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Articles 3601 - 3630 of 3840

Full-Text Articles in Physical Sciences and Mathematics

Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look May 1994

Low-Temperature Growth Of High Resistivity Gaas By Photoassisted Metalorganic Chemical Vapor Deposition, J. C. Roberts, K. S. Boutros, S. M. Bedair, David C. Look

Physics Faculty Publications

We report the photoassisted low‐temperature (LT) metalorganic chemical vapor deposition (MOCVD) of high resistivity GaAs. The undoped as‐grown GaAs exhibits a resistivity of ∼106 Ω cm, which is the highest reported for undoped material grown in the MOCVD environment. Photoassisted growth of doped and undoped device quality GaAs has been achieved at a substrate temperature of 400 °C in a modified atmospheric pressure MOCVD reactor. By using silane as a dopant gas, the LT photoassisted doped films have high levels of doping and electron mobilities comparable to those achieved by MOCVD for growth temperatures, Tg≳600 °C.

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Electrochemical Capacitance-Voltage Analysis Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Material, C. E. Stutz, B. Jogai, David C. Look, J. M. Ballingall, T. J. Rogers May 1994

Electrochemical Capacitance-Voltage Analysis Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Material, C. E. Stutz, B. Jogai, David C. Look, J. M. Ballingall, T. J. Rogers

Physics Faculty Publications

This work shows how electrochemical capacitance‐voltage (EC‐V) measurements can be used to evaluate delta‐doped pseudomorphic high electron mobility transistor material. These EC‐V measurements are compared with magnetic‐field‐dependent Hall effect (M‐Hall) measurements and a self‐consistent Poisson/k⋅p calculation of the band structure and electron concentration. The EC‐V technique can clearly delineate the cap layer, the delta‐doped layer, and the InxGa1−xAs channel layer, whereas the M‐Hall method characterizes only the cap and InxGa1−xAs channel layers. The amount of electron charge seen by …

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 4, April 1994, College Of Engineering And Computer Science, Wright State University Apr 1994

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 4, April 1994, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A ten page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Observation Of Free And Bound Excitons Associated With The 2-Dimensional Electron-Gas In Modulation-Doped Heterostructures, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz Apr 1994

Observation Of Free And Bound Excitons Associated With The 2-Dimensional Electron-Gas In Modulation-Doped Heterostructures, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Overlapping bulk and two-dimensional excitons have been observed in modulation-doped heterostructures. Their differing behavior in a magnetic field allows them to be studied separately. Both free and bound excitons, associated with the two-dimensional electron gas, have been observed in the photoluminescence spectra of these structures. These excitons show a reduced binding energy due to screening and are found in a region of the structure where band-gap renormalization occurs due to many-body interactions. The two-dimensional excitons are identified from measurements conducted in applied magnetic fields.

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 3, March 1994, College Of Engineering And Computer Science, Wright State University Mar 1994

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 3, March 1994, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A twelve page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 2, February 1994, College Of Engineering And Computer Science, Wright State University Feb 1994

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 2, February 1994, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A twelve page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Using Tickets To Enforce The Serializability Of Multidatabase Transactions, Dimitrios Georgakopoulos, Marek Rusinkiewicz, Amit P. Sheth Feb 1994

Using Tickets To Enforce The Serializability Of Multidatabase Transactions, Dimitrios Georgakopoulos, Marek Rusinkiewicz, Amit P. Sheth

Kno.e.sis Publications

To enforce global serializability in a multidatabase environment the multidatabase transaction manager must take into account the indirect (transitive) conflicts between multidatabase transactions caused by local transactions. Such conflicts are difficult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these difficulties, we propose to incorporate additional data manipulation operations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of …

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Rate Coefficient For The Reaction N + No, Jane L. Fox Jan 1994

Rate Coefficient For The Reaction N + No, Jane L. Fox

Physics Faculty Publications

Evidence has been advanced that the rate coefficient for the reaction N + NO → N2; + O has a small positive temperature dependence at the high temperatures (900-1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100-200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate …

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Hopping Conduction In Molecular Beam Epitaxial Gaas Grown At Very Low Temperatures, David C. Look, Z-Q. Fang, J. W. Look, J. R. Sizelove Jan 1994

Hopping Conduction In Molecular Beam Epitaxial Gaas Grown At Very Low Temperatures, David C. Look, Z-Q. Fang, J. W. Look, J. R. Sizelove

