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Winter 2013 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 Fall Term Colloquia is: Eric Corwin

Jan 10, 2013

Jay Davis

President, The Hertz Foundation

Nuclear Forensics: A Capability We Hope Never to Use

Stopping the transport of materials that could be used to make nuclear weapons depends in part on being able to identify their sources, and possibly those who have made or intended to use them. This identification is doubly important should a diverted or improvised device be detonated anywhere in the world. Who the actors are, how they obtained their materials, and who might have helped them are all urgent questions in such a case. The tools and capabilities to work these problems, the operational steps by which they are used, and the organizational issues with actually conducting such a reverse engineering operation for a nuclear device will be described. The problem has been famously described as “unbaking a cake.” Jay Davis has been working on this issue for twenty years in difficult venues ranging from Iraq to Washington. He claims no credit for the failure to date of the occurrence of such an event.

Host: Jim Brau

Jan 17, 2013

Benjamin Aleman

University of California, Santa Barbara

Physics at the nanoscale: Nanotubes, graphene, and spins in diamond

Carbon nanotubes, graphene, and diamond hold an important role in the exploration of new physics and applications at the nanoscale. As a result of their strength, large surface-to-volume ratio, and small physical size, carbon nanotubes and graphene have enabled the study of new regimes in nanoelectromechanical systems (NEMS). Also, single spins associated with the nitrogen-vacancy defect in diamond are opening pathways toward room-temperature quantum information processing and nanometer-scale sensing. Here, I discuss specific uses of carbon nanotube and graphene NEMS to improve the resolution of scanning probe microscopy and to study novel non-linear dynamics that emerge in NEMS. Furthermore, I will describe the use of optically trapped nanodiamonds as an approach to three-dimensional spin-based scanning probe magnetometry and thermometry in fluids.

Host: Hailan Wang

Jan 24, 2013

John Royer

National Institute of Standards and Technology

Precisely cyclic sand: phase diagram of periodically sheared frictional grains and self-organization

We perform molecular dynamics (MD) simulations of spherical grains subjected to cyclic, quasi-static shear in a 3D parallelepiped shear cell. Using a standard routine for MD simulations of frictional grains, we simulate thousands of shear cycles, measuring grain displacements, the local packing density and changes in the contact network. We find that cyclic shear leads to dynamic self-organization into several phases with different spatial and temporal order. We present a phase diagram in strain – friction space which shows chaotic dispersion, crystal formation, vortex patterns and most unusually a disordered phase in which each particle precisely retraces its unique path. Particles remain in these periodic trajectories despite the fact that the contact network reveals a sizable fraction of disconnects in this limit cycle.

Host: Eric Corwin

Jan 31, 2013

Dave Mitzi

IBM T. J. Watson Research Center

High performance CZTSSe: Device physics and material challenges

Kesterite Cu2ZnSn(Se,S)_4 (CZTSSe) materials are being pursued as an emerging solar cell technology, unrestrained by the material availability issues encountered by other leading thin-film technologies—e.g., CdTe and CuInGaSe (CIGS). Despite recent demonstration of solution-processed CZTSSe devices with world record power conversion efficiency of 11.1%, these devices still lag the 16-20% efficiency range achievable with more established CIGS/CdTe technologies. Here we review the current understanding of emerging CZTSSe material and device physics, using a series of characterization and comparison (relative to higher performing CIGS) studies to identify key performance bottlenecks in the new technology such as high Voc deficit and low fill factor. These findings help to highlight key areas of improvement needed to realize a future pervasive CZTSSe technology.

Host: Shannon Boettcher

Feb 7, 2013

Rose Honey

Harvard Graduate School of Education

Bull Trout & Bitterroots: Traditional Culture in Science Classrooms on the Flathead Indian Reservation

In many Indigenous communities around the world, there is no separation between traditional knowledge and scientific knowledge. The Cultural Border Crossing theory speculates that Indigenous students in mainstream science classrooms are faced every day with a conflict between the life they live and the world of mainstream science that challenges their ability to learn (Aikenhead & Jegede, 1999). Incorporating relevant aspects of their culture into science lessons is believed to help these students negotiate their life-world culture vs. the culture of school science. This study explores how 5th – 8th grade students who live on the Flathead Indian Reservation think about traditional knowledge as it relates to the science that they learn in school, and how intrinsically motivated they are to learn science that is related to their traditional culture. The participants attend either classrooms that integrate their culture into the science they are learning or classrooms that do not. Our results demonstrate that being taught by a teacher who is trained to incorporate cultural knowledge into their science lessons can be a significant predictor of how motivated the students are to learn. By relating cultural traditions to mainstream science, youth can be motivated to learn science and consequently consider STEM academic and career paths. This would develop leading future American Indian professionals who are better equipped to make well informed, culturally grounded, community based natural resource and land management decisions.

