Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 10 of 10
Full-Text Articles in Physics
Dark Matter Time Projection Chamber: Recent R&D Results, James B. R. Battat, S. Ahlen, M. Chernicoff
Dark Matter Time Projection Chamber: Recent R&D Results, James B. R. Battat, S. Ahlen, M. Chernicoff
Physics Faculty Research and Scholarship
The Dark Matter Time Projection Chamber collaboration recently reported a dark matter limit obtained with a 10 liter time projection chamber filled with CF4 gas. The 10 liter detector was capable of 2D tracking (perpendicular to the drift direction) and 2D fiducialization, and only used information from two CCD cameras when identifying tracks and rejecting backgrounds. Since that time, the collaboration has explored the potential benefits of photomultiplier tube and electronic charge readout to achieve 3D tracking, and particle identification for background rejection. The latest results of this effort is described here.
Methyl Group Rotation, H-1 Spin-Lattice Relaxation In An Organic Solid, And The Analysis Of Nonexponential Relaxation, Peter A. Beckmann, Evan Schneider
Methyl Group Rotation, H-1 Spin-Lattice Relaxation In An Organic Solid, And The Analysis Of Nonexponential Relaxation, Peter A. Beckmann, Evan Schneider
Physics Faculty Research and Scholarship
We report 1H spin-lattice relaxation measurements in polycrystalline 4,4′-dimethoxybiphenyl at temperatures between 80 and 300 K at NMR frequencies of ω0/2π = 8.50, 22.5, and 53.0 MHz. The data are interpreted in terms of the simplest possible Bloch-Wangsness-Redfield methyl group hopping model. Different solid states are observed at low temperatures. The 1H spin-lattice relaxation is nonexponential at higher temperatures where a stretched-exponential function fits the data very well, but this approach is phenomenological and not amenable to theoretical interpretation. (We provide a brief literature review of the stretched-exponential function.) The Bloch-Wangsness-Redfield model applies …
Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu
Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu
Physics Faculty Research and Scholarship
A growth diagram of Lu-Fe-O compounds on MgO(111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe2O4 film and is explained in terms of the effect of the impurity hexagonal LuFeO3 (h-LuFeO3) phase and structural defects.
Structure And Magnetotransport Properties Of Epitaxial Nanocomposite La0.67ca0.33mno3:Srtio3 Thin Films Grown By A Chemical Solution Approach, Ling Fei, Leyi Zhu, Xuemei Cheng, Haiyan Wang, Stacy M. Baber, Joshua Hill, Qianglu Lin, Yun Xu, Shuguang Deng, Hongmei Luo
Structure And Magnetotransport Properties Of Epitaxial Nanocomposite La0.67ca0.33mno3:Srtio3 Thin Films Grown By A Chemical Solution Approach, Ling Fei, Leyi Zhu, Xuemei Cheng, Haiyan Wang, Stacy M. Baber, Joshua Hill, Qianglu Lin, Yun Xu, Shuguang Deng, Hongmei Luo
Physics Faculty Research and Scholarship
Epitaxial La0.67Ca0.33MnO3:SrTiO3 (LCMO:STO) composite thin films have been grown on single crystal LaAlO3(001) substrates by a cost effective polymer-assisted deposition method. Both x-ray diffraction and high-resolution transmission electron microscopy confirm the growth of epitaxial films with an epitaxial relationship between the films and the substrates as (002)film||(002)sub and [202]film||[202]sub. The transport property measurement shows that the STO phase significantly increases the resistivity and enhances the magnetoresistance (MR) effect of LCMO and moves the metal-insulator transition to lower temperatures. For example, the MR values measured …
Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu
Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu
Physics Faculty Research and Scholarship
Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee′−Ee″ = 0.7 eV and Ea1′−Ee′ = 0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea1′>Ee′>Ee″ with slightly underestimated values and a bandgap of 1.35 eV.
