The h Bar

John Rennie

18:00

@TannerSwett I did some work with very high molecular weight linear silicones, so not elastomers, and they show the same very slow flow.

Tanner Swett

Another question is, when I manipulate a piece of Silly Putty, do those mechanical forces result in the covalent bonds in those molecules breaking and reforming, or do the molecules stay "intact" as they move around?

CooperCape

@JohnRennie Isn't that similar to something to do with super fluidity how things pour themselves out cause them molecules looooooooooong...

Emilio Pisanty

@ACuriousMind yeah, figures

CooperCape

And attachy

John Rennie

@CooperCape you're thinking of rheopectic flow - commonly described as snotty :-)

Slereah

18:02

Can't seem to find any metric generated by a torus

skullpatrol

@EmilioPisanty what did he do?

Slereah

or a cube

I did once find a paper for metrics generated by ellipsoids

John Rennie

@CooperCape it happens when you have an estensional flow regime because the extensional flow pulls the polymers out straight so it's almost like a braid of polymer molecules.

ACuriousMind

@CooperCape "Interesting but annoying" descriibes many aspects of coding ;P

CooperCape

You know one day I might understand more that 10% of the words in that sentence ;p

Phase

18:03

@TannerSwett I think it would be a bit strange if they broke the covalent bonds, that would imply that eventually you'd end up with something other than silly putty. I think you just have mechanical forces that overpower the intermolecular forces / tangling

That's sheer speculation though

John Rennie

And you're right it has that really quite disgusting tendency to keep flowing even when you want it to stop :-)

CooperCape

Currently I'm playing the 'forget the semicolon' game @ACuriousMind

Slereah

the thing with physics chats is that most people have different specialties

So most of the time, people don't know what the others are saying

ACuriousMind

@CooperCape Solution: Don't program in languages that require silly semicolons ;)

2

Slereah

unless it's pretty basic physics

@ACuriousMind all in assembly?

Phase

18:04

@Slereah 2 + 2 - 1 = ?

ACuriousMind

@Slereah I had something like Python in mind, but I guess that works, too

Slereah

@Phase In what algebraic structure are we working

@ACuriousMind Python is awful

John Rennie

@TannerSwett actually I'm not sure, but I think in general just manipulating the putty doesn't cause enough stress to split the silicone molecules. You just pull them free from each other.

Tanner Swett

Makes sense.

Emilio Pisanty

@skullpatrol I... should probably decline to answer that, just to put an end-cap on things. Since the person concerned might read this, I will say that making new accounts to get around question bans is not acceptable on this site. I have no evidence regarding whether or not that happened, but if it did then it is not acceptable. And that's all I say.

Phase

18:05

@Slereah sorry the answer is "Quick maffs"

John Rennie

It is possible to fracture polymers by imposing very high shear rates, and in fact that does happen in car engines where the polymers have been added to the engine oil.

Tanner Swett

I wonder if "snapping" the putty is an exception? "Snapping" the putty seems to make it undergo a mechanical failure similar to a piece of rubber or metal.

Phase

Is Lagrangian being a pain again

John Rennie

@TannerSwett no, you are just pulling the polymer molecules apart.

Phase

why can't some people read the rules of the site

skullpatrol

18:07

@EmilioPisanty thanks for saying something :-)

John Rennie

@TannerSwett Remember that even high Mw polymers have sizes of only a few microns

Tanner Swett

Now, kneaded erasers behave very similarly to Silly Putty. Both substances are "rubbery", and can be mixed by kneading.

But kneaded erasers are more "solid-like".

Silly Putty, when manipulated and then left alone, will form a flat "puddle" with a glossy sheen after a few minutes.

On the other hand, a kneaded eraser, when manipulated and then left alone, may deform a bit, but it will generally retain its shape, and will not attain a glossy sheen, even over the course of years.

