Browsing by Subject "Scattering (Physics)"
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Item A method of analyzing spin dependent effects in elastic electron scattering from gaseous targets(Texas Tech University, 1973-08) Bushell, Michael SNot availableItem An investigation into the possibility of an integral solution to the radical Schrodinger equation.(Texas Tech University, 1964-05) Walker, John DavidNot availableItem Chaotic scattering and the magneto-Coulomb map(2002) Hu, Bo; Horton, C. W.Item Complex quantum trajectories for barrier scattering(2007-12) Rowland, Bradley Allen, 1979-; Wyatt, Robert E. (Robert Eugene),We have directed much attention towards developing quantum trajectory methods which can accurately predict the transmission probabilities for a variety of quantum mechanical barrier scattering processes. One promising method involves solving the complex quantum Hamilton-Jacobi equation with the Derivative Propagation Method (DPM). We present this method, termed complex valued DPM (CVDPM(n)). CVDPM(n) has been successfully employed in the Lagrangian frame to accurately compute transmission probabilities on 'thick' one dimensional Eckart and Gaussian potential surfaces. CVDPM(n) is able to reproduce accurate results with a much lower order of approximation than is required by real valued quantum trajectory methods, from initial wave packet energies ranging from the tunneling case (E[subscript o]=0) to high energy cases (twice the barrier height). We successfully extended CVDPM(n) to two-dimensional problems (one translational degree of freedom representing an Eckart or Gaussian barrier coupled to a vibrational degree of freedom) in the Lagrangian framework with great success. CVDPM helps to explain why barrier scattering from "thick" barriers is a much more well posed problem than barrier scattering from "thin" barriers. Though results in these two cases are in very good agreement with grid methods, the search for an appropriate set of initial conditions (termed an 'isochrone) from which to launch the trajectories leads to a time-consuming search problem that is reminiscent of the rootsearching problem from semi-classical dynamics. In order to circumvent the isochrone problem, we present CVDPM(n) equations of motion which are derived and implemented in the arbitrary Lagrangian-Eulerian frame for a metastable potential as well as the Eckart and Gaussian surfaces. In this way, the isochrone problem can be circumvented but at the cost of introducing other computational difficulties. In order to understand why CVDPM may give better transmission probabilities than real valued counterparts, much attention we have been studying and applying numerical analytic continuation techniques to visualize complex-extended wave packets as well as the complex-extended quantum potential. Numerical analytic continuation techniques have also been used to analytically continue a discrete real-valued potential into the complex plane for CVDPM with very promising results.Item The effects of alignment on the dissociation of H₂ on Pd(111)(2002-05) Isakson, Marcia Joyce; Sitz, Greg OrmanThe effects of rotational alignment in surface scattering phenomena are studied. Alignment means a spatial preference for the plane of rotation. Specifically, changes in the reflection probability for H2 reaction with Pd(111) were studied for different molecular rotational alignments (helicopters vs. cartwheelers) and different incident translational energies. Experimentally, molecules were prepared with well-defined, non-statistical alignments using a linearly polarized laser before interaction with the surface. After scattering, the molecules were probed with another laser to determine their internal state. We found that the reflectivity of helicopter molecules was less than that of cartwheeler molecules. This effect increased with increasing incident energy. The result is interpreted as meaning that helicopters are more likely to dissociate than to scatter. The results are further evidence of steric forces in the H2/Pd interaction.Item Fully automatic hp-adaptivity for acoustic and electromagnetic scattering in three dimensions(2007-05) Kurtz, Jason Patrick, 1979-; Demkowicz, LeszekWe present an algorithm for fully automatic hp-adaptivity for finite element approximations of elliptic and Maxwell boundary value problems in three dimensions. The algorithm automatically generates a sequence of coarse grids, and a corresponding sequence of fine grids, such that the energy norm of error decreases exponentially with respect to the number of degrees of freedom in either sequence. At each step, we employ a discrete optimization algorithm to determine the refinements for the current coarse grid such that the projection-based interpolation error for the current fine grid solution decreases with an optimal rate with respect to the number of degrees of freedom added by the refinement. The refinements are restricted only by the requirement that the resulting mesh is at most 1-irregular, but they may be anisotropic in both element size h and order of approximation p. While we cannot prove that our method converges at all, we present numerical evidence of exponential convergence for a diverse suite of model problems from acoustic and electromagnetic scattering. In particular we show that our method is well suited to the automatic resolution of exterior problems truncated by the introduction of a perfectly matched layer. To enable and accelerate the solution of these problems on commodity hardware, we include a detailed account of three critical aspects of our implementations, namely an efficient implementations of sum factorization, several interfaces to the direct multi-frontal solver MUMPS, and some fast direct solvers for the computation of a sequence of nested projections.Item Isotope effects in gas-surface interactions: quantum-state resolved studies of D₂ scattering from Cu(100) and Pd(111)(2004) Shackman, Leah Caitlin; Sitz, Greg OrmanState resolved experiments are presented for the interaction of D2 and HD with Cu(100) and Pd(111). For this work, D2(v=1, J=2) molecules were scattered off of single crystal surfaces at near normal incidence. The reflected molecules were probed using quantum state specific spectroscopy. For D2 scattered from Cu(100) the survival probability and some transition probabilities were measured over a range of incident energies. The survival probability was found to be larger then that found previously for H2(v=1) scattered from the same surface. For H2 some of the incident flux was unaccounted for and could possibly have been lost by dissociative adsorption. In contrast, D2 molecules which do not reflect elastically from the surface are accounted for in other transition channels for most energies. The differences found for D2 compared to previous work with H2 are discussed in terms of the lower zero point energy and smaller vibrational energy spacings of D2. D2 translational energy exchange was studied for several different scattering channels and interpreted using simple classical calculations. These calculations agreed well with both the elastic scattering channel as well as the rotational relaxation channel. For rotational excitation some energy was gained by the molecule from the surface. The survival probability was also measured for D2(v=1) scattered from Pd(111) at one incident energy. Pd is very reactive for D2 dissociation and this survival probability was measured to be much smaller than that for H2(v=1) under similar conditions. Vibrational relaxation channels were studied for D2 scattering from both Cu(100) and Pd(111). The vibrational relaxation was also found to be smaller than that measured for comparable channels for H2. The smaller survival probability and vibrational relaxation probability for D2 on Pd(111) cannot be easily accounted for by the difference in zero point energy and vibrational energy spacings. Measurements were also done to study the rotational excitation of HD molecules scattered from one reactive surface, Pd(111), and two inert surfaces, Cu(100) and Pd(111):H(D). These measurements showed similar amounts of rotational excitation for HD molecules after scattering from these different surfaces.Item Laser-based instrumentation for particle size measurements(Texas Tech University, 1998-12) Markov, Dmitry A.Not availableItem Quadrupole elastic scattering by polarized nuclei(Texas Tech University, 1969-05) Landers, Melvin CharlesNot availableItem Quantum state-resolved studies of sticking and elastic scattering of H₂ from Cu(100)(2006) Kim, Jonghyuk; Sitz, Greg OrmanItem Scattering properties of periodically-driven open quantum systems(2002-05) Emmanouilidou, Agapi; Reichl, L. E.Item Study of Borrmann scattering in silicon crystal.(Texas Tech University, 1975-05) Hwa, TaiannNot availableItem The electric scattering of the polarizable nuclei(Texas Tech University, 1970-05) Tomlinson, Robert TruemanNot available