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I recently moved and our new home is equipped with a ventilation system that distributes fresh (outside) air through the house and recoups heat from the air that is exhausted. There is a problem with this system, though. Sometimes, for example when a neighbour lights their wood stove, the system pulls in smoke, even though… Continue reading Home Assistant-compatible air quality sensor
over a year ago

More from Willem Pennings

Fixing my heating system

The heating system in my apartment building consists of a group of heat pumps that deliver warm water to the underfloor heating system of about a dozen apartments, including mine. During the warm summer months, the system supplies cool water instead. The heat pumps figure out whether to supply warm or cool water, and a… Continue reading Fixing my heating system

9 months ago 44 votes
Balancing cube

This cube manages to balance itself on a corner, and can simultaneously rotate around its axis in a controlled manner. It does so using clever controls and a set of three reaction wheels. The original idea for this device comes from researchers at ETH Zürich, who demonstrate their “Cubli” in this video. Its design has… Continue reading Balancing cube

11 months ago 22 votes
ClockSquared improvements

My ClockSquared project has a long history – it goes all the way back to 2015, when it was simply called the “Birthday word clock”. I haven’t spent much time on the project in recent years, but I’ve upgraded the internals a while ago and finally felt like writing a post about it. Two things… Continue reading ClockSquared improvements

a year ago 15 votes
ClockSquared Mini, a word clock wristwatch

About a year ago, I had some time to spare over the summer and decided to challenge myself with a project that I call “Clocksquared Mini”. It is Clocksquared, but in a tiny wristwatch package. This gives rise to a major challenge, as everything has to be shrunk down approximately ten times from a 300x300x50… Continue reading ClockSquared Mini, a word clock wristwatch

over a year ago 9 votes

More in science

An update, + a paper as a fun distraction

My post last week clearly stimulated some discussion.  I know people don't come here for political news, but as a professional scientist it's hard to ignore the chaotic present situation, so here are some things to read, before I talk about a fun paper: Science reports on what is happening with NSF.  The short version: As of Friday afternoon, panels are delayed and funds (salary) are still not accessible for NSF postdoctoral fellows.  Here is NPR's take. As of Friday afternoon, there is a new court order that specifically names the agency heads (including the NSF director), saying to disburse already approved funds according to statute.   Looks like on this and a variety of other issues, we will see whether court orders actually compel actions anymore. Now to distract ourselves with dreams of the future, this paper was published in Nature Photonics, measuring radiation pressure exerted by a laser on a 50 nm thick silicon nitride membrane.  The motivation is a grand one:  using laser-powered light sails to propel interstellar probes up to a decent fraction (say 10% or more) of the velocity of light.  It's easy to sketch out the basic idea on a napkin, and it has been considered seriously for decades (see this 1984 paper).  Imagine a reflective sail say 10 m\(^{2}\) and 100 nm thick.  When photons at normal incidence bounce from a reflective surface, they transfer momentum \(2\hbar \omega/c) normal to the surface.  If the reflective surface is very thin and low mass, and you can bounce enough photons off it, you can get decent accelerations.  Part of the appeal is, this is a spacecraft where you effectively keep the engine (the whopping laser) here at home and don't have to carry it with you.  There are braking schemes so that you could try to slow the craft down when it reaches your favorite target system. A laser-powered lightsail (image from CalTech) Of course, actually doing this on a scale where it would be useful faces enormous engineering challenges (beyond building whopping lasers and operating them for years at a time with outstanding collimation and positioning).  Reflection won't be perfect, so there will be heating.  Ideally, you'd want a light sail that passively stabilizes itself in the center of the beam.  In this paper, the investigators implement a clever scheme to measure radiation forces, and they test ideas involving dielectric gratings etched into the sail to generate self-stabilization.   Definitely more fun to think about such futuristic ideas than to read the news. (An old favorite science fiction story of mine is "The Fourth Profession", by Larry Niven.  The imminent arrival of an alien ship at earth is heralded by the appearance of a bright point in the sky, whose emission turns out to be the highly blue-shifted, reflected spectrum of the sun, bouncing off an incoming alien light sail.  The aliens really need humanity to build them a launching laser to get to their next destination.)

11 hours ago 4 votes
Chatbot Software Begins to Face Fundamental Limitations

Recent results show that large language models struggle with compositional tasks, suggesting a hard limit to their abilities. The post Chatbot Software Begins to Face Fundamental Limitations first appeared on Quanta Magazine

2 days ago 3 votes
Links in Progress: We can still build beautifully

A tour of interesting developments built in the last two decades

2 days ago 4 votes
The Value of Foreign Diplomas

Is that immigrant high-skilled or do they just have a fancy degree?

2 days ago 10 votes
Incorruptible Skepticism

Everything, apparently, has a second life on TikTok. At least this keeps us skeptics busy – we have to redebunk everything we have debunked over the last century because it is popping up again on social media, confusing and misinforming another generation. This video is a great example – a short video discussing the “incorruptibility’ […] The post Incorruptible Skepticism first appeared on NeuroLogica Blog.

3 days ago 3 votes