Events Calendar View
Mathematical Physics Seminar
Kerr solution for a rotating black hole, cont.
Aug 20, 2009
Surface Enhanced Raman Scattering from Silver Nanorod Array
Dr. Bill Dennis is hosting Mr. Yongjun Liu of the University of Georgia Department of Physics and Astronomy who will give a talk entitled "Surface Enhanced Raman Scattering from Silver Nanorod Array."
Surface-enhanced Raman scattering (SERS) has been a powerful analytical tool in chemical and biosensing applications. Silver nanorod array fabricated by oblique angle deposition can give a very strong SERS enhancement (>108). For the Ag nanrod SERS substrates, we have performed detailed SERS characterizations and found that the SERS enhancement strongly depends on the length of nanorods, the incident angle of excitation light, the polarization states of excitation light, and the reflectance from the substrate. A modified Greenler's model based on the reflection from a single Ag nanorod and the substrate as well as dipole radiation has been proposed and can quantitatively explain these SERS characteristics. We have also designed experiments to selectively put Raman probe molecules on different locations of the Ag nanorods, and found that most SERS signals come from the gap between the Ag nanorods, which is consistent with our numerical calculations of the local electromagnetic field enhancement around Ag nanorod array. All those results show that the SERS mechanism of Ag nanorod arrays is very complicated, and more works need to be done to understand the essential mechanism. Acknowledgement: this work was supported by NSF ECS-0701787.
Aug 27, 2009
The Physics Behind Clear-Air Turbulence (CAT): An Unsolved Mystery
Dr. Robin Shelton is hosting Dr. John Knox of the University of Georgia this week and his talk is entitled "The Physics Behind Clear-Air Turbulence (CAT): An Unsolved Mystery."
Airplane passengers experience clear-air turbulence (CAT) when the flight becomes bumpy at high altitudes far away from thick clouds, thunderstorms, or other known sources of turbulence. Why does CAT happen, what are the physical processes leading to this phenomenon, and how can we forecast it better so pilots can avoid it? In this talk, I attempt to answer these surprisingly difficult questions in the context of fluid dynamics principles, specifically hydrodynamic instabilities and buoyancy waves in the atmosphere. I will present results from my own research collaboration with an experimental fluid dynamicist on a link between CAT and a recently discovered source of atmospheric buoyancy waves based on aeroacoustics research.
Sep 3, 2009
Making Surfaces Smart
Dr. Susanne Ullrich will be hosting Dr. Jason Locklin of the University of Georgia Department of Chemistry. His talk is entitled "Making Surfaces Smart."
Surface-initiated polymerization reactions are rapidly developing as methods to prepare functional, high-tech coatings. This is a technique based on the growth of polymer molecules at the surface of a substrate (such as glass, metal, or plastic) in situ from a surface bound initiator, which results in the covalent attachment of polymer molecules to this substrate. Polymer layers in which the polymer chains are irreversibly immobilized to the substrate are especially attractive for a wide variety of applications, as these layers have excellent long-term stability, even in rather adverse environments. In addition to improved stability, the number of functional groups present at a surface can be greatly enhanced by connecting large polymer molecules with functional groups (present in each monomer repeat unit) to the surface instead of binding the functional group directly to the surface. This transition from a two-dimensional to a three-dimensional arrangement has been called the "skyscraper" approach, and allows for high densities of functional groups to be obtained in a limited area. In this talk, we will highlight recent progress our group has made in applying polymer brush coatings to study the following: light induced mechanical motion, sensors for biological arrays, antimicrobial coatings and enzymatic biofuel cells.
Sep 10, 2009
New Horizons of Nanoplasmonics: from SPASER to Attoseconds
Dr. Michael Geller is hosting Dr. Mark Stockman of Georgia State University Department of Physics and Astronomy this week. His talk is entitled "New Horizons of Nanoplasmonics: from SPASER to Attoseconds."
Nanoplasmonics deals with collective electron dynamics on the surface of metal nanostructures, which arises as a result of excitations called surface plasmons. The surface plasmons localize and concentrate optical energy in nanoscopic regions creating highly enhanced local optical fields. They undergo ultrafast dynamics with timescales as short as a few hundred attoseconds. There are numerous existing applications of nanoplasmonics: nanoantennas for photovoltaic cells and LEDs, labels and tests for biology and medicine, etc. We will focus on the latest developments in nanoplasmonics. Among them is SPASER as a quantum nanoscale generator of optical fields, which has earlier been predicted and recently observed, generation of high harmonics in the EUV range, ultrafast optical modulator with THz bandwidth, generators and modulators of THz radiation, coherent control of ultrafast processes on the nanoscale, attosecond nanoplasmonic field microscope, etc.
Sep 17, 2009
What powers the intra-cluster filaments in large clusters of galaxies?
The Department of Physics and Astronomy and the Center for Simulational Physics will be hosting a joint colloquium this week. Dr. Phillip Stancil will be hosting Dr. Gary Ferland of the University of Kentucky. His talk is entitled "What powers the intra-cluster filaments in large clusters of galaxies?"
The first radio surveys of the sky discovered that some large clusters of galaxies contained powerful sources of synchrotron emission. Optical images showed that the intra-cluster medium was permeated by long linear filaments with bizarre emission line spectra. Recent observations in the infrared and radio show that these filaments have very strong emission lines of molecular hydrogen and carbon monoxide. The mass of molecular material is quite large, the gas is quite warm, and the filaments have not formed stars despite their multi-Gyr age. I will discuss the general astrophysical context of large clusters of galaxies and how large masses of molecular gas can be heated to produce what we observe.
Page 1 of 121, showing 6 records out of 723 total, starting on record 1, ending on 6