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Spring 2011 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: James Schombert

April 7

Corrinne Mills

Harvard University

Refreshments will begin at 3:40 in the Olum Atrium

W Physics at ATLAS

The 2010 LHC data from proton-proton collisons at sqrt(s) = 7 TeV give us our first look at matter and forces at an energy scale unprecedented at colliders. W bosons decaying to a charged lepton and a neutrino are a benchmark Standard Model process, with the highest cross section of any process producing isolated high-momentum leptons. Although the integrated luminosity of this first data is orders of magnitude below what is projected for the next few years of LHC running, there is already a sufficient number of W candidates to begin characterizing W production at the LHC. I will show a set of measurements by the ATLAS collaboration based on the W candidate event sample,including the inclusive cross section and the lepton charge asymmetry. These measurements test our understanding of a new detector and of physics at a new energy scale, establishing the foundation needed to search for evidence of new particles and phenomena.

James Brau

April 14

Stacey Sorensen

Lund University

Refreshments will begin at 3:40 in the Olum Atrium

Momentum imaging of molecules: a probe of photo-induced dynamics on the femtosecond time scale
image for colloquium abstract

X-ray photoexcitation of molecules initiates complex dynamics in a variety of ways. Isomerization of molecules is a classic case of nuclear dynamics that takes place over a wide range of time scales. The experimental approach is to photoexcite a molecule or molecular cluster to a selected electronic state. Dynamics taking place in the excited state can be probed indirectly by spectroscopic methods, but by using a coincident electron-ion three-dimensional momentum imaging technique we can infer both the geometry of the molecule, and identify the time scale of these dynamic processes. The imaging technique relies on efficient collection of charged particles and on the knowledge of the momentum of all fragments. The analysis of correlations between fragment energies and angles offers a detailed picture of dissociation channels and the molecular geometries reached in the ionized system. Of particular interest are fast isomerization in linear molecules and photochemistry in nanoparticles such as clusters. I will show a few examples on small molecules.

Host: Stan Micklavzina

May 5

Itai Cohen

Cornell University

Refreshments will begin at 3:40 in the Olum Atrium

Flight of the Fruit Fly
image for colloquium abstract

There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature’s most accomplished aviators – the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and a new technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.

Host: Raghu Parthasarathy

May 12

Russ Donnelly

UO Physics

Refreshments will begin at 3:40 in the Olum Atrium

Dynamic Similarity

Dynamic similarity is a systematic way to conduct research in nonlinear subjects such as fluid mechanics. It includes subjects such as dimensional analysis which most physics students will have learned. In fluid mechanics there are so many variables it would be almost impossible to do research without making the equations dimensionless. The most famous of these dimensionless groups is the Reynolds number. We will discuss Rayleigh numbers and other dimensionless groups relevant to thermal convection.

This talk will include examples from general relativity, wind tunnel testing, fluid mechanics and geophysical fluid mechanics,. We will show how dynamic similarity is being used in the most advanced research in fluid mechanics today


May 19

Michael Peskin

SLAC National Accelerator Laboratory

Refreshments will begin at 3:40 in the Olum Atrium

The Search for New Elementary Particles at the CERN Large Hadron Collider

The Large Hadron Collider at CERN in Geneva, Switzerland, has just begun its operation. This accelerator and its experiments are enormous in many respects – in the physical size of the facilities, in the sizes of the experimental teams, and also in the stakes for the study of physics at the smallest distance scales. In this colloquium, I will describe the physics questions that motivate the LHC experiments, the detectors that are designed to meet these goals, and the challenges that the experiments must overcome. I will show some of the first results from the LHC. I will describe methods that will be used in the coming year to search for completely new types of elementary particles and forces.

Host: Davison Soper

May 26

Mick Davis/Jennifer Hoy & Jason Matthews

UO PhD Graduate Students

Refreshments will begin at 3:40 in the Olum Atrium

Mick and Jennifer will be speaking on: Quantitative Characterization of Complex Behavior of Mice in the Morris Water Maze – Jason will be speaking on: Efficiency of Anisotropic Thermoelectric Materials

Mick & Jennifer’s Abstract: Research in the field of neurobiology has recently moved toward addressing the complex nature of biological systems by taking a comprehensive, multi-scale approach to investigating neurological processes. The Washbourne lab is currently engaged in such a study on the role of specific genes in the development of complex behaviors in mice that are relevant to many neurological disorders. Accurate and quantitative measures now exist for determining the influence of specific genes on morphology at the scale of proteins, neuronal cells, and neuronal networks. However many studies are currently limited by a lack of quantitative characterization of observed complex behavior. The neuroscience community in general currently struggles to describe and measure behavior in a consistent and quantitative way that could reliably reveal interesting components in relevant behaviors. We attempt to address these issues through a collaborative effort between students in the departments of neuroscience and physics at the University of Oregon. We have used digital image analysis methods typically used for characterization of complex physical structures to characterize the behavior of mice observed in the Morris Water Maze, a standard learning and memory test.

Jason’s Abstract: At an efficiency of 25%, the transportation sector has the lowest efficiency of all the energy sectors. One technology already in use to improve this figure is regenerative breaking in hybrid electric cars. An additional fuel savings technology that auto manufacturers and researchers have been looking at is thermoelectric generators. These generators operate by recovering a portion of the wasted heat energy leaving every car in the form of hot exhaust gasses. Vehicles demonstrating this technology have already shown efficiency increases of 1-2%. An open question though is which type of thermoelectric material should be used. Anisotropic thermoelectric (ATE) materials represent one class of thermoelectrics; however, their efficiency to generate electricity has not been studied to the same level of detail as the more common isotropic materials. To help fill this gap, I have used Finite Element Methods and analytical means to analyze the efficiency of ATE materials. Of the two possible modes of operation for an ATE, I will show that one has greater efficiency while the other is more versatile in its implementation. I will then conclude with a comparison between the efficiencies of isotropic and anisotropic materials.

Host: Oregon Center for Optics

June 2

Meredith Betterton

University of Colorado, Boulder

Refreshments will begin at 3:40 in the Olum Atrium

Motor Proteins that Change the Length of Filaments

In cells, motor proteins can walk along filaments that act as one-dimensional “tracks” for the motors. In some cases, the motors can also change the track by lengthening or shortening the filament from its end. This talk introduces this problem and its biological context, then discusses theory of this problem, based on a few simple ingredients: motors bind to, or unbind from a one-dimensional track, move along the track, and promote changes in track length at its end. Crowding effects can be important when multiple motors interact on the same track, and the coupled dynamics of the motors and track can show interesting new effects. Under the right conditions, coupled motor motion and filament shortening can act as a filament length sensor. In addition, the filament may have its own length-changing dynamics which can be altered by the motors. I’ll discuss biological applications of this model, particularly microtubule shortening by kinesin-8 proteins in mitotsis and the control of antiparallel microtubule overlaps by PCR1 and Xklp1 in anaphase.

Host: John Toner