Bulletin of the American Physical Society
2008 Joint Spring Meeting of the Texas Sections of APS, AAPT, and Zone 13 of SPS
Volume 53, Number 1
Thursday–Saturday, March 6–8, 2008; Corpus Christi, Texas
Session POS: Poster Session |
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Room: Omni Corpus Christi Hotel Marina Tower Foyer |
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POS.00001: Size-dependent Raman and infrared studies of PbSe nanoparticles Felicia Manciu, Francisco Carreto, Yudhisthira Sahoo, Paras Prasad The existence of optical phonon modes of PbSe nanoparticles (NP) prepared by colloidal chemistry were investigated by micro-probe Raman and far-infrared absorption spectroscopies. To the best of our knowledge, this is the first time when evidence of the surface phonon (SP) mode by Raman has been experimentally observed. The frequency of the SP mode is consistent with its prediction by a dielectric continuum model. While for different PbSe NP sizes the frequency of the SP mode is almost unaffected, there is a clear shift by approximately 4 cm$^{-1}$ toward higher frequency in the appearance of the longitudinal optical mode in the Raman spectra from the 3 nm to the 7 nm PbSe NPs. Far-infrared measurements demonstrate the presence of the transverse optical TO($\Gamma )$ and of the coupled phonon modes. The samples were also characterized by Transmission Electron Microscopy. [Preview Abstract] |
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POS.00002: FTIR, Raman, and XPS Studies of a Thioindigo/Palygorskite Pigment William Durrer, Felicia Manciu, Alejandra Ramirez, Jayesh Govani, Russell Chianelli We present FTIR, Raman and XPS studies of interactions between powdered thioindigo and palygorskite when these two substances are mixed and heated to produce a purple pigment similar to Maya Blue. In an ongoing investigation, we study the question of how thioindigo binds to palygorskite. We also address how such binding might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation. FTIR and Raman results corroborate to provide evidence of C=O bonding disruption in the dye. XPS results, though more difficult to interpret, support the FTIR and Raman results. They reveal several different binding states of the key elemental components oxygen, aluminum, and sulfur. Of these, the higher energy binding states of oxygen and aluminum are, most likely, indicative of strong metal-C=O interaction. [Preview Abstract] |
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POS.00003: Role of symmetry in dissociation of highly symmetric molecules Vandana Sharma, Bhas Bapat, Margaret Murnane, Henry Kapteyn Highly charged molecular ions, formed by either photoabsorption or charged particle impact, undergo dissociation. Dissociation leads to a sharing of the total molecular charge and conversion of the internal energy into translational energy of the fragment. Molecular ions Molecular ion possesses a set of configurations with a certain symmetry. All these configurations have different electronic energy and depending on the energies the molecular ion follows different decay pathways. To obtain the properties of electronic states of the precursor ion and to understand the energetics of the break up, it is necessary to measure complete kinematic parameter of all ionic fragments. We investigate dissociation dynamics of the multiply charged molecular ions, or precursors, by multiple ion coincidence imaging of fragment ions. We have probed dynamics of the unimolecular fragmentation of tetrahedral (CCl$_{4})$ and octahedral (SF$_{6})$ molecules which are highly symmetric. The common thread between the two is that the parent ion (SF$_{6}^{+}$ and CCl$_{4}^{+})$ did not appear at all in the mass spectrum of the two. Hence, it can be concluded that these ions are unstable in its symmetrical configuration and exhibit Jahn--Teller instability [1]. [Preview Abstract] |
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POS.00004: Optical properties of L-arginine doped potassium dihydrogen phosphate crystals Jayesh Govani, Felicia Manciu, Mihir Joshi, Ketan Parikh, Dipak Dave Potassium dihydrogen phosphate (KDP) exhibits superior nonlinear-optical properties and it has been exploited for variety of applications. Single crystals of organic nonlinear optical material of pure and L-arginine doped potassium dihydrogen phosphate (KDP) were grown by slow evaporation technique from its aqueous solution. The crystal structures of the grown crystals were determined using powder XRD. The powder X-ray diffraction patterns indicated a single phase with the unit cell parameters being unaltered by doping. Infrared and Raman spectroscopies were employed to study the active doping of potassium dihydrogen phosphate crystals with L-arginine amino acid. IR absorption spectra confirmed that the successful doping of L-arginine was achieved by exhibiting the presence of vibrational lines at 1401 cm$^{-1}$, 1637 cm$^{-1}$, 1716 cm$^{-1}$ and 3127 cm$^{-1}$. This affirmation is supported with more evidences from FT-Raman measurements [Preview Abstract] |
