Part of the Internet taken down by a leap second

As a graduate student working for LIGO (the Laser Interferometer Gravitational wave Observatory), one of my responsibilities was maintaining date-time code, including accounting for leap seconds, and calculating dates and time thousands of years in the past. 

What is a leap second? Well, the Earth's rotation rate is slowing down. So, as time goes on the length of the day is longer. This rate is very slow. Every few years, the added length must be taken into account, much like the leap day takes into account that the orbital period of the Earth around the Sun is not exactly 365 days. When a leap second must be inserted is not predictable. The International Earth Rotation and Reference Systems Service is tasked with making observations of the Earth, and producing a twice-yearly report on whether a leap second is due to be added. This comes out by email, and on their website. The report gives a 6-month or so lead time before the leap second is inserted, at midnight on Jan 1 and on Jul 1.

So, apparently, a leap second was inserted last night: all standard atomic clocks around the world paused for a second. This caused all sorts of havoc with computers and networking devices, causing lots of sites to go down. Notably, Google was prepared.

(via Gizmodo and Wired)


My first Processing program: algorithmically-generated plant

I have been meaning to try out Processing (a.k.a. Proce55ing) for ages, now.  Processing is a Java-like language which includes a simple development environment which makes generating graphics, animation, and sound simple. You can see some impressive examples at the Processing site's exhibition page.

I played with Processing for the past week or so, and my first non-trivial "sketch" is a modification of the Penrose Tile example written by Geraldine Sarmiento included with Processing. It is an algorithmically-generated plantlike form. The iterative method used is called an L-System, introduced by the botanist Aristid Lindenmayer (hence the "L"). 

Back in the 80s, when fractals, cellular automata, and other iterative and recursive things were the rage, this beautiful book (which I have a copy of) was produced: The Algorithmic Beauty of Plants, by Przemyslaw Prusinkiewicz and Aristid Lindenmayer.  It is out of print, but you can download a full high-resolution copy at that link, which also lists correction.

Click here for my sketch.


Total lunar eclipse coincides with Winter Solstice

The last time a total lunar eclipse coincided with the Winter Solstice was 372 years ago. This is the second time this has happened in the Common Era. Unfortunately, it was much too overcast for me to see the total eclipse. I caught a few brief glimpses as the partial eclipse began, with roughly a quarter of the moon in eclipse, and then with half in shadow.

TLE2010Dec21-ESTw


Plots, plots, plots

Busy making plots for the American Association of Physicists in Medicine annual conference at the end of the month. Some are pretty. Not as pretty as this old plot, but the stuff I learnt making that one helped me make this. I have a script that cranks out about 2 dozen plots semi-automatically.

Fixed Partial Denture Y55 Xz-1


Listening to “100 por Carlos Gardel” (Carlos Gardel), which my roomie brought home from her trip to Buenos Aires

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LIGO video

The project that I did my PhD in, Laser Interferometer Gravitational Wave Observatory (LIGO), has, with the National Science Foundation (NSF), produced a 20 minute video entitled “Einstein’s Messengers” targeted towards the general public. It’s a NOVA-style program. You can watch a streaming version online.

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Pretty picture

I spent the last few days playing with matplotlib, a nice graphics package for Python. The result, which is basically what I needed to accomplish, is below. I just need to scale the data properly, which is easy using the Python classes I wrote to encapsulate the dose and phantom outputs of EGSnrc, the Monte Carlo dose calculation code I use. Oh, and don’t worry: that’s not a real head. It’s a “phantom”, an artificial head made of plastic with a real skull, jaw bone, and teeth embedded into it.

Dental phantom

Listening to Michael Jackson from the album “On The Floor At The Boutique” by Fatboy Slim

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