Colloquia held Spring Semester, 2005
January 25, 2005
Dr. Yongbin Chang
Department of Physics
University of North Texas
"The Concept of Collision Strength"
In our experience we may have some intuition about whether a given collision is
strong or weak. However, no quantitative definition of collision strength has
previously been given that has universal acceptance. In this colloquium we first
will review older definitions of collision strength. Then we will present a new
definition that unifies the older definitions. Its advantages will be shown in
kinetic theory, chemical reaction theory, and plasma physics.
February 1, 2005
Dr. Samuel E. Matteson
Department of Physics
University of North Texas
"Doing Physics: Toward an Ethical Science"
In recent years notable scandals have shocked the physics community, prompting a
call for a review of ethical standards in the practice of physics. This lecture
will explore the various options for the formulation of a personal code of
professional ethics in our discipline and will, in particular, examine the Code
of Ethics adopted by the American Physical Society (APS). We will examine the
thesis that affirms that the common principles have pragmatic value and are
critical for the effective execution of the scientific enterprise. The lecture
will elaborate on these issues both by exposition and by audience participation
in case study analyses. The lecture is free and open to all interested parties.
February 8, 2005
Dr. Keith Johnston
Department of Chemical Engineering
University of Texas, Austin, TX
"Novel Strategies for Stabilization and Assembly of Metal and
Semiconductor Nanocrystals in Solution"
Silicon and germanium nanocrystals and nanowires are of interest in solid state
lighting, sensors, and many optoelectronic devices, including microprocessors.
Novel silicon and germanium nanoparticles and nanowires with discrete optical
transitions in the absorbance and photoluminescence excitation spectra have been
synthesized in solution at temperatures above 400 C. The high temperatures favor
crystallization. The solvent stabilizes hydrocarbon ligands providing steric
stabilization to control the particle size and optical properties.
Environmentally benigh carbon dioxide-based solvent formulations may be utilized
to replace toxic organic solvents for syn thesis and assembly of nanocrystals
and in processing of wafers in microelectronics. The nanocrystal interactions
may be manipulated by tuning the density of the supercritical solvent as
measured by small angle X-ray scattering (SAXS) and spectroscopy. The excellent
wetting properties of liquid carbon dioxide favor the formation of uniform
nanocrystal coatings. We observe the time-dependent structural reorganization of
monolayers of gold nanocrystals deposited from liquid carbon dioxide. The
nanocrystal organization kinetics are dominated by ensemble reorganization. The
final example uses water droplets formed by condensation from the gas phase into
evaporating organic solvent films to produce ordered holes. We describe the
single-step self-organization of nanocrystal superlattice films infused with
spatially ordered arrays of micrometer-size pores of interest for single-chip
integration of photonic and electronic technologies.
February 15, 2005
Dr. Wayne Holland
Department of Physics
University of North Texas
"Ion Beam Synthesis of Si-based Material for Photonic
Applications (and More)"
Ion beams are useful for structural and compositional analysis of materials, as
well as to modify the properties of materials. Different ion beam techniques
will be presented with examples given from a variety of material systems. Also,
ion beam synthesis of novel materials in silica with interesting luminescent
properties will be discussed. The list of synthesized materials ranges from a
variety6 of semiconducting silicides and their alloys to quantum-confined dots.
February 24, 2005
Dr. Marlan O. Scully
Department of Physics
Texas A&M University
"Information Erasers: From Maxwell's Demon to Wigner's Friend"
February 25, 2005
Dr. Miguel Mayorga Rojas
Departmento de Fisica
Universidad Autonoma del Estado de Mexico
"Phoretic Phenomena, Freezing and Glassy-structure Precursors in Colloids with
Tunable Interactions"
We show that control of thermal diffusion effects in colloidal dispersions can
be accomplished upon tuning interactions between particles. For the first time
we derive a virial expansion of the Soret coefficient which takes into account
the type of interaction potential as well as the nature of the particles. Our
results are compared with experiments in micellar dispersions and DNA. On the
other hand, using a non-equilibrium statistical mechanics approach, we study the
implications of changing the softness of the repulsive and th attractive part of
the phase transitions of sterically stabilized colloids. We identify structural
precursors of freezing in the pair correlation function using molecular dynamics
simulations. Even if such precursors are similar to the one observed in the hard
spheres systems, we emphasize that the structural features can emerge from
particles with soft tunable interactions too. We discuss the implications of
such tuning in the phase transition in colloids and in the dynamics of the slow
structural relaxation in supercooled colloidal liquids.
