It’s amazing how quickly medical science made radiography one of its main diagnostic tools. Medicine had barely emerged from its Dark Age of bloodletting and the four humours when X-rays were discovered, and the realization that the internal structure of our bodies could cast shadows of this mysterious “X-Light” opened up diagnostic possibilities that went far beyond the educated guesswork and exploratory surgery doctors had relied on for centuries.
The problem is, X-rays are one of those things that you can’t see, feel, or smell, at least mostly; X-rays cause visible artifacts in some people’s eyes, and the pencil-thin beam of a CT scanner can create a distinct smell of ozone when it passes through the nasal cavity — ask me how I know. But to be diagnostically useful, the varying intensities created by X-rays passing through living tissue need to be translated into an image. We’ve already looked at how X-rays are produced, so now it’s time to take a look at how X-rays are detected and turned into medical miracles.
Sometimes in fantasy fiction, you don’t want to explain something that seems inexplicable, so you throw your hands up and say, “A wizard did it.” Sometimes in astronomy, instead of a wizard, the answer is dark matter (DM). If you are interested in astronomy, you’ve probably heard that dark matter solves the problem of the “missing mass” to explain galactic light curves, and the motion of galaxies in clusters.
The Central Molecular Zone is a region near the heart of the Milky Way that has a very high density of interstellar gases– around sixty million times the mass of our sun, in a volume 1600 to 1900 light years across. It happens to be more ionized than it ought to be, and ionized in a very even manner across its volume. As astronomers cannot identify (or at least agree on) the mechanism to explain this ionization, the CMZ ionization is mystery number one.
Feynman diagram of electron-positron annihilation, showing the characteristic gamma-ray emission.
Mystery number two is a diffuse glow of gamma rays seen in the same part of the sky as the CMZ, which we know as the constellation Sagittarius. The emissions correspond to an energy of 515 keV, which is a very interesting number– it’s what you get when an electron annihilates with the antimatter version of itself. Again, there’s no universally accepted explanation for these emissions.
So [Pedro De la Torre Luque] and team asked themselves: “What if a wizard did it?” And set about trying to solve the mystery using dark matter. As it turns out, computer models including a form of light dark matter (called sub-GeV DM in the paper, for the particle’s rest masses) can explain both phenomena within the bounds of error.
In the model, the DM particles annihilate to form electron-positron pairs. In the dense interstellar gas of the CMZ, those positrons quickly form electrons to produce the 511 keV gamma rays observed. The energy released from this annihilation results in enough energy to produce the observed ionization, and even replicate the very flat ionization profile seen across the CMZ. (Any other proposed ionization source tends to radiate out from its source, producing an uneven profile.) Even better, this sort of light dark matter is consistent with cosmological observations and has not been ruled out by Earth-side dark matter detectors, unlike some heavier particles.
Further observations will help confirm or deny these findings, but it seems dark matter is truly the gift that keeps on giving for astrophysicists. We eagerly await what other unsolved questions in astronomy can be answered by it next, but it leaves us wondering how lazy the universe’s game master is if the answer to all our questions is: “A wizard did it.”
Building a Commodore 64 is among the easier projects for retrocomputing fans to tackle. That’s because the C64’s core chipset does most of the heavy lifting; source those and you’re probably 80% of the way there. But what if you can’t find those chips, or if you want more of a challenge than plugging and chugging? Are you out of luck?
Hardly. The video below from [DrMattRegan] is the first in a series on his scratch-built C64 that doesn’t use the core chipset, and it looks pretty promising. This video concentrates on building a replacement for the 6502 microprocessor — actually the 6510, but close enough — using just a couple of EPROMs, some SRAM chips, and a few standard logic chips to glue everything together. He uses the EPROMs as a “rulebook” that contains the code to emulate the 6502 — derived from his earlier Turing 6502 project — and the SRAM chips as a “notebook” for scratch memory and registers to make a Turing-complete random access machine.
[DrMatt] has made good progress so far, with the core 6502 CPU built on a PCB and able to run the Apple II version of Pac-Man as a benchmark. We’re looking forward to the rest of this series, but in the meantime, a look back at his VIC-less VIC-20 project might be informative.
If you’ve ever fumbled through circuit simulation and ended up with a flatline instead of a sine wave, this video from [saisri] might just be the fix. In this walkthrough she demonstrates simulating a Colpitts oscillator using NI Multisim 14.3 – a deceptively simple analog circuit known for generating stable sine waves. Her video not only shows how to place and wire components, but it demonstrates why precision matters, even in virtual space.
