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Spring 2012 Colloquium Series

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

The organizer of the Spring Term Colloquia is: Jens Nöckel


April 5

Jay Wacker

SLAC

Refreshments begin at 3:40 in the Olum Atrium

The Higgs and the LHC, a very long engagement

Host: Graham Kribs


April 12

Jens Nöckel

Department of Physics, University of Oregon

Morphology, materials and metastability in wave-chaotic micro-optics

As the miniaturization of photonic devices proceeds to smaller size scales and unconventional shapes, engineers encounter new challenges even in old disciplines such a classical electrodynamics. The venerable workhorses of optics, such as ray picture and paraxial approximations, reach their limits of validity when we try to confine light in spaces spanning only microns. However, lasers of such dimensions are of great technological interest, and the goal of this talk is to provide some physical understanding that can help guide optical design at these length scales in the “transition regime” between ray and wave optics. When rays in a resonator become non-paraxial, they generically exhibit chaos. We gain insights into the corresponding electromagnetics by exploiting ideas from quantum chaos, the study of quantum wave equations whose classical limit displays chaotic dynamics. New questions arise for this field because of the special role played by boundary conditions, material composition, and the openness of the system.

Host: Nöckel


April 19

Günter Radons

Chemnitz Technical University, Germany

Complex Hysteresis – The Memory of Magnets, Floods and Markets
image for colloquium abstract

Using a simple mechanical device the principles of complex hysteresis are explained and demonstrated experimentally. Subsequently it is shown, how these principles find ubiquitous applications in diverse fields of nature and society. Examples are magnetic materials – the basis of modern hard disc storage technology, soil-moisture hysteresis with its implications for flood prediction, or the dynamics of labor markets under external influences. Basic methods for the modeling of such systems are introduced. The interaction between systems showing complex hysteresis and their environment leads to novel challenges in the field of nonlinear dynamics. Some aspects thereof are highlighted.

Host: Nöckel


April 26

Craig Rasmussen

CASIT, University of Oregon

From Supercomputers to GPUs: What a physicist needs to know about current Computational Ability

Recent changes in supercomputer architectures include the addition of many homogeneous processor cores to each supercomputer node, as well as the addition of Graphical Processing Units (GPUs). When combined with a node count of 100K and more, this massive amount of parallelism holds the promise of substantially boosting the performance of scientific applications. However, this promise brings with it an additional increase in code complexity and additional programming costs necessary to realize these performance gains. So how is a physicist to view this maze and effectively use supercomputers to further scientific research? This talks breaks down the CS jargon and provides the minimal amount of detail necessary to understand how to effectively plan to use these new resources. To help understand the potential, various applications in the Department of Energy’s flagship SciDAC (Scientific Discovery through Advanced Computing) program are described. As another instance of acceleration of a scientific application, we describe the design of parallelism in the PetaVision framework, created for building simulations on this scale. For example, it has been demonstrated that a computational fluid dynamic (CFD) application can achieve up to a 40 times increase in performance on a single processor over a purely serial version of the original code. In addition, using distributed nodes of GPU accelerators, it is now possible to build neural simulations with nearly the computational power of the human visual cortex.

Host: Bothun


May 3

Marina Guenza

UO Department of Chemistry, Institute of Theoretical Science

Some challenges in the dynamics of macromolecules

Because it develops on a wide range of timescales, the dynamics of polymer liquids is difficult to formalize through a single theoretical approach and to study by computer simulations. This seminar is an overview of some unresolved questions in the field of polymer dynamics and of our attempts to address them.

We have proposed a Langevin approach to the dynamics of polymeric liquids, which directly relates the microscopic molecular structure to macroscopic dynamical properties. Different theories of polymer dynamics are conventionally used to describe dynamics in the unentangled and entangled regimes. Our approach is Langevin equation, where intermolecular interactions are explicitly accounted for, which applies in both regimes. Inputs to the theory are structure and semiflexibility of the polymeric chain, its degree of polymerization, and the specific thermodynamic conditions. Predicted dynamics, tested against data of dynamical properties observed experimentally and in simulations, show good agreement.

To overcome the limitations of computer simulations we have proposed a coarse-grained (CG) method where polymers are represented as soft spheres or chains of soft spheres. Our CG approach is based on liquid state theory, as it combines the rescaling of the pair distribution function with the PIRSM theory at the atomistic level. The simplicity of the model allows for analytical solutions of many of the relevant properties, both static and dynamic, and shows thermodynamic consistency for the CG model. A first-principles analytical rescaling procedure is presented for the dynamics and tested against experiments and atomistic simulations for polymer melts of different chemical structures, showing good agreement.

Host: Raymer


May 10

Spencer Chang

Department of Physics, University of Oregon

Underground Searches for Dark Matter in the Galactic Halo

In this talk, I will give an introductory overview of dark matter direct detection experiments, a class of underground experiments searching for dark matter in our galaxy. There is an elegant dark matter framework called the weakly interacting massive particle (WIMP), which suggests a detectable scattering cross section for dark matter off target nuclei. An overview of interesting past and future experiments will be given, focusing on a longstanding observation by the DAMA experiment of an annual modulation that is suggestive of dark matter. I will review both dark matter and background explanations of this modulation and find that both are lacking. In particular, I will show that cosmic ray muons, which are known to modulate, cannot be solely responsible for the signal. I will end with an outlook on how these hypotheses will be tested in the future.

