Friday, April 29, 2005

Earth sucks it up

This article is troubling. Not because it is new, but because most modeling of Earth weather circulation assume thermal equilibrium, which as it stands, does not seem to be a good assumption.

Wednesday, April 13, 2005

Look out for big lone stars

As I was hinting in a previous entry, the flower constellations of Daniele Mortari could also be used to construct large "objects" in space in order for us to give signals to ETs. If you take a look at some of the constellations that can be built, it does not take much time to realize that these are made by intelligent people, with a sense of art at that. In this article, Luc Arnold proposes to find ET life by looking at large objects, let us hope there is another Daniele Mortari, several parsecs away who has made the same discovery.

There is a good reason as to why these figures would be better detected with interferometry systems. One of the interesting feature of these constellations is that the human brain looks at them and figures they have a shape because they see three of more satellites as if they are always be forming a line. This is mainly an averaging effect but it is striking (Daniele can produce a constellation that reproduces the contour of a star, imagine that, a star looking at a star!) Since interferometric systems do make an average view (they have to collect enough light), we are also likely to see these lines in the interferometric data. And the best way to find them, will be use the curvelet transform. Since interferometric systems are also sparse, in term of light collection, it is likely that we will have incomplete data, Emmanuel Candes who has been working on curvelets, is also now working on incomplete fourier ensembles and he is aware of interferometric systems as witnessed in his recent paper entitled "Stable Signal Recovery from Incomplete and Inaccurate Measurements"

...Fourier ensemble. Suppose now that A is obtained by selecting p rows from the n×n discrete Fourier transform and renormalizing the columns so that they are unitnormed. If the rows are selected at random, the condition for Theorem 1 holds with overwhelming probability for S  C · p/(log n)3 [4]. This case is of special interest as reconstructing a digital signal or image from incomplete Fourier data is an important inverse problem with applications in biomedical imaging (MRI and tomography), Astrophysics (interferometric imaging), and geophysical exploration.

It looks like, it is just a matter of time before we go out on a search for a big lone star, you know the five legged one...

Tuesday, April 12, 2005

Modeling extinction

This article on exploding star and its relation to extinction led me to read the fascinating Model of Extinction: A Review by Newman and Palmer. I always wondered about periodicity of astronomical event and their influence on life on earth. It looks like that while the astronomical hypothesis is interesting, it does not seem to be the prevalent means of extinction.

Friday, April 08, 2005

Basis Pursuit

Here is a very interesting paper on the use of Basis Pursuit to find a correlation between different parametric models and data from time dependent PET scans. The nice thing that makes it clear is that there is no need for an ad-hoc procedure to make sure that some coefficients are non-negative (non physical.) We have this kind of problem in neutron transport. In that area, ways to deal with this type of problems are called flux fixing.

Monday, April 04, 2005

Divergence-free colliding thoughts

Have you ever read a subject of interest that was barely relevant to what you were doing right then and found out it was the solution of somebody else's problem. This just happened to me this week-end. I received the NA Digest newletters with a question on divergence free and interpolating functions. Well it just so happens that I found recently an excellent resource on campus here at Texas A&M University. They have begun digitizing all the M.S and Ph.D theses produced by this fine institution, they are available at: this database, I found the doctoral thesis of Svenja Lowitzsch on Approximation and interpolation employing divergence-free radial basis functions with applications.

Friday, April 01, 2005

It's full of stars...and comets

If you look closer to this picture taken yesterday from Huygens, you'll see a bunch of comets. Now the question I have is, does anybody tries to find new comets from these pictures ?