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00:00
That's probably a good way to think of why they're so nice.
Something like that
@DanielSank I think they're nice because they're $f(z)$ and not $f(x,y)$. If you have $y$ dependence you automatically have $x$ dependence in a nice way.
$f(x,y)=y^2$ is bad in a sense because $x$ is "lost"
Well not so bad, it's real analytic :P
@0celo7 Clearly not invertible.
@DanielSank Almost all functions are not invertible
(inb4 ACM memorized chapter 2 of Hirsch and is ready to fire with density theorems of diffeomorphisms)
(not that he would torture himself with that much analysis)
@0celo7 Yours isn't even locally invertible.
It's a fraud.
51
A: Why are differentiable complex functions infinitely differentiable?

John D. CookThe existence of a complex derivative means that locally a function can only rotate and expand. That is, in the limit, disks are mapped to disks. This rigidity is what makes a complex differentiable function infinitely differentiable, and even more, analytic. For a complex derivative to exist,...

00:06
@ACuriousMind Um, that doesn't explain why $C^1$ complex is so much more powerful than $C^1$ real.
Unless I'm reading it wrong, I mean that's the "standard" explanation.
Oh, also read the answer by Yuan above that
Being $az+b$ for complex numbers is a much more restricted kind of transformation in the plane than being $Ax + B$ for $A$ a real 2x2 matrix and $B$ a real 2-vector
Ah, interesting.
the first is: scale+rotation+translation, while the latter is an arbitrary affine transformation
I've never really given this much thought.
00:21
@BernardoMeurer That's reasonable.
@DanielSank I'm cheap
00:42
@BernardoMeurer Nah bro, it was a good trade.
@DanielSank Do you know anyone who's serious about Chess?
00:57
Danu
@Danu Are you around?
I want a travel set for chess, 10" or 12", foldable and if possible magnetic, wooden. Any recommendations on where to get good sets that won't warp and fall apart?
@BernardoMeurer I did in college.
I know someone now who is very good, but hasn't been playing competitively for a while.
@DanielSank I'm just looking for someone who might:
a) Have a set to sell used
b) Know of good (or bad) sets to direct me to/away
c) Know someone who has a set for sale
:)
@BernardoMeurer You want a fancy coffee-table one, or a portable one?
@DanielSank Portable, folding type with magnets
12" ideally
01:10
@BernardoMeurer o
What?
I found a couple of good ones, but it's too expensive
I currently play with one I got for 7€ at Flying Tiger, but it sucks horribly and it's about to break
lol
Tiger Direct?
Oops, meant flying tiger
@DanielSank I'm looking at classes. How bad would grad level probability be?
This is an absolutely awesome set
but way too expensive
01:16
@0celo7 Don't do it.
Art classes are time consuming and difficult.
@BernardoMeurer I'd offer to send it to you but customs will kidnap it.
@ACuriousMind :( both the advanced undergrad algebra and the graduate modern algebra classes take place during my heat transfer class, which I have to take.
@DanielSank Goddamn it, you are right
I must find an European store
sigh
I hate this country
@ACuriousMind I emailed the undergraduate chair to see about moving the undergrad one.
01:41
I might have more luck with moving modern algebra. I'd have to study over the summer to have a chance of succeeding though
Don't you want to take the summer off?
I applied for REUs, and if I don't get those i'll write my senior thesis
Google.
02:00
Yes Sir.
user228700
02:39
Hi, everyone :-)
Hi.
You're here out of your usual time zone?
03:00
@dmckee have you figured out what's going on with your avatar?
@skillpatrol Nope. Haven't even really been thinking about it. Too much happening in real life. Though I did see the ugly gravatar once.
Yup, it's ugly alright :-)
I think I told you once that your regular one looks like James Dean?
