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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 2006 Seminar Information

Friday January 27 at 1.00 p.m. in SWR 357

Pre-Dissertation:

FTIR Spectroscopy of Vanadium-Carbon and Chromium-Carbon Clusters

Sarah Bates
Department of Physics and Astronomy
TCU

Sponsor: Dr. Graham

Target-Thickness Dependence of Thin-Film Bremsstrahlung

Scott Williams
Department of Physics and Astronomy
TCU

Sponsor: Dr. Quarles

Friday March 3 at 1.00 p.m. in SWR 357

Diffraction Studies on Thermal Atomic Vibrations in Diamond and SiC Nano-Powdes and Nano-Ceramics

Dr. Svitlana Stelmakh
Institute of High Pressure Physics
Polish Academy of Sciences
Warsaw, Poland

Abstract:
Equilibrium conditions in nano-crystalline phases are different than those in large volume samples of the same composition.  Also, physical properties of nanomaterials deviate significantly from those in the bulk materials.  Undoubtedly, a nano-crystal cannot be considered as a fragment of a larger size solid:  it is a unique piece of matter with the properties specific for this individual object.  In a tentative model, a nanocrystal is a sort of a two-phase system formed by the grain core and the surface shell, both having their own characteristic dimensions.   
One of the key problems in "nanoscience" is in designing appropriate experiments which can serve for detection and precise measurements of specific materials parameters associated directly with the characteristic materials dimensions.  In this presentation we will focuss on determination of different amplitudes of thermal atomic vibrations in the grain interior and at the surface of nanocrystalline SiC and diamond.  Determination of thermal expansion coefficients (anharmonic thermal motions) and atomic temperature factors B (harmonic motions) for crystalline materials is a routine task.  Unfortunately neither of these parameters can be determined for a nanocrystalline material based on a conventional diffraction experiment.  However, by application of very large diffraction vector measurements, both Bragg-type scattering and the atomic Pair Distribution Function can be analysed and specific information on the atomic thermal motions, which are different in the grain core and at the surface, can be derived.
Examples of a succesfull analysis of the atomic thermal vibrations with application of neutron scattering will be presented.  In situ measurements were performed at LANSCE with HIPPO (from RT up to 1100^oC) and NPDF (from 15 K up to 225 ^oC) instruments.  Two different temperature atomic factors, which describe vibrations of the atoms in the grain interior (B_core) and at its surface (B_shell), were determined.  Differences between atomic vibrations in powders and nano-ceramics sintered under high-temperature high-pressures conditions, which are related to transformation of free surfaces into grain boundaries, were documented.  Changes of relative vibration amplitudes in the grain cores and surfaces with an increase in temperature will be presented.

Sponsor: Dr. Zerda

Friday March 10 at 1.00 p.m. in SWR 357

Microstructure and mechanical properties of ultrafine grained metals processed by severe plastic deformation

Dr. J. Gubicza
Institute of Physics
Eotvos Lorand University
Budapest, Hungary

Abstract:
Severe plastic deformation (SPD) is an effective tool for producing bulk ultrafine grained (submicron grain sized or nanostructured) metals. One of the most common SPD methods is equal channel angular pressing (ECAP) – a technique that results in a homogeneous ultrafine grained microstructure of the workpiece. The nanostructured materials processed by ECAP have unique mechanical properties which induced a great interest in these materials for industrial and medical applications. For example, ultrafine grained TiNi corkscrew is used in the treatment of stroke and the pure Ti processed by SPD is a raw material of surgical implants. For understanding the mechanical behavior of materials produced by ECAP, it is necessary to characterize their microstructure. In this presentation, the influence of SPD on the microstructure of different cubic and hexagonal metals is studied by transmission electron microscopy (TEM) and X-ray diffraction line profile analysis. High resolution X-ray diffraction experiments are performed using a special double-crystal diffractometer with rotating Cu anode. The crystallite size distribution and some characteristic parameters of the dislocation structure (e.g. density, character and arrangement of dislocations) are obtained from the evaluation of the line profiles. A brief review of this procedure is presented. The correlation between the parameters of the microstructure and the mechanical behavior is studied and discussed. The effect of alloying on the evolution of microstructure during ECAP is also investigated.

