Friday, May 30, 2008

The program is over - Friday 30th

Yesterday went on with a nice dinner at the restaurant Esperanza on Birger Jarlsgatan.

Here is a photo of the proceedings (courtesy of Petter Holme):

From left to right, clockwise: Meesoon Ha, Petter Holme, Mikko Alava, Haijun Zhou, Matti Peltomäki, Sumedha Sumedha, and Sang-hoon Lee. Thanks to Laila of Nordita for the choice....

Then we did some science to celebrate the end. A discussion session about the physics of peer-to-peer neworks was held in the morning of the Friday.

Supriya Krishnamurthy presented first the issue from a physicst's viewpoint, of networks and dynamics on dynamic networks. Then György Dan gave a computer science response, of what is important, and why, in the study of self-* (wild card) processes. A lively discussion ensued. Can a theoretical physicist show entrepreneurial spirit and contribute (while not becoming rich)?

A PS: their presentations are now on the program web page.

We thank Nordita in general for making the program possible, and hospitality, the participants (also of the workshop) for the scientific atmosphere, and the local Nordita folks for assisting, helping and many other little things that made PhysDIS possible. Erik Aurell has been ill for the last week: to a quick recovery!

Thursday, May 29, 2008

Thursday talk, 29th of May

Sumedha Sumedha talked today about her recent research on biophysics: how to understand transcription factor binding and its relation to how cells operate. The basic question boils down to an interplay of geometry, chemical potential, and the polymer physics (entropy of loops) of say DNA. For simple model systems the outcome is a funny model of random graphs with a link/degree restriction per vertex. Which, can be studied analytically and out comes a percolation transition which can be first or second order.

Later today, we will have a dinner...

3rd last blog post, Thursday morning

The SMDIS program is crawling closer and closer to its eventual end.

The previous Tuesday was without any formal program thanks to some parallel bioinformatics related activity here in Stockholm. Inspired by the nice spring/summer weather this gave way to a working day. Yesterday, Meesoon Ha presented some of her recent work on one-dimensional extensions of the Asymmetric Exclusion Process (ASEP). The main issue at hand is that the ASEP is one of the standard paradigms of non-equilibrium systems, and being a representation of the Kardar-Parisi-Zhang problem (or the Burgers' equation) exhibits shocks and nonlinearities. One can then modify the ASEP to look at various transitions that correspond most often to shock-formation in the KPZ, or to seek for new physics - like if one in the ASEP lets the particles to jump not by one lattice site but to the next cluster of particles.

Monday, May 26, 2008

Monday Markets (the 26th of May)

The life of the SMDIS program returned after an eventful weekend (with a boat-trip to the archipelago of Stockholm and Erik Aurell getting slightly ill) to normal: work and a talk.

Today, Matteo Marsili gave an overview of recent work on multi-asset markets, empirical data, and theoretical modelling. In practice this means that if a lot of investors behave in the same way, that is use a similar strategy to optimize their portfolios, then this starts to have a feed-back effect with the way the market itself acts. As often in these models (Matteo presented two approaches, one "physics-style" and another "economy-style". It was not quite clear how to get from the more complicated latter to the former...) one has the possibility of a transition between a state with large fluctuations and a state with small fluctuations.

Tomorrow we will have an only-working day thanks to a simultaneous bioinformatics event here in Stockholm.

Friday, May 23, 2008

Friday 23th and Google

Today, we heard Sang-Hoon Lee talk about his research on networks. The main idea is to use Google to find out about effective social networks, using the joint hits (e.g. for Mikko Alava and Albert Einstein, they are found as exact keywords together 7 times). So a graph is established with weights, and then one can study its properties and development and compare with other possible measures for the same ensemble connected by the "Google-network". Results on the U.S. senators were presented....

Report on Thursday 22nd

The main event of the Thursday was the talk of Satya Majumdar on the relation between the Integer Partitioning Problem and the statistics of extremes. By the right choice for the energy of the state ("number") one can map the problem to the statistics of a Bose gas. Then, even an interpretation can be found in how the Gumbel distribution a long ago found in mathematics arises. Many extensions could be foreseen (many of which were already resolved by Satya).

Meanwhile, the weather got better and warmer.

Thursday, May 22, 2008

A Wednesday passed (the 21st)

Yesterday we had one talk, by Matteo Palassini. He discussed some recent work in Barcelona on the p53 regulatory network: the appearance of noise-induced oscillations in its dynamics due to number (of molecules) fluctuations. A coupling of the eigenvalues of the dynamical system and the noise gives rise to this. Matteo had a bit of PowerPoint trouble, but at the end it was resolved by the traditional means of a (white)board which then enlivened the audience...

... meanwhile the weather got better.