Seminar Tuesday June 30 – Thomas Tolhurst

Speaker: Thomas Tolhurst
Location: Physics 175
Time: 3:30 June 30 2015

Next-generation phosphors for solid-state lighting studied with X-ray spectroscopy and density functional theory

Abstract: The recently reported nitridolithoaluminate Sr[LiAl3N4]:Eu2+ and nitridomagnesosilicate Sr[Mg3SiN4]:Eu2+ are leading candidates for use in the next generation of phosphor-converted light-emitting diodes (pc-LEDs). They have garnered special interest due the their uniquely narrow bandwidths for Eu2+doped phosphors and high emission intensities in the critical, red region of the electromagnetic spectrum. A presentation of key features of their electronic structures, determined through density functional theory calculations and experimental soft X-ray spectroscopy measurements, will be given. This study builds on previously reported results observed through X-ray diffraction, visible light excitation and electron energy loss spectroscopy. Both materials are found to have large, indirect band gaps and an overall similar electronic structure. Both are narrow emitters, but Sr[Mg3SiN4]:Eu2+ shows the narrowest emissions to date of any red-emitting, Eu-doped phosphor. Further, they emit at noticeably different wavelengths in the red spectral region and have vastly different thermal quenching properties. These key differences in their emission properties in the visible region can be tied to subtle differences in their respective electronic structures. This talk will outline these structural differences and how they lead to the observed differences in the visible emissions of these phosphors.

Seminar Tuesday June 23 – Ashton Reimer

Speaker: Ashton Reimer
Location: Physics 175
Time: 23 June 2015 , 3:30

Measurement Techniques and Signal Processing with SuperDARN Radars

Abstract: Studying and understanding Geospace (Near-Earth Space) Weather is increasingly important as we consistently rely on more satellite based technologies like GPS. Magnetospheric and Ionospheric processes, like patches, or F-region irregularities can disrupt services like GPS. The Super Dual Aurora Radar Network (SuperDARN) radars are used to measure the magnetospheric plasma circulation via ionospheric F-region irregularities. Often these irregularities are overspread (long range: > 1000 km and high velocity: ~1 km/s), therefore SuperDARN radars employ a multi-pulse technique to overcome these range-doppler ambiguities. The accuracy and quality of the radar measurements primarily depends on the transmitted waveform and the signal processing techniques used on the received signal. In this talk I will briefly describe some different measurement techniques and fitting processes and present some of my work attempting to improve current operations.

Seminar Tuesday June 16 – Dan Zawada

Speaker: Dan Zawada
Location: Physics 175
Time: 3:30 June 16 2015

Abstract: Ozone is an important trace gas in the atmosphere.   The ozone layer is responsible for the temperature inversion in the stratosphere, and attenuates UV radiation at the Earth’s surface.  Furthermore, ozone in the troposphere is a pollutant and is frequently monitored to make air quality predictions.   One method of measuring ozone is remote sensing using limb scattered sunlight.  Currently this technique relies on the assumption that the atmosphere is locally horizontally uniform, i.e. that ozone concentration varies only as a function of altitude.  This assumption breaks down in areas where there is a large horizontal gradient, for example, at the edge of the ozone hole or near the tropopause where small scale processes are prevalent. Future instruments will have higher sampling rates, which may make it possible to use tomographic techniques to retrieve ozone in more than one dimension simultaneously. In this talk I will briefly outline different methods of remote sensing ozone in the atmosphere with UV/visible radiation, and present some of my research related to ozone tomography.

Seminar Tuesday June 9 – Akbar Rohollahi

Speaker: Akbar Rohollahi
Location: Physics 175
Time: 3:30 June 09 2015

Abstract: Delivering fuel to the core of the tokamak fusion plasma to keep it in steady state mode and optimize energy confinement has meaningful importance in fusion technology. Several fueling methods such as edge gas puffing, pellet injection and compact toroid injection (CT) have been proposed. Among them, the CT is one of the most efficient methods for the core fuelling of large tokamak fusion reactors in the future. . The CT can deposit the fuel in the full controlled manner at the any depth of tokamak plasma. The CT is a self-contained high density plasmoid with an axial symmetry and a stalwart poloidal and toroidal magnetic field. To maximize the bootstrap current fraction, density and pressure profile optimizations are essential in tokamak reactors. Therefore deposition of a small amount of fuel in a desired location is required. These criteria could be achieved by using CT.   In addition to fueling usage, CT would inject a toroidal momentum into tokamak plasma. So the CT might provide additional tools to control plasma flows and rotation that could be effective in plasma confinement.

In this seminar I’ll briefly talk about STOR-M tokamak and after that I will provide you some information about the CT and recent development in the fueling technics of tokamak reactors.