John Rennie

@TannerSwett Erasers are extensively crosslinked. In effect all the polymer molecules are linked together to form a single giant molecule. That's why it won't flow.

Tanner Swett

Aha, that makes sense.

John Rennie

In silly putty the silicone polymers are distinct molecules that can flow over and around each other.

0celo7

18:15

@JohnRennie In fortran, how do I read a variable as both a real and an integer?

Phase

@ACuriousMind I haven't played a videogame in over a week, I'm trying to motivate myself to play Plainscape but I feel like if I play videogames again instead of just reading pdfs then I'm not dedicated enough. Do you ever get that?

ACuriousMind

@Phase No, I'm fine with not being very dedicated :)

John Rennie

@TannerSwett I spent 12 years working as a colloid scientist, and stuff like this was a routine part of the job :-)

0celo7

@Phase ACM never studies

he just knows things

also he plays DOTA 12 hours a day

skullpatrol

how is that even possible?

0celo7

18:17

ask him

Anonymous

@0celo7 Probably after Dec 14 I can (got semester exams coming up). I also intend to learn ODE, PDE and group theory during that time.

ACuriousMind

It's not 12 hours, that's a slight exaggeration :P

0celo7

@Blue Do you know measure theory and distribution theory?

Phase

Keyboard stopped existing temporarily

had to restart

skullpatrol

@0celo7 have you read this

Anonymous

18:19

@ACuriousMind Okay, so you do agree that "he just knows things" is not an exaggeration :P

Anonymous

Rather, you have no objections

0celo7

@skullpatrol No

Anonymous

lol

Anonymous

@0celo7 I know a bit of measure theory which I learnt from Reed-Simons and youtube videos

0celo7

@Semiclassical I was apparently the only one who struggled with the homework

for everyone else it just worked

Semiclassical

18:20

Huh

0celo7

all of the physicists used some python code

Semiclassical

lol

0celo7

it's built for solving ODEs with BCs like that

Semiclassical

Huh, neat

0celo7

anyway, trying to get fortran to compute Bessel functions now

Anonymous

18:22

@0celo7 I was planning to learn basic group theory and PDE from Arfken

0celo7

I haven't read that book

But I know what a PDE is

Anonymous

You can teach me then, in December :)

Anonymous

@0celo7 And group theory, lie algebra stuff?

Semiclassical

python is something I should try to pick up at some point

Anonymous

Balarka suggested Artin

Anonymous

18:24

I will probably read from both Artin and Arfken

Semiclassical

I actually did download python at one point

but I don't have a lot of problems to throw at it

Anonymous

Python is actually the best to write quick code

Anonymous

But you won't find mathematica type features in it

0celo7

@Blue I know that too

but it's objectively worse math

Anonymous

Some mathematica libraries are importable in python

Semiclassical

18:27

huh, nice

@0celo7 clarify?

Anonymous

@0celo7 Okay, I know your bias towards algebra :P

0celo7

"Status

Pre-Shipment"

jeez, snail mail is truly snail sometimes

eranreches

@EmilioPisanty Have you found more information on the notation from here physics.stackexchange.com/questions/369217/…?

0celo7

@Semiclassical analysis is far more intuitive and varied than algebra

it's the most physical math

Semiclassical

ohhh

I thought you were responding to something else

careless

as far as symbolic math, though, I'm not sure what else is out there besides Mathematica

I'm sure there's stuff, but

i'm pretty ignorant

@EmilioPisanty oh, I realized/remembered something about that spin problem I was working on

Anonymous

18:36

@Semiclassical Matlab?

