The h Bar

dmckee

1:07 AM

"We TOLD you it was hard." "Yeah, but now that I'VE tried, we KNOW it's hard."

::chortle::

And

smbc-comics.com/comic/how-to-photograph-science

It's a good day for science cartoons.

loltospoon

2:45 AM

Hello all

Anyone know what approximation method would be good in order to find the spin of an electron in the presence of a slowly precessing magnetic field?

0celouvskyopoulo7

3:34 AM

@loltospoon Adiabatic?

oh, the spin

you can solve that Hamiltonian directly, no?

@BalarkaSen lol

r/latestagecapitalism

"Private property is robbery"

Balarka Sen

5:15 AM

@0celouvskyopoulo7 that's more like it

user228700

5:25 AM

@JohnR: Morning! :-)

John Rennie

Morning :-)

Sorry for the slow response - just dealing with a troublesome server

user228700

No problemo :-)

user228700

5:41 AM

@JohnR: Yay! I've just bought a ticket to a cycling event on June 4 here in Chennai!

John Rennie

@Kaumudi.H Cool :-) What's the event? A group ride to some destination?

user228700

Yes! We start at 5:15 AM from a temple quite near to my home and cycle to a beach resort adjacent to the highway. We are s'posed to reach by 11 AM. At the resort, a buffet brunch of sorts will be provided :-)

user228700

Along the way, there are some rest points I think, where water and refreshments will be handed out to those who need it.

John Rennie

05:15!! I guess that's to avoid the worst of the days heat.

user228700

Yes, yes. This is right in the middle of the summer too!

John Rennie

5:45 AM

It sounds really good fun. I like cycling anyway, and cycling with a group is even better.

user228700

Yes! I hope to make some friends :-) I'm a bit worried about the coming back situation but there is hope! If I reach earlier than most, I can rent a bicycle from them and if I call them in advance, they can arrange for my cycle to be transported back while I come back in train/bus.

user228700

I have to see about that...

John Rennie

You're thinking you might be too tired for the ride home? And I guess the return journey would be right at the hottest part of the day.

user228700

Yes, it would. And yes, I will most certainly be too tired to ride all the way back home. I haven't got the stamina I once used to have, what with 9 months of sitting at home all day :-/

John Rennie

How far is it? How many miles?

user228700

5:49 AM

Only about 8 miles.

John Rennie

8 miles? And it's going to take you six hours?

user228700

Miles? Do u really use miles to measure distance?!

Phase

Yeah..

John Rennie

Yes. Mainland Europe uses km but Britain is still using miles even though we use metres for smaller distances.

Phase

It's the pain of the UK

we dont even use one system

It's like someone threw the metric and imperial system into a blender

John Rennie

5:50 AM

To be fair, converting all the signposts would be a major pain.

Phase

@JohnRennie at least we use celsius eh

user228700

@JohnRennie 5.5, but I suspect that we will be taking breaks in b/w. I'm also a bit confused as to why it would take that look but I am yet to look into the route, etc. I'm also not sure if it's 8 or more.

user228700

@JohnRennie Geez, that's messed up.

John Rennie

@Kaumudi.H not really. It works fine.

user228700

Oh, I'm sure it probably works just fine since you've had years to get used to it but it is a bit strange.

John Rennie

5:52 AM

There is rarely any overlap between measuring small distances in meters, e.g. buying carpet, and long distances in miles. They are two very different situations so the different units doesn't matter.

user228700

Right, right.

John Rennie

Anyway, you can certainly cycle 16 miles. Even without having done much exercise. I mean, you could walk 16 miles!

user228700

Oh wow, it's not even 8 miles!

user228700

Deleted that just in case :-P I'm not that great of a fighter.

John Rennie

Maybe they are taking a scenic route. Still, it isn't going to be a lot longer than the direct route.

This was yesterday's lunch BTW:

user228700

6:00 AM

Ooh, what is it?

John Rennie

Completely vegetarian! The meal was a cheese and broccoli quiche.

user228700

Nice! :-) It looks delicious.

