The h Bar

DanielSank

1:53 AM

Brother brought home a radio controlled four-prop flying done thingy.

It's a lot of fun, but it only flies for about five minutes before it needs forty five minutes of charging.

One of y'all budding physicists ought to work on energy storage density.

rob

@DanielSank Blugh, materials.

Secret

Last night dream has a weird quote:
Note on winning strategy
In a game involving tactics, while it is important in the degree of collaboration,but so are the number of ways to break a collaboration.

This is then followed by some video scenes in what appears to be some kind of orienteering event at a playground where there's a team. The scene is then replayed where a blue team run in the middle of them, splitting the group into 2 groups of people.

Otherwise, in the maths chat, Acuriousmind and Danielsank were discussing about undefined physical quantities with acuriousmind quoting how momentum $\hat{p}$ is undefined for all fractions of the form $\frac{1}{n\pi}$

According to the dream, the more important factor in winning a game is the number of possible ways to break a cohesive team, and less so on how cohesive the team is

whether the quote hold in some form in reality I have no idea...

DanielSank

2:15 AM

@rob yes. So so so important.

heather

3:18 AM

hello

@JohnRennie, the mysterious package was not a computer, but i did in a roundabout way get a better computer: my dad's got a couple of raspberry pi hooked up into a supercomputer that he gave to me and said he wasn't using them anymore, I can use them!

so now i have a bunch of raspberry pi-i (how do you pluralize raspberry pi?)

freecharly

Hello, this is the first time that I am entering this chat room. Today I noticed that the prolific user CountTo10, who a couple of times was really helpful to me, mysteriously disappeared. Does anybody know the reason for this?

heather

@0celo7, Merry Christmas! Guess what? I got Munkres' Topology =D

@freecharly, hello. I've noticed that as well, and I think that user just left, unfortunately. They deleted their account. I haven't heard about anything in particular happening.

user228700

3:37 AM

Hi, everyone :-) I have "quick" question about the order of ionisation energies of the following elements:

user228700

$_9F : 1s^2, 2s^2, 2p^5$

user228700

$_8O: 1s^2, 2s^2, 2p^4$

user228700

$_7N: 1s^2, 2s^2, 2p^3$

user228700

Ooh, never mind, I figured it out!

user228700

Although I do have another question. Since the electronic configuration of Fluorine is $1s^2, 2s^2, 2p^5$, I'm wondering whether no sort of, erm, rearrangement of electrons is possible to give $1s^2, 2s^1, 2p^6$, which is a more stable electronic configuration due to the half-filled $s$ and fully filled $p$ orbital, as in the case of Chromium.

user228700

3:48 AM

I mean, I know it doesn't happen but why not..?

dmckee

4:00 AM

Because it's not more stable?

Spin orbit interactions mean that in general higher $l$ states have more energy than the lower $l$ states at the same $n$.

That last electron can will one sub subshell or another, so that's not a difference between the proposed scenarios.

As atoms get bigger, the interaction between different orbitals become more and more important but at low $Z$ the naive understanding does pretty well.

Secret

If I recall, the s-p energy gap is he highest for $n=2$ (with p higher than s due to reasons given by dmckee) thus it is highly unlikely for an electron to treat them as degenerate

dmckee

@heather It is good to be wary of rm -rf. Treat it with respect as you would any other potentially dangerous tool: firearms, caustic chemicals, nuclear sources, teenagers...

4

Secret

yeah, on a linux, one can use rm -rf / to basically nuke one's computer. For the mac terminal, nowadays there are safeguards to avoid accidentally nuking the root directory

user228700

Hmm, okay, that makes sense. Thanks, guys :-)

user228700

4:22 AM

I have a bit of a homework-tsy question. I've been given the first and second ionisation energies for a given element in units of eV. I have to convert this to units of kJ/mol. My confusion is how the units of ionisation energy is eV and not eV/mol to begin with...

Sir Cumference

Uh, guys, is @Jim still around?

user228700

I mean, if it's the ionisation energy of a given element, then it's for 1 mol of the element by definition, so shouldn't the units be eV/mol?

Sir Cumference

Wait, nvm

@JohnRennie Would you happen to know the answer to this?

1

Q: Does gravity contract space or curve it?

(The answers to my earlier question explained, mathematically, how the Big Crunch was possible. Now I am generalizing the question to all of cosmology.) In cosmology, gravity serves to inhibit the expansion of the Universe, as seen in the equation for the Universe's acceleration: $$g=-\partial_...

user116211

4:37 AM

Hey @SirC! Happy Hanukkah!

user116211

Anyway, I just saw the Newton's Law form of Eikonal equation.

