Retrovirus Updated +Created
Integrates its RNA genome into the host genome.
Sounds complicated! The advantage is likely as in HIV: once inside the cell, it can remain hidden far away from the cell surface, but still infections.
Curl (mathematics) Updated +Created
Points in the direction in which a wind spinner spins fastest.
Reduced Planck constant Updated +Created
Appears in the Schrödinger equation.
Equals the quantum of angular momentum in the Bohr model.
PCR Updated +Created
More generic PCR information at: Section "Polymerase chain reaction".
Because it is considered the less interesting step, and because it takes quite some time, this step was done by the event organizers between the two event days, so participants did not get to take many photos.
PCR protocols are very standard it seems, all that biologists need to know to reproduce is the time and temperature of each step.
We did 35 cycles of:
  • 94˚C for 30 seconds
  • 60˚C for 30 seconds
  • 72˚C for 45 seconds
Figure 1.
Marshal Scientific MJ Research PTC-200 Thermal Cycler.
Source.
We added PCR primers for regions that surround the 16S DNA. The primers are just bought from a vendor, and we used well known regions are called 27F and 1492R. Here is a paper that analyzes other choices: academic.oup.com/femsle/article/221/2/299/630719 (archive) "Evaluation of primers and PCR conditions for the analysis of 16S rRNA genes from a natural environment" by Yuichi Hongoh, Hiroe Yuzawa, Moriya Ohkuma, Toshiaki Kudo (2003)
One cool thing about the PCR is that we can also add a known barcode at the end of each primer as shown at Code 1. "PCR diagram".
This means that we bought a few different versions of our 27F/1492R primers, each with a different small DNA tag attached directly to them in addition to the matching sequence.
This way, we were able to:
  • use a different barcode for samples collected from different locations. This means we
    • did PCR separately for each one of them
    • for each PCR run, used a different set of primers, each with a different tag
    • the primer is still able to attach, and then the tag just gets amplified with the rest of everything!
  • sequence them all in one go
  • then just from the sequencing output the barcode to determine where each sequence came from!
Input: Bacterial DNA (a little bit)
... --- 27S --- 16S --- 1492R --- ...

