Berkeley Lab Scientific Computing Seminar

Date:

Friday, December 14, 2007

Time:

1:00pm-2:00pm

Location:

Building 50F, 1647 Conference Room

Seminar Speaker:

Stefano Marchesini
Advanced Light Source
Lawrence Berkeley National Laboratory

Title:

Large Scale Inverse Problems in X-Ray Scattering

Abstract:

The most successful routine to image macro-molecular structures is by numerically processing the diffraction pattern of a structure replicated in a periodic system: X-ray crystallography. The next challenge, imaging entire cellular organisms with billions of resolution elements requires the solution to a large scale nonconvex problem. A nonconvex fixed point iteration has demonstrated practical solutions to giga-element nonlinear phase retrieval problems, escaping local minima and producing images at resolutions beyond the capabilities of lens-based optical methods. These methods have been applied to image object as complex as biological cells, quantum dots, nanaocrystals, and nanoscale aerogel structures. Other test patterns were captured in the fastest flash image ever recorded at suboptical resolution. With a 10¹⁰ increase in peak brightness of upcoming light sources, more powerful algorithms will be required to tackle problems of increasing scale. Acceleration strategies for the fixed point iteration using lower dimensional Newton and quasi-Newton methods will be discussed.

Sponsor of Seminar:

Chao Yang

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov