what's Q-cohomology

hi

Anyone can tell me what basically 'Engineering Physics' is all about. I will be going to my college this yr(hopefully get into an iit) and i am searching for a good branch.

Which is not conventional (like cs) but interesting with some physics involved.

@OBE HI.

@DanielSank tbh I don't know how to not get suspended

Apparently "the women are probably better here" is not allowed.

@0celo7 It's milder than some other stuff, but it is a little bit insensitive. I understand that you wouldn't have known it was a problem at the time you posted it, and that's okay, but now that you've seen the response, you do know not to post stuff like that again.

@DavidZ I honestly do not see the difference between that and saying that German comedians are not as good as American ones.

(For instance.)

I'm not trolling here. I really don't see the issue.

If I had said the men are better in America, would I have been suspended?

@0celo7 No, not for that

So we're not allowed to comment about women?

I don't get it.

Whether it's men or women makes little difference; neither of those things is suspension-worthy by itself

Then what's the issue?

@0celo7 The reason the difference matters is that certain classifications of people are more "touchy" than others - that is, more likely to lead the conversation in an undesirable direction. Among those classifications are gender, race, religion, and political preferences or affiliation.

You just said it wasn't suspension worthy.

By itself

Ok Mr. Cryptic, why was it then?

I thought chat flags did not take context into account?

Why was what what?

Why was it suspension worthy?

The flag reviewer saw only that one message, saying that the "women are probably better here"

I struggle to see how anyone can confirm that flag

I even said "that's probably cultural bias"

It wasn't worthy of imposing of a manual suspension by a moderator. I can't speak for why the person who confirmed that flag did so.

I mean jesus, I tried to cover all the bases here

Everyone loves sorority girls is what I was trying to say :P

@0celo7 that's another non-suspension-worthy yet moderately inappropriate message, for basically the same reason

Oh for love of god!

What's wrong with that!

It has high potential to steer the conversation in an undesirable direction. (Of course we're the only ones active at the moment, so it's not an issue right now)

Can you please explain the high potential?

still 9 hours 'til the doctor

bloody hell

why are you up?

it's like 2AM

I can't sleep more than 2 hours at once

@0celo7 For example, it might get people on to the topic of comparing sororities vs fraternities (gender), or the racial and economic segregation inherent in the Greek life system, or it could get people talking about sex, which has been a very problematic topic for this room

...Sigh. Why do people have to ruin everything?

You can't make a joke in this country without someone taking offense.

What is this about sex? I don't think I've ever seen it brought up in here.

@0celo7 Well, you can, if the people who would take offense don't hear/see/read it. But that condition generally does not hold in this chat room.

Getting there: Open Mapping Theorem used to be called the "Banach Homomorphism Theorem" and says you can quotient into an isomorphism, similar to first isomorphism theorem

(There are, of course, arguments one can make about why joking about certain topics is bad regardless of whether anyone who would take offense to it actually notices, but I'm not going to focus on that)

hey, math question.

the answer is $\pi/3$

with a right triangle ABC, construct a line perpendicular to A, and another perpendicular to C, call their intersection D, how can it be shown that when ABCD is a square, AC bisects angles A and C

@DavidZ As you can clearly see, I would not be interested in that either.

@Slereah hey, you got it! =P

@heather ha :-P

I can understand why it isn't always true that AC bisects A and C (AD and BC are parallel, and considering AC the transversal, angle BAC and angle BCA are consecutive interior angles, so they must add up to 180 degrees).

but then I have two problems:

1. bisecting the angles means that BCA and BAC would be 45 degrees each, which doesn't add up to 180 degrees, so I don't understand how that fits in with the consecutive interior thing

2. if this is true, I honestly can't figure out how having all four side lengths congruent allows for AC to bisect, though obviously I know it can.

I'm off to dinner otherwise I would answer that

enjoy dinner @DavidZ

Scientists create a new form of matter: Two studies show 'impossible' time crystals are real and could lead to quantum computer breakthrough / dailymail

↑ maybe circumstantial evidence for a QM LHV if you ask me o_O

@vzn, good news! I think I may have basically finished the prime factorization program

Howdy

@SirCumference, hello

@0celo7 @SirCumference @heather want to see some pics/vids I took in iceland this week?

how do we know it's you?

