Type of laser Created 2024-06-26 Updated 2025-07-16
Lasers vs other light sources Created 2024-06-26 Updated 2025-07-16
The key advantages of lasers over other light sources are:
- lasers emit a narrow spectrum
- it can be efficient collimated, while still emitting a lot of output power: Section "Why can't you collimate incoherent light as well as a laser?"
- can be phase and polarization coherent, though it is not always the case? TODO.
One cool thing about lasers is that they rely on one specific atomic energy level transition to produce light. This is why they are able to to be so monchromatic. Compare this to:As such, lasers manage to largely overcome "temperature distribution-like" effects that create wider wave spectrum
- incandescent bulbs: wide black-body radiation spectrum
- LED: has a wider spectrum fundamentally related to an energy distribution, related: Why aren't LEDs monochromatic
- TODO think a bit about fluorescent lamps. These also rely on atomic energy transitions, but many of them are present at once, which makes the spectrum very noisy. But would individual lines be very narrow?
Crazy difference between 5W laser and 5W LED by Brainiac75
. Source. Baseic but good. Uses a laser photometer. Laser spectrum Created 2024-06-26 Updated 2025-07-16
Twisted pair Created 2024-06-26 Updated 2025-07-16
Education of André-Marie Ampère Created 2024-06-26 Updated 2025-07-16
en.wikipedia.org/w/index.php?title=Andr%C3%A9-Marie_Amp%C3%A8re&oldid=1211946256:TODO find the source for this.
Jean-Jacques Ampère, a successful merchant, was an admirer of the philosophy of Jean-Jacques Rousseau, whose theories of education (as outlined in his treatise Émile) were the basis of Ampère's education. Rousseau believed that young boys should avoid formal schooling and pursue instead a "direct education from nature." Ampère's father actualized this ideal by allowing his son to educate himself within the walls of his well-stocked library.
André-Marie Ampère Created 2024-06-26 Updated 2025-07-16
Electrical cable Created 2024-06-26 Updated 2025-07-16
One more more electrical wires surrounded by an insulator.
Oliver Heaviside Created 2024-06-26 Updated 2025-07-16
He participated in the development of the electrical telegraph, and he did some good modeling work that improved the foundations of the field, notably creating the telegrapher's equations.
He was one of those idealists who just want to do some cool work even if they have to starve for it, people had to get a state pension for him for his contributions. Nice guy. en.wikipedia.org/w/index.php?title=Oliver_Heaviside&oldid=1230097796#Later_years_and_views:He also never married: www.nndb.com/people/627/000204015/
In 1896, FitzGerald and John Perry obtained a civil list pension of £120 per year for Heaviside, who was now living in Devon, and persuaded him to accept it, after he had rejected other charitable offers from the Royal Society.
CIA 2010 covert communication websites 2013 DNS census secureserver.net MX records intersection 2013 DNS Census virtual host cleanup Created 2023-07-19 Updated 2025-07-16
We intersect 2013 DNS Census virtual host cleanup with 2013 DNS census MX records and that leaves 460k hits. We did lose a third on the the MX records as of 260 hits since secureserver.net is only used in 1/3 of sites, but we also concentrate 9x, so it may be worth it.
We did a full Wayback Machine CDX scanning for JAR, SWF and cgi-bin in those, but only found a single new hit:
- 63.130.160.50 theglobalheadlines.com. Just barely missed with our 2013 DNS Census virtual host cleanup heuristic keyword searches as we did think of both "global" and "headlines" in the "news" themes!
Tcl Updated 2025-07-16
Photon Updated 2025-07-16
Initially light was though of as a wave because it experienced interference as shown by experiments such as:
But then, some key experiments also start suggesting that light is made up of discrete packets:and in the understanding of the 2020 Standard Model the photon is one of the elementary particles.
- Compton scattering, also suggests that photons carry momentum
- photoelectric effect
- single photon production and detection experiments
This duality is fully described mathematically by quantum electrodynamics, where the photon is modelled as a quantized excitation of the photon field.
1914 Nobel Prize in Physics Updated 2025-07-16
Not only did this open the way for X-ray crystallography, it more fundamentally clarified the nature of X-rays as being electromagnetic radiation, and helped further establish the atomic theory.
Crank (person) Updated 2025-07-16
Yet, all breakthroughs, comes from them, because the people who are crazy enough to believe they can change the world are the ones who actually do ;-)
Primitive recursive function Updated 2025-07-16
In intuitive terms it consists of all integer functions, possibly with multiple input arguments, that can be written only with a sequence of:and such that
- variable assignments
- addition and subtraction
- integer comparisons and if/else
- for loops
for (i = 0; i < n; i++)n does not change inside the loop body, i.e. no while loops with arbitrary conditions.n does not have to be a constant, it may come from previous calculations. But it must not change inside the loop body.Primitive recursive functions basically include every integer function that comes up in practice. Primitive recursive functions can have huge complexity, and it strictly contains EXPTIME. As such, they mostly only come up in foundation of mathematics contexts.
