hakonjdjohnsen

4 ms·

1.
by hakonjdjohnsen 6d ago
A fun fact about Cherenkov radiation is that research on making efficient Cherenkov detectors in the 1960s led to the development of optical principles still used to design illumination systems and solar concentrators today. The late profes
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How wave overhangs work [video](youtube.com)
2 points by hakonjdjohnsen 1mo ago|0 comments
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CARA 2.0 – “I Built a Better Robot Dog”(aaedmusa.com)
477 points by hakonjdjohnsen 5mo ago|65 comments
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by hakonjdjohnsen 7mo ago
Agreed, that was a really good talk! It is kind of scary how simple some of these exploits that find their way into smartwatched for children are
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39C3 – Watch Your Kids: Inside a Children's Smartwatch [video](youtube.com)
1 points by hakonjdjohnsen 8mo ago|0 comments
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by hakonjdjohnsen 11mo ago
This video by AlphaPhoenix is absolutely incredible! I do research in (nonimaging) optics and I am used to thinking about the propagation of light. Still, there is something amazing about seeing a real recording of the propagation of a real
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by hakonjdjohnsen 1y ago
Thermophotovoltaics is really cool. It is an old idea but recently several groups (including the group behind fourth power) have shown much better experimental performance than before, towards the level where this is starting to look like a
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by hakonjdjohnsen 1y ago
I think there is at least some plausible interpretation of this that points to more than marketing fluff. You want to count particles per volume of air, so conventional sensors use a fan to have a constant volumetric flow and then count par
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by hakonjdjohnsen 1y ago
Yeah good point! When I came across this amazing project and wanted to share it to HN, I was debating whether to post the youtube link or the project page. I decided to post the project page and mention the youtube link in the description f
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CARA – High precision robot dog using rope(aaedmusa.com)
1073 points by hakonjdjohnsen 1y ago|182 comments
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by hakonjdjohnsen 1y ago
See also the youtube video about the project: https://youtu.be/8s9TjRz01fo
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by hakonjdjohnsen 1y ago
I found this presentation from the Disobey 2025 conference to be a really good and entertaining watch! Last year the presenter also wrote a blog post about the attack, which received some discussion at the time: https://news.ycom
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Web security is fun (or how I stole your Google Drive files) [video](youtube.com)
2 points by hakonjdjohnsen 1y ago|1 comments
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by hakonjdjohnsen 2y ago
Cool concept! I do research in solar concentrator optics, so I enjoy seeing such completely different applications of concentrated sunlight. Still, I am not fully convinced in this specific case. I wonder if it is not a lot easier to provid
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by hakonjdjohnsen 2y ago
The reason we get a lot of light from the sun is not that the sun is particularily "bright" (high radiance) compared to other stars, it is because the the sun has an absolutely huge apparent size in the sky compared to all the oth
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by hakonjdjohnsen 2y ago
> You make a big ring (roughly of the same area of the spot you are trying to make on the ground) Unfortunately, this is not how the size of the spot on the ground is decided. Sunlight, even if reflected by a perfectly shaped mirror, spr
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by hakonjdjohnsen 2y ago
So the birdkill is actually from a separate focal spot near the absorber where standby heliostats are focused? Interesting, I did not know that! Makes me wonder why standby heliostats would need to be focused at all? Couldn't their aim
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by hakonjdjohnsen 2y ago
Looks really cool! I look forward to reading your paper. Do you know if a recording of the talk is/will be posted somewhere?
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by hakonjdjohnsen 2y ago
Interesting! I added an email address to my profile now
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by hakonjdjohnsen 2y ago
Yes, exactly. I have not looked at Mitsuba 2, but Mitsuba 3 is absolutely along these lines. It is just starting to be picked up by some of the nonimaging/illumination community, e.g. there was a paper last year from Aurele Adam's
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by hakonjdjohnsen 2y ago
This, very much this! I do research in a subfield of optics called nonimaging optics (optics for energy transfer, e.g. solar concentrators or lighting systems). We typically use these optical design applications, and your observations are
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Show HN: Optics Challenge – Design a solar concentrator for a non-round sun(nonimaging-conference.org)
10 points by hakonjdjohnsen 2y ago|0 comments
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by hakonjdjohnsen 2y ago
There are also two systems in Sydney, the big tall one on Rhodes Central [1] and the slightly smaller on One Central Park [2]. I think the idea is that by removing some of the shadowing from the high-rise buildings, the local authorities al
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DevCon24 – Flash Less, Do More: The Magic of Virtual Hardware [video](youtube.com)
1 points by hakonjdjohnsen 2y ago|0 comments
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by hakonjdjohnsen 2y ago
This is known as a charge pump, and is the third concept described in the linked article. The article only mention one flying capacitor, but you can use more than one and connect them in series to get a higher multiple of the input voltage.
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by hakonjdjohnsen 2y ago
This is a really cool concept! The term used for connecting mirrors to rotate together is a ganged heliostat. Most papers about ganged heliostats don't do anything fancy like what you describe, but there are some patents that show a ni
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by hakonjdjohnsen 2y ago
Great question, and this shows why we could never get a 100% efficient solar panel. Otherwise your scheme would brak thermodynamics. The most efficient possible way to convert sunlight to electricity is ~86% and is related to the second law
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by hakonjdjohnsen 2y ago
> Each cable is actually wrapped around the motor axis, then passed through the pulley and tied to a fixed ring in the corner of the panel. Thanks, when seeing the video again now it makes sense! I didn't catch the counterweight the
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by hakonjdjohnsen 2y ago
> ps. It's like making a VPN tunnel to the surface of the sun :-) Wow, I love that! Great analogy!
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by hakonjdjohnsen 2y ago
> Does the black body radiation send the energy back out? Exactly, this is the issue. If an object is able to absorb sunlight, it is also able to emit blackbody radition back towards the sun. When the temperature limit is reached, these

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