@anonymous are you in high school?

@DHMO yes

@anonymous I have heard of neither phenanthrene nor birch reduction in high school

@DHMO Really ? I have to learn them for board exams and JEE.

what the hell

Maybe your syllabus is different

sure

then what do you know about phenanthrene?

@DHMO umm? I just know the structure

birch reduction is only breifyl introduced in my 3rd year organic chem, but the mechanism and regioselectivity are not elaborated

then how are you supposed to know which carbon sodium will attack

@DHMO From its resonating structures...

not helpful

I will have to ask on Chem SE perhaps

sure

any integral?

@DHMO Yes a few were left Wait

Try :)

@DHMO

@anonymous interesting

indeed

$u=x^2-1$

Honestly, I have no clue as to how to compute $\displaystyle\int\frac{\mathrm dy}{(e^{2y}-1)^{3/2}}$ @anonymous

By parts? Try by parts on the original integral maybe

I only know that $\int\ln x\ \mathrm dx = x\ln x-x+C$

which I already used

wait

oh lol

$\displaystyle\int\frac{x\ \mathrm dx}{(x^2-1)^{3/2}}$

$=\displaystyle\frac12\int\frac{\mathrm d(x^2-1)}{(x^2-1)^{3/2}}$

Why does this give trans alkene with Na/NH3? ^

Shouldn't it give cis alkene ? :/

Strange

conformation

$\displaystyle = -\frac{1}{\sqrt{x^2-1}}+C$

@DHMO yes... i think that's the best way :)

this is its natural shape

Therefore:

$\displaystyle\int\frac{x\ln x\ \mathrm dx}{(x^2-1)^{3/2}}$

@DHMO Isn't this and that different ?

@anonymous single bonds can be rotated

$\displaystyle = \int \ln x \ \mathrm d\left(-\frac1{\sqrt{x^2-1}}\right)$

@DHMO Oh, so the negative charges remain as far as possible ? I see :)

@anonymous it's called "steric hindrance"

I knew that term, anyway thanks ! It didn't strike me at first

$\displaystyle = -\frac{\ln x}{\sqrt{x^2-1}} + \int \frac{\mathrm dx}{x\sqrt{x^2-1}}$

$\displaystyle = -\frac{\ln x}{\sqrt{x^2-1}} + \frac12 \int \frac{\mathrm d(x^2-1)}{(x^2-1+1)\sqrt{x^2-1}}$

@DHMO the second one will just give arcsec(x)

@anonymous I see

thanks

that was interesting

I have an equation for you to solve @anonymous

okay give

$\dfrac{\mathrm dy}{\mathrm dx}=\cos(x+y)$

z=x+y

substitute and done :P

you're a genius

do you have interesting differential equations?

It is just basic differential equation technique..a very standard method

@DHMO I will start that chapter next week probably. This week I am planning to master Definite integrals starting from tomorrow :)

@anonymous next integral?

you're crazy

@DHMO why?

how can one solve such integral

you can :)

try

it is easy

$\displaystyle = \int \frac{\cos x - \sin x}{(1+3\sin 2x)\sqrt{\sin x\cos x}}\ \mathrm dx$

Almost there!

it's impossible

(sin x+cos x)=y Find dy.

How to write sin(x)cos(x) in terms of y? Think.

beautiful

yep :)

$\displaystyle = \int \frac{\sqrt 2\mathrm dy}{(3y^2-2)\sqrt{y^2-1}}\ \mathrm dx$

Kutur putur!

$\displaystyle = \int \frac{\sqrt 2y^{-3}\mathrm dy}{(3-2y^{-2})\sqrt{1-y^{-2}}}\ \mathrm dy$

almost done

$z^2=1-y^{-2}$, $2z\ \mathrm dz=-2y^{-3}\ \mathrm dy$

$\displaystyle=\int\frac{-1}{\sqrt 2(2z^2+1)z^2}\ \mathrm dz$

then partial fraction and we're done

yesh! done

next?

