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Solar-Powered Nanosensors & The Trouble With Hydrogen Power (Patreon)

Published:
2023-01-19 04:00:34
Imported:
2023-03

Content

Solar-Powered Nanosensors

A group of Australian researchers has developed a microscopic sensor for nitrogen dioxide (a toxic component of gasoline car exhaust). It’s barely a few micrometers in size and runs on solar power. The researchers want to develop a chip that can detect a whole array of substances and communicate with nearby instruments. Paper is here, press release here.

High-Speed Signaling With Visible Light

I’d never heard of it until last week, but evidently, one way wireless communication might evolve is by just using visible light from LEDs superimposed with tiny variations that the human eye can’t see. This line of research seems to have been developed primarily in China. Recent review paper here.

Don’t Count MOND Out Quite Yet

I have gotten a lot of questions about a recent paper in Nature Astronomy claiming that the slightly planar alignment of the Milky Way’s satellite galaxies is compatible with the dark matter hypothesis. It had previously been claimed that this planar alignment is in severe tension with the dark matter hypothesis. I haven’t commented on that because I’ve heard several people raising doubts that the analysis in the paper is sound and I expect a comment on this to appear on the arXiv soon.

Comments

Anonymous
>>99936615

Hey Colleen, your question is not an easy one to answer because so much of galaxy formation and evolution is not well understood. The current thinking for disk/spiral galaxies like the Milky Way is that the different parts of the galaxy (halo, bulge, thick disk, thin disk) formed separately through different processes. The thin disk component is indeed thought to have been an initial spheroidal distribution of hot gas that flattened out sometime later due to conservation of angular momentum like the pizza dough in your analogy -- but consider that the orbital period of the Sun is something like 225 million years, so the gas cloud the Sun formed from and our subsequent solar system have orbited less than 60 times. The spiral pattern is NOT due to differential orbit rates of the stars/gas in the disk, but rather to a density wave propagating through the disk. The bulge and halo are both spheroidal and the halo, not the disk, contains most of the mass in a galaxy. So why doesn't the dark matter distribution also collapse into a disk like the baryonic matter? In order to "collapse" a gas must interact via collisions, radiation, etc and lose energy, and thus cool off. Energy is easy for a gas to get rid of, but not angular momentum, so the gas collapses to a disk. Dark matter, however, does not interact in the same way, so it is not capable of dissipating energy and it does not collapse to conserve angular momentum like the gas does. Now, about the little satellite galaxies, these likely formed at the same time as the bigger galaxies in the Local Group when everybody was a spheroidal protogalaxy. The presumed dark matter distribution that led to the clumping of matter to form galaxies (LambdaCDM) was rather homogeneous so that the galaxies were scattered randomly in the cluster. The orbits of the little galaxies would then also have no preferable orbital alignment around their big neighbor galaxies. Consider that the Large and Small Magellanic Clouds have only orbited the Milky Way something like 8 or 9 times since formation. The halo is spheroidal and is where most of the mass in the galaxy resides, so satellite galaxies would have no reason to settle into planar orbits along with the thin disk of their parent galaxy. The pickle for LambdaCDM is that when we actually map the locations and orbits of satellite galaxies around us and few other big, relatively nearby galaxies, there is some small, but statistically significant, degree of orbital alignment around the parent galaxy, at odds with simulations from LambdaCDM models and the hand-waving explanation I put forth in the previous paragraphs. Sure, satellite galaxy orbits _could_ end up being aligned, but that should be random and rare and not observed in all of the nearby systems that we can do this sort of mapping for. In the paper that Sabine noted a few weeks back, a group undertook new simulations that showed satellite galaxy alignment with LambdaCDM is slightly less rare than thought, however it looks like their computer model was missing some key parameters, as Sabine notes above. (I know you know all of this bit, Colleen, I'm recapping for anyone who may not have seen the earlier conversation.) I don't know if the slight degree of satellite orbit alignment matches with the predictions from MOND on size scales of a few million down to thousands of light years. Galaxy formation under MOND might predict something more in line with the pizza dough analogy, respecting the fact that satellites have only orbited their parent galaxies a handful of times since formation and the timescale for virialization of a galaxy cluster is dependent on the amount of dark matter in the simulations. I think I threw my back out with all of these hand-waving arguments, I need to go lie down now. :-)

Anonymous

Using small LEDs for data channels is a common topic with optical interconnect (between chips). Signalling rates are getting too high for electrons through a wire. The specific use of visible light for both communication AND illumination is just slightly creepy. Put differently, you do not want your Chinese-made smart light bulb to offer a back-door into your network?

Anonymous
>>99936615

Thanks for the comprehensive answer Tracey. I'd forgotten all about the simulations so it's good you mentioned that as well. I had never seen or heard the term 'virial' before so I'm a bit wiser now. 🙂

Anonymous

The assumption I'd make is that the satellite galaxies of the Milky Way or similar would be spun out flat like pizza dough being tossed for a pizza base. If not, what's the go? (Can someone humour my ignorance please. 😸)

Anonymous

Observation tells a different story and is probably caused by that underrated force Gravity!

Anonymous
>>99970458

But gravity is not a force. Even YouTube couldn’t argue with that 😆

Anonymous

Could you enlighten, I’m interested in your thoughts