Sir Cumference

@MAFIA36790 Thanks, Merry Christmas!

user116211

We need to reparametrize the path from arc-length parameter $s$ to $\sigma$ such that $\mathrm d\sigma = n^{-1}\mathrm ds\,.$

user116211

@SirCumference He said he would go to his mother's place so he might be busy.

Sir Cumference

@MAFIA36790 Oh, ok, thanks

@MAFIA36790 Aw, why'd you get rid of your gravatar on Physics?

Perhaps @ACuriousMind or @0celo7 knows the answer to the question I asked

vzn

4:49 AM

in theory salon, Aug 13 at 23:01, by vzn

re Tenev/ Horstemeyer https://arxiv.org/abs/1603.07655

Sir Cumference

@vzn Huh?

DanielSank

@dmckee teenagers are tools?

@MAFIA36790 o/

vzn

@SirCumference its new research relevant to your question. dont know if youre interested in new research or not. are you an undergrad physics student? what country?

user116211

@DanielSank \o

Sir Cumference

@vzn Yep, U.S.

user116211

4:59 AM

@SirCumference The pic from Cross Validated was not competent for this particular hat; so I switched to Maths.

Sir Cumference

@MAFIA36790 Yeah but you got rid of your physics gravatar entirely

user116211

O.o

Sir Cumference

user116211

Hello, @freecharly; welcome to The h Bar.

Secret

[How the existence of division by zero mess up all products of zero]

in Mathematics, 3 mins ago, by Secret

Theorem 3: Division by zero ensures the existence of zero terms $z0=b, b\neq 0$ for all $z\neq 1$
Proof:
If $\exists a, 0a=1=a0$, $\forall x,y,z, (xy)z=x(yz)$ and $x0=0x=0,x\neq 1$ then

$$0a=(x0)a=x(0a)=x$$

Therefore contradiction

user116211

5:01 AM

@SirCumference yes, the Elementary Hat.

Secret

so unlike the zero term $0a=a=a0$, the influence to the algebraic structure is NOT localised to an underlying subset

user116211

Wait, how does it look like Newton's Law $$\frac{\mathrm d^2 \mathbf r}{\mathrm d\sigma^2}= \frac12 \frac{\partial n^2}{\partial \mathbf r}?$$

user116211

Hey @0celo7; merry Christmas and Happy Holidays!

vzn

@DanielSank like the tshirt idea. how about a free swag shirt for special talk volunteers. they seem to need more incentive/ motivation :|

user116211

Only single physicist (DD Holm) used this form, I'm seeing.

user228700

5:14 AM

Is anybody here familiar with Fajan's rule?

user116211

Wait, got a paper; let me check...

DanielSank

@vzn haha, perhaps.

user116211

@vzn Why not a can of beer/ hot chocolate? Huh? Hmm.

user228700

I just watched a video in which the teacher argues that the distortion of electron clouds of the anion causes the compound in question to become more covalent, because part of the polarised electron cloud comes in b/w the two ions, thus giving a sort of covalent effect. That's basically what he said. Is this how it works..?

user116211

@MAFIA36790 all efforts in vain.

user116211

5:19 AM

@Kaumudi.H kinda so.

vzn

@Secret what software is that?

@MAFIA36790 tshirts are easier to ship. participants can ofc brew up their own beverages :)

Secret

It's a unity game, it can be found here

newgrounds.com/portal/view/685942

user228700

@MAFIA36790 kinda..? Is there anything else to it..?

vzn

@DanielSank did you volunteer to ship tshirt anywhere in that meta post? "Im happy to distribute the pieces"? not sure what you meant by that

David Z

I guess shipping is not quite the same thing as paying shipping costs

user116211

5:22 AM

@Kaumudi.H Well, no, you can go with it.

user228700

Okay, thanks :-)

David Z

For swag, personally I would like to have something more interesting than T-shirts. Like how the Chemistry people got flasks.

user116211

@DavidZ Meh; I can't have coffee in those.

user116211

@DavidZ Notepad?

