The US’s New Nuclear Weapons, Mysterious Fogbanks And Inertial Confinement Fusion

October 11, 2024 by Maya Posch 51 Comments

Keeping the United States’ nuclear arsenal ready for use is an ongoing process, one which is necessarily shrouded in complete secrecy. In an article by The War Zone these developments and the secrets behind it are touched upon, including a secret ingredient for these thermonuclear warheads that is only officially known as ‘Fogbank’, but which is very likely aerogel.

As noted by a commentator, this is pretty much confirmed in an article published by Los Alamos National Laboratories (LANL) in the 2nd 2009 issue (PDF) of Nuclear Weapons Journal. On page nine the article on hohlraum-based inertial confinement fusion notes the use of aerogel to tamp the radially inward motion of the wall material, suggesting a similar function within one of these thermonuclear warheads.

The research at the Nuclear Ignition Facility (NIF) over at Lawrence Livermore National Laboratory (LLNL) is directly related to these thermonuclear weapons, as they are based around inertial confinement fusion (ICF), which is what the NIF is set up for to study, including the role of aerogel. ICF is unlikely to ever be used for energy production, as we noted in the past, but makes it possible to study aspects of detonating a thermonuclear weapon that are difficult to simulate and illegal to test with real warheads.

Currently it seems that after decades of merely reusing the Fogbank material in refurbished warheads, new material is now being produced again, with it likely being used in the new W93 warhead and the low-yield W76 and life-extended W76-1 variants. All of which is of course pure conjecture, barring the details getting leaked on the War Thunder forums to settle a dispute on realistic US thermonuclear weapon yields.

On-Site Viral RNA Detection In Wastewater With Paper And Wax Microfluidics

October 9, 2024 by Maya Posch 4 Comments

Schematic version of on-site wastewater analysis using the microfluidic strips (Credit: Yuwei Pan et al., Cell, 2024)

Wastewater sampling has become a popular way over the years to keep track of the health of a population, including human ones, as pathogens are often detectable in the effluence from toilets. Since most houses connected to the centralized sewer systems, this means that a few sampling sites suffice to keep tabs on which viruses are circulating in an area. While sampling this wastewater is easy, the actual RNA analysis using PCR (polymerase chain reaction) still has to be performed in laboratories, adding complex logistics. An approach for on-site analysis using microfluidics was tested out by [Yuwei Pan] et al., as recently published in Cell.

This particular approach uses RT-LAMP (reverse-transcription loop-mediated isothermal amplification) to increase the amount of genetic material, which has the significant benefit over PCR that it does not require multiple thermal cycles, instead being run at a constant temperature. The filter paper used as the basis has wax microchannels printed on it, which help to guide the filtered wastewater to the reaction chambers. This is in many ways reminiscent of the all too familiar linear flow self-tests (RAT: rapid antigen test) that have become one of the hallmarks of the SARS-CoV-2 pandemic.

What this paper microfluidic device adds is that it doesn’t merely contain antigens, but performs the lysis (i.e. breakdown of the virus particles), genetic material multiplication using RT-LAMP and subsequent presence detection of certain RNA sequences to ascertain the presence of specific viruses. Having been used in the field already since 2020 in the UK, the researchers envision this type of on-site analysis to be combined with a smartphone for instant recording and transmission to health authorities.

Some of the benefits of this approach would be lower cost, easier logistics and faster results compared to shipping wastewater samples to central laboratories.

Lagrange Points And Why You Want To Get Stuck At Them

October 9, 2024 by Maya Posch 34 Comments

Visualization of the Sun-Earth Lagrange points.

Orbital mechanics is a fun subject, as it involves a lot of seemingly empty space that’s nevertheless full of very real forces, all of which must be taken into account lest one’s spacecraft ends up performing a sudden lithobraking maneuver into a planet or other significant collection of matter in said mostly empty space. The primary concern here is that of gravitational pull, and the way it affects one’s trajectory and velocity. With a single planet providing said gravitational pull this is quite straightforward to determine, but add in another body (like the Moon) and things get trickier. Add another big planetary body (or a star like our Sun), and you suddenly got yourself the restricted three-body problem, which has vexed mathematicians and others for centuries.

The three-body problem concerns the initial positions and velocities of three point masses. As they orbit each other and one tries to calculate their trajectories using Newton’s laws of motion and law of universal gravitation (or their later equivalents), the finding is that of a chaotic system, without a closed-form solution. In the context of orbital mechanics involving the Earth, Moon and Sun this is rather annoying, but in 1772 Joseph-Louis Lagrange found a family of solutions in which the three masses form an equilateral triangle at each instant. Together with earlier work by Leonhard Euler led to the discovery of what today are known as Lagrangian (or Lagrange) points.

