Biomedical subjects

Stefan P Hau-Riege

Publications and source records attributed to Stefan P Hau-Riege.

4 recordsLinked to original sources

PubMed2005

Pulse requirements for x-ray diffraction imaging of single biological molecules.

In this paper we estimate the required pulse parameters for the future application of x-ray free electron lasers to imaging single biological molecules. The parameters are determined by a tradeoff between minimizing image degradation due to damage and maximizing the image signal-to-noise ratio. We discuss several means to alleviate the pulse requirements, and compare the requirements with parameters of two planned x-ray lasers.

Biopolymers↗

PubMed2004

SPEDEN: reconstructing single particles from their diffraction patterns.

SPEDEN is a computer program that reconstructs the electron density of single particles from their X-ray diffraction patterns, using a single-particle adaptation of the holographic method in crystallography [Szöke, Szöke & Somoza (1997). Acta Cryst. A53, 291-313]. The method, like its parent, is unique because it does not rely on 'back' transformation from the diffraction pattern into real space and on interpolation within measured data. It is designed to deal successfully with sparse, irregular, incomplete and noisy data. It is also designed to use prior information for ensuring sensible results and for reliable convergence. This article describes the theoretical basis for the reconstruction algorithm, its implementation, and quantitative results of tests on synthetic and experimentally obtained data. The program could be used for determining the structures of radiation-tolerant samples and, eventually, of large biological molecular structures without the need for crystallization.

Algorithms↗

PubMed2004

Dynamics of biological molecules irradiated by short x-ray pulses.

Very short and intense x-ray pulses can be used for diffraction imaging of single biological molecules. Inevitably, x-ray absorption initiates damage that degrades the molecule's image. This paper presents a continuum model of the physics that leads to damage when a small particle absorbs a large x-ray dose. The main processes are found to be ionization and Coulomb-force driven atomic motion. Trapping of electrons, Debye shielding, and nonuniform collisional ionization all have a significant effect on the overall damage kinetics.

Biophysics↗

PubMed2003

Correction of figure errors on optical surfaces by laser-induced contraction of Mo/Si multilayers.

We demonstrate that laser annealing of Mo/Si multilayers can be used to make controlled modifications of the surface figure of an optical substrate on a nanometer scale. In this experiment a superpolished optical flat was exposed to single pulses from an excimer laser to produce surface depressions of widths that varied from 10 microm to 0.5 mm and of depths in the range 2-50 nm. Simulations of thermally induced contraction of the Mo/Si multilayers are in good agreement with the observed deformations and indicate that the technique can be extended to larger deformations and higher resolution.

Journal Article↗