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Brigham Young University

1999

Articles 1 - 22 of 22

Full-Text Articles in Physical Sciences and Mathematics

Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston Dec 1999

Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston

Faculty Publications

We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2×10^9 cm^-3, and the temperatures of electrons and ions are as low as 100 mK and 10 uK, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.

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Dual Function Euv Multilayer Mirrors For The Image Mission, David D. Allred, R. Steven Turley, Matthew B. Squires Nov 1999

Dual Function Euv Multilayer Mirrors For The Image Mission, David D. Allred, R. Steven Turley, Matthew B. Squires

Faculty Publications

We have developed a new family of EUV multilayer mirror coatings using uranium. Using this approach we have coated a set of six mirrors for the EUV Imager, a component of the IMAGE mission. This mission is a Medium Explorer (MIDEX) program, which is scheduled for launch early in 2000. The EUV Imager will study the distribution of He+ in the Earth's plasmasphere by detecting its resonantly scattered emission at 30.4 nm (41 eV) and will produce images of the structure and dynamics of the cold plasma on a global scale. There is, however, a bright at 58.4 nm (21 …

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Selective Excitation And Thermal Quenching Of The Yellow Luminescence Of Gan, John S. Colton, P. Y. Yu, K. L. Teo, E. R. Weber, P. Perlin, I. Grzegory, K. Uchida Nov 1999

Selective Excitation And Thermal Quenching Of The Yellow Luminescence Of Gan, John S. Colton, P. Y. Yu, K. L. Teo, E. R. Weber, P. Perlin, I. Grzegory, K. Uchida

Faculty Publications

We report the observation of narrower structures in the yellow luminescence of bulk and thin-film n-type GaN, using the technique of selective excitation. These fine structures exhibit thermal quenching associated with an activated behavior. We attribute these fine structures to phonons and electronic excitations of a shallow donor-deep acceptor complex, and determine its activation energy for delocalization. Our results suggest that in addition to distant donor-acceptor pairs, the yellow luminescence can also involve emission complexes of shallow donors and deep acceptors.

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Phonon And Elastic Instabilities In Moc And Mon, Gus L. W. Hart, Barry M. Klein Oct 1999

Phonon And Elastic Instabilities In Moc And Mon, Gus L. W. Hart, Barry M. Klein

Faculty Publications

We present several results related to the instability of MoC and MoN in the B1 (sodium chloride) structure. These compounds were proposed as potential superconductors with moderately high transition temperatures. We show that the elastic instability in B1-structure MoN, demonstrated several years ago, persists at elevated pressures, thus offering little hope of stabilizing this material without chemical doping. For MoC, another material for which stoichiometric fabrication in the B1 structure has not proven possible, we find that all of the cubic elastic constants are positive, indicating elastic stability. Instead, we find X-point phonon instabilities in MoC (and in MoN as …

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Mathematical Modelling Of Extracellular Matrix Dynamics Using Discrete Cells: Fiber Orientation And Tissue Regeneration, J. C. Dallon, J. A. Sherratt, P. K. Maini Aug 1999

Mathematical Modelling Of Extracellular Matrix Dynamics Using Discrete Cells: Fiber Orientation And Tissue Regeneration, J. C. Dallon, J. A. Sherratt, P. K. Maini

Faculty Publications

Matrix orientation plays a crucial role in determining the severity of scar tissue after dermal wounding. We present a model framework which allows us to examine the interaction of many of the factors involved in orientation and alignment. Within this framework, cells are considered as discrete objects, while the matrix is modeled as a continuum. Using numerical simulations, we investigate the effect on alignment of changing cell properties and of varying cell interactions with collagen and fibrin.