Physics Faculty Publications

Conductivity and Hall effect measurements have been performed on 2 μm thick molecular beam epitaxial layers grown at very low substrate temperatures, 200 to 400°C. For growth temperatures below 300°C, the conduction is dominated by hopping between arsenic antisite defects of concentrations up to 1020 cm−3. Below measurement temperatures of about 130 K, the hopping conduction can be quenched by strong IR light illumination, because the antisite then becomes metastable. The antisite has a thermal activation energy of , and thus is not identical to the famous EL2. Both nearest‐neighbor and variable‐range hopping mechanisms are considered in …

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 1, January 1994, College Of Engineering And Computer Science, Wright State University Jan 1994

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 10, Number 1, January 1994, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A fourteen page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Evidence For Day-To-Night Ion Transport At Low Solar Activity In The Venus Pre-Dawn Ionosphere, J. F. Brannon, Jane L. Fox, H. S. Porter Dec 1993

Evidence For Day-To-Night Ion Transport At Low Solar Activity In The Venus Pre-Dawn Ionosphere, J. F. Brannon, Jane L. Fox, H. S. Porter

Physics Faculty Publications

Periapsis of the Pioneer Venus spacecraft dropped below 180 km on August 28, 1992 near midnight, and 42 orbits of low altitude data at moderately low solar activity in the pre-dawn sector were obtained before contact was lost to the spacecraft in October, 1992. Through a combination of analysis of data from the PV orbiter ion mass spectrometer (OIMS) and modeling, we consider here what can be learned about the relative importance of plasma transport from the dayside and electron precipitation in maintaining the nightside ionosphere during the re-entry period. In particular, we examine here the atomic ion density profiles. …

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 10, December 1993, College Of Engineering And Computer Science, Wright State University Dec 1993

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 10, December 1993, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A ten page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Recombination Of 2-Dimensional Electrons With Free Light And Heavy Holes In Alxga1-Xas-Gaas Single Heterojunctions In A Magnetic-Field, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz Dec 1993

Recombination Of 2-Dimensional Electrons With Free Light And Heavy Holes In Alxga1-Xas-Gaas Single Heterojunctions In A Magnetic-Field, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Landau-level oscillations are observed in the photoluminescence from an AlxGa1-xAs-GaAs single heterojunction in an applied magnetic field. Extrapolating the oscillations back to zero field gives the energy of the transition from the two-dimensional (2D) electrons to the free heavy holes (hh1 and hh2) and free light holes (lh) weakly confined in the GaAs active layer. The measured energy separation between hh1 and lh is 1.8 meV, which agrees very well with the calculated value of 2.2 meV. The measured energy separation between hh1 and hh2 is 3.8 meV, in good agreement with the calculated value of …

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 9, November 1993, College Of Engineering And Computer Science, Wright State University Nov 1993

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 9, November 1993, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A fourteen page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Controllability And Stabilizability Of Coupled Strings With Control Applied At The Coupled Points, Lop-Fat Ho Nov 1993

Controllability And Stabilizability Of Coupled Strings With Control Applied At The Coupled Points, Lop-Fat Ho

Mathematics and Statistics Faculty Publications

Controllability and stabilizability of a system of coupled strings with control applied at the coupled points is studied. By investigating the properties of certain exponential series, it is shown that the system is approximate controllable if and only if related systems of uncoupled strings do not share a common eigenvalue. A sufficient condition for exact controllability is also obtained in terms of the Riesz basis properties of those exponential series.

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 8, October 1993, College Of Engineering And Computer Science, Wright State University Oct 1993

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 8, October 1993, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A ten page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Harmonic-Analysis Of Fractal Measures Induced By Representations Of A Certain C*-Algebra, Palle Jorgensen, Steen Pedersen Oct 1993

Harmonic-Analysis Of Fractal Measures Induced By Representations Of A Certain C*-Algebra, Palle Jorgensen, Steen Pedersen

Mathematics and Statistics Faculty Publications

We describe a class of measurable subsets Ω in Rd such that L2(Ω) has an orthogonal basis of frequencies eλ(x) = ei2πλ.x(x ε Ω) indexed by λ ∈ Λ ⊂ Rd. We show that such spectral pairs (Ω, Λ) have a self-similarity which may be used to generate associated fractal measures μ with Cantor set support. The Hilbert space L2(μ) does not have a total set of orthogonal frequencies, but a harmonic analysis of mu may be built instead from a natural representation of the Cuntz …

