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Physical Sciences and Mathematics Commons™

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

1990

Brigham Young University

Articles 1 - 16 of 16

Full-Text Articles in Physical Sciences and Mathematics

The Effect Of Externally Applied Oscillating Electric Fields On The L=1 And L=2 Diocotron Modes In Non-Neutral Plasmas, Ross L. Spencer Oct 1990

The Effect Of Externally Applied Oscillating Electric Fields On The L=1 And L=2 Diocotron Modes In Non-Neutral Plasmas, Ross L. Spencer

Faculty Publications

A high-frequency oscillating electric field can change the properties of diocotron modes in non-neutral plasmas. The effect depends crucially on the azimuthal mode number, m, of the applied field. For m=0, plus or minus 1 there is no effect, and for applied standing waves there is also no effect. But if the applied field has the form of a traveling wave with the norm of m greater than or equal to 2, the frequency of stable diocotron modes can be modified and for the norm of m greater than or equal to 3, the l=2 instability of hollow density profiles …

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Techniques For Cubic Algebraic Surfaces Ii, Thomas W. Sederberg Sep 1990

Techniques For Cubic Algebraic Surfaces Ii, Thomas W. Sederberg

Faculty Publications

A survey of some techniques that may have potential for free-form modeling with algebraic surfaces is continued. Classical results as well as several recent innovations are included. Specific attention is paid to cubic algebraic surfaces, although many of the ideas presented have application to algebraic surfaces of any degree. Topics addressed include piecewise constructions, interpolation to points and space curves, and parameterization.

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Techniques For Cubic Algebraic Surfaces I, Thomas W. Sederberg Jul 1990

Techniques For Cubic Algebraic Surfaces I, Thomas W. Sederberg

Faculty Publications

The tutorial presents some tools for free-form modeling with algebraic surfaces, that is, surfaces that can be defined using an implicit polynomial equation f(x, y, z )=0. Cubic algebraic surfaces (defined by an implicit equation of degree 3) are emphasized. While much of this material applies only to cubic surfaces, some applies to algebraic surfaces of any degree. This area of the tutorial introduces terminology, presents different methods for defining and modeling with cubic surfaces, and examines the power basis representation of algebraic surfaces. Methods of forcing an algebraic surface to interpolate a set of points or a space curve …

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Eigenvalue Problems Of Ginzburg–Landau Operator In Bounded Domains, Kening Lu, Xing-Bin Pan Jun 1990

Eigenvalue Problems Of Ginzburg–Landau Operator In Bounded Domains, Kening Lu, Xing-Bin Pan

Faculty Publications

In this paper we study the eigenvalue problems for the Ginzburg–Landau operator with a large parameter in bounded domains in [openface R]2 under gauge invariant boundary conditions. The estimates for the eigenvalues are obtained and the asymptotic behavior of the associated eigenfunctions is discussed. These results play a key role in estimating the critical magnetic field in the mathematical theory of superconductivity.

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Tomlinsonia Stichkania Sp. Nov., A Permineralized Grass From The Pliocene To (?)Pleistocene China Ranch Beds In Sperry Wash, California, William D. Tidwell, E. M. V. Nambudiri Jun 1990

Tomlinsonia Stichkania Sp. Nov., A Permineralized Grass From The Pliocene To (?)Pleistocene China Ranch Beds In Sperry Wash, California, William D. Tidwell, E. M. V. Nambudiri

Faculty Publications

Permineralized specimens of grasses assignable to Tomlinsonia as a new species Tomlinsonia stichkania occur in the China Ranch beds of Pliocene to possible Pleistocene age in Sperry Wash in the Alexander Hills of southeastern California. The round culm of these grasses is generally solid or occasionally hollow with collateral vascular bundles in the distinct outer and indistinct inner rings. Two-ranked leaf sheaths alternately encircle and overlap the culm. Ridges and furrows occur in the abaxial surfaces of the sheaths. The epidermis of the leaf sheaths is similar to that of the culm. The leaf lamina consists of a three-layered mesophyll. …

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Consistency And Generalization In Incrementally Trained Connectionist Networks, Tony R. Martinez May 1990

Consistency And Generalization In Incrementally Trained Connectionist Networks, Tony R. Martinez

Faculty Publications

This paper discusses aspects of consistency and generalization in connectionist networks which learn through incremental training by examples or rules. Differences between training set learning and incremental rule or example learning are presented. Generalization, the ability to output reasonable mappings when presented with novel input patterns, is discussed in light of the above learning methods. In particular, the contrast between humming distance generalization and generalizing by high order combinations of critical variables is overviewed. Examples of detailed rules for an incremental learning model are presented for both consistency and generalization constraints.

