The h Bar

Jake Rose

12:02 AM

What?

Lozansky

Ah, I thought you meant problem as in exercise but perhaps you mean in a test setting?

Jake Rose

No I mean an exercise

Note I said “can’t”

Lozansky

Well, it is my view that exercises should be (sufficiently) challenging

And when you get stuck, you ask the nice folk here:P

danielunderwood

@enumaris enjoy the training! I'm a month in and just now getting to actually work on things

With nice little bits of "oh we actually have to put in a ticket for you to access that"

Also Randall Monroe is publishing another book! xkcd.com/how-to

dm__

1:49 AM

hello

how is the spherical basis motivated? defined here: en.wikipedia.org/wiki/Spherical_basis. seems like it is popping out of thin air.

Scientist Smith YT

@All I know the magnetic field is made up of invisible photons but what are invisible photons exactly and how do we see them? With what instrument?

dm__

you have to talk to a hermit on a mountain top.

Jake Rose

@ScientistSmithYT I don’t think the description of a magnetic field being made up of photons is useful. Better to think of it as a field.

@dm__ what do you mean motivated? It’s motivated by spherically symmetric problems being easier to solve in that basis

Scientist Smith YT

2:04 AM

@JakeRose How do I predict how the magnetic field reacts with different elements if I just think of it as a field?

Jake Rose

What do you mean ‘reacts’?

dm__

for example, why choose $e_{+} = -\frac{1}{\sqrt{2}}(e_{x}+i e_{y})$? it is complex, so I'm assuming I should not be thinking about it physically.

Jake Rose

PS you’re even using the term field when you describe it

@dm__ have you covered spherical polar coordinates?

Scientist Smith YT

@JakeRose By react I mean how the elements behave when a certain magnetic field at a certain gauss measurement is exposed to the element.

dm__

yeah, but I am failing to see the connection

Jake Rose

2:08 AM

What type of problems are you trying to solve? @dm__

@ScientistSmithYT you have to consider lots of things such as the materials relative permeability etc. Maxwells equations provide a solid bases to get most things and lots of nice tricks have been derived to deal with the problems.

Nowadays most things are done computationally though as real life situations don’t always have such nice symmetries

@ScientistSmithYT you should always think of the magnetic field as a field. Because that’s what’s it’s fundamentally defined to be.

Scientist Smith YT

@JakeRose Yeah, I get how real life symmetries aren’t as nice. The reason why I ask is because I’m trying to visualize how the magnetic field gets transferred into a material for a split second. Then become magnetized past a certain limit.

dm__

wigner eckhart one, but figure there's no use without understanding what this spherical basis is all about. all the vector operators are rewritten with it, but I don't see the physical connection to spherical coords

Scientist Smith YT

Such as the compounds NdFeB and Iron Nitride

Jake Rose

@dm__ I thought you might be working on something else and accidentally stumbled upon the wrong wiki. I’m afraid I’m only a second year and don’t know much about what you’re doing sorry :’)

Scientist Smith YT

@JakeRose Then I’m trying to visualize that with the individual elements.

dm__

2:14 AM

no worries :)

Jake Rose

@ScientistSmithYT it depends on the dimensions of the object. The values for relative permeability will be in a table somewhere and thus you can calculate how it behaves.

Scientist Smith YT

The dimensions of the NdFeB compound is 1 inch diameter by 1 inch thick. It is a cylinder shape.

Jake Rose

@ScientistSmithYT it’s also gonna depend on the field it’s placed in

you only have to do the calculations if you want to know precisely how the field will look

Scientist Smith YT

A 3 Tesla magnetic field is what the material is going to be placed into.

Jake Rose

you can make approximations in the centre of the cylinder and ignoring edge effects etc

3 Tesla?

Scientist Smith YT

2:17 AM

Yes

Jake Rose

where did you steal an MRI machine from :’)

Scientist Smith YT

I made one myself through help and wanting a bore of 3 Tesla strength

Jake Rose

If the material is isotopic and has a linear magnetisation then you can calculate the field

yiu can also do it if it isn’t linear but it probably requires computational efforts

Scientist Smith YT

For me that part is somewhat unknown.

Jake Rose

Probanly bets to try and find some hysteresis curves for the magerial

Scientist Smith YT

2:20 AM

I do know that after 6,000 gauss the compound has it magnetic properties back.

Jake Rose

Thatll contain everything (I think) you want to know

not familiar with the gauss unit sorry

what is it you want to know?

Scientist Smith YT

Oh that’s alright :) I want to know the exact Tesla measurement for getting to the full magnetization of the compound NdFeB.

As well as the measurement for iron nitride

Jake Rose

Best to look at hysteresis curves I think then

I’m not an expert in this topic (I’ve only done one in depth EMAG course)

But hysteresis curves should contain a lot of the information

Scientist Smith YT

What will the hysteresis graph show me? I’ve seen one multiple times before but I’m shown the generic graph.