03:49
Thanks for the detailed response. So I guess this falls into the class of "it's not clear what exchange is other than it is an effect"? I'm fine with that. It's just not super satisfying... I would nuance the part of your answer where you say electrostatics blow up when two electrons are at the same position because that would seem to imply we can't find any two electrons at the same position, but we can find opposite spin electrons at the same position. You clarify that later though. Thanks for putting in the work to write all this out though! It's nice to see exactly where exchange shows up. — jheindel Oct 18 '16 at 18:18
Well it has no classical interpretation, but what about the quantum interpretation? What is the state doing when it contribute to the energy via the exchange integral, is it just long range correlations between electrons of like spin?
04:10
Ah I see, so the requirement that the wavefunction is antisymmetric impose a correlation to all electrons, because the observables obtained for one or a set of electrons can only take certain values constrained by the wavefunction compared to the case where the antisymmetry is not imposed. Since it involve the whole moelcular wavefunction, it is manifestly nonlocal
Now the question is: Can we make this nonlocal effect stronger by external application of magnetic fields?
(to be investigated)
04:27
@Secret It is worth keeping in mind that statistical effects can be quite surprising. There are spherical cow models of polymers in which a force manifests trying to shorten the chain even there there is no energetic difference between a straight (and therefore long) and bendy (and therefore short) one. The cause: entropy maximazation.
And these models do a good job of representing macroscopic properties of tensile polymers like rubber bands.
It's one of the most surprising elementary results I am aware of.
@dmckee I also heard about similar thing before in the context of protein folding (where the entropic drive of the surrounding water moelcules facilitates the folding), but if it is nonlocal, then how can it manifest without any transfer of information between two distant ends, or is it they collectively achieve this, I wonder if the notion on how fast an emergent effect spread across the system is well defined?
Ok, perhaps another way to phrase my question is that: Are statistical effects (such as the entropic driven shortening of polymer chains) nonlocal?
04:48
Certainly not in the sense that relativity requires locality, but that doesn't mean that the overall effect can be easily understood by examining a small region.
hmm, so it is kinda a collective result of all the components interacting...
speaking of relativity, the usefulness of just remembering the lorentz transformation for 4-vectors came out on our E&M midterm
the first question was a 1 GeV $\pi^0$ decaying into two photons and asked the probability of one photon having a energy >0.9 GeV
(solved by doing a Lorentz transformation of the forward-facing photon's energy in the CoM frame)
user228700
05:05
I have a quick question about the dependence of electrical resistivity on temperature. This is the formula to be used (as given in my textbook) for small changes in temperature: $R=R_o(1+\alpha(T-T_o)$
user228700
(This formula is originally for resistivity $\rho$. However, $R \propto \rho$ for small changes in temperature because the fraction $l/A$ remains more or less constant)
user228700
My question is this: My textbook has asked me to refrain from using this formula in those cases in which $T-T_o$ is any more than...well, no strict boundary value has been given--all I know is that it definitely can't be 273 degree Celsius.
user228700
So OK, my question would be: what is the max. value of $T-T_o$ for which this formula would be applicable?
user228700
OK OK, never mind, it turns out that I'm an idiot--it's right here, that this max. value is 100 degree Celsius.
06:07
I am slightly less ill
Hurra
user228700
@Slereah Congrats :-P
Still not fun but it's not quite unbearable
@GPhys I haven't done a non-hyperbolic Lorentz transform in a while
06:36
@2017 you have made a basic arithmatic error in your question ...
Top of the morning you @JohnRennie
Morning. You're very Irish this morning :-)
Yup :-)
Does the IRA still exist, officially?
Depends
I think there's the "new IRA", but it depends if you consider it the same as the old one
IRA had some pretty great tunes, tho
user228700
@JohnR: Morning :-)
06:42
great tunes to mail bombs by
The "old IRA" used to conduct tarring and feathering.
Classic
Although "tarring" isn't as cartoonishly innocent as you'd think
Since tar is pretty blisteringly hot
@JohnRennie Good morning. I changed the question a bit to make it more clear. I wanted to find the percentage of the initial number of moles expelled. Any idea on how to do it ? (By the way what arithmetic error are you talking about?)
