The h Bar

Because you have now 2 Cr atoms on the left, and 2 Cr atoms on the right. The Cr atoms on the left have oxidation number of +6, yet the Cr atoms on the right have oxidation number of +3. Since there are 2 Cr atoms (Cr2 on left and 2Cr on right) the total change is 2*3 = 6

Similarly, you now have 3 S atoms on the left (3S) with oxidation numbers of 4 per atom, adn you have 3 S atoms on the right (3S) with oxidation number of 6 per atom. So the total change is 3*-2 = -6

Swapnil Das

Cool!

Mew

10:57 AM

give us another example

Swapnil Das

I'm still finding them :P

Regards, Dr. @EmilioPisanty

Mew

@heather, are you here?

Swapnil Das

He seems to have left.

Mew

but i had something to show him

Swapnil Das

Oh.

Mew

11:02 AM

my new physics site

i'll show u

physicsproblems.nfshost.com

Swapnil Das

Wow!

Mew

ty please sign up

feel free to ask a quesiton

just created now

Swapnil Das

My pleasure! I always needed something like that.

Mew

awesome, yeah i always thought a site like this would be helpful to many

Swapnil Das

What kinda questions could we ask?

Mew

11:05 AM

I haven't written the rules yet, but I think it will be homework time problems, kinda like the ones you've been asking tonight but more for physics

homework type* problems

doesn't have to be homework, but the emphasis will be on solving physics problems rather than on concepts

Swapnil Das

I like it.

Mew

thanks

Swapnil Das

BTW, what subtopic of physics did you use for grad studies?

Something like gr or so.

Mew

I did a degree

I didn't do PhD

Swapnil Das

Oh. Was it integrated physics?

Mew

11:09 AM

I did a bachelor's degree in physics and maths

and honours

but then didn't persue post grad

went to the workforce instead

Swapnil Das

Oh that's cool

I'll perhaps be asking some questions on your site very soon. I'm working for PhO

Mew

nice

what topic?

Swapnil Das

It might be optics, or Newtonian. Chances of circuits and stuff also exist.

How should the questions be posted?

With/ without references to own approach

Mew

This will be decided

For now post whatever you think is good quality

then as the site develops we can formulate rules by looking at the xamples we like and dislike

Latex hasn't been added

Swapnil Das

I'll show you an example of type of questions I'm gonna post.

Mew

11:15 AM

Just post it

I'm sure it wil be fine

I can put a comment on the site if I think it needs editing

Swapnil Das

Like this.

I solve such kinda problems

Mew

Ok, but if you include the screenshot, please don't include the bit on the right

with the submit etc.

it makes it look like a homework question and puts people off

i mean obviously its homework

but remove the bit that makes it look like an assignment

Swapnil Das

Oh sure, I was showing an example only

Mew

cool

but yeah the content is good

Swapnil Das

Was it too easy?

Mew

11:26 AM

na

@SwapnilDas, you may have previously seen an error at the top of the site

this has now been fixed

physicsproblems.nfshost.com

Swapnil Das

Yes

Cool

Mew

@SwapnilDas, please post up a question

I will answer

Swapnil Das

Screenshot would work? Or a pic?

Mew

Not sure give it a try

Swapnil Das

Ok

Mew

11:33 AM

Hi Andreas

Swapnil Das

Can't attach pic from tab :(

Mew

why not?

Swapnil Das

Idk

Mew

There is an attach picture option

I"ll have a go

Swapnil Das

No option available

Sure

Andras Deak

11:37 AM

morning(ish)

Mew

@SwapnilDas, I know what you can do

did you see there is a picture icon

on the post form

Swapnil Das

Yes

Mew

select that

and then it asks for a URL

Andras Deak

@ACuriousMind @0celo7 @BernardMeurer just to be clear: I left because it was past 3 AM and I had to get some amount of sleep:P I did find the trolling interlude tiresome and childish, but my general stance is not giving a crap, so no need to worry about me:)

Mew

well whenever you paste a picture in this chat

it creates a URL

Swapnil Das

11:39 AM

I was thinking the same!