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Interactive Morphometrics From Three-Dimensional Surface Images, William A. Barrett, Shawn C. Becker May 1990

Interactive Morphometrics From Three-Dimensional Surface Images, William A. Barrett, Shawn C. Becker

Faculty Publications

Techniques have been developed for extracting three-dimensional (3D) measurements directly and interactively from 3D representations of surface anatomy. In order to obtain 3D measurements the anatomical surface is interrogated directly through the use of morphometric tools. Morphometric tools include points, 3D graphical "probes", and logical sectioning functions which interact with the surface through depth buffer compositing operations. Tools are interactively positioned on or through the surface to measure surface dimensions and partial volumes, or to define intersecting functions which allow surface anatomy to be visualized in the context of surrounding anatomy. Visualization is also enhanced because tools reveal much pertaining …

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Introductory Dataperfect® Instruction, Frances Jenson Larsen Apr 1990

Introductory Dataperfect® Instruction, Frances Jenson Larsen

Theses and Dissertations

The project should be used in a beginning computer class. These units contain projects from simple to complex. The first instructional unit uses a database that comes with the DataPerfect® program. The students build and manipulate a small database. Reports are prepared, and finally the students design an original database. These instructional units are intended to be used in a high school classroom with the DataPerfect® computer program. DataPerfect® is a copyrighted program marketed by WordPerfect Corporation of Orem, Utah.

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Photoluminescence Studies In Znxcd1-Xte Single Crystals, David D. Allred, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred Mar 1990

Photoluminescence Studies In Znxcd1-Xte Single Crystals, David D. Allred, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The crystalline quality of ZnxCd1-xTe single crystals prepared by a modified Bridgman method with 0≤x≤0.05 has been analyzed using photoluminescence. The spectrum of a typical sample is dominated by lines originating from the recombination of free and bound excitons. Lines due to free excitons in their ground and first excited states are observed in both the pure CdTe and the mixed crystals. Excitons bound to Dc vacancies are observed in the pure CdTe crystal but not in the mixed crystal. Weaker and broader features appearing at energies below the exciton emission range were associated with transitions involving free-to-bound and bound-to-bound …

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Annealing Behavior Of The Photoluminescence Lines In Cdte And Znx Cd1-X Te Single Crystals, David D. Allred, A. Reyes-Mena, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred Jan 1990

Annealing Behavior Of The Photoluminescence Lines In Cdte And Znx Cd1-X Te Single Crystals, David D. Allred, A. Reyes-Mena, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The main lines in the photoluminescence spectra of Zn1Cd1-xTe single crystals grown by a modified Bridgman method in the compositional range of 0≤X≤0.25 have been identified. All crystals show only near-band-edge emission. To assist in the identification, various samples with different compositions were annealed under a Cd atmosphere. In the pure crystals, the prominent (A°, X) bound exciton line, as well as the doublet at longer wavelengths, disappear after the annealing. In contrast, the treatments do not change significantly the PL spectra of the mixed crystals.

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Deposition Of Zinc Selenide By Atomic Layer Epitaxy For Multilayer X-Ray Optics, J.K. Shurtleff, David D. Allred, R. T. Perkins, J. M. Thorne Jan 1990

Deposition Of Zinc Selenide By Atomic Layer Epitaxy For Multilayer X-Ray Optics, J.K. Shurtleff, David D. Allred, R. T. Perkins, J. M. Thorne

Faculty Publications

Thin film deposition techniques currently being used to produce multilayer x-ray optics (MXOs) have difficulty producing smooth, uniform multilayers with d-spacings less than about twelve angstroms. We are investigating atomic layer epitaxy (ALE) as an alternative to these techniques. ALE is a chemical vapor deposition technique which deposits an atomic layer of material during each cycle of the deposition process. The thickness of a film deposited by ALE depends only on the number of cycles. Multilayers deposited by ALE should be smooth and uniform with precise d-spacings which makes ALE an excellent technique for producing multilayer x-ray optics. We have …

