Covert Lab lead.
Ciro Santilli really likes this dude, because Ciro really likes simulation.
How to build a computer model of a cell by Markus Covert (2020)
Source. If you pass parallel light.
This notation is so confusing! People often don't manage to explain the intuition behind it, why this is an useful notation. When you see Indian university entry exam level memorization classes about this, it makes you want to cry.
The key reason why term symbols matter are Hund's rules, which allow us to predict with some accuracy which electron configurations of those states has more energy than the other.
web.chem.ucsb.edu/~devries/chem218/Term%20symbols.pdf puts it well: electron configuration notation is not specific enough, as each such notation e.g. 1s2 2s2 2p2 contains several options of spins and z angular momentum. And those affect energy.
This is why those symbols are often used when talking about energy differences: they specify more precisely which levels you are talking about.
Basically, each term symbol appears to represent a group of possible electron configurations with a given quantum angular momentum.
We first fix the energy level by saying at which orbital each electron can be (hyperfine structure is ignored). It doesn't even have to be the ground state: we can make some electrons excited at will.
The best thing to learn this is likely to draw out all the possible configurations explicitly, and then understand what is the term symbol for each possible configuration, see e.g. term symbols for carbon ground state.
It also confusing how uppercase letters S, P and D are used, when they do not refer to orbitals s, p and d, but rather to states which have the same angular momentum as individual electrons in those states.
It is also very confusing how extremelly close it looks to spectroscopic notation!
The form of the term symbol is:
The can be understood directly as the degeneracy, how many configurations we have in that state.
Bibliography:
- chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electronic_Spectroscopy/Spin-orbit_Coupling/Atomic_Term_Symbols
- chem.libretexts.org/Courses/Pacific_Union_College/Quantum_Chemistry/08%3A_Multielectron_Atoms/8.08%3A_Term_Symbols_Gives_a_Detailed_Description_of_an_Electron_Configuration The PDF origin: web.chem.ucsb.edu/~devries/chem218/Term%20symbols.pdf
- chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Coordination_Chemistry_(Landskron)/08%3A_Coordination_Chemistry_III_-_Electronic_Spectra/8.01%3A_Quantum_Numbers_of_Multielectron_Atoms
- physics.stackexchange.com/questions/8567/how-do-electron-configuration-microstates-map-to-term-symbols How do electron configuration microstates map to term symbols?
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 00000The
> indicates the current entry to be replaced.And after a page linear address and after a second translation of
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 0000000007 to 00009 it becomes: valid linear physical
----- ------ --------
1 00003 00005
1 00007 00009
> 0 00000 00000
0 00000 00000Now 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. Average number of steps until reaching a state of a Markov chain by 
Ciro Santilli 35 Updated 2025-01-10 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-01-10 +Created 1970-01-01TODO how to calculate
Big goals:
- the pursuit of AGI
- physics simulations, including scientific visualization software
- formalization of mathematics
For some reason, this is one of the things that makes Ciro Santilli want to puke the most. More than surgery or blood.
A directed weighted graph where the sum of weights of all outgoing edges equals 1.
Paging is implemented by the CPU hardware itself.
Paging could be implemented in software, but that would be too slow, because every single RAM memory access uses it!
Operating systems must setup and control paging by communicating to the CPU hardware. This is done mostly via:
- the CR3 register, which tells the CPU where the page table is in RAM memory
- writing the correct paging data structures to the RAM pointed to the CR3 register.Using RAM data structures is a common technique when lots of data must be transmitted to the CPU as it would cost too much to have such a large CPU register.The format of the configuration data structures is fixed _by the hardware_, but it is up to the OS to set up and manage those data structures on RAM correctly, and to tell the hardware where to find them (via
cr3).Then some heavy caching is done to ensure that the RAM access will be fast, in particular using the TLB.Another notable example of RAM data structure used by the CPU is the IDT which sets up interrupt handlers.The OS makes it impossible for programs to change the paging setup directly without going through the OS: - CR3 cannot be modified in ring 3. The OS runs in ring 0. See also:
- the page table structures are made invisible to the process using paging itself!
Processes can however make requests to the OS that cause the page tables to be modified, notably:
- stack size changes
brkandmmapcalls, see also: stackoverflow.com/questions/6988487/what-does-brk-system-call-do/31082353#31082353
The kernel then decides if the request will be granted or not in a controlled manner.
Physical address extension.
With 32 bits, only 4GB RAM can be addressed.
This started becoming a limitation for large servers, so Intel introduced the PAE mechanism to Pentium Pro.
To relieve the problem, Intel added 4 new address lines, so that 64GB could be addressed.
Page table structure is also altered if PAE is on. The exact way in which it is altered depends on weather PSE is on or off.
PAE is turned on and off via the
PAE bit of cr4.Even if the total addressable memory is 64GB, individual process are still only able to use up to 4GB. The OS can however put different processes on different 4GB chunks.
Paging is done by the Memory Management Unit (MMU) part of the CPU.
Like many others (e.g. x87 co-processor, APIC), this used to be by separate chip on early days.
It was later integrated into the CPU, but the term MMU still used.
As of 2022:
- www.ox.ac.uk/students/fees-funding/fees/rates gives study fees. Almost all courses are about 9k pounds / academic year. Courses take minimum 3 years, with an optional 4th year masters. The costs of masters can be higher however, though most aren't much.It is funny to note how Public Policy is comically priced at 45,890 for a course without laboratories, how can a country be so corrupt? :-) It was later brought to Ciro's attention that the reason is that those courses are not usually paid by individuals, but by their employers...Another eye popping one is Mathematical & Computational Finance MSc for £36,370.
- www.ox.ac.uk/students/fees-funding/living-costs gives living costs, an average 12k for the usual 9 month period
- there is the Crankstart scholarship: www.ox.ac.uk/admissions/undergraduate/student-life/help-with-the-cost/crankstart-scholarships which gives 5k/year to students whose families have less than 27k/year income, and values decrease from there to 60k/year income where they become zero.It is funny to note that the scholarship was previously named after a Welsh billionaire who studied there and donated and his wife, Michael Moritz and wife Harriet Heyman. It is actually the Welsh who are creating those scholarships for the English! It is so funny to see. His background is quite amazing, from historian to journalist to venture capitalist.It was later renamed Crankstart after the Crankstart Foundation, presumably to help gather funds from others, but it is just still led by Michael.It does appear that most/all of the natural sciences ones are reasonably priced, perhaps they are subsided.
The median household income at the time was 31k[ref]. Clearly, putting one child through university with that income would be basically impossible, you would pay 19 - 5 = 14k/year, almost half of your income. Two children would be impossible. Remember how each family needs to have two children minimum to perpetuate life?
- cherwell.org/2023/10/02/27000-for-a-library-card/ £27,000 for a library card? published on the Cherwell
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