Indefinite problem set over :P

I gave you all the tough problems I faced

nice

I will start with definite integration tomorrow

Are you interested in that ?

then we'll have even more tricks

@anonymous yes

the trick that I like the most is to turn it into two variables

@DHMO Okay! Lets start tomorrow then! Bye for today. Goodnight :)

bye

(I hope it is night at your place :P)

me too

@Mostafa: according to this: tinyurl.com/h6ehc9c "dual nationals who also hold US citizenship are OK, since US citizens cannot be denied entry to the US". This would cover Vafa.

There are almost zero refugees going to the US from Iran; most are students (and tourists).

@ZeroTheHero Actually, when it comes to terrorist attacks, Iran is safer than the US itself.

@Mostafa Lol, of course the place that sponsors terrorism would, almost by definition, be "safer" than the ones they're at war against.

Of course, that also completely ignores the truths of, for instance, the genocides occurring there where ~1000 people have been killed (primarily Christians & in the last 2 years) which pales in comparison to the 36 who have died in America over the course of about 10 years.

(though if you start from ca. the 1990's, the number of American deaths is in the three thousand range, due mostly to 9/11)

@KyleKanos : one of your links refers to Christians killed but none in Iran...or am I misreading something...

@ZeroTheHero Uhh, yes. That is Iraq, not Iran.

Can't edit it now, but I'll concede the point of wrong geography

Mostafa will be happy for the clarification :)

I think my first point though is still mostly right: a place that is okay with terrorism is of course less likely to be attacked than a country that is not okay with it

It would certainly seem to be foolish for one to attack their own safe haven

Columbia (the country) comes to mind. Peru b

oups.. Peru and the Shining Path...

granted not examples of state-sponsored terrorism.

Anyone else having trouble with \frac markup in MathJax just now.

Reference: physics.stackexchange.com/questions/308408/…

where I have screwed something up and can't seem to get it back.

@dmckee Looks okay to me there

AH, so it is at my end, perhaps.

I'll try forced reloading and then close and re-start my browser. Thanks

Probably need a new OS

@KyleKanos Nah. I'm not running any flavor of windows.

Yeah, probably time to switch to Kali Linux

I just have circa 100 tabs up in Firefox.

@KyleKanos From what you said, it's clear that you have no idea who are the terrorists, what is their ideology, who is fighting who and why and where, how terrorism works and in general what's going on (about terrorism) in the MiddleEast and elsewhere.

About your first statement (the place that sponsors...): When they say Iran is sponsoring terrorism, they mean Iran's financial aids to the Shia groups, mostly Hezbollah in Lebanon; You may want to know that they are at the forefront of the war with ISIS. Actually Iran is the #1 enemy of ISIS, because their ideology is a new branch of Islam called Wahhabism that sees Iran Muslims as infidels.

They're a bunch of asshole who want to kill people. Their reasons and ideologies don't matter much to me.

(want to kill people and are willing to die to accomplish that goal)

That's okay but then please don't make such statements generalizing them to Iranians. Not a single Iranian individual is known as terrorist; unlike many from other countries.

Where did I say that Iranians were terrorists?

Pretty much in all of the paragraphs above (maybe implicitly).

All I said about Iran was that they sponsor terrorism (which it seems you admitted as much above, and several nations of the world have complained about)

And I generalized that it would seem a bad idea for terrorists to attack a place that appears to be a safe haven for them

That's exactly the point. They've been trying their best to attack Iran but that's not how terrorism works. That's why Turkey is having many terrorist attacks, the US had some, but Iran had none.

Terrorists don't take orders from anybody if they grow strong enough somewhere.

Whoever used terrorism as a tool, it's now firing back.

data.stackexchange.com/physics/query/621192/…

Apparently the faq is pretty good for rep

And metric-space is not

I see 50 items in the queues :(

(sorta, there's 50 marked there, but I see 0 to be done)

It's really sad that popular science is ranked so high in the list.

