Synthesis Of Goldene: Single-Atom Layer Gold With Interesting Properties

April 25, 2024 by Maya Posch 16 Comments

The synthesis of single-atom layer versions of a range of atoms is currently all the hype, with graphene probably the most well-known example of this. These monolayers are found to have a range of mechanical (e.g. hardness), electrical (conduction) and thermal properties that are very different from the other forms of these materials. The major difficulty in creating monolayers is finding a way that works reliably and which can scale. Now researchers have found a way to make monolayers of gold – called goldene – which allows for the synthesis of relatively large sheets of this two-dimensional structure.

In the research paper by [Shun Kashiwaya] and colleagues (with accompanying press release) as published in Nature Synthesis, the synthesis method is described. Unlike graphene synthesis, this does not involve Scotch tape and a stack of graphite, but rather the wet-etching of Ti₃Cu₂ away from Ti₃AuC₂, after initially substituting the Si in Ti₃SiC₂ with Au. At the end of this exfoliation procedure the monolayer Au is left, which electron microscope studies showed to be stable and intact. With goldene now relatively easy to produce in any well-equipped laboratory, its uses can be explored. As a rare metal monolayer, the same wet exfoliation method used for goldene synthesis might work for other metals as well.

The Myth Of Propellantless Space Propulsion Refuses To Die

April 25, 2024 by Maya Posch 83 Comments

In a Universe ruled by the harsh and unyielding laws of Physics, it’s often tempting to dream of mechanisms which defy these rigid restrictions. Although over the past hundred years we have made astounding progress in uncovering ways to work within these restrictions — including splitting and fusing atoms to liberate immense amounts of energy — there are those who dream of making reality a bit more magical. The concept of asymmetrical electrostatic propulsion is a major player here, with the EmDrive the infamous example. More recently [Dr. Charles Buhler] proposed trying it again, as part of his company Exodus Propulsion Technologies.

This slide from Dr. Buhler’s APEC presentation shows the custom-made vacuum chamber built to test their propellantless Propulsion drive in a simulated space environment. Image Credit: Exodus Propulsion Technologies, Buhler, et al.

The problem with such propellantless space propulsion proposals is that they violate the core what we know about the physical rules, such as the conclusion by Newton that for any action there has to be an opposite reaction. If you induce an electrostatic field or whatever in some kind of device, you’d expect any kind of force (‘thrust’) this creates to act in all directions equally, ergo for thrust to exist, it has to push on something in the other direction. Rocket and ion engines (thrusters) solve this by using propellant that create the reaction mass.

The EmDrive was firmly disproven 2021 by [M. Tajmar] and colleagues in their paper titled High-accuracy thrust measurements of the EMDrive and elimination of false-positive effects as published in CEAS Space Journal, which had the researchers isolate the EmDrive from all possible outside influences. Since the reported thrust was on the level of a merest fraction of a Newton, even the impact from lighting in a room and body heat from the researchers can throw off the results, not to mention the heat developed from a microwave emitter as used in the EmDrive.

Meanwhile True Believers flock to the ‘Alt Propulsion Engineering Conference’ (APEC), as no self-respecting conference or scientific paper will accept such wishful claims. In the case of [Buhler], he claims that their new-and-improved EmDrive shows a force of 10 mN in a ‘stacked system’, yet no credible paper on the experiments can be found other than APEC presentations. Until their prototype is tested the way the EmDrive was tested by [M. Tajmar] et al., it seems fair to assume that the rules of physics as we know them today remain firmly intact.

Dual-Wavelength SLA 3D Printing: Fast Continuous Printing With ROMP And FRP Resins

April 22, 2024 by Maya Posch 10 Comments

As widespread as 3D printing with stereolithography (SLA) is in the consumer market, these additive manufacturing (AM) machines are limited to a single UV light source and the polymerization of free-radical polymerization (FRP) resins. The effect is that the object is printed in layers, with each layer adhering not only to the previous layer, but also the transparent (FEP or similar) film at the bottom of the resin vat. The resulting peeling of the layer from the film both necessitates a pause in the printing process, but also puts significant stress on the part being printed. Over the years a few solutions have been developed, with Sandia National Laboratories’ SWOMP technology (PR version) being among the latest.

