Colloquia held Spring Semester, 2007

January 30, 2007
Dr. Paolo Grigolini
Department of Physics
University of North Texas
"From Schastic Resonance to Complexity Matching"
We propose a definition of complexity based on the observation that self-organization and synchronization of individual constituents (“neurons”) generate non-ergodic and non-Poisson renewal events. We define a system as complex if it produces non-ergodic and non-Poisson sequences of events. A complex system is characterized by a complexity index m, ranging from 1 to 2. We also illustrate a technique of statistical analysis of real data to assess if a system is complex and what is its complexity index. We show how this technique works with applications to EEG data and to music composition. We prove that complex systems do not respond to harmonic perturbations. The popular phenomenon of stochastic resonance can be interpreted as a form of rate matching. This explains why systems without a fixed time scale cannot respond to perturbations producing a finite number of events per unit of time. With the same arguments we conclude that the transfer of information from a complex perturbation with index m(P) to a complex system with index m(S) reaches a maximum efficiency at the matching point m(P) = m(S).

February 6, 2007
Department of Physics
University of North Texas
"The Day After Trinity"
We will show the DVD entitled "The Day After Trinity" about the atomic bomb project that features interviews with some of the people who were directly involved including J. Robert Oppenheimer, the director of the project.

February 13, 2007
Department of Physics
University of North Texas
"BigIdeas Video: 'Einstein's Dream' "
This video focuses on the efforts to complete Einstein's quest for a unified field theory that would explain all the four fundamental forces of nature - strong, electromagneta, weak, and gravitational forces.  The video has interviews with physicists working on string theory and M-theory, like Edward Witten, Nathan Seiberg, and Juan Maldacena.  Freemason Dyson gives a more skeptical view of string theory.  Segments highlighting Einstein's research are also included.  (57 min., color)

February 20, 2007
Professor M. Howard Lee
Department of Physics
University of Georgia
Athens, Georgia
"How Valid is Boltzmann's Ergodic Theory?"
Statistical mechanics considers Boltzmann's ergodic hypothesis one of its foundations.  But is the hypothesis really valid?  If so, how widely?  In 1931 G. D. Birkhoff, a noted mathematician, gave a theorem which is said to prove the hypothesis under certain terms. But the terms are so abstract (e.g. metrical transitivity, sets of measure zero) that it is difficult for most physicists to know whether the hypothesis is valid in a given case. In 2001 I deduced an ergodic condition from physical theory.    It is simple enough to show when a system is ergodic and why it is. This ergodic condition is applied  to Birkhoff's theorem to reveal the domain of its validity.*

*Based on an article by the speaker entitled "Is Birkhoff's ergodic theorem realizable through many-body response function? (to appear in Phys Rev Lett 2007)

February 27, 2007
Dr. Gennady Shvets
Department of Physics
University of Texas, Austin
Austin, Texas
"Metamaterials Based on SiC Films: How to Make a Superlens in Mid-infrared"
The wavelength of light places a natural limit on the resolution of an optical system. Overcoming this limit and constructing a “super-lens” is one of the main motivations of the recently emerged area of Negative Index Meta-materials (NIMs) with negative dielectric permittivity e and magnetic permeability m. While several designs of optical NIMs based on antenna-type resonances have been recently put forward, the key challenge remains: how to miniaturize a unit cell of a NIM to be much smaller than the wavelength. A new approach to miniaturizing NIMs based on resonant plasmonic nanostructures and the corresponding super-lens will be described.  Even when m > 0, near-field super-lensing is possible with e < 0 materials. Experimental demonstration of a near-field super-lens in the mid-infrared (around 11 microns) range will be described. The lens is implemented using crystalline SiC films that have remarkable infrared properties: they support surface polaritons with less damping than most metals. Two demonstrations of super-lensing with  l/20 spatial resolution will be demonstrated: (a) using FTIR microscopy, and (b) by direct near-field probing with NSOM. Both amplitude and phase-sensitive imaging is demonstrated. It is also demonstrated that super-lensing can be used for deep sub-surface imaging.  We will also describe our recent experimental and theoretical work on extraordinary optical transmission and absorption through subwavelength hole array in mid-IR and describe possible applications to developing highly efficient sources of tunable thermal radiation.

