Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 12 of 12

Full-Text Articles in Physics

Magnetic Flux Motion And Flux Pinning In Superconductors , Steven C. Sanders Jan 1992

Magnetic Flux Motion And Flux Pinning In Superconductors , Steven C. Sanders

Retrospective Theses and Dissertations

Magnetization measurements on the two high-temperature superconductors Nd[subscript]1.85Ce[subscript]0.15CuO[subscript]4-y and Ba[subscript]0.6K[subscript]0.4BiO[subscript]3 have been undertaken in order to study the reversible and irreversible magnetic behavior and compare these two different materials with other high-temperature superconductors (HTSC). While the other HTSC are known to have hole carriers and layers of CuO[subscript]2 planes in anisotropic crystal structures, Nd[subscript]1.85Ce[subscript]0.15CuO[subscript]4-y (NCCO) has electron carriers as well as hole carriers, and Ba[subscript]0.6K[subscript]0.4BiO[subscript]3 (BKBO ...


Magnetic Properties Of High-T[Subscript C] Superconductors , Junho Gohng Jan 1992

Magnetic Properties Of High-T[Subscript C] Superconductors , Junho Gohng

Retrospective Theses and Dissertations

Magnetic properties of high-T[subscript] c superconductors have been studied in order to determine the free-energy surface, the characteristic critical fields, order parameters structure, and the grain size effect on magnetization. Studies of the thermodynamic reversibility for YBa[subscript]2Cu[subscript]3O[subscript]7-[delta] show the rounding in magnetization vs. temperature curves is a reflection of the thermodynamic fluctuations near T[subscript] c. Specific heat jump C(0)-C(H) values that have been calculated from the free-energy surfaces show good agreement with the direct calorimetric measurements;Comparative studies of the free-energy surfaces, flux creep and critical currents for ...


A Study Of Isolated Photons In Z0 Hadronic Decays Using The Delphi Detector At Lep , Randall R. Holmes Jan 1992

A Study Of Isolated Photons In Z0 Hadronic Decays Using The Delphi Detector At Lep , Randall R. Holmes

Retrospective Theses and Dissertations

We present a study of the production of energetic isolated photons in the reaction e[superscript]+e[superscript]-→ Z[superscript]0→ q[macron]q[gamma] using the DELPHI detector at LEP. Within the context of the Standard Model, our results for final state radiation show no evidence for anomolous photon production due to rare or new processes. We present a comparison of our data with these theoretical expectations and present upper limits at the 95% CL on the cross section times the branching ratio to hadrons and a photon for the rare or new processes: (1) [sigma](e[superscript]+e ...


Theoretical Study Of Electron-Phonon Interaction In Β-Phase Niti And Ni-Al Alloys , Guang-Lin Zhao Jan 1992

Theoretical Study Of Electron-Phonon Interaction In Β-Phase Niti And Ni-Al Alloys , Guang-Lin Zhao

Retrospective Theses and Dissertations

NiTi and Ni-Al alloys are two well known examples of materials which exhibit martensitic phase transformations, with the equiatomic NiTi alloy especially well known as the best shape memory material. At high temperature, both alloys possess the CsCl-type or B2 structure with a simple cubic (SC) lattice. They are often called [beta]-phase alloys. As temperature is lowered, the [beta]-phase NiTi and Ni-Al alloys undergo premartensitic phase transformations or premartensitic anomalies before the martensitic phase transformation. Neutron scattering measurements have found that the TA[subscript]2 (110) phonon modes in the [beta]-phases are temperature dependent and exhibit anomalous ...


Quantum Action Variable Description Of Bound And Scattering States , Mirley K. Balasubramanya Jan 1992

Quantum Action Variable Description Of Bound And Scattering States , Mirley K. Balasubramanya

Retrospective Theses and Dissertations

We present generalized definitions of the classical and quantum radial action variables for both bound and scattering states of a particle moving in the Yukawa potential. The classical action variable is defined as an integral over a contour in the complex radial coordinate plane of the classical momentum function. The quantum action variable is similarly defined as an integral over the same contour of the quantum momentum function. The extension of these definitions of the action variable to other central potentials is discussed.


The Design, Construction And Applications Of A Novel Double-Axis Helium Atom Spectrometer , Robert L. Folkerts Jan 1992

The Design, Construction And Applications Of A Novel Double-Axis Helium Atom Spectrometer , Robert L. Folkerts

Retrospective Theses and Dissertations

A novel helium atoms spectrometer has been developed for the study of elastic and inelastic collisions with surfaces. The spectrometer is a double-axis design, providing the experimentalist with the capability of using an analyzer crystal to provide energy resolution for either elastic or inelastic experiments. The spectrometer is novel in that scattering angle at both axes may be adjusted during the experiment, allowing great flexibility in the design and execution of experiments of solid surfaces;The mechanisms and operating characteristics of the spectrometer are described. The initial tests of the spectrometer, using the well characterized LiF(001) surface, are also ...


Distortions Of Parton Distributions Due To Multiquark Effects , Athanasios Petridis Jan 1992

Distortions Of Parton Distributions Due To Multiquark Effects , Athanasios Petridis

Retrospective Theses and Dissertations

It has been observed that the momentum distributions of partons in bound nuclei are distorted relative to those of free protons and neutrons. This phenomenon was first observed in deep inelastic scattering experiments with muon and neutrino beams on nuclear targets and is known as the EMC effect. Similar phenomena have been observed in other high energy interactions such as the Drell-Yan process, the hadroproduction of direct photons, and the resonance production of charmonium and bottomonium states. In this work we investigate the possibility that these effects are predominantly of partonic origin. Standard nuclear quantum mechanics predicts that there is ...