Unlike the more common FRP-based SLA resins, SWOMP (Selective Dual-Wavelength Olefin Metathesis 3D-Printing) uses ring-opening metathesis polymerization (ROMP), which itself has been commercialized since the 1970s, but was not previously used with photopolymerization in this fashion. For the monomer dicyclopentadiene (DCPD) was chosen, with HeatMet (HM) as the photo-active olefin metathesis catalyst. This enables the UV-sensitivity, with an added photobase generator (PBG) which can be used to selectively deactivate polymerization.

Continue reading “Dual-Wavelength SLA 3D Printing: Fast Continuous Printing With ROMP And FRP Resins” →

The Hunt For MH370 Goes On With Barnacles As A Lead

April 22, 2024 by Lewin Day 41 Comments

On March 8, 2014, Malaysia Airlines Flight 370 vanished. The crash site was never found, nor was the plane. It remains one of the most perplexing aviation mysteries in history. In the years since the crash, investigators have looked into everything from ocean currents to obscure radio phenomena to try and locate the plane. All have thus far failed to find the wreckage.

It was on July 2015 when a flaperon from the aircraft washed up on Réunion Island. It was the first piece of wreckage found, and it was hoped it could provide clues to the airliner’s final resting place. While it’s yet to reveal a final answer as to the aircraft’s fate, some of the ocean life living on it could help investigators need to find the plane. The picture is murky right now, but in an investigation where details are scarce, every little clue helps.

Continue reading “The Hunt For MH370 Goes On With Barnacles As A Lead” →

The MUSE Permanent Magnet Stellarator: Fusion Reactor With Off-The-Shelf Parts

April 21, 2024 by Maya Posch 24 Comments

(a) The 12 permanent magnet holder subsegments. (b) The 16 planar, circular toroidal field coils are positioned inside the water-jet cut support structure. (c) The glass vacuum vessel is joined by 3D-printed low-thickness couplers. Glass ports were hot welded to the torus. (Credit: T.M. Qian et al., 2023)

When you think of a fusion reactor like a tokamak or stellarator, you are likely to think of expensive projects requiring expensive electromagnets made out of exotic alloys, whether superconducting or not. The MUSE stellarator is an interesting study in how to take things completely in the opposite direction. Its design and construction is described in a 2023 paper by [T.M. Qian] and colleagues in the Journal of Plasma Physics. The theory is detailed in a 2020 Physical Review Letters paper by [P. Helander] and colleagues. As the head of the Stellarator Theory at the Max Planck Institute, [P. Helander] is well-acquainted with the world’s most advanced stellarator: Wendelstein 7-X.

As noted in the paper by [P. Helander] et al., the use of permanent magnets can substantially simplify the magnetic-field coils of a stellarator, which are then primarily used for the toroidal magnetic flux. This simplification is reflected in the design of MUSE, as it only has a limited number of identical toroidal field coils, with the vacuum vessel surrounded by 3D printed structures that have permanent magnets embedded in them. These magnets follow a pattern that helps to shape the plasma inside the vacuum vessel, while not requiring a power supply or (at least theoretically) cooling.

Naturally, as noted by [P. Helander] et al, a limitation of permanent magnets is their limited field strength, inability to be tuned, and demagnetization at high temperatures. This may limit the number of practical applications of this approach, but researchers at Princeton Plasma Physics Laboratory (PPPL) recently announced in a self-congratulatory article that they will ‘soon’ commence actual plasma experiments with MUSE. The lack of (cooled) divertors will of course limit the experiments that MUSE can be used for.

The experimental setup – a Commodore 64 is connected to a monitor through a composite video to HDMI converter, with the code cartridge inserted into the expansion port.

Trolling IBM’s Quantum Processor Advantage With A Commodore 64

April 20, 2024 by Maya Posch 8 Comments

The memory map ofthe implementation, as set within the address space of the Commodore 64 - about 15kB of the accessible 64kB RAM is used. 8kB of this is reserved for code, although most of this is unused. Each of the two bitstrings for each Pauli string is stored separately (labeled as Pauli String X/Z) for more efficient addressing. — The memory map of
the implementation, as set within the address space of the Commodore 64 – about 15kB of the accessible 64kB RAM is used.