Using V/T=constant I only get the final volume but that is not what I want
I think I'm terribly confused :-P
When you increase the temp by a factor of 5 so the volume increases from V to 5V. A volume V stays in the bottle so 4V is expelled. The expelled air is 400% of the original volume not 500%.
on the other hand
Hilarious to do
Cruel, but hilarious
06:47
@JohnRennie Oh yes yes. Sorry about that
Take that, stamp act
Since 4V out of 5V is expelled the volume left in the bottle is 1/5V of the original air so 20% is left in the bottle and 80% is expelled.
@JohnRennie Oh dammit! All this time I was thinking like 4V is expelled from the initial V volume! I've gone mad today :-P
Thanks a lot :-)
That would be -3V, no?
@skullpetrol ;-) No. But I would be graciously awarded with -3 marks in my exam for that. :-)
06:53
Ouch! I forgot about your negative marks grading system :(
Punishment for trying.
@skullpetrol Hehe, that's true!
user228700
I have a QQ about backbonding in case anybody here knows; my textbook says that the extent of backbonding is inversely proportional to the lewis acid character of the atom. Is this due to the fact that the tendency to donate electrons to the atom with empty orbital will decrease if the atom with the non-bonded electrons is already trying to do this for another atom?
user228700
(Also, I dunno if I've asked this question before .__. )
Whoever thought up that system was definitely a lazy grader of exams @2017
Like seriously isn't zero low enough?
@skullpetrol They are devils who are keen on grilling us :-P However it is a sort of necessary evil to deter students from attempting question they aren't confident of and wasting time in the process (for the question which they know) .
user228700
07:01
@skullpetrol It's a screening test. Their aim is to get rid of as many students as possible at one go.
user228700
Also uuugh, it looks like I've asked that exact same question before -__- Never mind, guys.
That's a good point @2017 sort of like a built in time management system?
user228700
@skullpetrol It's really only to get rid of as many students as possible. As a general rule, the examiners couldn't care less about the students.
@Kaumudi.H That is an interesting question. It surely has something to do with size of orbitals.
Like 2p-2p back bonding will be better than 2p-3p
user228700
@2017 Lol, no. My textbook has switched it around; they meant to say that lewis acid character is inversely proportional to back-bonding. Does it make sense this way around?
07:08
@Kaumudi.H Lewis acid character is inversely proportional to size of orbitals, no?
hey
hey
why W$_{irrev}$ is always greater than W$_{rev}$
@skullpetrol I consider it to be something like that to pacify my poor soul :-P
user228700
@2017 Yep.
@2017 time management during an exam is extremely important.
@Kaumudi.H And how is size of orbital related to back bonding?
More diffuse orbitals will have less back bonding I suppose
But your book says the opposite
user228700
07:12
Yep, that is correct and I see where you're going with this.
@hey it's the other way round.
In the history of science, the principle of maximum work was a postulate concerning the relationship between chemical reactions, heat evolution, and the potential work produced there from. The principle was developed in approximate form in 1875 by French chemist Marcellin Berthelot, in the field of thermochemistry, and then later in 1876 by American mathematical physicist Willard Gibbs, in the field of thermodynamics, in a more accurate form. Berthelot's version was essentially: "every pure chemical reaction is accompanied by evolution of heat." (and that this yields the maximum amount of work...
See also:
1
Q: work done in reversible and irreversible process

nayana vAccording to maximum work theorem work done maximum work is done during reversible process . consider a reversible adiabatic and irreversible adiabatic process that occurs between two states of the system. Now work done in an irreversible adiabatic process is less. Change in internal energy is sa...

user228700
:-/ It seems that my textbook is wrong in more than one sense; the tendency to form back-bonding will only increase if the atom in need is also a lewis acid.
Chemistry is so hard because there are so many apparently random rules to learn. Give me physics any day!
user228700
...wokay, I understand now. What my textbook is saying that after back-bonding, the atom which used to be in need of electrons has lesser lewis acid character than before.