John Rennie

Actually I ate two of the quiches, but both wouldn't fit on the plate at the same time :-)

user228700

Hehe I see :-)

John Rennie

And some of those toasted cheese rolls that I like.

user228700

6:01 AM

Ah, yes :-)

John Rennie

But now the holiday is over, sigh, and it's back to healthy eating :-)

user228700

I went out for dinner yesterday and the day before that.

John Rennie

Wow! Living the high life! :-)

user228700

:-P I had vegetable stuffed naan with PBM on the day before and last night, I had stuffed kulcha with kaju masala :-) Chocolate ice cream for dessert on both days!

John Rennie

I hadn't heard of kulcha before - I've just Googled it.

It looks fairly similar to naan.

user228700

6:05 AM

Yes, it's quite similar. The texture is a bit different but they tasted the same at the restaurant to which I went :-/

John Rennie

Cooked in a clay oven according to Wikipedia. That sounds very similar to a tandoor.

user228700

Ah, hmm...

John Rennie

Anyway, I'm looking forward to a nice quiet week. I've finished the big programming job I had to do, so this week I just have to nursemaid it through the first week it runs in anger.

user228700

Ah, nice :-) This week I have all the things to do!!

John Rennie

It'll give me a chance to catch up on all the little jobs I've been putting off.

@Kaumudi.H When are the last two exams?

user228700

6:10 AM

Like cleaning your house? :-P

user228700

@JohnRennie May 17th and 21st.

John Rennie

@Kaumudi.H I'll be far too busy to do that! :-)

@Kaumudi.H three weeks - so I guess you'll be ramping up the revision big time.

user228700

Yup!

John Rennie

Oh well, at least the end is in sight.

user228700

It is! And I even have a cycling event lined up after that! :-)

John Rennie

6:12 AM

And at least by the time you get to the big exam (JEE advanced) you'll be pretty used to doing exams.

user228700

Yep yep!

Secret

7:20 AM

[A summary] We have:
FRB
SPRITE
Supernovae
X-ray burst
GRB

paracetamol

8:09 AM

@JohnR Hola o/

John Rennie

Morning

paracetamol

How much high-school kinematics do you remember? :3

@JohnRennie (noon here ;) )

John Rennie

High school kinematics is just Newtonian mechanics, so I should be able to manage it.

paracetamol

Woo! \o/

Specifically: Motion of projectiles along an inclined plane ._.

Gimme a second...

Uploads pictures

^ That make sense? (I'm fine with that...it's the next section that's a peeve)

John Rennie

At the moment I'm reading through a report of server status logs, so I can't look in detail at your problem. However it's straightforward enough. Just calculate the time taken to ascend and descend then multiply that by the horizontal component of the velocity.

paracetamol

8:15 AM

> However it's straightforward enough

^ Yep...

Except for the "Range" of the projectile along the plane ._.

See that bit (in the 3rd picture), where:

> OC = Horizontal component of velocity x Time of flight

^ Shouldn't that be:

OC = Component of velocity parallel to the inclined plane x Time of flight?

^Going by the logic employed when determining the Time of flight (picture 2) ._.

John Rennie

Horizontal distance, i.e. displacement in the $y$ direction, is $v_y t$. Divide that by $\cos\beta$ to get the distance along the plane.

paracetamol

Runs off to get a pen and some paper

@JohnRennie Horizontal distance is the displacement along the y direction? O_o

Boggle

John Rennie

Oops, $x$ direction :-)

That's what comes of trying to answer physics questions while also working on a server :-)

paracetamol

\o/

@JohnRennie Sorry ._.

@JohnR Whoa, wait a second... what do you make of of picture 3?

(Should've worded my question better, sorry)

Gimme a couple of minutes...

Slereah

8:31 AM

Oh hell

I think my ethernet cable is busted

John Rennie

@paracetamol your third picture does exactly the calculation I've just described.

paracetamol

> (Should've worded my question better, sorry)

> Gimme a couple of minutes...