David Z

Notepads aren't terribly interesting

vzn

5:24 AM

@Secret thx interesting, clicking around this seems to be the homepg loju.co.uk/causality.html ... that reminds me have you ever heard of crazy machines? luv that game :)

user116211

hmm

David Z

Plus they're consumable

vzn

@DavidZ yeah ok how about lamborghinis

David Z

That would work :-P

Secret

I have played similar things before

user116211

5:26 AM

I can think of bookmarks.

user116211

But they are not interesting.

vzn

maybe we can get simons to fund it all :)

David Z

@MAFIA36790 yeah, pretty much anything interesting is not going to be cheap

user116211

@DavidZ indeed ;)

freecharly

@heather Hi Heather, ist seems rather strange, CountTo10 was so active every day. What could have possibly have happened to him?

user116211

5:35 AM

Was only T-shirt given during the first swag distribution?

user116211

Or something more?

freecharly

@MAFIA36790 Hello @Mafia36, I wonder what proof of spirits you get at this bar...

DanielSank

@vzn I mean that if the SE staff or mods don't want to do it, I'm happy to order the shirts and then distribute them to users who want them.

user116211

@freecharly Well, unfortunately, he left; speculation, though can be made, is futile actually.

DanielSank

@DavidZ Hmm, what do physicists get in parallel with chemists getting flasks?

Lock-in amplifiers?

I can't think of a characteristic tool that I use.

user116211

5:44 AM

There are theorists and experimentalists both.

DanielSank

@MAFIA36790 Actually, I kind of like that idea.

user116211

:))

DanielSank

Consumable is fine with me... shirts don't last forever anyway.

At least the notepad is somehow related to physics.

user116211

$\uparrow$ valid point.

DanielSank

Ooooooooooh! How about actual lab/computation notebooks!

user116211

5:46 AM

@DanielSank I don't think it's a bad idea. Sounds good.

DanielSank

Oh, @heather: beginnings of my public journal post on Super Metroid

user116211

Morning @JohnRennie!

John Rennie

Morning all :-)

user116211

@JohnRennie That hat is awesome!!

user116211

Made for you ;)

DanielSank

5:47 AM

That's a hat?

user116211

@DanielSank Fiery hat.

DanielSank

I thought John had simply experienced a mid life crisis.

John Rennie

It does look good doesn't it :-)

user116211

@JohnRennie indeed!! You rock it!

vzn

@DanielSank "distribute"="ship"? what about shipping costs? youve seen the JR-karmaudi saga no doubt right?

user228700

5:48 AM

@JohnR: Morning! :-) How was Christmas?

DanielSank

@vzn Yes.

user116211

@DanielSank ;P

John Rennie

@DanielSank no, that'll be when I grow a ponytail and buy an open top sports car :-)

I have it scheduled in for next year.

DanielSank

@vzn Depends on how many people go for it. To put it plainly, if it's only a dozen or so, I'd willingly pay out of pocket to get some fun swag going on this site. I hope and prefer the SE staff to take over though.

vzn

@DanielSank fyi heard SE gave up on the swag stuff due to "fulfillment challenges"

DanielSank

5:49 AM

@JohnRennie Ah, carry on then.

John Rennie

@Kaumudi.H Morning. Christmas was quiet but good. The guinea fowl was delicious :-)

vzn

@JohnRennie sounds like the perfect midlife crisis. dont forget the younger woman :P

user228700

Nice :-)

John Rennie

@DanielSank and start writing papers on the philosophy of science :-)

user116211

@freecharly This place is awesome; you can share your ideas, problems, get help, exchange views, and much more. I like this place for I can get help here, get to know new things; get corrected by mods on actions; this place is indeed awesome.

DanielSank

5:50 AM

@vzn I'm waiting to hear from one of the mods as to whether the SE staff will back us. dmkee indicated that it would be a week or two before we hear from them.

@JohnRennie eh?

vzn

@DanielSank what do you mean by "back"?

user228700

Oh, BTW, is anybody familiar with the condition of arthritis? If so, is it common in 17 year-old girls?

DanielSank

@vzn Provide $$ and/or deal with distribution.

John Rennie

@DanielSank that's the usual first signs of a mid life crisis in physicists ...

DanielSank

@JohnRennie Oh indeed? I didn't know that.

John Rennie

5:51 AM

@Kaumudi.H Yes. No. My goodness you are a hypochondriac :-)

vzn

@DanielSank it seems like they have officially bailed on that long ago with their swag-closing announcement years back. havent ever heard of them doing anything otherwise on group-by-group basis, has anyone else? they recently closed community blogs also... :(

DanielSank

@Kaumudi.H Yes, we're familiar. No, you don't have it.