Mew

copy that url and paste it in the url section

cool

This is obviously a short term solution and in the long term i will work on getting the desktop upload to work

Swapnil Das

Mew

hello @2physics

2physics

@Mew Hi, I was away for a few minutes. How are you?

Swapnil Das

Typo

Mew

11:43 AM

pretty good 2physics, how do you feel about the idea of new phyics problem solving site

Andras Deak

@heather linearity of a circuit element means that the I-V characteristic of the element is linear. This just means that it has an ohmic part and optionally capacitive/inductive parts. The point of linear circuits is that superposition works, so for a set of voltages and currents {V1,I1} and another {V2,I2} that solve the circuit, {V1+V2,I1+I2} will also be a solution. Every method to determine the voltages/currents in a circuit rely on this, I believe.

For instance, the loop current method works with overlapping currents where loops overlap.

nonlinearity starts with fun stuff such as diodes and transistors

Mew

@SwapnilDas, your image is massive

I have edited permissions

you will be able to upload normally now

without having to use lnik

2physics

@Mew what do you mean? sth different from SE you mean?

Mew

@Sanya, please see new site physicsproblems.nfshost.com

Andras Deak

testing in production, eh?;)

Mew

11:46 AM

yeah just was created today

2physics

@Mew what's the difference?

Mew

well this site is for physics problems rather than concepts

4

Physics Problem Solving

Proposed Q&A site for problem solving techniques in Physics at the High School,Undergraduate and Graduate level.

Closed before being launched.

^ is the site that wasn't accepted for SE and several users were interested in potentailly having an external site that caters to people who have "homework" like questions

not necessarily homework, but "how to solve this" type questions that may not be a good fit for SE

GPhys

It's too bad physics isn't good for solving things that aren't homework problems

Mew

@SwapnilDas, I've edited your question physicsproblems.nfshost.com/?qa=1/…

check it out

I've improved the quality

Note for future you can upload directly from your computer now, no need for external link

2physics

ok. it's interesting.

Mew

11:53 AM

Thanks man

2physics

is it yours??

Mew

Yeah

I just set it up today

2physics

nice. good luck

Mew

thanks i'll need it

innisfree

40

A: What is an instant of time?

I believe you're asking about a paradox in the style of Zeno's paradoxes. Your paradox is most similar to 'Paradox of the Grain of Millet'. You want to know how an infinite sum of infinitesimal instants could equal a finite length of time, $$ \int~\mathrm dt = t. $$ Well, the above is nothing but...

Mew

12:02 PM

nice answer

41 upvotes in one day well done

innisfree

Why did it get so popular? When I answered it, I thought the question might be closed and wasn't that happy with my answer

Mew

very popular question over 3k views

and probably a good answer to a silly question

innisfree

Why? Even after seeing so many questions, I still can't judge which ones with gather interest

Mew

yah i saw this question and thought it would be soon closed

but i think the "masses" love the philosophical questions involving time and the like

Andras Deak

@innisfree the answer is HNQ (hot network questions)

the stupidest and simplest questions end up there, and all sorts of people on the SE network appreciate it if they find something they understand -> upvotes galore

Mew

12:05 PM

yeah that's right, but it must have been popular to get to that stage too

true Andreas

*Andras

it's just my accent

ok, Mao:P

lol

Yes, maybe questions about simple misconceptions inevitably have broad appeal

Andras Deak

12:07 PM

yup

and see also the bike shed effect

similar vein

innisfree

And then it's a matter of, is it so basic it's closed? If not, it explodes

Mew

wow that's pretty interesting Andras

innisfree

Yes, that's interesting

I wonder if any algorithm could predict question popularity/suggest closing a question

user116211

@innisfree, the answer was good and I upvoted it firstly. the only reason that you got 40 other votes is because the paradox questions become quite popular and most of the time it hit the HNQ. And you know HNQ. The post is easier to read - that is oe other reason for it being so popular.

