The continued down-scaling of electronic devices has led to size scales where the regime of classical diffusive transport, in which these devices operate, will eventually break down and quantum mechanics come into play. New concepts, perhaps founded on unusual principles, will be required for the next generation of microelectronic devices. Single electron device is one of the potential candidates for future electronic circuits. In this talk, I will review the basic physics of single electron devices and discuss their current and prospective applications

Metastable phases are ubiquitous in nature, and they have been viewed with fascination by resesarchers for almost three centuries. Examples range from supercooled water to the quark-gluon plasma. Such phases are easily mistaken for true equilibrium phases, and unless they are strongly perturbed, they can exist for a very long time. Typically, a metastable phase decays suddenly to the true equilibrium through the random nucleation of one or many critical droplets of the equilibrium phase. In this talk I will discuss some aspects of the nucleation theory of metstable decay, with particular emphasis on finite-size effects that are important when considering real systems. The principles will be illustrated with simulation results on magnetization switching in models of magnetic nano-particles and ultrathin films. As the recording density of magnetic disks rapidly increases, this is an area of critical interest to the computer industry.

Metallocenes are soluble organometallic compounds that are used as catalysts to take polyolefin plastics such as polyethylene and polypropylene. As in many cataly-tic processes, subtle structural variations and mechanistic details at the molecular level can have great practical importance. Even though these details have been studied extensively for many years, we still don't have a complete, self-consistent mechanism. This seminar describes our effort to develop an alternative spectro- scopic method for exploring key chemical pathways in the mechanism of metallo-cene-catalyzed olefin polymerization.

In materials science, theory's role is to predict and/or interpret experimental results, or to explain unusual phenomena. Of course, one must be aware of what experiment actually measured - or, more typical, how those results were interpreted. Often interpretation relies on a model, and understanding is only as good (or bad) as the model. So how can theory impact our understanding and prediction of experiment?

I will briefly present two complimentary electronic-structure-based thermodynamic theories: the cluster-expansion and concentration-functional methods. Examples of ordering predictions in binary and multi-component materials and their electronic origin are discussed and direct comparison to experimental scattering and TEM data is made. I will highlight how one can uniquely interpret data from characterization experiments, e.g., ordering in bcc-based Nb-Ti-Al (Phil. Mag. Letts, 79, 551 (1999)), and provide insight to resolve discrepancies between theory and experiment or between multiple experiments, e.g., ground-state and precipitate structures in hcp- and fcc-based Al alloys (Acta Mater. 50, 2443 (2002)), or ordering energetics in Ni3V (Phys. Rev. B 62, R11917 (2000).

By using a transmission x-ray microscope with precision zone plate optics, imaging can be achieved with a demonstrated spatial resolution finer than 25 nm. Image contrast can be obtained with x-ray magnetic circular dichroism, allowing direct imaging of the element-specific orientation of the magnetization within samples. The ability to magnetically characterize samples with 25 nm resolution gives a deeper understanding of magnetic properties and paves the way for future progress in such technically relevant fields as high-density magnetic storage in hard disk drives. Recent experiments at the Advanced Light Source Storage Ring in Berkeley include analyzing aligned images of both magnetization and crystal structure to probe the complicated relationship between the two in magnetic materials. Additionally, research is focusing on the modification of magnetic properties by using ion irradiation. A new technique of ion irradiation through a self-assembled mask has the potential to magnetically pattern samples below the 10 nm scale. While the current emphasis of experimentation with the microscope is on understanding magnetic properties on the nanometer scale, a brief synopsis will also be given of other recent research, including a study of electromigration in passivated interconnects and high-resolution tomography of biological samples.

Advances in the quality and current of polarized electron beams at high energy electron accelerators in the 1990's has made possible high precision measurements of the scattering of polarized electrons on unpolarized protons. In particular, we can now reliably measure the small (few parts per million) difference in the elastic scattering rate of left-handed versus right-handed electrons on the proton. These measurements allow us to extract intersting new nucelon structure information - the contribution of the strange quark sea to the proton's electromagnetic properties. I will describe the results of the completed SAMPLE experiment at the MIT-Bates LINAC and the plans for the G0 experiment at Jefferson Lab which is just being commissioned. This technique can also be used as a sensitive test of the Standard Model at low energies. I will describe plans for a newly approved experiment to test the Standard Model in low energy parity-violaring electron scattering - the Qweak experiment at Jefferson Lab.

