2011 - 2012 Academic Year Colloquium Series
Monday, November 7, 2011
Monday, October 17, 2011
Dr. Andrew M. Rappe, Department of Chemistry, Department of Materials Science and Engineering, Pennergy: the Penn Center for Energy Innovation, University of Pennsylvania
Ab initio design of materials and surfaces for Green Energy Applications
The present search for new ways to harness, store, convert, and use energy inspires modern research in many fields. First-principles electronic structure calculations offer a window into materials, revealing how favorable properties arise and offering opportunities to propose new materials with improved properties. In this talk, three examples of theoretical modeling guiding the development of surfaces and near-surface materials for energy applications will be described.
1. The simple creation of epitaxial nonstoichiometric surfaces through annealing will be presented, and their potential as novel catalysts discussed.
2. The use of ferroelectricity to control surface composition and structure will be highlighted, focusing on bare surface catalysis, oxide control of deposited metal morphology, and
oxide control of metal reactivity.
3. The use of aliovalent dopants to make ferroelectric oxides efficient single-phase photovoltaic materials will be presented. Through these examples, the interplay
between theoretical and experimental design of novel materials for energy applications with be emphasized.
Monday, September 26, 2011
Dr. Steven May, Department of Materials Science & Engineering, Drexel University
Oxide Interfaces: Emerging Routes to Enhanced Material Functionality
Scientific interest in ABO3 perovskite oxides remains intense due to the wide range of physical behavior present in these materials, such as high-TC superconductivity, electronic correlations, metal-insulator transitions, ferroelectricity and magnetism. Recent advances in thin film deposition techniques, such as molecular beam epitaxy, have made it possible to synthesize perovskite heterostructures and superlattices with unit cell precision. This talk will focus on how the formation of oxide heterostructures and interfaces can be used to realize novel electronic and magnetic properties. I will first describe how the electronic properties of oxide interfaces can give rise to novel magnetic properties. Next, I will discuss how interfacial structural coupling can be used to stabilize non-equilibrium bond angles and lengths, thereby altering a wide of functional properties.
2010 - 2011 Academic Year Colloquium Series
Thursday, April 14, 2011
Dr. Frans Pretorius, Department of Physics, Princeton University
When: 4:00 PM
Where: Mendel 101
Refreshments will be served at 3:30 PM
Black Holes: Probes of the Cosmos & Fundamental Physics
The class of spacetimes with event horizons contain some of the most fascinating solutions to the equations of general relativity. Over the past few years, numerical simulations of the field equations have begun to reveal some of the more dynamical, strong-field solutions not amenable to exact analytical or perturbative treatments.
In this talk, I will describe 3 such scenarios. First, the inspiral and merger of two black holes, which is thought to occur frequently in the universe. Such events are powerful emitters of gravitational waves, and a concerted world-wide effort is currently underway to observe the universe through gravitational waves.
Second, I will discuss the ultra-relativistic collision of two solitons. Arguments suggest that at sufficiently high velocities gravity dominates the interaction, causing a black hole to form regardless of the internal structure or nature of any non-gravitational interaction. These arguments underly claims that the Large Hadron Collider will produce black holes in speculative large extra dimension scenarios. Finally, I will show results elucidating the fate of a black string in 5 dimensions, subject to the Gregory-Laflamme instability. Rather remarkably, the event horizon exhibits dynamics akin to a low viscosity fluid stream suffering the Raleigh-Plateau instability, where the horizon starts to form spherical "beads" connected by ever thinner string segments that are themselves unstable, and the instability unfolds in a self-similar cascade. This process reveals arbitrarily large spacetime curvatures to an external observer, culminating in naked singularities. This is therefore a generic example of cosmic censorship violation in higher dimensional Einstein gravity.
Thursday, April 7, 2011
Dr. David Goldberg, Department of Physics, Drexel University
When: 4:00 PM
Where: Mendel 101
Refreshments will be served at 3:30 PM
"Where's the Matter with Clusters?"
Clusters of galaxies are the largest collapsed structures in the universe. Their mass maps reveal properties of the primordial density field, and their mass distribution as a function of time is a sensitive probe of Lambda-CDM cosmology. However, it has been known for nearly a century that the luminous matter in clusters is not necessarily a good indicator of the mass. In this talk, I will describe how to map rich clusters using gravitational lensing, what numerical simulations have led us to expect, and what the differences between observation and theory can tell us about the nature of the universe.
Thursday, February 24, 2011
Dr. V. Parameswaran Nair, Department of Physics, City College of the CUNY
When: 4:00 PM
Where: Mendel 101
Refreshments will be served at 3:30 PM
Feyman's Last Problem 30 years later: Liquid Helium and QCD
In 1954, Feynman gave a beautiful analysis of superfluid Helium using general properties of wave functions and of the space of particle configurations. In the 1970s, starting with the discovery of asymptotic freedom and the emergence of QCD, the question of quark confinement and the generation of a mass gap was recognized as an important question about the nonperturbative behavior of nonabelian gauge theories. Needless to say, this has proved to be a very difficult problem to analyze. Two spatial dimensions would provide the simplest case of a nontrivial gauge theory which could exhibit confinement and mass gap. In 1981, Feynman tried to use a set of arguments similar to what he had developed for superfluidity to argue for the existence of a mass gap for these theories. Did he succeed? Did he fail? If so, to what extent? I shall give a brief recapitulation of Feynman's arguments for Helium and then present his arguments for YM(2+1), in a slightly modernized and more precise language, so that we may gain some perspective on how much progress has been made. The emphasis will be on concepts more than on detailed formulae.
Thursday, October 21, 2010
Dr. Marija Drndic, University of Pennsylvania
When: 3:30 PM
Where: Mendel 115
Refreshments will be served at 3:00 PM
Nanosculpting Solid-State Devices with Electrons and their Biophysics Applications
Manipulation of matter on the scale of atoms and molecules is an essential part of realizing the potential that nanotechnology has to offer. I will describe a method to nanosculpt matter by controllably exposing it to an intense and highly focused beam of electrons. Electron irradiation can be used to controllably displace or ablate regions of the material, such as thin metal films and graphene sheets, with nearly atomic resolution. I will discuss the impact of this work in biophysics, including DNA translocation studies through graphene nanopores and detection of small nucleic acids down to 10 base pairs with nanopores in ultrathin membranes.
Thursday, October 7, 2010
Dr. Bhuvnesh Jain
When: 3:30 PM
Where: Mendel 115
Refreshments will be served at 3:00 PM
Gravitational Lensing in the Accelerating Universe
Thursday, September 30, 2010
Dr. Joseph Schick, Department of Physics, Villanova University
When: 3:30 PM
Where: Mendel 115
Refreshments will be served at 3:00 PM
Theory of Gallium Diffusion In Gallium Arsenide and Its Effects
Gallium arsenide has been a material of continuing technological interest for many years. Despite the length of time it has been under investigation, both experimentally and theoretically, gaps in a full understanding of this material remain. One such area has to do with the movement of atoms in the material, which can be both useful, in controlling the properties of the material, and harmful, in disrupting the usefulness of devices once they are in operation. In this presentation I will provide a brief overview of the theoretical methods that can address this situation. I will present results of my application of density functional theory to a comprehensive study of all the native point defects in this material. Additionally I will discuss how these results shed light on one particular set of experiments that are aimed at determining how gallium atoms diffuse ....