Do your hands hurt?

@vzn Yes well sometimes if you actually do work and ask, people will help.

So I'd like to ask the SE staff for help. If they say no then nothing is lost.

user228700

@JohnRennie I don't think so. Yes, my hands hurt, I am often very fatigued despite getting up to 9 hours (I checked yesterday by sleeping in) of sleep. Not only my hands, actually. Loads of places, like my ankles, calves, etc.

vzn

@DanielSank lol as my grandfather used to say "cant get hung for trying" but one can also read/ familiarize prior history on it too :| ... anyway as you may have noticed SE mgt is very "hands off"/ near lassaiz faire

John Rennie

@Kaumudi.H That sounds like stress to me.

DanielSank

5:53 AM

@vzn Indeed. If there were a post saying "we're never doing this again of our own accord, nor will we entertain requests from communities to organize swag", then I'd not ask.

user228700

@JohnRennie Even the aching? -_-

John Rennie

@Kaumudi.H Which is entirely reasonable given the stress you're under at the moment.

vzn

@DanielSank ok. did you see the announcement where they closed the swag system a few yrs ago?

DanielSank

Let us all take a moment to point out that we're not medical doctors and are not giving medical advice.

John Rennie

@Kaumudi.H Yes, stress can cause pain like that as well.

user228700

5:54 AM

@DanielSank Sure, sure, I know.

DanielSank

@vzn No. A link would be nice.

I haven't heard of or experience stress-induced joint pains.

Do both hands hurt or just the one with which you write?

user228700

Okay, let me submit that it's 28 degree Celsius here and I can't walk/have my feet be on the ground without getting all kinds of pains. So I'm wearing socks AND slippers and ooh, even an effing sweater.

vzn

← quite happy to play a credible doctor in cyberspace

DanielSank

@Kaumudi.H Did this happen suddenly or slowly?

user228700

@DanielSank It's been awhile, actually.

vzn

5:56 AM

@DanielSank thought somebody posted it in here let me try to dig it up

DanielSank

@Kaumudi.H It's 28C and you feel cold?

freecharly

@MAFIA36790 Thanks @Mafia36 for your positive perspective. From now on I will surely show up here more often...

John Rennie

@Kaumudi.H When did you first notice it?

user228700

@DanielSank Yeah :-/

DanielSank

@Kaumudi.H That's odd. How long has that been going on?

@freecharly Very good!

user228700

5:57 AM

@JohnRennie It was quite clear about two months ago when it was north of 25 degree celcius and I still needed to wear an oversized sweater.

DanielSank

@Kaumudi.H Have you lost a noticeable amount of weight recently and are you sleeping regularly?

user228700

My mom has arthritis so I checked for its symptoms just now and BAM, literally everything matches my experience.

David Z

@vzn They closed the store, but I think they still give out swag in the early days of newly graduated sites. Though I haven't checked in a while...

DanielSank

@Kaumudi.H It's rather unlikely that you have arthritis at your age.

user228700

@DanielSank It's been awhile since I checked my weight but oh yeah, sleeping problems? Totally.

DanielSank

5:58 AM

@DavidZ Yeah, somehow I missed out on the signal processing one >:(

@Kaumudi.H If I were you I'd do this:

user228700

Hm..?

DanielSank

1. Record my weight and do it every week for a while. Find out what my last measured weight was e.g. at the doctor.
2. Deal with the sleeping issues. Poor sleep is the gateway to endless health problems. Bad sleep habits can be very hard to break so it's best to establish good sleep while you're young. It can be difficult and I'd be happy to talk at length about this.
3. Go talk to a doctor. Feeling cold in that temperature is not normal.

user228700

That sounds like reasonable advice from a physicist who is not also a doctor, thanks :-)

DanielSank

That you've been feeling cold for a month suggests that you don't have an acute illness, but that's still abnormal and should be resolved with a medical professional.

vzn

180

Q: What happened to the Stack Exchange Store?

There used to be a place where you could buy Stack Exchange branded gear, what happened to it?

support shop

user228700

6:01 AM

@DanielSank What's it got to do with feeling cold for a month?

