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Full-Text Articles in Condensed Matter Physics
Advanced Topographic Characterization Of Variously Prepared Niobium Surfaces And Linkage To Rf Losses, Chen Xu
Dissertations, Theses, and Masters Projects
Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. The shallow penetration (∼ 40 nm) of the RF into superconducting niobium lends great importance to SRF cavity interior surface chemistry and topography. These in turn are strongly influenced by the chemical etching "surface clean-up" that follows fabrication.;The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions …
Solid State Nmr Characterization Of Conductive Polyanilines, Yanina Anatolievna Goddard
Solid State Nmr Characterization Of Conductive Polyanilines, Yanina Anatolievna Goddard
Dissertations, Theses, and Masters Projects
Different forms of ring deuterated polyaniline with different conductivity have been characterized by solid state deuteron nuclear magnetic resonance.;Quadrupole echo (QE) spectra of all forms of polyaniline consist of a superposition of lineshapes for nearly rigid aromatic rings and a small fraction of rings which undergo fast 180?? flips. The intensity of the fast flipping component is temperature dependent and different for conductive emeraldine salt (ES) and non-conductive emeraldine base (EB). This is a manifestation of the different structure and morphology of these polymers.;Simultaneous measurements of QE lineshapes and the relaxation time anisotropies allowed an accurate description of motion in …
Microstructural Characterization Of An Ultra-High-Performance Polyimide, April Heather Baugher
Microstructural Characterization Of An Ultra-High-Performance Polyimide, April Heather Baugher
Dissertations, Theses, and Masters Projects
The motivation for this study was to further characterize a relatively new high-temperature polymer for application as a matrix resin for carbon fiber composites. The two primary questions addressed in this study dealt with the structural and chemical changes occurring in these polymers on exposure to high temperature.;To investigate the structural changes in the heat-treated samples, a positron annihilation lifetime spectrometer was designed, built and optimized. Because the lifetime of a positron in a material reflects the electronic structure of the material in which it annihilates, measurements by positron annihilation lifetime spectroscopy can be used to investigate changes in a …
First Principles Linear Response Calculations Of Lattice Dynamics, Cheng-Zhang Wang
First Principles Linear Response Calculations Of Lattice Dynamics, Cheng-Zhang Wang
Dissertations, Theses, and Masters Projects
First principles calculations, using the density-functional theory and particularly the local density approximation (LDA), have achieved remarkable success in studying the properties of solid state systems. Although the basic results of these calculations are the electronic structures (eigenvalues, eigenfunctions, etc.) and the total energy of ground state, many other related physical properties can be deduced from them by investigating their response under external perturbations. Using the linear response method with linearized-augmented-plane-wave (LAPW) basis, we have calculated lattice dynamical properties of important semiconductors CuCl, SiC and ferroelectric KNbO{dollar}\sb3.{dollar} CuCl is known to exhibit large anharmonic effects and possibly a complicated multi-well …
A Study Of Molecular Order And Motion In Nematic Liquid Crystal Mixtures, Jon Michael Goetz
A Study Of Molecular Order And Motion In Nematic Liquid Crystal Mixtures, Jon Michael Goetz
Dissertations, Theses, and Masters Projects
Materials which flow like fluids, but possess anisotropic properties like molecular crystals, are called 'liquid crystals'. Studies of liquid crystals contribute to our understanding of how molecular orientation influences macroscopic properties. This thesis presents experimental and theoretical investigations of molecular order and dynamics in nematic liquid crystal systems. First, deuterium nuclear magnetic resonance is used to determine the degree of orientational order of both components of a liquid crystal mixture simultaneously. The temperature dependence of the four order parameters is interpreted using a newly developed mean field theory of nematic binary mixtures composed of biaxial molecules. Next, mean field theory …