We compute conductance fluctuations in a variety of disordered mesoscopic systems through direct numerical evaluation of the Kubo-Greenwood formula for the conductivity. / Our model Hamiltonian is quite different from the Anderson tight-binding Hamiltonian which has been most commonly used in studies of electronic structure and properties of disordered systems. It is reminiscent of the Kronig-Penney model in that $ delta$-like atomic potentials are specified by a single parameter. / Our model structures range from substitutional binary alloys to topologically disordered "glasses", and include systems where the disorder is caused by random small displacements of atoms from their crystalline lattice positions. / We test the universal nature of conductance fluctuations for the model with substitutional disorder. We study systems which are always larger than the elastic mean free path, but not always smaller than the localization length of the electron wavefunctions. In those systems where universality is expected, we confirm the ergodic theorem of Lee and Stone and observe the universal amplitudes of the fluctuations both in two-dimensional systems with and without a magnetic field, and in quasi-one-dimensional geometry. / We have also performed the first studies of conductance fluctuations in strongly disordered systems and observed a universal relationship between the amplitude of the fluctuations and the value of the conductance itself: this relationship does not depend upon the nature of the disorder.

A theoretical and experimental study of the spatial spread of electron dose distributions for pencil and broad electron beams in various media is presented. We discuss in detail two methods for measurement of electron beam kinetic energies, describe our technique for the measurement of the optical density versus dose relationship for radiographic films, and present the experimental set-up for the measurement of the spatial spread of electron dose distributions for pencil and broad electron beams. / The Fermi-Eyges theory for the small angle multiple Coulomb scattering describes the spatial electron distribution in scattering media. The spatial spread of a pencil electron beam in a phantom as predicted by the Fermi-Eyges theory is an increasing function of depth in phantom irrespective of the depth. Our experiments, on the other hand, show that the spatial spread indeed increases with depth until depths close to 2/3 of the practical electron range, but at larger depths the spatial spread saturates, then decreases and vanishes at depths greater than the range of electrons in the material. To describe the observed saturation and the decrease of the spatial spread at depths beyond 2/3 of the practical electron range we introduce an electron absorption term containing four empirical parameters into the original Fermi differential equation and show that its solution describes the experimental results obtained for pencil electron beams of various energies in polystyrene, cork and aluminum phantoms. We also compare with experimental results the spatial electron dose distributions predicted by the Fermi-Eyges theory and the modified Fermi-Eyges theory for collimated broad electron beams.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2007. / (UMI)AAI3261460. Source: Dissertation Abstracts International, Volume: 68-04, Section: B, page: 2532. Adviser: Thomas A. Lipo.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6633. Adviser: Weng Cho Chew. Includes bibliographical references (leaves 143-146) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1068. Adviser: Paul T. Debevec. Includes bibliographical references (leaves 94-100) Available on microfilm from Pro Quest Information and Learning.

This thesis is an experimental study of structural and magnetic properties, and hyperfine interactions in crystalline alloys Cu2GdIn, CrNiP, CrNiAs, EuCu2Si2, Cr2FeSe4 and icosahedral quasicrystals Al60Cr19.9Fe0.1Ge 20, Ag50In36Gd14, Zn77Fe 7Sc16. The Heusler alloy Cu2GdIn is shown to crystallize in the L21 crystal structure (space group Fm3¯ m) with a lattice constant of 6.6643(3) A. It is an antiferromagnet with the Neel temperature of 9.6(1) K, the effective magnetic moment of 7.98(4) muB per Gd atom, and the paramagnetic Curie temperature of --41.2(9) K. Its Debye temperature is 229(5) K. The alloys CrNiP and CrNiAs crystallize, respectively, in the Co 2P-type structure (space group Pnma) and the Fe 2P-type structure (space group P6¯2 m), with the lattice parameters a = 5.7965(1) A, b = 3.5337(1) A, c = 6.8123(2) A, and a = 6.1128(2) A, c = 3.6585(1) A. CrNiP is shown to be a three-dimensional Heisenberg ferromagnetic with the Curie temperature of 142.9(6) K, whereas CrNiAs is demonstrated to be a mean-field ferromagnet with the Curie temperature of 171.9(1) K. A long standing controversy concerning the Ni magnetic moment in these alloys is solved unequivocally: Ni atoms carry a magnetic moment of 0.14 muB in CrNiP and 0.15(3) mu B in CrNiAs. The Debye temperatures of CrNiP and CrNiAs are, respectively, 261(3) K and 221(1) K. EuCu2Si2 is one of the first Eu-based alloys in which intermediate valence behavior of Eu was observed. It is demonstrated here that there are no valence fluctuations of Eu in this alloy: Eu atoms are divalent in the temperature range 2-300 K. The Debye temperature of EuCu 2Si2 is shown to be 236(4) K. Cr2FeSe4 is found to have antiferromagnetism with weak ferrimagnetism due to the two different distortions of the octahedral Cr3+ and the octahedral Fe2+. A negative magnetization is found in a magnetic field of 5 De and below due to the coercive-field magnetization reversal. The magnetization reversal disappears in a magnetic field larger than 65 Oe. The icosahedral quasicrystals Al60Cr19.9Fe 0.1Ge20, Ag50In36Gd14, and Zn77Fe7Sc16 are shown to have a primitive six-dimensional Bravais lattice with a six-dimensional lattice constant of 6.558(2) A, 7.805(2) A, and 8.087(1) A, respectively. Al 60Cr19.9Fe0.1Ge20 is a paramagnet with the effective magnetic moment of 0.312(3) muB per Cr/Fe atom. Its Debye temperature is 463(15) K. The temperature dependence of the electrical conductivity of Al60Cr19.9Fe0.1Ge20 is well accounted for quantitatively by theories of quantum interference effects. Ag50In36Gd14 and Zn77Fe 7Sc16 are shown to be spin glasses with the spin freezing temperature of 4.25(5) K and 7.75(2) K, respectively. The hyperfine magnetic fields at 155Gd and 57Fe nuclei in g50 In36Gd14 and Zn77Fe7Sc 16 are shown to set in at temperatures larger than the corresponding freezing temperatures. The frequency dependence of the freezing temperature in Zn77Fe7Sc16 is shown to be equally well accounted for by the Vogel-Fulcher law and the power law. Analysis of the aging effects observed in Zn77Fe7Sc16 leads to a major finding that the nature of the spin-glass state in this quasicrystal is fundamentally different from that of a canonical spin glass. The Debye temperatures of Ag50In36Gd14 and Zn 77Fe7Sc16 are, respectively, 199(2) K and 443(8) K.

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