Semiclassical

for symbolic math?

eranreches

@Semiclassical yes, there is symbolic package for matlab

0celo7

@Semiclassical It can do symbolic

there's Maple

Semiclassical

namely, Sz and Sx^2-Sy^2 are symmetric w/r/t the reflection y->-y

@eranreches huh

Emilio Pisanty

@eranreches nothing beyond my latest comment

Semiclassical

18:39

and (I think) that's why both of them end up commuting with the operator diag(1,-1,1,-1,...)

doh, should've been Sx^2-Sz^2 above

(another level of explanation is just that Sz, Sx^2-Sz^2 join states with m-m' = even)

Emilio Pisanty

> In the majority of complex spectra the terms are so numerous that it is impracticable to designate them by their configurations. For these spectra the prefixes, a, b, c, d are assigned to the low terms of each type (even or odd) and z, y, x, etc., to those that combine with them (odd or even). The high terms of the same type as the low ones start with the prefix e and continue through, g, etc.

> This notation for complex spectra is first used for Sc n in the present volume. It is also used for all subsequent spectra of the Cai sequence and for the spectra of the Sc i, Ti i, and V i sequences. These spectra are discussed further in sec. 7.5.
In many complex spectra it is impossible to group all known levels into spectroscopic terms. Miscellaneous levels are assigned numbers, and the superscript “ ° ” if they belong to the odd set.

... wait, what?

Semiclassical

oook

Emilio Pisanty

"to those that combine with them"?

"the high terms"?

Semiclassical

that seems pretty confusing

eranreches

I'm also a bit confused. I'm trying to search something relevant on the internet, yet to find something.

Emilio Pisanty

18:45

it is notable that that is the first appearance of the word "high" in that pdf

at least as recognized by ctrl+f

Semiclassical

where mine is going is that I'm pretty sure one should restrict Sz,Sx^2-Sz^2 to the two subspaces of diag(1,-1,1,..)

if I want nontrivial commuting operators

Emilio Pisanty

@Semiclassical that sounds vaguely plausible but I dunno if it'll fit inside my brain atm

Semiclassical

another way to put it is that, if you reorder the basis as {s,s-2,s-4,...,s-1,s-3,...} then Sz is (still) diagonal and Sx^2-Sz^2 is block diagonal

in which case it's obvious that both will commute with diag(1,1,1,1...,-1,-1,-1,...)

...hmmm

eranreches

@EmilioPisanty Is this of relevance? chemistry.stackexchange.com/questions/59211/…

Emilio Pisanty

@eranreches no, those are molecular term symbols

it's much more standard and much more widely used

cf. e.g. chemistry.stackexchange.com/questions/4318/…

eranreches

18:55

I see, though it seems that the letter code is very similar

Emilio Pisanty

@eranreches yeah, I guess that makes sense

it's definitely an additional marker for when you have different states with the same ~~term symbol~~ angular momentum

but it has a bunch of rough edges

if it were just a,b,c,d,e,f,g,... upwards in order of energy for all the terms of the same angular momentum, I'd be fine with it

but what's with a,b,c,d meaning different stuff to e,f,g,...?

dmckee

@ACuriousMind So ... using tikz in LaTeX is out, then?

Emilio Pisanty

and what does z,y,x,... mean?

@dmckee yes

just because of how painful tikz is

regardless of semicolons or the lack thereof

dmckee

::chuckels::

Abcd

@EmilioPisanty what's "cf"?

dmckee

19:00

I've been using it on and off for years, and I'm still at the mokey-see-monkey-do stage.

It's horrible, but it works.

Emilio Pisanty

@Abcd abbreviation of the latin confer, compare

Abcd

Ok.

dmckee

Sadly for snobbery, but probably to the benefit of widespread comprehension most editors are recommending against using such Latin abbreviations, these days.

But I'm finding it hard to break the habit.

Emilio Pisanty

(not to be confused with i.e. = id est = that is)

@dmckee are we getting rid of et al.?

dmckee

Or with e.g. the latic for which I don't know but which means "for example".

2

@EmilioPisanty I'm not: "and others" takes up to much space in my resume.

Emilio Pisanty

19:04

@dmckee "exempli gratia"

e.g.

dmckee

And a lot of those editors are forgiving of 'etc.' as well.

