Graduate Seminar
Presentations
May 1, 2008
| Speaker: | Guoxun Tian |
| Topic: | Oxygen Measurement using Photoacoustics |
| Date: | Thursday, May 1, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Available instrumentation includes innovative optical and acoustic instruments for the real-time quantification of particulate matter (PM) and its optical properties. Instruments have been designed to measure aerosol extinction, dots scattering and absorption components, and are being used for ambient measurements in air quality studies. We use oxygen as a sample and built a photo-acoustic detection system to measure the absorption of oxygen by using frequency and amplitude modulation of a laser at the same time. Compared with the theoretical spectrum, measurements using this system match very well. |
April 24, 2008
| Speaker: | Sudarshan Dhugana |
| Topic: | Electrons in an External Oscillator Potential |
| Date: | Thursday, April 24, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | The problem of the Schrödinger equation for one electron in harmonic oscillator potential is exactly solvable. The same problem for two electrons (interacting with Coulomb potentials) can have an approximate analytical solution. For large separation distance between the two electrons, the corresponding potential is cast in the form of a parabolic potential and hence the problem can be solved exactly using quantum mechanics. The consequence arising due to the presence of two electrons will be discussed. A small separation distance between the two electrons leads to the anharmonic oscillator problem which may be solved by the perturbation method. The three-dimensional Schrödinger equation for three electrons in a simple harmonic confinement potential can be decoupled into three pairs of problems, provided the expectation value of the center of mass vector R is small compared with the average distance between the electrons. The solutions for different correlation limits will be discussed. |
April 17, 2008
| Speaker: | Mei-Ju Lu |
| Topic: | Measurements of Spin-Relaxation Collisions for Cold Atoms with Orbital Angular Momentum |
| Date: | Thursday, April 17, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Atoms with nonzero orbital angular momentum have highly anisotropic interactions resulting in strong coupling between their internal quantum state and their motion. While the collisional properties of these atoms have been studied theoretically for decades, there is little experimental data at cold temperatures. We use helium buffer gas cooling, optical pumping, and laser spectroscopy to measure spin-relaxation collisions in anisotropically-interacting atoms. We also use electromagnetically-induced-transparency to measure spin-decoherence collisions. The presentation will include experimental methods and results for Ti-He inelastic collisions. |
April 3, 2008
| Speaker: | Marin Djendjinovic |
| Topic: | Volumetric Properties of Solvated Protein: A Molecular Dynamics Study |
| Date: | Thursday, April 3, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Proteins are large organic molecules whose building blocks, amino acids, are arranged in a linear chain and joined together by peptide bonds. A functioning protein is solvated inside of a living cell, and has its amino acids arranged in a 3D conformation, called native state. A change in environment (such as change in pressure, temperature, a solvent pH value or other) can cause protein to "unfold" to a linear chain (denatured state). In denatured state, protein cannot perform its biological function. This transition, which is a reversible thermodynamic process, is yet to be fully understood. It has been shown, however, that the understanding of volumetric properties of solvated proteins in the native state, namely the coefficient of thermal expansion and compressibility, is crucial to the understanding of the transition between the two states. In this presentation,a recent computer simulation study of the compressibility of the BPTI protein will be discussed. |
March 20, 2008
| Speaker: | Rajan K. Chakrabarty |
| Topic: | Aerosol Classification by Morphology using Electrostatic Charge |
| Date: | Thursday, March 20, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | A novel technique to select fractal-like aerosol agglomerates based on their morphology using electrostatic classifiers will be presented. Given a population of agglomerates with similar mobility diameters, the technique distinguishes agglomerate morphology based on the net charge carried by the agglomerate. This talk will discuss the successful application of this technique to flame-soot agglomerates where singly and doubly net-charged particles corresponding to mobility diameters of 220 and 460 nm, respectively, were size selected using electrostatic classifiers and shown to have different morphologies. The flexibility and simplicity of this technique does not limit its application to aerosols, but makes it an attractive candidate for performing particle shape selection of different types of nano and micro materials. |
March 13, 2008
| Speaker: | Kiattichart Chartkunchand |
| Topic: | Laser Photodetached Electron Spectroscopy of Negative Ion Beams |
| Date: | Thursday, March 13, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Laser Photodetached Electron Spectroscopy (LPES) is an important technique in the study of negative ions. Here a beam of negative ions produced by a cesium-sputter source is crossed perpendicularly with monochromatic laser light, ejecting the excess electron in a process known as photodetachment. The photodetached electrons, or photoelectrons, are then measured by an electron energy spectrometer to produce a photoelectron kinetic energy spectrum. Along with providing measurements of the electron affinity of the neutral species which makes up the negative ion, the LPES technique also facilitates the measurement of photodetachment differential cross sections through angular distribution measurements of the ejected photoelectrons. Use of the LPES technique on both atomic and molecular negative ion beams, with particular emphasis on the hydrogen molecular anion, will be discussed. |
