The Geometry Of Transistors

December 13, 2023 by Bryan Cockfield 10 Comments

Building things in a lab is easy, at least when compared to scaling up for mass production. That’s why there are so many articles about fusion being right around the corner, or battery technology that’ll allow aviation to switch away from fossil fuels, or any number of other miraculous solutions that never come into being. They simply don’t scale or can’t be manufactured in a cost effective way. But even when they are miraculous and can be produced on a massive scale, as is the case for things like transistors, there are some oddities that come up as a result of the process of making so many. This video goes into some of the intricacies of a bipolar junction transistor (BJT) and why it looks the way it does.

The BJT in this video is a fairly standard NPN type, with three layers of silicon acting as emitter, base, and collector. Typically when learning about electronics devices the drawings of them are simplified two-dimensional block diagrams, but under a microscope this transistor at first appears nothing like the models shown in the textbook. Instead it resembles more of a bird’s foot with a few small wires attached. The bird’s foot shape is a result of attempting to lower the undesirable resistances of the device and improve its performance, and some of its other quirks are due to the manufacturing process. That process starts with a much larger layer of doped silicon that will eventually become the collector, and then the other two, much smaller, layers of the transistor deposited on top of the collector. This also explains while it looks like there are only two layers upon first glance, and also shows that the horizontal diagram used to model the device is actually positioned vertically in the real world.

For most of the processes in our daily lives, the transistor has largely been abstracted away. We don’t have to think about them in a computer that much anymore, and unless work is being done on high-wattage power electronics devices, radios, or audio amplifiers it’s not likely that an average person will run into a transistor. But this video goes a long way to explaining the basics of one of the fundamental building blocks of the modern world for those willing to take a dive into the physics. Take a look at this video as well for an intuitive explanation of the close cousin of the BJT, the field-effect transistor.

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Some Bacteria Could Have A Rudimentary Form Of Memory

December 12, 2023 by Lewin Day 9 Comments

When we think of bacteria, we think of simple single-celled organisms that basically exist to consume resources and reproduce. They don’t think, feel, or remember… or do they? Bacteria don’t have brains, and as far as we know, they’re incapable of thought. But could they react to an experience and recall it later?

New research suggests that some bacteria could have a rudimentary form of memory of their experiences in the environment. They could even pass this memory down across generations via a unique mechanism. Let’s dive into the latest research that is investigating just what bacteria know, and how they happen to know it.

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Homemade Raman Laser Is Shaken, Not Stirred

December 12, 2023 by Dan Maloney 12 Comments

You wouldn’t think that shaking something in just the right way would be the recipe for creating laser light, but as [Les Wright] explains in his new video, that’s pretty much how his DIY Raman laser works.

Of course, “shaking” is probably a gross oversimplification of Raman scattering, which lies at the heart of this laser. [Les] spends the first half of the video explaining Raman scattering and stimulated Raman scattering. It’s an excellent treatment of the subject matter, but at the end of the day, when certain crystals and liquids are pumped with a high-intensity laser they’ll emit coherent, monochromatic light at a lower frequency than the pumping laser. By carefully selecting the gain medium and the pumping laser wavelength, Raman lasers can emit almost any wavelength.

Most gain media for Raman lasers are somewhat exotic, but luckily some easily available materials will work just fine too. [Les] chose the common solvent dimethylsulfoxide (DMSO) for his laser, which was made from a length of aluminum hex stock. Bored out, capped with quartz windows, and fitted with a port to fill it with DMSO, the laser — or more correctly, a resonator — is placed in the path of [Les]’ high-power tattoo removal laser. Laser light at 532 nm from the pumping laser passes through a focusing lens into the DMSO where the stimulated Raman scattering takes place, and 628 nm light comes out. [Les] measured the wavelengths with his Raspberry Pi spectrometer, and found that the emitted wavelength was exactly as predicted by the Raman spectrum of DMSO.

It’s always a treat to see one of [Les]’ videos pop up in our feed; he’s got the coolest toys, and he not only knows what to do with them, but how to explain what’s going on with the physics. It’s a rare treat to watch a video and come away feeling smarter than when you started.

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Impact Of Imperfect Timekeeping On Quantum Control And Computing

December 9, 2023 by Maya Posch 12 Comments

In classical control theory, both open-loop and closed-loop control systems are commonly used. These systems are well understood and rather straightforward, controlling everything from washing machines to industrial equipment to the classical computing devices that make today’s society work. When trying to transfer this knowledge to the world of quantum control theory, however, many issues arise. The most pertinent ones involve closed-loop quantum control and the clocking of quantum computations. With physical limitations on the accuracy and resolution of clocks, this would set hard limits on the accuracy and speed of quantum computing.

The entire argument is covered in two letters to Physical Review Letters, by Florian Meier et al. titled Fundamental Accuracy-Resolution Trade-Off for Timekeeping Devices (Arxiv preprint), and by Jake Xuereb et al. titled Impact of Imperfect Timekeeping on Quantum Control (Arxiv preprint). The simple version is that by simply increasing the clock rate, accuracy suffers, with dephasing and other issues becoming more frequent.

