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TCU Box 298840
Fort Worth, TX 76129
Phone: (817) 257-7375
Fax: (817) 257-7742
Email:physics@tcu.edu

This page maintained
by Kaoru Yoshida

Spring 2003 Seminar Information

Friday February 28 at 3:00 p.m.
Tucker Technology Center, TTC 139
(Professional Development Center)
Refreshments and the Dissertation Oral Examination will follow

Dissertation:

Kenneth Yawn
Lockheed-Martin
Department of Physics and Astronomy
TCU

Gravitational Dynamics in One Dimension

Abstract:

Due to the apparent ease with which they can be numerically simulated, one-dimensional gravitational systems were first introduced by astronomers to explore different modes of gravitational evolution. These include violent relaxation and the approach to thermal equilibrium. Careful work by dynamicists and statistical physicists have shown that many claims made by astronomers regarding these models have proved to be incorrect. Unusual features of the evolution include the development of long lasting structures on large scales, which can be thought of as one-dimensional analogues of Jupiter's red spot or a galactic spiral density wave or bar. The existence of these structures demonstrates that in gravitational systems evolution is not entirely dominated by the second law of thermodynamics and also appears to contradict the Arnold diffusion anzsatz. Thus it is correct to assert that the one dimensional planar sheet gravitational system is the non-extensive analogue of the Fermi-Pasta-Ulam model of dynamical systems. In this talk I will first define the class of models. Then I will discuss the historical characterization of the system, including violent relaxation, thermalization, and the equilibrium state. The central focus of the talk will be my own dynamical studies and analysis which make use of stochastic modeling, local and global time averaging, and temporal and spatial correlation functions for the single component system and, in addition, equipartition, and mass segregation for the double component system. Using these tools I will show that global measures support relaxation to equilibrium, but local measures do not.

 

Sponsor: Dr. Miller

Friday March 21 at 1:30 p.m.
SWR 357
Refreshments will follow

Dr. B. Palosz
Polish Academy of Sciences, Warsaw

Analysis of short and long range atomic order in nanocrystals

Abstract:

Fundamental limitations, with respect to nanocrystalline materials, of the traditional elaboration of powder diffraction data like the Rietveld method are discussed. A tentative method of the analysis of powder diffraction patterns of nanocrystals is introduced which is based on the examination of the variation of lattice parameters calculated from individual Bragg lines (named the "apparent lattice parameter", alp). We examine the application of our methodology using theoretical diffraction patterns computed for models of nanocrystals with a perfect crystal lattice and for grains with a two-phase, core-shell structure. We use the method for the analysis of X-ray and neutron experimental diffraction data of nanocrystalline diamond and SiC powders of several to 30 nm in diameter. The effects of an internal pressure and strain at the grain surface is discussed. The results are based on the dependence of the alp values on the diffraction vector Q and on the PDF analysis. It is shown, that the experimental results support well the concept of the two-phase structure of nanocrystalline diamond.

Sponsor: Dr. Zerda

Tuesday April 1 at 1:00 p.m.
SWR 357

Dr. Tamas Ungar
Budapest, Hungary

Dislocation density in diamond crystals