March 1, 2005
Dr. Janos A. Bergou
Department of Physics and Astronomy
Hunter College, City University of New York
"State Discrimination: A Novel Quantum Information Paradigm"
In quantum information and quantum computing, the carrier of information is a
quantum system and information is encoded in its state. We want to find the
optimum measurement that extracts the maximum information about the state which
is a task in measurement optimization. Reading out the informatio requires the
determination of the state of the system. It is different from the usual quantum
measurement since we are not interested in the average value of some physical
observable. Every time a system reaches the output we want to determine its
state. Since the state is not an observable, this sounds at first as an
impossible task. However, quantum processors are designed in such a way that
their output is a member of a set of known states, so we are facing the more
modest problem of determining which of these states was realized. If the
possible target states are not mutually orthogonal the problem is difficult and
optimization with respect to some reasonable criteria leads to highly nontrivial
measurement strategies. Finding the optimal measurement strategy is the subject
of state discrimination. We discuss programmable quantum state discriminators
that are universal, i.e., they perform optimally on average, independently of
the actual states used for the communication scheme. We conclude with possible
experimental implementations of this device along with algorithmic and
cryptographic applications.
March 8, 2005
Dr. James L. Horwitz
Department of Physics
University of Texas at Arlington, TX
"Space Plasma Research at the University of Texas at
Arlington"
To zeroth order the Earth's magnetosphere is a comet-shaped magnetic cavity
embedded in the solar wind plasm flow. However, plasmas of varying density,
composition and energy are in fact found throughout the magnetosphere. The
sources for this magnetospheric plasma are the solar wind and the terrestrial
ionosphere. We describe recent spacecraft observations and simulations of
characteristics and transport of ionospheric plasma between the topside
ionosphere and lower magnetosphere at high latitudes. The ionospheric plasma
observations are from instruments aboard the POLAR, SMSP and IMAGE spacecraft,
particularly the Thermal Ion Dynamics Experiment (TIDE) on POLAR. The
simulations are from our Dynamic Fluid-Kinetic (DyFK) model, which couples a
fluid treatment of the ionosphere to a semi-kinetic or hybrid (ions as
particles) treatment for the transport. Among the processes incorporated in
these simulations are the effects of ionospheric ionization and thermal electron
heating from soft auroral electron precipitation and wave-driven transverse ion
heating at higher altitudes. We discuss observations of field-aligned
ionospheric ion flows in the vicinityh of auroral forms, near-simultaneous
multi-spececraft observations of topside/magnetospheric field-aligned flows,
simulations of the syn ergistic effects of soft electron precipitation and
transverse ion heating on the outflows, and observations of a recurrent "trough"
feathere in O+ densities in the polar cap region.
March 22, 2005
Dr. Wolfgang Schleich
Abteilung fur Quantenphysik
Universitaet Ulm, Ulm, Germany
"Michelangelo Sculpturing of a Non-spreading Wave Packet in
Imaginary Potentials"
We propose and experimentally demonstrate a method to prepare a non-spreading
atomic wave packet. Our technique relies on a spatially modulated absorption
constantly chiseling away from an initially broad de Broglie wave. Heisenberg's
uncertainty principle puts a limit to this contraction and determines the final
complex Gaussian form of the packet. Experimentally we confirm the predicted
formation process of the wave packet by observing the evolution of the momentum
distribution. Moreover by employing interferometric techniques we measure the
predicted quadratic phase across the wave packet.
March 29, 2005
Dr. August Lau
Senior Scientist, Apache Corporation
Houston, TX
"Geophysics and Topology: Applications to Oil Exploration and
Theoretical Wave Propagation"
My talk is in two related parts. Part I will deal with the use of geophysics
(specifically seismic methods in oil and gas exploration and in Part 2 will
describe theoretical wave propagation in complex topology. In Part I will be
about the seismic experiment that can be roughly divided into three aspects. (1)
Acquisition involves seismic sources and receive in the field. (2) Processing
involves converting seismic traces to 2- or 3-dimensional images of the earth.
(3) Interpretation involves the interpreting seismic images to find places to
drill for oil and gas. Examples will be given to show how seismic experiments
are used to find oil and gas reserves, which is a multi-billion dollar business.
Part 2 is motivated by multiple scattering (simply called multiples). The
multiples in wave propagation have led to misinterpretation of seismic data
which may mean unsuccessful wells. Theoretical wave propagation in complex
topology has helped in understanding many imaging problems in seismic
processing. We will introduce complex topology by using inverse limit space and
semigroup concepts. These seemingly abstract constructs have yielded better
models of multiples.
