# Physics

## Seminars in Fall 2015

All seminars are held at 4:10 PM in Bio 19, unless otherwise noted.
Refreshments will be served at 4:00 PM.

#### Upcoming Seminar

September 9, 2015
Student summer research talks

Aug 31 Thesis Start-Up Meeting Student summer research talks Student summer research talks Michael Kellman, Institute of Theoretical Science and Department of Chemistry and Biochemistry, University of Oregon"Quantum Thermodynamics, Entropy of the Universe, Free Energy, and the Second Law"We take the view that the standard von Neumann definition, in which the entropy $$S^{vN}$$ of a pure state is zero, is in obvious conflict with the statement of the second law that the entropy of the universe $$S_{univ}$$ increases in spontaneous processes, $$\Delta S_{univ} > 0$$. In a spirit similar to von Neumann himself in lesser-known work, we seek an alternative definition of the entropy of the universe that is in accord with the second law. We perform simulations of time dependent dynamics for a model quantum system becoming entangled with a quantum environment. We test the new definition of the entropy of the system-environment universe against the standard thermodynamic relation $$\Delta F_{sys} = - T \Delta S_{univ}$$, calculating system properties using the reduced density matrix and standard von Neumann entropy. Good agreement is obtained, showing the compatibility of an entropy for a pure state of a universe with the statement of the second law and the concept of free energy. Interesting deviation from microcanonical behavior within the zero order energy shell is observed in a context of effectively microcanonical ergodization within the much larger total basis of the time dependent universe. Shep Doeleman ’86, MIT Haystack Observatory"The Event Horizon Telescope: Imaging and Time-Resolving a Black Hole"A convergence of high bandwidth radio instrumentation and Global mm and submm wavelength astronomical facilities are enabling assembly of the Event Horizon Telescope (EHT): a short-wavelength Very Long Baseline Interferometry (VLBI) array, which can observe the nearest supermassive black holes with Schwarzschild Radius resolution. Initial observations with the EHT have revealed event horizon scale structure in SgrA*, the 4 million solar mass black hole at the Galactic Center, and in the much more luminous and massive black hole at the center of the giant elliptical galaxy VirgoA. Over the next 2-3 years, this international project will add new sites and increase observing bandwidth to focus on astrophysics at the black hole boundary. EHT data products will have an unprecedented combination of sensitivity and resolution with excellent prospects for imaging strong General Relativistic signatures, detecting magnetic field structures through full polarization observations, time-resolving black hole orbits, testing GR, and modeling black hole accretion, outflow and jet production. This talk will describe the project and the latest EHT observations. Student summer research Regina Jorgenson, Department of Physics, Willamette University"From the Shadows to the Light: Revealing the Mysteries of Galaxy Formation and Evolution using Damped Lyman alpha Systems"Since their discovery over 30 years ago, the true nature of damped Lyman alpha systems (DLAs) has remained a mystery. Notoriously difficult to detect directly in emission, DLAs are typically identified by their large equivalent width absorption features in the spectra of background quasars. Thanks to the Sloan Digitized Sky Survey (SDSS), over a thousand DLAs are now known and their absorption line properties well studied. Given their large column densities of neutral hydrogen gas, DLAs are believed to be the reservoirs of neutral gas for star formation across cosmic time. Evolution in DLA metallicity with redshift as well as the inferred star formation rates measured in roughly half of the DLA population indicate the presence of on-going star formation. However, numerous efforts to directly detect the galaxies that host these neutral gas-rich absorbers have failed. I will discuss the difficulties of this endeavor and the recent technological advances, namely Laser Guide Star Adaptive Optics (LGSAO) and the Keck/OSIRIS Integral Field Spectrograph, that have made possible significant strides in this field. I will present the first spatially resolved, direct detection of a DLA host galaxy and discuss the implications for the field of galaxy formation and evolution. Combining the power of absorption line and emission line diagnostics has the potential to yield unprecedented insight into the physics of high redshift galaxy formation. I will conclude by looking ahead to what advances near-future observational facilities such as JWST and ALMA will bring. Fall Break Davide Lazzati, Department of Physics, Oregon State University"Gamma-ray bursts" Janet Tate, Department of Physics, Oregon State University"Experimental thin films" Stephen Henderson, Washington State University - Vancouver"The mechanics of nutrient mixing in a submerged surfzone"Many lakes are beset by elevated nutrient levels, depleted oxygen levels, and algal blooms. Although the surfaces of small lakes often appear calm, submerged high-accuracy instruments reveal a rich variety of flow patterns controlling mixing of nutrients and pollutants. In Lacamas Lake, WA, we measured waves with 12-24 hour period, driven by density differences between surface and bottom waters, propagating upward through the lake. As waves traveled up the sloping lakebed, density contours pitched forward, leading to breaking in an underwater surf zone. The waves transported water upslope, and a compensating downslope mean current developed, analogous to the undertow observed on beaches. This undertow likely increases the importance of neared mixing. Similar density-driven waves are widespread in the ocean, and the dynamics discussed here may be relevant to mixing in a range of environments. Lucas Illing, Department of Physics, Reed College Thanksgiving Christopher Lee ‘00, Los Alamos National Laboratory"Resummation of perturbative expansions in quantum field theory"