|||
|||
vvv

Output: PCR output (a lot of)
Barcode --- 27S --- 16S --- 1492R
Code 1.
PCR diagram
.
Finally, after purification, we used the Qiagen QIAquick PCR Purification Kit protocol to purify the generated from unwanted PCR byproducts.
History of polarization Updated +Created
Particularly cool is to see how Fresnel fully understood that light is somehow polarized, even though he did not know that it was made out of electromagnetism, clear indication of which only came with the Faraday effect in 1845.
spie.org/publications/fg05_p03_maluss_law:
At the beginning of the nineteenth century the only known way to generate polarized light was with a calcite crystal. In 1808, using a calcite crystal, Malus discovered that natural incident light became polarized when it was reflected by a glass surface, and that the light reflected close to an angle of incidence of 57° could be extinguished when viewed through the crystal. He then proposed that natural light consisted of the s- and p-polarizations, which were perpendicular to each other.
Applications of Josephson Junctions Updated +Created
Fusion power Updated +Created
Most promising approaches as of 2020:
Video 1.
Why Private Billions Are Flowing Into Fusion by Bloomberg (2022)
Source.
  • Joint European Torus
  • General Fusion: compress with liquid metal. Intends to demo in JET site.
  • Helion Energy: direct fusion to electricity conversion without steam, direct from magnetic field movements
  • First Light: shoot microscopic objct at a target to crush it so much that fusion happens
It is interesting that there are several different approaches to the problem. This feels a bit like quantum computing's development at the same time, increases hope that at least one will work.
Bell circuit Updated +Created
A quantum circuit which when fed with input produces the Bell state.
Figure 1.
Quantum circuit that generates the Bell state
. Source.
The fundamental intuition for this circuit is as follows.
First the Hadamard gate makes the first qubit be in a 50/50 state.
Then, the CNOT gate gets controlled by that 50/50 value, and the controlled qubit also gets 50/50 chance as a result.
However, both qubits are now entangled: the result of the second qubit depends on the result of the first one. Because:
  • if the first qubit is 0, cnot is not active, and so the second qubit remains 0 as its input
  • if the first qubit is 1, cnot is active, and so the second qubit is flipped to 1
Create a test user in PostgreSQL Updated +Created
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:
psql -c "create role NewRole with login password 'secret'"
Can't find a way using the createuser helper.
We can then login with that password with:
psql -U user0 -h localhost
which asks for the password we've just set, because the -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 localhost
Now 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:
psql -c '\l'
which now contains:
                                  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/ciro
The permission letters are explained at:
user0 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;'
One key insight, is that the matrix of a non-trivial quantum circuit is going to be huge, and won't fit into any amount classical memory that can be present in this universe.
This is because the matrix is exponential in the number qubits, and is more than the number of atoms in the universe!
Therefore, off the bat we know that we cannot possibly describe those matrices in an explicit form, but rather must use some kind of shorthand.
But it gets worse.
Even if we had enough memory, the act of explicitly computing the matrix is not generally possible.
This is because knowing the matrix, basically means knowing the probability result for all possible outputs for each of the possible inputs.
But if we had those probabilities, our algorithmic problem would already be solved in the first place! We would "just" go over each of those output probabilities (OK, there are of those, which is also an insurmountable problem in itself), and the largest probability would be the answer.
So if we could calculate those probabilities on a classical machine, we would also be able to simulate the quantum computer on the classical machine, and quantum computing would not be able to give exponential speedups, which we know it does.
To see this, consider that for a given input, say 000 on a 3 qubit machine, the corresponding 8-sized quantum state looks like:
000 -> 1000 0000 == (1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0)
and therefore when you multiply it by the unitary matrix of the quantum circuit, what you get is the first column of the unitary matrix of the quantum circuit. And 001, gives the second column and so on.
As a result, to prove that a quantum algorithm is correct, we need to be a bit smarter than "just calculate the full matrix".
Which is why you should now go and read: Section "Quantum algorithm".
This type of thinking links back to how physical experiments relate to quantum computing: a quantum computer realizes a physical experiment to which we cannot calculate the probabilities of outcomes without exponential time.
So for example in the case of a photonic quantum computer, you are not able to calculate from theory the probability that photons will show up on certain wires or not.
Universal quantum gates Updated +Created
Just like as for classic gates, we would like to be able to select quantum computer physical implementations that can represent one or a few gates that can be used to create any quantum circuit.
Unfortunately, in the case of quantum circuits this is obviously impossible, since the space of N x N unitary matrices is infinite and continuous.
Therefore, when we say that certain gates form a "set of universal quantum gates", we actually mean that "any unitary matrix can be approximated to arbitrary precision with enough of these gates".
Or if you like fancy Mathy words, you can say that the subgroup of the unitary group generated by our basic gate set is a dense subset of the unitary group.
Jackdaw Playing With Water Updated +Created
A Jackdaw is a type of crow: en.wikipedia.org/wiki/Western_jackdaw
Considered one of the 10 famous Chaozhou music pieces TODO list.
Was also adapted by Liu Baoshan (1937-1997) as a pipa song. Ciro Santilli prefers the pipa version.
Video 1.
Jackdaw Playing With Water performed by Xu Lingzi on the guzheng at the Wiener Musikverein
. Source.
Video 2.
Jackdaw Playing With Water performed by Lin Shicheng on the pipa
. Source.
Applications of superconductivity Updated +Created
Superconductivity is one of the key advances of 21st century technology:
Jacques Monod Updated +Created
Form of government Updated +Created
Rasselas Prince of Abyssinia CHAPTER VIII www.gutenberg.org/cache/epub/652/pg652-images.html:
Oppression is, in the Abyssinian dominions, neither frequent nor tolerated; but no form of government has been yet discovered by which cruelty can be wholly prevented. Subordination supposes power on one part and subjection on the other; and if power be in the hands of men it will sometimes be abused. The vigilance of the supreme magistrate may do much, but much will still remain undone. He can never know all the crimes that are committed, and can seldom punish all that he knows.
Available battery voltages Updated +Created
Only certain battery voltages exist, because this voltage depends intrinsically on the battery's chemical composition.
learn.sparkfun.com/tutorials/battery-technologies/all (CC BY-SA) has a very good summary list, reordered from lowest to highest voltage:
Battery ShapeChemistryNominal VoltageRechargeable?
AA, AAA, C, D (Rechargeable)NiMH or NiCd1.2VYes
AA, AAA, C, and DAlkaline or Zinc-carbon1.5VNo
Coin CellLithium3VNo
Silver Flat PackLithium Polymer (LiPo)3.7VYes
9VAlkaline or Zinc-carbon9VNo
Car BatterySix-cell lead acid12.6VYes
JAVA_HOME Updated +Created
This ultimately determines which Java is used by a bunch of tools.
TODO is there a way to update it sanely in Ubuntu: askubuntu.com/questions/175514/how-to-set-java-home-for-java to always match the default java executable?
Java library Updated +Created
Jami (software) Updated +Created
Ciro Santilli worked on it for a brief time in 2016, when it was still called Ring, before he got fired. :-)
The people were quite nice and the project idea is fine, Ciro hopes they succeed.
Video 1.
Ring - Peer to peer network for real time communication - FOSDEM 2016 by Ciro Santilli
. Source.

Unlisted articles are being shown, click here to show only listed articles.