Physical Sciences and Mathematics Commons^™

Effect Of Ammonia Flow Rate On Impurity Incorporation And Material Properties Of Si-Doped Gan Epitaxial Films Grown By Reactive Molecular Beam Epitaxy, Wook Kim, A. E. Botchkarev, H. Morkoç, Z-Q. Fang, David C. Look, David J. Smith

Physics Faculty Publications

Effect of ammonia flow rate on the impurity incorporation and material properties of Si-doped GaN films grown by reactive molecular beam epitaxy (RMBE) process is discussed. It appears that the ammonia flow rate has a marginal effect on the incorporation of impurities into the Si-doped GaN films except there was a little decrease in O and Si with increasing ammonia flow rate when the Si concentration in the film is higher than 10¹⁸ cm⁻³. Electron Hall mobility of Si-doped GaN films grown by RMBE varies with ammonia flow rate used during film growth. From deep level transient …

Student Fact Book, Fall 1998, Twenty Second Annual Edition, Wright State University, Office Of Student Information Systems, Wright State University

Wright State University Student Fact Books

The student fact book has general demographic information on all students enrolled at Wright State University for Fall Quarter, 1998.

A Structural Result Of Irreducible Inclusions Of Type Iii Lambda Factors, Lambda Is An Element Of (0,1), Phan Loi

Mathematics and Statistics Faculty Publications

Given an irreducible inclusion of factors with finite index N ⊂ M, where M is of type III_λ1/m, N of type III_λ1/n, 0 < λ < 1, and m,n are relatively prime positive integers, we will prove that if N ⊂ M satisfies a commuting square condition, then its structure can be characterized by using fixed point algebras and crossed products of automorphisms acting on the middle inclusion of factors associated with N ⊂ M. Relations between N ⊂ M and a certain G-kernel on subfactors are also discussed.

Evolution Of Mixed-State Regions In Type-Ii Superconductors, Chaocheng Huang, Tom Svobodny

Mathematics and Statistics Faculty Publications

A mean-field model for dynamics of superconducting vortices is studied. The model, consisting of an elliptic equation coupled with a hyperbolic equation with discontinuous initial data, is formulated as a system of nonlocal integrodifferential equations. We show that there exists a unique classical solution in C^1+α(Ω₀) for all t > Ω, where Ω₀ is the initial vortex region that is assumed to be in C^1+α. Consequently, for any time t, the vortex region Ω_t is of C^1+α, and the vorticity is in C^α(Ω_t).

Deep Centers In N-Gan Grown By Reactive Molecular Beam Epitaxy, Z-Q. Fang, David C. Look, W. Kim, Z. Fan, A. Botchkarev, H. Morkoç

Physics Faculty Publications

Deep centers in Si-doped n-GaN layers grown by reactive molecular beam epitaxy have been studied by deep-level transient spectroscopy as a function of growth conditions. Si-doped GaN samples grown on a Si-doped n⁺-GaN contact layer at 800 °C show a dominant trap C₁ with activation energy E_T = 0.44 eV and capture cross-section σ_T = 1.3×10⁻¹⁵ cm⁻², while samples grown at 750 °C on an undoped semi-insulating GaN buffer show prominent traps D₁ and E₁, with E_T = 0.20 eV and σ_T = 8.4×10⁻¹⁷ cm …

High Mobility Algan/Gan Heterostructures Grown By Gas-Source Molecular Beam Epitaxy, L. K. Li, J. Alperin, W. I. Wang, David C. Look, Donald C. Reynolds

Physics Faculty Publications

We report on the growth of high electron mobility AlGaN/GaN heterostructures on sapphire substrates by gas-source molecular beam epitaxy (GSMBE) using ammonia as the nitrogen source. Improvements in structural, electrical, and optical properties of GaN and AlGaN layers have been made to achieve this goal. For the growth of AlGaN layers, the reflection high-energy electron diffraction revealed a twofold surface reconstruction, indicative of atomic smoothness of the film surface. High mobility two-dimensional electron gas has been achieved in both unintentionally doped (by piezoelectric effect induced by lattice mismatch strain) and modulation doped AlGaN/GaN heterostructures. The modulation-doped n+-Al_0.2Ga …

Neutral-Donor-Bound-Exciton Complexes In Zno Crystals, D. C. Reynolds, David C. Look, B. Jogai, C. W. Litton, T. C. Collins, W. C. Harsch, G. Cantwell

Physics Faculty Publications

Neutral-donor–bound-exciton transitions have been observed in ZnO. The isolated neutral donors are made up of defect pair complexes. The neutral-donor nature of these pair complexes was determined from magneticfield measurements and from two-electron transitions. Excited states of the neutral-donor bound excitons were observed in the form of rotator states analogous to rotational states of the H₂ molecule.

Logical Information Modeling Of Web-Accessible Heterogeneous Digital Assets, Kshitij Shah, Amit P. Sheth

Kno.e.sis Publications

This paper introduces the MREF framework for representing and correlating information at a higher semantic level than is possible with Web-based information systems today. The role that metadata plays in this framework is described, together with a metadata based infrastructure to support our media independent information correlation paradigm. To keep it consistent with evolving standards, broader acceptance and ease of implementation, MREF abstraction is structured on top of RDF and XML. Its central role in the context of the InfoQuilt system, for exploiting heterogeneous digital media using a federated and scalable architecture, is briefly described.

