The h Bar - 2017-02-23 (page 5 of 8)

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5:00 PM

lol

Physics
Physics description
800
out of a range of
200 to
800
My Score Range: 770-800
88th
Your National Percentile

Your percentile indicates the percentage of test takers in the prior year’s cohort taking this test who had scores below your score.

1 out of every 9 students gets an 800 in Physics

^ same for chemistry

@YashasSamaga hmm, but do you know what a ball is?

?

@YashasSamaga This is not from any official source.

Give me a link.

@anonymous it is from my SAT profile lol

5:01 PM

@YashasSamaga ball in metric space

it is official

@0celo7 no idea

and that's what's wrong with India...

@YashasSamaga That is your score card -_- That is not called statistics.

@anonymous The score card gives the percentile pff

percentile is a proper stastical measure

I hate this genius mass production through standardized tests trend in Asian countries.

(including mine)

5:03 PM

Percentile gives your position among all the test takers. Many many many people get same score and same percentile @YashasSamaga

@Mostafa The problem is that the SAT syllabus is our regular 10th grade syllabus

how can someone possibly studying in 12th grade not score full?

@YashasSamaga Your claim still doesn't hold.

@anonymous 800 is the maximum score

@anonymous if my percentile is 80th

that means that 20% of the people have scored the same marks as mine

@YashasSamaga So what? 10,000 can get 400.

what?

I don't care about 400 or 500

I said one out of every 5 people get 800/800

You don't need any more evidence to prove that.

5:04 PM

@YashasSamaga That is wrong and I will prove it.

@YashasSamaga I'm in college and could not get full score

omg

In 48 hours.

You can say I'm bad at math but you can't back that up

SAT is about test taking, not knowing the material

percentile = (students who scored the same marks or greater)/total no. of students

5:05 PM

Also you sound like a major [redacted]

I scored 800/800 and that is the maximum

so if my percentile is 80

then 20% of the people have got 800

because you cannot get more than 800, the 20% MUST have got 800

20% = 1/5

so 1/5 of the students get 800

AccidentalFourierTransform

I got 801/800

SAT scores are multiples of 10

Not sure why they chose 200 to 800 instead of 20 to 80

TOEFL is even worse

the maxmimum marks you can score is 118 or 576

where did they get those numbers from ? lol

@ACuriousMind Ok Mr. LES I can't figure out these LES :P

ACT maximum is 36

5:08 PM

@AccidentalFourierTransform lol

@YashasSamaga isn't it 120?

@Mostafa Let me check.

its 120

I wonder which test has max marks as 118 then

@ACuriousMind The part I should be looking at is $$H_n(U)\oplus H_n(V)\to H_n(M-\{x\})\to H_{n-1}(U\cap V)\to H_{n-1}(U)\oplus H_{n-1}(V),$$right?

AccidentalFourierTransform

it depends. Is $p$ a prime?

Here I take $V$ to be a ball or half-ball minus the point $x$

5:10 PM

Right. What is $U\cap V$ homotopy equivalent to?

I'm not sure. I can arrange it so that it's either an annulus or half an annulus, right?

Exactly

Umm, what's the homology of an annulus?

Well, what's the simplest shape it is homotopy equivalent to?

The half annulus is contractible.

@ACuriousMind $(n-1)$-sphere.

5:12 PM

Exactly

So that has trivial $n$-homology?

Ah, then you need to look at the $n-1$ homology.

Oh crap, MV for homology goes the wrong way

So it's $\Bbb Z$ in one case and $0$ in the other?

@0celo7 The $n-1$th homology of $U\cap V$, yes

So now what?

Suppose first that $V$ is a ball minus a point

Then it has homology $\Bbb Z$

5:15 PM

Now you need to recall enough about exact sequences to figure out what this tells you about $H_n(M-x)$.

So we get $$H_n(U)\to H_n(M-\{x\})\to \Bbb Z\to H_{n-1}(U)\oplus\Bbb Z?$$

no

it's a homotopy $(n-1)$-sphere

@0celo7 Yes, exactly.

pun intended I imagine

Now compare this to the result for $V$ the half-ball

@YashasSamaga how output chatacterstics are controlled by input characterstics

5:17 PM

CE?

$$H_n(U)\to H_n(M-\{x\})\to 0\to ?$$

@YashasSamaga yep

@0celo7 Okay, what's to the left of $H_n(U)$ in both cases?