Yes that is [email protected]
Take the case of BF3 BCl3 BBr3 and BI3
user228700
07:17
Sigh, this is no place for them to bring in the $\propto$ symbol -_- They could've just said it in words.
@JohnRennie why did you do chemistry for so long then?
Extent of back bonding decreases from BF3 to BI3 and LA char increases..
hey
hey
7
A: Formula of entropy change

Fred Senese A process is thermodynamically reversible if it is essentially at equilibrium. Specifically, the system and its surroundings stay infinitesimally close to equilibrium with each other throughout a reversible process. Small changes in intensive variables of the system are perfectly balanced by cha...

Btw @Kaumudi.H which book? Ncert?
user228700
@TheCuriousOne Right, yeah. The Lewis Acid character is most in BI3.
hey
hey
07:18
@JohnRennie in this it is given Work in irreversible is more
Ok. But i don't think ncert has that statement.
user228700
@TheCuriousOne Nope. It's another book but I literally dunno the name of the author.
@skullpetrol physical chemistry
Ok. Best of luck for 2 Apr @Kaumudi.H
Specifically colloid science, which is kind of physics really :-)
user228700
07:19
Thanks. Best of luck to u as well :-) (BTW, why the heck is ur profile "Not found"? O_o)
@Kaumudi.H Yes. That's it. That was a confusing statement anyway!
Oh try PhysiBoy i recently changed my name
@Kaumudi.H
user228700
Lol, OK...
user228700
@JohnRennie Not the way my textbook has presented it -__-
Okay @JohnRennie that makes sense :-)
07:22
@Kaumudi.H Colloid science is one of those multidisciplinary areas that requires you to know a bit of everything. That's one of the resons it's so much fun to study.
user228700
Riight.
@JohnRennie can you guide me on what is Engineering Physics?
@JohnRennie Physics, chemistry, mathematics, engineering, biology, sociology, fine arts, gender studies, hospitality and history
@PhysiBoy It is basically a combo of electronics and UG physics with some coding.
Um what? @2017 do our iit's have that course?
07:25
@PhysiBoy Precisely.
user228700
This place is soon going to explode with "What does <name of course> entail?" questions.
BOOM!!!
@Kaumudi.H True. In May its surely gonna happen and I'll be one of them asking :-P
(Provided I qualify!)
user228700
June, most likely.
ah yes
07:29
How many hours is the exam?
hey
hey
3
user228700
3 $\times$ 2 = 6 hours.
I should be offline now. Bye people :-)!
hey
hey
Ah yes two papers
07:30
@Slereah and drinking. The evening bar sessions at colloid science conferences were ... lively :-)
was there anything in suspension in those drinks?
white russian would be a fine colloidal drink
Did you have lava lamps? :P
For those following along :-)
user228700
BTW, Coca Cola+Red Bull= Trainwreck
user228700
Tastes like cough syrup mixed with coke >.<
07:43
Train wreck = ?
user228700
Tastes extremely crappy is what I meant.
user228700
I gotta do what I gotta do, I guess :-/ Red Bull is too expensive to keep buying, which is why I mixed it with a bottle of coke. Fml.
user228700
Plus, I can't drink it cold--the chance of acquiring tonsillitis is too damn high.
user228700
Lukewarm red bull and coke. Yep. Fml indeed.
user228700
07:48
No sympathies? :'-( OK.
Life is tough.
You said it already you gotta do what you gotta do.
[A quantum exercise to be done] investigate the relative angle of the spin vector of two electrons separated by a distance r on their coloumbic repulsion
user228700
@skullpetrol :-/ Yeah, I guess.
I don't mean to sound unsympathetic.
user228700
:-) I understand.
user228700
07:51
Boy, all this caffeine is making me hungry.
:-)
I was just about to comment on the effects of caffeine.
user228700
@skullpetrol I'm quite aware. I'm not drinking this alarming concoction for the heck of it; gots to stay awake.