Solving the riddle of closed-loop quantum control theory is a hard one, as noted by Daoyi Dong and Ian R Peterson in 2011. In their paper titled Quantum control theory and applications: A survey, the most fundamental problem with such a closed-loop quantum control system lies with aspects such as the uncertainty principle, which limits the accuracy with which properties of the system can be known.

In this regard, an accurately clocked open-loop system could work better, except that here we run into other fundamental issues. Even though this shouldn’t phase us, as with time solutions may be found to the timekeeping and other issues, it’s nonetheless part of the uncertainties that keep causing waves in quantum physics.

Top image: Impact of timekeeping error on quantum gate fidelity & independent clock dephasing (Xuereb et al., 2023)

Nanobots Self Replicate

December 9, 2023 by Al Williams 11 Comments

Hey, what if you could have a factory that makes robots that is run by… robots? This is hardly an original thought, but we are a long way from having an assembly line of C3POs self-replicating. On the other hand, animals — including humans — self-replicate all the time using DNA. Now, scientists are making tiny nanorobots from DNA that can assemble more DNA, including copies of themselves.

Assembling 3D structures with DNA has deep implications. For example, it might be possible to build drugs in situ, delivering powerful toxins only to cancer cells. Another example would be putting DNA factories in diabetes patients to manufacture the insulin they can’t.

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Japan’s JT-60SA Generates First Plasma As World’s Largest Superconducting Tokamak Fusion Reactor

December 6, 2023 by Maya Posch 35 Comments

Comparison of toroidal field (TF) coils from JET, JT-60SA and ITER (Credit: QST)

Japan’s JT-60SA fusion reactor project announced first plasma in October of this year to denote the successful upgrades to what is now the world’s largest operational, superconducting tokamak fusion reactor. First designed in the 1970s as Japan’s Breakeven Plasma Test Facility, the JT-60SA tokamak-based fusion reactor is the latest upgrade to the original JT-60 design, following two earlier upgrades (-A and -U) over its decades-long career. The most recent upgrade matches the Super Advanced meaning of the new name, as the new goal of the project is to investigate advanced components of the global ITER nuclear fusion project.

Originally the JT-60SA upgrade with superconducting coils was supposed to last from 2013 to 2020, with first plasma that same year. During commissioning in 2021, a short circuit in the poloidal field coils caused a lengthy investigation and repair, which was completed earlier this year. Although the JT-60SA is only using hydrogen and later deuterium as its fuel rather than the deuterium-tritium (D-T) mixture of ITER, it nevertheless has a range of research objectives that allow for researchers to study many aspects of the ITER fusion reactor while the latter is still under construction.

Since the JT-60SA also has cooled divertors, it can sustain plasma for up to 100 seconds, to study various field configurations and the effect this has on plasma stability, along with a range of other parameters. Along with UK’s JET, China’s HL-2M and a range of other tokamaks at other facilities around the world, this should provide future ITER operators with significant know-how and experience long before that tokamak will generate its first plasma.

Anthrobots can promote gap closures on scratched live neuronal monolayers. (Credit: Gumuskaya et al., 2023)

Anthrobots: Tiny Robots From Tracheal Epithelium Cells That Can Fix Neural Damage

December 6, 2023 by Maya Posch 10 Comments

Although we often regard our own bodies and those of the other multicellular organisms around us as a singular entity, each cell that makes up our body is its own, nano-robot. One long-existing question was whether these cells can be used for other tasks — like biological robots — after they have specialized into a specific tissue type, with a recent study by [Gizem Gumuskaya] and colleagues in Advanced Science (with Nature news coverage) indicating a potential intriguing use of adult human epithelial cells recovered from the trachea.

Human bronchial epithelial cells self-construct into multicellular motile living architectures. (Credit: Gumuskaya et al., 2023)

After extraction, these adult cells were kept in an extracellular matrix (ECM, Matrigel) in conditions promoting cell division, followed by ECM dissolution after 14 days and subsequent culturing of the spherical clumps of cells that had thus formed in a water-based, low-viscosity environment. This environment, along with the addition of retinoic acid promoted the development of outward-facing cilia, rather than the typical inward type with a gel-based ECM.

These spheroids (anthrobots, referencing their human origin) generally showed the ability to move using these cilia, with the direction largely determined by the symmetry of the sphere. Multiple of these motile spheroids were then placed on a layer of human neural tissue, in which a scratch had damaged a number of the neurons to form a gap. The anthrobots grouped together over the course of days to form a bridge across the gap, with the neural tissue observed to regrow underneath this bridge, a behavior that could not be repeated by using a dummy support consisting out of agarose on another neural sample, indicating that it is this living bridge that enabled neural regeneration.

Although the researchers rightfully indicate that they are uncertain which factors actually induce this restorative effect in the neurons, it offers exciting glimpses into a potential feature where neural damage is easily repaired, and biological robots made from our own cells can be assembled to perform a variety of tasks.