Astrology For Teh Win!

Symbol for Spaghittarius, one of the twelve astrological signs

I’ve had it with science and plan to convert this site to be completely about astrology. Astrology (as Wikipedia puts it: “Not to be confused with Astronomy.”) is a shortcut to the truth. After all, if the truth is in the stars (“De Trut Is Uit Daar” as we paraphrase the tagline from The X-Files in Dutch), gathering and analyzing data…


Submitted on 1 April 2013

The Looming Effect


The animation demonstrates the looming effect that you get when something (a motorbike in this case) approaches you at a constant speed. At first nothing seems to happen, but then the bike suddenly jumps into view. A general explanation of this dangerous effect that often causes motorbikes to be missed by other drivers is…


Submitted on 4 March 2013

Skill Bubbles

Skill Bubbles

This colorful bubble chart is a simple way of freshening up your CV by adding the time dimension to your skill list. A simple list has relatively little value, since it doesn’t indicate the importance of each skill. This can be improved by including an estimate of its strength. To do this, you could simply add the number of years of experience, but I propose to go a bit further…


Submitted on 1 February 2013

How to Ensure that Visitors Always See Cached Pages in Drupal 7

All the standard caching options of my Drupal 7 site are enabled. I expected those mechanisms to ensure that the access to a cached page would always be quick, both for human visitors and for web spiders like Googlebot. However, for a small site, this is not so. The Drupal caching mechanism does not work as you might expect. For me, there is a clear difference between…


Submitted on 21 January 2013

7 Cool Reference Sites on Mathematics

We all have to look things up once in a while, and I can tell you right now that Wikipedia is the best source for practical information on mathematics. But, there are some others out there that are also worth knowing. Most of these sites are encyclopedic, and not meant for browsing top down, so I’ve used the entry for eigenvector as an example for…

Submitted on 9 January 2013

Skirmish with Spam

I was going to call this article War on Spam. But, given how well my experiments went, I had to retitle it Skirmish with Spam. Lately, the number of spam attempts has risen so much that even Mollom lets through enough spam to get me a bit miffed. So, I decided to go “old school”… I was going to add math problems of increasing difficulty until…


Submitted on 22 December 2012

Tomography, Part 4: Algebra!

The first three articles on tomography focused on analytic techniques, in which the reconstruction problem is attacked using mathematical analysis. When the step to real world scanners is made, the problem is discretized. Both the projections and the reconstruction area are divided into pixels, and a numerical approximation of the true mathematical technique is introduced. The algebraic techniques assume…

Submitted on 9 December 2012

Tomography, Part 3: Reconstruction

Fourier slice theorem

At the end of the second article on tomography, I left you with a very blurry reconstruction of the scanned object. Indeed, naive backprojection is not sufficient to create high-quality reconstructions. Why is that so? Intuitively, a simple backprojection cannot be expected to create a perfect reconstruction, since the contribution of…

Submitted on 25 November 2012