Focus on that.
user228700
OK, I'll shut up :-P
hello
Why drink redbull for?
08:03
caffeine
yes but redbull isn't good for the body
better to drink some tea
yes, because of caffeine
no a little bit of caffeine is actually good for the body
yes, but not really good for a caffeine boost
yes a large caffeine boost isnt' good for the body
08:05
trust me if you're accustomed to redbull, tea isn't gonna do anything to you
I once drank a can of redbull and then took a nap
lol
that's crazy bro
Redbull should be illegal
user228700
Pretty sure my veins are running with pure caffeine, not blood at this point.
it's quite tiresome
Eh.
it can cause arythmias
Redbull isn't any worse than an expresso
08:06
@Kaumudi.H why do you need the caffeine? Exams coming up?
user228700
Yep.
oh wen r dey?
user228700
They start on April 2nd.
wow
goodluck
user228700
Thanks :-)
08:07
how many
user228700
6-7 over the course of two months.
yea
what r u gonna do after dat?
user228700
In the summer "break"? No idea. I'm probably gonna try to get my drivers' license.
user228700
...OK, I've decided against buying some more cans of it.
Good decision.
There really are no short cuts this close to the examination period. It's all about practicing and extending your time management skills at this point.
1 hour ago, by skullpetrol
@2017 time management during an exam is extremely important.
@Kaumudi.H
08:38
In the Maxwell distribution why is it correct to say that $\frac{T_2}{M_B} > \frac{T_1}{M_A}$ from the above graph ? If A and B were the same gases then it would be correct to say that $T_2>T_1$. However I've no idea how $\frac{T_2}{M_B} > \frac{T_1}{M_A}$ is a valid conclusion from this graph. Any suggestions ?
@JohnRennie Are you around ?
I'm working for the next few minutes. Back in a bit ...
Sure sure
Oh, btw $M_A$ stands for molar mass of gas A
And $M_B$ for B...
Ah, I think it might be because the most probable speed is given as $$\sqrt\frac{2RT}{M}$$. As the MPS is higher for gas B that's why perhaps
Oh oh that is it I guess ^
user228700
@skullpetrol Uhh, thanks, I guess, but I'm only doing this so that it's possible for me to survive on less sleep than usual.
user228700
Anyhoo.
Maxwell plot is difficult to grasp at first :-P. I think I got it now.
@skullpetrol Indeed it is! Most people spend 2 hours on Physics section and don't have time left to do the easy Chemistry questions
It is important to select questions properly
I always do all the easy questions first :-)
08:51
You should've decreased your hours slept gradually over many months then @Kaumudi.H if that was your goal, right?
@skullpetrol How can reducing sleep be a goal ? LOL
It damages the brain slowly
user228700
@skullpetrol To 3 hours a day for several months on end? Nope, that wasn't the goal.
Some people can do it.
Look at med interns.
It is better to reduce the time one spends procrastinating :-)
Now that^ is good time management.
08:57
Claim: Science is generous, magic is selfish
:-/
Too vague.
Easy: note how in most stories that has both science and magic, science can be done by anyone (because it is objective) but magic is only possible for a small community even if it is well known in the setting
Harry Potter and Star Wars does confuse things further though, by suggesting a scientific mechanism to acquire their respective magic
Genetics and midochondrians respectively
user228700
Does anybody here know about gerade and ungerade molecular orbitals?
@Kaumudi.H Yeah, what is the question
gerade just means symmetric
user228700
I'm having some trouble understanding what my textbook is saying about them.
user228700
09:10
In the following sentence:
user228700
> "If the wave function is centrosymmetric, i.e. has the same sign at the same distance in opposite directions from the center of symmetry..."
user228700
What do they mean by "center of symmetry"?
They mean MOs like these^
user228700
Oh, so the center of symmetry is just...the center of symmetry. Stupid me .__. OK, thanks.