Mew

No I don't think so innisfree

many questions that should be closed would become popular if they weren't clsoed

it's very subjective business

innisfree

12:13 PM

Lots of low quality questions that get closed also have poor grammar and spelling, or are excessively long. Without knowing anything about physics, I think an algorithm could catch them, with a reasonable mistag rate

Mew

@MAFIA36790, check this out : physicsproblems.nfshost.com

innisfree

Guessing popular q's could be trickier

Mew

Yeah, I think the popular questions may be of similar topics, e.g. time, space, blackhole etc.

but the questions that are popular to the masses are likely not of interest to the regular users of physics.SE

so there is a question of whether there is any point in trying to identify the popular questions ahead of time

innisfree

True, I'd just be curious about how well they could be characterised

Mew

spoken like a true theoretical physicist

innisfree

12:18 PM

interesting software behind the site. Open source q&a platform

Mew

yeah that's right

it only took about 20 minutes to set up

everything is customizable too

innisfree

Oh you did it?

Mew

yeah

innisfree

They've scooped phys overflow, one of their nobler aims was to make an open source q&a platform, I think

Jim

@BernardMeurer Your welcome. And don't worry about it; my help is always free.

innisfree

12:20 PM

Oh hang on, maybe I'm confused, maybe that is what phys overflow uses

Mew

you could be right

there is a Q2A search

ype

yep

physics overflow is powered by questions2answers

I"m suprised by that

good pick up

user228700

12:36 PM

@AndrasDeak "yup"? Who starred "yup"?!

user116211

@Kaumudi Starring is anonymous. So, I think it's futile to ask who starred what.

user228700

Sometimes, people say if they did star something so it's not entirely futile to ask.

user116211

Well, it depends on them.

user228700

Yeah.

Mew

ok the theme for the physics problems website has been updated:

physicsproblems.nfshost.com

user116211

12:42 PM

Now, it is looking better.

Ramanujan

0

Q: Area of triangle formed from equation of of its sides.

The area of triangle formed by the lines $$a_1x + b_1y + c_1z=0$$ $$a_2x + b_2y + c_2z=0$$ $$a_3x + b_3y + c_3z=0$$ Is $$\frac {\Delta^2}{2\lambda_1 \lambda_2 \lambda_3}$$ Where $$\Delta = \begin{vmatrix} a_1 & b_1 & c_1 \\ a_2 & a_2 & c_2 \\ a_3 & b_3 & c_3...

@MAFIA36790 you might know this ^

@Kaumudi hi

Andras Deak

@Mew yup, definitely looks better

BTW does Swapnil's question really need an answer? It's pretty easy

0celo7

What is the .ps file format?

Mew

Andras, yes it does

Andras Deak

@0celo7 postscript

Mew

12:52 PM

If you're able to answer it please do

Andras Deak

but surely I misunderstood your question

@Mew nah, I'll pass

0celo7

@AndrasDeak I can google.

But why use it over pdf?

Andras Deak

@0celo7 hence "but surely I misunderstood"

@0celo7 because author is a dummy

David Z

hey, that's not very nice ;-)

Andras Deak

.ps is for printers, except if somebody is being hardcore and writes postscript by hand

David Z

12:54 PM

@0celo7 these days, there's basically no reason

0celo7

@DavidZ the EMS (Euro. Math. Soc.) uses it for all their notices, apparently

Andras Deak

:S

David Z

ugh, that's silly

Andras Deak

you can also have a prematurely interrupted latex->dvips->ps2pdf cycle (but you might ask "why not pdflatex?", and I would have no answer)

David Z

I guess people can always convert it to PDF, but it's a waste of 80% of the file size not to do that in the first place

Mew

12:56 PM

Hey guys

user116211

@0celo7 There are many papers in this format. Just convert it to pdf; there are many free softwares available online.

0celo7

@DavidZ Did you hear about last night's romp?

