New job, new country

I just started a new job, and in the way of academic life, I had to move. I put some things in storage, hopped on a plane with two suitcases, and hey presto, I live in the Netherlands now. The new job is with ASTRON, the Dutch institute for radio astronomy, and it's going really well. Living in a new country actually takes more getting used to.

For one thing, in spite of the fact that I live in arguably the most pedestrianized city in Europe, and in a densely-populated country with good transit systems and cities built when rapid transit meant corn-fed horses, I find myself tempted to carpool to work. See, the thing is, ASTRON was built in the middle of a national park in order to minimize interference with the radio telescope that was also being built. Since the fifties, though, radio astronomy has made a few strides, and the telescope is now used chiefly in education. The telescopes we do use are all off-site, so we're in the middle of the park for historical reasons. It means we're twelve kilometers from the nearest train station, and even the bus drops you off in the village of Lhee, a kilometer or so away from work. So a ride to work is tempting. Fortunately, this is the Netherlands, so I've been biking.

Differentiating the solutions to differential equations

A kind of problem that turns up quite often in physics and elsewhere is to find the solution of an ordinary differential equation, given some initial conditions. That is, you have a system with some state $x$ represented as a vector of real numbers, you have an initial state $x_0$, and you have a rule describing the evolution of the state: $$ \frac{dx}{dt} = F(x,t) $$ And your goal is to find $x(t)$. This standard problem has some standard solution techniques, some quite advanced - Runge-Kutta methods, symplectic methods, Hermite integrators. A few are implemented in scipy. But it sometimes happens that solving this problem is only part of a more complicated process, say of fitting, where it would be nice to have the derivatives of the solution with respect to the various initial conditions. It turns out this isn't too hard to work out, usually.

Weighted Poisson Uncertainties

I recently ran across a rather awkward mathematical problem. I'm trying to make a histogram of photon arrival phases, complete with an uncertainty on the number of photons in each bin. Normally this is done by just taking the square root of the number of photons, which is at least approximately right based on Poisson statistics. But in my problem — data from the Fermi space telescope, which is not very good at localizing low-energy gamma rays — the photons are weighted: for each photon I have a probability that it really came from the source. So the values in the histogram should be the total probability. But what should the uncertainty be? The short version is: the square root of the sum of the squares of the weights.

ETA: This is in the literature, without justification as far as I can tell. See below.

git tear-hair

I use git. It's fast, it's convenient, it gives you github, and mostly it works. But several times now I've managed to bollix a git repository, been faced with impenetrable messages, and been unable to continue using git unless I sort them out. This latest time I had enough stubbornness to figure out how to un-bollix my repository, and I wanted to record it for posterity (specifically, for people whose problem-solving technique involves Googling for the specific error message). The error I received was:

error: object file .git/objects/86/5d2dffe9a3d72917934ed9693c7167efb6d8d5 is empty
fatal: loose object 865d2dffe9a3d72917934ed9693c7167efb6d8d5 (stored in .git/objects/86/5d2dffe9a3d72917934ed9693c7167efb6d8d5) is corrupt

Read on for how it happened, my understanding of what it means, and how I fixed it. Or skip this even-more-technical-than-usual post; I'll try to post something with corals or kittens soon.

Justice

Available from Amazon

I recently read (listened to? What's the right way to say that for an audio book?) "Justice: What's the right thing to do?" by Michael J. Sandel. It's an interesting book, though rather heavier going than Nate Silver's breezy book on prediction. The basic question it addresses is, how do you decide what's right? Not just what's legal — you need some basis for deciding which laws are just. He talks through several approaches, including some ideas of his own. While he talks about several currently-debated topics, he refrains from stating his position on any of them, instead pointing out what the conflicting ideas of justice are that motivate the two sides.

