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Articles 3061 - 3090 of 3436

Full-Text Articles in Physical Sciences and Mathematics

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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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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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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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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A Work Minimization Approach To Image Morphing, Peisheng Gao, Thomas W. Sederberg Dec 1998

A Work Minimization Approach To Image Morphing, Peisheng Gao, Thomas W. Sederberg

Faculty Publications

An algorithm is presented for morphing two images, often with little or no user interaction. For two similar images (such as different faces against a neutral background) the algorithm generally can create a pleasing morph completely automatically. The algorithm seeks the minimum work to deform one image into the other, where work is a function of the amount of warping and recoloration. A hierarchical method for finding a minimal work solution is invoked. Anchor point constraints are satisfied by imposing penalties on deformations that disobey these constraints. Good results can be obtained in less than ten seconds for 256 x …

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Monte Carlo Simulation Of An Ion-Dipole Mixture As A Model Of An Electrical Double Layer, Douglas Henderson, Dezso Boda, Kwong-Yu Chan Nov 1998

Monte Carlo Simulation Of An Ion-Dipole Mixture As A Model Of An Electrical Double Layer, Douglas Henderson, Dezso Boda, Kwong-Yu Chan

Faculty Publications

Canonical Monte Carlo simulations were performed for a nonprimitive model of an electrical double layer. The ions and the solvent molecules are modeled as charged and dipolar hard spheres, respectively, while the electrode as a hard, impenetrable wall carrying uniform surface charge. We found that the ion-dipole model gives a reasonable description of the double layer for partially charged ions with small to moderate dipole moments, or equivalently for an "effective" dielectric constant. Density, polarization and mean electrostatic potential profiles are reported. Strong layering structure, and at higher charges, charge inversion in the second layer were found. With appropriate choices …

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Interior Blowup In A Convection-Diffusion Equation, Christopher P. Grant Nov 1998

Interior Blowup In A Convection-Diffusion Equation, Christopher P. Grant

Faculty Publications

This paper addresses the qualitative behavior of a nonlinear convection-diffusion equation on a smooth bounded domain in Rn, in which the strength of the convection grows superlinearly as the density increases. While the initial-boundary value problem is guaranteed to have a local-in-time solution for smooth initial data, it is possible for this solution to be extinguished in nite time. We demonstrate that the way this may occur is through nite-time "blow up," i.e., the unboundedness of the solution in arbitrarily small neighborhoods of one or more points in the closure of the spatial domain. In special circumstances, such as the …

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A Theory Of Satisficing Decisions And Control, Richard L. Frost, Michael A. Goodrich, Wynn C. Stirling Nov 1998

A Theory Of Satisficing Decisions And Control, Richard L. Frost, Michael A. Goodrich, Wynn C. Stirling

Faculty Publications

The existence of an optimal control policy and the techniques for finding it are grounded fundamentally in a global perspective. These techniques can be of limited value when the global behavior of the system is difficult to characterize, as it may be when the system is nonlinear, when the input is constrained, or when only partial information is available regarding system dynamics or the environment. Satisficing control theory is an alternative approach that is compatible with the limited rationality associated with such systems. This theory is extended by the introduction of the notion of strong satisficing to provide a systematic …

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A Continuum Analysis Of The Chemotactic Signal Seen By Dictyostelium Discoideum, J. C. Dallon, H. G. Othmer Oct 1998

A Continuum Analysis Of The Chemotactic Signal Seen By Dictyostelium Discoideum, J. C. Dallon, H. G. Othmer

Faculty Publications

We develop a mathematical model of cell-to-cell-signalling in Dictyostelium discoideum that predicts the cAMP signal seen by individual cells in early aggregation. The model employs two cells on a plane and is designed to predict the space-time characteristics of both the extracellular cAMP signal seen by one cell when a nearby cell relays, and the intracellular cAMP response produced by the stimulus in the receiving cell. The effect of membrane bound phosphodiesterase is studied and it is shown that cells can orient effectively even in its absence. Our results give a detailed picture of how the spatio-temporal characteristics of the …

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Analysis Of The Interpolation Error Between Multiresolution Images, Bryan S. Morse Oct 1998