March 6, 2007
Professor Efstathios E. (Stathis) Michaelides
Mechanical and Energy Engineering
University of North Texas
Denton, Texas
"Analogies in the Transient Equation of Motion and Energy Equation for Particles, Bubbles, and Drops"
The transient Lagrangian equation of motion for spheres under creeping flow conditions is composed of three terms:  the steady-state term, the added/virtualmass term and the history/Basset term.  The last two terms are transient and arise from the potential flow of the fluid around the sphere and from the diffusion of vorticity.  The presence of the history term makes the equation of motion an integrodifferential equation and hence, more complex to solve.  The rigorous solution of the transient heat/mass transfer equations around a sphere at creeping flow conditions (very low Pe) also reveals the existence of a history term associated with the diffusion of the temperature gradients.  The added mass term in the momentum equation arises from the potential flow around the sphere. An analogous term does not exist in the transient energy equation.  We examines the analogies of the form of the transient equations for momentum and energy at zero and finite Reynolds and Peclet numbers for spheres and ellipsoids as well as the effect of shape of the particles on the form of transient terms.  It also addresses the question as to when the contribution of these history terms is significant in the heat and mass transfer processes from particles, bubbles and droplets.

March 13, 2007
"Starman" Ron DiIulio
Planetarium and Astronomy Lab Director
Department of Physics
University of North Texas
Denton, Texas
"Astronomical Spectroscopy: New Tools and Techniques"
Meaningful Astronomical Spectroscopy was previously limited to astrophysicists with large research budgets. With the recent developments in CCD imaging technology as well as the introduction of several reasonably-priced high-resolution spectrographs, UNT students have some additional opportunities to gather data that can assist professional astronomers in several areas of study. I will briefly review that history and development of spectroscopy as an astronomical tool. Several new spectroscopes will be presented, and software will be demonstrated that dramatically enhances data collection. Also, several student/professional partnership projects will be presented.

March 19, 2007
Professor Chi Wu
Departments of Chemistry and Physics
The Chinese University of Hong Kong
Hong Kong, China
"Ultra-filtration of Macromolecules through Nanopores"
Using a special double-layer membrane to avoid interaction among flow fields generated by different pores, we have, for the first time, observed the predicted discontinuous first-order transition in ultra-filtration of flexible linear polymer chains. Namely, the chain could pass through a pore much smaller than its unperturbed radius only when the flow rate is higher than a certain value. When only one chain and one pore considered in theory, such a threshold is surprisingly independent of both the chain length and the pore size. Our results reveals that for a membrane with many pores and at a microscopic flow rate  (q) lower than the threshold, the inevitable blocking of some pores by longer non-stretched coiled chains increases q in those non-blocked pores because the macroscopic flow rate (Q) is a constant.  Our results reveal that the force to stretch a polymer coil in an athermal solvent is only ~10 fN. Further, using this method, we are able to measure how "soft" a polymer chain is and how strong the inter-chain interaction is when they are collapsed and entangled with each other.

March 27, 2007
Dr. Reiko Lukic-Zrnic
Department of Physics
University of North Texas
Denton, Texas
"Temperature Dependence of the Energy Gap of GaAsSb Alloys grown by MBE"
Ternary and quaternary III-V semiconductor alloys are of significant technological importance because they can be tailored to achieve important electro-optical properties, such as lattice constant, energy gap and carrier potential profile, by variation of the alloy composition. It was first believed that the energy gap of III-V alloy depends only on the composition. However energy gap variations of more than 100 meV were observed in GaInP alloys grown lattice matched on GaAs substrates. This variation was described as a result of atomic ordering, which refers to additional periodicity imposed on the initial crystal structure. To date, many experimental and theoretical works have demonstrated that atomic ordering will not only reduce the energy gap, but will also affect other properties, such as valence band splitting, change in the carrier effective mass, anisotropy of the transport and optical properties. The new crystal symmetry that results from atomic ordering leads to significant changes in the electronic band structure of semiconductor alloys. As a consequence, the electronic and optical properties of the material are altered, e.g., the energy gap decreases, carrier lifetimes are increased, new optical transitions are possible, and the ordered material shows a distinct optical polarization anisotropy due to a valence band splitting and altered optical selection rules.

We will report on our investigation of spontaneous atomic ordering in a series of GaAs1-xSbx epilayers (0.51 < x < 0.71) grown by molecular beam epitaxy (MBE) on GaAs substrates with different surface orientations.

April 3, 2007
Department of Physics
University of North Texas
"World Within Worlds: Development of 20th-Century Physics"
This DVD explores the world of the atom and traces the history of men and ideas that have made the 20th century one of the greatest achievements of human imagination.  It is volume 10 in the series "Ascent of Man."