Zebra Image Access System, Srilekha Mudumbai, Kshitij Shah, Amit P. Sheth, Krishnan Parasuraman, Clemens Bertram

Kno.e.sis Publications

The ZEBRA system, which is part of the VisualHarness platform for managing heterogeneous data, supports three types of access to distributed image repositories: keyword based, attribute based, and image content based. A user can assign different weights (relative importance) to each of the three types, and within the last type of access, to each of the image properties. The image based access component (IBAC) supports access based on computable image properties such as those based on spatial domain, frequency domain or statistical and structural analysis. However, it uses a novel black box approach of utilizing a Visual Information Retrieval (VIR) …

Electron-Irradiation-Induced Deep Level In N-Type Gan, Z-Q. Fang, Joseph W. Hemsky, David C. Look, M. P. Mack

Physics Faculty Publications

Deep-level transient spectroscopy measurements of n-type GaN epitaxial layers irradiated with 1-MeV electrons reveal an irradiation-induced electron trap at E_C−0.18 eV. The production rate is approximately 0.2 cm⁻¹, lower than the rate of 1 cm⁻¹ found for the N vacancy by Hall-effect studies. The defect trap cannot be firmly identified at this time. ©1998 American Institute of Physics.

Strictly Level-Decreasing Logic Programs, Pascal Hitzler, Anthony K. Seda

Computer Science and Engineering Faculty Publications

We study strictly level-decreasing logic programs (sld-programs) as defined earlier by the present authors. It will be seen that sld-programs, unlike most other classes of logic programs, have both a highly intuitive declarative semantics, given as a unique supported model, and are computationally adequate in the sense that every partial recursive function can be represented by some sld-program P. Allowing for a safe use of cuts, an interpreter based on SLDNF-resolution, as implemented for example in standard Prolog systems, is shown to be sound and complete with respect to this class of programs. Furthermore, we study connections between topological …

Orthogonal Harmonic Analysis Of Fractal Measures, Palle Jorgensen, Steen Pedersen

Mathematics and Statistics Faculty Publications

We show that certain iteration systems lead to fractal measures admitting an exact orthogonal harmonic analysis.

Solar Cycle Variability Of Hot Oxygen Atoms At Mars, Jhoon Kim, Andrew F. Nagy, Jane L. Fox, Thomas E. Cravens

Physics Faculty Publications

The population of hot oxygen atoms in the Martian exosphere is reexamined using newly calculated hot O production rates for both low and high solar cycle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O₂⁺ ions. These calculations take into account the calculated vibrational distribution of O₂⁺ and the new measured branching ratios. Furthermore, these calculations also consider the variation of the dissociative recombination cross section with the relative speed of the participating ions and electrons, the rotational energy of the O₂⁺ ions, and the spread of …

Effect Of High-Temperature Annealing On Electrical And Optical Properties Of Undoped Semi-Insulating Gaas, Z-Q. Fang, D. C. Reynolds, David C. Look, N. G. Paraskevopoulos, T. E. Anderson, R. L. Jones

Physics Faculty Publications

A comprehensive characterization, including room temperature Hall effect, near infrared absorption, temperature dependent dark current and photocurrent (using 1.13 eV light), normalized thermally stimulated current (NTSC), photoluminescence at 4.2 K in both near band edge and deep level regions, and selective pair photoluminescence (SPL) at 2 K, has been carried out on undoped semi-insulating GaAs samples, cut from four wafers which were grown by the low pressure liquid encapsulated Czochralski technique and annealed by three different schedules: a 1100 °C anneal with either fast or slow cooling, or a 1000 °C standard anneal. The 1100 °C anneal clearly introduces higher …

Interestingness Of Discovered Association Rules In Terms Of Neighborhood-Based Unexpectedness, Guozhu Dong, Jinyan Li

Kno.e.sis Publications

One of the central problems in knowledge discovery is the development of good measures of interestingness of discovered patterns. With such measures, a user needs to manually examine only the more interesting rules, instead of each of a large number of mined rules. Previous proposals of such measures include rule templates, minimal rule cover, actionability, and unexpectedness in the statistical sense or against user beliefs.

In this paper we will introduce neighborhood-based interestingness by considering unexpectedness in terms of neighborhood-based parameters. We first present some novel notions of distance between rules and of neighborhood of rules. The neighborhood-based interestingness of …

Generalized Ultrametrics, Domains And An Application To Computational Logic, Anthony K. Seda, Pascal Hitzler

Computer Science and Engineering Faculty Publications

Fixed points of functions and operators are of fundamental importance in programming language semantics in giving meaning to recursive definitions and to constructs which involve self-reference. It follows therefore that fixed-point theorems are also of fundamental importance in theoretical computer science. Often, order-theoretic arguments are available in which case the well-known Knaster-Tarski theorem can be used to obtain fixed-points. Sometimes, however, analytical arguments are needed involving the Banach contraction mapping theorem as is the case for example in studying concurrency and communicating systems. Situations arise also in computational logic in the presence of negation which force non-monotonicity of the operators …