What is the newest installment of 'Random Thoughts' on Physics Forums?

[ergospherical]

Reserves $j$ for $\sqrt{-1}$, engineer style?

Seems to use $i$ for that too, at least in the copy I have to hand at the moment (elasticity theory).

 

[Jonathan Scott]

Does anybody know why Landau never uses the letter $j$ as a suffix? It's always only $i,k,l,m...$ for the Latin alphabet. Looks to similar to $i$, perhaps?

My guess is that it's because he wrote in Russian, and the English version is a translation. I suspect that Russian doesn't have an equivalent of "j" distinct from "i".

 

[ergospherical]

That's a point! I found a Wikipedia article explaining the romanisation of the Russian alphabet. Some features:

"и" --> "i"
"й" --> "i", "j", or "y"
"к" --> "k"
"л" --> "l"
etc.

so it does indeed seem like there isn't an equivalent for "j"; and the closest possibility, "й", looks far too similar to "и".

 

[WWGD]

Those who use together either of the pairs (i, j) or (u,v) on a blackboard, should be shot. They're undistinguishable for 99% of writers.
I heard there are places that have electronic blackboards that can print out what's written. Always tough to coordinate listening with writing.

Edit: I think that method is outdated e and may not last too long.

 

[WWGD]

Will get together with my Nigerian friend. I'll have café con Kelechi.

 

[fresh_42]

Does anybody know why Landau never uses the letter $j$ as a suffix? It's always only $i,k,l,m...$ for the Latin alphabet. Looks to similar to $i$, perhaps?

@Jonathan Scott's obviously correct explanation teaches us how important context is!

E.g. I try to avoid i as an index on PF because it is unnecessarily hard to distinguish from 1,l, or j but mainly because my texts ended up in a mess after i was rendered to 'start italic' one time too many. k as summation index is much better to grasp. Another possible context in a historical text is, that they probably used a typewriter. I knew somebody who used variable names according to the optimization problem: "Minimize the number of necessary selectrics and their changes!"

 

[WWGD]

I understand the pronoun 'i' in English is capitalized to make it easier to identify/keep track of, despite theories on it being a reflection of individualism in English culture.

 

[fresh_42]

Those who use together either of the pairs (i, j) or (u,v) on a blackboard, should be shot. They're undistinguishable for 99% of writers.
I heard there are places that have electronic blackboards ...

Whiteboards. You need to wrap them for the scanning process. After thousands of tries, someone figured out that slabs of slate cannot be bent and inevitably break.

 

[WWGD]

Whiteboards. You need to wrap them for the scanning process. After thousands of tries, someone figured out that slabs of slate cannot be bent and inevitably break.

Ah, yes, just went with the default ' blackboard' to stand for any type of board. Thought it wouod be obvious. Though maybe instead they could be automatically sent to students as an attachment.

 

[WWGD]

Still, a rule of thumb I use for buying a Math/Physics book is whether it has a clear, comprehensive notational reference in it. It suggests author made a real effort to be helpful and didn't just write it to have his name on a book.

 

[fresh_42]

Ah, yes, just went with the default ' blackboard' to stand for any type of board. Thought it wouod be obvious. Though maybe instead they could be automatically sent to students as an attachment.

I think they were mainly invented for meeting protocols and addressed consultants rather than students. Their, the consultants', obsession for fancy, and otherwise superfluous gadgets has been likely the reason that they were sold at all.

 

[WWGD]

I think they were mainly invented for meeting protocols and addressed consultants rather than students. Their, the consultants', obsession for fancy, and otherwise superfluous gadgets has been likely the reason that they were sold at all.

I'm not sure it's superfluous. Not a bad thing to devote your attention fully towards listening rather than go back and forth between listening and writing. And having nice notes to look at, instead of smudged up pencil /pen notes.

 

[gmax137]

But is pronunciation, accent (Edit : Significantly-) different between regions

My high school german teacher told us to say "wie gehts, y'all" when in Bavaria.

