pglpm

https://fanfox.net/manga/onepunch_man_one/c150/1.html

I was reading some works – true pearls! – by Synge: his conference contribution Tensorial integral conservation laws in general relativity (1959/1962) and his book Relativity: The General Theory (1960). In these works Synge introduces an extremely interesting definition of four-momentum and of rotational momentum, based on two-point tensors. The definition is interesting because (1) it involves the full Riemann tensor, not just the Einstein tensor, (2) it includes the (or rather, defines a) four-momentum and rotational momentum of the gravitational field, (3) it obeys a conservation law as opposed to a balance law (the equation ∇⋅T=0 expresses in general just balance, not conservation).

The definition for rotational momentum is also interesting because it appears as the natural generalization of the one in Newtonian mechanics, which is based on the affine structure of its 3D space. Roughly speaking, in Newtonian mechanics we have (r-a)∧p, where a is a fixed point, r the point of interest, and p the momentum (density) at the point r. Synge essentially replaces the difference "r-a", which relies on an affine structure, with the geodesic distance between two points R and A in spacetime, through his two-point "world function". In his book he explains that general relativity requires the appearance of a reference point (a or A) also in the definition of four-momentum, whereas such reference point is superfluous in Newtonian mechanics.

OK this was a very poor summary, just to pique your interest. For details see Synge's conference contribution, and chapter VI, especially §4, of his book (refs below).

Bryce DeWitt even commented "Je suis tout à fait de l'avis du professeur Synge qui insiste sur le fait que ces fonctions de deux points se montreront très importantes dans le futur développement de la théorie de la relativité générale" on the conference contribution. Two-point tensors were quite fashionable in the 1960s, they are used in interesting ways also in Truesdell & Toupin's The Classical Field Theories (see Part F and Appendix III there).

Yet, these definition venues seem to have been abandoned today. Here are my questions to you: why? just for unfathomable sociology-of-science reasons, or because of physical-mathematical ones? Are there works today which further explore these venues?

References:

• Synge: Tensorial integral conservation laws in general relativity, in Lichnerowicz,Tonnelat: Les théories relativistes de la gravitation (CNRS 1962), pp. 75–83. https://libgen.is/book/index.php?md5=74345AB69DDF9EE233FA55F55FDCB057

• Synge: Relativity: The General Theory (North-Holland 1960). https://libgen.is/book/index.php?md5=7AE08880CF8086FED4D3BCF732BE8E54

• Truesdell, Toupin: The Classical Field Theories, in Flügge: Handbuch der Physik: III/1 (Springer 1960), pp. I–VII, 226–902. https://doi.org/10.1007/978-3-642-45943-6_2 https://libgen.is/book/index.php?md5=728F54156B632C44EAC2C559F120DDAB

A little advertisement for a new free online course about the foundations of data science, machine learning, and – just a little – artificial intelligence. It's been designed for students in computer science and data science, who could be uncomfortable with a head-on probability-theory or statistics approach, and who might have a lighter background in maths. The main point of view of the course is how to build an artificial-intelligence agent who must draw inferences and make decisions. As a course, it's still a sort of experiment.

https://pglpm.github.io/ADA511/

In more technical terms, the course is actually about so-called "Bayesian nonparametric density inference" and Bayesian decision theory.

http://m.fanfox.net/manga/onepunch_man_one/c148/1.html

http://m.fanfox.net/manga/onepunch_man_one/c149/1.html

Can't help imagining Saitama putting a definite end, without so much back-and-forth, to Mahito's hateful smirk. One punch is all that's needed.

What are the comparative and superlative of the adjective "fun"? I'd say "more fun" and "most fun"...

But I'm somehow slightly tempted by "funnier" and "funniest", which should be for "funny" though, not "fun"...

I didn't find anything about this in the main dictionaries.

...and thought of randomly posting it here.

I wanted to tag SDF today. A #sdf came up, but it seems to refer to something(s) different. I also saw a #sdfdotorg.

Is there a tag that's sort of "standard" to refer to SDF? Standard in the sense that it's typically used by ~~SDF members~~ [Edit:] Mastodon users interested in SDF.

Personal websites often give an email address for contact, as a mailto:blah@blah.blah link. And the address is often obfuscated in a variety of ways to avoid its harvesting by spam bots.

If one wants to give one's Matrix address in a website, what's the correct way of writing it as link? is it recognized as any kind of MIME (like mailto:)?

And is Matrix-address spamming something possible and common? In this case, how should one obfuscate a Matrix address given in a website?

Lots of questions from a noob :) Thank you for your explanations!

Edit for others with the same question: as per @QuazarOmega@lemmy.world's explanation in the comments, the Matrix address can be given as the link

https://matrix.to/#/@[yourusername]:[your.server]

cross-posted from: https://lemmy.ca/post/2217942

In my desktop Firefox I use Cookie Autodelete to keep a whitelist of sites whose cookies won't be deleted. All other cookies are deleted as soon as all tabs for a particular site are closed.

Android's Firefox, from what I gather, only give you two choices: delete all cookies upon quitting (not tab closing), or save them across sessions.

Unfortunately the extension above does not work on Firefox Android, and I haven't found any other alternatives.

Do you know of any alternatives or other solutions, to get a behaviour similar to the desktop one? (And also: how come that extension is not supported on Firefox on Android?)

Cheers!

In my desktop Firefox I use Cookie Autodelete to keep a whitelist of sites whose cookies won't be deleted. All other cookies are deleted as soon as all tabs for a particular site are closed.

Android's Firefox, from what I gather, only give you two choices: delete all cookies upon quitting (not tab closing), or save them across sessions.

Unfortunately the extension above does not work on Firefox Android, and I haven't found any other alternatives.

Do you know of any alternatives or other solutions, to get a behaviour similar to the desktop one? (And also: how come that extension is not supported on Firefox on Android?)

Cheers!

I wonder how many in this community resonate with this.