And not the unsymmetrical ones like i.sstatic.net/FVet9.png
09:13
@2017 Yes. In the MB distribution $T$ and $m$ only appear as the ratio $T/m$. So the distribution is in effect a function of $T/m$.
user228700
Right. We can't classify these are being either gerade or ungerade, yes?
@Kaumudi.H Right
user228700
Alright, thanks very much :-)
@JohnRennie Right! Thanks...I figured that out after a couple of minutes :-)
Thank you !
Maxwell's plot is really strange
:-P
user228700
...under those terms, why is it that $\sigma_{1s}$ is gerade?
user228700
09:17
user228700
When flipped about the vertical, the signs do change, which means that it's not gerade, right?
Wait a second! Since when did s orbitals start carrying (+) or (-) sign ?
Is that some other convention?
Feynman once said, "what makes planets go around the sun? At the time of Kepler some people answered this problem by saying that there were angels behind them beating their wings and pushing the planets around an orbit. As you will see, the answer is not very far from the truth. The only difference is that the angels sit in a different direction and their wings push inward." @Secret Now is that magic or science?
user228700
@2017 I was literally just wondering about that :-|
@Kaumudi.H that's the anti-bonding orbital ...
user228700
09:20
Geez, yes, that is the anti-bonding orbital.
user228700
...in any case, I think I understand now. Woot! Thanks.
The antibonding orbitals won't be gerade it seems.
user228700
@2017: From where did u learn about this?
user228700
@2017 Yes, they'd be ungerade...
@Kaumudi.H I don't remember actually :-P It is not in syllabus anyway
user228700
09:24
I've been struggling to get a grip on all these terms and definitions for awhile now. Does anybody know of a good source? (Other than Google)
user228700
@2017 It certainly is in syllabus...
@Kaumudi.H ask jeeves
@Kaumudi.H It is not in ncert..
user228700
@2017 So..?
user228700
@Slereah -___-
09:24
and neither in jee advanced
user228700
How are u sure about this?
I actually don't know. There are two things to consider here:
1. Science models works because they can reproduce the experimental observations independent of the party using it, and can also predict what happens next (even statistically speaking). Therefore saying that planets move around in orbit in the above terminology involving angels is equally valid as saying they are following the geodesic imposed by the warping of spacetime, as long both models agree with the experiments (in fact, for what is worth, you can even claimed those angels are invisible in order to get away with the issue
@Kaumudi.H Check their official syllabus
user228700
@2017 I'm pretty sure this comes under "Linear Combination of Atomic Orbitals".
As a rule of thumb...any terminology system that is not mentioned in ncert isn't asked in advanced...it has never happened in the last 15 years
anyway if you wish learn it
user228700
09:27
(Besides, I'm sure that this is in syllabus because it's given in the book sold by Resonance, an institute, which is definitely fairly credible)
okay whatever
i've got a hell lot of things to learn already
user228700
Chill mate, I wasn't forcing you to learn it or anything :-P
I concur @Secret
Here's an extended food for thought, largely inspired by watching Doctor Strange:

If one day scientist have discovered that the laws of physics not only can change, but can be manipulated in a manner similar to a programmer rewriting and editing a program, will we still call that physics even if everyone can do it?
Let's get back to studying @2017 @Kaumudi.H :-)
user228700
09:29
@skullpetrol Get back..? :-)
user228700
09:45
@skullpetrol: With regard to your advice on time-management; I'm no noob, mate :-) I've been at this for several years now. I didn't feel the need to sleep only for 3 hours before but it's become a necessity (only) now. I appreciate your advice of sorts anyway, thanks.
user228700
10:12
@2017: Dyou know if we have calculation of errors (using derivatives) in our syllabus?
10:52
@Secret why change the name of the science?
@Kenshin Well if one can show reality warping is a law of science, (which means the very laws can be changed easily) will that still be science, or have completely moved into magic or something even more (insert term)?
That's what that food for thought is trying to ponder about
Perhaps it wouldn't be "physical" anymore.
it will still be physical
we would just have a new understand of what "physical" actually is

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