Fall 2001/ Spring 2002 Physics Colloquium Schedule

Unless otherwise noted, Colloquium is held on Monday, at 2:30 pm, in room P-148.
Refreshments are served at 2.15 pm.

Last updated on Thursday, April 11, 2002, 11:12 PDT
 
 

9/17/2001

Welcoming reception for graduate and undergraduate students

9/24/2001

Prof. Matt Anderson
Department of Physics
San Diego State University
Measuring Ultrashort Laser Pulses in a Noisy World

10/1/2001

Prof. Bjarne Andresen
Öersted Laboratory
Niels Bohr Institute for Astronomy, Physics and Geophysics
Copenhagen, Denmark
Global Optimization Using Simulated Annealing and Statistical Mechanics

10/8/2001

Prof. Jon Lawrence
Department of Physics and Astronomy
University of California, Irvine
The Coherent Fermi Liquid State of Intermediate Valence Compounds

10/15/2001

Prof. Graham Oberem
Department of Physics
California State University San Marcos
Research as a Guide to Improving Student Learning in Introductory Physics Courses

10/22/2001

Dr. Francisco Solis
Department of Physics and Astronomy
Arizona State University
How to build a theory for DNA condensation

10/29/2001

Prof. Joseph F. Dolan
Department of Astronomy, SDSU and
NASA Goddard Space Flight Center
Dying Pulse Trains: Another Test of General Relativity

11/5/2001

Prof. Douglas E. MacLaughlin
Department of Physics
University of California, Riverside
Death of a paradigm: non-Fermi-liquid metals ?

11/12/2001

Dr. Stefano Spagna
Quantum Design, San Diego, CA
Microfabricated Silicon Layers for Torque Magnetometry

11/19/2001

No Colloquium -- Thanksgiving Week

11/26/2001

Prof. William Welsh
Department of Astronomy
San Diego State University
Mapping Quasar Black Holes Environments with Light Echoes

12/3/2001

Prof. Arlette Baljon
Department of Physics
San Diego State University
Contact time dependence of adhesive energy

Winter Break

Winter Break

2/4/2002

Prof. Herbert Levine
Department of Physics
University of California San Diego
Biological Applications of Pattern-Formation Physics

2/11/2002

Prof. Steven Gross
Department of Physics
University of California Irvine
How do cells create and maintain order:
A biophysical look at molecular motors

2/18/2002

Prof. Galen Pickett
Department of Physics
California State University Long Beach
Self-Assembly in Branched and Charged Polymers

2/25/2002

Prof. Paola Cessi
Physical Oceanography Research Division
Scripps Institution of Oceanography
Delayed oscillations in the mid-latitude climate system

3/4/2002

Prof. Kim Griest
Department of Physics
University of California San Diego
The Dark Matter of the Universe

3/11/2002

Prof. Katherine McCall
Department of Physics
University of Nevada Reno
Cold Neutrons: The Perfect Way to Study Hot Rocks?

3/18/2002

No Colloquium
March Meeting of the American Physical Society
Indianapolis, IN - March 18-22

3/25/2002

Prof. Richard Haskell
Department of Physics
Harvey Mudd College
Optical Coherence Tomography (OCT): A non-invasive imaging technique for biological tissue

4/1/2002

No Colloquium
Spring recess week

4/8/2002

Prof. Jose P. Rodriguez
Department of Physics
California State University Los Angeles
Vortex Dynamics in the Mixed Phase of High-Temperature Superconductors

4/15/2002

Dr. Barbara Jones
IBM Almaden Research Center
Nanotechnology Overview

4/22/2002

Prof. Giovanni Zocchi
Department of Physics and Astronomy
University of California Los Angeles
Intermediate states in the melting transition of DNA oligomers

4/29/2002

Dr. Maria Caponi
TRW Inc.
Hydrodynamic Models Relevant to Remote Sensing of the Ocean