Emilio Pisanty

... which makes your comment pretty funny =P

Phase

My favourite latin abbreviation is Q.E.D. Which means "I wasn't sure what to do for the last step of this proof so I'll just say it's trivial and my result is my hypothesis"

Emilio Pisanty

frankly, cf. / e.g. / i.e. / et al. / id. / ibid. / viz. are perfectly standard

dmckee

'quod erat demonstratum' or something like that.

Emilio Pisanty

19:07

I'd go as far as classing attempts to get rid of them as anti-snobbery snobbery

Phase

close

demonstrandum iirc

Semiclassical

reverse snobbery

Abcd

"Hence Proved" is better than Q.E.D @Phase, isn't it?

Emilio Pisanty

@Abcd if you just want to convince your readers, then yes

dmckee

@Abcd Or just "Ta da!".

Abcd

19:10

lol.

Emilio Pisanty

though I'd question why you're using either of those instead of just putting a Halmos box

Phase

@Abcd I prefer "Just fucking mark it right already"

I have legitimately lost marks for not explicitly stating that (-1 * -1) = 1 going from one line to another

I take no chances anymore

Emilio Pisanty

hmmmmm, lemme try something, $$\ \tag{∎}$$

2

oooh, yeah, that's a nice Halmos

... though of course MathJax's display of unicode symbols is inconsistent and changes depending on the viewer's browser's standard font

dmckee

@EmilioPisanty Have you noticed the number of questions about drawing those things on [latex.se]?

Emilio Pisanty

@dmckee probably

dmckee

19:12

But I translate them in my head to QED because that is what my textbook on Euclid said in 9th grade..

Emilio Pisanty

I never know how to make them and I'm never satisfied with how easy it is to find a good answer

@dmckee they taught you straight from Euclid in 9th grade?

when was this?

1850?

dmckee

1985. But it was one of the best public school districts in the nation and I was on the advanced math track. And it was the book on Euclid, not Euclid's book. Sorry.

Emilio Pisanty

still

Phase

That must've been before @ACuriousMind was even coded

Emilio Pisanty

ah

dmckee

19:14

@EmilioPisanty My teacher did keep a translation of Euclid around, it was much denser than our text.

Emilio Pisanty

@dmckee ah, good

I did about six weeks of straight-from-Euclid at the start of uni

complete waste of time

dmckee

I didn't get along with that teacher at all, but looking back she was a good egg.

I feel sorry for what I put her through.

Emilio Pisanty

particularly since we were meant to be doing analytical geometry

$\qed$?

ok, no

$\qedsymbol$

also no

GPhys

@dmckee latex.se is just a front for code golf with TikZ pictures

3

Semiclassical

$\square$

Emilio Pisanty

19:22

@Semiclassical too square

so to speak

Semiclassical

pff

Phase

19:41

$\Box$

God damn it

Box is identical to Square it would seem

user685252

Hi @Lagranian

CooperCape

isn't there a weird one like $\bat$ ?

That might just be the word one

Emilio Pisanty

@CooperCape that produces an actual bat?

CooperCape

I think so

dextify says textmode only

Emilio Pisanty

that'll behave differently on mathjax vs latex, and on the latter it'll depend on what packages you're loading

CooperCape

19:46

yeah

says it reqs

\usepackage{ marvosym }

Emilio Pisanty

but here you can try $\Huge 🦇$

didn't work

CooperCape

did for me

Phase

@EmilioPisanty I see the bat

CooperCape

huge bat emoji thing

Anonymous

It's showing a three legged bat

Emilio Pisanty

19:48

35 mins ago, by Emilio Pisanty

... though of course MathJax's display of unicode symbols is inconsistent and changes depending on the viewer's browser's standard font

Anonymous

Or is that a tail or something?

Phase

@Blue ;)

CooperCape

Ahh I see... I really wanna get LaTeX nerdy ;p

Phase

It's a well endowed bat

obviously

CooperCape

Oh yeah @Blue we discussed dibasic acids in chem today... not quite the tri but... 2/3rds of the way there... if you think about it that way..