March 6, 2008
| Speaker: | Madhu Gyawali |
| Topic: | “NASA-A TRAIN” Coordinated Satellite Measurements of The Earth’s Atmosphere |
| Date: | Thursday, March 6, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | The “NASA-A Train” constellation of seven Earth–orbiting satellites remotely sense clouds, aerosols, water vapor, and trace gases such as CO2, NO2, and O3. The satellites orbit the earth sun–synchronously at an altitude of 705 km with Aqua in the lead, followed in order by CALIPSO, CloudSat, PARASOL, and Aura (two more satellites OCO and Glory will join the constellation at the end of 2008). With Aqua in the lead and Aura at the tail, this formation has been termed the afternoon constellation or A-Train, and all satellites cross the equator within a few minutes around 1:30 pm local time (ascending node). These satellites employ revolutionary measurement methods to probe the Earth’s atmosphere, and will improve our weather and climate forecasts. Data from these satellites can be used together to obtain comprehensive information about atmospheric processes. This talk will give an overview of the active and passive remote- sensing measurement techniques used on satellite as well as description of the importance of the atmospheric properties being measured. A discussion will be presented on the importance of synergistic measurements of the satellite suite. |
February 28, 2008
| Speaker: | Tasha Goodrich |
| Topic: | A Semi-Analytic Liner Implosion Model for Flux Compression on ATLAS |
| Date: | Thursday, February 28, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | A flux compression experiment is being designed for the Atlas pulsed power facility. The purpose is to investigate generation of megagauss fields with liner technology in the geometry needed for compression of a stabilized diffuse z pinch. To survey possible parameters quickly and conveniently, a semi-analytic model has been developed that computes liner motion under the assumption that the liner remains cylindrically symmetric during the implosion and the metal of the liner is incompressible. Thus the liner thickness increases during implosion in a predictable way to conserve liner mass. Equations are derived for the time variation of liner position and circuit current including the effect of back pressure from the compressed flux. The model allows using realistic Atlas circuit parameters. The equations are integrated using the Matlab program and a standard Runge Kutta method. Recently the model has been extended to account for a shunt resistor and the resulting time-dependent current that would be generated inside the liner. The important advantage of a shunt resistor is that an auxiliary power supply is not needed to generate the seed flux which liner motion will compress. By tapping the power of Atlas to generate the seed flux, the incremental cost of a flux compression experiment is minimized. The selection of shunt material and dimensions must consider both the heating of the shunt and the amount of trapped flux, which along with the liner kinetic energy determines the final level of compressed magnetic field. Initial results suggest that readily available materials (a steel shunt and an aluminum liner) and properly chosen dimensions give a workable combination that generates magnetic field of several megagauss. |
February 21, 2008
| Speaker: | Nicholas Ouart |
| Topic: | Measurements of plasma conditions in precursor plasmas on the 1-MA Zebra generator |
| Date: | Thursday, February 21, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Precursor plasmas have been observed on many z-pinch experiments at various facilities, including low current (~1 MA, MAGPIE, Zebra, COBRA) and high current (>15 MA, Z) facilities. The impact of the precursor on stagnated plasmas and inertial confinement fusion targets is still under evaluation. Experiments have been performed on Zebra to study precursor plasmas with copper cylindrical wire arrays in collaboration with Sandia National Labs. Significant precursor radiation at photon energies >1 keV was observed on filtered PCDs. Precursor temperatures and densities have been obtained from modeling of the Cu L-shell emission recorded from a time-gated x-ray spectrometer. The precursor plasma temperatures are consistently >250 eV, which is higher than previously observed. |
February 14, 2008
| Speaker: | Essam Yasin |
| Topic: | Plasma Micro and Macro Instabilities |
| Date: | Thursday, February 14, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | Plasma instabilities are of great importance, especially in controlled fusion research. This seminar will focus on the classification of plasma instabilities, how they develop and what are their roles in studying plasma. The seminar will focus on the two-stream instability and its importance, particularly in beam physics. |
February 7, 2008
| Speaker: | Brian Chrisman |
| Topic: | Intensity Scaling of Hot Electron Coupling in Cone-Guided Fast Ignition |
| Date: | Thursday, February 7, 2008 at 4:00 pm |
| Location: | LP 208 |
| Abstract: | A critical issue for the fast ignition of inertial fusion targets, where compressed fuel is ignited by injection of an intense short laser pulse, is whether the hot electrons produced in the interaction are in an energy range conducive to efficient heating of the core. This work presents the first comprehensive two dimensional kinetic simulation of the cone-guided approach to fast ignition. Simulation results predict the hot electron temperature to be much lower than previous expected, which indicates the possibility to use them for optimum core heating. Furthermore the roles of collisional versus kinetic processes for transport and as heating mechanisms of the core plasmas are clarified. The core heating efficiency scales linearly with intensity at ranges of 1019 - 1020 W/cm2, but falls below this range due to deflection of hot electrons in strong magnetic filaments behind the cone target. |