Host: Nöckel


May 17

Richard Taylor

Department of Physics, University of Oregon

Fractal vision: using retinal implants to restore vision to the blind

Technological advances over the past few decades have transformed the concept of bionic eyes from the wild speculations of science fiction into the practicalities of science fact. For one thing, the number of sensors that capture light in digital cameras is fast approaching the 127 megapixels of the human eye. Furthermore, surgeons can now insert electronic chips into the retina. With over one million people diagnosed with retinal diseases each year, the grand hope is to restore vision by replacing damaged rods and cones with artificial photoreceptors. Clinical trials are already under way using retinal implants based on camera chip technology. However, there are crucial differences between how the human visual system and the camera “see”. These differences arise because, while the camera uses the Euclidean shapes favored by engineers, the eye exploits the fractal geometry that is ubiquitous throughout nature. In this talk, I will discuss the advantages predicted for fractal-based implants. These include an increase in visual acuity by over an order of magnitude, potentially allowing people to read text and facial expressions – essential capabilities for performing every day tasks. Furthermore, unlike current designs, fractal implants will trigger the physiological mechanism used by the human visual system to prevent our stress-levels from soaring. This latter effect holds crucial implications for society: the U.S. spends over 0 billion annually on stress-induced illnesses, and stress is increasingly blamed for precipitating debilitating disorders such as schizophrenia and cancer.

Host: Nöckel


May 24

Dedra Demaree

Department of Physics, Oregon State University

Applying current research findings from cognitive and neurosciences to physics education
image for colloquium abstract

In 2007, Dedra Demaree was hired to lead reform of the introductory courses at Oregon State University. Her assessment work has led (among other projects) to a PhD student developing a validated survey on student physics identity, and extensive consideration of learning environments and what motivates student participation. In parallel work, Dr. Demaree collaborates with the University of Cape Town to evaluate bridging programs at the undergraduate and graduate level to help under-prepared students succeed in physics programs. Part of this work has centered on studying what impacts how a student responds to a physics question, and has led to the development of a cognitive model for activation of resources and effective use of working memory during problem solving. These projects seem very unrelated: community learning environments and resource activation/working memory use however, the latest research findings from cognitive and neurosciences provide a compelling information on how the brain is wired that requires us to see these as intrinsically connected. To borrow from Steve Alsop (2005) “the complexity of science education necessitates recognition of the mutually constitutive nature of cognition and affect…. At all levels, cognition and affect are seen as fused, inseparable… affect should be seen as axiomatic, at times making science education difficult, but above all else, actually making science education possible.” This talk will share these latest research findings in the context of physics education.

Host: Nöckel


May 31

John Toner

Department of Physics, University of Oregon

Birth, Death, and Flight: A Theory of Malthusian Flocks

May 31, 2012
4:00 pm
100 Willamette Hall
Physics Colloquium
John Toner
Department of Physics, University of Oregon
Birth, Death, and Flight: A Theory of Malthusian Flocks
Reception begins at 3:40 in the Olum Atrium
Abstract: I study “Malthusian Flocks”: moving aggregates of self-propelled entities (e.g., organisms, cytoskeletal actin, microtubules in mitotic spindles) that reproduce and die. Long-ranged order (i.e., the existence of a non-zero average velocity) is possible in these systems, even in spatial dimension d=2. Their spatiotemporal scaling structure can be determined exactly in d=2; furthermore, they lack both the longitudinal sound waves and the giant number fluctuations found in immortal flocks. Number fluctuations are very persistent, and propagate along the direction of flock motion, but at a different speed.

Host: Nöckel


June 7

William Cresko

Center for Ecology and Evolutionary Biology

Drinking from a fire hose: Exploring evolution using massive amounts of genomic data

Our understanding of the biological world was revolutionized in 1996 by the sequencing of the first complete genome of an organism. Because of the high cost of DNA sequencing, research in this first phase of the ‘genomics revolution’ focused on traditional laboratory model organisms. Advances in DNA sequencing over the last five years have led to an open source genomics revolution, in which sequencing has become much more economical and has moved from large genome centers to individual laboratories. These new sequencing technologies are easily modified to produce tools that are tailored to biological problems such as defining the complete set of DNA sequence variants among multiple individuals, enumerating the changes in the amount to which genes are activated, and linking genetic variation to differences among healthy and diseased organisms. I will describe some of our discoveries using these data concerning the genomic basis of rapid evolution in populations of organisms as well as populations of cells destined to become tumors. These experiments involve billions (and soon trillions) of data points, and the manner in which they should be analyzed is still not clear. I will therefore discuss our initial attempts at developing analytical theory and computational tools for these data, highlight similarities in problems and approaches between physics and engineering with respect to genomics, and briefly describe the emergence of the field of functional systems biology. My ultimate goal is to highlight a few novel ways that physics and biology can cross pollinate and lead to even deeper understanding of evolution.

Host: Parthasarathy