Khan Academy Updated 2025-07-16
Kudos for being a not-for-profit. Also, anyone can create content: e-learning websites must allow students to create learning content. Oh, but TODO is possible for anyone to make content publicly visible? Course join links lik: www.khanacademy.org/join/MJZ6NSV7 require login. webapps.stackexchange.com/questions/165132/how-to-create-a-course-that-is-publicly-visible-without-the-need-to-login-on-kha If that's the case, it is a fatal flaw not shared by OurBigBook.com.
Another cool aspect is that they have the "physical world teacher pull student accounts in" approach built-in quite well at course creation. This is a very good feature.
As of 2021 they were a bit struggling for money it seems: www.youtube.com/watch?v=I8XdUy-wyyM?
Kilogram Updated 2025-07-16
Unit of mass.
Defined in the 2019 redefinition of the SI base units via the Planck constant. This was possible due to the development of the Kibble balance.
NuNET Updated 2025-07-16
SQL transaction isolation level Updated 2025-07-16
Each transaction isolation level specifies what can or cannot happen when two queries are being run in parallel, i.e.: the memory semantics of the system.
Remember that queries can affects thousands of rows, and database systems like PostgreSQL can run multiple such queries at the same time.
Type-II superconductor Updated 2025-07-16
Figure 1.
Sketch of the typical superconducting phase diagram of a Type-II superconductor
. Source.
Particle decay Updated 2025-07-16
Can produce two entangled particles.
x86 Paging Tutorial / Application Updated 2025-07-16
Paging makes it easier to compile and run two programs or threads at the same time on a single computer.
For example, when you compile two programs, the compiler does not know if they are going to be running at the same time or not.
So nothing prevents it from using the same RAM address, say, 0x1234, to store a global variable.
And thread stacks, that must be contiguous and keep growing down until they overwrite each other, are an even bigger issue!
But if two programs use the same address and run at the same time, this is obviously going to break them!
Paging solves this problem beautifully by adding one degree of indirection:
(logical) ------------> (physical)
             paging
Where:
  • logical addresses are what userland programs see, e.g. the contents of rsi in mov eax, [rsi].
    They are often called "virtual" addresses as well.
  • physical addresses can be though of the values that go to physical RAM index wires.
    But keep in mind that this is not 100% true because of further indirections such as:
Compilers don't need to worry about other programs: they just use simple logical addresses.
As far as programs are concerned, they think they can use any address between 0 and 4 GiB (2^32, FFFFFFFF) on 32-bit systems.
The OS then sets up paging so that identical logical addresses will go into different physical addresses and not overwrite each other.
This makes it much simpler to compile programs and run them at the same time.
Paging achieves that goal, and in addition:
  • the switch between programs is very fast, because it is implemented by hardware
  • the memory of both programs can grow and shrink as needed without too much fragmentation
  • one program can never access the memory of another program, even if it wanted to.
    This is good both for security, and to prevent bugs in one program from crashing other programs.
Or if you like non-funny jokes:
Figure 1.
Comparison between the Linux kernel userland memory virtualization and The Matrix
. Source. Is this RAM real?
After a translation between linear and physical address happens, it is stored on the TLB. For example, a 4 entry TLB starts in the following state:
  valid  linear  physical
  -----  ------  --------
> 0      00000   00000
  0      00000   00000
  0      00000   00000
  0      00000   00000
The > indicates the current entry to be replaced.
And after a page linear address 00003 is translated to a physical address 00005, the TLB becomes:
  valid  linear  physical
  -----  ------  --------
  1      00003   00005
> 0      00000   00000
  0      00000   00000
  0      00000   00000
and after a second translation of 00007 to 00009 it becomes:
  valid  linear  physical
  -----  ------  --------
  1      00003   00005
  1      00007   00009
> 0      00000   00000
  0      00000   00000
Now if 00003 needs to be translated again, hardware first looks up the TLB and finds out its address with a single RAM access 00003 --> 00005.
Of course, 00000 is not on the TLB since no valid entry contains 00000 as a key.
Krusader Updated 2025-07-16
The most powerful GUI file manager ever?? Infinite configurability??
Ciro Santilli wasted some time on it before he gave up on file managers altogether and started using only the CLI with a few aliases.
Nash equilibrium Updated 2025-07-16
The best example to look at first is the penalty kick left right Nash equilibrium.
Then, a much more interesting example is choosing a deck of a TCG competition: Magic: The Gathering meta-based deck choice is a bimatrix game, which is the exact same, but each player has N choices rather than 2.
The next case that should be analyzed is the prisoner's dilemma.
The key idea is that:
  • imagine that the game will be played many times between two players
  • if one player always chooses one deck, the other player will adapt by choosing the anti-deck
  • therefore, the best strategy for both players, is to pick decks randomly, each with a certain probability. This type of probabilistic approach is called a mixed strategy
  • if any player deviates from the equilibrium probability, then the other player can add more of the anti-deck to the deck that the other player deviated, and gain an edge
    Therefore, using equilibrium probabilities is the optimal way to play
Steven Pruitt Updated 2025-07-16
Video 1.
Meet the man behind a third of what's on Wikipedia
. Source.

There are unlisted articles, also show them or only show them.