@JohnRennie Whup! You're right, sorry about that. And thanks for taking some time off your server-work to help me clear my mess :P Appreciate it...

@Slereah Maybe a curry-wurst might help fix it? ;)

Slereah

Gee are you still on that joke?

paracetamol

^ I found it pretty funny, actually :D

John Rennie

@paracetamol One data point doesn't constitute a trend :-)

paracetamol

8:39 AM

(Largely because I've never heard of a curry-wurst before)

Slereah

It's a German delicacy

paracetamol

@JohnRennie Oh yeah...speaking of which: User @Slereah, If you find my incessant curry-wurst pinging offensive/irritating/lacking in taste, etc, do feel free to tell me. [JohnR reminded me...otherwise ACM would've gotten on my case ._.]

@Slereah A wurst? Okay. But a curry-wurst... that's new XD

John Rennie

Note that just because Sam is French you should not consider his comments on German cuisine to be in any way biased :-)

paracetamol

:D

John Rennie

For the record, I'm sure curry sausages exist in the UK, but I have never seen one.

paracetamol

8:44 AM

@Slereah You're french? :O

@JohnRennie :O

Shudders

paracetamol

9:00 AM

Psst @JohnR, I put up this answer on Chem.SE, I'd like your opinion ~~and upvote~~ on it 0:)

4

A: Why is there no neutron in protium?

@Jan's put up a nice and crisp, answer. My answer is merely a supplement to that ;) It's because the hydrogen ("protium", if you will) nucleus has no need for neutrons. What's this "need for neutrons", you ask? Every element (apart from hydrogen) has multiple protons (it's the number of proton...

^ It's based on my shallow/measly high-schooler knowledge of nuclear physics ._.

@JohnRennie Cheese = Vegetarian? 3:D

John Rennie

In the UK we tend to distinguish between vegetarian and vegan. Only vegans refuse to eat anything that originates with an animal, so they would reject cheese. However vegetarian but non-vegan eaters would still consume cheese, milk, eggs, etc.

paracetamol

Oh... ._.

John Rennie

I should note I observe no dietary restrictions so I'm equally happy eating a vegetarian meal and one containing meat.

paracetamol

@JohnRennie From the Bio. perspective the vegan-vegetarian argument seems...silly :P

@JohnRennie Bu...but... being a vegetarian's sustainable! :)

John Rennie

One of the (very few) bits of wisdom that comes with old age is that criticising other people's beliefs is a poor way to make friends and influence people, so most of the time I don't do it.

paracetamol

9:09 AM

@JohnRennie That's your belief?!

:O

Um..

Speechless

I thought you were just telling me the Brit. convention for these terms/things ._.

Sheepish expression

Albert Einstein

Hello @JohnRennie

John Rennie

@AlbertEinstein Morning

Albert Einstein

Good morning. How are you?

John Rennie

@paracetamol It's not a belief, it's an experimental observation.

@AlbertEinstein Good thanks, and you?

paracetamol

@JohnRennie Mercy! I'm too young!!! (No...i'm not trying to rub it in ._.)

Albert Einstein

9:15 AM

, @JohnRennie, The horizontal range of projectile is $4\sqrt {3}$ times its maximum height, then the angle of projection will be

$1$. $30^\circ $

$2$. $45^\circ $

$3$. $60^\circ $

$4$. $76^\circ $

We have,

$$\textrm {R_{max}}=\dfrac {u^2.\sin. 2\theta }{g}$$
$$4\sqrt {3} x=u^2$$
Where,

$x=$ maximum height
$\theta =$angle of projection

paracetamol

o_o

John Rennie

I probably wouldn't use those formulae to do the calculation. I'd go back to the basics.

Slereah

9:56 AM

To be fair they don't ask physicists to wear a labcoat

You just have to stand in front of a board with equations

Albert Einstein

10:17 AM

@JohnRennie, so how should it be done?

John Rennie

This guy doesn't give up easily!