You’ll notice the emphasis on wiring accuracy at multi-node junctions, something many tutorials skim over. [saisri] points out that a single misconnected node in Multisim can cause the circuit to output zilch. She guides viewers step-by-step, starting with component selection via the “Place > Components” dialog, through to running the simulation and interpreting the sine wave output on Channel A. The manual included at the end of the video is a neat bonus, bundling theory, waveform visuals, and circuit diagrams into one handy PDF.
If you’re into precision hacking, retro analogue joy, or just love watching a sine wave bloom onscreen, this is worth your time. You can watch the original video here.
Using steam to produce electricity or perform work via steam turbines has been a thing for a very long time. Today it is still exceedingly common to use steam in this manner, with said steam generated either by burning something (e.g. coal, wood), by using spicy rocks (nuclear fission) or from stored thermal energy (e.g. molten salt). That said, today we don’t use steam in the same way any more as in the 19th century, with e.g. supercritical and pressurized loops allowing for far higher efficiencies. As covered in a recent video by [Ryan Inis], a more recent alternative to using water is supercritical carbon dioxide (CO2), which could boost the thermal efficiency even further.
In the video [Ryan Inis] goes over the basics of what the supercritical fluid state of CO2 is, which occurs once the critical point is reached at 31°C and 83.8 bar (8.38 MPa). When used as a working fluid in a thermal power plant, this offers a number of potential advantages, such as the higher density requiring smaller turbine blades, and the potential for higher heat extraction. This is also seen with e.g. the shift from boiling to pressurized water loops in BWR & PWR nuclear plants, and in gas- and salt-cooled reactors that can reach far higher efficiencies, as in e.g. the HTR-PM and MSRs.
In a 2019 article in Power the author goes over some of the details, including the different power cycles using this supercritical fluid, such as various Brayton cycles (some with extra energy recovery) and the Allam cycle. Of course, there is no such thing as a free lunch, with corrosion issues still being worked out, and despite the claims made in the video, erosion is also an issue with supercritical CO2 as working fluid. That said, it’s in many ways less of an engineering issue than supercritical steam generators due to the far more extreme critical point parameters of water.
If these issues can be overcome, it could provide some interesting efficiency boosts for thermal plants, with the caveat that likely nobody is going to retrofit existing plants, supercritical steam (coal) plants already exist and new nuclear plant designs are increasingly moving towards gas, salt and even liquid metal coolants, though secondary coolant loops (following the typical steam generator) could conceivably use CO2 instead of water where appropriate.
In the dark ages, before iOS and Android phones became ubiquitous, there was the PDA. These handheld computers acted as simple companions to a computer and could often handle calendars, email, notes and more. Their demise was spelled by the smartphone, but the nostalgia of having a simple handheld and romanticizing about the 90’s and 2000’s is still there. Fortunately for the nostalgic among our readers, [Ashtf] decided to give us a modern take on the classic PDAs.
Back in the day, one of the few reasons to prefer compact cassette tape to vinyl was the fact you could record it at home in very good fidelity. Sure, if you had the scratch, you could go out and get a small batch of records made from that tape, but the machinery to do it was expensive and not always easy to come by, depending where you lived. That goes double today, but we’re in the middle of a vinyl renaissance! [ronald] wanted to make records, but was unable to find a lathe, so decided to take matters into his own hands, and build his own vinyl record cutting lathe.
[ronald’s] record cutting lathe looks quite professional.It seems like it should be a simple problem, at least in concept: wiggle an engraving needle to scratch grooves in plastic. Of course for a stereo record, the wiggling needs to be two-axis, and for stereo HiFi you need that wiggling to be very precise over a very large range of frequencies (7 Hz to 50 kHz, to match the pros). Then of course there’s the question of how you’re controlling the wiggling of this engraving needle. (In this case, it’s through a DAC, so technically this is a CNC hack.) As often happens, once you get down to brass tacks (or diamond styluses, as the case may be) the “simple” problem becomes a major project. Continue reading “DIY Record Cutting Lathe Is Really Groovy”→
![photograph of [ronald's] setup](https://hackaday.com/wp-content/uploads/2025/04/groovy_lathe.png?w=301)