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POS.00005: Fragmentation dynamics of highly symmetric molecules Vandana Sharma, Bhas Bapat, Margaret Murnane, Henry Kapteyn We have probed the fragmentation dynamics of CCl$_{4}$ and SF$_{6}$ molecules which are highly symmetric. The common thread between the dissociation pattern of the two molecules is the formation of an ion which is not `obvious' (Cl$_{2}^{+}$:CCl$_{4}$ and F$_{2}^{+}$: SF$_{6})$. The ground state geometry of the two does not support the formation of these unusual dissociative products. This implies that the geometry of the dissociating molecular ion is significantly altered from the geometry of the parent neutral. These observations suggest relocation of certain atoms within the molecular ion during dissociation. We made a successful attempt to determine the geometry of electronically excited dicationic precursor in the CM frame. Experimentally determined geometry is in good agreement with the theoretically generated structure. [Preview Abstract] |
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POS.00006: Optical Characterization of Biological Tissues L. Mimun, Frederick Barrera, Dhiraj Sardar, Andrew Tsin University of Texas at San Antonio, San Antonio, Texas 78249 An in-depth characterization of the optical properties of biological tissues has been performed. The wavelength-dependent total diffuse reflection (R$_{d)}$ and total transmission (T$_{t})$ measurements have been taken for individual tissues by using a double-integrating sphere setup. The index of refraction of the tissues will be determined using conventional optical techniques. The Kubelka Munk theory is applied to determine the scattering and absorption coefficients of these samples from the measurements of diffuse transmission and reflection. A thorough study of the scattering characteristics of these tissues has been made. *This work was supported in part by the NSF sponsored Center for Biophotonics Science and Technology (CBST) at UC Davis under Cooperative Agreement No. PHY 0120999. [Preview Abstract] |
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POS.00007: The Relationship Between Magnetosheath and Solar Wind Parameters Phyllis Whittlesey, Crystal Red Eagle, Elizabeth Mitchell, Ramon Lopez In general, the solar wind drives magnetospheric activity and is used to quantify it. In reality, it is the magnetosheath which is in contact with the magnetosphere. The magnetosheath therefore dictates magnetospheric activity. We expect that the relationship between solar wind and magnetosheath parameters will have a linear relationship at low solar wind magnetic field values. However, at high solar wind magnetic field values, the LFM Global MHD code predicts a non-linear relationship between the solar wind and magnetosheath parameters. Using simultaneous spacecraft observations from WIND and GEOTAIL, we examine two periods of magnetosheath and solar wind measurements to confirm the observed relationship between the magnetosheath and solar wind parameters. For low solar wind magnetic field, we examine a period of quiet solar wind and magnetospheric activity on January 5, 1995. For high solar wind magnetic field, we examine the well-known January 10, 1997 storm period. [Preview Abstract] |
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POS.00008: Is All v*Bz Equal? Felipe Mulford, Jorge Landivar, Elizabeth Mitchell, Ramon Lopez Solar wind electric field, v*Bz, is generally viewed to be the major driver of magnetospheric activity. A major diagnostic of magnetospheric activity is the potential imposed on the ionosphere. In this study we examine if, in fact, the ionospheric potential is the same for similar values of v*Bz or whether the average potential depends on how big the v and Bz are relative to each other. We use data from DMSP spacecraft collected during periods when v*Bz is less than 3 mV/m, in order to avoid the effect of polar cap potential saturation. Global MHD models suggest that there should be a difference in the magnetospheric response. We will present our findings from the data. [Preview Abstract] |
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POS.00009: DMSP Observations of Auroral Arcs that Brighten Jose Barona, Randall Bradshaw, Robert Bruntz, Ramon Lopez Using images from the POLAR UVI substorm movie database, we have identified the local time, latitude, and universal time, to within a couple of minutes, of auroral brightenings. Using that list we have identified a number of events in which DMSP spacecraft pass directly over the portion of the arc that either was about to brighten or had just brightened. In some of these cases, there is apparent evidence of an ion acceleration region in the magnetotail. Our presentation will discuss in general the characteristics of electron and ion precipitation during these events. [Preview Abstract] |
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