In the early 1950s, the only thing scarier than the threat of nuclear war was the annual return of polio — an easily-spread, incurable disease that causes nerve damage, paralysis, and sometimes death. At the first sign of an outbreak, public hot spots like theaters and swimming pools would close up immediately.
One of the worst polio epidemics in the United States struck in 1952, a few years into the postwar baby boom. Polio is more likely to infect children than adults, so the race to create a vaccine reached a fever pitch.
Most researchers were looking into live-virus vaccines, which had worked nicely for smallpox and rabies and become the standard approach. But Jonas Salk, a medical researcher and budding virologist, was keen on the idea of safer, killed-virus vaccines. He believed the same principle would work for polio, and he was right. Within a few years of developing his vaccine, the number of polio cases in the United States dropped from ~29,000 in 1955 to less than 6,000 in 1957. By 1979, polio had been eradicated in the US.
Jonas Salk is one of science’s folk heroes. The polio vaccine was actually his sophomore effort — he and Thomas Francis developed the first influenza vaccine in the 1940s. And he didn’t stop with polio, either. Toward the end of his life, Salk was working on an AIDS vaccine.
Before Tesla devised beautifully simple rotary machinery, he explored other methods of generating alternating current. One of those was the mechanical oscillator, and [Integza] had a go at replicating the device himself. (Video, embedded below the break.)
Initial attempts to reproduce the technology using 3D-printed parts were a failure. The round cylinder had issues sealing, and using O-ring seals introduced too much friction to allow the device to oscillate properly. A redesign that used external valving and a square cylinder proved more successful.
Once the oscillator was complete, the output shaft was fitted with magnets and a coil to generate electricity. After generating a disappointing 0.14 volts, [Integza] went back and had a look at the Maxwell-Faraday equations. Using this to guide the design, a new coil was produced with more turns, and the magnetic flux was maximised. With this done, the setup could generate seven volts, enough to light several LEDs.
While it’s not a particularly efficient generator, it’s a great proof-of-concept. Yes, Tesla’s invention worked, but it’s easy to see why he moved on to rotary designs when it came to real-world applications. We’ve seen [Integza] take on other builds too, like the ever-popular Tesla turbine.
After spending much of the 20th century languishing in development hell, electric cars have finally hit the roads in a big way. Automakers are working feverishly to improve range and recharge times to make vehicles more palatable to consumers.
With a strong base of sales and increased uncertainty about the future of fossil fuels, improvements are happening at a rapid pace. Oftentimes, change is gradual, but every so often, a brand new technology promises to bring a step change in performance. Silicon carbide (SiC) semiconductors are just such a technology, and have already begun to revolutionise the industry.
Mind The Bandgap
Traditionally, electric vehicles have relied on silicon power transistors in their construction. Having long been the most popular semiconductor material, new technological advances have opened it up to competition. Different semiconductor materials have varying properties that make them better suited for various applications, with silicon carbide being particularly attractive for high-power applications. It all comes down to the bandgap.
Electrons in a semiconductor can sit in one of two energy bands – the valence band, or the conducting band. To jump from the valence band to the conducting band, the electron needs to reach the energy level of the conducting band, jumping the band gap where no electrons can exist. In silicon, the bandgap is around 1-1.5 electron volts (eV), while in silicon carbide, the band gap of the material is on the order of 2.3-3.3 eV. This higher band gap makes the breakdown voltage of silicon carbide parts far higher, as a far stronger electric field is required to overcome the gap. Many contemporary electric cars operate with 400 V batteries, with Porsche equipping their Taycan with an 800 V system. The naturally high breakdown voltage of silicon carbide makes it highly suited to work in these applications.
One of the nice things about a road trip is you often get to see something that really surprises you. A recent trip through Texas may have resulted in my second most surprising sighting. There’s a strange tower that looks oddly like a Tesla tower in the middle of rural Texas, right off the main interstate. What is it? Although Google did answer the question — sort of — I’m still not sure how legitimate its stated purpose is.
I was driving between Wimberly and Frisco — two towns that aren’t exactly household names outside of Texas. Near Milford, there’s a very tall structure that looks like a giant mechanical mushroom on top of a grain silo. If the mushroom were inverted or pointing towards the horizon, it would be easy to imagine it was some very odd antenna. This dish, however, is pointed right down its own odd-shaped mast. The top of the thing sure looks like the top of a Van de Graf generator.
Starlink is a project run by SpaceX to provide internet via satellite, using a variety of techniques to keep latency down and bandwidth high. There’s talk of inter-satellite laser communications, autonomous obstacle avoidance, and special designs to limit the amount of space junk created. We’ve covered the technology in a comprehensive post earlier this year.
The Starlink craft have long worried astronomers, who rely on a dark and unobstructed view of the sky to carry out their work. There are now large numbers of the satellites in relatively low orbits, and the craft have a high albedo, meaning they reflect a significant amount of the sunlight that hits them. With the craft also launching in a closely-packed train formation, there have already been impacts on research operations.
We’ve seen 3D image projection tried in a variety of different ways, but this is a new one to us. This volumetric display by Interact Lab of the University of Sussex creates a 3D image by projecting light onto a tiny foam ball, which zips around in the air fast enough to create a persistence of vision effect. (Video, embedded below.) How is this achieved? With a large array of ultrasonic transducers, performing what researchers call ‘acoustic trapping’.
This is the same principle behind acoustic levitation devices which demonstrate how lightweight objects (like tiny polystyrene foam balls) can be made to defy gravity. But this 3D display is capable of not only moving the object in 3D space, but doing so at a high enough speed and with enough control to produce a persistence of vision effect. The abstract for their (as yet unreleased) paper claims the trapped ball can be moved at speeds of up to several meters per second.
It has a few other tricks up its sleeve, too. The array is capable of simultaneously creating sounds as well as providing a limited form of tactile feedback by letting a user touch areas of high and low air pressure created by the transducers. These areas can’t be the same ones being occupied by the speeding ball, of course, but it’s a neat trick. Check out the video below for a demonstration. Continue reading “Behold A 3D Display, Thanks To A Speeding Foam Ball”→
Once an exotic component, solid state heat pumps or Peltier devices are now pretty mainstream. The idea is simple: put electricity through a Peltier device and one side gets hot while the other side gets cold. [DroneBot] recently posted a video showing how these cool — really cool — devices work. You can see the video, below.
Many things in physics are reversible, and the Peltier is no exception. The device is actually a form of thermocouple, and in a thermocouple a temperature difference causes a voltage difference. This is known as the Seebeck effect as opposed to the Peltier effect in which current flowing between voltage differences causes a temperature difference. It was known for many years, but wasn’t very practical until modern semiconductor materials arrived.