@heather I can help you when I'm done with my homework

@0celo7 in what sense?

@0celo7 thank you =)

I don't know any geometry but we'll see

@0celo7 He uses a blue filter, probably

no lol

We'll know it's him

@SirCumference could be done in post

so that's not evidence

the ice cave I went to was ULTRA BLUE

naturally

want to see a vid of it I took?

I'm sure you were blasting FUTURE HNDRXX, right?

@OBE Confirmed. Everything was blue.

huh?

In seriousness, though, that's sounds so cool

No pun intended

sounds or looks?

Both

yeah water was flowing down into the cave

@OBE He's messing with you

anyway I have more pics and also real "evidence" I can show you on skype.

Can't say the word "trolling" anymore

Against the rules

lol

because I don't know who you are?

where is obe

does he know there's an imposter?

I just made my name caps lol

@OBE If you're really obe, what're the last three digits of my zip?

let me look

you're going to beat it out of him!

I have to scroll all the way through skype -_-

Thought you didn't share skypes?

good night everyone

'night

finally

@0celo7 check your skype

"What angle would the object in part B subtend at the eye? Express your answer in minutes"

What???

Minutes?

minutes of arc?

$60' = 1°$

@OBE ah, it's you

why the completely new name?

completely new?

how is anyone supposed to know who you are?

no idea

lol

So I have $3.355\times 10^{-4}$ rad

How many minutes is that?

So 0.019223 degrees

so, divide by 60?

multiply?

I can't into math, halp

you don't have to do it in your head or figure out what to multiply by just solve the equation for what it will be in minutes.

no thinking required.

I don't know how to do that

you do lol

@OBE actually no, I got the answer wrong

this is for engineering?

no

@heather Ok, what's up

quickly

@0celo7 Sixty arcminutes = 1 degree

@heather :(

I didn't sleep for 35 hours a few days ago

new record by far.

why do illnesses exist

h a l p

did you sleep lately?

yes

My sleep is piecewise continuous

not you @OBE

true that

@Slereah why?

guilty conscience?

Too sore to sleep too long

@heather Your question doesn't make sense. ABC denotes the three vertices, no? So what is a line perp to A supposed to b?

@heather hey great news how about a link? do you have sample output? how many numbers did you try it on? example "test harness": call it 10 times in loop with random numbers and have it output answer. also nice to sort the factors. glad you followed thru on it =D

@OBE 56 is my record

...not that I keep a record

@Slereah Cold?

or something yeah

mb the flu

@SirCumference what the fuck

why???

@OBE Insomnia is a bitch

Oh wait, am I allowed to say that?

oh insomnia

so you tried sleeping?

Yep

wait, no, i've gone 4 days before

Going to classes is hell when you don't have sleep

May I ask a quick general physics question here?

It's like having a constant migraine and I keep having to wake myself up

huh?

Worst part is I get a lot of chills so I bundle up and then sweat up everything and have to change T-shirts

I'm up to the 4th one or so

@Slereah but sweat doesn't smell bad immediately

yeah but thne it gets cold

true

@AndrewLi just ask

@Slereah I've had the stomach flu in the middle of a class

Twice

It sucks

Okay, so I need to find the acceleration of a pendulum along its path at the maximum height. I know the angle and mass of the bob, but shouldn't I need to know the length of the pendulum too?

the length doesn't affect the acceleration.

unless I'm super dumb

@OBE welp, I'm sorry to be the one to tell you this...

lmao

@AndrewLi I do think you need to know the amplitude of the oscillation

angular amplitude at least

@0celo7 wait what?

how does the length affect the acceleration?

after all $F=-mg\theta$ @AndrewLi

okay I'm retarded

Yeah. I'm just wondering if I should ask for more info. At the current state I don't know if I can solve it

I should sleep

@AndrewLi Ask whom?

@0celo7 My instructor :P

he'd be the one to ask I guess

wait dafuq

I'm not wrong

@0celo7 Okay, will do. Thanks

am I? @0celo7

@AndrewLi I know that for an oscillator, the max acceleration is $A\omega^2$. You know $\omega$ from the length. But you need $A$.