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Advanced Infrared Optically Black Baffle Materials, David D. Allred, Ronald D. Seals, C. M. Egert Jan 1990

Advanced Infrared Optically Black Baffle Materials, David D. Allred, Ronald D. Seals, C. M. Egert

Faculty Publications

Infrared optically black baffle surfaces are an essential component of many advanced optical systems. All internal surfaces in advanced infrared optical sensors that require stray light management to achieve resolution are of primary concern in baffle design. Current industrial materials need improvements to meet advanced optical sensor systems requirements for optical, survivability, and endurability. Baffles are required to survive and operate in potentially severe environments. Robust diffuse-absorptive black surfaces, which are (1) thermally and mechanically stable to threats of x-ray, launch, and in-flight maneuver conditions, with specific densities to allow an acceptable weight load, (2) handleable during assembly, (3) cleanable, …

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Diffuse Absorbing Beryllium Coatings Produced By Magnetron Sputtering, David D. Allred, C. M. Egert Jan 1990

Diffuse Absorbing Beryllium Coatings Produced By Magnetron Sputtering, David D. Allred, C. M. Egert

Faculty Publications

Beryllium coatings with varying thicknesses and columnar grain sizes were deposited by low temperature magnetron sputtering and wet chemically etched to enhance diffuse absorption of light. After etching these coatings exhibited a matte black surface finish and low specular reflectance (below 2%) in the IR up to a critical wavelength dependent upon the original grain size of the coating. Extremely thick coatings (350 µm) with original grain sizes of 10 to 12 µm were produced which exhibited specular reflectances below 0.5% up to 50 µm wavelength and a Lambertian BRDF at 10.6 µm averaging 4.3x10-3 ster-1. Scanning electron micrographs are …

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Characterization Of Metal/Carbon Multilayers By Raman Spectroscopy, David D. Allred, Qi Wang, Jesus González-Hernández Jan 1990

Characterization Of Metal/Carbon Multilayers By Raman Spectroscopy, David D. Allred, Qi Wang, Jesus González-Hernández

Faculty Publications

Laser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the …

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Photoconductive Characterization Of Znxcd1-Xte (0≤X≤0.25) Single Crystal Alloys, David D. Allred, Elías López-Cruz, Jesus González-Hernández, Worth P. Allred Jan 1990

Photoconductive Characterization Of Znxcd1-Xte (0≤X≤0.25) Single Crystal Alloys, David D. Allred, Elías López-Cruz, Jesus González-Hernández, Worth P. Allred

Faculty Publications

Large grain polycrystalline and single crystals of ZnxCd1-xTe grown by a modified Bridgman method were studied using the photoluminescence and photoconductivity techniques. The temperature dependence of the band gap, as determined by photoluminescence, follows the Varshni equation for measuring temperature in the range of 15-290 K. One of the fitted parameters, the Debye temperature, monotonically decreases with the increase of the atomic zinc concentration. A close correlation between the photoluminescence and photoconductivity measurements is also found. Samples in which the photoluminescence spectra exhibit emission bands associated to cadmium vacancies and other structural defects, show a photoresponse curve which includes, in …

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Design Of High Performance Soft X-Ray Windows, Raymond T. Perkins, David D. Allred, Larry V. Knight, James M. Thorne Jan 1990

Design Of High Performance Soft X-Ray Windows, Raymond T. Perkins, David D. Allred, Larry V. Knight, James M. Thorne

Faculty Publications

X-ray windows are used in sources and detectors to separate the neighborhood of the x-ray generation or detection from the use environment. While each use has its own requirements, there are some principles that should be used in designing an optimal x-ray window. Because x-rays are absorbed to some extent by all materials, minimizing absorption is one criterion in preparing windows. Also, for most uses there is a pressure difference across the window so that ensuring pinhole-free structure and sufficient mechanical strength to support the differential is another criterion for window design. Traditionally, absorption is minimized by fabricating the window …

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