Analysis Of The Interpolation Error Between Multiresolution Images, Bryan S. Morse

Faculty Publications

Many rendering or image-analysis systems require calculation of versions of an image at lesser resolutions than the original. Because the filtering required to perform such calculations accurately cannot typically be done in real time, many systems use interpolation between images at precalculated resolutions. This discrete sampling of the scale component of multiresolution image spaces is analogous to spatial sampling in discrete images. This paper quantifies and bounds the error that can be introduced during such interpolation as a function of the scale-space sampling rate used. A method is presented that uses the diffusion equation to relate spatial derivatives to scale …

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Isophote-Based Interpolation, Bryan S. Morse, Duane Schwartzwald Oct 1998

Isophote-Based Interpolation, Bryan S. Morse, Duane Schwartzwald

Faculty Publications

Standard methods for image interpolation are based on smoothly fitting the image intensity surface. Recent edge-directed interpolation methods add limited geometric information (edge maps) to build more accurate and visually appealing interpolations at key contours in the image. This paper presents a method for geometry-based interpolation that smoothly fits the isophote (intensity level curve) contours at all points in the image rather than just at selected contours. By using level set methods for curve evolution, no explicit extraction or representation of these contours is required (unlike earlier edge-directed methods). The method uses existing interpolation techniques as an initial approximation and …

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A Zero Point And Accidental Errors For Published Values Of [Fe/H] For Cool Giants, B. J. Taylor Sep 1998

A Zero Point And Accidental Errors For Published Values Of [Fe/H] For Cool Giants, B. J. Taylor

Faculty Publications

This paper is one of a series based on published values of [Fe/H] for late-type evolved stars. Only values of [Fe/H] from high-dispersion spectroscopy or related techniques are used. The narrative in this paper begins at a point where mean values of [Fe/H] have been derived for xiVir, alphaBoo, betaGem, and the Hyades giants. By using these stars as standard stars when necessary, a zero-point data base is assembled. This data base is then expanded into its final version by correcting and adding additional data in a step-by-step process. As that process proceeds, data comparisons are used to establish rms …

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An Analysis Of Temperature Dependent Photoluminescence Line Shapes In Ingan, John S. Colton, K. L. Teo, P. Y. Yu, E. R. Weber, M. F. Li, W. Lui, K. Uchida, H. Tokunaga, N. Akutsu, K. Matsumoto Sep 1998

An Analysis Of Temperature Dependent Photoluminescence Line Shapes In Ingan, John S. Colton, K. L. Teo, P. Y. Yu, E. R. Weber, M. F. Li, W. Lui, K. Uchida, H. Tokunaga, N. Akutsu, K. Matsumoto

Faculty Publications

Photoluminescence (PL) line shapes in InGaN multiple quantum well structures have been studied experimentally and theoretically between 10 and 300 K. The higher temperature PL spectra can be fitted qualitatively with a thermalized carrier distribution and a broadened joint-density-of-states. The low temperature PL line shapes suggest that carriers are not thermalized, as a result of localization by band-gap fluctuations. We deduce a localization energy of ~7 meV as compared with an activation energy of ~63 meV from thermal quenching of the PL intensity. We thus conclude that this activation energy and the band-gap fluctuation most likely have different origins.

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Catalogs Of Temperatures And [Fe/H] Averages For Evolved G And K Stars, B. J. Taylor Sep 1998

Catalogs Of Temperatures And [Fe/H] Averages For Evolved G And K Stars, B. J. Taylor

Faculty Publications

A catalog of mean values of [Fe/H] for evolved G and K stars is described. The zero point for the catalog entries has been established by using differential analyses. Literature sources for those entries are included in the catalog. The mean values are given with rms errors and numbers of degrees of freedom, and a simple example of the use of these statistical data is given. For a number of the stars with entries in the catalog, temperatures have been determined. A separate catalog containing those data is briefly described.

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Solute-Solvent Pair Distribution Functions In Highly Asymmetric Additive Hard Sphere Mixtures, Douglas Henderson, Kwong-Yu Chan Jun 1998

Solute-Solvent Pair Distribution Functions In Highly Asymmetric Additive Hard Sphere Mixtures, Douglas Henderson, Kwong-Yu Chan

Faculty Publications

Contact values for the solute-solvent pair distribution function in an additive hard sphere mixture, as computed from the Henderson-Chan (HC) formulas, are compared with the recent Monte Carlo (MC) data and formula of Matyushov and Ladanyi (ML) [J. Chem. Phys. 107, 5815 (1997)]. The agreement is found to be excellent. The negative finding of ML is due to a misprint in one of the HC publications. We find the HC formula to be superior to the ML formula when compared to our MC data [Mol. Phys. 91, 1137 (1997)] for the case where the ratio of diameters is large and …

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Constructing High Order Perceptrons With Genetic Algorithms, Timothy L. Andersen, Tony R. Martinez May 1998

Constructing High Order Perceptrons With Genetic Algorithms, Timothy L. Andersen, Tony R. Martinez

Faculty Publications

Constructive induction, which is defined to be the process of constructing new and useful features from existing ones, has been extensively studied in the literature. Since the number of possible high order features for any given learning problem is exponential in the number of input attributes (where the order of a feature is defined to be the number of attributes of which it is composed), the main problem faced by constructive induction is in selecting which features to use out of this exponentially large set of potential features. For any feature set chosen the desirable characteristics are minimality and generalization …

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Optimal Control Using A Neural/Evolutionary Hybrid System, Tony R. Martinez, Dan A. Ventura May 1998

Optimal Control Using A Neural/Evolutionary Hybrid System, Tony R. Martinez, Dan A. Ventura

Faculty Publications

One of the biggest hurdles to developing neurocontrollers is the difficulty in establishing good training data for the neural network. We propose a hybrid approach to the development of neurocontrollers that employs both evolutionary computation (EC) and neural networks (NN). EC is used to discover appropriate control actions for specific plant states. The survivors of the evolutionary process are used to construct a training set for the NN. The NN leams the training set, is able to generalize to new plant states, and is then used for neurocontrol. Thus the EC/NN approach combines the broad, parallel search of EC with …

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Quantum Associative Memory With Exponential Capacity, Tony R. Martinez, Dan A. Ventura May 1998

Quantum Associative Memory With Exponential Capacity, Tony R. Martinez, Dan A. Ventura

Faculty Publications

Quantum computation uses microscopic quantum level effects to perrform computational tasks and has produced results that in some cases are exponentially faster than their classical counterparts by taking advantage of quantum parallelism. The unique characteristics of quantum theory may also be used to create a quantum associative memory with a capacity exponential in the number of neurons. This paper covers necessary high-level quantum mechanical ideas and introduces a simple quantum associative memory. Further, it provides discussion, empirical results and directions for future work.

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Breakpoint Skeletal Representation And Compression Of Document Images, William A. Barrett, Bryan S. Morse, Eric N. Mortensen Mar 1998

Breakpoint Skeletal Representation And Compression Of Document Images, William A. Barrett, Bryan S. Morse, Eric N. Mortensen

Faculty Publications

We present a new method for representation and (lossy) compression of bitonal document images. The technique extracts a skeletal medial axis from each object using a true Euclidean distance map of the image and then finds piecewise linear breakpoints in the skeleton to create a breakpoint skeletal representation, bps, (Fig. 1). The bps is encoded for each object as a set of triples {, <Δx2,Δy2,Δr2>, . . . <Δxn,Δyn,Δrn>} where contains the coordinate and distance (radius, r1) of the initial breakpoint from the closest point on the perimeter of the object and <Δxi,Δyi,Δri> represents the difference in location and radius between …

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Recognizing Constant Curvature Discrete Groups In Dimension 3, J. W. Cannon, E. L. Swenson Feb 1998

Recognizing Constant Curvature Discrete Groups In Dimension 3, J. W. Cannon, E. L. Swenson

Faculty Publications

We characterize those discrete groups Gwhich can act properly discontinuously, isometrically, and cocompactly on hyperbolic 3-space H^3 in terms of the combinatorics of the action of G on its space at infinity. The major ingredients in the proof are the properties of groups that are negatively curved (in the large) (that is, Gromov hyperbolic), the combinatorial Riemann mapping theorem, and the Sullivan-Tukia theorem on groups which act uniformly quasiconformally on the 2-sphere.