@0celo7 explain this

I think I'll ask about it tomorrow. Thanks again anyways

@OBE what do you want?

how does the length affect the acceleration?

the length doesn't

EXACTLY

the angular displacement does

so what the fuck then

why'd you say that

Where did I say that?

I said that it doesn't affect the acceleration unless I'm dumb

and you're like I'm dumb

Oh, well.

interpret that how you wish

wow

ban @0celo7 xd

...on a brighter note

anyone want to suggest ideas for an astronomy ad?

enough with the astronomy ad already lol

but...the old one is already up and driving me insane XD

I'll just design one someday when I'm feeling creative

just wait a bit

@0celo7 flagging :'(

xd

another problem with the sore throat is that I'm drinking a ton of water to make it better

Starting to feel a bit sick of it

You NEED to see a doctor immediately @Slereah

got an appointment this morning

Get some antibiotics.

Well the doctor will decide of that

I tried for 2 months to fight a flu.

I realize now it was unnecessary suffering.

jesus christ

@skullpetrol ok that's an exaggeration

@Mystic I'm not sure on what basis you think that I didn't read it. Anyway, I would not consider that a frivolous flag.

most people can just tough out a cold

What message did I delete immediately after posting?

@OBE no need to say that you're flagging things. If something really needs to be flagged, flag it, otherwise don't flag it, but either way there is no point in announcing it.

@0celo7 it's not an exaggeration. This flu had a nasty way of mutating and coming back.

Btw I don't take flu shots.

@Mystic ...

do you know what a joke is?

or what a reference is?

@Mystic The message you quoted there was not the subject of the discussion you replied to.

@DavidZ Can you please check out the suggested edits on physics.stackexchange.com/review/suggested-edits/165754 at the very bottom...

Good idea @Mystic

Let it go.

@Mystic There are lots of deleted posts in chat. It's best not to assume I know which one you're talking about.

White knighting is so boring.

@ZeroTheHero I can, but why exactly does that need my attention?

@Mystic There are lots of deleted posts which were flagged.

@Mystic Depending on the context I would

what I see is the suggested edits add "weiners weiner's weiner's" as a suggested edit.

@ZeroTheHero yes, so?

That's your problem. No need to flag.

I saw the entire context.

Flagging is abused in this chat.

@0celo7 That doesn't sound correct

@DavidZ When I flagged everything that I had a problem with, I was told to stop.

I really don't understand this damn policy.

Be nice.

@0celo7 Yes, because you were casting frivolous flags. The flags we're discussing now were not frivolous.

I am very nice.

But not civil.

@DavidZ I did not think they were frivolous.

So is what's offensive up to me or not?

No.

No what?

@0celo7 No, it's not.

^

@DavidZ Then I don't understand this.

::makes popcorn::

Flagging is a sure-fire way to suspend someone. We've been over this.

(Relatively sure.)

What does "civil" mean to you pal?

I don't know what it means.

Think about it :-)

Shhh... Let him think please.

Cya.

@0celo7 My best guess is that your standard for what is flaggable and what isn't was very far out of line with the community's expectations. That led you to cast flags which you thought were appropriate, but which actually weren't.

@DavidZ But if the flags were validated, what is the issue?

@0celo7 If the flags were valid, there is no issue. That's not quite the same as being validated. Ideally, only valid flags would be validated, but in practice it doesn't quite work that way.

But from what I remember, many of the flags were not valid.

@ACuriousMind Suppose $T:\Omega\to \mathscr B(X)$, where $X$ is a finite-dimensional v.sp. and $\Omega\subset\Bbb C$ is open and contains zero. In perturbation theory we want to solve $\det(T(z)-\lambda(z))=0$ for $\lambda(z)$. Assuming $T$ is analytic, then this is an algebroidal equation for $\lambda(z)$.

Is there a simple argument for why $\lambda$ should be analytic, with at most isolated algebraic singularities (poles)?

$\lambda$ might of course be multi-sheeted.

Now we know that this can be written as a polynomial $p_n(z)\lambda^n(z)+\cdots p_1(z)\lambda(z)+p_0(z)=0,$ where the $p_j$'s are the components of $T$ in some basis.

But the dependence of the $p_j$'s on $z$ could be pretty bad, so I'm not sure what to do now.