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The Little Neuron That Could, Timothy L. Andersen, Tony R. Martinez Jul 1999

The Little Neuron That Could, Timothy L. Andersen, Tony R. Martinez

Faculty Publications

SLPs (single layer perceptrons) oflen exhibit reasonable generalization performance on many problems of interest. However, due to the well known limitations of SLPs very little effort has been made to improve their performance. This paper proposes a method for improving the performance of SLPs called "wagging" (weight averaging). This method involves training several different SLPs on the same training data, and then averaging their weights to obtain a single SLP. The performance of the wagged SLP is compared with other more complex learning algorithms (bp, c4.5, ibl, MML, etc) on 15 data sets from real world problem domains. Surprisingly, the …

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The Robustness Of Relaxation Rates In Constraint Satisfaction Networks, Tony R. Martinez, Dan A. Ventura, D. Randall Wilson, Brian Moncur Jul 1999

The Robustness Of Relaxation Rates In Constraint Satisfaction Networks, Tony R. Martinez, Dan A. Ventura, D. Randall Wilson, Brian Moncur

Faculty Publications

Constraint satisfaction networks contain nodes that receive weighted evidence from external sources and/or other nodes. A relaxation process allows the activation of nodes to affect neighboring nodes, which in turn can affect their neighbors, allowing information to travel through a network. When doing discrete updates (as in a software implementation of a relaxation network), a goal net or goal activation can be computed in response to the net input into a node, and a relaxation rate can then be used to determine how fast the node moves from its current value to its goal value. An open question was whether …

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Combining Cross-Validation And Confidence To Measure Fitness, Tony R. Martinez, D. Randall Wilson Jul 1999

Combining Cross-Validation And Confidence To Measure Fitness, Tony R. Martinez, D. Randall Wilson

Faculty Publications

Neural network and machine learning algorithms often have parameters that must be tuned for good performance on a particular task. Leave-one-out cross-validation (LCV) accuracy is often used to measure the fitness of a set of parameter values. However, small changes in parameters often have no effect on LCV accuracy. Many learning algorithms can measure the confidence of a classification decision, but often confidence alone is an inappropriate measure of fitness. This paper proposes a combined measure of Cross- Validation and Confidence (CVC) for obtaining a continuous measure of fitness for sets of parameters in learning algorithms. This paper also proposes …

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Extending The Power And Capacity Of Constraint Satisfaction Networks, Tony R. Martinez, Xinchuan Zeng Jul 1999

Extending The Power And Capacity Of Constraint Satisfaction Networks, Tony R. Martinez, Xinchuan Zeng

Faculty Publications

This work focuses on improving the Hopfield network for solving optimization problems. Although much work has been done in this area, the performance of the Hopfield network is still not satisfactory in terms of valid convergence and quality of solutions. We address this issue in this work by combing a new activation function (EBA) and a new relaxation procedure (CR) in order to improve the performance of the Hopfield network. Each of EBA and CR has been individually demonstrated capable of substantially improving the performance. The combined approach has been evaluated through 20,000 simulations based on 200 randomly generated city …

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Cross Validation And Mlp Architecture Selection, Timothy L. Andersen, Tony R. Martinez Jul 1999

Cross Validation And Mlp Architecture Selection, Timothy L. Andersen, Tony R. Martinez

Faculty Publications

The performance of cross validation (CV) based MLP architecture selection is examined using 14 real world problem domains. When testing many different network architectures the results show that CV is only slightly more likely than random to select the optimal network architecture, and that the strategy of using the simplest available network architecture performs better than CV in this case. Experimental evidence suggests several reasons for the poor performance of CV. In addition, three general strategies which lead to significant increase in the performance of CV are proposed. While this paper focuses on using CV to select the optimal MLP …

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A Neural Model Of Centered Tri-Gram Speech Recognition, Tony R. Martinez, Dan A. Ventura, D. Randall Wilson, Brian Moncur Jul 1999

A Neural Model Of Centered Tri-Gram Speech Recognition, Tony R. Martinez, Dan A. Ventura, D. Randall Wilson, Brian Moncur

Faculty Publications

A relaxation network model that includes higher order weight connections is introduced. To demonstrate its utility, the model is applied to the speech recognition domain. Traditional speech recognition systems typically consider only that context preceding the word to be recognized. However, intuition suggests that considering both preceding context as well as following context should improve recognition accuracy. The work described here tests this hypothesis by applying the higher order relaxation network to consider both precedes and follows context in speech recognition. The results demonstrate both the general utility of the higher order relaxation network as well as its improvement over …

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A Comparison Of Eclectic Learning And Stagger, J. Cory Barker, Jargalsaihan Batsaihan Jul 1999

A Comparison Of Eclectic Learning And Stagger, J. Cory Barker, Jargalsaihan Batsaihan

Faculty Publications

This project compares two machine-learning methods, Stagger and Eclectic on their classification correctness. Both systems were tested with real-world data sets previously used and tested in other machine learning and statistical literature. The Eclectic System performed better than Stagger on every data set.

