Colloquia held Fall Semester, 2004

Sept. 14, 2004
Dr. Floyd D. McDaniel
Department of Physics
University of North Texas
"Physics Research at UNT"

Sept. 21, 2004
Dr. Tom Cundari
Department of Chemistry
University of North Texas
"de Novo Structural Predictions for Chemical Compounds"

Sept. 28, 2004
Dr. Michael Fanelli
Department of Physics
University of North Texas
"Early-type Galaxies in Extremely Isolated Environments: Probing Galaxy Evolution"
We explore the nature and evolutionary paths for nine early-type galaxies known to exist in extremely isolated environments. These systems forma a baseline for understanding the role of interactions in galaxy evolution. One goal is to assess whether these systems are the remnants of a merged galaxy group. A second goal is to search for "pristine" galaxies, systems expected to be amongst the first generation of galaxies. We find that this sample is under luminous by at least a magnitude compared with objects interpreted as merged galaxy groups. The properties of four objects are consistent with merger remnants, as indicated by their disturbed morphology, apparent tidal features, and blue optical colors. Two systems appear to be isolated lenticular galaxies with no evidence of a merger history. Based on their red colors, global light distribution, and the absence of morphological peculiarities, two galaxies are found to be excellent candidates for possibly-evolving primordial elliptical galaxies, formed early in cosmic time.

October 5, 2004
Dr. Wolfgang Schleich
Abteilung fur Quantenphysik
Universitat Ulm, Germany
"Quantum Ulm Sparrow: Scattering of Rotor from a Slit"
In classical physics scattering of an object from a slit is determined by the geometrical cross section. This statement summarizes the lesson drawn from the Ulm sparrow. But how does this situation translate into the microscopic world? In this talk we consider the scattering of a rotor from a slit in the limit when the length of the rotor is larger than the size of the slit. We show that due to the wave nature of the rotation the transmission probability is reduced by an exponential factor originating from the tunneling through a potential imposed by the boundary conditions of the slit. Moreover, we discuss possibilities to realize such an experiment using fullerenes and Bose-Einstein-condensates.
Background:
Once upon a time, the continuing construction of the Ulmer Munster towers made it necessary to haul big pieces of lumber through the narrow gates of the city. It is a famous tale that once a teamster and his cart were prevented from entering the city by logs which lay crosswise on the cart, but were wider than the gate. The first reaction of the stupefied citizens was to enlarge or tear down the gate. Fortunately, this desperate measure was made unnecessary when the people observed a sparrow with a straw in his beak trying to fly through the narrow entrance of his nest. While passing the slit he rotated the straw to line it up with his path. Since then the sparrow has become a symbol of Ulm and until today he rests on the roof top of the Ulmer Munster.
 

October 19, 2004
Dr. Constantino Tsallis
Brazilian Center for Physics
Rio de Janeiro
"Complexity and Nonextensive Entropy"
Boltzmann-Gibbs entropy and statistical mechanics are well fitted for systems whose dynamical microscopic evolution is consistent with strong sensitivity to initial conditions. This appears not to be the case for vast classes of natural and artificial complex system that exhibit weak sensitivity to initial conditions instead. For these systems we propose an entropy that is non-extensive and generalizes that of Boltzmann-Gibbs. This non-extensive statistical mechanics has typical functions that are power laws instead of exponentials. This theory has a natural connection with at least many complex systems. An introduction to the subject will be given, as well as some recent applications to paradigmatic nonlinear dynamical systems. 
Bibliography:  
(1) Non-extensive Entropy - Interdisciplinary Applications, Eds. M. Gell-Mann and C. Tsallis (Oxford University Press, New York, 2004); (ii) http://tsallis.cat.cbpf.br/biblio.htm 

October 26, 2004
Dr. Terry Golding
Department of Physics
University of North Texas
"Next Generation Opto-electronic Materials: the Need to Integrate with Silicon"
Silicon is the foundation material for the vast majority of electronic devices. However, it possesses an indirect band-gap that makes it far from ideal for opto-electronic device applications. The increasing commercial and military need for photon detectors and emitters, such as infrared, wireless communications, solid state lighting, and intelligent lighting sources necessitates the continuing development of optically active materials that target these technologies. Si electronics are so ubiquitous that integration of these materials with Si is almost demanded in all but the most customized of devices. It is expected that future generation opto-electronic devices will require either direct synthesis on Si, or be based on Si. In this talk I present the physics, materials, and engineering considerations of three materials systems and/or programs that are being developed by us specifically for applications ranging from visible light emitting diodes to the next generation infrared focal plane arrays. 

