The h Bar

/o \o how do you type emoji?

rob

@Secret I don't

user228700

@rob Yes!

user228700

It looks like this on my device:

user228700

rob

8:21 AM

DONE

8:40 AM

From: sadanduseless.com/2016/10/life

user116211

Is it some new version of XKCD?

user116211

3

user116211

@JohnRennie This is awesome ;))

user116211

$$\textrm{TASTY}\cap\textrm{CHEAP}\cap\textrm{HEALTHY}=\emptyset$$

actually at leats to me, it is not empty: The initersection is salad

user116211

8:57 AM

Some Olives, a bit pepper, lettuce, cabbage leaves, cucumbers, tomatoes and carrots.

user116211

Yeh, I do like this combo.

Vegetable risotto would be my candidate. Take whatever veg you have lying around, chop it up, add fresh chilis, garlic and vegetable stock and make a risotto.

user116211

I love a bit burnt dried chilli; it adds an all new flavour to the salad.

user116211

Hey @BalarkaSen.

Balarka Sen

hi

9:26 AM

Could anyone link some mole concept notes and problems? Thanks.

@SwapnilDas that's an awfully vague request. What sort of thing did you have in mind?

Challenging problems and conceptual notes :-)

About what a mole is i.e. 6.023 x 10^23 particles?

9:47 AM

I've got a mole problem, could you help me? @JohnRennie

OK, what's the problem?

If the atomic weight of C-12 was 24 u, then find the value of the duplicate avogadro constant.

Is it 2x N_A?

Well N_A is defined as the number of atoms in 12g of Carbon-12. The question isn't clear, but I assume it's asking how many atoms there would be in 12g of Carbon-24.

Yes, perhaps.

Thoughts?

My thoughts are that it's a stupid question because it isn't clear what it is asking.

10:07 AM

@MAFIA36790 nice

cool find

Since the molar mass of $^1$H is 1gmol-1, we can perhaps assume the molar mass of protons and neutrons are 1gmol-1, thus the isotopic mass of $^{24}$C should be roughly 24gmol-1

then we should be able to obain the no. of moles of 12g $^{24}$C that way

@JohnRennie wait, what?

where are you going to get this magical carbon 24?

you can get ahold of some carbon 22

for something like a few milliseconds

@EmilioPisanty It's a stupid question. Trying to look too deeply into it is pointless.

Isotopes of carbon

Carbon (C) has 15 known isotopes, from 8C to 22C, of which 12C and 13C are stable. The longest-lived radioisotope is 14C, with a half-life of 5,700 years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenically by the reaction 14N + 1n → 14C + 1H. The most stable artificial radioisotope is 11C, which has a half-life of 20.334 minutes. All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is 8C, with a half-life of 2.0 x 10−21 s. Averaging over natural abundances, the relative atomic mass for...

@JohnRennie I dunno

you could ask "If I did manage to put together 12g of carbon 24, what would happen?"

to which the answer is probably "a small nuclear explosion"

@JohnRennie that's the thing

how large of an explosion?

$^{24}$C is probably not really that unicorn sounding, thus can still be reasoned with. But yes it wil be extremely radioactive, probably more so than Ts

10:16 AM

@Secret how is it not unicorn-sounding?

it's got three times as many neutrons as it should

Table of nuclides (complete)

Well no laws of physics say we cannot make such isotope, except it will almost immediately fell apart based on the isotopic table trends

probably first via beta decaying into some higher elements by converting excessive neutrons into protons

A unicorn concept is a different thing, it is forbidden by the laws of physics thus you cannot realise it even in principle or in theory

The isotope table below shows isotopes of the chemical elements, including all with half-life of at least one day. They are arranged with increasing atomic numbers from left to right and increasing neutron numbers from top to bottom. Cell colour denotes the half-life of each isotope; if a border is present, its colour indicates the half-life of the most stable nuclear isomer. In graphical browsers, each isotope also has a tool tip indicating its half-life. == Isotope table == == See also == Island of stability == References == == External links == Interactive Chart of Nuclides (Broo...

Ok nvm, it seems I knew almost nothing about nuclear chemistry

10:31 AM

Hey @JohnRennie

on that track

so carbon 24 isn't on any list

but I'm getting some contradictions on how carbon 22 decays

Wikipedia puts it at beta decay into nitrogen 22

but Mathematica's data puts it mostly at BetaDelayedNeutronEmission into nitrogen 21

with <1% going to nitrogen 22 through BetaDelayedTwoNeutronEmission

There may be some amusement factor in learning about improbable isotopes of carbon, but the original question was just supposed to check students understanding of what Avagadro's number is. And the question is so poor as to be meaningless.

