We always enjoy [FloatHeadPhysics] explaining any math or physics topic. We don’t know if he’s acting or not, but he seems genuinely excited about every topic he covers, and it is infectious. He also has entertaining imaginary conversations with people like Feynman and Einstein. His recent video on tensors begins by showing the vector form of Ohm’s law, making it even more interesting. Check out the video below.
If you ever thought you could use fewer numbers for many tensor calculations, [FloatHeadPhysics] had the same idea. Luckily, imaginary Feynman explains why this isn’t right, and the answer shows the basic nature of why people use tensors.
It should probably come as no surprise to anyone that the images which we look at every day – whether printed or on a display – are simply illusions. That cat picture isn’t actually a cat, but rather a collection of dots that when looked at from far enough away tricks our brain into thinking that we are indeed looking at a two-dimensional cat and happily fills in the blanks. These dots can use the full CMYK color model for prints, RGB(A) for digital images or a limited color space including greyscale.
Perhaps more interesting is the use of dithering to further trick the mind into seeing things that aren’t truly there by adding noise. Simply put, dithering is the process of adding noise to reduce quantization error, which in images shows up as artefacts like color banding. Within the field of digital audio dithering is also used, for similar reasons. Part of the process of going from an analog signal to a digital one involves throwing away data that falls outside the sampling rate and quantization depth.
By adding dithering noise these quantization errors are smoothed out, with the final effect depending on the dithering algorithm used.
If you need to cool something, the gold standard is using a gas compressor arrangement. Of course, there are definite downsides to that, like weight, power consumption, and vibrations. There are solid-state heat pumps — the kind you see in portable coolers, for example. But, they are not terribly efficient and have limited performance.
However, researchers at Johns Hopkins, working with Samsung, have developed a new thin-film thermoelectric heat pump, which they claim is easy to fabricate, scalable, and significantly more efficient. You can see a video about the new research below.
Manufacturing requires similar processes to solar cells, and the technology can make tiny heat pumps or — in theory — coolers that could provide air conditioning for large buildings. You can read the full paper in Nature.
CHESS stands for Controlled Hierarchically Engineered Superlattice Structures. These are nano-engineered thin-film superlattices (around 25 μm thick). The design optimizes their performance in this application.
The new devices claim to be 100% more efficient at room temperature than traditional devices. In practical devices, thermoelectric devices and the systems using them have improved by around 70% to 75%. The material can also harvest power from heat differences, such as body heat. The potential small size of devices made with this technology would make them practical for wearables.
Humans have forever been using all manner of techniques to better secure the food we need to sustain our lives. The practice of agriculture is intimately tied to the development of society, while techniques like selective breeding and animal husbandry have seen our plants and livestock deliver greater and more nourishing bounty as the millennia have gone by. More recently, more direct tools of genetic engineering have risen to prominence, further allowing us to tinker with our crops to make them do more of what we want.
Over the course of evolution microorganisms have evolved pathways to break down many materials. The challenge with the many materials that we humans have created over just the past decades is that we cannot wait for evolution to catch up, ergo we have to develop such pathways ourselves. One such example is demonstrated by [Nick W. Johnson] et al. with a recent study in Nature Chemistry that explicitly targets PET plastic, which is very commonly used in plastic bottles.
The researchers modified regular E. coli bacteria to use PET plastic as an input via Lossen rearrangement, which converts hydroxamate esters to isocyanates, with at the end of the pathway para-aminobenzoate (PABA) resulting, which using biosynthesis created paracetamol, the active ingredient in Tylenol. This new pathway is also completely harmless to the bacterium, which is always a potential pitfall with this kind of biological pathway engineering.
In addition to this offering a potential way to convert PET bottles into paracetamol, the researchers note that their findings could be very beneficial to studies targeting other ‘waste’ products from biological pathways.
X-ray crystallography, like mass spectroscopy and nuclear spectroscopy, is an extremely useful material characterization technique that is unfortunately hard for amateurs to perform. The physical operation isn’t too complicated, however, and as [Farben-X] shows, it’s entirely possible to build an X-ray diffractometer if you’re willing to deal with high voltages, ancient X-ray tubes, and soft X-rays.
[Farben-X] based his diffractometer around an old Soviet BSV-29 structural analysis X-ray tube, which emits X-rays through four beryllium windows. Two ZVS drivers power the tube: one to drive the electron gun’s filament, and one to feed a flyback transformer and Cockroft-Walton voltage multiplier which generate a potential across the tube. The most important part of the imaging system is the X-ray collimator, which [Farben-X] made out of a lead disk with a copper tube mounted in it. A 3D printer nozzle screws into each end of the tube, creating a very narrow path for X-rays, and thus a thin, mostly collimated beam.
To get good diffraction patterns from a crystal, it needed to be a single crystal, and to actually let the X-ray beam pass through, it needed to be a thin crystal. For this, [Farben-X] selected a sodium chloride crystal, a menthol crystal, and a thin sheet of mica. To grow large salt crystals, he used solvent vapor diffusion, which slowly dissolves a suitable solvent vapor in a salt solution, which decreases the salt’s solubility, leading to very slow, fine crystal growth. Afterwards, he redissolved portions of the resulting crystal to make it thinner.
The diffraction pattern generated by a sodium chloride crystal.
For the actual experiment, [Farben-X] passed the X-ray beam through the crystals, then recorded the diffraction patterns formed on a slide of X-ray sensitive film. This created a pattern of dots around the central beam, indicating diffracted beams. The mathematics for reverse-engineering the crystal structure from this is rather complicated, and [Farben-X] hadn’t gotten to it yet, but it should be possible.
We would recommend a great deal of caution to anyone considering replicating this – a few clips of X-rays inducing flashes in the camera sensor made us particularly concerned – but we do have to admire any hack that coaxed such impressive results out of such a rudimentary setup. If you’re interested in further reading, we’ve covered the basics of X-ray crystallography before. We’ve also seen a few X-ray machines.
The inside of this AF117 transistor can was a thriving whisker ecosystem. (Credit: Anthony Francis-Jones)
AF114 germanium transistors and related ones like the AF115 through AF117 were quite popular during the 1960s, but they quickly developed a reputation for failure. This is due to what should have made them more reliable, namely the can shielding the germanium transistor inside that is connected with a fourth ‘screen’ pin. This failure mode is demonstrated in a video by [Anthony Francis-Jones] in which he tests a number of new-old-stock AF-series transistors only for them all to test faulty and show clear whisker growth on the can’s exterior.
Naturally, the next step was to cut one of these defective transistors open to see whether the whiskers could be caught in the act. For this a pipe cutter was used on the fairly beefy can, which turned out to rather effective and gave great access to the inside of these 1960s-era components. The insides of the cans were as expected bristling with whiskers.
The AF11x family of transistors are high-frequency PNP transistors that saw frequent use in everything from consumer radios to just about anything else that did RF or audio. It’s worth noting that the material of the can is likely to be zinc and not tin, so these would be zinc whiskers. Many metals like to grow such whiskers, including lead, so the end effect is often a thin conductive strand bridging things that shouldn’t be. Apparently the can itself wasn’t the only source of these whiskers, which adds to the fun.
In the rest of the video [Anthony] shows off the fascinating construction of these germanium transistors, as well as potential repairs to remove the whisker-induced shorts through melting them. This is done by jolting them with a fairly high current from a capacitor. The good news is that this made the component tester see the AF114 as a transistor again, except as a rather confused NPN one. Clearly this isn’t an easy fix, and it would be temporary at best anyway, as the whiskers will never stop growing.