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Toboggan-Based Intelligent Scissors With A Four-Parameter Edge Model, William A. Barrett, Eric N. Mortensen Jun 1999

Toboggan-Based Intelligent Scissors With A Four-Parameter Edge Model, William A. Barrett, Eric N. Mortensen

Faculty Publications

Intelligent Scissors is an interactive image segmentation tool that allows a user to select piece-wise globally optimal contour segments that correspond to a desired object boundary. We present a new and faster method of computing the optimal path by over-segmenting the image using tobogganing and then imposing a weighted planar graph on top of the resulting region boundaries. The resulting region-based graph is many times smaller than the previous pixel-based graph, thus providing faster graph searches and immediate user interaction. Further, tobogganing provides an new systematic and predictable framework for computing edge model parameters, allowing subpixel localization as well as …

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Multiscale Image Registration Using Scale Trace Correlation, Bruce B. Hansen, Bryan S. Morse Jun 1999

Multiscale Image Registration Using Scale Trace Correlation, Bruce B. Hansen, Bryan S. Morse

Faculty Publications

This paper presents a method for registering images at different magnifications (scales) by treating the problem not only as one of scaling the image coordinates but also as one inherently involving multiresolution information. While some existing methods for multiresolution registration do consider the way the resolution (scale) affects the image, they often consider the image one scale at a time, using geometric properties within that scale. Others use multiscale information, usually to produce more robust results, but only to register same-magnification images (e.g., stereo). A scale trace is the set of values that a single pixel takes on as magnification …

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Model Predictive Satisficing Fuzzy Logic Control, Richard L. Frost, Michael A. Goodrich, Wynn C. Stirling Jun 1999

Model Predictive Satisficing Fuzzy Logic Control, Richard L. Frost, Michael A. Goodrich, Wynn C. Stirling

Faculty Publications

Model-predictive control, which is an alternative to conventional optimal control, provides controller solutions to many constrained and nonlinear control problems. However, even when a good model is available, it may be necessary for an expert to specify the relationship between local model predictions and global system performance. We present a satisficing fuzzy logic controller that is based on a receding control horizon, but which employs a fuzzy description of system consequences via model predictions. This controller considers the gains and losses associated with each control action, is compatible with robust design objectives, and permits flexible defuzzifier design. We demonstrate the …

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Metallicity Calibration Of A Ddo Cn Index And Other Low-Resolution Indices For G And K Stars, B. J. Taylor May 1999

Metallicity Calibration Of A Ddo Cn Index And Other Low-Resolution Indices For G And K Stars, B. J. Taylor

Faculty Publications

Metallicity calibrations of low-resolution parameters are potentially useful for (at least) two problems: the properties of moving groups, and the supermetallicity problem in K giants. In this paper, metallicity calibrations are derived for six sets of parameters. One of these parameters is the DDO CN index deltaCN. This parameter and three others are calibrated for use with evolved G and K stars. Two additional sets of low-resolution parameters are calibrated for use with G and K dwarfs. The calibrations are derived by comparing the input data with two catalogs of homogenized high-dispersion results from diverse authors (see Taylor 1995, 1999a). …

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The Mean Spherical Approximation For A Dipolar Yukawa Fluid, Douglas Henderson, Dezso Boda, Istvan Szalai, Kwong-Yu Chan May 1999

The Mean Spherical Approximation For A Dipolar Yukawa Fluid, Douglas Henderson, Dezso Boda, Istvan Szalai, Kwong-Yu Chan

Faculty Publications

The dipolar hard sphere fluid (DHSF) is a useful model of a polar fluid. However, the DHSF lacks a vapor–liquid transition due to the formation of chain-like structures. Such chains are not characteristic of real polar fluids. A more realistic model of a polar fluid is obtained by adding a Lennard–Jones potential to the intermolecular potential. Very similar results are obtained by adding a Yukawa potential, instead of the Lennard–Jones potential. We call this fluid the dipolar Yukawa fluid (DYF). We show that an analytical solution of the mean spherical approximation (MSA) can be obtained for the DYF. Thus, the …