The cool thing about primitive recursive functions is that the number of iterations is always bound, so we are certain that they terminate and are therefore computable.
This also means that there are necessarily functions which are not primitive recursive, as we know that there must exist uncomputable functions, e.g. the busy beaver function.
Adding unbounded while loops of course enables us to simulate arbitrary Turing machines, and therefore increases the complexity class.
More finely, there are non-primitive total recursive functions, e.g. most famously the Ackermann function.
CRC-32 Updated 2025-07-16
Printed circuit board Updated 2025-07-16
CIA 2010 covert communication websites secure subdomain search on 2013 DNS Census Updated 2025-07-16
Grepping the 2013 DNS Census first by overused CGI comms subdomains
secure. and ssl. leaves 200k lines. Grepping for the overused "news" led to hits:- secure.worldnewsandent.com,2012-02-13T21:28:15,208.254.40.117
- ssl.beyondnetworknews.com,2012-02-13T20:10:13,66.104.175.40
Also tried but failed:
sports:- secure.motorsportdealers.com,2012-04-10T20:19:09,64.73.117.38 web.archive.org/web/20110501000000*/motorsportdealers.com
OK, after the initial successes in New results: only one...
secure., we went a bit more data intensive:- took all
secure.*ssl.*URLs in the 2013 DNS Census, 70k entries - cleaned up a bit, e.g. only
.comor.net. this left only, 30k entries only - lopped over all of them in archive CDX: Wayback Machine CDX scanning, searching for those that also end in
.cgiweb.archive.org/cdx/search/cdx?url=$domain&matchType=domain&filter=urlkey:.*.cgi&to=20140101000000. Took an afternoon, but no rate limit block. - this leaves about 1000, so we loop over all of them manually on web archive with a script, and opened any that had the pattern of very vew hits between 2010 and 2013 only, and on those check for visual/thematic style match. Careful not to make more than 15 requests per minute or else 5 min blacklist!
- 208.254.42.205 secure.driversinternationalgolf.com,2012-02-13T10:42:20,
After 2013 DNS Census virtual host cleanup heuristic keyword searches we later understood why there were so few hits here: the 2013 DNS Census didn't capture the
secure. subdomains of many domains it had for some reason. Shame, because if it had, this method would have yielded many more results. TeachMeAsap.com Updated 2025-07-16
They sent one of the rare spams Ciro actually was interested in!!! Likely going down lists of top Stack Overflow users.
They have some kind of cryptocurrency, TCHME token, as a reward. Ciro wonders if the value of TCHME will ever be high enough to serve as a valid incentive.
Also, what is the total TCHME supply? Can the website devs issue as much as they want? They do giveaways e.g. as shown at: twitter.com/TeachMeAsap/status/1621353671840899072
And a centralized system with a certralized marketplace would work just as well for the initial phases. But fair play, the idea is interesting.
Telecommunication Updated 2025-07-16
A very cool thing about telecommunication is, besides how incredibly fast it advanced (in this sense it is no cooler than integrated circuit development), how much physics and information theory is involved in it. Applications of telecommunication implementation spill over to other fields, e.g. some proposed quantum computing approaches are remarkably related to telecommunication technology, e.g. microwaves and silicon photonics.
This understanding made Ciro Santilli wish he had opted for telecommunication engineering when he was back in school in Brazil. For some incomprehensible reason, telecommunications was the least competitive specialization in the electric engineering department at the time, behind even power electronics. This goes to show both how completely unrelated to reality university is, and how completely outdated Brazil is/was. Sad stuff.
Tensor Updated 2025-07-16
Because a tensor is a multilinear form, it can be fully specified by how it act on all combinations of basis sets, which can be done in terms of components. We refer to each component as:where we remember that the raised indices refer dual vector.
Explain it properly bibliography:
- www.reddit.com/r/Physics/comments/7lfleo/intuitive_understanding_of_tensors/
- www.reddit.com/r/askscience/comments/sis3j2/what_exactly_are_tensors/
- math.stackexchange.com/questions/10282/an-introduction-to-tensors?noredirect=1&lq=1
- math.stackexchange.com/questions/2398177/question-about-the-physical-intuition-behind-tensors
- math.stackexchange.com/questions/657494/what-exactly-is-a-tensor
- physics.stackexchange.com/questions/715634/what-is-a-tensor-intuitively
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