Friday, July 31, 2009

Imaginary time projection method for construction of localized basis sets

In the preprint arXiv:0907.5053v1, the authors Zhou and Ceperley present an efficient method to construct a localized basis set for a Hubbard lattice model of bosonic atoms in a disordered potential at a given instance of disorder. This is achieved by a projection technique based on propagation in imaginary time, which is related to diffusion processes of the atoms.

Thursday, July 23, 2009

Apollo 11 code published online

Parts of the code running on Apollo 11's control system have been published on Google code, based on the transcription of scanned images of the assembler source code from the MIT Museum. The codes can be run on an open source Apollo guidance computer emulator.

Tuesday, July 21, 2009

FPGAs solve N=26 queens problem

While NQueens@Home is still working on it, the Queens@TUD project has solved the N=26 queens problem, that is, in how many different ways 26 queens can be placed on a chessboard without the possibility of capture among them. The solution is 22,317,699,616,364,044. Are local, "uncrowded" solutions faster after all? ;)

Saturday, July 18, 2009

Games motivating human computing power

Tasks like image recognition can generally not be reliably performed by computers yet, but for humans this is relatively easy. While I would say that the scope of computational physics essentially involves problems that are too complex to be solved by hand, there are problems where intuition will help finding a solution instead of barely relying on e.g. brute force computational-only approaches, i.e. the road from theory(thinking/modeling) to computational physics would be extended once more by cognitive power.

In the following I've listed three projects in the order I've come across them, each of them one step closer to the use of parallel human computing power in the field of computational condensed matter physics.

Read on

In this first video, Luis von Ahn illustrates how a large crowd can be motivated using "games with a purpose" to e.g. label images or to build up common-sense facts databases.

This video is about the game "Foldit", in which the score of a player is based on the optimality of a interactively folded protein.

In the following video, the spectral game (link; journal ref) is introduced.

It is intended as an educational game, but I guess a similar game could aim at predicting crystal structures by allowing the player to select a space group and to choose the sites of the elements of a given formula - the score would be based on how well e.g. powder diffraction patterns are reproduced (however, I have to admit that this wouldn't be a game I'd like to play). More fun could be the interactive construction of candidate structures by "mating" given starting cells (mixing slices etc.), in the spirit of genetic algorithm approaches to the crystal symmetry prediction problem.

Since "knowledge/intuition-based image processing" is something where games are very useful, it would be nice if "less visual" problems could be mapped onto kind of a 2D-image analysis problem.

Saturday, July 11, 2009

3D layered FQHE

Read on

Simulation of a 3D FQHE system. Suggested reading:

Fractional charges fly between planes
Burnell, Sondhi
Physics 2, 49 (2009)

Gapless layered three-dimensional fractional quantum Hall states
Levin, Fisher
Phys. Rev. B 79, 235315 (2009)

Bismuth in strong magnetic fields: Unconventional Zeeman coupling and correlation effects
Alicea, Balents
Phys. Rev. B 79, 241101(R) (2009)