Eh, think of the HNQ effect

@KyleKanos: can you explain D/U ratio and AvgScore. For instance, tag faq has 1213 upvotes and 29 downvotes, but none of these numbers comes close to D/U=2.33 or AvgScore=44.93.

Guys may I ask a short question here?

@ZeroTheHero Look at the coooooodddde! D/U = 100 * downvotes / (net vote)

It's actually a percentage of the number of downvotes on the question to total votes

Poorly labeled, but I'm totally going to blame the original author of the code I forked

@JannikPitt No, only long questions are allowed....j/k, ask away

good enough thanks.

Haha Kyle Kanos :D

Does anybody know where to find the equations of the coupling constants of the fundamental forces as a function of Energy? As shown in this graph: physicsmasterclasses.org/exercises/keyhole/en/theory/…

@JannikPitt arxiv.org/abs/1601.08143 might be of use

Thanks, I'll have a look!

@KyleKanos about your 2nd statement (a place that is okay with terrorism is of course less likely to be attacked than a country that is not okay with it): Totally wrong.

[Wahhabi Islam (aka ISIS Islam or the Saudi government Islam) is explicitly such a belief system, but virtually every other system has the potential]

Come on you guys, make a room for yourselves, the h-bar is fine without the drama that comes from politics

@Mostafa I really enjoy politics, and if anyone wants to go into another room to talk about and fight each other to death and never talk again that's awesome, I love fighting. I just don't like it when it's not in the proper place, so I was just putting in my 2 cents :)

@KyleKanos Interesting how the tag homework-and-exercises is the largest by tag size but near the bottom of the AvgScore ranking.

Given the "debate" on Meta regarding this topic, this is doubly interesting.

*second largest

::sigh:: When a poster isn't actually interested in an answer it is very tempting to simply dismiss the question, but perhaps it is worth answering in hopes of heading someone else off before they head down the same wrong road.

I have a question that says toner ink has a charge of -20e and the electric field must be at least twice the weight of the toner ink for it to work in a photocopy situation. It wants the electric field, so I did $F = mg$ and $E = 2F$ so $E = 2mg$, but the book says $F = qE$ so $qE = 2mg$. My conclusion seems valid too. Why is it wrong?

@Anon234_4521 How does $E=2F$ come about? The electric field does not have dimensions of force.

@ZeroTheHero Hm, I think it's interesting only in so far as it supports the view that homework questions just tend to be not very good/interesting questions, with a few exceptions.

@ZeroTheHero I'm afraid that some people downvote homework questions as a way of showing disapproval (as opposed to evaluating the quality of the question ab initio), which might make that observation less diagnostic than it could be.

Not that I think it is without value, as other people seem to upvote them with little apparent concern for quality as well

@ACuriousMind the example says "the electric force on a toner particle must exceed twice its weight", so I concluded $E > 2F$ and $E = 2F$ is the minimum electric force. I know the book uses $F = qE$ and $qE = mg$ so $E = mg/q$, but how can I avoid concluding that E = 2F?

@Anon234_4521 $E$ is usually the symbol for the electric field, not the electric force!

The field is related to the force precisely by $F = qE$.

I know it means that E is the field, but if electric force must exceed double weight, how is $E > 2F_{weight}$ invalid?

@Anon234_4521 Because on one side you have a field, on the other a force - they don't have the same units, it doesn't make sense to compare them

What you know is that $F_\text{electric} \geq 2 F_\text{weight}$, i.e. $qE \geq 2 F_\text{weight}$.

Oh, I read "electric field" every time I was supposed to read "electric force". Never understood why sometimes I can't see what's smacking me in the face repeatedly. Mmk, thanks.

@dmckee Not sure all homework questions are inherently uninteresting, but my (limited) experience is that in many case the OP is not particularly interested in much more than a quick answer. I wonder if it is possible to correlate "homework questions" with activity, i.e is it likely that posters who post homework questions have a time-limited activity.