There’s been a lot of fuss about the ‘quantum advantage’ that would arise from the use of quantum processors and quantum systems in general. Yet in this high-noise, high-uncertainty era of quantum computing it seems fair to say that the advantage part is a bit of a stretch. Most recently an anonymous paper (PDF, starts at page 199) takes IBM’s claims with its 127-bit Eagle quantum processor to its ludicrous conclusion by running the same Trotterized Ising model on the ~1 MHz MOS 6510 processor in a Commodore 64. (Worth noting: this paper was submitted to Sigbovik, the conference of the Association for Computational Heresy.)

We previously covered the same claims by IBM already getting walloped by another group of researchers (Tindall et al., 2024) using a tensor network on a classical computer. The anonymous submitter of the Sigbovik paper based their experiment on a January 2024 research paper by [Tomislav Begušić] and colleagues as published in Science Advances. These researchers also used a classical tensor network to run the IBM experiment many times faster and more accurately, which the anonymous researcher(s) took as the basis for a version that runs on the C64 in a mere 15 kB of RAM, with the code put on an Atmel AT28C256 ROM inside a cartridge which the C64 then ran from.

The same sparse Pauli dynamics algorithm was used as by [Tomislav Begušić] et al., with some limitations due to the limited amount of RAM, implementing it in 6502 assembly. Although the C64 is ~300,000x slower per datapoint than a modern laptop, it does this much more efficiently than the quantum processor, and without the high error rate. Yes, that means that a compute cluster of Commodore 64s can likely outperform a ‘please call us for a quote’ quantum system depending on which linear algebra problem you’re trying to solve. Quantum computers may yet have their application, but this isn’t it, yet.

Thanks to [Stephen Walters] and [Pio] for the tip.

Mechanisms of pulse current charging for stabilizing the cycling performance of commercial NMC/graphite LIBs. (Credit: Jia Guo et al., 2024)

Why Pulse Current Charging Lithium-Ion Batteries Extends Their Useful Lifespan

April 16, 2024 by Maya Posch 54 Comments

For as much capacity lithium-ion batteries have, their useful lifespan is generally measured in the hundreds of cycles. This degradation is caused by the electrodes themselves degrading, including the graphite anode in certain battery configurations fracturing. For a few years it’s been known that pulsed current (PC) charging can prevent much of this damage compared to constant current (CC) charging. The mechanism behind this was the subject of a recent research article by [Jia Guo] and colleagues as published in Advanced Energy Materials.

Raman spectra of a) as-cycled and b) surface-removed graphite anodes aged under CC and Pulse-2000 charging. FE-SEM images of the cross-sections of graphite electrodes aged with CC (c,d) and Pulse-2000 (e,f) charging. d,f) are edge-magnified images of (c,e). g) shows the micrograph and O and C element mapping of the surface of CC-aged graphite electrode. TEM images of h) fresh, i) CC, and j) Pulse-2000 aged graphite anodes. (Credit: Jia Guo et al., 2024)

The authors examined the damage to the electrodes after multiple CC and PC cycles using Raman and X-ray absorption spectroscopy along with lifecycle measurements for CC and PC charging at 100 Hz (Pulse-100) and 2 kHz (Pulse-2000). Matching the results from the lifecycle measurements, the electrodes in the Pulse-2000 sample were in a much better state, indicating that the mechanical stress from pulse current charging is far less than that from constant current charging. A higher frequency with the PC shows increased improvements, though as noted by the authors, it’s not known yet at which frequencies diminishing returns will be observed.

The use of PC vs CC is not a new thing, with the state-of-the-art in electric vehicle battery charging technology being covered in a 2020 review article by [Xinrong Huang] and colleagues as published in Energies. A big question with the many different EV PC charging modes is what the optimum charging method is to maximize the useful lifespan of the battery pack. This also applies to lithium-metal batteries, with a 2017 research article by [Zi Li] and colleagues in Science Advances providing a molecular basis for how PC charging suppresses the formation of dendrites .

What this demonstrates quite well is that the battery chemistry itself is an important part, but the way that the cells are charged and discharged can be just as influential, with the 2 kHz PC charging in the research by [Jia Guo] and colleagues demonstrating a doubling of its cycle life over CC charging. Considering the amount of Li-ion batteries being installed in everything from smartphones and toys to cars, having these last double as long would be very beneficial.

Thanks to [Thomas Yoon] for the tip.