Mew

what do you think of the name for the external physics problem site?

how about physicsDoJo.com

Andras Deak

@Mew it's problematic

0celo7

@Mew too silly?

user116211

12:56 PM

Hey @ACuriousMind; hope you got a good sleep.

David Z

@0celo7 I looked at the transcript

Mew

@0celo7, perhaps

@0celo7, this is the current prototype: physicsproblems.nfshost.com/?qa=questions

We need our own domain name without nfshost

ACuriousMind

@Danu cc @MikeMiller thanks for linking me to the same new paper by Joyce :) Alas, I don't think I'll need cohomology valued in Novikov rings...

user116211

Why is my profile pic changed for no reason ._.

Andras Deak

There are two different puppers between your chat and stats profile. Is that change?

Well, same pupper, different shots

user116211

1:01 PM

yes.

Andras Deak

well, did you change it?:P

user116211

I am using my stats account. So, the pic should be that account's and not this one now ;(

0celo7

@ACuriousMind I see there's a new AMS book on Galois theory via Riem geo. Maybe that's what I need to start liking algebra

user116211

Why did it change suddenly?

Andras Deak

And where did that image come from? I'm fairly certain it didn't pop out of nowhere

ACuriousMind

1:02 PM

Currently I'm trying to extract from the older works of Joyce why the physicists claim for one of his simplest examples that we know that the volume of the desingularized sets goes to zero. I've found only calibrated cycles that explicitly are not part of the singular set thus far.

user116211

@AndrasDeak It is of Math.SE account of mine.

0celo7

Maybe not Riem geo. But certainly analysis.

Andras Deak

@MAFIA36790 yeah that's odd, your profile is still linked to your stats one

guess you have to revert it manually

user116211

I'm not getting that too; it changed suddenly.

user228700

@Ramanujan: Hey :-)

0celo7

1:04 PM

@ACuriousMind What does the manifold G2 actually look like?

Slereah

What is G2

ACuriousMind

@0celo7 G2 is 14 dimensional, so I can't answer that question.

user228700

@MAFIA36790: How old is that dog of urs? ^.^

0celo7

@ACuriousMind Is is compact?

user116211

2 yrs.

ACuriousMind

1:06 PM

@Slereah One of the exceptional Lie groups :P

Slereah

Oh right

user228700

I see. Man, he/she looks real sad ._.

Slereah

One of THOSE

Is there a GUT with G2

ACuriousMind

@0celo7 The form I'm dealing with, yes, but there are also non-compact versions of it (with the same Lie algebra)

Ramanujan

@Kaumudi I have some doubt in mathematics

ACuriousMind

1:07 PM

@Slereah It does contain $\mathrm{SU}(3)$, but I don't think you can fit the whole SM gauge group in there

Slereah

too bad

I mean it has 14 dimensions

Shouldn't the SM lurk in some of those dimensions

Just by statistics

Then again E8 has like 200

ACuriousMind

Well, $\mathrm{SU}(3)\times\mathrm{SU}(2)$ has... 8+3 = 11 dimensions, so the SM is 12-dimensional. You can't expect a 14 dimensional group to have any 12-dimensional subgroup you can think of.

Slereah

How many subgroups does E8 have, I wonder

ACuriousMind

@Slereah Lie subgroups, you mean? For that, it's probably easier to classify the Lie subalgebras of the algebra, but I don't know either way

Danu

lol @ACuriousMind :D

Btw it's not a paper by Donaldson :P

In any case, Joyce even says explicitly it might be relevant in $G_2$-compactifications :D

ACuriousMind

1:18 PM

@Danu No, it's Joyce, the guy who invented the examples I'm currently reading about

And yes, finding the calibrated cycles is in general interesting for $G_2$-compactifications

Oh, lol, now I see, I wrote Donaldson up there :D

Danu

Enjoying the moderator message-editing powers? :)

user228700

@Ramanujan What's ur question? (I'm sorry, I cannot guarantee that I will be able to help you-I have quite a lot of things to get done and have limited time)