April 10, 2007
Professor Wolfgang Schleich
Abteiling fuer Quantum Physik
University of Ulm
Ulm, Germany
"Factorization using Gauss Sums: Experiments and Ghost Factors"
Gauss sums play an important role in number theory. Moreover, they allow us to factor numbers. Factorization of numbers is an important issue in the context of cryptography. We first briefly introduce the method how to factor numbers using Gauss sums and then report several experiments [1]  that implement this factorization technique. We finally address the problem of ghost factors that appear in this method. In particular, we address the scaling properties of ghost factors.

[1] M. Mehring, K. Mueller, I. Sh. Averbukh, W. Merkel, and W. P. Schleich NMR experiment factors numbers with Gauss sums Phys. Rev. Lett.  98, 120502 (2007)

April 20, 2007
Dr. Jai N. Dahiya
Department of Physics
Southeast Missouri State University
Cape Girardeau, Missouri
"Significance of Microwaves in the the Environment"
The chemistry of carbon dioxide is one of the most interesting topics for scientists in this modern age of technology. Science has made such a tremendous progress in several fields and humanity is reaping the rewards of this important progress. But at the same time this progress in technology has a big price tag for humanity to pay in terms of pollution that we as human beings have to face. The Green House Effect is one of the hottest topics of this modern technological era. A significant percentage of this problem is the presence of carbon dioxide in the atmosphere that is depleting the ozone layer. This is a very critical problem and the problem is based on the unavoidable production of carbon dioxide in this modern technological world. In the research experiment there is a possible solution to this problem in which one can make use of the CO₂ molecule and avoid it’s exposure to the atmosphere. The main goal of this research experiment is to activate and utilize the CO₂ molecule by using microwave technology.

April 23, 2007
Dr. Miguel Mayorga-Rojas
Department of Physics
Universidad Autonoma del Estado de Mexico
Toluca, Mexico
"Effect of Tuning Interactions in Colloids"
We show the existence of precursors of crystalline and amorphous phases prior to the appearance of freezing and glass transitions in colloidal systems. The formation of crystalline or amorphous clusters can be controlled by tuning the parameters of a proposed continuous potential and by altering the packing conditions. The resulting arrays are driven by diffusion. When the system is under a temperature gradient, the control of thermal diffusion effects in colloidal dispersions can also be accomplished by tuning their interactions. When the temperature gradient is created by radiation from a laser beam, we discuss the conditions to design thermophoretic traps in order to characterize and micromanipulate colloids. As a final part of the talk we review the current graduate research program of the physics department at UAEM.

April 24, 2007
Dr. Roberto Reno
Department of Financial Mathematics
University of Siena
Siena, Italy
"Volatility of Financial Data"
I will illustrate econometric techniques to measure the volatility of financial data and its link with volume and serial correlation.

Roberto Reno is Associate Professor at the Faculty of Economics of the University of Siena since 2006. He joined the University of Siena in 2001, as Assistant Professor. He has a Ph.D. in Financial Mathematics from Scuola Normale Superiore, Pisa, Italy, and a Degree in Physics from the University of Pisa. His research interests are mainly focused on financial econometrics: volatility modelling and measuring, links with volume and serial correlation, nonparametric estimation of continuous time stochastic processes. He is a coauthor of several publications in international journals.

April 27, 2007
Professor Marlan O. Scully
Department of Physics
Texas A&M University
College Station, Texas
and
Princeton University
Princeton, New Jersey
"Dimensional Scaling Approach to the Chemical Bond"
We present a new dimensional (D-) scaling transformation of the Schrödinger equation for the two-electron bond that is simple and surprisingly accurate. There also emerges an intuitively appealing semi-classical picture in the large-D limit, similar to Bohr’s model. A first-order perturbation correction in 1/D improves agreement with the exact ground-state energy. The method provides potential curves for the lowest singlet, triplet, and excited states of H₂. Other application will also be discussed

Click here to see Dr. Scully's PowerPoint Presentation

May 1, 2007
Dr. Gerard Aquino
Max-Planck-Institut fuer Physik Komplexer Systeme
Dresden, Germany
"Memory Effects in Solvable Model for Structural Glasses"
Temperature shift protocols first applied by A.J. Kovacs on glassy polymers [Adv. Polym. Sci. 3, 394 (1963)], are known to produce surprising "memory effects" in the response of the system.  We implement these protocols in an exactly solvable dynamical model for structural glasses.  This model is characterized by interacting fast and slow modes represented respectively by spherical spins and harmonic oscillator variables. Due to this fundamental property, the model is able to reproduces both the characteristic non-monotonic evolution known as the "Kovacs effect" and the classical "memory" effect on the susceptibility, first observed in spin glasses. The Kovacs effect is observed in polymers, in granular materials and models of molecular liquids when similar experimental protocols are implemented.