Ok OMT is obvious now: a map $f : X \to Y$ is open if the notion of approximation on $X$ can be embedded into the notion of approximation on $Y$, i.e. $f$ maps open sets to open sets. Thus $f : (-1,1) \to [0,1) | f(x) = x^2$ is not open because while you do map $(0,a)$ to $(0,a^2)$ you also end up mapping $(-a,a)$ to $[0,a^2)$. Restricting to maps between linear spaces,

the notion of approximation is linear approximation, and so we expect to be able to embed the notion of linear approximation on one space into any other when the map is continuous, however the case of rationals and reals implies an additional dependence on completeness of your approximations, hence the open mapping theorem

Civilized people live in a civilization in which they act civilly towards one another @0celo7

...the story of two goats who met on a bridge which was too narrow for either to pass or turn back. When one goat lay down to let the other walk over him, civility was born.

...I'm not advocating letting people walk all over you, but that's how the story goes pal.

Hi, everybody.

Hello.

Our memory depends on the motion of the thing we saw

The darknet has a decentralised network topology and high adaptivity to foil most attacks

Electron proton interactions involve two photons being exchanged, with one high in energy and another not so

@Secret Do you work as a bot part-time?

Nah, I just have a habit of reading latest research news and share them as part of idea mixing. The dumping does somehow make me look like a bot though, so you might be technically correct

Nice.

A strange device eh?

@Kaumudi.H Morning :-)

Indeed.

It depends on whether you allow accelerating frames i.e. non-inertial frames

The acceleration is $dv/dt$. If you're in an inertial frame moving at some constant velocity $V$ relative to me then you measure the velocity as $v-V$. But $d(v-V)/dt = dv/dt$ because $V$ is a constant.

So we agree on the value of $dv/dt$ i.e. the acceleration.

But if your velocity relative to me is not a constant then $dV/dt \ne 0$ and we will get different values for $dv/dt$.

The argument used in that answer seems very confused to me

Frankly, if you can't write down an equation to support your statement then there is a high probability that you're talking bollocks.

Who wrote your textbook?

The proper acceleration of, and therefore force on, an object is the acceleration measured in the rest frame of the object, and this is an invariant. In fact it's an invariant even in GR.

In that sense there is a force that is independent of the reference frame.

The trouble is that the original statemnt is poorly defined because it doesn't explain exactly what it means by force.

Any time you want me to make bitchy statements about other people's anwers just let me know :-)

Have you asked your prof?

It's been my life's ambition to be a mad professor :-)

Is laptop obsession a sign of clinical insanity?

BTW I'm using the new big laptop in anger for the first time (while I'm staying at my Mum's) and it's almost perfect,

Only almost because the keyboard isn't as nice as the keyboard on my older smaller laptop. Oh well.

@Kaumudi.H The paddle only did net work on the ball if the kinetic energy of the ball has changed.

Well the bat brings the ball momentarily to a halt, so the KE of the ball has changed and therefore work has been done.

But as the ball bounces back the KE increases again. If it increases back to its original value (i.e. an elastic collision) no net work is done.

Yes.

Conservation of energy guarantees that.

Or is that true only in the centre of mass frame ... hmm ...

What does the textbook say?

If you're considering a collision, which I guess we are, then in the centre of mass frame the point of contact doesn't move.

With inelastic collisions we need to use a more realistic model than a rigid body collision.

As the ball hit the bat it deforms, and the centre of mass of the ball moves during this deformation process. So work is done on the ball, and that converts its kinetic energy into elastic potential energy.

Then as the ball rebounds work is done on the ball and the leastic potential energy is converted back to kintic energy.

In an inelastic process less work is done in the rebound stage so the KE of the ball ends up lower. The remaining energy goes into heat or whatever.

So in a real collision you can't really just say the point of contact doesn't move so the work is zero because you have to consider deformation of the colliding objects.

@Kaumudi.H in frames other than the COM frame things get a bit moe involved. Is it worth going into this? It's less interesting than you might think :-)

A wise decision :-)

Does anyone have studied string theory?

*here

@KiarashN ACuriousMind is currently doing a masters on string theory

He'll probably be in the chat room later on today.

@JohnRennie Thank you, John!

He's a clever chap though woefully ignorant of colloid science :-)