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Semantics-Based Information Brokering: A Step Towards Realizing The Infocosm, Vipul Kashyap, Amit P. Sheth Oct 1993

Semantics-Based Information Brokering: A Step Towards Realizing The Infocosm, Vipul Kashyap, Amit P. Sheth

Kno.e.sis Publications

The rapid advances in computer and communication technologies, and their merger, is leading to a global information market place. It will consist of federations of very large number of information systems that will cooperate to varying extents to support the users' information needs. We propose an architecture which may facilitate meeting these needs. It consists of three main components: information providers, information brokers and information consumers. We also propose an approach to information brokering. We discuss two of it's tasks: information resource discovery, which identities relevant information sources for a given query, and query processing, which involves the generation of …

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Student Fact Book, Fall 1993, Wright State University, Office Of Student Information Systems, Wright State University Oct 1993

Student Fact Book, Fall 1993, 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, 1993.

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On The Escape Of Oxygen And Hydrogen From Mars, Jane L. Fox Sep 1993

On The Escape Of Oxygen And Hydrogen From Mars, Jane L. Fox

Physics Faculty Publications

Escape rates of oxygen atoms from dissociative recombination of O2+ above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process, and our recently revised understanding of the Martian dayside ionosphere. Only about 60% of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured …

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Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 7, September 1993, College Of Engineering And Computer Science, Wright State University Sep 1993

Wright State University College Of Engineering And Computer Science Bits And Pcs Newsletter, Volume 9, Number 7, September 1993, College Of Engineering And Computer Science, Wright State University

BITs and PCs Newsletter

A ten page newsletter created by the Wright State University College of Engineering and Computer Science that addresses the current affairs of the college.

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Specifying And Enforcing Intertask Dependencies, Paul Attie, Munindar Singh, Amit P. Sheth, Marek Rusinkiewicz Aug 1993

Specifying And Enforcing Intertask Dependencies, Paul Attie, Munindar Singh, Amit P. Sheth, Marek Rusinkiewicz

Kno.e.sis Publications

Extensions of the traditional atomic transaction model are needed to support the development of multi-system applications or workflows that access heterogeneous databases and legacy application systems. Most extended transaction models use conditions involving events or dependencies between transactions. Intertask dependencies can serve as a uniform framework for defining extended transaction models. In this paper we introduce event attributes needed to determine whether a dependency is enforceable and to properly schedule events in extended transaction models. Using these attributes and a formalization of a dependency into the temporal logic CTL, we can automatically synthesize an automaton that captures the computations that …

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Semi-Insulating Nature Of Gas Source Molecular Beam Epitaxial Ingap Grown At Very Low Temperatures, David C. Look, Y. He, J. Ramdani, N. Elmasry, S. M. Bedair Aug 1993

Semi-Insulating Nature Of Gas Source Molecular Beam Epitaxial Ingap Grown At Very Low Temperatures, David C. Look, Y. He, J. Ramdani, N. Elmasry, S. M. Bedair

Physics Faculty Publications

InxGa1−xP lattice matched to GaAs (x≂0.51) has proven to be useful in many device applications. Here we show that undoped, semi‐insulating InGaP is possible by growing with gas source molecular beam epitaxy at very low temperatures, 150–250 °C. The material grown at about 200 °C is n‐type with a 296‐K resistivity of 9×105 Ω cm, a mobility of 120 cm2/V s, and a donor activity energy of 0.48 eV. When annealed at 600 °C for 1 h, the resistivity increases to greater than 109 Ω cm and the …

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Electron-Beam Modification Of Gaas Surface-Potential - Measurement Of Richardson Constant, S. M. Lindsay, Joseph W. Hemsky, David C. Look Aug 1993

Electron-Beam Modification Of Gaas Surface-Potential - Measurement Of Richardson Constant, S. M. Lindsay, Joseph W. Hemsky, David C. Look

Physics Faculty Publications

The surface potential of GaAs is strongly modified in the presence of a high‐energy electron beam due to the creation of electron‐hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A∗T2/Ib(dE/dz)η, where Ib is the beam current density, A∗ is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η−1 is the average energy required to …

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Electron-Drift Velocities In Argon-Boron Trichloride Gas-Mixtures, Donald L. Mosteller Jr., Merrill L. Andrews, Jerry D. Clark, A. Garscadden Aug 1993

Electron-Drift Velocities In Argon-Boron Trichloride Gas-Mixtures, Donald L. Mosteller Jr., Merrill L. Andrews, Jerry D. Clark, A. Garscadden

Physics Faculty Publications

Electron drift velocities were measured for argon gas mixtures containing 25 ppm to 0.5% boron trichloride additive using a pulsed-Townsend drift tube. These results show a marked sensitivity to mixture ratio and the gas mixtures also show negative differential conductivity and strong attachment at low electric field/gas number density.

