bhauth
This was a quick and short post, but some people ended up liking it a lot. In retrospect I should’ve written a bit more, maybe gone into the design of recent running shoes. For example, this Nike Alphafly has a somewhat thick heel made of springy foam that sticks out behind the heel of the foot, and in the front, there’s a “carbon plate” (a thin sheet of carbon fiber composite) which also acts like a spring. In the future, there might be gradual evolution towards more extreme versions of the same concept, as recent designs become accepted. Running shoes with a carbon plate have become significantly more common over the past few years. That review says:
The energy return is noticeably greater than that of a shoe without any plating, especially when you lay down some serious power. And that stiffness doesn’t always compromise as much comfort as you’d think.
So that’s the running-optimized version of shoes with springs using modern materials, while I was writing more about high heels worn for fashion.
Biomechanics is a topic I could write a lot about, but that would be a separate post. On the general topic of “walking” I also wrote this post. (japanese version here)
What have you learned since then? Have you changed your mind or your ontology?
I’ve learned even more chemistry and biology, and I’ve changed my mind about lots of things, but not the points in this post. Those had solid foundations I understood well and redundant arguments, so the odds of that were low.
What would you change about the post? (Consider actually changing it.)
The post seems OK. I could have handled replies to comments better. For example, the top comment was by Thomas Kwa, and I replied to part of it as follows:
Regarding 5, my understanding is that mechanosynthesis involves precise placement of individual atoms according to blueprints, thus making catalysts that selectively bind to particular molecules unnecessary.
No, that does not follow.
I didn’t know in advance which comments would be popular. In retrospect, maybe I should’ve gone into explaining the basics of entropy and enthalpy in my reply, eg:
Even if you hold a substrate in the right position, that only affects the entropy part of the free energy of the intermediate state. In many cases, catalysts are needed to reduce the enthalpy of the highest-energy intermediate states, which requires specific elements and catalyst molecules that form certain bonds with the substrate intermediate state. Affecting enthalpy by holding molecules in certain configurations requires applying a proportional amount of force, which requires strong binding to the substrate, which requires flexible and substrate-specialized holder molecules, and now you have enzymes again. It’s also necessary to bind strongly to substrates if you want a very low level of free ones that can react at uncontrolled positions. (And then some basic explanation of what entropy/enthalpy/etc are, and what enzyme intermediate states look like.)
When you write a post that gets comments from many people, it’s not practical to respond to them all. If you try to, you have less time than the collective commenters, and less information about their position than they have about yours. So you have to guess about what exactly each person is misunderstanding, and that’s not usually something I enjoy.
What do you most want people to know about this post, for deciding whether to read or review-vote on it?
Of the 7 (!) posts of mine currently nominated for “Best of 2023”, this is probably the most appropriate for that.
Of the 2023 posts of mine not currently nominated, my personal favorites were probably:
https://www.lesswrong.com/posts/BTnqAiNoZvqPfquKD/resolving-some-neural-network-mysteries
https://www.lesswrong.com/posts/PdwQYLLp8mmfsAkEC/magnetic-cryo-ftir
https://www.lesswrong.com/posts/rSycgquipFkozDHzF/ai-self-improvement-is-possible
https://www.lesswrong.com/posts/dTpKX5DdygenEcMjp/neuron-spike-computational-capacity
https://www.lesswrong.com/posts/6Cdusp5xzrHEoHz9n/faster-latent-diffusion
Clearly my opinion of my own posts doesn’t correlate with upvotes here that well.
My all-time best post in my view is probably: https://bhauth.com/blog/biology/alzheimers.html
How concretely have you (or others you know of) used or built on the post? How has it contributed to a larger conversation
Muireall Prase wrote this, and my post was relevant for some conversations on twitter. I suppose it also convinced some people I had some understanding of chemistry.
So, I have a lot of respect for Sarah, I think this post makes some good points, and I upvoted it. However, my concern is, when I look at this particular organization’s Initiatives page, I see “AI for math”, “AI for education”, “high-skill immigration assistance”, and not really anything that distinguishes this organization from the various other ones working on the same things, or their projects from a lot of past projects that weren’t really worthwhile.
Note that due to the difference being greater at higher frequencies, the effect on speech intelligibility will probably be greater for most women than for you.
We can see the diaphragm has some resonance peaks that increase distortion. Probably it’s too thick to help very much, but it has to resist the pressure changes from breathing.