Non-smooth dynamical systems are characterized by sudden and abrupt changes in system characteristics, as in the occurrence of contact in a mechanical system, the triggering of a relay in an electronic circuit, or the activation of a chemical reaction above some critical energy level. Non-smooth systems are inherently nonlinear, even if their description is entirely linear in between system discontinuities. It is clear that their analysis requires tools that generalize those applicable to everywhere-smooth systems.

This talk presents a rigorous mathematical technique for the intentional exploitation of the presence of discontinuities in non-smooth dynamical systems in order to control the local stability of periodic or other recurrent motions. In particular, the formalism allows one to predict the effects of the control strategy based entirely on information about the reference trajectory in the absence of control.

The methodology is illustrated with examples from impacting systems, namely a model hopping robot, a Braille printer, and a class of passive bipedal walkers. It is shown how initially unstable motions can be successfully stabilized at negligible cost and without active energy injection. In particular, in the case of the walking mechanisms, small, discrete, corrective adjustments to swing-foot geometry are employed to affect the local stability properties of a periodic reference gait. It is demonstrated that successful stabilization can be accomplished for otherwise strongly unstable motions of vertically constrained as well as entirely unconstrained model mechanisms.

Biomolecular recognition and self-assembly have attracted substantial interest as a novel route to synthesize nanomaterials with predicted structure and functions. In the first part of this talk, I will present the initial results of our efforts in designing nanoscale architectures on surfaces through the ligand-receptor interaction. The second part of this talk will be the results of our efforts in designing polymeric bata-sheet nanotapes, ribbons, and fibrils through the self-assembly of oligopeptides.

As an important research direction in nano-science and nano-technology, carbon nanotubes have aroused great interest in the research community worldwide. Carbon nanotubes have either metallic or semiconducting electronic properties depending on their chiralities and diameters, and they can be used as elementary building blocks for nanoelectronic devices, such as one-dimensional quantum wire, nano-probes, biosensors, field emitters, field-effect transistors and logic circuits. Since carbon-carbon covalent bonds are one of the strongest in nature, carbon nanotubes with a perfect arrangement of these bonds along their axes are exceedingly strong material. Possessing properties of high strength, stiffness, stability, elastic deformability, low density and novel electronic properties, carbon nanotubes can be extraordinary fillers in polymer for not only structural application but also functional application such as electrical conductivity, luminescence, electromagnetic interference shielding and optoelectronics.

In the present talk, the basic structure, properties and potential applications of carbon nanotubes will be introduced. A versatile technique invented through a combination of chemical vapor deposition and template effect for fabricating large scale of aligned carbon nanotube arrays will be demonstrated. The technique has been implemented to synthesize large quantity of carbon nanotubes with controllable structures which are required for different applications. Direct synthesis, structure and formation mechanism of three-point junction (Y-junction) carbon nanotubes have been investigated. Periodic free standing carbon nanotubes arrays, double-walled carbon nanotubes, nanotubes incorporated nanocomposite and gas storage will be briefly discussed.

Physicists are used to thinking about the universe as a 3+1 dimensional stage on which material things move and act. However, recent developments in theoretical physics have suggested far more subtle pictures. The observed spacetime dimension of physical systems can be dependent on energy scales or the cosmological epoch or location in the universe. It can even change dynamically. There are even situations where the constructs we know as 3+1 dimensional spacetime and the gravitational force are merely emergent properties of fundamental dynamical systems that contain neither. I will review these remarkable theoretical developments and discuss how we might explore them experimentally.