Synthesis And Magnetic Properties Of Novel Ln[Subscript 2-X]Mxcuo[Subscript 4+Y] Compositions (Ln = La,Pr,Nd,Sm,Eu,Gd; M = Ca,Sr,Ba; 0<=X<=0.2; -0.5<=Y<=0.5) , Jin Hyung Cho Jan 1992

Synthesis And Magnetic Properties Of Novel Ln[Subscript 2-X]Mxcuo[Subscript 4+Y] Compositions (Ln = La,Pr,Nd,Sm,Eu,Gd; M = Ca,Sr,Ba; 0<=X<=0.2; -0.5<=Y<=0.5) , Jin Hyung Cho

Retrospective Theses and Dissertations

Ln[subscript]2CuO[subscript]4 (Ln = La, Pr, Nd, Sm, Eu, Gd) undergo structural transitions to oxygen-reduced structures Ln[subscript]2CuO[subscript]4-d with Ln = La, d = 1/3 and Ln = Pr, Nd, Sm, Eu, Gd, d = 1/2. The Nd[subscript]2CuO[subscript]4-type (T[superscript]'-phase) La[subscript]2CuO[subscript]4+d is observed after reoxygenation of oxygen-reduced La[subscript]2CuO[subscript]3.67 structure below 500°C. The magnetic properties of T/O (K[subscript]2NiF[subscript]4-type structure)-phase La[subscript]2CuO[subscript]4 systems show quite different behaviors compared with those of conventional solid state ...


Neutron Diffraction Study Of The Electronic Structure Of High-T[Subscript C] Superconductor-Related Compounds , Xun-Li Wang Jan 1992

Neutron Diffraction Study Of The Electronic Structure Of High-T[Subscript C] Superconductor-Related Compounds , Xun-Li Wang

Retrospective Theses and Dissertations

Neutron diffraction techniques have been used to study the electronic structure of La[subscript]2NiO[subscript]4 and Sr[subscript]2CuO[subscript]2Cl[subscript]2 by measuring the antiferromagnetic form factor of the single-crystal samples at 15 K. The antiferromagnetic form factor was obtained from the integrated intensities of several magnetic reflections. In both cases, the experimentally determined form factor exhibits a plateau at low Q values (up to 3 A[superscript]-1), similar to that observed for La[subscript]2CuO[subscript]4. Detailed modelling of the experimental data of these three compounds suggests that the observed plateau may be ...


Electrical, Optical And Magnetic Resonance Studies Of Novel [Pi]-Conjugated Polymers , Qing-Xiao Ni Jan 1992

Electrical, Optical And Magnetic Resonance Studies Of Novel [Pi]-Conjugated Polymers , Qing-Xiao Ni

Retrospective Theses and Dissertations

Conductivity, optical properties including visible and infrared (IR) absorption and photoluminescence (PL), and magnetic resonance properties including electron spin resonance (ESR) and optically detected magnetic resonance (ODMR) have been studied in polydiethynylsilanes (PDES) and poly(2,5-dibutoxyparaphenyleneacetylene) (PDBOPA), which were recently synthesized by Dr. T. J. Barton's group at the Ames Laboratory. PDES and PDBOPA blend and PDBOPA-based electroluminescent preliminary diodes which were fabricated by the author were also explored;The undoped one-dimensional gap of PDES polymers, which have average molecular weight from ~2 x 10[superscript]5 to 1 x 10[superscript]6, is 2.0 eV in ...


Radiation Induced Flux Pinning In Yba2cu3o7-[Delta] Single Crystal , Qiang Qian Jan 1992

Radiation Induced Flux Pinning In Yba2cu3o7-[Delta] Single Crystal , Qiang Qian

Retrospective Theses and Dissertations

Radiation damage studies have been carried out to determine the changes in superconducting critical current density that result for different choices of radiation direction and magnetic field direction relative to the crystallographic axes. Single crystals of YBa[subscript]2Cu[subscript]3O[subscript]7-[delta] were irradiated with a beam of 200 MeV protons directed either parallel to the a-b plane or parallel to the c-axis. These beams created rather light damage in the form of interstitials and voids that subsequently coalesced to clusters of extra atoms in the a-b plane directed along the (100) direction. For low fluence, the main ...


Optical Properties Of Γ- And Α-Ce By Spectroscopic Ellipsometry, Joo Yull Rhee Jan 1992

Optical Properties Of Γ- And Α-Ce By Spectroscopic Ellipsometry, Joo Yull Rhee

Retrospective Theses and Dissertations

We have built a rotating analyzer type ellipsometer with an ultra high vacuum sample chamber. We measured the dielectric functions of [gamma]- and [alpha]-Ce in the energy range from 1.5 to 5.4 eV to investigate the role of the 4f electron in the isostructural phase transition. [gamma]- and [alpha]-Ce were made in situ by evaporation of Ce on sapphire substrates at room temperature and at 25 K, respectively. All measurements were performed inside a UHV chamber at pressures lower than 1 x 10[superscript]-10 Torr.;The measured dielectric functions showed a thickness dependence. The thicker ...