Having a few spots in an N-body configuration where you can be reasonably certain that your spacecraft won’t suddenly bugger off into weird directions that necessitate position corrections using wasteful thruster activations is definitely a plus. This is why especially space-based observatories such as the James Webb Space Telescope love to hang around in these spots.

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Recycling Tough Plastics Into Precursors With Some Smart Catalyst Chemistry

October 8, 2024 by Lewin Day 33 Comments

Plastics are unfortunately so cheap useful that they’ve ended up everywhere. They’re filling our landfills, polluting our rivers, and even infiltrating our food chain as microplastics. As much as we think of plastic as recyclable, too, that’s often not the case—while some plastics like PET (polyethylene terephthalate) are easily reused, others just aren’t.

Indeed, the world currently produces an immense amount of polyethylene and polypropylene waste. These materials are used for everything from plastic bags to milk jugs and for microwavable containers—and it’s all really hard to recycle. However, a team at UC Berkeley might have just figured out how to deal with this problem.

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Memristors Are Cool, Radiation-resistant Memristors Even Moreso

October 5, 2024 by Donald Papp 9 Comments

Space is a challenging environment for semiconductors, but researchers have shown that a specific type of memristor (the hafnium oxide memristor, to be exact) actually reacts quite usefully when exposed to gamma radiation. In fact, it’s even able to leverage this behavior as a way to measure radiation exposure. In essence, it’s able to act as both memory and a sensor.

Being able to resist radiation exposure is highly desirable for space applications. Efficient ways to measure radiation exposure are just as valuable. The hafnium oxide memristor looks like it might be able to do both, but before going into how that works, let’s take a moment for a memristor refresher.

A memristor is essentially two conductive plates between which bridges can be made by applying a voltage to “write” to the device, by which one sets it to a particular resistance. A positive voltage causes bridging to occur between the two ends, lowering the device’s resistance, and a negative voltage reverses the process, increasing the resistance. The exact formulation of a memristor can vary. The memristor was conceived in the 1970s by Leon Chua, and HP Labs created a working one in 2008. An (expensive) 16-pin DIP was first made available in 2015.

A hafnium oxide memristor is a bit different. Normally it would be write-once, meaning a negative voltage does not reset the device, but researchers discovered that exposing it to gamma radiation appears to weaken the bridging, allowing a negative voltage to reset the device as expected. Exposure to radiation also caused a higher voltage to be required to set the memristor; a behavior researchers were able to leverage into using the memristor to measure radiation exposure. Given time, a hafnium oxide memristor exposed to radiation, causing it to require higher-than-normal voltages to be “set”, eventually lost this attribute. After 30 days, the exposed memristors appeared to recover completely from the effects of radiation exposure and no longer required an elevated voltage for writing. This is the behavior the article refers to as “self-healing”.

The research paper has all the details, and it’s interesting to see new things relating to memristors. After all, when it comes to electronic components it’s been quite a long time since we’ve seen something genuinely new.

Interactive Project Teaches Lessons About Electromagnets And Waves

October 4, 2024 by Lewin Day 3 Comments

Whether you’re a kid or a nerdy adult, you’ll probably agree that the interactive exhibitions at the museum are the best. If you happened to get down to the Oregon Science Festival in the last couple of years, you might have enjoyed “Catch The Wave!”—a public education project to teach people about electromagnets and waves. Even better, [Justin Miller] has written up how he built this exciting project.

Catch The Wave! consists of four small tabletop cabinets. Each has physical controls and a screen, and each plays its role in teaching a lesson about electromagnets and sound waves, with a context of audio recording and playback.

The first station allows the user to power up an electromagnet and interact with it using paper clips. They can also see the effect it has on a nearby compass. The second illustrates how reversing current through an electromagnet can reverse its polarity, and demonstrates this by using it to swing a pendulum. The third station then ties this to the action of a speaker, which is effectively a fancy electromagnet—and demonstrates how it creates sound waves in this way. Finally, the fourth station demonstrates the use of a microphone to record a voice, and throws in some wacky effects for good fun.

If you’ve ever tried to explain how sound is recorded and reproduced, you’d probably have loved to had tools like these to do so. We love a good educational project around these parts, too.

Static Electricity And The Machines That Make It

September 30, 2024 by Lewin Day 19 Comments

Static electricity often just seems like an everyday annoyance when a wool sweater crackles as you pull it off, or when a doorknob delivers an unexpected zap. Regardless, the phenomenon is much more fascinating and complex than these simple examples suggest. In fact, static electricity is direct observable evidence of the actions of subatomic particles and the charges they carry.

While zaps from a fuzzy carpet or playground slide are funny, humanity has learned how to harness this naturally occurring force in far more deliberate and intriguing ways. In this article, we’ll dive into some of the most iconic machines that generate static electricity and explore how they work.

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