The first planet not known since antiquity.
The knowledge that light is polarized precedes the knowledge of the existence of the photon, see polarization of light for the classical point of view.
The polarization state and how it can be decomposed into different modes can be well visualized with the Poincaré sphere.
One key idea about photon polarization is that it carries angular momentum. Therefore, when an electron changes orbitals in the Schrödinger equation solution for the hydrogen atom, the angular momentum (as well as energy) change is carried out by the polarization of the photon!
- www.varsity.co.uk/features/24648 ‘It felt impossibly romantic’: the nightclimbers of Cambridge by Varsity (2022)
Merger between Cambridge Quantum Computing, which does quantum software, and Honeywell Quantum Solutions, which does the hardware.
The term "IBM Q" has been used in some promotional material as of 2020, e.g.: www.ibm.com/mysupport/s/topic/0TO50000000227pGAA/ibm-q-quantum-computing?language=en_US though the fuller form "IBM Quantum Computing" is somewhat more widely used.
They also internally named an division as "IBM Q": sg.news.yahoo.com/ibm-thinks-ready-turn-quantum-050100574.html
CEO: Jeremy O'Brien
Raised 215M in 2020: www.bloomberg.com/news/articles/2020-04-06/quantum-computing-startup-raises-215-million-for-faster-device
Good talk by CEO before starting the company which gives insight on what they are very likely doing: Video "Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)"
PsiQuantum appears to be particularly secretive, even more than other startups in the field.
They want to reuse classical semiconductor fabrication technologies, notably they have close ties to GlobalFoundries.
In this section we will use the file nodejs/bench_mem.js, tests are run on Node.js v16.14.2 from NVM, Ubuntu 21.10, on Lenovo ThinkPad P51 (2017) which has 32 GB RAM.
Related answer: stackoverflow.com/questions/12023359/what-do-the-return-values-of-node-js-process-memoryusage-stand-for/72043884#72043884
First using
topp
from stackoverflow.com/questions/1221555/retrieve-cpu-usage-and-memory-usage-of-a-single-process-on-linux/40576129#40576129 let's observe the memory usage of some baseline cases.A C hello world with an infinite loop at the end has:
- 2.7 MB
- 770 KB
For a Node.js infinite loop nodejs/infinite_loop.jsThis gives approximately:
topp infinite_loop.js
- RSS: 20 MB
- VSZ: 230 MB
Adding a single hello world to it as in nodejs/infinite_hello.js and running:leads to:We understand that Node.js preallocates VSZ wildly. No big deal, but it does mean that VSZ is a useless measure for Node.js.
topp infinite_hello.js
- RSS: 26 MB
- VSZ: 580 MB
Forcing garbage collection as in nodejs/infinite_hello.js brings it down to 20 MB however:
topp node --expose-gc infinite_hello_gc.js
Finally let's see a baseline for which gives initially:but after a few seconds randomly jumps to:so we understand that
process.memoryUsage
nodejs/infinite_memoryusage.js:node --expose-gc infinite_memoryusage.js
{
rss: 23851008,
heapTotal: 6987776,
heapUsed: 3674696,
external: 285296,
arrayBuffers: 10422
}
{
rss: 26005504,
heapTotal: 9084928,
heapUsed: 3761240,
external: 285296,
arrayBuffers: 10422
}
heapUsed
seems constant at 3.7 MBheapTotal
is a very noisy, as it starts at 7 MB, but randomly jumps to 9 MB at one point without apparent reason
Now let's run our main test program.
First a baseline case with an array of length 1:This gives the same results as with:
node --expose-gc bench_mem.js n 1
node --expose-gc infinite_memoryusage.js
. The same result is obtained by doing:a = undefined
node --expose-gc bench_mem.js dealloc
Not let's vary the size of which gives:
n
a bit with:node --expose-gc bench_mem.js n N
N | heapUsed | heapTotal | rss | heapUsed per elem | rss per elem |
---|---|---|---|---|---|
1 M | 14 MB | 48 MB | 56 MB | 10 | 30 |
10 M | 122 MB | 157 MB | 176 MB | 18 | 15 |
100 M | 906 MB | 940 MB | 960 MB | 9 | 9.3 |
"
rss
per elem" is calculated as: rss
- 26 MB, where 26 MB is the baseline RSS seen on n 1
.Similarly "
heapUsed
per elem" deduces the 4 MB (approximation of the above 3.7 MB) seen on n 1
.Note that to reach MAX_SAFE_INTEGER we would need 8 bytes per elem worst case.