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Modes And Quasi-Modes For M = 1,2 In A Gyrokinetic Model For A Non-Neutral Plasma, S. Neil Rasband, Ross L. Spencer May 1999

Modes And Quasi-Modes For M = 1,2 In A Gyrokinetic Model For A Non-Neutral Plasma, S. Neil Rasband, Ross L. Spencer

Faculty Publications

Modes and quasi-modes for m = 1,2 are studied in a gyro-kinetic model for a pure-electron plasma. Only z-independent perturbations are considered. Numerical methods are used to solve the relevant differential equations for smooth, analytic density profiles. Different temperatures and representative profiles are considered and comparison is made with the familiar cold fluid model from which the results depart but little, except at higher temperatures. A continuum component to the spectrum, present in the cold-fluid model, remains in the gyro-kinetic model to the order considered.

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Monte Carlo Study Of The Capacitance Of The Double Layer In A Model Molten Salt, Douglas Henderson, Dezso Boda, Kwong-Yu Chan Mar 1999

Monte Carlo Study Of The Capacitance Of The Double Layer In A Model Molten Salt, Douglas Henderson, Dezso Boda, Kwong-Yu Chan

Faculty Publications

Monte Carlo simulations are reported for charged hard spheres at high density near a charged wall. This system is a simple model for a molten salt double layer. Unfortunately, the reduced temperatures that correspond to experiment are very small. This results in a large Boltzmann factor. As a result, we are unable to obtain meaningful results for such low values and report results only for moderately low values of the reduced temperature. Even so, our results should be a useful benchmark. Further, we are able to give a qualitative answer to an interesting question. We find that at low temperatures …

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Some Aspects Of The Adsorption Of A Lennard-Jones Gas On A Rough Surface, Douglas Henderson, Pawel Bryk, Stefan Sokolowski Jan 1999

Some Aspects Of The Adsorption Of A Lennard-Jones Gas On A Rough Surface, Douglas Henderson, Pawel Bryk, Stefan Sokolowski

Faculty Publications

We study the adsorption, including wetting, of a Lennard-Jones gas on a rough surface consisting of rough layer on a smooth substrate with which the gas interacts via a 9-3 potential. The rough layer is two molecular diameters thick and consists of a disordered quenched matrix of hard spheres. As well as interacting with the other matrix spheres by the hard-sphere potential, the matrix molecules interact with the gas molecules by the hard-sphere potential. Hence, on average, the degree to which the gas molecules can approach the substrate depends only on the density of the matrix layer. The density of …

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Performance Surface Prediction For Wan-Based Clusters, Mark J. Clement, J. Kelly Flanagan, Glenn M. Judd, Bryan S. Morse, Joy L. Peterson Jan 1999

Performance Surface Prediction For Wan-Based Clusters, Mark J. Clement, J. Kelly Flanagan, Glenn M. Judd, Bryan S. Morse, Joy L. Peterson

Faculty Publications

The last five years have been a period of exponential growth in the number of machines connected to the Internet and the speed at which these machines communicate. The infrastructure is now in place to consider a nationwide cluster of workstations as a viable parallel processing platform. In order to achieve acceptable performance on this kind of a machine, performance prediction tools must provide information on where to place computational objects. Incorrect object placement can result in poor performance and congestion in the network. This research develops a new paradigm for predicting performance in the Wide Area Network (WAN) based …

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Assessment Of The Availability And Exploitation Of Hydric Resources In The Choquenaira Community, Luis Lizardo Iturry Urquizo Jan 1999

Assessment Of The Availability And Exploitation Of Hydric Resources In The Choquenaira Community, Luis Lizardo Iturry Urquizo

Theses and Dissertations

The precipitation data of the El Alto, Tambillo and Comanche stations are homogenous and consistent. The meteorological data from Irpa Chico, Collana and Viacha are consistent, but heterogeneous. The monthly precipitation in Viacha in December, January, March and April are better examples of a normal distribution in comparison to the months of October, November and February. The average annual precipitation in Viacha, in a thirty-four year time period, is 559 mm. Some 76% of this precipitation occurs in November to March. The minimum precipitation in Viacha, with an 80% probability of absence for the vegetative period, from October to April …

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