-1

Q: Mixing two liquids.

There are two container. First container has water at 100°C with 200g, second container has water at 200°C with 100g. How do i calcuate equilibarium temperature?

@AlbertEinstein do you know how to calculate the maximum height of the object?

Albert Einstein

@JohnRennie, u^2/2g

Slereah

I have done that experiment before, except with vodka and milk

John Rennie

@AlbertEinstein OK, and in that equation $u$ is the vertical component of the velocity so it is: $$u = v \cos\theta$$ making the height: $$ h = \frac{v^2\cos^2\theta}{2g} $$ Is that OK?

ACuriousMind

@JohnRennie I'm a little impressed at the persistence, I must admit.

John Rennie

10:23 AM

@ACuriousMind it's obviously become a mission for him :-)

@AlbertEinstein: are you still with me?

Fawad

10:43 AM

0

Q: How to calcuate equilibrium

There are two container. First container has water at $100°C$ with $200g$, second container has water at $200°C$ with $100g$. How do i calcuate equilibarium temperature? I found an answer: $53,33°C$ but I don't think that its true answer

temperature

@JohnRennie yes^

Slereah

@ACuriousMind Help me, I am going into weirder and weirder topological spaces

I am currently looking up branched manifolds

Phase

My god

At least he's providing an answer he's tried

He's evolving

John Rennie

@Fawad just so long as the Chemistry SE don't migrate that question to us :-)

ACuriousMind

@Slereah What's there to help with? Have fun ;)

Slereah

I am under the suspiscion that for non-Hausdorff manifolds $M$, there is some homeomorphism between branched manifolds and $M / \sim$, with $x \sim y$ if $x$ and $y$ are adjacent

Basically turning the branching real line into an actual branch

or "train track", as the branched manifold terminology goes

ACuriousMind

10:51 AM

Odd, ChatJax doesn't seem to work

$\text{test}$ $$\text{test}$$

Slereah

same here

Maybe their server is down

ACuriousMind

Hm, double dollars work, but singles don't

Oh, right!

There was that not-April's Fools announcement about the CDN server going offline at the beginning of May

Fawad

in Mathematics, 1 hour ago, by SteamyRoot

@Astyx @s.harp Replace "2.7.0" by "2.7.1" inside the url in the MathJax bookmark. It should work then

Phase

$4x^2$ its working for me

Secret

1

Q: Definition o branched 1-manifold

i'm studying a papper which has this term "branched 1-manifolds", but the papper does not explain this, according to Wikipédia: "A finite graph whose edges are smoothly embedded arcs in a surface, such that all edges incident to a given vertex v have the same tangent line at v, is a branched ...

dg.differential-geometry ds.dynamical-systems definitions

Slereah

10:54 AM

there's no 2.7 at all in the script

Fawad

javascript:(function(){if(window.MathJax===undefined){var script = document.createElement("script");script.type = "text/javascript";script.src = "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX (..... Continued)

@Slereah you its in last line^

Slereah

Mine reads

ACuriousMind

You likely have an older bookmark, just like me. You need to replace the cdn.mathjax... in script.src by h‌ttps://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AM‌S_HTML

Slereah

script.src%20=%20"https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-A‌MS_HTML"

Alright

ACuriousMind

Yeah, that's what I had, too

Slereah

10:58 AM

there we go

still doesn't work

$x$

nope

ACuriousMind

works for me, reload the page, then start the script

Slereah

I did

I'd better look up the full script

there, all fixed

For branched manifolds $K$ there's a collection of subsets $\{ U_i \}$ such that $\bigcup \text{Int}(U_i) = K$

Is the interior requirement really necessary?

It's a subset of $K$, obviously the boundary will be within the space itself

Or is there some pathological case where you can have $\bigcup U_i = K$ but not $\bigcup \text{Int}(U_i) \neq K$

Seems unlikely, since that's a bigger set

Oh wait, maybe it's for branched submanifolds?

