As a quick and dirty rule of thumb measuring parts per million in anything except time or frequency will get expensive. Temperature drifts will cause expansions and contractions on that order if you’re measuring lengths.
By 1870 pi was known to several hundred decimal digits, for something like this calculation where you have other large sources of error Archimedes approximation from 2 millennia earlier would probably be fine. (<1% error)
The explanation is really well done, it captures the essence of the Pauli exclusion principle without delving too deeply into the weeds. In my opinion the best part of the video is the explanation of the "hole" quasiparticle at 6:10 (I learned this as a pseudo-particle but will defer to Wikipedia [1]).
While a great introduction to semiconductor behavior this does gloss over a very important detail namely direct vs indirect semicondoctors as some others have mentioned. In the video the detail that's glossed over relates to the nature of crystals, namely that they're highly ordered repeating structures but that they don't look the same when viewed from every direction. This means that there isn't a single band-gap but multiple ones depending on the direction of the crystal you're contemplating.
At this point you may reasonably ask why the direction matters and now we unfortunately get deep into the weeds with quantum mechanics again. When a single photon is absorbed in the semiconductor system both momentum and energy must be conserved. The momentum of the photon for something like the Silicon bandgap is quite small (something like the equivalent of an electron traveling at 1500m/s) while the momentum of room-temperature conduction electrons is substantially faster [2] so as a very slight simplification transitions due to the absorption of photons are not accompanied by a change in momentum and so we only care about the band structure (and the accompanying free carriers) associated with a particular crystal direction.
In particular in Silicon you have what's called an indirect bandgap, namely the minimum energy conduction band electrons have a different momentum from the valence band holes ([3]) and as a consequence while you can _absorb_ a photon in order to make a detector you cannot make it efficiently _emit_ a photon as an LED should (something the video got wrong).
None of this matters for the heart of the video, which focuses blue LEDs in the GaN materials system which is definitely a direct bandgap material, however if someone does manage to create a manufacturable light emitter in pure Silicon expect an absolute revolution with regards to optical computing and photonics. (Not for lack of trying, this has been the holy grail for at least 20 years, possibly longer)
Funny story, that demo only exists because the designer was mis-categorized as a software engineer after an acquisition by Apple. After nearly getting the person in question fired it ultimately resulted in a successful job category change for them.
From the paper it looks like most of the interesting work with the laser and optical train use an external board to recreate the feedback and control circuitry already present and required for normal operation in a DVD/BluRay drive. It would be great if you could have more control over the existing hardware in these drives.
I found a project that started the reverse engineering process on a popular bluray drive [1] but it really looks like an uphill slog against undocumented CPUs and motor control chips among other obstacles. Anyone know of any other resources for reusing the existing hardware but modifying the control software?
There's an episode of James Burke's Connections that explores this idea with a bit of depth, I recommend watching the whole series if you have the time.
With regards to how you locate it, the paper proposes looking at existing data from FERMILAT, a gamma ray telescope which could possibly pick up anihilations from a dark matter cloud surrounding such a black hole. Since the object itself is so tiny (I’ve never seen a 1:1 scale figure in an astronomy paper before) you need to detect its presence in some other way.
You can use the phenomenon of negative differential resistance to improve the design of some very common circuit elements. For example you can move from a classic six transistor SRAM cell to a two transistor design. It's a bit dense reading but here is a research synopsis from one group working on this in silicon/SiGe. http://www2.ece.ohio-state.edu/~berger/summ_ritd05.html
Unless the planets happen to orbit very stable stars in the plane that sometimes puts them between earth and their star. With Kepler and some earth-bound telescopes you can discern the brightness dips from these and sometimes glean minimal spectroscopic information on the planet. Direct imaging is possible with interferometric methods and some more innovative approaches [1] but require funding.
I use Better Touch Tool [1] which is mostly about expanding defaults for multitouch gestures. I haven't gotten around to using the Better Snap tool which focuses on window management yet.