This talk offers an overview of the ongoing optics research at OSER with an emphasis on the opportunities provided to undergraduate students.* We have recently begun to fabricate and study colloidal CdSe quantum dots. This program is based on the application of quantum dots to the development of a spectrally multiplexed, fluid-based DNA microarray system. The advantages of such a system over conventional biochip technology will be discussed. Because of their unique optical properties, the quantum dots are also finding use as sensors and molecular tags. We are also applying fiber-based sensors to eldercare. A "smart bed" is being developed to monitor patients while they sleep and identify long-term changes in their health. This type of home monitoring system will be very important as the population ages and healthcare becomes more distributed.

* Including Physics Undergraduate Students: R. Bowers (QD's), P. Granger (QD's), J. Bennett (Fiber Sensor), M. Mayer (Fiber Sensor), E. Spiegel (Hyperspectral Imaging)

Talk postponed to February 7, 2003 due to snow.

Several companies have attempted since about 1990 to commercialize variable tint eyewear based on electrochromic technology. We will review and compare the various approaches from a technical perspective. We will then concentrate on the most recent attempt made by PPG Industries, Inc. with its "Intelligent Optics" product. We will also discuss the optical and electrochemical behavior of electrochromic materials and PPG's attempt to push the optical performance of these devices to their limit. Finally, both the standard and optimized product will be demonstrated along with some perspective on the commercialization of electrochromic technology.

Dr Lehan is a 1985 graduate (B.S. Physics) of Virginia Tech. He was president of the VT SPS chapter for 1984-85 and did undergraduate research with Dr. Jerome Long. Following Virginia Tech he earned his Ph.D. from the Optical Sciences Center of the University of Arizona. He was subsequently employed in California by Optical Coating Laboratory and by Airco before moving East to Pittsburgh's PPG Industries. His colloquium topic is derived from his work at PPG. He recently joined Universities Space Research Association at Maryland's Goddard Space Flight Center.

In the early universe, microseconds after the Big Bang, quarks and gluons were not confined within hadrons, but were free to roam around in a hot quark-gluon plasma (QGP). Today, accelerator technology has developed sufficiently that this original state of matter may be created and studied in a laboratory. The Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory was built specifically for the purpose of creating the quark-gluon plasma by colliding Au nuclei in head-on collisions with a total energy of almost 40 TeV. This facility has four beam interaction regions instrumented with large detectors, STAR, PHENIX, PHOBOS and BRAHMS, which are used to search for the expected signatures of the QGP. Conclusive evidence for formation of the quark-gluon plasma has not yet been found, but measurements of the number of charged particles emitted in a collision indicate that the energy density achieved is sufficiently high for the quark-gluon plasma to form. In this talk I'll discuss these and other early results from the RHIC physics program concentrating on measurements made by the PHOBOS collaboration.

Talk postponed to April 25 due to snow.

We give an overview of some of recent work in queueing network theory, particularly work leading to optimal control and differential games for deterministic continuous-state models. Some of these arise from ``risk-averse'' limits, which resemble semiclassical approximations in Physics. We will mention the notion of viscosity solutions to Hamilton-Jacobi equations, and in particular how to formulate Neumann boundary conditions in a weak/viscosity sense. Some of our own work will be described, along with the directions taken by others.

Many systems in physics, biology, and ecology can be described in terms of effective ‘chemical’ reaction-diffusion networks. These are usually captured in terms of coupled mean-field rate equations. In low dimensions, however, stochastic fluctuations become important, and reaction-induced correlations may alter the scaling behavior of these processes qualitatively. Based on a mapping of the corresponding classical master equation to many-particle ‘quantum’ Hamiltonians, and their field-theoretic representation, we can systematically analyze such non-equilibrium systems by means of the renormalization group. Cellular-automation type Monte Carlo simulations support our findings. In this talk, I shall discuss simple pair annihilation processes, A + A → 0, A + B → 0, and a generalization to q particle species. Non-equilibrium transitions in diffusion-limited reactions often separate active phases with non-zero particle density n in the stationary state from inactive, absorbing phases, where n(t) → 0 as t → ∞, and where consequently fluctuations vanish as well. I will give an overview of the known universality classes for such dynamic phase transitions, which include directed perco-lation and parity-conserving branching and annihilating random walks. Finally, I will present an interesting model of reaction-controlled anomalous diffusion, and mention possible applications to biological systems.