Anonymous

19:49

CooperCape

Can't you draw circuit diagrams in LaTeX or something crazy like that?

Wait they have fingers wth...

Emilio Pisanty

$\Large 🙈 🙉 🙊 🐵🐒 🦍🐶 🐕 🐩 🐺 🦊🐱 🐈 🦁 🐯 🐅🐆🐴 🐎🦄🦓🐮🐂🐃🐄🐷🐖🐗🐽$ $\Large 🐏🐑 🐐 🐪🐫🦒🐘 🦏🐭 🐁 🐀🐹 🐰 🐇 🐿 🦔🦇🐻 🐨 🐼🐾🦃 🐔 🐓🐣🐤 🐥 🐦 🐧 🕊$ $\Large 🦅🦆🦉🐸🐊🐢 🦎🐍 🐲 🐉 🦕🦖🐳 🐋 🐬 🐟 🐠 🐡 🦈🐙 🐚 🦀 🦐🦑🐌 🦋🐛 🐜 🐝 🐞 🦗🕷 🕸 🦂 ☃ ⛄ $

2

damn

Phase

jesus

of the screen it g-. Everytime I type a message it pushes my screen to the right

Thanks for editing

Emilio Pisanty

$\displaystyle \Huge 🐲$

4

nice

Phase

"show math as tex command"

It's so useful.

Emilio Pisanty

19:55

@Phase or just reload chat

Phase

yeah but either way

no dragon :'(

CooperCape

I can just click on the messages and it comes up with the command to the right of it

Emilio Pisanty

55

Q: Smileys in LaTeX

I would like to include smileys in my LaTeX document. Is there any package with lots of different smileys? In mnsymbol and wasysym, I found some general symbols: \documentclass{article} \usepackage{MnSymbol,wasysym} \begin{document} wasysym: \smiley{} \frownie{} \blacksmiley{} MnSymbol: \(\smi...

user685252

Someone has waaay too much time on their hands :P

Phase

"55 score"

Emilio Pisanty

19:59

Anybody who uses $🐲$ as a variable symbol in a scientific paper, using the xelatex/lualatex+unicode emoji route above or otherwise, gets 100 internet points

Phase

🐲

Oh I can copy and paste it, makes it easier

$\frac{d}{d🐲} 🐲^🐲 = 🐲^🐲 (ln(🐲) + 1)$

6

user685252

nice

CooperCape

Phase I appreciate that that is actually 100% legit maths

Can't even argue with that

crikey

Phase

Do you take me for a phoney? I got my A level tier maths on point

CooperCape

Pretty sure in my A level course we don't even differentiate x^x

Phase

20:04

You've probably differentiated by raising / lowering powers though right?

CooperCape

yeah ofc

Phase

I mean logarithmically btw

CooperCape

Oh no

Phase

Do you get the integral above?

user685252

@EmilioPisanty how much did you cover?

Emilio Pisanty

20:05

@user685252 no idea

CooperCape

I mean I understand it as a thing but I couldn't personally work out $\frac{d}{dx}x^x$

Emilio Pisanty

too much

Anonymous

@CooperCape If you see such stuff, just take log :P

Phase

If $y = 🐲^🐲$, then you can make it easier by using $ln(y) = ln(🐲^🐲) = 🐲ln(🐲)$. Then differentiate it, and you'll get $\frac{1}{y} y' = \frac{🐲}{🐲} + ln(🐲) = ln(🐲) + 1$, then since you have an explicit form of y you can multiply across and get $y' = 🐲^🐲 (ln(🐲) + 1)$

It's cool I wrote it all out

CooperCape

Ahhhh okay

that's really cool

thanks

Phase

20:08

Proposal to change the convention of $x$ for single variable functions to $🐲$

CooperCape

Create a latex package that does that?