Talking about radio astronomy

McGill has a modest observatory on the roof, with a 14-inch (optical) telescope. It was installed quite some time ago, then left to molder for a few years. This annoyed me, just on principle, so I talked my way into rehabilitating it as best I could, with my radio astronomer's skills. Even with it working again, it was just used by the occasional grad student who wanted to take her friends up to see Jupiter, or the surface of the moon, or whatever. Fortunately, we recently acquired an enthusiastic and organized post-doc who pushed hard and set up a public outreach program. Typical nights start with a public lecture, then we take folks outside to two portable telescopes and the bigger one on the roof to look at the stars. Of course, we can't predict the weather, so we have a few demos we can do inside - comet-making, liquid nitrogen, a muon detector, but really the appeal is going out and looking up at the sky. But especially in the summer, we need to entertain the public until it gets dark. Since it's once a month, we have a perennial need for speakers. So I volunteered, to give a one-hour talk on radio astronomy for the general public. I had never given a one-hour talk before, and radio astronomy doesn't produce as many pretty pictures as I would like, but I think it came out pretty well. And we had a videographer who recorded the whole thing, so if you're curious, here it is.

Prediction

The book can be bought from Amazon

I recently finished reading Nate Silver's book "The Signal and The Noise: Why Most Predictions Fail But Some Don't". Nate Silver is currently somewhat famous because his election predictions - he runs the blog fivethirtyeight for the New York Times - his election predictions were basically spot on. The book, timed to come out shortly before the election (in what I think was a sort of gamble to capitalize on a successful prediction) is about prediction, generally defined. Structured as a sort of collection of case studies, the book talks about all the ways prediction can go wrong, and about what to do to try to get it right. There's no nice one-line answer, but I think he gives some pretty good advice.

The Maya-Muon experiment

This week's Friday colloquium talk really had me feeling like I was in a science fiction show. The speaker is building machines to use cosmic-ray muons to see the interiors of still-buried Mayan ruins. Does this not sound like a line of technobabble from Stargate SG-1? But it's nearly feasible.

Higgs liveblog

A candidate Higgs event; see below.

The Higgs detection (?) announcement is being broadcast live. So I thought I'd blog my comments as it unfolds.

Fireworks

In honor of Canada Day (and for my neighbours to the south, the fourth of July) here's a video:

While this might look like a meteor, and in fact it is asteroidal material falling to Earth, it's actually some extremely expensive fireworks. It's the Hayabusa spacecraft returning to Earth after visiting asteroid 25143 Itokawa, and the material it brought back was safely encapsulated.

The Too-wide Web

For some reason, computer monitors have been getting wider and wider for years. This puzzles me, since like most people, when I'm working, I tend to use tall narrow documents, both to read and to edit. Sometimes I can arrange things so that I have two panels on the screen, which restores them to a more sensible shape, but the Web is a problem. Web pages seem to have begun adapting to wide monitors by adding wider and wider margins, often filled with ads and/or navigation materials. For me, these margins are often too wide for me to use a two-panel setup (it's just a laptop) but often they leave so much width when used full-screen that the text is tiresomely long. Typesetters have a rule of thumb that you shouldn't put more than about twelve words on a line because it's hard to read. Fortunately, I found a Chrome hack that lets me solve the problem.

The RepRap wiki is too wide.

USB Stick

My sister Margaret has a pretty awesome job: in the summers, she works for Fish and Game in Alaska, studying salmon, and (being a government job in Alaska) they pay well enough that she can spend the rest of the year repairing and sailing her boat. There seems to be a great deal of repairing, but one dictionary I had as a kid defined a boat as "a hole in the water into which you pour money". In any case, Margaret has been sailing around the Caribbean; she delivered beans to Haiti in the wake of the earthquake, and she hosted a skill-sharing conference for sailors this last winter. It's an awesome life, and I'm totally envious, but it's a little hard on consumer electronics. Just last year she lost a camera full of pictures (which I totally wanted to see!). So I thought I'd try to make her an indestructible USB stick. I think it worked out pretty well.

Broken centerboard from her dinghy, Scout

Recipe/Remedy

I'm fighting off the tail end of a cold, that stage where you're all congested and just can't seem to clear your lungs. So I figured I'd whip up a home remedy that is also dinner. Simple, easy, and effective. Black beans and corn.

NuSTAR about to launch

NASA is getting ready to launch a new X-ray satellite, NuSTAR. This satellite will observe harder X-rays than we are currently able to. More specifically, this satellite is able to produce high-resolution images of the hard X-rays that come from the decay of isotopes produced in supernovae; the ability to observe hard X-rays with high spectral resolution should also let us probe neutron star formation. Plus it may help us pin down that hard X-ray emission from anomalous X-ray pulsars that nobody understands.