Abstracts


Measuring Ultrashort Laser Pulses in a Noisy World

Prof. Matt Anderson
Department of Physics, San Diego State University
The two tag-lines of technological progress can arguably be categorized as faster and smaller. I would like to add a third category to that list: shorter (this could, conceivably, be a simple amalgam of its two precursors.) With regards to temporal duration, there is a constant emphasis towards creating shorter and shorter physical events. Ultrashort-pulsed lasers have been a major player in this drive, with infrared pulses of light being generated that last for an incredibly short five femtoseconds (10-15 seconds). Recently, new experiments with high-harmonic generation have produced packets of photon energy beyond the femtosecond regime, with temporal durations of 250 attoseconds (10-18 seconds)! Of critical importance to this field is the proper characterization of the laser pulse itself, including its amplitude and phase. There are several methods available to measure accurately an ultrashort pulse. One such technique, spectral phase interferometry for direct electric-field reconstruction (SPIDER), has found success in various laboratories throughout the world. Indeed, our SPIDER apparatus here indicated that our laser was working properly. But how well is your pulse measurement device working? Surely there is noise on the signal and error in the measured pulse. This is an important question: How precisely can a pulse measurement device work in the presence of noise? In our experiments here at SDSU, we have been analyzing the performance of our SPIDER apparatus under non-optimal conditions, such as low beam-power, high electronic noise, and limited detector quantization. Results from this latest study will be presented along with an overview of the ultrashort-pulsed laser arena and the directions we are heading.
Back to page top


Global Optimization Using Simulated Annealing and Statistical Mechanics

Prof. Bjarne Andresen
Örsted Laboratory, University of Copenhagen, Denmark
The first solidly founded algorithm for statistical mechanical modelling of molecular properties on fast electronic computers was published in 1953 by Metroplis et al. They sampled state space randomly, accepting all suggested moves that went to lower energy states with probability one, uphill moves only with the reduced probability exp(-DE/kT). Repeated application of this rule will eventually lead to a Boltzmann distribution at the temperature T.
Thirty years later, Kirkpatrick et al. developed a general optimization algorithm, simulated annealing, based on the same principle and intended for systems of a magnitude like the number of molecules in a macroscopic gas, i.e. of the order of 1023 or more, where statistical mechanics gives a good representation of reality. Their cleverly added new feature was to allow the temperature T to decrease slowly during the calculation, thereby focusing on the low energy states, hoping eventually to find the global minimum of the objective function. The method of simulated annealing will be explained and additional features, based on statistical mechanics and finite-time thermodynamics will be described.
Back to page top
 
 

The Coherent Fermi Liquid State of Intermediate Valence Compounds

Prof. Jon Lawrence
Department of Physics and Astronomy,
Universityof California, Irvine
The ground state of rare earth intermediate valence (IV) compounds is that of a heavy mass Fermi liquid. This means that the statistics are those of a noninteracting electron gas; the main effect of the strong electron-electron interactions is to renormalize the electron mass to a large effective value. I will show that while many of the properties of the IV ground state can be understood as those of a collection of noninteracting Anderson/Kondo impurities, key properties require an underdstanding of how coherence between the "impurities" develops at low temperature.
Back to page top
 

Research as a Guide to Improving Student Learning in Introductory Physics Courses

Prof. Graham Oberem, Department of Physics,
California State University, San Marcos
Students do not learn as much as we think from our introductory physics courses. This finding appears to be independent of the ranking of the school or the quality of the instruction. In the past decade, several innovative approaches to teaching introductory physics have been proposed. Most of these new approaches have been based on careful research by physicists and physics educators into how students learn physics. The approaches range from a radical restructuring of the introductory physics courses to the incorporation of some innovative techniques into traditional classrooms. Ongoing research is indicating the effectiveness of methods that engage students in active learning. In this talk, I will review some of the research that has guided these developments and present some of the results of implementing changes. I will also discuss the constraints that I have faced in bringing innovations to a rapidly growing new CSU campus and present results of my work at Cal State San Marcos.
Back to page top


How to build a theory for DNA condensation

Dr. Francisco Solis, Department of Physics,
Arizona State University
DNA, actin fibers, colloidal particles, and flexible polymer chains such as polystyrene sulphonate are examples of polyelectrolytes: systems that in aqueous solution dissociate into macro-ions with high charge and a large number of accompanying counterions of smaller and opposite charge. A seemingly paradoxical but fairly common phenomena is the onset of effective attractions between the macro-ions which due to their same-sign charges are expected to repel each other. An especially interesting and extreme case of this behaviour is the "condensation" of DNA: upon addition of multivalent salt to a DNA solution the DNA chains attract each other, form bundles, and precipitate. The explanation of this phenomena and, more in general, the theoretical description of the structural, thermodynamical, and kinetic properties of polyelectrolytes requires adequate considerations of many factors: their multi-component nature, the constrains imposed by the geometry of the macro-ions, the long range of the electrostatic interactions as well as the fine details of charge distributions, interaction screening due to counterions, and the role of the solvent. In this talk I will discuss recent ideas and approaches to the construction of a polyelectrolyte theory and their application to the problem of DNA condensation.
Back to page top