Modification Of Turbulent Transport With Continuous Variation Of Flow Shear In The Large Plasma Device, David A. Schaffner, T. A. Carter, G. D. Rossi, D. S. Guice, J. E. Maggs, S. Vincena, B. Friedman
Modification Of Turbulent Transport With Continuous Variation Of Flow Shear In The Large Plasma Device, David A. Schaffner, T. A. Carter, G. D. Rossi, D. S. Guice, J. E. Maggs, S. Vincena, B. Friedman
Physics Faculty Research and Scholarship
Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) has been achieved using a biasable limiter which has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and transport in the LAPD. The LAPD rotates spontaneously in the ion diamagnetic direction; positive limiter bias first reduces, then minimizes (producing a near-zero shear state), and finally reverses the flow into the electron diamagnetic direction. Degradation of particle confinement is observed in the minimum shearing state and a reduction in the turbulent particle flux is observed with increasing shearing in both …
Sheared-Flow Induced Confinement Transition In A Linear Magnetized Plasma, S. Zhou, W. W. Heidbrink, H. Boehmer, R. Mcwilliams, T. A. Carter, S. Vincena, B. Friedman, David A. Schaffner
Sheared-Flow Induced Confinement Transition In A Linear Magnetized Plasma, S. Zhou, W. W. Heidbrink, H. Boehmer, R. Mcwilliams, T. A. Carter, S. Vincena, B. Friedman, David A. Schaffner
Physics Faculty Research and Scholarship
A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn/n~eδφ/kTe~0.5) are observed at the plasma edge, accompanied by a large density gradient (Ln=∣∣∇lnn∣∣−1~2cm) and shearing rate (γ~300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (Vbias) on the obstacle and the axial magnetic field …
Energy Dynamics In A Simulation Of Lapd Turbulence, B. Friedman, T. A. Carter, M. V. Umansky, David A. Schaffner, B. Dudson
Energy Dynamics In A Simulation Of Lapd Turbulence, B. Friedman, T. A. Carter, M. V. Umansky, David A. Schaffner, B. Dudson
Physics Faculty Research and Scholarship
Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flute- like (kk 1⁄4 0) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to kk 61⁄4 0 fluctuations, the nonlinear instability accesses …
Single-Crystal X-Ray Diffraction, Isolated-Molecule And Cluster Electronic Structure Calculations, And Scanning Electron Microscopy In An Organic Solid: Models For Intramolecular Motion In 4,4'-Dimethoxybiphenyl., Xianlong Wang, Loolita Rotkina, Hong Su, Peter A. Beckmann
Single-Crystal X-Ray Diffraction, Isolated-Molecule And Cluster Electronic Structure Calculations, And Scanning Electron Microscopy In An Organic Solid: Models For Intramolecular Motion In 4,4'-Dimethoxybiphenyl., Xianlong Wang, Loolita Rotkina, Hong Su, Peter A. Beckmann
Physics Faculty Research and Scholarship
This paper brings together field emission scanning electron microscopy, single-crystal X-ray diffraction, and density functional electronic structure calculations in both an isolated molecule and a cluster of seven whole and fourteen half molecules of 4,4′-dimethoxybiphenyl to investigate coupled methyl-group rotation (over a barrier) and methoxy-group libration (meaning a rotation from the ground state not all the way to the transition state and back again). The structure of the isolated molecule, determined by the electronic structure calculations, is compared with the structure of the molecule found in the crystal. As the methyl group rotates from its ground state to its transition …
Nonexponential Solid State 1h And 19f Spin–Lattice Relaxation, Single-Crystal X-Ray Diffraction, And Isolated-Molecule And Cluster Electronic Structure Calculations In An Organic Solid: Coupled Methyl Group Rotation And Methoxy Group Libration In 4,4′-Dimethoxyoctafluorobiphenyl, Donald P. Fahey, William G. Dougherty Jr, W. Scott Kassel, Xianlong Wang, Peter A. Beckmann
Nonexponential Solid State 1h And 19f Spin–Lattice Relaxation, Single-Crystal X-Ray Diffraction, And Isolated-Molecule And Cluster Electronic Structure Calculations In An Organic Solid: Coupled Methyl Group Rotation And Methoxy Group Libration In 4,4′-Dimethoxyoctafluorobiphenyl, Donald P. Fahey, William G. Dougherty Jr, W. Scott Kassel, Xianlong Wang, Peter A. Beckmann
Physics Faculty Research and Scholarship
We investigate the relationship between intramolecular rotational dynamics and molecular and crystal structure in 4,4′-dimethoxyoctafluorobiphenyl. The techniques are electronic structure calculations, X-ray diffractometry, and 1H and 19F solid state nuclear magnetic resonance relaxation. We compute and measure barriers for coupled methyl group rotation and methoxy group libration. We compare the structure and the structure-motion relationship in 4,4′-dimethoxyoctafluorobiphenyl with the structure and the structure-motion relationship in related compounds in order to observe trends concerning the competition between intramolecular and intermolecular interactions. The 1H spin–lattice relaxation is nonexponential in both the high-temperature short-correlation time limit and in the low-temperature long-correlation time limit, …