Swapnil Das

Hello guys. Gotta ask a serious doubt now.

vzn

basically the history is that they distributed swag from the store, and then "mostly" discontinued the swag after the store closed ("administrative nightmare")... but maybe the site graduation swag is still in play, can attest to getting a few shirts over the yrs... have always wished they would expand it... they have a program to distribute $$$ donations based on mod choices, maybe they could modify it some

DanielSank

@Kaumudi.H If you had influenza or similar, you wouldn't be able to go a month without realizing you were rather ill ;)

user228700

Ah, yes, okay :-)

user228700

Wokay, thanks! I'll do something about this...

Swapnil Das

6:03 AM

Umm. I'm gonna post a screenshot, please have a look.

DanielSank

@Kaumudi.H, please address your sleep issues.

Swapnil Das

I used the Daum equation editor for quick latex.

DanielSank

Sleep is a prerequisite to being an effective human. You cannot cheat sleep. You can try, but then in the end you wind up sick, unable to think as well, and all kinds of other things. If you get used to not sleeping it's even worse because then you don't realize that you're not at your full potential.

I had a lot of problems with this and I am happy to discuss in details if you need. For now, I need to go to sleep ;-)

vzn

this is starting to remind me of 0celo7 eye drama o_O ... KH have some sleep suggestions too, some stuff has worked for me. actually there is some great writing by huffington on the subj. she actually took up the issue wrt trump who sometimes brags he rarely sleeps or sleeps few hrs... she had a personal drama of fainting due to lack of sleep etc

DanielSank

PSA: Huffington Post is also not an authoritative medical resource.

vzn

6:06 AM

@DanielSank lol neither is DS :P

DanielSank

^ correct

Swapnil Das

DanielSank

@SwapnilDas FYI you can type mathjax here.

$$\int f(x) \, dx$$ etc.

vzn

@DanielSank she is a advocate/ persuasive writer/ soap box stander etc.

DanielSank

good night, all.

Swapnil Das

6:07 AM

night.

Umm so. I copy pasted that latex to the Physics Q&A site.

As it was a part of the question I needed to ask.

John Rennie

@heather Coooooooooooooooooooool!! :-) The Raspberry Pi computers (see how I avoided that awkward plural there :-) are hugely entertaining to play with and there's a large community of people doing stuff with them.

Swapnil Das

Now, why doesn't this LaTex execute? Is there any technical error? Please point out, Computer gurus.

vzn

another recent SE swag case study... entitled "choose your own swag! what were we thinking?!?"

78

Q: Choose your own swag - the craziest contest idea ever! What were we thinking?

Contest Has Ended Thanks to everyone for participating. I will be contacting those who participated for shipping details and item verification within the week. Keep a lookout for the email! Tired of seeing all the Stack Overflow swag everywhere? Want something different? Well, now's you...

discussion swag contest

user228700

@DanielSank I've been trying but I dunno how.

user228700

I get 7 hours of sleep everyday but I feel tired af anyway.

user228700

6:12 AM

Oh, u're gone. Okay, goodnight :-)

John Rennie

@Kaumudi.H I echo Daniel's point that the medical advice you get here is worth roughly what you pay for it, but I still think it sounds like stress to me.

Swapnil Das

user228700

Yeah, okay :-/ I'll just keep on keeping on, then.

Swapnil Das

<I'm just creating an URL, please ignore>

John Rennie

In which case the symptoms will miraculously disappear once the exams are over.

user228700

6:13 AM

(Y) Okay :-(

John Rennie

Have you tried asking your parents what they think? They know you rather better than we do.

user228700

Lol, yes. I asked my mom and she says that it's because I'm not studying well enough and that I feel bad about that and that's why I feel fatigued and all-work harder is basically what she said.

user228700

(She's not a doctor either)

Swapnil Das

@Kaumudi.H Sorry to interrupt, but do you aspire to become a doctor?

user228700

Nope.

Swapnil Das

6:17 AM

Ohk, fine.

user228700

@JohnR: My mom's advice works?

John Rennie

What you're doing is really hard. I'm honestly not sure I could do it.

Having to revise all of science, on your own without peer support, is a really stressful thing to do.

Swapnil Das

John Rennie

Stress is a funny thing - you don't necessarily feel like you're being stressed. Just the continuous low level pressure of having to work every day and worrying whether you're doing enough is easily sufficient to cause stress symptoms.

vzn

@Kaumudi.H maybe youre tired because you (already) study a lot? ~7hrs/ day is considered healthy for most

John Rennie

6:22 AM

I used to get similar symptoms when I was working full time. Difficulty sleeping, and continuously feeling tired, is the one I really remember.