Rose Honey did her undergraduate thesis in Russell Donnelly’s laboratory studying the properties of turbulence generated by a horizontal grid oscillating vertically in a tank of water. This difficult experiment is now the subject of two papers being written with Rose for the Physical Review. Russell will explain briefly what the physics issues are about. In the meantime Rose has decided to get a doctorate in teaching science to American Indians and she will explain her methods to us.

Host: Russ Donnelly

Feb 14, 2013

Mariangela Lisanti

Princeton University

Confronting the Dark Matter Puzzle

The nature of the dark sector is one of the most important questions to be addressed by current astro- and particle physics experiments. I will review how the confluence of data sheds light on the properties of dark matter, from its particle interactions to its distribution in the sky. I will then discuss our recent theoretical work suggesting the presence of more substructure in the local halo than previously expected. These results have important implications for direct detection experiments and offer the possibility of mapping out local dark matter structure using low-metallicity stars in the stellar halo.

Host: Spencer Chang

Feb 21, 2013

Laura Clarke

North Carolina State University

Embedded metal nanoparticles as light-driven, localized heaters within polymeric solids

Metal nanoparticles strongly absorb specific wavelengths of visible/infrared light with no (or only a very weak) radiative relaxation by which to release this energy. As a result, the absorbed energy is efficiently converted to local heat (a photothermal effect). With an effective cross-section of up to 10 times its physical size, each particle acts as a “super-sized” absorber even when embedded within a transparent material environment, resulting in dramatic heating originating at the particles. Thus, with spatially-uniform illumination, one can metaphorically reach inside the sample and apply heat to pre-selected subsets (e.g., causing them to dramatically change properties due to actuation, cross-linking, crystallization, or chemical reaction) without heating the surface or strongly affecting the remainder of the material. I’ll discuss recent results demonstrating selective heating of metastable nanostructured samples, anisotropic processing by using the polarized absorption of rod-like particles, measurement of average internal sample temperatures via a sensitive, relative fluorescence approach with embedded molecules, estimation of the particle temperature from rotational diffusion, and how this temperature gradient changes as a function of irradiation intensity.

Host: Raghu Parthasarathy/Eric Corwin

Feb 28, 2013

Eric Brown

University of California, Merced

Organized flow structures in turbulence

Turbulence is of tremendous important in a wide range of astrophysical, geophysical, and engineering flow problems. Unfortunately, the equations of motion are notoriously difficult to solve. On the other hand, turbulent flows often contain large, coherent, flow structures such as convection rolls in the atmosphere or ocean currents. These structures provide an organizing feature which I use to model flows with relatively few equations, which leads to solvable models. As an example, I will present results of Rayleigh-Benard convection experiments, in which a container is filled with water and heated from below. Buoyancy drives a flow which organizes into a roll-shaped circulation which spontaneously breaks the symmetry of the system. As a consequence, this roll exhibits a wide range of dynamics including erratic meandering, spontaneous flow reversals, and several oscillation modes. A simple model consisting of stochastic ordinary differential equations quantitatively reproduce these observed flow dynamics. These results may lead to more general and relatively easy to solve models for turbulent flows with potential applications to climate, weather, and even the turbulent dynamo that is responsible for Earth’s magnetic field. To test the generalization of these models, I am building a laboratory experiment that will use magnetic particles suspensions in liquid metals to produce the universe’s smallest dynamo.

Host: Eric Corwin

Mar 7, 2013

Alan Litke

Santa Cruz Institute of Particle Physics at UC Santa Cruz

What Does the Eye Tell the Brain? A Journey from High Energy Physics to Neural Systems

The back of the eye is lined by an extraordinary biological pixel detector, the retina. This living neural network is able to extract vital information about the external visual world, and transmit this information in a timely manner to the brain. In this talk, after a brief introduction to the retina, I will describe how we measure its functional properties, show what we have learned about its functional organization, and discuss studies aimed at guiding the design of retinal prosthetic devices. This project was inspired by the development of particle detectors for high energy physics experiments, including the search for the (now discovered) Higgs Boson.

Host: Cris Niell, Biology

Mar 14, 2013

Mike Thorpe

Arizona State University and Oxford University

Rigidity Theory and Applications

Many interesting phenomena occur in macromolecules and material structures that are poised between rigid and flexible. We describe the modern theory of rigidity and show how it can be used to analyze networks of constraints. The percolation phase transition from rigid to flexible can be either second order or first order as shown by exactly soluble models, and relates the random packing of spheres etc. The rigid region decomposition of a network can be used as input to geometrical simulation, where the various rigid parts of a system are moved, while maintaining all the constraints; both equalities and inequalities. Hence local stereochemistry is maintained during conformational changes. This approach, which is used in video-games, can be applied to zeolites that are important for cracking petroleum and proteins where flexibility is often associated with function.

Host: Eric Corwin/Roger Haydock