 

[WWGD]

My high school german teacher told us to say "wie gehts, y'all" when in Bavaria.

I'm still stuck at' Farverhnugen' ( Sp?).

 

[WWGD]

Kind of bizarre the level of precision used by Worldometer Corona in it's population ( by country) numbers. Example, China has 1,439,678,217 people. They don't just round to 1,440 ,000,000.

 

[Keith_McClary]

Kind of bizarre the level of precision used by Worldometer Corona in it's population ( by country) numbers. Example, China has 1,439,678,217 people. They don't just round to 1,440 ,000,000.

China Population (LIVE)​

updates every three seconds.

 

[WWGD]

China Population (LIVE)​

updates every three seconds.

I understand thst for a population feed , but Worldometer is not intended to be one. I noticed that World Almanac and book of facrs uses the same level of precision.

What's next, though live feed of Chinese births?

 

[WWGD]

How to dispose of 3G phones to avoid personal info extracted? Smash it? DeGauss it?

 

[Astronuc]

Lithium-ion batteries are fueling the fire on a burning cargo ship full of Porsches​

https://qz.com/2130711/electric-vehicles-make-it-harder-to-quell-fire-on-felicity-ace-cargo-ship/

The cargo ship Felicity Ace is aflame from bow to stern with a lithium-ion battery fire that can’t be put out with water alone.

The fire has been burning since Wednesday (Feb. 16), as the ship drifts in the Atlantic about 200 miles southwest of Portugal’s Azores Islands. Its 22-person crew abandoned ship and was rescued on Thursday.

The ship left Germany on Feb. 10 and headed for the US with about 4,000 Porsches, Bentleys and other luxury cars aboard, and some of those were electric vehicles.

Maybe they need to rethink packing electric vehicles in enclosed spaces. All it takes is one bad battery, and 'poof'. At least have fire walls and decks. Inert gas (nitrogen, CO2 or otherwise) would be necessary. But then the crew must use pressurized air to avoid asphyxiation.

https://news.yahoo.com/firefighters-struggle-douse-fire-luxury-110457510.html

Cabeças previously said that "everything was on fire about five meters above the water line" and the blaze was still far from the ship's fuel tanks. It is getting closer, he said.

"The fire spread further down," he said, explaining that teams could only tackle the fire from outside by cooling down the ship's structure as it was too dangerous to go on board.

They also cannot use water because adding weight to the ship could make it more unstable, and traditional water extinguishers do not stop lithium-ion batteries from burning, Cabeças said.

 

[Astronuc]

How to dispose of 3G phones to avoid personal info extracted? Smash it? DeGauss it?

https://www.consumerreports.org/cro/2013/11/remove-personal-data-from-any-device/index.htm

https://www.cnet.com/tech/mobile/how-to-wipe-your-phone-or-tablet-before-selling/

 

[fresh_42]

Maybe they need to rethink packing electric vehicles in enclosed spaces. All it takes is one bad battery, and 'poof'. At least have fire walls and decks. Inert gas (nitrogen, CO2 or otherwise) would be necessary. But then the crew must use pressurized air to avoid asphyxiation.

I remember watching a documentary on TV about the fire on a ferry. It was full of trucks, many with refrigeration systems. However, there were more such trucks than on-board power supplies, so some of them continued to run their diesel-powered refrigeration units. And the injection - I can't remember if it was water or carbonic dioxide - failed because the switches were labeled incorrectly.

 

[WWGD]

https://www.consumerreports.org/cro/2013/11/remove-personal-data-from-any-device/index.htm

https://www.cnet.com/tech/mobile/how-to-wipe-your-phone-or-tablet-before-selling/

Thank you. Do you know where Android stores it's content? SD card? Flash memory? How to tell what's stored in the phone and what's stored in the provider's server? I mean, no reason you should hsve an idea, but just in case :).

 

[Astronuc]

Do you know where Android stores it's content? SD card?

I thought I saw something about an SD card under the SIM card.