I dunno

Basically branched manifolds seem to be the same as manifolds except defined on closed sets

Phase

11:24 AM

I just accidentally necro'd

Is necro'ing allowed here?

Slereah

If you have good things to reply, yes

There's even a necroing achievment

Phase

Ok well I think I did

Oh

It's just that I felt none of the answers responded to a point in the post

Slereah

it's fine

Remember that a lot of people don't get to questions via the front page

a lot just find them by googling

Phase

true

0celouvskyopoulo7

11:45 AM

Chatham doesn't work?

Time to abandon the chat

Slereah

if you mean chatjax cf above

they changed the version

So you have to slightly change the script

0celouvskyopoulo7

How

I can't program

Slereah

pastebin.com/6n0L6twZ

use this instead of the current script

paracetamol

12:06 PM

Pssst

Basic physics question, anyone?

(It's about significant figures)

._.

Slereah

Shoot

paracetamol

\o/

Q- How many significant numbers are there in the pure number 410?

^ I'm torn between 3 and... infinity

Slereah

I don't think you count significant digits when everything is zeros afterward

Although note that "significant digit" is not a mathematical concept

paracetamol

"3" because...I know how to count with my fingers; and "infinity", because it theory 410 is 410.0000000....

Slereah

There's nothing rigorous about them

paracetamol

12:11 PM

@Slereah Yep

Slereah

The significant figures of a number are digits that carry meaning contributing to its measurement resolution. This includes all digits except:

All leading zeros;
Trailing zeros when they are merely placeholders to indicate the scale of the number (exact rules are explained at identifying significant figures); and
Spurious digits introduced, for example, by calculations carried out to greater precision than that of the original data, or measurements reported to a greater precision than the equipment supports.

So I'd say only two

paracetamol

@Slereah Alrighty then!

Slereah

4 and 1

paracetamol

^ Ouch...but that makes sense ._.

Thanks o/

Runs off

Slereah

One good way to show that significant digits are not that significant is that it's not basis independant :p

Why do we assume a normal distribution for measurements, anyway

It's not like if I measure myself often enough, eventually I'll be 10 feet tall

Sir Cumference

12:27 PM

Whoever invented rainy mornings sucks

Staying awake is 20x harder

0celouvskyopoulo7

Yeah, f u god!!

Slereah

Sexy prime

In mathematics, sexy primes are prime numbers that differ from each other by six. For example, the numbers 5 and 11 are both sexy primes, because they differ by 6. If p + 2 or p + 4 (where p is the lower prime) is also prime, then the sexy prime is part of a prime triplet. The term "sexy prime" stems from the Latin word for six: sex. == n# notation == As used in this article, n# stands for the product 2 · 3 · 5 · 7 · … of all the primes ≤ n. == Types of groupings == === Sexy prime pairs === The sexy primes (sequences A023201 and A046117 in OEIS) below 500 are: (5,11), (7,13), (11,1...

Happy ending problem

The "happy ending problem" (so named by Paul Erdős because it led to the marriage of George Szekeres and Esther Klein) is the following statement: Theorem: any set of five points in the plane in general position has a subset of four points that form the vertices of a convex quadrilateral. This was one of the original results that led to the development of Ramsey theory. The happy ending theorem can be proven by a simple case analysis: if four or more points are vertices of the convex hull, any four such points can be chosen. If on the other hand, the point set has the form of a triangle with two...

Proton-enhanced nuclear induction spectroscopy

Proton-enhanced nuclear induction spectroscopy (PENIS), also sometimes called Cross Polarisation (CP), is a nuclear magnetic resonance technique invented by Michael Gibby and Alexander Pines while they were graduate students in the lab of Professor John S. Waugh at the Massachusetts Institute of Technology. It was one of the first of Pines' experiments transferring spin orientation from one atomic nucleus to another, which has been one of the running themes throughout his career as a leading pioneer in the applications of NMR to the study of non-liquid samples. The PENIS technique was patented...

0celouvskyopoulo7

12:54 PM

Ok how do I get the chat jax to work?