Spring 2007 Physics Colloquium Schedule
Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. Abstracts are included below the schedule. The ORNL Physics Division Seminar Schedule might also be of interest. Professor John Quinn is chair of the colloquium program. He may be contacted via e-mail at: firstname.lastname@example.org.
Hitoshi Murayama, University of California-Berkeley
What is the Universe made of? How did it come to be? Why do we exist? This kind of fundamental questions about the Universe used to be just philosophy, but are now coming into the realm of quantitative science. The key is in quantum physics of elementary particles that determined the evolution of the Universe when it was very young. I will discuss this amazing connection between the large (the Universe) and the tiny (elementary particles), in the context of current and forthcoming experiments.
Bronson Messer, ORNL Center for Computational Sciences
Type Ia supernovae (SNe) are a class of stellar explosions that are distinguished by a lack of hydrogen in the observed spectra. Several observational campaigns for Type Ia SNe have produced strong evidence that the universe is undergoing an accelerated expansion caused by a mysterious "dark energy." A number of current programs and future projects also plan to use Type Ia SNe observations to constrain the properties of this dark energy. All of these projects depend on the notion that Type Ia SNe are standard candles, requiring a thorough knowledge of the explosion mechanism in order to properly calibrate their intrinsic brightness. I will discuss some of the issues associated with modeling these explosions and matching these simulations with observations.
Cosmas Zachos, Argonne National Laboratory
Wigner's 1932 quasi-probability Distribution Function in phase-space is a special (Weyl) representation of the density matrix. It has been useful in describing quantum flows in: semiclassical limits; quantum optics; nuclear physics; decoherence (eg, quantum computing); quantum chaos; "Welcher Weg" puzzles. It is also of importance in signal processing (time-frequency analysis). Nevertheless, a remarkable aspect of its internal logic, pioneered by the late J Moyal, has only emerged in the last quarter-century: It furnishes a third, alternate, formulation of Quantum Mechanics, independent of the conventional Hilbert Space, or Path Integral formulations, and perhaps more intuitive, since it shares language with classical mechanics. It is logically complete and self-standing, and acommodates the uncertainty principle in an unexpected manner. Simple illustrations of this fact will be detailed.
Mark Reed, Yale University
The scaling of charge-based devices is projected to reach it's limits in approximately 2016, and a search is underway for successors. This talk will review the physics and technology of atomic and molecular-scale electronic systems, and their applications. Special emphasis will be given to molecular and self-assembled systems. The interfaces of electronics to chemical and biological systems is an additional opportunity enabled by nanosclae devices, and their applications will be explored.
Ziqiang Wang, Boston College
The sodium cobaltates NaxCoO2 are transition metal oxides where the Co
atoms form a layered triangular lattice structure. They have received
widespread interests since the recent discovery of unconventional superconductivity
in this system. A broad spectrum of experiments has been performed, yielding
a rich and exotic phase diagram with many unexpected and fascinating properties.
I review some of the essential experimental findings and argue that the
material is a novel strongly correlated system with important similarities
and differences to the high Tc cuprates. We will then discuss a few examples
where some of the experimental puzzles can be explained qualitatively
based on theories that consider the effects of strong Coulomb repulsion
at the Co sites.
Mu Wang, Nanjing University
Branching is probably the most common growth mode in Nature. Examples include river networks, snow flakes, and lightening sparks. In this talk, we will focus on the growth of crystalline branches in accurately controlled diffusion-limited aggregates. Two model systems will be used to exhibit the self-organized nature of the spatio-temporal oscillations on a laboratory desktop. In the crystallization of inorganic salt, imhomogeneous surface tension may greatly affect the nucleation process in lateral growth, resulting in fascinating zigzag branches. The second example is the electrochemical growth from an ultrathin electrolyte layer, where spontaneous oscillations of electric potential/current occur, inducing periodic nanostructures. These approached can be exploited to fabricate novel nanostructures with unique properties, such as metallic wires for applications in surface plasmonics.
Hagar Landsman, IceCube collaboration, University of Wisconsin,
The quest for ultra high energy neutrinos from astrophysical sources requires detectors with huge effective volume and a long exposure time. The massive amount of clear ice at the South Pole makes it an ideal place for such experiments. I will review the importance and challenge of high energy neutrino detection, and present the high energy neutrino detectors at the south pole - air, surface and ice.
Martin B Einhorn, Kavli Institute of Theoretical Physics
Thirty years ago, Hawking discovered that quantum corrections imply that classically stable black holes should actually radiate and lose energy. He also found that the spectrum of radiation was thermal, like that of a black body. This suggested that the evaporation of a black hole would actually contradict basic principles of quantum mechanics. This paradox will be explained, and a possible solution to the conundrum elaborated.
Dr. Jayne Wu, UT Electrical and Computer Engineering
Microfluidic devices are instrumental to the realization or improvement of miniature bio/chemical diagnostic kits, biochips for drug screening etc. As device dimension scales down, pressure driven flow becomes increasingly inefficient due to high surface-volume ratio. In contrast, electrokinetics is gaining popularity as a microfluidic actuation mechanism, due to its no moving parts and easy implementation. Traditional electrokinetic pumping requires applying high DC voltage across the microchannel, and the electric field drives the mobile charges at the fluid/channel interface (i.e. electroosmosis) to transport fluid. High voltage causes bubble generation and pH gradients from electrochemical reactions. To minimize these adverse effects, AC electrokinetics (ACEK) has emerged recently for on-chip pumping and particle manipulation for its low voltage operation.
ACEK investigates the behavior of particles in fluid and the motion of electrolytic fluids when they are subjected to AC electrical fields. Charges are induces in the buld of the fluids where there is an interface (e.g. electroosmosis) or gradients in fluid attributes (e.g. electrohermal effect). Because the electric fields and induced charges in fluid change polarity simultaneously, / steady (not oscillatory)/ fluid motion can be generated in ACEK. There are mainly three types of ACEK phenomena, dielectrophresis (studies since 1991), AC electroosmosis (since 1999) and AC electrothermal effect. The seminar will present the concept and development of various ACEK techniques for applications in nano-bio-technology.
Steven G. Louie, Department of Physics, University of California at Berkeley, and
Materials Sciences Division, Lawrence Berkeley National Laboratory
The restricted geometry and symmetry of nanostructures often give rise to novel properties that are also potentially useful in applications. In this talk, I discuss some recent progress on using theory and computation to understand and predict their electronic, transport, optical, and mechanical properties. Examples of systems of interest include carbon and BN nanotubes, Si nanowires, graphene nanoribbons, and molecular junctions. These nanostructures exhibit a number of unexpected behaviors -- novel conductance characteristics, extraordinarily large excitonic effects, strange friction forces, and a field-induced half-metallic state for the graphene nanoribbons, among others. The physical mechanisms behind these unusual behaviors are examined.
Robert R. Jones, University of Virginia Department of Physics
Rydberg atoms have one or more electrons in highly excited orbitals. Their large size and weak binding energies endows them with exaggerated properties which can be exploited to study a variety of phenomena in quantum and classical physics. We utilize ultrashort laser pulses to both prepare Rydberg electrons in well-defined wavepackets and measure time-dependent changes in their quantum states, enabling us to characterize and/or control the coherent interactions which affect them. For example, we are currently using Rydberg wavepackets to investigate schemes for suppressing quantum decoherence in single-electron systems as well as for probing and manipulating electron correlation in two-electron atoms.
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