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Physics & Astronomy Colloquium
Thursdays, 3:30 p.m.
P.S. 306
Call us at: (323) 343-2100
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Spring Quarter 2007 Schedule

Physical Sciences Building, P.S. 306
Refreshments - 3:15 p.m., Colloquium - 3:30 p.m

Faculty Research
Department Colloquium Pizza Party

Prof. Jose Rodriguez

"Vortex Dynamics in High-Temperature Superconductors"

Prof. Radi Al-Jishi


Prof. Milan Mijic

"Cosmology and Scientific Visualization"


Nina Abramzon
Department of Physics, California State Polytechnic University, Pomona

"Hot Topics in Cold Plasmas "

Abstract: Gas discharge plasmas are environments where radiation, ions, electrons, and reactive radicals are present simultaneously. In non-thermal, or “cold” plasmas the electrons may be much hotter (in the range of 10,000 to 100,000 Kelvin) than the ions and neutrals, which typically remain at about room temperature. Cold plasmas are particularly interesting, because their relatively low operating temperatures allow them to be used in a wide range of applications in the medical, environmental, food industries, material processing and beyond. In this talk, I will describe optical emission spectroscopy techniques used to study plasma composition. In addition, I will discuss different applications of non-thermal plasmas. In particular, I will present results on the interaction of plasmas with microorganisms including spores and bacterial biofilms.


Wedesday, April 18, 11:30 a.m.
P.S. 317

Amir Huda
Department of Physics, California State University, Fresno

"The New Undergraduate Biomedical Physics Program
at CSU Fresno "

Abstract: What is Biomedical Physics? This talk will focus on the burgeoning field of Biomedical Physics and the career opportunities. The curriculum at Fresno State provides fundamental groundwork in biology, physics, and mathematics, with specialized courses such as magnetic resonance imaging and spectroscopy, nuclear medicine, radiation measurement systems, radiation oncology, and others.

Dr. Thorsten Ritz
Department of Physics and Astronomy, University of California, Irvine

"Magnetic Sensing in Animals:
Mysteries, Myths and Biophysical Mechanisms"

Abstract: One of the last remaining mysteries of sensory biology is the ability of migratory birds and other animals to detect the geomagnetic field and use it to obtain information about direction and position. However, neither the receptors nor the physical mechanism underlying magneto sensing are known. Recently, the idea that magnetically sensitive spin chemical reactions underlie magnetic sensing has received renewed attention. I will review recent exciting results from behavioral and neurophysiological studies of the avian magnetic compass. As behavioral studies still yield by far the most reliable information, choosing intelligent stimuli appears one of the most promising avenues to identify the underlying biophysical mechanism. In principle, one expects that combined oscillating and static magnetic fields can yield much more detailed information as in magnetic resonance studies. I will review results from a collaborative research program conducted during the past several years, in which birds are tested in magnetic orientation experiments with both static and oscillating fields present. Model and semi-realistic calculations provide the necessary framework to demonstrate that the results  indicate that the magnetic compass of birds is based on a radical pair mechanism. Finally, I will review current efforts by my and other groups to elucidate not only the mechanism, but also the receptor molecules and neural representation of magnetic information.


Dr. Shan-Wen Tsai
University of California, Riverside

"Fermions and bosons in natural and artificial lattices"

Abstract: With the rapid advances in the field of cold atoms, it is now possible to engineer strongly correlated mixtures of Fermi and Bose gases in optical lattices, where new quantum phases may be accessible through the fine-tuning of atom and lattice parameters. The fermion-boson problem is also important in solid state systems.  Experimental results indicate that in many strongly correlated materials, such as organic conductors and superconductors, filled skutterudites, cuprates, and charge-density-wave inorganics, both electron interactions and electron-phonon coupling may play an important role. I will present a recently developed renormalization-group method that treats interacting fermions and fermion-boson couplings on an equal footing, and discuss results for both cold atoms in optical lattices and electrons and phonons in solids.