Jake Rose

Tells you the magnetic field inside a material for s given applied external field

Scientist Smith YT

2:26 AM

Oh ok.

I will look into the hysteresis graphs then. Any good links for me or should I start with the wiki

Jake Rose

If you want specific ones to your materials you should look in academic journals

You may have to pay for these. If you’re part of an academic institute they usually have licenses you can piggy back on (like mine does)

Scientist Smith YT

Ok, thanks :)

I’ll be willing to pay.

Are they within the $100 range?

Jake Rose

They’re quite pricey

can be

but no guarantee that the paper you pay for is the one that has your material in

better to buy subscriptions so you can look at lots of oaoers

Scientist Smith YT

I’ll do that instead then

Thanks :)

dmckee

3:51 AM

@ScientistSmithYT The library at your local institution of higher learning almost certainly has an on-line catalog.

The journals themselves may well be in the stacks meaning you have to make a trip down there, but you should be able to tell if they have any prospects before you leave home.

Digging relevant papers out of bound copies on dusty shelves may seem every so twentieth century, but it is free to look and xerox charges are pretty low.

spillthrill

4:33 AM

How was the "Chernobyl won't be inhabitable for 20,000 years" estimate calculated? I thought the 137Cs has a t1⁄2 of only 30 years (and 238Pu is less than 90 years, 241Am is less than 500 years). Or is that figure just for the immediate area of the New Safe Containment? And if that is the case, are there public estimates available for the how long the area <in a 10 km radius, 100 km radius, etc.> will be uninhabitable?

dm__

5:31 AM

hellur?

can someone explain reducible cartesian tensor vs irreducible spherical tensor to me?

Anonymous

6:08 AM

Hmm, I didn't know Spivak has a mechanics book. It seems way less terse and much more readable than Arnold. Thanks to this answer.

dmckee

7:02 AM

Meh. Kids should get off my lawn. And stuff.

A bare answer of "Because definition.", just doesn't do it for me.

We've seen several of these kinds of questions and answers lately, and they are right as far as they go. But to my mind the more interesting question is "How close to the currently defined value was this quantity when we were using historical definitions?" And I suppose the answer is mostly "Within the then achievable tolerance.", but those would be the interesting details. — dmckee ♦ 5 mins ago

dm__

7:39 AM

you fancy spherical tensors?

Slereah

8:47 AM

how does one sphere a tensor

...an effect size of 1.68 (95% CI: 1.56 (95% CI: 1.52 (95% CI: 1.504 (95% CI: 1.494 (95% CI: 1.488 (95% CI: 1.485 (95% CI: 1.482 (95% CI: 1.481 (95% CI: 1.4799 (95% CI: 1.4791 (95% CI: 1.4784...

heh

PM 2Ring

12:32 PM

@Blue and @Chair You may like to look at our rules for the Python room. They work well for us, mostly. Of course, some of those rules won't be relevant here. But I think "Don't ask for answers to your fresh question on the main site" would work here. We do permit people to ask for meta-help to improve the question, though.

user351417

12:52 PM

@PM2Ring Indeed, if I hadn't known that the SO Python room had those rules, I wouldn't have written an answer for our meta post which talked about making chat a bit more active/interesting. However, I'm more concerned about making the rules direct regulars in the appropriate manner too (see ACM's answer to our meta discussion).

user351417

@ACuriousMind @Blue @JohnRennie Since you guys are probably the most active mods/ROs here, could you suggest what I should mention about the actions expected when someone thinks that there's some behavior getting out-of-hand? The SO python page has "If any behaviour in the room makes you feel uncomfortable, you may ping (@username) one of the room owners and we'll do our best to sort it out.
If you wish to contact the room owners privately, email us." Obviously I'm not planning to mention the whole thing about messages being deleted/users chat-banned, since most of us agree that it's not so…

user351417

(I'm planning to write a basic version today and make it a CW post on our meta so everyone can help fix the messy parts)

user351417

I was thinking that we could make the guide a CW question, and we could keep the answers for suggestions (by people who aren't sure if they actually want to edit the guide). Does that seem OK?

user351417

On the other hand, making it CW may open it to abuse from people who don't like it. I imagine almost every physics chat user would have CW edit privileges, so if they don't like it, they could pull some vandalism. Rollbacks are easy of course, but that may get annoying.

user351417

I'm basing that idea upon the homework policy, wherein a lot of the people who rebel against that would probably be new users.

user351417

1:04 PM

Thoughts?

PM 2Ring

1:36 PM

@Chair Ah, right. :)

Mithrandir24601

@Chair flagging is an option

user351417

@Mithrandir24601 You mean a chat flag? Wouldn't that go to any mod, not necessarily one who's aware of the room expectations?