Dying Pulse Trains: Another Test of General Relativity

Prof. Joseph Dolan, Department of Astronomy,
San Diego State University
The X-ray emitting component in the Cyg XR-1/HDE226868 system is a leading candidate for a stellar-mass sized black hole. The detection of an event horizon surrounding the point singularity in such a system would constitute a positive identification of a black hole as predicted by general relativity. One signature of an event horizon would be the existence of dying pulse trains emitted by material spiraling into it from the last stable orbit in an accretion disk around the black hole. We observed the Cyg XR-1 system at three different epochs in a 1400 - 3000 A bandpass with 0.1 ms time resolution using the Hubble Space Telescope's High Speed Photometer. Two series of pulses with characteristics similar to those expected from dying pulse trains were detected in 3 hours of observation.
Back to page top


Death of a paradigm: non-Fermi-liquid metals ?

Prof. Douglas MacLaughlin, Department of Physics
University of California Riverside

For seventy years the quantum theory of metals has been based on an extremely simple picture, in which the behavior of a metal is mainly due to two properties of the conduction electrons: (1) they move nearly freely, and (2) they obey Fermi statistics. L. D. Landau elaborated this so-called Fermi-liquid theory in the mid-fifties (at the height of the cold war) and it has dominated our thinking about metals ever since, much like the "standard model" in particle physics. Recent experiments, and the theory devised to explain them, demonstrate the possibility of profound breakdowns of Fermi-liquid theory in certain materials, including "heavy fermion" metals and high-temperature superconductors. This talk will survey recent exciting developments and the current state of this fascinating subfield of condensed-matter physics.
Back to page top


Microfabricated Silicon Layers for Torque Magnetometry

Dr. Stefano Spagna, Quantum Design
We describe a fully automated and highly integrated torque magnetometer system designed to measure the magnetic torque of small anisotropic samples (up to 10 mg). The torque magnetometer features microfabricated, silicon torque-chips and u ses a piezoresistive technique to measure the torsion, or twisting of the torque lever about the lever's symmetry axis. The levers have been optimized to yield high sensitivity together with minimal temperature dependence and substantial i mmunity from gravitational effects. A typical torque resolution of 10-9 Nm can be achieved using relatively fast acquisition times (40 sec) with a measurement dynamic range of 10-5 Nm . An integrated loop on the torque lever is used to produce a well defined magnetic moment which can be used as a calibrating standard with an accuracy of 1 %. We present details of the torquemeter as well as angular dependent magnetic torque measurements on a variety of samples up to 14 Tesla.
Back to page top


Mapping Quasar Black Holes Environments with Light Echoes

Prof. William Welsh, Department of Astronomy
San Diego State University

Many galaxies exhibit a remarkable phenomenon: an exceedingly luminous, highly variable, non-stellar energy source in their core. These "active galactic nuclei" (AGN) are important because they require exotic physics - gravitational accretion onto a supermassive black hole. The accretion flow is too distant to resolve with any current or near-future telescope. However, we can measure structures in an AGN through the "echo mapping" technique which uses light-travel time delays to measure size scales. It is analogous to sonar or radar, except that the AGN is creating both the signal and the echo - we are passive observers. In addition to constraining the geometry, echoes in different parts of Doppler-broadened emission lines can be used to map the velocity flow. In short, echo mapping is an indirect imaging technique that uses light echoes (time delays) between continuum and line emission to determine the geometry and kinematics of the gas flow inside a quasar or any other type of AGN. From these observations the mass of the black hole can be measured.
Back to page top


Contact time dependence of adhesive energy

Prof. Arlette Baljon, Department of Physics
San Diego State University

The work required to pull a polymeric material from a solid surface with which it is in contact through hydrogen bonding, has been studied through Molecular Dynamics simulations. As in experiments, the work varies with the time the polymeric material and the surface have been in contact. As contact lasts longer, more hydrogen bonds form. However, the increase is insufficient, to account for the full contact time dependence of the work required to break the bond. What needs to be studied to understand the strength of this bond is not so much the configuration at contact time as the rupture process in its full complexity. We will show the changes in hydrogen bond configuration during the rupture process and relate this to the required work. We employed the Povray package to visualize the rupture and a few short movies will be shown.