Armen Kocharian
California State University, Los Angeles

"Inhomogeneous phase separation instabilities and pairing
in ensemble of bipartite and frustrated Hubbard clusters"

Abstract:The exact diagonalization and thermodynamic calculations in canonical and grand canonical ensembles elucidate the origin of Mott-Hubbard like metal-insulator transition, electron pairing and superparamagnetism in Hubbard clusters under doping and magnetic field. The theory dismisses existing controversy about nature of the Nagaoka spin-flip instability with minimal spin in bipartite and frustrated clusters. The negative charge energy gap and electron pairing give strong evidence for the existence of inhomogeneous phase separation in planar and three dimensional clusters. The rigorous conditions are established for the existence of strong superparamagnetism and electron pairing fluctuations at finite temperatures and off half filling. The calculated phase diagrams illustrate a number of inhomogeneous phases discovered in fullerene molecules, nanoparticles, and eventually, composite nanomaterials and high T_c cuprates.


Douglas Leonard
Department of Physics and Astronomy,
San Diego State University

“The Geometry of Supernova Explosions ''

Abstract: Is the mechanism that drives the explosion of massive stars spherical? While simple to pose, this question belies a menacing observational challenge, since all extragalactic supernovae are unresolvable during the critical early phases of their evolution.  Fortunately, geometric information is encoded in the polarization properties of supernova light, and it is through the technique of spectropolarimetry that we have begun to observationally address explosion geometry.  In this talk I will review the small but growing database of spectropolarimetry of core-collapse events, with an emphasis on how polarization and, hence, degree of inferred asymmetry, changes as a function of progenitor envelope mass.  By focusing particular attention on SN 2004dj, the closest and most well-observed supernova of the past decade, I will argue that the innermost regions of these stellar explosions are severely distorted, the result of an explosion mechanism that is strongly non-spherical in nature.


Theresa Lynn
Harvey Mudd College

“Ultra-High Energy Cosmic Rays: The Mystery of Nature's Most Powerful Particle Accelerators”

Abstract: Stargazing is perhaps one of humanity's oldest pastimes. As modern astronomers have learned to image the universe in wavelengths across the electromagnetic spectrum, each added picture has answered old questions and uncovered new wonders. In recent years a few observatories have concentrated on very different messengers from the cosmos: subatomic particles called cosmic rays which reach us from as nearby as the Sun and as far away as distant galaxies. The rarest and most energetic of these particles are called ultra-high energy cosmic rays, or UHECRs; a single UHECR proton can carry more than a Joule of kinetic energy. We know that UHECRs originate outside our own galaxy, but we remain puzzled by exactly what sources accelerate particles to such immense energies, and how distant these sources are. CHICOS, an array of particle detectors at schools across the Los Angeles area, monitors ultra-high energy cosmic rays to determine their energies and look for clues to their origins. The rare particles we observe are messengers from some of the most violent activity in the cosmos, and could even provide hints of new physics at the smallest scales as well. [Several Cal State LA undergraduates have contributed to CHICOS through summer research and outreach activities.]


Roya Zandi
Department of Physics and Astronomy,
University of California, Riverside

“Origin of  Icosahedral Symmetry in Viruses”

Abstract: With few exceptions, the shells (“capsids”) of sphere-like viruses have the symmetry of an icosahedron and are composed of coat proteins (“subunits”) assembled in special motifs, the “T-Number” structures. While the synthesis of artificial protein cages is a rapidly developing area of materials science, the design criteria for self-assembled shells that can reproduce the remarkable properties of viral capsids are only beginning to be understood.  In this talk, I  will discuss the mechanisms and physical principles controlling the self-assembly of viral capsids. I will present a minimal model for capsid self-assembly and, using Monte Carlo simulation, I will show that the model reproduces the main structures of viruses in vivo-T-Number icosahedra - as well as important non-icosahedral structures (with octahedral and cubic symmetry) observed in vitro. I will also analyze the remarkable mechanical properties of these viral nanocontainers, and discuss different genome release scenarios.

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