Mithrandir24601

1:52 PM

@Chair yeah, sure - if someone has done something that's generally not considered OK in a specific room, if that's mentioned in a flag, then another mod can either read the rules and act appropriately or actively find someone who does know the rules - it's also a way of getting more attention to something that needs to be dealt with, instead of pinging one person and hoping they're around (when there's something that needs to be dealt with now)

user351417

Ok okee, thanks! I'll mention flagging in the post then.

Mithrandir24601

@Chair I'd say that flags aren't generally a great idea if it's just 'can you do this thing at some point?', as opposed to e.g. 'this person is misbehaving'

PM 2Ring

Flags are visible to all 10k+ users over the whole of the chat network which the room belongs to, so they can be annoying. But if someone is being rude / disrespectful, and no room owners are available, a flag is appropriate.

user351417

@PM2Ring I see a flag-for-moderation option, though I'm not sure how user-friendly this whole system is. To some extent, I'm not even sure who would be raising those issues involving room conduct violations.

Mithrandir24601

2:09 PM

@PM2Ring mod-flags are only visible to mods though

PM 2Ring

@Mithrandir24601 True.

PM 2Ring

2:58 PM

@Chair Thanks for fixing the question from the "I can't accept negative values" kid. I did try to get him to break up his wall of text on a previous question (now deleted), but he didn't get it.

user351417

@PM2Ring I was hesitant to try that one, since he'd been a bit uncouth with a large number of comments the last time we interacted, but I figured that that post was salvageable to a certain extent.

user351417

I figured I'd give it a shot since he spent a week away (to cool down, if I remember).

user351417

He just doesn't learn that titles should be concise and text should have punctuation and paragraphs, does he? If he tries rollbacks, I'll actually be pretty damn pissed.

PM 2Ring

Sure, Indian writing systems are radically different to what we do in English, eg words often join together in a long stream with no spacing between the words, but that's no excuse, since English is taught in Indian schools from an early age.

user351417

@PM2Ring I dunno, my Hindi isn't that bad and I don't think that happens frequently. Of course, I was taught a pretty urban Hindi and I don't know if the shudh (pure) hindi uses english-like commas.

user351417

3:04 PM

Even Kannada (which I can understand but not read/speak) has commas. I don't know about the others, but apparently the structures of a lot of the other languages are similar enough to hindi.

Anonymous

@Chair ...

Anonymous

1. If someone's using outright offensive or crude language aimed at some other user, simply go ahead and flag it. If someone just swearing but it's not aimed at anyone, then you may or may not flag it. Use your discretion. In general, we're OK with playing along if someone drops the occasional undirected expletive. But if you get flagged for it (i.e. someone else finds it rude/offensive), you need to deal with it: you may have to sit out a 30-min suspension.

Anonymous

2. There are also some other subtle cases which are unhealthy for the general atmosphere of the room. For instance, if someone's trying to be passive aggressive at you or someone else, and you're uncomfortable, ping one of the mods or ROs in a one-to-one room or request one of the mods to start a private chat room with you. We'll sort it out.

Anonymous

3. If you're feeling uncomfortable about someone monologuing too much, ping one of the mods or ROs either in the main room or in a one-to-one room. We'll probably shift those messages to another room and deal with the specific user appropriately. However, be sensible while making such requests. If it's just a few lines of monologue (and isn't a regular pattern), then just let it be.

PM 2Ring

I don't know any Hindi, but I briefly studied Sanskrit for a while, a few decades ago. IIRC, punctuation marks don't really exist, but you may get a vertical bar marking the end of a line in poetry & scripture.

Anonymous

3:07 PM

Those are some points for now. I'll think of more. :)

user351417

@Blue Yikes, that's a bit much! Could I instead put 'monologue' under the 'generally-not-appreciated' catoegory (like pinging specific users), and just leave the 'what-should-I-do-when-I-don't-like-what's-going-on' section at flags for offensive stuff and one-to-one rooms for other unhealthy general stuff?

user351417

I'd like to avoid focusing on that because it could end up looking like we're too paranoid/we're expecting lots of misbehavior.

Anonymous

@Chair Sure, sure. I was just giving some pointers. :)

user351417

@Blue Maybe we could put that as one of the 'answers'... it's like side information which wouldn't be in the actual concise guide.

Anonymous

@Chair Good idea. Once you put that up, I'll add a bit more to this, and write it as an answer.

PM 2Ring

3:12 PM

@Chair Yes, the dominant Indian languages (and their writing systems) are all fairly close to Sanskrit, with Hindi being one of the closest. And modern Indian languages have been influenced by outside influences, from the Mogul and European invasions.

user351417

@PM2Ring Yeah, apparently Sanskrit's kinda strange in several ways. Honestly, I think that everything I've ever heard about it is extremely biased, one way or the other, so I'm not sure what I think of it. It never really seemed like a good idea to check it out for myself.