Back to page top


Biological Applications of Pattern-Formation Physics

Prof. Herbert Levine, Department of Physics
University of California San Diego

In the past several decades, physicists have made great strides in understanding how spatial patterns can arise in systems driven form from equilibrium. These successes have relied on a synergistic approach, combining carefully controlled experimentation, mathematical analysis of nonlinear equations and the judicious use of the vast increase in computational power at the modeler's workbench. Thus, we now have sensible frameworks for systems ranging from snowflake growth to rotating waves of chemical activity, from convective rolls in heated fluids to fracture patterns in strained solids. Of course, many important issues and significant challenges remain. But, with this sense of progress, many researchers began addressing the question of whether the study of pattern formation could help elucidate the formation of structure in biological systems, often called morphogenesis. Of course, living matter is much more complex than non-living. Yet, this talk will hopefully convince you that not only is this physics-based approach possible, but is in fact extremely promising. There are many processes one could choose to discuss; for definiteness, I will focus on the life cycle of the soil amoeba Dictyostelium discoideum. In this organism, starvation triggers a day-long series of transformations that take solitary amoebae and create a cooperative multicellular organism; the process culminates in a plant-like fruiting body containing spore cells specialized for survival in harsh conditions. Ideas from the physics of pattern formation have been used to help explain the wavefield used for cell guidance, the streaming of cells into the aggregate and the collective motions seen in multicellular stages. Currently, several groups are working on the singe-cell chemotactic response from a similar perspective.

Back to page top


How do cells create and maintain order: A biophysical look at molecular motors

Prof. Steven Gross, Department of Developmental and Cell Biology
University of California Irvine

Cells are highly structured, and much of that structure is created and maintained through the use of active transport. Such transport occurs through the action of molecular motors, small enzymes that move along directed polymers and drag 'cargos' such as vesicles from one place in the cell to the other. The details of how these molecular motors work are to some extent unclear: much is known about their single-molecule properties, but how those properties determine their activity in an intact organism is not at all obvious. In this talk I will provide an introduction to molecular motors, describe the biophysical tools used to investigate them, and go on to discuss the link between their single molecule properties an what we know to date about their function inside of cells.

Back to page top


Self-Assembly in Branched and Charged Polymers

Prof. Galen Pickett, Department of Physics
California State University Long Beach

Polymers are long-chain molecules which, when gathered together into dense clusters, produce materials of remarkable properties and stuctures dominated essentially by packing (no two chain segments can overlap) and the proliferation of internal degrees of freedom (allowing each chain to adopt many, many different conformations). When the chains are regularly branched, these packing and configurational effects are greatly enhanced. Adding electric charges to the polymers introduces long-ranged interactions. The balance between short and long-ranged forces in these systems gives rise to structures involving many chains on a mesoscopic length scale (much larger than individual polymer segments, but still macroscopically small).

Back to page top


Delayed oscillations in the mid-latitude climate system

Prof. Paola Cessi, Scripps Institution of Oceanography
University of California San Diego

A simplified model of the midlatitude ocean-atmosphere system is formulated, by enforcing global heat and momentum balances. The formulation shows that the wind-driven oceanic circulation influences the atmospheric winds by controlling the strength of the oceanic northward heat transport, and thus the atmospheric northward heat transport and temperature distribution. Because the ocean takes decades to adjust to changes in the winds, there is a delayed feedback between the atmosphere and the ocean which leads to an equilibrated state which is periodic in time. The period of the oscillatory solution is proportional to the transit time of oceanic Rossby waves across the basin, and thus of the order of decades. The variability of the coupled system is associated with periodic North-South displacements of the storm-track position accompanied by out of phase changes in oceanic currents. This out of phase relation between oceanic and atmospheric heat transports might lead to enhanced predictability of climate shifts on decadal time-scales.

Back to page top


The Dark Matter of the Universe

Prof. Kim Griest, Department of Physics
University of California San Diego

It is remarkable that we still do not know what the most common substance in the Universe is. It dominates gravity on the largest scales and controls the fate of galaxies and determines the motion of the Sun, but its nature is completely mysterious. I will discuss the reasons we believe Dark Matter exists, including the recent discovery that vacuum energy, the energy of empty space, is probably even more common than regular dark matter, and is the dominant component of the Universe. Then I will discuss various ideas of what the dark matter might be and some experiments that are searching for it. I will especially discuss our gravitational microlensing experiment that may have identified a portion of the dark matter and the questions our findings leave unresolved.

Back to page top


Cold Neutrons: The Perfect Way to Study Hot Rocks?

