Physics

Seminars in Spring 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

February 4, 2015

Douglas H. Kelley, Department of Mechanical Engineering, University of Rochester

Flux and burn: Coherent structures in scalar and reactive mixing

Jan 28

Matthew Ross, Department of Chemistry, University of Washington
Understanding Quantum Mechanics in Solution: Spectroscopy with Lasers, X-rays, and X-ray Lasers

While the simple solutions to Schroedinger's equations have served as the foundation of our understanding of quantum mechanics for nearly 100 years, even today's fastest computers struggle to compute wavefunctions for systems larger than a few dozen atoms.  One of many methods to understand quantum mechanics of complex chemical systems is through the use of spectroscopy to measure both static energy levels and system dynamics. In particular, laser spectroscopy can cover many orders of magnitude in the energy scales of chemical and atomic systems. In this talk, I will discuss how laser, X-rays, and X-ray lasers can be used to study the quantum mechanics of chemical species in solution.

Feb 4

Douglas H. Kelley, Department of Mechanical Engineering, University of Rochester
Flux and burn: Coherent structures in scalar and reactive mixing

Fluid mixing is a key process that must be understood in order to make predictions about physical phenomena ranging from marine phytoplankton growth to dynamo action to next-generation battery technology. I will talk about two recent projects elucidating the fundamentals of mixing. One focuses on scalar mixing and connecting it to coherent structures in the underlying flow. I will show that the widely-used Lagrangian Coherent Structures (LCS) relate not only to the kinematics of flow, but also to dynamics of scale-to-scale energy flux. In the second project, my team and I study mixing of reacting materials, where propagating reaction fronts interact with underlying fluid flow. By simultaneously measuring both flow and front location, we are characterizing reaction-diffusion-advection systems. Our goal is to develop a robust theory of coherent structures that generalizes LCS.

Feb 11

Christopher E. Malec, Material Physics Division, Naval Research Laboratory
Detecting Single Domain Walls with a Hall Sensor

Ferromagnets have long challenged physicists with a rich variety of phenomenon to study and explain.  Because of their largely unique hysteretic properties, they have also long played a dominant role in memory storage.  Today, the density and stability of magnetic hard drives (magnetic based memory) battle with the speed of RAM (floating gate technologies).  New schemes for manipulating magnetic information will be required in the future, combining advantages of both methods and adding to them lower power consumption and new functionalities.  The manipulation of ferromagnetic domain walls is currently seen as a possible route towards new memory devices.  As part of my own work on this topic I will discuss a new electronic device making use of an InAs heterostructure and the Hall effect to detect a single domain wall in a nano-fabricated ferromagnet. I will discuss how the device is made at the NRL, operational principles, and current results.

Feb 18

Paul D. Nuñez, Jet Propulsion Laboratory, California Institute of Technology
Resolving Stars and Their Environments with Optical Interferometry

Optical long-baseline interferometry has allowed achieving the highest angular resolution on stars and their environments. Stars are no longer seen as point sources, but as extended objects with surface structures and circumstellar (dusty) environments as close as a fraction of an astronomical unit. We have been using the Center for High Angular Resolution Astronomy (CHARA) to study the near-Infrared light emitted from hot dust near the habitable zone of stars, providing clues on exo-planet formation and detectability. The "corner-stone" of optical interferometry is the acquisition of interference fringes between separate telescopes. Obtaining even more detailed images of stars and their environments requires the combination of light from many telescopes, which has motivated the construction of a prototype multi-telescope interferometer known as the Hypertelescope. I will discuss the interpretation of interferometry in terms of correlations between different space-time points of the wave-front. By exploiting higher orders of correlation we will measure classical interferometric observables while being insensitive to atmospheric turbulence and optical imperfections.

Feb 24

Harry L. Swinney, Department of Physics, The University of Texas at Austin
DIVISION OF MATHEMATICS AND NATURAL SCIENCES PUBLIC LECTURE: How the Zebra got her stripes: Emergence of ordered patterns in physical, chemical, and biological systems

From spatial patterns like the stripes on a zebra to temporal patterns like the rhythmic beating of the heart, patterns are ubiquitous in Nature. Understanding how these patterns emerge is one of the science’s most enduring mysteries. In this lecture, geared toward a general audience, Professor Harry Swinney of the University of Texas at Austin will discuss how ordered patterns emerge as systems are driven away from thermodynamic equilibrium by imposed gradients (e.g., pressure, temperature, or nutrient concentration gradients). While no general theory of pattern formation currently exists, Prof. Swinney will discuss how new analysis techniques, experiments, and computational methods can general insights into pattern formation in a diversity of physical, chemical, and biological systems.

Feb 25

Harry L. Swinney, Department of Physics, The University of Texas at Austin
How competing bacterial colonies survive by killing siblings

We examine the growth of colonies of a rod-shaped bacterium that is commonly found in soil. Bacteria within a colony exhibit a swarming behavior reminiscent of fish in schools. When neighboring colonies of these bacteria grow toward one another, the growth slows and stops. Analysis of the gel between the competing colonies reveals the presence of a previously unknown lethal protein. Why doesn’t this toxin kill the bacteria secreting it?  A mathematical model helps answer this question. Further, sub-lethal concentrations of the toxin induce the rod-shaped bacteria to switch to a spherical shape that is unaffected by the toxin. Thus the bacteria adapt to adverse environmental conditions by a change in form, but this change is reversible -- if favorable conditions are recovered, the bacteria revert to the rod-shaped motile form.

Mar 4

Keith R. Dienes, Department of Physics, University of Arizona
Dynamical Dark Matter: A New Framework for Dark-Matter Physics

In this talk, I will provide an introduction to an alternate framework for dark-matter physics which we call "Dynamical Dark Matter" (DDM).  Within this framework, the requirement of dark-matter stability is replaced by a balancing of lifetimes against cosmological abundances across an ensemble of individual dark-matter components. Within this framework, it is this DDM ensemble which collectively serves as the dark-matter "candidate" and carries the observed dark-matter abundance WCDM. This leads to a highly dynamical cosmology in which quantities such as WCDM experience non-trivial time-dependences beyond those normally associated with the expansion of the universe. DDM ensembles arise naturally in many extensions to the Standard Model, including string theory and theories with large extra spacetime dimensions. Moreover, the DDM framework can lead to many striking signatures at colliders as well as at direct- and indirect-detection dark-matter experiments - signatures which transcend those usually associated with traditional dark-matter candidates.

Mar 11

Student Summer Research Talks

Mar 18

Senior Thesis Presentations

Mar 25

Spring Break - No Physics Seminar

Apr 1

Senior Thesis Presentations

Apr 8

Senior Thesis Presentations

Apr 15

Senior Thesis Presentations

Apr 22

Senior Thesis Presentations

Apr 29

Senior Thesis Presentations