Swapnil Das

My sleep record is 14 hours (don't curse me now, I was child then)

vzn

@JohnRennie because "low level pressure" ≈ stress

user228700

@JohnRennie Hmm, okay.

user228700

Like I said, I guess I'll just keep on keeping on, then.

vzn

@JohnRennie "revise all of science on your own without peer support"?

John Rennie

6:24 AM

@vzn I think to a large extent stress is whatever you think it is. Some people can take lots of pressure and not care. Others react badly to even a little pressure. For my own part I can deal with short term pressure but not if it continues for any length of time.

user228700

I have a quick question. Binary compound = Compound formed from two non-mentals? (As given in my excellent textbook. Google disagrees. Decided to settle it here, as always)

Swapnil Das

two elements. No?

vzn

@JohnRennie there are mental, physical, environmental factors. aka "bio psycho social"... the whole indian exam systems sounds more stressful than US SATs, but surely both are stressful...

user228700

@SwapnilDas Huh?

John Rennie

@Kaumudi.H isn't it just any compound $A_nB_m$ ?

Swapnil Das

6:26 AM

@Kaumudi.H My idiotic book stated that it is a kinda compound made out of two distinct elements.

user228700

@JohnRennie With A and B being anything, metal/non-metal? Yeah, that's what Google says.

John Rennie

@Kaumudi.H Yes.

user228700

@SwapnilDas Your book is not so idiotic. That kinda summarises it, as given on Google, at least.

user228700

Wokay, thanks! :-)

Swapnil Das

:-)

I still got a perfect in Physics + Mathematics and 0 in Chem -_-

user228700

6:38 AM

Okay, this isn't exactly a question related to the concept but my I'm making notes and my textbook says: "The periodic table is the most important concept in both principle and in practice"

user228700

What does the italicised phrase mean?

Swapnil Das

Theoretical conclusions of the periodic table have experimental evidences?

user228700

Umm, I don't know if that's correct...(At the same time, I also don't know what is)

Swapnil Das

Neither do I, was just a guess =P

John Rennie

@Kaumudi.H I'm not sure the comment has any great significance. Whether it's worth a lot of effort figuring out what it means is debatable ...

user228700

6:43 AM

Okay, I suspected as much. ::Drops it and decides to move on:: :-P

koolman

7:23 AM

Hii @JohnRennie

John Rennie

Morning :-)

koolman

Morning (afternoon) :-)

Could you explain what is the difference between emf and potential difference

In my book it is written as

The potential difference between the two terminals of a source when no
energy is drawn from it is called the "Electromotive force" or "EMF" of the source

In this what energy they are talking about @JohnRennie

John Rennie

I can't be sure what your book means, but maybe they're referring to fact that any voltage source has some internal resistance. So for any current greater than zero the voltage at the source terminals will be reduced by the internal resistance.

koolman

So there is no relation of energy

John Rennie

If E is the EMF, V the potential difference, R the internal resistance and I the current then the potential difference will be $V = E - IR$

The word energy seems rather vague in this context.

koolman

7:30 AM

Yes

So this is the only difference

John Rennie

As far as I know that's how the terms EMF and potential difference are usually used.

koolman

Does by energy they mean heat energy I$^2$R

John Rennie

@koolman don't know. I wouldn't attach too much significance to the exact wording that your book uses.

koolman

Ohk

Thanks for helping

user116211

7:52 AM

-2

Q: General Physics Error

Is it not really annoying how stupid people on stackexchange/ stackoverflow ban questions just because they find that it is too hard to actually answer them and because of that they cover up by saying that the question is irrelevant and not explained correctly. Pretty sure that this question is a...

kinematics

user116211

Mods, check this post, this is going crazy.

user116211

And now there is answer too, which is also nonsense.

user228700

8:15 AM

I've got a quick question again!

user116211

@JohnRennie, guess what I got...

user116211

The BlueFeet hat!!

user228700

This is what my textbook says:

user228700

> "Lothar Meyer determined the atomic volumes of elements by dividing their atomic masses with their densities in solid state. He plotted a graph of atomic mass against their respective atomic volumes for a number of elements and found the following observations:"

user228700

> "1) Elements with similar properties occupied similar positions on the curve...3) Transition metals occupied the troughs"

user228700

8:19 AM

Why do they have the smallest atomic volumes? They are fairly big in size, no?

John Rennie

There's a nice graph of atomic radii here

I'm not sure how far this supports what your books says ...

user228700

Neither am I :-/ I'm still looking through that ^ ...

user228700

Hmm, a quick Google tells me that indeed, the volumes of the transition metals are smaller than that of the representative elements, but I can't seem to find exactly why this is...

