Browsing by Subject "Crystals"
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Item An application of KAM theory to a model for particle channelling in crystals and some related numerical simulations(2010-05) Maciejewski, James Michael; Llave, Rafael de la; Bichteler, KlausIt has been seen in physical experiments as early as the 1960’s that when a positively charged particle is injected into a crystal in certain directions and with sufficiently high energy, the particle can penetrate into the crystalline structure to a depth which is unexpectedly long. Such motions in the crystal are referred to as channelling trajectories. Herein, we consider a Hamiltonian model for particle motion in a crystal. We then proceed to show that the results of KAM theory are applicable to the model, and moreover that these result predict the existence of trajectories for the fired particle which do indeed penetrate the crystal deeply. Finally, we present the results of two series of numerical simulations which strongly suggest that this behaviour is observable in our model.Item Energy band mixing and compositional dependences of semiconducting mixed crystals(Texas Tech University, 1971-08) Yoo, Hee KNot availableItem LCAO-MO studies of neutral interstitial hydrogen in zincblende BN and BP(Texas Tech University, 1989-08) Chu, Chong HwanThe purpose of this study is to calculate the potential energy surfaces and electronic structures of neutral interstitial hydrogen in zincblende BN and BP. The present calculations are the first theoretical study of any defect in these hosts. The calculations are done at the approximate ab-initio Hartree-Fock level with the method of partial retention of diatomic differential overlap in a variety of clusters saturated with hydrogen atoms. The results show that neutral hydrogen can be found at three interstitial sites in each host: near the center of a covalent bond (with H^ primarily bound to the group III atom) and at the two tetrahedral interstitial sites. The equilibrium configurations are compared to those previously obtained in diamond and silicon. The characteristics of yet unobserved fiSR spectra are predicted. Some properties of interstitial hydrogen in III-V compounds are directly related to the ionicity of the hosts.Item Scattering Properties of Oriented Hexagonal Ice Crystals(2010-01-14) Zhang, FengTo interpret the data from spaceborn lidar measurements, one must have a basic understanding of the backscattering of oriented ice particles. The conventional raytracing method is not applicable to the scattering of light by oriented particles. In this study, the dipole approximation (DDA) method is employed to the scattering of light on oriented hexagonal ice columns and plates with various tilting angles. It is found that the oriented hexagonal ice particles tend to have strong backscattering intensity with low depolarization ratios which are strongly dependant on the tilting angle of oriented particles. The present results show that the e ffect of particle orientation plays an important role in determining the optical properties of ice clouds consisting of horizontally oriented ice crystals.