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Iowa State University

2001

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Articles 31 - 37 of 37

Full-Text Articles in Physics

X-Ray Resonant Exchange Scattering Investigations Of Rare Earth Intermetallic Compounds: Tbni2b2c, Tbcu2ge2, And Gdagsb2 , Changyong Song Jan 2001

X-Ray Resonant Exchange Scattering Investigations Of Rare Earth Intermetallic Compounds: Tbni2b2c, Tbcu2ge2, And Gdagsb2 , Changyong Song

Retrospective Theses and Dissertations

A coherent review on the x-ray resonant exchange scattering and basic recapitulation of phenomenological aspects of magnetic interactions were attempted in this thesis. Further, application of the XRES technique to understand the physical origin of various magnetic structures of TbNi2B2 C, TbCu2Ge2 and GdAgSb2 single crystals were tried as a main effort.;TbNi2B2C orders in a longitudinal spin wave structure below TN = 14.5 K. Concomitant with the magnetic ordering, structural phase transition from tetragonal phase (T > TN) to orthorhombic phase occurred. The modulation direction was resolved to be along the longer axis in the basal plane. The wave vector ...


Photoemission Study Of Mnbi And Gdni2ge2 , Derek Paul Brammeier Jan 2001

Photoemission Study Of Mnbi And Gdni2ge2 , Derek Paul Brammeier

Retrospective Theses and Dissertations

Photoelectron spectroscopy was performed on single crystals of MnBi and GdNi2Ge2 utilizing synchrotron radiation as the light source. MnBi is known for its large magneto-optical Kerr rotation and GdNi 2Ge2 is studied for its intriguing magnetic properties at low temperature, including a spin density wave (SDW) that is reported to occur at 27.1 K. Angle resolved photoemission was used to investigate the electronic band structures of both materials. Resonant photoemission was used to characterize valence band features. The shallow core levels were also investigated using angle integrated photoemission. Results from MnBi measurements are compared with recent theoretical bandstructure and ...


Critical Phenomena Of The Disorder Driven Localization-Delocalization Transition , Marc Rühländer Jan 2001

Critical Phenomena Of The Disorder Driven Localization-Delocalization Transition , Marc Rühländer

Retrospective Theses and Dissertations

The critical behavior of non-interacting electrons in disordered systems is investigated. The scaling functions of the localization lengths in two-dimensional systems with a magnetic field perpendicular to the plane and anisotropic hopping are rescaled to the isotropic one. The geometric mean of the critical values of the scaling functions equals the critical value of the isotropic scaling function. The critical exponent of the localization lengths in the two anisotropic directions is found to be equal and also equal to that of the isotropic system. The critical energy is independent of the direction of propagation. If disorder is strong enough, the ...


Search For An Msugra Signature In The Electron + Jets + [Missing Transverse Energy] Final State In [Proton-Antiproton] Collisions At [Square Root Of S] = 1.8 Tev , Zhang Zhou Jan 2001

Search For An Msugra Signature In The Electron + Jets + [Missing Transverse Energy] Final State In [Proton-Antiproton] Collisions At [Square Root Of S] = 1.8 Tev , Zhang Zhou

Retrospective Theses and Dissertations

We describe a search for a Minimal Supergravity (mSUGRA) signature in Run 1 data taken by the DO detector at the Fermilab Tevatron from 1995--1996. The total data luminosity is 92.7 pb-1. The data were examined for events with a single electron, four or more jets and large missing transverse energy. The major backgrounds are from W+jets, QCD, tt[macron], and WW events. We observed no excess of events in our data. Based on the data and the expected signal rate we obtain new limits on new physics in terms of mSUGRA model parameters.


Electromechanical Characterization Of Ultrasonic Nde Systems , Changjiu Dang Jan 2001

Electromechanical Characterization Of Ultrasonic Nde Systems , Changjiu Dang

Retrospective Theses and Dissertations

An ultrasonic nondestructive evaluation (NDE) measurement system is a complex collection of many elements such as the pulser/receiver, the cabling, the transducers, and the material configuration being tested. To completely model an ultrasonic measurement system, a system model, called the electroacoustic measurement (EAM) model , was developed. This model allows one to analyze the measurement system at many different levels, ranging from individual details to the entire system itself. The EAM model has been implemented in software using the MATLAB development environment such that one has control over the specification of the detailed system components. On the other hand, the ...


Theoretical Studies Of Isolated Silicon And Germanium Clusters, And Silicon Clusters On Si(111)-7x7 Surface , Bei Liu Jan 2001

Theoretical Studies Of Isolated Silicon And Germanium Clusters, And Silicon Clusters On Si(111)-7x7 Surface , Bei Liu

Retrospective Theses and Dissertations

We have performed a systematic search for the ground state geometry of Si+n and Si-n in the size range 3 ≤ n ≤ 20 within the framework of density functional theory (DFT) with the local density approximation (LDA) and generalized gradient approximation (GGA). Various properties such as ionization potentials for neutral clusters, vertical detachment energies and photoelectron spectra for anions, fragmentation pathways and dissociation energies for cations, and mobilities for both anions and cations, are calculated and compared with experiments. The structures for medium-sized clusters (10 ≤ n ≤ 20) generally follow the prolate "stacked Si9 tricapped trigonal prism (TTP)" pattern. Both bulk ...


Thermodynamic Critical Field And Superconducting Fluctuation Of Vortices For High Temperature Cuprate Superconductor: La-214 , Yung Moo Huh Jan 2001

Thermodynamic Critical Field And Superconducting Fluctuation Of Vortices For High Temperature Cuprate Superconductor: La-214 , Yung Moo Huh

Retrospective Theses and Dissertations

Thermodynamics has been studied systematically for the high temperature cuprate superconductor La2-xSrxCuO4-d , La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H∥ c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below Tc, magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range ...