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Winter 2008/9 Colloquium Series

Colloquia are at 4pm, Thursdays, in 100 Willamette Hall and are preceded by coffee, tea, and cookies at 3:40 in the Wilamette Atrium.

The organizer of the Winter Term Colloquia is Jens Nöckel.

January 8

Dave Soper

Department of Physics
University of Oregon

Perturbative Quantum Chromodynamics

We use perturbative quantum chromodynamics to make predictions for what we will see in high energy hadron-hadron collisions, in particular at the Large Hadron Collider. The predictions are based on having just the Standard Model, having the Standard Model plus supersymmetry, or any number of other possibilities. Whatever new particles and interactions there are, getting from the new particles and interactions to predicted signals involves calculations. This talk concerns how we know what calculations to do and whether they are relevant to the experiments.

Host: Nöckel

January 15

Rubin Landau

Department of Physics
Oregon State University

Computational Physics as an Improved Model for Physics Education

The inclusion of research into a student’s education, even at the undergraduate level, is one of the hallmarks of a high quality education. Computational Physics encompasses a variety of topics, tools and modes of thinking that promises to enliven, enrich, and expand an undergraduate physics curriculum that has become narrow and self-absorbed. The talk will survey the need for CP education, some current research developments that have benefited from CP, and current thinking regarding the key elements in a Computational Science education.

Host: Nöckel

January 22

Daniel P. Lathrop

Department of Physics
University of Maryland

Laboratory models of planetary cores

The Earth’s main magnetic field is dynamic and evolving in a way that suggests we are headed for a magnetic reversal. As there is no predictive science of geomagnetism we currently lack even simple forecasts. Our scientific understanding is hampered by the complex state of flows within planetary cores that are responsible for generating the magnetic field. We probe aspects of the dynamics of flows in planetary cores and stars using experiments in liquid sodium, liquid helium, liquid nitrogen or water (not of course mixed together!). Using these, we explore how turbulence is affected by rotation, magnetic fields or both. These different approaches to using laboratory experiments are opening up a new direction to understanding the dynamics of the Earth’s outer core, other planetary interiors, and a host of astrophysical objects.

Host: Nöckel

January 29

Chris Benmore

Argonne National Laboratory

Quantum water

The quantum mechanical behavior of water is essential for sustaining life. Ever since the first x-ray diffraction measurements on water physicists have searched for evidence of small structural quantum effects in the liquid state. By substituting regular H2O with heavy water (D2O) quantum effects can be partially turned off, providing experimentalists with a unique tool to directly probe the hydrogen bond at the quantum level. In this talk I will review what we know about the structure of water and the role of quantum effects.

Host: Nöckel

February 5

Oksana Ostroverkhova

Department of Physics
Oregon State University

Recent Advances in Organic (Opto)electronic Materials

There is growing interest in using organic (opto)electronic materials for applications in electronics and photonics. In particular, organic semiconductor thin films offer several advantages over traditional silicon technology, including low-cost processing, the potential for large-area flexible devices, high-efficiency light emission, and widely tunable properties through functionalization of the molecules. Over the past decade, remarkable progress in materials design and purification has been made, which led to applications of organic semiconductors in light-emitting diodes, polymer lasers, photovoltaic cells, high-speed photodetectors, organic thin-film transistors, holographic displays, and many others. Most of the applications envisioned for organic semiconductors rely on their (photo)conductive and/or luminescent properties. In this presentation, I will review the current state of the field and summarize our recent results on photoconductivity and photoluminescence of novel high-performance organic semiconductors.

Host: Nöckel

February 12

Sarah Veatch

Department of Chemistry and Chemical Biology
Cornell University

Lipid rafts reach a critical point

Multicomponent lipid bilayer membranes can contain two coexisting liquid phases, named liquid-ordered and liquid-disordered. Recently, we demonstrated that large (micron-scale) and dynamic critical fluctuations are found in ‘simple’ ternary bilayer membranes prepared with critical compositions. Remarkably, robust critical behavior is also found in compositionally complex biomembrane vesicles isolated directly from living cell plasma membranes. This finding strongly suggests that cells tightly regulate plasma membrane protein and lipid content to reside near a critical point at physiological temperatures. Critical fluctuations may provide a physical basis of functional membrane heterogeneity in living cells. Current work focuses on characterizing the lateral organization of proteins and lipids on the intact cell surface and investigating possible functional implications of critical behavior in membrane biology.

Host: Parthasarathy

February 19

Nathan Kutz

Department of Applied Mathematics
University of Washington

Models for High-Power Pulsed Lasers

In general, there exist no analytical methods for quantitative analysis of the nonlinear propagation of ultrashort optical pulses in fiber, which underlies the operation of femtosecond-pulse fiber lasers. Such methods are needed now as the current generation of fiber lasers promise to greatly enhance the performance of practical instruments. In general, a pulse undergoes large changes in its temporal shape, spectral shape, and phase or frequency as it traverses a fiber laser, which in turn pose severe challenges to mathematical models. Self-similar pulse evolution is remarkable because monotonically-evolving, asymptotic solutions of the governing wave equation exist, despite the periodic boundary condition of a laser resonator. Highly-chirped pulse solutions can also exist in the presence of strong dissipation, and these so-called dissipative solitons represent a new class of laser pulses that offers remarkable behavior and performance. Quantitative models for lasers based on these pulses will be developed from first principles. These models will be studied in appropriate parameter regimes where simplified nonlinear dynamical systems theory can be utilized. In all cases, stability of the pulse solutions is the crucial issue. The theoretical efforts are highly interdisciplinary: combining asymptotic and perturbation methods, scientific computation, and rigorous mathematical analysis with models that are based on, and validated by, experimental observations.

Host: Deutsch

February 26

Michael Peskin

SLAC National Accelerator Laboratory
Stanford University

The Next Spectroscopy: New Elementary Particles at the Large Hadron Collider

A new particle accelerator, the Large Hadron Collider (LHC), is now beginning its operation at CERN in Geneva. Particle physicists expect that this accelerator will open to view the next set of interactions beyond the familiar strong, weak, and electromagnetic forces. In this colloquium, I will introduce the LHC physics program for proton-proton collisions. I will review experimental results in particle physics and astrophysics that point to a new particle spectroscopy at the LHC. I will discuss the difficulties of experimentation at the LHC and how they can be overcome. And, I will give some examples of spectroscopic measurements that might be possible at in the LHC experiments.

Host: Soper

March 12

Joe Eberly

Department of Physics and Astronomy
University of Rochester

Classical Trajectories and the Photoelectric Effect

An anomaly observed in atomic double ionization by intense short laser pulses appears to signal an electron-electron correlation four orders of magnitude stronger than photo-electric theory predicts. We will review this surprising new effect, and trace its development using laser-guided electron trajectories that behave almost entirely classically. The consequences for triple ionization are beginning to be explored.

Host: Raymer

March 13

Ido Golding

Department of Physics
University of Illinois at Urbana-Champaign


Information Processing in Bacterial Cells: Beyond First Approximations

In my lab, we attempt to better understand the way living cells represent information about their environment through the activity of their genes. To achieve this aim, one has to reexamine “first approximations” currently used when quantifying cellular information processing: (1) the description of cellular response in terms of a single “transcription rate” rather than in terms of discrete events; (2) the treatment of cellular reactions as governed by diffusion and occurring in a “well-mixed” cell. As a model system, we use the bacterium E. coli and its virus, phage lambda. We study their complex interaction at the level of individual events in space and time, thus going beyond the aforementioned “first approximations”.

Host: Kevan