What exactly are people looking for from (the site-suggested) self-reviews?
As a “physicist and dabbler in writing fantasy/science fiction” I assume you took the 10 seconds to do the calculation and found that a 1km radius cylinder would have ~100 kW of losses per person from roller bearings supporting it, for the mass per person of the ISS. But I guess I don’t understand how you expect to generate that power or dissipate that heat.
After being “launched” from the despinner, you would find yourself hovering stationary next to the ring.
Air resistance.
That is, however, basically the system I proposed near the end, for use near the center of a cylinder where speeds would be low.
This happened to Explorer 1, the first satellite launched by the United States in 1958. The elongated body of the spacecraft had been designed to spin about its long (least-inertia) axis but refused to do so, and instead started precessing due to energy dissipation from flexible structural elements.
picture: https://en.wikipedia.org/wiki/Explorer_1#/media/File:Explorer1.jpg
a space habitat design
That works well enough, but a Vital 200S currently costs $160 at amazon, less than the cheapest variant of the thing you linked, and has a slightly higher max air delivery rate, some granular carbon in the filter, and features like power buttons. The Vital 200S on speed 2 has similar power usage and slightly less noise, but less airflow, but a carbon layer always reduces airflow. It doesn’t have a rear intake so it can be placed against a wall. It also has a washable prefilter.
Compared to what you linked, the design in this post has 3 filters instead of 2, some noise blocking, and a single large fan instead of multiple fans. Effective floor area usage should be slightly less, but of course it has to go together with shelving for that.
overengineered air filter shelving
First, we have to ask: what’s the purpose? Generally aircraft try to get up to their cruise speed quickly and then spend most of their time cruising, and you optimize for cruise first and takeoff second. Do we want multiple cruise speeds, eg a supersonic bomber that goes slow some of the time and fast over enemy territory? Are we designing a supersonic transport and trying to reduce fuel usage getting up to cruise?
And then, there are 2 basic ways you can change the bypass ratio: you can change the fan/propeller intake area, or you can turn off turbines. The V-22 has a driveshaft through the wing to avoid crashes if an engine fails; in theory you could turn off an engine while powering the same number of propellers, which is sort of like a variable bypass ratio. If you have a bunch of turbogenerators inside the fuselage, powering electric fans elsewhere, then you can shut some down while powering the same number of fans. There are also folding propellers.
The question is always, “but is that better”?
electric turbofans
Yes, helium costs would be a problem for large-scale use of airships. Yes, it’s possible to use hydrogen in airships safely. This has been noted by many people.
Hydrogen has some properties that make it relatively safe:
it’s light so it rises instead of accumulating on the ground or around a leak
it has a relatively high ignition temperature
and some properties that make it less safe:
it has a wide range of concentrations where it will burn in air
fast diffusion, that is, it mixes with air quickly
it leaks through many materials
it embrittles steel
it causes some global warming if released
Regardless, the FAA does not allow using hydrogen in airships, and I don’t expect that to change soon. Especially since accidents still happen despite the small number of airships.
In any case, the only uses of airships that are plausibly economical today are: advertising and luxury yachts for the wealthy. Are those things that you care about working towards?
see also: These Are Your Doges, If It Please You
IKEA already sells air purifiers; their models just have a very low flow rate. There are several companies selling various kinds of air purifiers, including multiples ones with proprietary filters.
What all this says to me is, the problem isn’t just the overall market size.
Apart from potential harms of far-UVC, it’s good to remove particulate pollution anyway. Is it possible that “quiet air filters” is an easier problem to solve?
I’m not convinced that far-UVC is safe enough around humans to be a good idea. It’s strongly absorbed by proteins so it doesn’t penetrate much, but:
It can make reactive compounds from organic compounds in air.
It can produce ozone, depending on the light. (That’s why mercury vapor lamps block the 185nm emission.)
It could potentially make toxic compounds when it’s absorbed by proteins in skin or eyes.
It definitely causes degradation of plastics.
And really, what’s the point? Why not just have fans sending air to (cheap) mercury vapor lamps in a contained area where they won’t hit people or plastics?
I think this is a pretty good post that makes a point some people should understand better. There is, however, something I think it could’ve done better. It chooses a certain gaussian and log-normal distribution for quality and error, and the way that’s written sort of implies that those are natural and inevitable choices.
I would have preferred something like: