Colloquia held Fall Semester, 2006
September 12, 2006
Dr. Christopher Littler
Department of Physics
University of North Texas
"Physics Research at the University of North Texas"
Various research groups at the University of North Texas, Department of Physics,
will give short presentations about their research and research groups.
September 19, 2006
Dr. Carlos Bertulani
Department of Physics
University of Arizona
"Stellar Reactions on Earth"
The most fundamental question in nature is where do we come from or from what
are we made? At the heart of this question is the process of nucleosynthesis. I
will discuss the challenges in obtaining the nuclear physics input for the Big
Bang and stellar evolution. Then I will show how a new generation of theoretical
developments and experiments can shed light on the complex nuclear processes
that control the evolution of stars and stellar explosions.
September 26, 2006
Endre Kajari
Abteilung fur Quantenphysik
University of Ulm, Germany
"The Sagnac Effect in Goedel's Universe"
A Sagnac interferometer serves as a measuring device for any kind of rotation,
whether it comes from a rotation of a reference frame or the curvature of
spacetime itself. After an overview of the operation of a Sagnac interferometer
and its general applications in every day life, I will show to describe a Sagnac
interferometer within the framework of general relativity. In this context, the
Sagnac time delay for a rotating frame of reference in flat Minkowski spacetime
will be compared with the analogous time delay in the spacetime described by
Goedel's universe. I will give a short introduction to some curious properties
of Goedel's universe, such as closed timelike worldlines that provide the
opportunity for time travel. The Sagnac time delay in both spacetimes is almost
the same.
October 3, 2006
Dr. Wolfgang Schleich
Abteilung fur Quantenphysik
University of Ulm, Germany
"Quantum Physics and Number Theory"
An intimate connection appears to exist between quantum mechanics and number
theory. This connection appears in (1) factorization of numbers using a quantum
computer, (2) security of codes due to the use of single photons and (3) the
similarity of the statistics of energy levels of a billiard and the zeros of the
Riemann zeta function. We illustrate this connection using two additional
examples. i) Numbers can be factored using Gauss sums. In particular we report
on an NMR experiment using this technique that has factored a six-digit number.
ii) The connection between Schrödinger cats and the Riemann-Siegel formula that
describes the asymptotic behavior of the Riemann zeta function.
October 10, 2006
Dr. Jiuqing Liang
Institute of Theoretical Physics
Shanxi University
"Macroscopic Quantum Effects in Molecular Magnets"
In this talk we present a review of recent developments in experimental and
theoretical studies of quantum tunneling and macroscopic quantum effects in
molecular magnets. These molecular magnets not only possess properties of
macroscopic magnets, but also exhibit quantum behaviors like quantum tunneling
of the magnetization vector. We explain how to realize macroscopic quantum
coherence, namely the superposition of Schroedinger cat states and quantum phase
interference by means of quantum tunneling. The instanton method for evaluation
of tunneling rates for both ground states and excited states is introduced to
investigate tunneling effects in molecular magnets.
October 24, 2006
Dr. Laura Whitlock
Louisiana State University
Shreveport, LA
"Unraveling the Mystery of Gamma Ray Bursts"
Gamma-Ray Bursts (GRB) are one of the greatest mysteries in modern astrophysics
since their discovery in the late 1960s. These amazing events (1) emit
incredible amounts of energy, (2) are seen to occur roughly once a day from a
random location in the sky, (3) last for a few milliseconds to a few hundred
seconds, and (4) then never recur from the same location. Results from NASA's
Swift mission will be presented that allow us for the first time to get a handle
on GRB progenitors and dynamics. These results lead us to the next generation of
questions.
October 25, 2006
Dr. Bruce J. West
Department of Physics, Duke University &
Mathematics Division, Army Research Office
"Where Medicine Went Wrong"
Where Medicine Went Wrong explores how the idea of an average value has been
misapplied to medical phenomena, distorted understanding and lead to flawed
medical decisions. Through new insights into the science of complexity,
traditional physiology is replaced with fractal physiology, in which variability
is more indicative of health than is an average. The capricious nature of
physiological systems is made conceptually manageable by smoothing over
fluctuations and thinking in terms of averages. But these variations in such
aspects as heart rate, breathing and walking are much more susceptible to the
early influence of disease than are averages.
October 31, 2006
Dr. George Starkschall
University of Houston, Texas
"Frontiers in High-Precision Radiation Therapy"
The potential for improving the quality of radiation therapy for the treatment
of cancer has been enhanced by several technological developments over the past
several years, which continue to be the subject of considerable investigation.
Four-dimensional computed tomography imaging allows us to image explicit
respiratory motion, allowing custom design of radiation treatment portals for
the treatment of lung cancer based on the actual motion of the patient's tumor
during respiration. Image-guided radiation therapy images the patient
immediately prior to treatment delivery, allowing for major reductions in
uncertainties in patient setup and corrections for interfractional variations in
patient anatomy. The use of protons for radiation therapy reduces the radiation
dose to tissue lying beyond the tumor target so less radiation is delivered to
uninvolved critical anatomic structures and consequently less reaction.
Challenges still remain in the translation of these technologies from the
research laboratory into the routine practice of radiation oncology.
November 2, 2006
Dr. Arkadii Krokhin
Department of Physics
University of North Texas
Optics of Photonic Crystals
Photonic crystals are new artificial optical structures that give a possibility
to control light similar to the way semiconductors to control electric currents.
Photons propagating in a photonic crystal “feel” a periodic distribution of the
dielectric material. Due to this periodicity the dispersion law for photons
becomes very different from the dispersion in a homogeneous dielectric. A
photonic crystal can be specially designed to possess optical properties that do
not exist in natural optical crystals, e.g. photonic band gaps, strong
anisotropy, negative index of refraction, etc. I will present a theory that
predicts and explains some exotic optical properties of photonic crystals.
November 7, 2006
Dr. Peter Halevi
Instituto Nacional de Astrofisica, Optica y Electronica (INAOE)
Tonantzintla, Puebla, Mexico
Photonic Metamaterials
This talk is an introduction to novel materials that can do funny things to
light; for example, refract a ray "the wrong way"! That's a negative angle of
refraction - and a negative refractive index! Metamaterials have thus rightfully
earned the prefix "meta", meaning "beyond" in Greek - beyond Nature. A photonic
metamaterial is constituted from a microstructure (for instance, some
configuration of thin wires), which is then repeated in all three spatial
directions. A recent "mean-field" theory, developed in collaboration with F.
Perez-Rodriguez, paves the way to a very general continuum description of the
constitutive relations between the fields E, B, D, and H.
November 14, 2006
Dr. Wolfgang Rindler
Department of Physics
University of Texas at Dallas
Richardson, Texas
Goedel, Einstein, Gamow, Lanczos and the Universe
Since this year is the centenary of Kurt Goedel's birth, it is fitting that we
celebrate his work, even in a physics department, though Goedel was a
mathematician. His one contribution to physics was the famous and paradoxical
rotating Goedel Universe of 1949, a birthday gift to his friend Albert Einstein.
I shall sketch the background to this discovery, Georg Gamow's crucial role in
it, and how Cornelius Lanczos nearly scooped Goedel 25 years earlier. I shall
also sketch out a simplified construction of this model and give a simple
description of its properties.
November 21, 2006
Professor Masaru Kuno
Department of Chemistry and Biochemistry
University of Notre Dame
South Bend, Indiana
Solution-based Semiconductor Nanowires: New Opportunities in
One Dimension
I will describe recent developments in the synthesis and characterization of
solution-based semiconductor nanowires (NWs). We have found low temperature
routes to high quality CdSe, CdTe and PbSe NWs with diameters < 12 nm. The wires
are within the confinement regimes of each material. Variations in the synthesis
lead to branched NWs with characteristic tripod, v-shape, y-shape, t-shape and
“merge-y” morphologies. “Higher order” NWs exhibiting multiple branching points
are also observed. The branching can be explained through the presence of phase
admixtures in the wires, as well as through a “geminate” NW nucleation
mechanism. Optical studies of the NWs both at the ensemble and single wire
levels have also been conducted. While ensemble transient differential
absorption experiments provide various intraband and interband relaxation rates,
single NW measurements have shown unusual optical heterogeneity. Both spectral
diffusion and fluorescence intermittency are observed in straight and branched
CdSe NWs. Identical power law blinking kinetics, as seen in colloidal CdSe
quantum dots, are seen. This suggests a direct connection between the two
pheonomena. Current studies are focused on addressing the physical origins of
intermittency in NWs. External electric field measurements have been very
suggestive of the possible role mobile surface charges play in the phenomenon.
We have utilized the NWs in polarization sensitive photodetectors using our
ability to align the wires using dielectrophoresis. Clear polarization sensitive
responses are seen with anisotropies in line with corresponding values from
ensemble/single wire absorption/emission polarization anisotropy measurements.
November 28, 2006
Dr. Bibhudutta Rout
Louisiana Accelerator Center
University of Louisiana at Lafayette
Lafayette, Louisiana
Materials Analysis and Micro-fabrication with High-Energy
Focused Ion Beams
High Energy Focused Ion Beam Systems (HEFIB) are extremely powerful tools that
utilize ion beam analytical techniques as microscopies with probe dimensions in
the micro-nano meter range. It is now possible to carryout routine
multi-dimensional materials analysis in a wide range of fields involving
semiconductors to biomaterials. Recently the HEFIB systems have been used quite
extensively for synthesis of patterned micro-nano structures in resists as well
as semiconductor materials. We will be discussing the capabilities of these ion
microprobes in materials analysis as well as micro-fabrications with some
classic examples.