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.

The Performance Impact Of C++’s `final` Keyword For Optimization

April 24, 2024 by Maya Posch 21 Comments

In the world of software development the term ‘optimization’ is generally reason for experienced developers to start feeling decidedly nervous, especially when a feature is marked as an ‘easy and free optimization’. The final keyword introduced in C++11 is one of such features. It promises a way to speed up object-oriented code by omitting the vtable call indirection by marking a class or member function as – unsurprisingly – final, meaning that it cannot be inherited from or overridden. Inspired by this promise, [Benjamin Summerton] figured that he’d run a range of benchmarks to see what performance uplift he’d get on his ray tracing project.

To be as thorough as possible, the tests were run on three different systems, including 64-bit Intel and AMD systems, as well as on Apple Silicon (M1). For the compilers various versions of GCC (12.x, 13.x), as well as Clang (15, 17) and MSVC (17) were employed, with rather interesting results for final versus no final tests. Clang was probably the biggest surprise, as with the keyword added, performance with Clang-generated code absolutely tanked. MSVC was a mixed bag, as were the GCC versions other than GCC 13.2 on AMD Ryzen, which saw a bump of a few percent faster.

Ultimately, it seems that there’s no free lunch as usual, and adding final to your code falls distinctly under ‘only use it if you know what you’re doing’. As things stand, the resulting behavior seems wildly inconsistent.

New JEDEC DDR5 Memory Specification: Up To 8800 MT/s, Anti-Rowhammer Features

April 23, 2024 by Maya Posch 5 Comments

Rapid row activations (yellow rows) may change the values of bits stored in victim row (purple row). — “Row hammer” by Dsimic – Own work. Licensed under CC BY-SA 4.0 via Wikimedia Commons.

As DDR SDRAM increases in density and speed, so too do new challenges and opportunities appear. In the recent DDR5 update by JEDEC – as reported by Anandtech – we see not only a big speed increase from the previous maximum of 6800 Mbps to 8800 Mbps, but also the deprecation of Partial Array Self Refresh (PASR) due to security concerns, and the introduction of Per-Row Activation Counting (PRAC), which should help with row hammer-related (security) implications.

Increasing transfer speeds is primarily a matter of timings within the limits set by the overall design of DDR5, while the changes to features like PASR and PRAC are more fundamental. PASR is mostly a power-saving feature, but can apparently be abused for nefarious means, which is why it’s now gone. As for PRAC, this directly addresses the issue of row hammer attacks. Back in the 2014-era of DDR3, row hammer was mostly regarded as a way to corrupt data in RAM, but later it was found to be also a way to compromise security and effect exploits like privilege escalation.

The way PRAC seeks to prevent this is by keeping track of how often a row is being accessed, with a certain limit after which neighboring memory cells get a chance to recover from the bleed-over that is at the core of row hammer attacks. All of which means that theoretically new DDR5 RAM and memory controllers should be even faster and more secure, which is good news all around.

Amazon Ends California Drone Deliveries While Expanding To Arizona

April 23, 2024 by Maya Posch 17 Comments

The outgoing MK27 drone used by Amazon today for deliveries. (Credit: Amazon)

When Amazon started its Prime Air drone delivery service in 2022, it had picked College Station (Texas) and Lockeford (California) as its the first areas where the service would be offered. Two years later, Amazon has now announced that it will be expanding to the West Valley of the Phoenix Metro area in Arizona from a new Tolleson center, while casually mentioning buried in the press release that the Lockeford area will no longer be serviced. No reason for this closure was provided, but as a quite experimental service drastic shifts can be expected as Amazon figures out what does and does not work.

Amazon Prime Air features custom drones that can transport packages up to 5 lbs (~2.27 kg) to its destination within an hour, if the item is listed as Prime Air capable for your area. Along with the change in service areas, Amazon is also testing its new MK30 drone (pictured, top), which should be much quieter due to a new propeller design and have twice the range of the old MK27 as well.

Even if flying drone delivery isn’t quite a blow-away success yet, Amazon doesn’t seem to be letting up on investing in it, and it could be argued that for certain items like medication or perishables, it does make a certain sense over traditional delivery and pick-up methods.

Programming Ada: First Steps On The Desktop

April 23, 2024 by Maya Posch 51 Comments

Who doesn’t want to use a programming language that is designed to be reliable, straightforward to learn and also happens to be certified for everything from avionics to rockets and ICBMs? Despite Ada’s strong roots and impressive legacy, it has the reputation among the average hobbyist of being ‘complicated’ and ‘obscure’, yet this couldn’t be further from the truth, as previously explained. In fact, anyone who has some or even no programming experience can learn Ada, as the very premise of Ada is that it removes complexity and ambiguity from programming.

In this first part of a series, we will be looking at getting up and running with a basic desktop development environment on Windows and Linux, and run through some Ada code that gets one familiarized with the syntax and basic principles of the Ada syntax. As for the used Ada version, we will be targeting Ada 2012, as the newer Ada 2022 standard was only just approved in 2023 and doesn’t change anything significant for our purposes.

Continue reading “Programming Ada: First Steps On The Desktop” →

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” →