John Rennie

The transition metals do have relatively small radii.

That's basically because (e.g. for the first transition metals) the 3d orbitals are buried inside the 4s orbital. As you increase the number of 3d electrons the increased effective nuclear charge pulls the 4s orbital inwards.

user228700

@JohnRennie What? Okay..?

user228700

8:31 AM

It boils down to the fact that the d-orbitals cannot shield very well, right?

dmckee

@DanielSank I don't know about you, but I was a total tool throughout my teenage years.

John Rennie

6

Q: Why do screening effect decreases due to d-orbital?

I am currently learning about p-block elements. In that in 13th group from Boron to Aluminium atomic radii increases. From Aluminium to Gallium atomic radii decreases. From Gallium to Indium atomic radii increases. And from Indium to Thallium atomic radii decreases. The reason for this irregular...

periodic-table periodic-trends

user228700

Yes, right.

user228700

Wokay, thanks! :-)

user228700

@JohnR: I see you are now open to all kinds of questions here and that you've given anybody the permission to ping you? :-)

Swapnil Das

8:47 AM

@Kaumudi.H Even he answered my math doubt very efficient long ago. He's a genius.

user228700

I see :-)

user228700

@JohnR: I didn't know that I had mail :-o

user228700

9:18 AM

@JohnR: You've finally got that mail I've been telling u I'll send!

John Rennie

@Kaumudi.H sorry for the slow response. My mother sent me out to buy papers. There's no paper delivery on boxing day so I had to go to the supermarket. I'll check my mail now.

Swapnil Das

I beg for a kind help, I literally do.

Where online can I find a place to learn iupac nomenclature?

user228700

@JohnRennie Oh, boxing day? I will google this after taking a nap for 15 minutes!

Swapnil Das

Do I seriously gotta memorize all those rubbish priority stuff?

John Rennie

Boxing Day

Boxing Day is a holiday celebrated on the day following Christmas Day in the United Kingdom and Commonwealth nations. Boxing Day occurs on 26 December, although the attached bank holiday or public holiday may take place either on that day or a day later. In the liturgical calendar of Western Christianity, Boxing Day is the second day of Christmastide, and also St. Stephen's Day. In some European countries, notably Germany, Poland, the Netherlands and the Nordic countries, 26 December is celebrated as a Second Christmas Day. == Etymology == There are competing theories for the origins of the term...

Silly religious festivals :-)

user228700

9:29 AM

Oh, nice, another holiday :-)

user228700

@SwapnilDas Actually, I advise you to buy a book. After searching and searching, I wasn't able to find anything online.

Swapnil Das

@Kaumudi.H Which book do you follow?

user228700

I am currently following Solomon & Fryhles but I moved on to other bits of O.C just to escape IUPAC for a bit.

Swapnil Das

I'm fed up with chemistry, I hope I could stab it 100 times, aaahh!

user228700

Chill! It'll get better :-) Chemistry doesn't suck that bad. Just don't give up on it.

user228700

9:32 AM

Now nap-time!

Swapnil Das

Bye!

Thanks :)

Pissed off layman

10:16 AM

@JohnRennie have you watched the quiz show university challenge?

John Rennie

Yes. I watched it last night. Some decades ago I went to support my college on UC (I wasn't in the team).

Pissed off layman

Nice, I read Timothy Gowers is going to be on it?

John Rennie

That will be interesting. It's a general knowledge quiz so I'm not sure being a brilliant mathematician is that great a qualification.

Pissed off layman

Watching the alumni play is interesting.

Pissed off layman

10:37 AM

@SwapnilDas have you looked at this?

Secret

11:18 AM

[Division by zero] The mere existence of a multiplicative inverse of zero with a compatible additive identity is sufficient to impose a partial order to the structure where $0^2$ is the least element.

in Mathematics, 2 mins ago, by Secret

Theorem 4: Suppose + is a commutative monoid and * contains a zero inverse $0a=1$. Then the two sided zero term $0^2$ is a least element under +. i.e. $\forall z, 0^2\leq z0$

Proof: From theorem 3, the existence of a zero inverse implies all zero terms with $z\neq 1$ exists. Now consider any $a$:

$$(0+a)0=a0$$
$$0^2+a0=a0$$

Now by commutativity, $$0^2+0a=0a$$

By definition of dominance, $0^2 \leq 0z$ as required.