Output characteristics is a plot of $I_C$ with $V_{CE}$

It should be $n+1$ homologies but those vanish

5:19 PM

each line in the graph is for a fixed value of the base current

In 2014, 583 students got full marks in SAT all over the world (qph.ec.quoracdn.net/…). Out of them majority were from US. Now suppose even 50 students from India got full marks, remember that there are over 15,000 Indian appearing for SAT each year (quora.com/How-many-people-take-the-SAT-in-India). So the percentage of people who got full marks is 0.33 %. Much less than what you claimed.

@YashasSamaga

@YashasSamaga yeah

@Koolman output admittance is calculated using $h = \frac{\Delta I_C}{\Delta V_{CE}}$

@anonymous SAT is not SAT subject test

just SAT = Evidence based Reading and Writing, Math test

@ACuriousMind So a $0\to $ for both?

@YashasSamaga When did I say so?

5:20 PM

The one I was talking about was Physics, Chemistry, Math Level 2 subject test

@YashasSamaga what is output admittance

@0celo7 Yes.

@anonymous If you consider the SAT full test, not even 5 people from India get full

@ACuriousMind So for $0\to H_n(U)\to H_n(M-\{x\})\to 0,$ this means $H_n(U)\to H_n(M-\{x\})$ is an isomorphism.

@Koolman is it in the syllabus? If not, then ignore it.

Do you know how the CE circuit works? @Koolman

@Koolman What's in your syllabus for CE configuration?

5:22 PM

@ACuriousMind aaand I'm lost again

@Koolman I had a crash course on solid-state physics & semiconductors at National Science Camp

I have no idea about NCERT syllabus

In the other case I have $0\to H_n(U)\to H_n(M-\{x\})\to \Bbb Z$

But the $H_n(U)$'s could be different

@YashasSamaga Level 2 tests? Those are easy for anyone who studies science at high school irrespective of the country.

SAT 1 is the most important.

@anonymous No it isn't.

@anonymous I didn't break 700 IIRC

5:24 PM

@anonymous The U.S. National Percentile for 800 Math 2 is 97%

Our's is 80

@0celo7 Make the open set homeomorphic to a half-ball contained in the full ball. Then you can achieve an $U$ for the half-ball that you also can use for the full ball

@anonymous I never talked about SAT 1 and SAT 1 isn't important for international candidates.

Which open set, which full ball?

@anonymous even MIT accepts international students with 100 TOEFL score

Harvard does that too

@0celo7 ...the neighbourhood of $x$ homeomorphic to $\mathbb{R}^n$.

5:25 PM

@ACuriousMind $V$?

user228700

@JohnR: 3 hours of sleep--fatal or not?

Are you saying I can pick the same $U$ for both?

@0celo7 Well, $V$ was that with $x$ itself removed, but yes

@0celo7 Yes

But then it's not clear I can arrange the intersections to be what we had

@anonymous There are cases where MIT, Harvard have picked U.S. students with very bad SAT score :) becaz it is a holistic process unlike JEE... the tests are used to filter out students (can't speak English? then you won't get accepted)

5:26 PM

How would I do this? $x\in M$ is contained in some set $A$ diffeo to $\Bbb R^n$.

@0celo7 It is, at least to me.

@anonymous Those with 2400/2400 on SAT full test get regularly rejected by the Ivies

But I'm just going off my mental picture here, so you will probably not be satisfied :P

Should I take $A$ to be a ball? What's happening here

@Kaumudi.H you've just woken up after 3 hours sleeping?

5:27 PM

@anonymous talk.collegeconfidential.com/discussion/comment/20150269/…

2400/2400 in both SAT Sub tests & full test getting deffered from MIT :)

user228700

@JohnRennie No, I'm asking if--and you do already know that I have done a fair bit of research on sleep--getting 3 hours of sleep would kill me.

@ACuriousMind So I have a ball $B$ and an open set $U$ such that $x\in U\subset B$ and $U\cap B$ is an annulus and $U\cup B=M$

@anonymous That guy even has 11 APs with 5s

@YashasSamaga does China have a JEE type test?

@skullpetrol I don't know but they can't take SAT or ACT

5:28 PM

Ivies are unpredictable.

@skullpetrol Yes.

@ACuriousMind Are you saying I should fit a half-ball inside of $B$?

@0celo7 yes

I...I...I don't know if that works without proving what we're trying to do...

Wait

@Kaumudi.H Getting less than eight hours a night on a regular basis will reduce your concentration and memory. Getting three hours a night on a regular basis will leave you a shuffling zombie. But it isn't going to kill you, just make you wish you were dead.

half-balls are a basis of the topology

@ACuriousMind Ok never mind, that works.