If all this sounds hopelessly technical, sorry. It's still impressive to me that they're going to take this hundred million dollar spaceship, fill it with what amounts to high explosives, strap it underneath a discontinued Lockheed airplane, fly it up into the air near Kwajalein, then drop it and light the fuse. The rocket will then burn for a few hundred seconds, dropping several stages and winding up in low Earth orbit. Once there, the mast holding the mirrors will extend from its one-meter storage canister to its full ten-meter length, the satellite will extend its solar arrays, and scientists will begin debugging and calibrating the instruments. That's if everything goes well; no Pegasus launcher (which this is) has ever actually exploded, though one pair of satellites failed to exit its fairing. So there are some people chewing fingernails, and there's some real drama here. You can watch it online.

Sorry for the hurried nature of the post; I'm planning to watch it live and report on the results as soon as we know.

Edited to add: Success! At least so far. The satellite is in orbit and the solar panels work. The last big worry-point is the extension of the boom; the ten-meter beam that holds the mirrors in position relative to the cameras is currently folded into a one-meter canister. Supposedly, the scientists were reassured that "we can't give you any details, but we know how" to build such a boom, but it won't extend for another week. That'll be followed by a few weeks worth of testing and calibration. But so far so good.

Error 451: Unavailable for legal reasons

Proposed new HTTP error code (like the well-known 404): 451 (Unavailable for legal reasons). Contains the usual hacker humour, including a thank-you to Ray Bradbury (may he rest in peace) and the following example:

HTTP/1.1 451 Unavailable For Legal Reasons
Content-Type: text/html

<html>
<head>
<title>Unavailable For Legal Reasons</title>
</head>
<body>
<h1>Unavailable For Legal Reasons</h1>
<p>This request may not be serviced in the Roman Province of
Judea due to Lex3515, the Legem Ne Subversionem Act of AUC755,
which disallows access to resources hosted on servers deemed
to be operated by the Judean Liberation Front.</p>
</body>
</html>

Of course, this particular error might have been the result of hacking by the People's Front for Judea.

French word of the day: bidouilleurs

A brief comment about background: I was born in Montreal, which is supposedly the third-largest French-speaking city in the world after Paris and Kinshasa, but as a result of family history and linguistic segregation (which has some nasty history) I grew up speaking English. These days I work in English, like most scientists, but I speak a lot of French socially. So from time to time I come across a neat French word. I think it might be good for my general education to post little comments on them here.

There's going to be a mini Maker faire here in Montreal at the end of the summer. Neat! But what caught my eye was that it seems the French word for "maker" is "bidouilleur". So what? you ask. The French word "bidule" is a kadigan roughly equivalent in meaning and seriousness to the English "thingamajig", so a bidouilleur (or bidouilleuse!) is someone who operates on thingamajigs. Which is pretty accurate, really. 

Fabric triangulations

D dress from Continuum Design

What with cheap and easy 3D scanning and laser cutting, I see very interesting possibilities for bespoke clothing. But I think there are some technological issues to resolve, and in particular, there's a particular mathematical problem I'm not quite sure anyone has studied. Or at least, I'm not sure how to find the work on it (suggestions welcome!).

Old-school UNIX nerdery

I've never owned a Windows machine, or a Mac. It's not that I'm particularly hardcore about open source, it's just that I got used to a command line back in the old VIC-20/DOS/DesqView days and never really got away from it. Our undergrad computer network was very convenient, but made up of about four flavours of UNIX, and in fact they had a load-distributing program at login that meant your initial login was not just to a random machine but to a random UNIX flavour. Somehow the IT folks made this work tolerably well. After a few years of that, when I finally got a home computer, I chose to run Linux on it.

I for one welcome our new robot overlords

A common theme in science fiction is the idea that robots will take over our world. This doesn't seem very likely, but suppose it were to happen. What would the first steps look like? How would we first begin to notice that it was happening?

Police violence and crowd control

In the last few weeks, we've seen a number of events where large crowds of unruly people have gathered. Police response to these crowds has varied substantially, and I think it's instructive to think about what these responses say about us, as a society.