Secret

[rambles,warning, may cause apathy...] I am a selfish person, but in a nontrivial way. For example, the resource I thrive on other people is the very fact that person is in positive chemistry with me. And I don't harm friends not (just) because it is cruel and immoral, but because when they are miscerable, the positive chemistry will be broken and I will become frustrated as a result.
Do I genuinely care for them? I have no idea. From the outside (and the emotions and wellbeing of the friends), every selfish motive I did just happens to be isomorphic(?) to what a genuinely caring person doe…

On the other hand, I have no desire nor need to cultivate that positive chemsitry. I just let it evolve naturally by just being myself (and so does my friends)

Mew

@Secret, interesting philosophy

if it feels good to be kind, it may help to ignore whether you are ultimately doing it for selfish purposes

a kind action is a kind action, regardless of the motives right?

HDE 226868

@ACuriousMind I'm quite the imposter, aren't I?

Secret

1:33 PM

Well, for years I have been wondering what "genuiely care" means, because I am so selfish and my autistic traits means I have low sense of empathy, yet most people seemed happy to be with me because of all those coincidence

I think I think too much in terms of logic for something that otherwise should not be seen in the view of logic

Mew

@Secret, yeah that's right. Social interaction is largely instinctive and when you start to analyse too much, it can counterintuitively make you worse at it

i think practice makes you better, and thinking makes you worse

kind of like sports. When a golfer was asked to explain exactly how they put to someone else, they performed a worse put than when they just putted without talking about it before hand

0celo7

My parents text each other at 5 in the morning. How are they up that early? I must be adopted

user116211

WTH.

Mew

@Secret, have you seen the new problem solving site? physicsproblems.nfshost.com/?qa=questions

bit of work to do, but was just created today

Secret

I sometimes think too hard that there are times I am happy, I wonder "why am I happy?" "How do I happy" etc. On the plus side, the same kind of analysis when I am angry can cause me to forget the anger when I cannot find any valid answer to justify why I am angry

@Mew Make sure not to attract homework vampires, as from the look of it, the questions seems way too much "do my work for me with no effort"

Mew

1:40 PM

@Secret, yes, there are only 2 questions at the moment and I"m keen for more poeple to post up the questions they would like to see on the site

once we have more volume we can then decide what to keep and what to cull as we define the site

Secret

Also I am not sure if you want to add a comment bar beneath the questions and answers just like in SE, but the lack of a chat room may be a problem when it gets too long

Mew

yeah

great ideas

i'll look into getting a chat room added, a meta added where we can discuss the site and the chat bars

comment bars*

ACuriousMind

You sure you want to make that site public without having a meta, proper privacy policy (my email will not be shared, fine, what about my IPs, accessed sites, etc?) or any sort of formal post declaring what kind of questions you want or don't want?

Might be worth it to configure those things before letting other users post stuff

Mew

@Secret, comments can now be posted on questions

@ACuriousMind, one can think of this as a demo, the official site will have a different URL

the data is private currently but I agree it is worth having a privacy statement and site definition

ACuriousMind

@Mew Then that would also be a good thing to tell people somewhere on the front page or when asking a question

Mike Miller

1:47 PM

@ACuriousMind I didn't suppose you were interested in that, but his arguments about what you can't get as deformation invariants are interesting.

In particular, G2 instantons balanced out by counts of associative submanifolds (though that's not quite what Walpuski has been trying to count).

Physics Meta

1

Q: Should this "homework-like" question about the AKLT Hamiltonian be undeleted?

It's been suggested via a flag that this question, which was deleted by Community after being closed for ten days, has value to other users asking similar questions. I personally don't understand the closure of this question: in its current form, it's a thoughtful, conceptual question that happe...

discussion homework specific-question

Mew

@ACuriousMind, good point I've included this on the front page

@heather, please see this prototype physicsproblems.nfshost.com

user116211

@PhysicsMeta Aren't you getting older? For you are really slow.

Mike Miller

@ACuriousMind Are deformation invariants not interesting in physics? Eg if you didn't know GW didnt depend on the almost complex structure, would that be fine?

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