me, I guess that was published in A&A

He laughed (he's the editor of ApJ)

I do not get it

We were making fun of A&A

Unrelated edit question: Do I approve an edit that is an improvement, but is an edit of a closed post and does not adress the closing reason?

7:17 PM

yes

@KyleKanos I don't even know what A&A is :P

@ACuriousMind Astronomy and Astrophysics. It's a journal that's often where observers publish their data. ApJ = Astrophysical Journal is often where theorists published

@ACuriousMind Yeah, why not?

and was the data point not supposed to be on the x-axis?

It shouldn't be if you want people to recognize that it's there!

@KyleKanos Because edits send these questions into the reopen queue - suggesting that edits to closed questions should strive to make them on-topic

7:19 PM

@ACuriousMind We'll get a free Reopen Queue count out of it

review the suggested edit, not the post it's in

Alright, I approved it

@KyleKanos Well, you could always color the point or something...

or make it a triangle

or have error bars for experimental data

It's a cross!

user image

And no error bars

The circle is mine

Ok, that's horrible :D

7:23 PM

they cut off the bottom of the cross, no wonder you can't tell it's there

If I were a reviewer, I'd have asked them why they just didn't stop at 9.5

They'd have said, "Oh there's a point at -10" and I would have said, "Oh, why didn't you go to -10.5?"

3 authors on the paper too

-10.5 isn't a pretty number

Maybe

Then I guess -11 it is

Or any number where it's visible!

not as even as -10

....observers....

7:26 PM

they observe everything but how their graphs look

It seems that way

haha! 990!

So you're trying to converge?

I'd not mind passing the asymptote either. Really I just can't stand always being the same amount separated

it's too coincidental

One of us needs a good HNQ answer to stop it

7:30 PM

HNQ?

hot network question

Hot Network Question

Aaaaand 1000

what!?

Noooooooo!

30

A: How did they take photos of Jupiter?

This was just going to be a comment, but it got too long. Technically the picture is a fake. It's actually a composite image of what we would see with our eyes (visible light) blended with light seen in 3 different filters (see this NASA article on the different filters on-board Cassini, the p...

Just a moment ago

it's a conspiracy. I swear it

7:32 PM

And apparently another 10

Is that back on the front page or something?

well you just put it on chat. It was probably A Curious Mind for the second 10

No, not there

Brandon Enright

@Jim me

Maybe

or Brandon

7:32 PM

Ah, that 'splains it

well, as long as it's not exactly 1000 anymore

Hold on...finding 2 questions to upvote

:D

but I could use a bit of a rep cushion to put my mind at ease

2?

Wait, no

We're the same again

Well, same 1k difference

Brandon Enright

Congruent mod 1000.

7:35 PM

now y'all are just exacerbating the problem

Or maybe you're just too worked up over it?

me? impossible

A Jim is never too worked up. Nor is he not worked up enough. He gets worked up precisely as much as he means to

I wish some other Jims were around so I'd ask them if that's true

Even if they said differently, as King of the Jims, I'm automatically right about all matters pertaining to Jimistan

What if I ask the Queen of Jims?

Or the pope, if you're not a heathen nation ;)

7:42 PM

I throw glitter at you, claim diplomatic immunity, and run away

Glitter?

What color?

multi-coloured

Fancy

Also, brilliant Gandalf reference

You may call me Jimdalf the Grey

5

I think you just found a new username

7:46 PM

Okay Jimdalf the Grey

@KyleKanos ahem I believe there's a suffix

Thank you. I didn't go through 4 years of colour graduate school to be called Jimdalf the whatever-colour-is-in-right-now

So should we call you Dr Jimdalf the Grey, instead of Mr Jimdalf the Grey?

Well, if you go back to slightly earlier posts, it's technically King Jimdalf the Grey

but, I don't want to seem too aloof

Dr King Jimdalf the Grey?

or King Dr Jimdalf the Grey?

Or

Should we just go with Tim

Jim the Enchanter?

7:52 PM

Now you've got an Identity Crisis

user image

3

.....that is what you've been doing the last 10 minutes?

lol no. Just the last 5

Photoshop lvl: Master

And that's not even Gandalf under that...thing, unless my memory betrays me

No, it's Tim the Enchanter

8:07 PM

Ahhhh

I'm using my work computer

no photo editor of any kind

Wish I had those powers....I'd just blow things up all day long

It'd be fun

1 hour later…

9:29 PM

@Danu sorry for the late reply, been busy. Yeah was a nice comeback by Anand, such a tough game. All options back on table again. 2 last draws been also fun. I think tomorrow will be a bloodbath on the board.

9:41 PM

0

Q: Scalable tool (engine) for simulating the universe

Does there exist a large scale scalable tool (engine) for simulating the universe that incorporates both quantum mechanics and cosmology, i.e. micro & macro scales? (It would be best if this tool simulated the entire universe using quantum mechanics only, without any corrections to the model tha...

quantum-mechanics simulation software

This guy's a bit optimistic about what we can do...

I think optimism is an understatement

9:57 PM

Gaahhhh no!!!! I edited the wrong file :(. 3 hours later, and it showed the same thing.

I almost feel like crying inside

But I guess I can just run it tonight whilst doing nothing

@Jim no, that's Tim

NOBODY EXPECTS THE MANISH INQUISITION

8

bans everyone

Well played!

(not that my name rhymes with spanish, but for the sake of the joke fine :p )

@ManishEarth How is it pronounced? Mahn-eesh?

Well, if it means anything to you, I always pronounce it as if it does rhyme with Spanish

And it's time for me to head out

see ya guys later!

10:04 PM

@ACuriousMind Muh-neesh

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