PM 2Ring

Many Indian members of the Stack communities have excellent English. But those that don't always seem to mess up the punctuation & capitalization. ;)

Anonymous

@Chair Well, initially we could make it CW so that the chat/site regulars can alter and modify a bit here and there. After a week or so, we can retract the CW status so that we can avoid the potential issues you mention.

user351417

@PM2Ring I think the reason why I can watch the Hindi news channels is that they say all the important words in English and the Hindi words are primarily just in the peripheral stuff.

user351417

@Blue That sounds perfect.

user351417

3:16 PM

@PM2Ring I sometimes feel that mine is deteriorating... my capitalization/punctuation is usually appropriate, but I think I loose track of the subject-verb things every now and then... which is pretty embarrassing since I have always studied in an english-medium school.

PM 2Ring

@Chair I didn't want to actually learn it, per se. I just wanted to get an overview, because I'm interested in linguistics, and Sanskrit is close to Proto-Indo-European. I did learn how to read & write devanagari, but that knowledge is now rather rusty, due to lack of practice.

user351417

With 5 answers there already, I think his post is about to go HNQ.

Anonymous

@Chair Are you writing up the draft in something like Google Docs?

user351417

@Blue I'm using the SE editor :P I could try a google docs thing though.

Anonymous

It's okay. Maybe before you post that, you could show it to us in Google Docs or something similar. That way, the other regulars here can give their inputs too, before the first version is posted on meta. :)

Anonymous

3:21 PM

Oh, and I've been thinking of relevant food and music references...and have been repeatedly failing to come up with something catchy. :P

user351417

I'm a bit hesitant to put my email-related stuff up though... I recently had an SE user send me some Viagra ads, and I think that linking it to my personal google account would make some of that information visible. While I have my first name on my about-me and I've had my last name around too, I'm not sure if I want the email id there.

user351417

I'll check out the system to see how it works though.

Anonymous

Actually, you could directly copy paste it to chat. It's simpler that way. :P

user351417

Loong though.

Anonymous

I'm sure there are "anonymous" alternatives to Google Docs, but I haven't used one. Lemme check.

user351417

3:24 PM

Eh I'll think of something once I've gotten most of the content together.

PM 2Ring

@Chair I hope not. But at least this question is better than the deleted one. And I guess the answers are useful.

user351417

@Blue I'm sure that even a quick screenshot of the thing would suffice; y'all can type the feedback in messages and edit the CW post once it's up.

user351417

@PM2Ring You mean deleted ones. :P But yes, it is approaching the doubt from a different perspective. Though my comment mentions that there are certain unclear bits, I do think that the question is understandable in the end.

Anonymous

@Chair Yup. Or even something like PasteOfCode could work. Anyway, no use of overthinking this beforehand. We'll see when the time comes!

user351417

In the context of food-related hbar titles, does anyone have any cool ideas?

Anonymous

3:29 PM

Pinned it. Let's hope someone can come up with a good idea. :P

Anonymous

Yesterday's ideas were all flop.

Anonymous

23 hours ago, by Blue

Relax...the h Bar is always open
We are programmed to receive
You can check out any time you like
But you can never leave!

user351417

@Blue I don't know why people hate that song so much. It's quite fun!

user351417

Try replacing all the "I"s with "Greg"s.

user351417

It makes every song even more interesting.

Anonymous

3:30 PM

Lol. Maybe they just find it creepy. I was amazed at the number of conspiracy theories about the Hotel California lyrics. :P

Anonymous

Read through the comment thread here for instance.

user351417

Me thinking of food puns is like

user351417

Anonymous

Lolol

user351417

I dare you to redact that one :P

Anonymous

3:32 PM

I'm cool with tetrathonks. ;)

user351417

I have leaked a highly sensitive image of myself, so you might as well get rid of it ;)

user351417

Or star it.

user351417

Whichever one works better.

Anonymous

Star!

Anonymous

On a serious note, I gotta go and finish my homework. Cya, all! :P

user351417

3:34 PM

This isn't the last you've seen of me!

Anonymous

Happy Tetrathonking!

user351417

You should have said "I'll be back" terminator-style instead.

user351417

Can we have a poll regarding the best food picture we've had here over the last few weeks/months? I think one picture would make a nice addition to that meta post I'm writing. We can use stars to vote because it'll fill our starboard with nice stuff.

user351417

(regarding that removed message) No, maybe that'd be a bad idea. Never mind.

Captain Bohemian

5:21 PM

eating a meal makes me listless. I don't particularly like that Sour Spicy noodles. I eat them just to stave off hunger.

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