Prof. Katherine McCall, Department of Physics
University of Nevada at Reno

Neutron spectroscopy is widely used in materials science and solid state physics where the composition of the material studied can be carefully controlled. Geologic material (rock) tends to be quite uncontrolled, disordered, and inhomogeneous. However, there are some excellent reasons to use neutrons to study the physical properties of rock. One example of a question that can be asked is: How fast is the very little, but finite amount of water in rock at Yucca Mountain moving? Is it moving fast enough to facilitate contaminant transport? (Yucca Mountain, NV is the proposed site of storage for high level nuclear waste.)

Back to page top


Optical Coherence Tomography: a non-invasive imaging technique for biological tissue

Prof. Richard Haskell, Department of Physics
Harvey Mudd College

Optical Coherence Tomography arose about ten years ago to meet an imaging need in ophtalmology. It was then quickly adopted as a non-invasive probe of skin, and, because the instrument is fiber-based, it has been used through an endoscope to examine the linings of the esophagus and the gastrointestinal tract, as well as through a catheter to aid in the identification and removal of occlusions in arteries. It also serves as an ideal research tool to study dynamic processes in the early development of animals and plants. In this talk, the physical principles of OCT will be described, including its reliance upon a near-infrared light source with a short coherence length, and its sensitivity to Bose-Einstein photon bunching. The motion-sensitive technique of Doppler OCT that is used to measure blood flow in small vessels will also be described. As an illustrative example, time-lapses movies will be shown of gastrulation in a frog, the first major developmental event in the life of a vertebrate.

Back to page top


Vortex Dynamics in the Mixed Phase of High-Temperature Superconductors

Prof. Jose' Rodriguez, Department of Physics
California State University Los Angeles

High-temperature superconductors are perhaps the best-known examples of layered superconductors with short coherence lengths. Thermal and disorder-induced fluctuations of the Abrikosov vortex lattice in external magnetic field become extremely important in such case, leading to an extended vortex liquid phase that eventually freezes into a vortex solid phase. We shall discuss recent theoretical studies of these interesting forms of vortex matter via duality analyses of the layered XY model with uniform frustration.

Back to page top


Nanotechnology Overview

Dr. Barbara Jones, IBM Almaden Research Center

In the last few years there has been a marked increase in interest in nanostructures, from research, governmental, and industrial points of view. There are currently significant program initiatives from the governmental funding agencies. Just as significantly, industry is facing challenges due to fundamental limits affecting size in the semiconductor and storage industries, to name just two, as well as an increased realization of the potential of nanostructures for future devices. And finally, due to advances in lithography and imaging techniques, experiments are finally being able to see and explore structures on length scales previously only part of the theorists' models. Nanostructures may be defined as structures with restricted geometry in two or more dimensions, with accompanying length scales such that quantum effects are predominant. There are fundamental open questions which exist, which are being addressed by research ranging from very basic to the quite applied. I give an overview of some forefront research in nanoscience and incipient nanotechnology from theoretical, computational (simulations), and experimental points of view, including the promises of quantum computation and of structures engineered on the atomic scale.

Back to page top


Intermediate states in the melting transition of DNA oligomers

Prof. Giovanni Zocchi, Department of Physics and Astronomy
University of California Los Angeles

Although DNA denaturation has been studied extensively, the nature of the melting transition is still controversial. Here we combine UV spectroscopy with a separation method based on gel electrophoresis to quantify the presence of intermediate states (partially open molecules) throughout the melting transition of DNA oligomers. We find that the transition can be continuous or discontinuous, depending on the base sequence. In the first case, the relative length of melted segments (the "bubble size") is seen to increase smoothly to 1 (bubble size = molecule size) with increasing temperature; in the second case, the bubble size reaches a limiting value < 1 , then abruptly jumps to 1 (strands separate).

Back to page top


Hydrodynamic Models Relevant to Remote Sensing of the Ocean

Dr. Maria Z. Caponi, TRW Inc. Space and Electronics

A description will be presented of some of the dominant mechanisms responsible for the generation and evolution of the ocean surface spectrum and its relation to sensor returns, with emphasis on radar sensors. The modeling and simulation and the issues associated with the physics of the generation of waves by wind, their nonlinear wave-wave interaction and the dissipation due to breaking will be discussed. In particular, a simple model to study the stability of wind generated short waves and the modification of the stability region due to long waves will be summarized as well as the formulation to compute the evolution of a surface wave train due to nonlinear wave-wave interactions and a perturbation model to compute the scattering from these complex surfaces. The implementation of these models in an end-to-end numerical simulation will be presented and computational results will be compared with laboratory experimental results.

Back to page top