Slereah

imperial.ac.uk/media/imperial-college/…

This seems interesting

Swapnil Das

1:08 PM

@Pissedofflayman I didn't,indeed. If I can't bear the gigantic number of principles of other sites, what could I do with wiki?

heather

1:32 PM

hello

DanielSank

@heather yo

heather

@DanielSank, how are you?

DanielSank

@dmckee totally set that one up.

@heather meh. You?

heather

1:53 PM

@DanielSank Pretty good...my dad gave me his rasberry pi supercomputer because he was no longer using it. And I got some cool books. And other stuff. It was a good Christmas =D

So now, whenever @BernardoMeurer needs to do some computing, he can use four very nice raspberry pi computers to do his bidding.

=)

@dmckee well, I don't know if teenagers should go on that list =P

Hari Prasad

hii

DanielSank

2:16 PM

@heather supercomputer?

heather

@DanielSank four hooked up so they can do calculations in parallel.

DanielSank

Cool

Swapnil Das

Yo

heather

hmm...why would python be saying isinstance((2**8191)-1,int) is False?

oh, nvm

that doesn't work for large numbers

DanielSank

2:39 PM

@heather because it's a bigint?

I'm curious now.

heather

@DanielSank I'm not sure, here's the answer I was looking at:

106

A: Check if a number is int or float

Use isinstance. >>> x = 12 >>> isinstance(x, int) True >>> y = 12.0 >>> isinstance(y, float) True So: >>> if isinstance(x, int): print 'x is a int!' x is a int! *EDIT:* As pointed out, in case of long integers, the above won't work. So you need to do: >>> x = 12L >>> import numbers

Slereah

2:56 PM

So I am reading up on the Rarita Schwinger equation

One important element seems to be the Monge cone

So I investigated it a bit

And I found this :

How to Pronounce Monge Cone

►

DanielSank

3:08 PM

@heather Yeah ok makes sense.

heather

3:48 PM

oh, you saw Rogue One a little bit ago, right @DanielSank? How'd you like it?

Emilio Pisanty

4:09 PM

Damn, this was my 1000th answer? I was hoping for something a bit more momentous.

0

A: Surface charge density of uniformly Polarised Sphere

Yes, that is precisely the point. The surface charge is not uniform - it is zero at the equator, where it changes sign, and maximal at the poles - and this spatial variation is directly captured by the changes in the inner product between the polarization vector (which is constant) and the changi...

heather

+1 for 1000th answer =)

hey, I just looked: I'm at exactly 100 answers.

huh. a cool badge would've been nice. =P

-4

Q: My question is about alien time perception

I saw this in a Through the Wormhole episode. Can we perceive times other than our own? For example, can I be a being who's seeing the world as it will be 25 hours ahead from now?

time perception

^-1, vtc as non-mainstream, perhaps?

or unclear?

DanielSank

@heather I did see it. Probably shouldn't discuss here though (see star board).

heather

@DanielSank good point =) I saw it as well yesterday

DanielSank

@heather lemme make a new room...

Rogue One criticism and discussion

Discussion, with spoilers, of Rogue One

koolman

4:25 PM

Hii @user140278

Welcome to PSE

DanielSank

@heather ^

John Rennie

4:37 PM

@Pissedofflayman Timothy Gowers was on University Challenge in 2015, as party of the Trinity, Cambridge team. He isn't on this years programme.

Emilio Pisanty

@JohnRennie I thought the challenge was for students

Having Gowers in it sounds distinctly unfair

It's like having Terry Tao at a math olympiad or something

John Rennie

@EmilioPisanty At Christmas they do a "Celebrity University Challenge".

I guess Timothy Gowers counts as a celebrity because of his popular maths books.

Actually I've never read any of his books, but that nice Mr. Amazon has just provided me with an ebook of "Mathematics: A Very Short Introduction" and I'll tackle that tonight.

amazon.co.uk/Mathematics-Very-Short-Introduction-Introductions/…

Emilio Pisanty

@JohnRennie oh, ok, fair enough

John Rennie

Chairman of the winning team last night was Val McDermid who is a writer of detective fiction. But she was really good. I suppose being an author means you temd to accumulate esoteric knowledge.

Emilio Pisanty

4:58 PM

Terry Tao on the olympiad is no joke, though

Look up The Legend Of Problem 6 on numberphile

Rogue One criticism and discussion

Transcript for