Bulletin of the American Physical Society
2006 Texas Section APS/AAPT/SPS Joint Spring Meeting
Thursday–Saturday, March 23–25, 2006; San Angelo, Texas
Session APS1: APS1: Contributed Oral Presentations |
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Chair: Stefan Zollner, Freescale Semiconductor, Inc. Room: UC 203 |
Friday, March 24, 2006 3:00PM - 3:12PM |
APS1.00001: What Marfa Lights Probably Aren't Karl Stephan Since 2002, numerous photographs and eyewitness accounts of what are popularly known as ``Marfa lights'' were recorded by a researcher named James Bunnell, who has installed unmanned monitoring stations outside Marfa, Texas. In this paper, we describe highlights of the observational data Bunnell has collected. These include estimates of visible-radiation intensity and extensive information on location and movement. In view of these data, we examine several leading proposed explanations for these lights, including auto headlights, mirages, natural gas, and more unlikely ones such as antimatter and evaporating black holes. Although headlights and mirages are visible at the site, these are generally easy to distinguish from the phenomena of interest. A one-cubic-meter volume of methane gas at atmospheric pressure provides sufficient chemical energy of combustion to account for many of the observed effects, but not for all of them. Nauenberg and Ruderman (Phys. Letters 22, 512 (1966)) showed that any antimatter object would rapidly suffer annihilation even in the rarefied atmosphere at high altitudes. Evaporating black holes would either produce much more power than the observations indicate for the observed lifetimes, or would be much too massive and long-lasting to account for the observed power estimates. Applications of these problems for physics instruction at the high-school and college level will be described. [Preview Abstract] |
Friday, March 24, 2006 3:12PM - 3:24PM |
APS1.00002: Judd-Ofelt Intensity Analysis of Tb$^{3+}$ in TbAlO$_{3}$ Kelly Nash, Raylon Yow, John Gruber, Dhiraj Sardar, Uygun Valiev, Edvard Kokanyan Spectroscopic and laser properties of Tb$^{3+}$ in TbAlO$_{3}$ are analyzed using the standard Judd-Ofelt (J-O) theoretical model. The J-O model has been applied to the room temperature absorption spectra of Tb$^{3+}$ in TbAlO$_{3}$ to determine the radiative decay rates, branching ratios, and radiative lifetimes. The quantum efficiency of the $^{5}$D$_{4} \quad \to $ $^{7}$F$_{5}$ transition is determined using the radiative and fluorescence lifetimes. Finally, the spectroscopic results of Tb$^{3+ }$in TbAlO$_{3}$ are compared with those of Tb$^{3+}$ in other hosts. [Preview Abstract] |
Friday, March 24, 2006 3:24PM - 3:36PM |
APS1.00003: Spectral Line Shapes in Helium Gas A. Anand, J. Roberts, T. Imholt, D. Henley, J.N. Dahiya Microwave stimulated emission lines in helium gas were studied through their shapes. Lorentzian shape profiles were assumed to establish a reference for comparison between the emission lines shapes and the assumed profiles. Departures from the Lorentzian shapes are explained in terms of overlapping spectral line profiles and possible weak fine structure components arising in the spectra. Comparison of spectral line shapes is made for two species of helium. [Preview Abstract] |
Friday, March 24, 2006 3:36PM - 3:48PM |
APS1.00004: Optical Properties of Bovine Ocular Tissues in the Near Infrared Region Guang-yin Swanland, Raylon Yow, Dhiraj Sardar, Andrew Tsin, Robert Thomas Optical properties of bovine ocular tissues have been determined in the near infrared region. The indices of refraction ($n)$ of these ocular tissues were measured with a Michelson interferometer. The total diffuse reflectance ($R_{d})$, total diffuse transmittance ($T_{d})$, and collimated transmittance ($T_{c})$ on the individual tissues have been measured using a double-integrating sphere setup. The inverse adding doubling (IAD) method based on the diffusion approximation and radiative transport theory is applied to the measured values of $n$, $R_{d}$, $T_{d}$, and $T_{c}$ to calculate the optical absorption and scattering coefficients as well as the scattering anisotropy of bovine ocular tissues. [Preview Abstract] |
Friday, March 24, 2006 3:48PM - 4:00PM |
APS1.00005: pH-dependent Photodamage of $\beta $-lactoglobulin Mediated by Hydrophobic and Hydrophilic Porphyrins Nick Fernandez, Fang Tian, Lorenzo Brancaleon Dyes like the hydrophobic Protoporphyrin IX (PPIX) and hydrophilic m-Tetraphenylporphine sulfonato (TSPP) bind proteins via non-covalent interactions. The dyes' binding to $\beta $-lactoglobulin ($\beta $-lg) is pH dependent and their irradiation can generate photochemical events that alter the conformation of the protein. We investigated how the irradiation of the non-covalent complexes, at different pH, contributed to altering the structure of the protein. Our investigation used a combination of optical spectroscopic techniques that probe changes in the conformation of polypeptides. Irradiation of the dyes produces measurable changes in the fluorescence intensity and lifetime of the protein, that could be correlated with conformational of the protein. These changes were most significant above pH 7 where $\beta $-lg undergoes a conformational change that makes the binding site more accessible. Above pH 7, irradiation of both PPIX and TSPP produces a 1-2 nm shift in the emission maximum of the protein which does not occur at lower pH values. The effect of irradiation on the emission lifetime of $\beta $-lactoglobulin is even more dramatic as it lengthened the average lifetime of the protein's fluorescence from 1.68 to 1.95ns (for PPIX), from 1.53 to 1.98ns (for TSPP). The data suggest that at pH where they have access to the binding site of the protein, PPIX and TSPP have the chance of producing a photochemical reaction that modifies the conformation and damage $\beta $-lg. [Preview Abstract] |
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