Meanwhile, here are some instructions for Android phones.
https://www.theverge.com/21419919/delete-data-android-phone-sell-trade-how-to

I also found this in instructions of Android phones.

Step 7: Remove Your Micro SD Storage Card and SIM Card​

This step is probably the easiest. Use the SIM card ejector tool that was included with your phone or a paperclip to open the SIM card slot and take out your SIM card and any external memory cards you have.

https://www.compareandrecycle.co.uk...roid#steps-to-remove-all-data-from-an-android
from https://www.compareandrecycle.co.uk/blog/how-to-remove-data-from-iphone-android

How to Securely Delete Photos and Clear All Data From Your Android Phone​

https://gadgets360.com/mobiles/feat...elete-all-data-from-your-android-phone-603731

From Samsung
https://www.samsung.com/ie/support/...on-on-my-samsung-galaxy-s5-via-factory-reset/

Google support
https://support.google.com/accounts/answer/81987?hl=en&co=GENIE.Platform=Android

 

[martinbn]

My guess is that it's because he wrote in Russian, and the English version is a translation. I suspect that Russian doesn't have an equivalent of "j" distinct from "i".

This is a wrong guess for a number of reasons. For one, in Russian you still use the Latin (and Greek) letters for notations. For example you write triangle $ABC$, not triangle $АБВ$. Vectors $\vec{i}, \vec{j}, \vec{k}$ not $\vec{и}, \vec{й}, \vec{к}$.

 

[martinbn]

@Jonathan Scott's obviously correct explanation teaches us how important context is!

I will need some context here, because to me his explanation is obviously wrong!

 

[Jonathan Scott]

I will need some context here, because to me his explanation is obviously wrong!

I was not suggesting that the notation would use Russian letters, but rather that since Russian is one of several languages where "i" and "j" are not distinct letters, it would not seem natural to do so.

 

[martinbn]

Those who use together either of the pairs (i, j) or (u,v) on a blackboard, should be shot. They're undistinguishable for 99% of writers.

Looking at L&L, which of course is not just Landau, it does seem that they avoid 'j' as an index with plenty of indices in the second volume. But they use the notation $j^i$ for the 4-current. If you had taken a course with him, this would have made you shoot him yourself

 

[fresh_42]

I will need some context here, because to me his explanation is obviously wrong!

Well, this is as wrong as ...

This is a wrong guess for a number of reasons. For one, in Russian you still use the Latin (and Greek) letters for notations. For example you write triangle $ABC$, not triangle $АБВ$. Vectors $\vec{i}, \vec{j}, \vec{k}$ not $\vec{и}, \vec{й}, \vec{к}$.

... is. Will say, that your statement is as speculative as Jonathan's is. You simply cannot know.

Fact: Landau used ${ik}$ and not ${ij}$ as indices. I have checked. Did you?

From there on it is pure speculation why. I consider it plausible not to use $j$ if you are a native Russian speaker since it is simply not in your natural reservoir. Another idea is what I said earlier: they used typewriters at the time and $i$ and $j$ might have been hard to distinguish, at least harder than $i$ and $k$.

But if you continue claiming that you know what had driven Landau, I'm looking forward to being invited to your seance.

 

[martinbn]

I was not suggesting that the notation would use Russian letters, but rather that since Russian is one of several languages where "i" and "j" are not distinct letters, it would not seem natural to do so.

I see, why? I, as a Bulgarian, have always used 'j' along as any other. For example the elements of a matrix for me are most naturally $a_{ij}$.

 

[WWGD]

Is there a substitute for Ctrl+A for gmail, to select all emails in a search result?

Looking at L&L, which of course is not just Landau, it does seem that they avoid 'j' as an index with plenty of indices in the second volume. But they use the notation $j^i$ for the 4-current. If you had taken a course with him, this would have made you shoot him yourself

Im referring to using them in a blackboard/whiteboard setting where the letters in the pair tend to be indistinguishable at plain sight. And I forgot the pair (m,n) too. Not so bad in a typeset book, but not a bsd idea to avoid .