5:30 PM

@0celo7 Just take any half-ball and restrict the homeomorphism from $H^n$ to an arbitrarily small region around the image of $x$

user228700

@JohnRennie ...alright :-|

@ACuriousMind But now the half-ball is disjoint from $U$...

@YashasSamaga i think ,it is not in the syllabus

it doesn't generate $M$

do I need to take the half-ball first?

@Koolman Do you have the output characteristics graph?

5:31 PM

@Kaumudi.H maybe I put that a little harshly, but getting enough sleep is absolutely vital and something that frequently escapes teenagers :-)

@Koolman $I_C$ vs $V_{CE}$ graph

@JohnRennie 8 hours is not realistic

I get 7

will I die?

user228700

@JohnRennie No, u put it perfectly nicely :-)

Hm...this might not deliver what I wanted it to deliver. One could take $U = M-x$ and we're none the wiser

I get 0 hours of sleep on some days, I get 15 hours of sleep on some days

5:32 PM

@YashasSamaga trying to understand it

@0celo7 Hey, I'm a physicist. it was an order of magnitude estimate :-)

@YashasSamaga yeah

@Koolman you need to understand the circuit to understand the graph

Hmmm, maybe take $U=M$? Nah, that's not allowed...

@JohnRennie so anything between 80 and 0.8 hours of sleep is ok?

5:33 PM

80 hours sleep a day could be challenging

3

Time dilation.

@YashasSamaga struggling for that

@Koolman Check out Pradeep Kshetrapal lectures.

@ACuriousMind Why would we be non the wiser?

On transistors

5:34 PM

is there nothing wrong with $$0\to H_n(U)\to H_n(M-\{x\})\to \Bbb Z$$ being exact?

@anonymous okay

It really burns me when not only can OPs not be bothered to type out a question, but they can't even be bothered to orient the photo properly.

-1

Q: How do I solve this question (jee problem, 119)?

I tried to find the torque on sphere due to normal reaction by rod by balancing it over the center of mass of rod but the normal reaction passes through the centre of mass sphere so I couldn't find an equation to calculate friction force. Answer is 0.8

homework-and-exercises newtonian-mechanics rotational-dynamics rotational-kinematics

@0celo7 Because it doesn't tell us anything, does it?

hn.premii.com/#/article/13713480

A SHA-1 hash collision has been found!

I had this idea what me might "see the change" between the homology of $M$ and $M-x$ in this way without actually doing relative homology but it doesn't seem to work

5:37 PM

@ACuriousMind Physics-Chat-Bot, define "homology".

@DanielSank A measure for how many holes a space has

@ACuriousMind Groovy. I learned about this a bit in Munkres's Analysis on Manifolds.

There's that whole business about closed forms being exact, unless there are holes.

user228700

I wonder, do mods have the standard "Hi <name> Welcome to Physics SE! ..." comment to post on "bad" questions saved in a notepad file or something?

And then if there's one hole, there's exactly one closed but not exact form, up to addition of exact forms.

@Kaumudi.H I type it every time.

...but I'm not a mod.

...and I try to tailor the message to the particular user.

I actually have those in a text file on my desktop lol

user228700

5:40 PM

I suppose I meant "People who regularly try to answer/review questions", not mods.

@DanielSank Yes, exactly - the closed-but-not-exact forms measure something "dual" to homology though, they're deRham cohomology

user228700

@DanielSank Damn...

user228700

@YashasSamaga I see x'D

@ACuriousMind Are they "dual" because the forms are not holes, but have a correspondence to holes?

368

Q: AutoReviewComments - Pro-forma comments for SE

No more re-typing the same comments over and over! This script adds a little 'auto' link next to all comments boxes. When you click the link, you see a popup with 6 configurable auto-comments (canned responses), which you can easily click to insert. This script was inspired by answers to thi...

script comments

4

5:41 PM

...in the way indicated above?

user228700

@ACuriousMind Whaaat?! Nice!

@ACuriousMind I did not know that existed.

Thanks.

@ACuriousMind Heheheh, yet here you are, talking cohomology with an experimentalist. You're a glutton for punishment.

@DanielSank Yes

Gluttony is a sin.

@ACuriousMind Lee seems to think it can be done with homology and de Rham cohomology

5:43 PM

@ACuriousMind Cool. Thanks. When I learned about deRham cohomology, it was one of the most satisfying moments of my life in mathematics.

