Colloquia held Fall Semester, 2007

September 4, 2007
Dr. Christopher Littler
Department of Physics
University of North Texas
"Research in the Physics Department at UNT"
Dr. Chris Littler will welcome new students and introduce new faculty.  Faculty members will introduce themselves and give a short summary of their research interests.  

September 11, 2007
Dr. Paolo Grigolini
Center for Nonlinear Science
Department of Physics
University of North Texas
"Interacting Complex Networks"
My colloquium illustrates the approach to brain dynamics developed at the UNT Center for Nonlinear Science (CNS). According to this approach the stochastic synchronization of the neurons located on sites of a complex network generates intermittent clusters of synchronized neurons. The abrupt transmissions of synchronization from one cluster to another are non-ergodic and non-Poisson events, which control the brain’s response to external stimuli. This theoretical approach has shed light on the response of the brain to music. We show that a rigorous theoretical foundation of this effect rests on a new form of linear response, which is the basic theoretical tool to explain how complex networks interact.
 
Background: In the literature there is an increasing interest for the subject of complex networks. This interest has been generated by Watts and Strogatz, with their 1991 paper in Nature, proposing complex networks as a generalization of the random network theory developed by Renyi and Erdos in the late 50’s and early 60’s. The complex networks are considered to be a convenient representation of the structures of self-organized systems and are widely used for biological, sociological and technological applications. Neurophysiologists adopt this theoretical perspective to study the brain. There is an increasing conviction that brain function, including its cognitive aspects, emerges from fast process of neuron synchronization, which is favored by the complex network structure of the brain.

September 18, 2007
Dr. Zygmunt Gryczynski
Department of Molecular Biology and Immunology
University of North Texas
Health Science Center
"Fluorescence and FRET: Biophysical Applications"
In the last 20 years fluorescence spectroscopy becomes one of the dominant technologies in biology and biomedicine. Forster (Fluorescence) Resonance Energy Transfer (FRET) is probably one of very few exact physical approaches that is widely applied to study biomolecular processes with subnanometer resolution. Over the past decade we have witnessed remarkable advances in the application of FRET and optical microscopy to visualize dynamic processes in-vitro and inside the living cells. In this presentation we will address the technological developments in fluorescence, FRET, and FRET microscopy from the viewpoint of fundamental concepts, methods, and biological applications.  

September 25, 2007
DVD
NOVA Films
"Einstein's Big Idea: Understanding the equation that changed the world"
Part 1 of a NOVA DVD Based on David Bodanis’s best selling book, E=mc².  NOVA dramatizes how an obscure young patent clark, Albert Einstein, came up with his shattering 1905 discovery that the realms of matter and energy are inescapably linked.  A suspenseful epic, this film reveals the roots of this astonishing breakthrough in the human stories of men and women whose innovative thinking across four centuries helped to lead to E=mc², and ultimately to the release of energy from the nucleus.

This film includes the stories of Michael Faraday, Antoine Lavoisier, and Lisa Meitner and shows how they developed some of the basic ideas on which Einstein built.

October 2, 2007
Dr. Sam Matteson
Department of Physics
University of North Texas
Denton, Texas
"Knock on Wood: An Investigation of a Neglected Percussion Instrument"
Motivated by a desperate request from two of his former students to guide them in the construction of a set of “tuned” woodblocks to be used in a percussion recital, the author undertook a theoretical analysis and an experimental investigation of the acoustics of an instrument of innocuous simplicity, the orchestral woodblock.  Instead of a boring straightforwardness, he found that in this lowly instrument is a fascinating demonstration of the physics of flexural waves, the subtlies of the resonances of rectangular air ducts, the coupling of dissipative systems, as well as, an exhibition of the mechanical properties of wood, all encompassing several unsolved problems.  In the process the author has discovered that the woodblock comprises two coupled systems—a plate idiophone and a slot resonator, each with its unique and remarkable features. The lecture will provide a colorfully illustrated introduction to the subject of the acoustics of percussion instruments for the undergraduate and graduate physics student but will also be of interest to non-specialists, all of whom will find that the apparent simplicity of this neglected instrument belies the richness of its acoustics. 