Dr Lau's Power-Point
Presentation - Click
on button
April 7, 2005 (Thursday)
Dr. William P. Latham
Air Force Research Laboratory
Directed Energy Directorate
Tactical Laser Systems Branch AFRL/DELS
"Ultrashort-Pulse Laser Interaction with Matter: Novel Sources
for Materials Research"
Abstract: Ultrashort pulse lasers have rapidly progressed over the past several
years. These laser sources are now capable of producing pulses that are less
than one femtosecond in duration with extremely high irradiances and peak powers
that are well over a Petawatt. Since their invention, femtosecond lasers have
been utilized as probes to understand the basic interaction rates in solid
materials. As the pulse lengths have continued to be reduced, the experiment and
theory of the interaction of ultrashort pulse lasers with materials has been
continued to improve the physical understanding of physical processes within
these materials. The area has become a vast and active area of research
throughout the international laser, physics, and materials community. When
interacting with some materials, ultrashort pulse lasers can generate
high-energy particles or high-energy electromagnetic radiation. Ultrashort pulse
laser driven table-top sized particle accelerators, hard X-ray devices, and ion
accelerators will soon be available. Small-scale particle accelerators could
potentially replace large scale national facilities. I will discuss the current
status of ultrashort-pulose lasers and their application for particle
accelerators and electromagnetic wave generation. I will also review the current
status of material response and hot electron properties due to irradiation of
metals with ultrashort laser pulses.
April 12, 2005
Dr. Arup Neogi
Department of Physics
University of North Texas
"Nanoscale Material System for Optoelectronics and
Biophotonics"
Abstract: A novel nanoscale material system based on wide-bandgap semiconductor
quantum dots and micro-structures has been developed for optoelectronic emitters
and biomolecular detectors. Far-field and near-field emission techniques have
been used to investigate the optical properties of self -assembled GaN quantum
dots. We are also studying high contrast photonic crystals based on hybrid
organic-inorganic semiconductors to modify the spontaneous emission rate of a
quantum confined system. Nanophotonic detection schemes based on semiconducting
oligonucleotide sequences developed for the detection of biomolecular species
will also be discussed.
April 19, 2005
Dr. Charley Myles
Department of Physics
Texas Tech University
"Clathrate Semiconductors: Novelo Crystalline Phases of Group
IV Elements"
Abstract: In this talk, the clathrates and their crystalline structures will be
introduced. The results of calculations of equations of state, structural
parameters, electronic bandstructures, and vibrational spectra of some Si Ge and
Sn - based Type I and Type II clathrates will then be presented and compared
with experiment. These calculations were carried out using a first principles,
planewave, pseudopotential method. If time permits, some recent results on the
properties of the (so far hypothetical) C based clathrates will be discussed.
Dr. Myles PowerPoint presentation - click on button
April 26, 2005
Dr. Mike Fanelli
Department of Physics
University of North Texas
"Luminous Blue Compact Galaxies: Local Probes of Cosmic
Evolution"
Abstract: We discuss a program to explore the structural properties and
evolutionary history of luminous blue compact galaxies (LBCGs). These systems
are intrinsically bright [M(B) < -18.5], blue [-0.3 < (B-V) , 0.6]. IR-luminous
systems, whose morphological and photometric properties imply that they are
undergoing an episode of strongly enhanced massive star formation, on a scale
comparable to star formation rates expected of young galaxies in the early
universe. Luminous blue galaxies can be used to define local templates for
exploring galaxy evolution at all epochs. We have compiled a sample of LBCGs
using extant surveys of UV-far-IR and radio data from the literature. We derive
star formation rates (SFRs) for our primary sample based on their luminosities
as measured by IRAS For the -30 objects for which we have obtained optical
imaging data, we fine SFRs ranging from 1.8 to 47 M. yr-1, with a mean value of
~12.4. We compare the derived SFRs with values determine for normal and other
starburst systems. We also discuss initial results from the imaging campaign.
May 17, 2005
Dr. Wolfgang Schleich
Abteilung fur Quantenphysik
University of Ulm, Germany
"Hitler's Bomb"
Abstract: Recently a book “Hitlers Bombe” by Rainer Karlsch [1], published in
German has shattered the conventional wisdom about German nuclear weapons.. This
book claims that three tests of nuclear tactical weapons took place in the last
months of World War II. The first test supposedly performed on the Island of
Ruegen in October 1944 and two other ones in Thuringia in March 1945. In the
second experiment supposedly a few hundred inmates of a concentration camp were
killed. The experiments were conducted by the infamous SS and were directed by
Dr. Diebner and the head of the Uranverein, Professor Gerlach. Moreover, the
book claims that Dr. Diebner had a reactor that became critical in the fall of
1944. The book is highly controversial in Germany, but has received endorsements
from experts, such as Professor Mark Walker in America. In my talk I will give
an overview over the German efforts to harness nuclear energy. I will summarize
the main claims of the book without judging them. [1] Rainer Karlsch: Hitlers
Bombe (Deutsche Verlagsgesellschaft, Berlin, 2005)