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Upper Limits To The Nightside Ionosphere Of Mars, Jane L. Fox Jul 1993

Upper Limits To The Nightside Ionosphere Of Mars, Jane L. Fox

Physics Faculty Publications

The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, …

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Prominent Thermally Stimulated Current Trap In Low-Temperature-Grown Molecular-Beam Epitaxial Gaas, Z-Q. Fang, David C. Look Jul 1993

Prominent Thermally Stimulated Current Trap In Low-Temperature-Grown Molecular-Beam Epitaxial Gaas, Z-Q. Fang, David C. Look

Physics Faculty Publications

By far, the largest thermally stimulated current trap in molecular beam epitaxial GaAs grown at 200–250 °C is T5, with an activation energy of 0.27 eV and most likely related to VGa. After an anneal at 300–350 °C, another trap T6☒ appears, with an activation energy of 0.14 eV and closely identified with VAs or the complex, VAs‐AsGa. Proposed defect reactions in this As‐rich material include VGa+AsAs→VAs‐AsGa, and VGa+AsGa→VGa‐AsGa.

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Annealing Dynamics Of Molecular-Beam Epitaxial Gaas Grown At 200°C, David C. Look, D. C. Walters, G. D. Robinson, J. R. Sizelove, M. G. Mier, C. E. Stutz Jul 1993

Annealing Dynamics Of Molecular-Beam Epitaxial Gaas Grown At 200°C, David C. Look, D. C. Walters, G. D. Robinson, J. R. Sizelove, M. G. Mier, C. E. Stutz

Physics Faculty Publications

By separating a 2‐μm‐thick molecular‐beam‐epitaxial GaAs layer grown at 200 °C from its 650‐μm‐thick substrate, we have been able to obtain accurate Hall‐effect and conductivity data as functions of annealing temperature from 300 to 600 °C. At a measurement temperature of 300 K, analysis confirms that hopping conduction is much stronger than band conduction for all annealing temperatures. However, at higher measurement temperatures (up to 500 K), the band conduction becomes comparable, and a detailed analysis yields the donor and acceptor concentrations and the donor activation energy. Also, an independent absorption study yields the total and charged AsGa concentrations. …

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Analytical Two-Layer Hall Analysis - Application To Modulation-Doped Field-Effect Transistors, David C. Look, C. E. Stutz, Christopher A. Bozada Jul 1993

Analytical Two-Layer Hall Analysis - Application To Modulation-Doped Field-Effect Transistors, David C. Look, C. E. Stutz, Christopher A. Bozada

Physics Faculty Publications

The classical magnetic‐field‐dependent Hall coefficient and conductivity equations are inverted to give the mobilities μ1 and μ2 and carrier concentrations n1 (or p1) and n2 (or p2) in two degenerate bands. The two‐band solution holds for arbitrary magnetic‐field strength as long as quantum effects can be ignored (i.e., kT≳ℏeB/m∗), and it is argued that the analysis can also be applied to two separate layers up to reasonable field strengths. The results are used to determine the two‐dimensional electron gas mobility and carrier concentration in a modulation‐doped field‐effect …

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A Framework For Controlling Cooperative Agents, Kuo-Chu Lee, William H. Mansfield, Amit P. Sheth Jul 1993

A Framework For Controlling Cooperative Agents, Kuo-Chu Lee, William H. Mansfield, Amit P. Sheth

Kno.e.sis Publications

Presents an overview of the ITX (Interacting Transaction) system, which supports complex interactions among cooperating agents in the presence of user interventions that change application objectives and system failures. The system's components and its unique fixed-point criterion for feedback control of iterative interactions are described. An example of a simplified multimedia teleconferencing application is discussed to illustrate the features of the ITX system.

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