@JohnRennie oh, yeah, forget about the original question

hmmmm

That carbon-22 exists at all surprises me. Ten extra neutrons and it still exists long enough to have a measurable lifetime?

or it looks like the Mathematica curated data might not be that accurate

@JohnRennie yup. and in the millisecond regime.

then again it's a weak decay, which can be a fair bit slower

but still

anyways, what do you make of these branching ratios?

from www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html

oh, never mind

> Note on percentage normalization:
> ec β+ 100%
> β+ p 23%
> means that all decays are ec β+, of which 23% is β+ p

user116211

10:49 AM

An entire book on self-force:

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amazon.com/Self-Force-Inertia-Light-Lecture-Physics/dp/…

user116211

WoW!

user116211

Those two chapters of Feynman in Vol I and vol II were really some sort of badass.

user116211

amazon.com/Classical-Charged-Particles-Fritz-Rohrlich/dp/…

A bit of a vague question, but that's also because I can't make a clear picture in my head. Say I have a diagram with two spins, just some arrows pointing up and down with some dotted line or something in between. Does anyone have a good idea on how to depict a vibrational environment in such a diagram? As in, to depict that the entire system is shaking, in a way. Some finite temperature regime.

I've been looking for diagrams in papers where they include some photonic environment pictorially but I can't seem to stumble upon one

10:59 AM

@user129412 what's your hamiltonian exactly?

that description is a little vague

@EmilioPisanty I'm writing it up now, its a bit involved

@user129412 do the spins couple individually, or collectively?

Individually, in principle. But this might get very confusing in a picture.

@user129412 ...but in practice collectively?

If it's collectively, I'd just put a circle around the two spins and then wriggly-line-couple that circle to some box

If it's individually, I'd put the box at the bottom with (fainter) wriggly lines to each of the spins

No, not collectively in practice. But as a first approximation in the picture.

@EmilioPisanty it would be something along the lines of $$H = -\frac{\omega_1}{2}\sigma_{z,j} -\frac{\omega_2}{2}\sigma_{z,j} + J_{12} (\sigma^{+,1}\sigma^{-,2} + \sigma^{+,2}\sigma^{-,1}) + \sum_{j=1,2} \sum_l(a^\dagger^j_l a^j_l + 1/2)$$

11:10 AM

@user129412 something went wrong with that tex

Okay, that didn't work out just yet.

Still updating it.

$$H = -\frac{\omega_1}{2}\sigma_{z,j} + -\frac{\omega_2}{2}\sigma_{z,j} + J_{12} \left(\sigma^{+,1}\sigma^{-,2} + \sigma^{+,2}\sigma^{-,1}\right) + \sum_{j=1,2} \sum_l({a^\dagger}^j_l a^j_l + 1/2) + \sum_{j=1,2} \sum_l \chi^j_l \sigma_{z,} ({a^\dagger}_l^j + a_l^j) $$

yeah, there we go

Right, with a redundant plus sign and some terrible notation.

ok, hang on

why the double index on the $a$s?

or do you mean

$$ \sum_{j=1,2} \sum_l \chi^j_l \sigma_{z,j} ({a^\dagger}_l^j + a_l^j) $$

Because each of the spins has its own phononic bath

11:13 AM

on that last term

Yes, indeed

That was a typo, to forget the j.

no worries

But indeed, I'm trying to make a diagram of this situation

then I would make two separate boxes under the arrows

and match them with wriggly lines to each spin

Hm. Okay, I have to say I don't completely see that exactly. The box would indicate the environment, in some way?

Sort of connecting them to a mass via a spring?

11:15 AM

don't think of it as a spring

make it gray

I see, I see. Good idea.

and make the wriggly line tightly-wound half-circles

Sounds like a plan.

anyways, I'm off to lunch

Great, I'll probably give this a try then. Thanks for the idea

user116211

11:23 AM

And here is the Frenkel theory: dx.doi.org/10.1016/S0031-9163(64)91989-4

heather

hello everyone

user116211

hello

user228700

Hi, g'morning :-)

user228700

12:22 PM

Anybody familiar with parabolas and circles here?

user228700

I've a quick question:

user228700

in Mathematics, 46 mins ago, by Kaumudi

I've a quick question (again :-P). I'm given the equation of a parabola and been asked to find the equation of the circle having center at the focus of this parabola and it's also given that the circle touches the parabola.

user228700

in Mathematics, 46 mins ago, by Kaumudi

I've attempted it and got the answer but I want to know what the perfect reasoning is, behind my steps. I'm afraid mine may not be correct, even tho I got the correct answer.

user228700

Anyone? What would u take the radius to be?

user228700

12:45 PM

Anyone? Pls? _/_

btw, if I may

user116211

Did you draw a figure?