October 9, 2007
Dr. Wes Borden
Department of Chemistry
University of North Texas
Denton, Texas
"Effects of Quantum Mechanical Tunneling on Reactions Rates in Organic Chemistry"
Quantum mechanical tunneling contributes to the rates of many chemical reactions. This lecture will discuss the conditions under which tunneling is likely to be important. The results of calculations of tunneling rates for several types of reactions will be presented. These results provide some purely experimental criteria that can be used to identify chemical reactions in which tunneling plays a dominant role.

October 16, 2007
Michael Eckart
Institute of Quantum Physics
University of Ulm
Ulm, Germany
"What's So Hot About Cold Atoms?"
The advent of Bose-Einstein Condensation at the end of the last century has stimulated unforeseen theoretical and experimental activities in the field of ultracold atomic physics. Efficient cooling methods paved the way for this development and will be reviewed in the first part of the talk. Thereafter we will discuss a variety of recent experiments to illustrate the broad scope of activities which make cold atoms such a hot topic. In the remainder of the talk two of our projects will be discussed which deal with the theoretical desciption of atoms in microgravity and in low dimensions, respectively.

October 23, 2007
Professor Tae-Youl Choi
Department of Mechanical and Energy Engineering
University of North Texas
Denton, Texas
“Small-Scale Thermal Science and Engineering”
I will introduce two nanosystems, and discuss how they are implemented in micro/nano-scale thermal science and engineering. The first part will focus on the utilization and characterization of nanosystems, i.e., carbon nanotubes. The measurement of thermal conductivity of carbon nanotube is presented. The thermal conductivity of individual multiwalled carbon nanotubes (outer diameter of 20~45 nm) is obtained by employing the 3-ω method. To this end, the third-harmonic amplitude as a response to the applied alternate current at fundamental frequency (ω) is expressed in terms of thermal conductivity. A microfabricated device composed of a pair of metal electrodes 1 μm apart is used to place a single nanotube across the designated metal electrodes by utilizing the principle of dielectrophoresis. Nanoengineering by focused ion beam milling (FIB) is implemented to provide a platform for nanoscale measurement. In the second part, small time-scale science and engineering will be discussed, in which a femtosecond laser is used for studying plasma and ablation dynamics. This ultrashort pulse laser is used to machine small features in dielectric materials and thin films.

October 30, 2007
Dr. W.P. Schleich
Institut für Quantenphysik
Universität Ulm
Ulm, Germany
“Factorization of Numbers with Classical and Quantum Interference”
The problem of finding the factors of a large integer is of central importance to cryptography with applications to security issues in transmission of signals as well as bank transfers. In the present talk we summarize recent developments of a new approach towards factorization based on Gauss sums [1]. In particular, we review four experiments implementing this algorithm, relying on NMR [2, 3], cold atoms [4], and the temporal Talbot effect [5]. Moreover, we also draw attention to the problem of ghost factors [6]. Finally we highlight features common to the Shor and the Gauss sum algorithms. Here we try to bring out most clearly the role of entanglement as a mechanism to reduce the complexity of the factoring problem.
[1]           See for example, W. Merkel et al., in : Elements of Quantum Information, edited by W. Schleich and H. Walther (Wiley-VCH, Weinheim, 2007)
[2]           M. Mehring et al., NMR experiment factors numbers with Gauss sums, Phys. Rev. Lett. 98, 120502 (2007)
[3]           T. S. Mahesh et al., Factorizing numbers with the Gauss sum technique: NMR implementations, Phys. Rev. A, 75, 062303 (2007)
[4]            M. Gilowski et al., Gauss sum factorization with cold atoms, submitted to PRL, (Preprint 0709.1424v1)
[5]            D. Bigourd, Factorization of Numbers with the temporal Talbot effect: Optical implementation by a sequence of shaped ultrashort pulses, submitted to PRL (Preprint 0709.1906v1)
[6]            M. Stefanak et al., Factorization with Gauss sums: scaling properties of ghost factors,New J. Phys. 9, 370 (2007)
Dr. Schleich's Presentation

