Room 851, 5F, Building No.8, Kagurazaka Campus
March 16 (Friday) 2012.

Tokyo University of Science
http://www.tus.ac.jp/info/access/kagcamp.html

Morning session 10:30-12:00
Regularizing Iterations for ODF Reconstruction
by Professor Per Christian Hansen, Technical University of Denmark

A fundamental imaging problem in microstructural analysis of metals is the reconstruction of local crystallographic orientations from X-ray diffraction measurements. This work develops a fast, accurate, and robust method for the computation of the 3D orientation distribution function for individual grains of the material in consideration. We study an iterative large-scale reconstruction algorithm, CGLS, and demonstrate that right preconditioning is necessary to provide satisfactory reconstructions. Our right preconditioner is not a traditional one that accelerates convergence; its purpose is to modify the smoothness properties of the reconstruction. We also show that a new stopping criterion, based on the information available in the residual vector, provides a robust choice of the number of iterations for these preconditioned methods.

Afternoon session 1 13:30-15:00
Total Variation and Tomographic Imaging from Projections
by Professor Per Christian Hansen, Technical University of Denmark

Total Variation (TV) regularization is a powerful technique for image reconstruction tasks such as denoising, in-painting, and deblurring, because of its ability to produce sharp edges in the images. In this talk we discuss the use of TV regularization for tomographic imaging, where we compute a 2D or 3D reconstruction from noisy projections. We demonstrate that for a small signal-to-noise ratio, this new approach allows us to compute better (i.e., more reliable) reconstructions than those obtained by classical methods. This is possible due to the use of the TV reconstruction model, which incorporates our prior information about the solution and thus compensates for the loss of accuracy in the data. A consequence is that smaller data acquisition times can be used, thus reducing a patient's exposure to X-rays in medical scanning and speeding up non-destructive measurements in
materials science.

Afternoon session 2 15:15-16:00
Sampling acoustic fields : a few case studies
by Professor Laurent Daudet, Universite Paris Diderot-Paris 7

There are a number of applications where one wishes to know an acoustic field over an extended domain, whereas in most cases one can only perform point measurements (e.g. with a microphone). Even when few sources are active, it remains a challenging problem due to reverberation, that may be hard to characterize. This is typically a sampling problem, that raises a number of interesting questions: how many sampling points are needed, what are good distributions of sampling points, etc?
In this talk we will review a few test studies, in 2D (plates) and 3D (rooms), with numerical and experimental data, where a physicsbased sparse model for the acoustic wavefield is successfully used for its reconstruction, using significantly less measurements then would be required by classical Shannon sampling.

Free discussion 16:00-17:00

Party 18:00-