The fact that the special closed but not exact form corresponds to the electric field of a point charge in 3D, and to the magnetic field of a line current in 2D (and to the vector field associated with a simple pole in complex analysis) made me feel very happy and amazed.

@Kaumudi.H I have a comment for homework questions saved as a text (notepad) file. But that's the only such comment.

@DanielSank Basically, you view a form as a map on submanifolds (by integrating the form over it), so differential forms are linear maps on submanifolds of fixed dimension, i.e. they are dual in the sense of linear algebra to them. And homology is computed in terms of subspaces/submanifolds.

The rate at which we star messages in this room defeats its purpose!

Oh the irony :-)

Irony squared

Someone had earlier mentioned the same.

AccidentalFourierTransform

5:46 PM

remember when Slereah pointed out that we were just about to hit 9000 starred messages? that was a couple of weeks ago... now we are at ~9300 :-/

I need an adult

@AccidentalFourierTransform this one

user228700

@JohnRennie OK :-)

AccidentalFourierTransform

@YashasSamaga lol yeah, exactly

Riots!

:: a room owner reaches for the Cancel stars button ::

AccidentalFourierTransform

5:48 PM

please do

Riot act in effect.

@JohnRennie Why? Just leave it be.

2

AccidentalFourierTransform

@DanielSank you anarchists are ruining this chat room

Oh?

Oh dear. 20 stars in the last 2 minutes.

user228700

5:49 PM

Oh dear God...

Look, I don't like the star board to be cluttered either, but I think it would be much better for us to convince the vandals that it's better to not clutter it, instead of the room owners making unilateral decisions about what can be starred and what can't.

2

Apparently someone disagrees.

LOL

@DavidZ recently helped me understand the idea of consensus. I appreciate this very much and I think it's something we ought to keep in mind.

Never challenge the stars

2

user228700

The Fault (is) in Our Stars

5:52 PM

It is written in the stars.

It starts again.

Are suspensions issued for star abuse?

AccidentalFourierTransform

it stars again

@DanielSank Starring is anonymous, there's no accountability at all - how do you propose to convince people when you don't even know who you're talking to or why they're doing what they're doing?

@YashasSamaga no

@ACuriousMind Voting is also anonymous, yet I've seen you make statements about how one should vote.

It doesn't lend itself to prolonged abuse either - you get like 20 stars per day and then you can star anymore

5:54 PM

I don't see accountability as a prerequisite to discussing behavior. Do you shy away from discussing government and politics because voting is anonymous?

user228700

@ACuriousMind What? I wasn't aware of this!

In short, I do not understand how anonymity is relevant at all.

user228700

::When you (think ) have made a really good (by your standards) pun but it goes completely unnoticed because nobody gets the reference:: :'-(

@Kaumudi.H I got it :-)

@Kaumudi.H I still don't get it.

5:55 PM

@ACuriousMind Am I to assume you no longer wish to discuss this?

AccidentalFourierTransform

the book, right?

user228700

@JohnRennie :-) Ah, one at last! (:-P)

@YashasSamaga What is the product of reaction of hydroxyl amine and nitrous acid?

user228700

@AccidentalFourierTransform Yeah. There was a movie as well.

@anonymous oxidation?

user228700

5:56 PM

The Fault in Our Stars

The Fault in Our Stars is the sixth novel by author John Green, published in January 2012. The title is inspired by Act 1, Scene 2 of Shakespeare's play Julius Caesar, in which the nobleman Cassius says to Brutus: "The fault, dear Brutus, is not in our stars, / But in ourselves, that we are underlings." The story is narrated by Hazel Grace Lancaster, a sixteen-year-old girl with cancer. Hazel is forced by her parents to attend a support group in the "Literal Heart of Jesus" where she subsequently meets and falls in love with 17 year old Augustus Waters, an ex-basketball player and amputee. A feature...

@YashasSamaga I can't find it in my book. Don't know.

Hello everyone

@anonymous Nitrous acid :/

Very strong oxidizing agent

@YashasSamaga Yeah. So what is the oxidized product?

What can an hydroxyl amine give?

5:58 PM

HNO2 isn't a very good oxidizer btw

It is a weak oxidizer

It can be reduced to HNO?

It is both oxidizing and reducing.

@YashasSamaga That is improbable.

It can also disproportionate.

Why is it that a system can be entirely "described" by its Hamiltonian? I see the Hamiltonian as only an operator. Isn't the wave function the true way to fully describe a system?

and produce nitric acid

5:59 PM

It came in JEE some years back. I need to check the solution key.

@anonymous Guesses will always be right in Organic Chemistry

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