November 3, 2004
Dr. Zhibing Hu
Department of Physics
University of North Texas
"Smart Gels for Biomedical and Pharmaceutical Applications"
That interdisciplinary research can lead to technology breakthroughs is illustrated by a case study of smart gels. These materials are water-based, gelatin-like polymers that can be programmed to expand and contract in response to changes in temperature, pH or electric fields. They are particularly useful in biomedical and pharmaceutical applications due to their high water content, which is similar to natural tissue. Some water-based gels also are compatible with human physiology - they are nontoxic and easy for the human body to break down. Some examples are given drawn from current studies by both our group and others, including applications to disposable diapers, magnetic resonance imaging, protein separation, biodegradable vascular stents, contact lenses, and controlled drug delivery devices for the treatment of diabetes. Recently, gels with nano-structures have been created, for applications in everything from novel jewelry to sensors that can detect glucose concentration in the body. 

November 9, 2004
Dr. Greg Sherman
Department of Physics
Texas Christian University
"Synchronous Inter-ferometric Probing of Microscopic and Nano-scale Materials"
A new method for the rapid detection and tracking of individual microscopic and nano-scale particles is demonstrated, based on inexpensive, low-power, diode-laser light sources and photodiode receivers. Using a swept standing-wave laser probe and a phase-sensitive detector, single micrometer-sized particles are simply and easily monitored via the scattered light in the far field. This presentation will report on the verification and testing of the method via detailed measurements and theoretical modeling of signals from mounted and oriented micro-fibers. Also, results of particle sizing measurements for distributions of metallic and nonmetallic micro-particles will be given, with comparative sizing obtained from optical and electron microscopy.

Nov. 16, 2004
Dr. Vsevolod Gantmakher
Institute of Solid State Physics
Moscow, Russia
"Metal-Insulator Transition in High-Density Electron Gas"
Analysis of experimental data shows that the metal-insulator transition is possible in materials composed of atoms of only metallic elements. Such a transition may occur in spite of the high concentration of valence electrons. It requires stable atomic configurations to act as deep potential traps absorbing dozens of valence electrons. This means that bulk metallic space transforms into an assembly of identical quantum dots. Depending on the parameters, such a material either contains de-localized electrons (metal) or does not contain such electrons (insulator). The degree of disorder is one of these parameters. Two types of substances with such properties are discussed: liquid binary alloys with both components being metallic, and thermodynamically stable quasi-crystals.

Nov. 23, 2004
Dr. Anju Sharma
Department of Physics, University of North Texas
"Radiation-induced Effects in Silicate Glasses: Applications in Photonics"
Silica based glasses are widely used in photonics. Glasses can be doped with rare-earth ions, high refractive index ions or micro-crystallites, which give them a great potential to be used as lasers, optical amplifiers and non-linear optical materials. I will talk about the radiation-induced effects in silicate glasses and their applications to photonics. An in situ study of the modification of glass structure under x-rays and/or very low energy electron beam using x-ray photoelectron spectroscopy (XPS) is reported. I will discuss structure and optical properties of the defect centers created during irradiation. Radiation-enhanced ionic mobility in glasses is used to confirm the point-defect centers created during irradiation. Radiation-enhanced ionic mobility in glasses is used to confirm the point-defect model for ion-transport in glasses. These radiation-induced effects may be applied to the fabrication of metallic nano-clusters and control of their size-distribution in metal-doped, metal-implanted glasses, to wave guide fabrication, and to radiation sensors.