Signaling theory Updated 2025-07-16
Wheeler-Feynman absorber theory Updated 2025-07-16
What they presented on richard Feynman's first seminar in 1941. Does not include quantum mechanics it seems.
AGI-complete Updated 2025-07-16
Gaussian function Updated 2025-07-16
Kibble balance Updated 2025-07-16
The Kibble balance is so precise and reproducible that it was responsible for the 2019 redefinition of the Kilogram.
NIST-4 Kibble balance
. Source. 
It relies rely on not one, but three macroscopic quantum mechanical effects:How cool is that! As usual, the advantage of those effects is that they are discrete, and have very fixed values that don't depend either:One downside of using some quantum mechanical effects is that you have to cool everything down to 5K. But that's OK, we've got liquid helium!
- atomic spectra: basis for the caesium standard which produces precise time and frequency
- Josephson effect: basis for the Josephson voltage standard, which produces precise voltage
- quantum Hall effect: basis for the quantum Hall effect, which produces precise electrical resistance
- on the physical dimensions of any apparatus (otherwise fabrication precision would be an issue)
- small variations of temperature, magnetic field and so on
The operating principle is something along:Then, based on all this, you can determine how much the object weights.
- generate a precise frequency with a signal generator, ultimately calibrated by the Caesium standard
- use that precise frequency to generate a precise voltage with a Josephson voltage standard
- convert that precise voltage into a precise electric current by using the quantum Hall effect, which produces a very precise electrical resistance
- use that precise current to generate a precise force on the object your weighing, pushing it against gravity
- then you precisely measure both:
- local gravity with a gravimeter
- the displacement acceleration of the object with a laser setup
- youtu.be/ZfNygYuuVAE?t=854: they don't actually use the Quantum Hall effect device during operation, they only use it to calibrate other non-quantum resistors
Once more unto the breach Updated 2025-07-16
On the Law of Distribution of Energy in the Normal Spectrum Updated 2025-07-16
The Planck's law paper.
Ain't Nobody Got Time For That Updated 2025-07-16
Fractional quantum Hall effect for Updated 2025-07-16
Fractional quantum Hall effect for Updated 2025-07-16
Matrix exponential Updated 2025-07-16
Is the solution to a system of linear ordinary differential equations, the exponential function is just a 1-dimensional subcase.
Note that more generally, the matrix exponential can be defined on any ring.
The matrix exponential is of particular interest in the study of Lie groups, because in the case of the Lie algebra of a matrix Lie group, it provides the correct exponential map.
Algebraic equation Updated 2025-07-16
Algebraic number Updated 2025-07-16
China Central Television Updated 2025-07-16
Chinese book Updated 2025-07-16
Create a test user in PostgreSQL Updated 2025-07-16
In order to create a test user with password instead of peer authentication, let's create test user:
createuser -P user0
createdb user0-P makes it prompt for the users password.Alternatively, to create the password non-interactively stackoverflow.com/questions/42419559/postgres-createuser-with-password-from-terminal:Can't find a way using the
psql -c "create role NewRole with login password 'secret'"createuser helper.We can then login with that password with:which asks for the password we've just set, because the
psql -U user0 -h localhost-h option turns off peer authentication, and turns off password authentication.The password can be given non-interactively as shown at stackoverflow.com/questions/6405127/how-do-i-specify-a-password-to-psql-non-interactively with the
PGPASSWORD environment variable:PGPASSWORD=a psql -U user0 -h localhostNow let's create a test database which
user0 can access with an existing superuser account:createdb user0db0
psql -c 'GRANT ALL PRIVILEGES ON DATABASE user0db0 TO user0'We can check this permission with:which now contains:The permission letters are explained at:
psql -c '\l' List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
user0db0 | ciro | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =Tc/ciro +
| | | | | ciro=CTc/ciro +
| | | | | user0=CTc/cirouser0 can now do the usual table operations on that table:PGPASSWORD=a psql -U user0 -h localhost user0db0 -c 'CREATE TABLE table0 (int0 INT, char0 CHAR(16));'
PGPASSWORD=a psql -U user0 -h localhost user0db0 -c "INSERT INTO table0 (int0, char0) VALUES (2, 'two'), (3, 'three'), (5, 'five'), (7, 'seven');"
PGPASSWORD=a psql -U user0 -h localhost user0db0 -c 'SELECT * FROM table0;' Crowdsourcing website Updated 2025-07-16
Indian classical musician Updated 2025-07-16
Raga by time of the day Updated 2025-07-16
Robert Noyce: The Man Behind the Microchip by Leslie Berlin (2006) Updated 2025-07-16
Borrow from the Internet Archive for free: archive.org/details/manbehindmicroc000berl/page/n445/mode/2up
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