Muss es sein? So wrote Beethoven in an epigraph to his last string quartet. Today, with regard to that great quest of the Theory of Everything, physics is led to ask the same: must it be so? Does all interactions and all particles of nature fundamentally originate from a cosmic string quartet?

In this talk we take the audience on a bird's-eye view of the theory of superstrings, before moving on to the study of D-branes, gauge theories and singularities. We will see such beautiful physics and mathematics such as Calabi-Yau manifolds, Mirror Symmetry and conformal field theories. Our own Standard Model, may ultimately be a subsector of the theories which arise in the low-energy limit of string theory in non-trivial backgrounds.

We often call the ground state of a quantum system the "vacuum", implying that it consists of nothing. But for example, the ground state in an electron system consists of a Fermi or Dirac sea, and many seemingly counterintuitive effects result from such a non-trivial ground state. One I will discuss is the existence of fractional charge, which means that excitations over a ground state have a charge a fraction of the electron. I will show how fractional charge appears in many theories familiar in condensed-matter and particle physics, and describe how it has been observed in the fractional quantum Hall effect.

Symmetries considerably simplify the mathematical models describing physical systems. A particular example for this is conformal symmetry in quantum field theory. Conformal symmetry is a generalization of scale invariance. It has a variety of applications in many different areas of physics.

In this talk the basic features of conformal symmetry will be introduced. Moreover two very different applications will be discussed: First to the Kondo effect in condensed matter physics and secondly to the AdS/CFT correspondence in theoretical elementary particle physics and string theory.

We describe several simple systems in terms of phase-space dynamics, a description that simultaneously treats both position and momentum. We emphasize systems which have extra invariants that render them super-integrable. A phase-space approach often gives a clearer picture of processes, both classically and quantum mechanically, and provides considerable insight. For the quantum case, a phase-space description requires using distributions, usually the so-called Wigner functions, that are specific realizations of density operators. We discuss some key features of Wigner functions, especially their time evolution. In phase-space there is a surprising amount of latitude in how one describes time evolution. We exploit this freedom to define "Nambu" time for various models.

The Belle Experiment at the KEKB electron-positron colliding beam accelerator in Japan is designed to probe the phenomenon of CP (charge conjugation and parity) asymmetry by comparing the decays of B mesons and their antiparticles. This matter-antimatter symmetry is one of the ingredients in the early moments after the Big Bang that led to the matter domination in our present universe. I will discuss the technical issues associated with designing, building and operating this facility, the physics output (CP asymmetry measurements as well as others, time permitting), and the future plans for the detector and accelerator.

The fluctuation-dissipation theorem (FDT) links the heat dissipation in a solid or a fluid, with the fluctuations that are, of necessity, present. Recently there has been a resurgence of interest in generalizing that theorem to encompass thermostatted systems driven so hard that the FDT no longer applies. A liquid crystal driven into an electroconvective state seems to be a good candidate for studying the new effects that arise. Experiments in this and other systems will be discussed against the background of theoretical ideas.

Quantum Chromodynamics provides a fundamental and remarkably elegant description of hadronic and nuclear phenomena in terms of quark and gluon quanta. QCD also predicts exotic phenomenological effects such as "color transparency", "intrinsic charm", "hidden color", shadowing and antishadowing, as well as novel spin correlations. I will also discuss the application of light-front quantization for obtaining the spectrum and relativistic wave-functions of hadrons in QCD.

After an introductory review of the essential concepts of superstring/M-theory, a discussion is presented to discribe the challenge to this paradigm that is presented by the apparent astrophysical observation of a de Sitter geometry in our universe.

String theory challenges our current understanding of space-time, as one of it basic implications is that Riemanian geometry, the mathematical language of general relativity, requires modifications. First of all, string theory predicts that the number of space-time dimensions is eleven, rather than four. Furthermore supersymmetry, required for string consistency, calls for supersymmetric partners of space time-coordinates. Strings dualities and topology changes relate strikingly different space-time geometries and tear apart the fabric of space-time. Finally, string theory questions the very nature of space-time coordinates, by suggesting that they might not commute, and hence pointing to a novel type of uncertainty principle.