 Sponsor: Dr. Zerda

Monday March 20 at 2.30 p.m. in SWR 357

Refreshments at 3:30 pm in SWR 313
The Dissertation Oral Examination will follow at 3:45 pm in SWR 357

Dissertation:

Yuejian Wang
Department of Physics and Astronomy
TCU

Silicon Carbide Nanowires and Composites Obtained from Carbon Nanotubes

Sponsor: Dr. Zerda

The Tenth Annual
Joseph Morgan Lecture
(General information on the Morgan Lecture)

Tuesday March 21, 2006 at 7:30 p.m.
Lecture Hall 3, Sid Richardson Building
(Map for locating the Sid Richardson Building)

Refreshments will be served following the lecture

Dr. Eugene M. Izhikevich

Senior Fellow in Theoretical Neurobiology
The Neurosciences Institute
San Diego, CA

``Simulating large-scale brain models''

Biographical Information

Dr. Izhikevich received the M.S. in applied mathematics from Moscow State University
in 1992, and the Ph.D. in Mathematics from Michigan State University in
1996. He was a postdoctoral fellow and then a visiting professor at the Center for
Systems Science in Arizona State University. He joined the Neurosciences Institute
in 2000. Dr. Izhikevich has made important contributions to the theory of
coupled nonlinear oscillators, culminating in the 1997 book “Weakly Connected
Neural Networks”, co-authored with Frank Hoppensteadt. Using methods of bifurcation
theory, he classified all possible types of bursting dynamics that can be
observed in physical, chemical, and biological systems. He identified many new
types of bursters that were then found experimentally. Recently, he suggested a
novel approach to model spiking and bursting dynamics of biological neurons,
which for the first time allows simulations of large-scale neuronal models having
the size comparable with that of the human brain.

In 1963 Hodgkins and Huxley won the Nobel Prize for developing a quantitative model of the squid giant axon. They demonstrated that the behavior of a neuron could be modeled mathematically. Since that time, with the goal of someday achieving a better understanding of brain function, interest has grown in modeling networks of interacting neurons with computer simulation. The computational methods that have proven to be indispensable in physics and engineering are slowly percolating into neuroscience. Today most experimental neuroscientists accept simulations of single neurons as a legitimate scientific tool. Dr. Izhikevich is going to discuss the challenges and pitfalls of large-scale simulations of realistic brain models.

Dr. Izhikevich will also give a more technical colloqium on March 22 entitled:

"Polychronization: Computation with spikes"

Wednesday Match 22, 2005, at 2:00 p.m.
Tucker Technology Center 139

Abstract

The speaker will present a minimal spiking network that can polychronize, i.e., exhibit reproducible time-locked but not synchronous firing patterns with millisecond precision.
The network consists of cortical spiking neurons with axonal conduction delays and spike-timing-dependent plasticity (a ready-to-use MATLAB program and C++ program code are available at the author's webpage). It exhibits sleep-like oscillations, gamma (40 Hz) rhythms, conversion of firing rates to spike-timings, and other interesting regimes. Due to the interplay between the delays and plasticity, the spiking neurons spontaneously self-organize into groups and generate patterns of stereotypical polychronous activity. The number of co-existing polychronous groups far exceeds the number of neurons in the network, resulting in an unprecedented memory capacity of the system. The speaker is going to speculate on the significance of polychrony to the theory of neuronal group selection (TNGS, Neural Darwinism), cognitive neural computations, binding and gamma rhythm, mechanisms of attention, and consciousness as "attention to memories".

This talk is based on the recent paper published in Neural Computation and available at http://www.nsi.edu/users/izhikevich/publications/spnet.pdf

For directions to the Sid Richardson Building see map, or contact the TCU Department of Physics and Astronomy at 817-257-7375.

Contact person: Dr. Miller