Phase

I suppose I could if I understood LaTeX

Unfortunately I don't

user685252

Descartes is rolling over in his grave :P

CooperCape

propose it to emilio...

Phase

Hmmm...

Emilio Pisanty

20:11

@Phase just write f(\x) and d/d\x and define a macro \x that'll do what you want

if you can do something in latex, then you can automate it inside a macro

Phase

@0celo7 is there an isomorphism from the space of vector elements like 🐲 to the space of vector elements like 🐉, such that $🐉 = <🐉*, ->$, such that $🐉:🐲 \to 🐍 \in 🦎$

I've actually never used LaTeX

CooperCape

jeez...

Sir Cumference

Variable star designation

Variable stars are designated using a variation on the Bayer designation format of an identifying label (as described below) combined with the Latin genitive of the name of the constellation in which the star lies. See List of constellations for a list of constellations and the genitive forms of their names. The current naming system is: Stars with existing Greek letter Bayer designations are not given new designations. Otherwise, start with the letter R and go through Z. Continue with RR...RZ, then use SS...SZ, TT...TZ and so on until ZZ. Use AA...AZ, BB...BZ, CC...CZ and so on until reaching...

This has to be the worst naming system I've ever seen

> Stars with existing Greek letter Bayer designations are not given new designations.
Otherwise, start with the letter R and go through Z.
Continue with RR...RZ, then use SS...SZ, TT...TZ and so on until ZZ.
Use AA...AZ, BB...BZ, CC...CZ and so on until reaching QZ, omitting J in both the first and second positions.
Abandon the Latin script after 334 combinations of letters and start naming stars with V335, V336, and so on.

Phase

@SirCumference i dont get pretty much the entirety of Astro tbh.

Sir Cumference

@Phase Astronomy just has really bad terminology

2

Phase

20:19

ahahaha

Sir Cumference

This annoys so many chemists

Phase

You should split that table into two sections "light metals" and "heavy metals"

i think thats the most detail my lecturers have used : /

Sir Cumference

@Phase They also have a unique name for every kind of apsis.

Like we couldn't have just stuck with "apapsis" and "periapsis"?

Phase

Astro people name things in such a boring way compared to particle physicists

Sir Cumference

@Phase Why particle physics in particular? Nothing really stands out there imo

Phase

20:25

Flavour, for one

Strangeness

Charm

etc

user685252

Quark

Phase

^ universally mispronounced by half the people who've read it

user685252

Same as "tomato" :P

CooperCape

it's pronounced similar to cork right?

but with a bit of a 'qu'

Sir Cumference

@Phase I'd say chemistry has the most consistent, though most boring name for things

CooperCape

20:31

I blame IUPAC

Sir Cumference

It blows my mind though that no one can agree on a single definition for "acid"

(in the chemistry sense >_>)

Phase

@SirCumference it's something that bubbles, is faintly green and in cartoons

damn it beat me to it

Anonymous

@SirCumference It's perfectly defined in chemistry, what's the problem ? There are just different categories of acids Arrhenius acid, Lewis acids, etc..

Anonymous

You can define each of them separately

user685252

The definition of an acid is that which is acidic :P

GPhys

20:39

I need a vacation

can PhD students take vacations?

Anonymous

@GPhys Why not? :P

Anonymous

Go for a Mars trip

user685252

Pre-sabbatical?

0celo7

@GPhys weakling

user685252

since when did you become an intellectual ironman?

0celo7

20:47

Since always

Emotions are BS chemical signals

user685252

even iron rusts :P

Anonymous

@0celo7 Yeah, but you do show emotions, a lot XD

0celo7

I fake those

Anonymous

I don't believe :P

user685252

it's hard to make an accurate judgment in here

too much missing information

<_<

emoticons are not emotions

0celo7

20:58

@Blue I’m a sociopath

Anonymous

Me too.

Anonymous

I just pretend not to be

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