Everything below 100 million (8) is therefore very memory wasteful in terms of RSS.
If we use we see that the memory is now, unsurprisingly, accounted for under Results for different N:We see therefore that typed arrays are much closer to what they advertise (4 bytes per element), even for smaller element counts, as expected.
Int32Array
typed array buffers instead of a simple Array
:node --expose-gc bench_mem.js array-buffer n N
arrayBuffers
, e.g. for N
1 million:{
rss: 31776768,
heapTotal: 6463488,
heapUsed: 3674520,
external: 4285296,
arrayBuffers: 4010422
}
|| N
|| `arrayBuffers`
|| `rss`
|| `rss` per elem
| 1 M
| 4 MB
| 31 MB
| 5
| 10 M
| 40 MB
| 67 MB
| 4.6
| 100 M
| 40 MB
| 427 MB
| 4
Now let's try one million objects of type gives:Disaster! Memory usage is up to 70 MB! Why?? We were expecting only about 24, 4 baseline + 2 * 10 for each million int?!
{ a: 1, b: -1 }
:node --expose-gc bench_mem.js obj
{
rss: 138969088,
heapTotal: 105246720,
heapUsed: 70103896,
external: 285296,
arrayBuffers: 10422
}
And now an equivalent version using gives the same result.
class
:node --expose-gc bench_mem.js class
Let's try Array:is even worse at 78 MB!! OMG why.
node --expose-gc bench_mem.js arr
{
rss: 164597760,
heapTotal: 129363968,
heapUsed: 78117008,
external: 285296,
arrayBuffers: 10422
}
Let's change the number of fields on the object? First as a sanity check:produces as expected the smae result as:so adding properties one by one doesn't change anything from creating the literal all at once. Good.
node --expose-gc bench_mem.js obj 2
node --expose-gc bench_mem.js obj
Now:gives
node --expose-gc bench_mem.js obj N
heapUsed
:- 1: 70M
- 2: 70M
- 3: 70M
- 4: 70M
- 5: 110M
- 6: 110M
- 7: 110M
- 8: 134M
- 9: 134M
- 10: 134M
- 11: 158M
Focal length
Each side is a sphere section. They don't have to have the same radius, they are still simple to understand with different radiuses.
The two things you have to have in mind that this does are:
- This is for example why you can use lenses to burn things with Sun rays, which are basically parallel.Conversely, if the input is a point light source at the focal length, it gets converted into parallel light.
- image formation: it converges all rays coming from a given source point to a single point image. This amplifies the signal, and forms an image at a plane.The source image can be far away, and the virtual image can be close to the lens. This is exactly what we need for a camera.For each distance on one side, it only works for another distance on the other side. So when we set the distance between the lens and the detector, this sets the distance of the source object, i.e. the focus. The equation is:where and are the two distances.
Mitochondria have DNA because they need to be controlled individually by Ciro Santilli 34 Updated 2024-12-15 +Created 1970-01-01
Argued at Power, Sex, Suicide by Nick Lane (2006) page 212.
Basically, energy supply has to be modulated rather quickly, because we spend a lot sometimes, and very little other times.
Even not turning it off quickly enough is a problem, as it starts to generate free radicals which fuck you up.
If control came from the nucleus, it has no way to address different mitochondria. But it might be that only one of the mitochondria needs the change. If the nucleus tells all mitochondria to stop producing when only one is full, the others are going to say: "nope, I'm not full, continue producing!" and the one that need to stop will have its signal overriden by the others.
Special-purpose acquisition company by Ciro Santilli 34 Updated 2024-12-15 +Created 1970-01-01
This is some fishy, fishy business.
Why do multiple electrons occupy the same orbital if electrons repel each other? by Ciro Santilli 34 Updated 2024-12-15 +Created 1970-01-01
That is, two electrons per atomic orbital, each with a different spin.
As shown at Schrödinger equation solution for the helium atom, they do repel each other, and that affects their measurable energy.
However, this energy is still lower than going up to the next orbital. TODO numbers.
This changes however at higher orbitals, notably as approximately described by the aufbau principle.
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