November 6, 2007
Dr. Zhiming Wang
Institute of Nanoscale Science and Engineering
Department of Physics
University of Arkansas
Fayetteville, Arkansas
“Molecular-Beam Epitaxy of Semiconductor Nanostructure”
Epitaxial semiconductor nanostructures provide one of the most fascinating playing fields for nanoscale physics. Among the epitaxial techniques, molecular-beam epitaxy with the ability to control and monitor at atomic level, is state-of-the-art for the growth of semiconductors. However, it remains challenging for nanostructure fabrications due to the lack of control on multiple dimensions. On the shoulders of our past achievements of strain-driven self-assembly and droplet epitaxy, we developed a hybrid approach to architecturally designed nanostructures of novel morphologies, such as nanoholes, nanorods, quantum dot molecules, and quantum rings. Follow-up characterizations and calculations reveal their rich spectrum of potential applications in optoelectronics, photonics and quantum information processing. Here, I will take you on a voyage through the nanostructure world that we discovered in the past five years.

November 13, 2007
Professor Gerald Cleaver
Center for Astrophysics, Space Physics & Engineering Research
Department of Physics
Baylor University
Waco, Texas
“The String Landscape, the Multiverse, and the Anthropic Principle”
I first review string theory in its expanded form, generally referred to as "M-theory", and the new related cosmological features. I explain why the estimated 100 billion to a few trillion vacua (unique universes) of string theory has been replaced by something on the order of 10^500 vacua of M-theory. Over the last few years this unimaginable number of possible universes has led to development of the concept of a "string landscape." The predicted physical manifestation of the string landscape is an actual multiverse, in which our universe would be but one "bubble," which presents a picture much like that of chaotic inflation. My talk concludes with the philosophical implications of the string landscape, especially relating to the anthropic principle.
Dr. Cleaver's PowerPoint Presentation

November 20, 2007
Dr. Jesus Arriaga
Instituto de Física
Universidad Autonoma de Puebla
Puebla, Mexico
“Electrotunable Band Gaps of Photonic Crystals Structures”*
In this talk we discuss one-  and two-dimensional photonic crystals based on silicon with infiltrated liquid crystals. We show that the photonic band gap can be continuously tuned by changing the orientation of the director of the liquid crystal. We consider arbitrary directions of propagation of electromagnetic waves in the structures and show that for the two-dimensional case there does
not exist a complete photonic band gap in the system for both polarizations. We used the plane
wave expansion method to solve Maxwell’s equations for anisotropic systems.
*Work done in collaboration with L. Dobrzynski, B. Djafari-Rouhani, Université des Sciences et Technologies de Lille, France.

November 27, 2007
Professor Pier A. Mello
Instituto de Física
  U.N.A.M., Mexico, D.F.
“Statistical Scattering of Waves in Disordered Waveguides: Universal Properties”
The statistical theory of certain complex wave interference phenomena, like the statistical fluctuations of transmission and reflection of waves, is of considerable interest in many fields of physics. In this talk we shall be mainly interested in those situations where the complexity derives from the quenched randomness of scattering potentials, as in the case of disordered conductors, or, more generally, disordered waveguides. In studies performed in such systems one has found remarkable statistical regularities, in the sense that the probability distribution for various macroscopic quantities involves a rather small number of relevant physical parameters, while the rest of the microscopic details serves as mere “scaffolding.” We shall review past work in which this feature was captured following a maximum-entropy approach, as well as later studies in which the existence of a limiting distribution, in the sense of a generalized central-limit theorem, has actually been demonstrated. We then describe a microscopic potential model that was developed recently, which gives rise to a further generalization of the central-limit theorem and thus to a limiting macroscopic statistics.
Dr. Mello's Presentation