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Some Harmonic N-Slit Mappings, Michael Dorff Feb 1998

Some Harmonic N-Slit Mappings, Michael Dorff

Faculty Publications

The class SH consists of univalent, harmonic, and sense-preserving functions f in the unit disk, ∆, such that f = h+g where h(z) = (see PDF), g(z) = (see PDF) . SOH will denote the subclass with b1 = 0. We present a collection of n-slit mappings (n ≥ 2) and prove that the 2-slit mappings are in SH while for n ≥ 3 the mappings are in SOH. Finally we show that these mappings establish the sharpness of a previous theorem by Clunie and Sheil-Small while disproving a conjecture about the inner mapping radius.

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Thermal Equilibrium Of Warm Clouds Of Charge With Small Aspect Ratio, Deborah L. Paulson, Ross L. Spencer Feb 1998

Thermal Equilibrium Of Warm Clouds Of Charge With Small Aspect Ratio, Deborah L. Paulson, Ross L. Spencer

Faculty Publications

Global thermal equilibrium computations are presented for non-neutral plasmas whose radial size is much larger than their axial thickness. Axial and radial density profiles are computed for both ideal and nonideal Penning trap fields. Simple results are obtained in the limits of both low and high central density. Comparison is made to the grid calculations of Mason et al. [Phys. Plasmas 3 (5), 1502 (1996)].

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Measurement Of The He Ground State Lamb Shift Via The Two-Photon 1 1S-2 1S Transition, Scott D. Bergeson, A. Balakrishnan, K. G. H. Baldwin, T. B. Lucatorto, J. P. Marangos, T. J. Mcilrath, T. T. O'Brian, S. L. Rolston, C. J. Sansonetti, Jesse Wen, N. Westbrook, C. H. Cheng, E. E. Eyler Jan 1998

Measurement Of The He Ground State Lamb Shift Via The Two-Photon 1 1S-2 1S Transition, Scott D. Bergeson, A. Balakrishnan, K. G. H. Baldwin, T. B. Lucatorto, J. P. Marangos, T. J. Mcilrath, T. T. O'Brian, S. L. Rolston, C. J. Sansonetti, Jesse Wen, N. Westbrook, C. H. Cheng, E. E. Eyler

Faculty Publications

We have extended two-photon Doppler-free spectroscopy to the vacuum ultraviolet spectral region, to accurately measure the He 11S-21S transition at 120 nm. Our result is 4984872315(48) MHz. This yields a ground state Lamb shift of 41104(48) MHz, in fair agreement with theory and other experiments. This approach has the potential for significantly better accuracy once improvements in the laser and the wavelength metrology are implemented.

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Time-Resolved Studies Of Ultracold Ionizing Collisions, Scott D. Bergeson, C. Orzel, S. Kulin, S. L. Rolston Jan 1998

Time-Resolved Studies Of Ultracold Ionizing Collisions, Scott D. Bergeson, C. Orzel, S. Kulin, S. L. Rolston

Faculty Publications

Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of Xe2^+ molecular ions through associative ionization. We estimate the rate of molecule formation in excited-state collisions, and directly measure the role of both flux enhancement and excited state survival in the collisional enhancement process. Conceptually simple theoretical models are used to predict the dynamics of the collisional shielding.

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A Mathematical Model For Fibroblast And Collagen Orientation, J. C. Dallon, J. A. Sherratt Jan 1998

A Mathematical Model For Fibroblast And Collagen Orientation, J. C. Dallon, J. A. Sherratt

Faculty Publications

Due to the increasing importance of the extracellular matrix in many biological problems, in this paper we develop a model for fibroblast and collagen orientation with the ultimate objective of understanding how fibroblasts form and remodel the extracellular matrix, in particular its collagen component. The model uses integro-differential equations to describe the interaction between the cells and fibers at a point in space with various orientations. The equations are studied both analytically and numerically to discover different types of solutions and their behavior. In particular we examine solutions where all the fibroblasts and collagen have discrete orientations, a localized continuum …

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Bias And The Probability Of Generalization, Tony R. Martinez, D. Randall Wilson Dec 1997

Bias And The Probability Of Generalization, Tony R. Martinez, D. Randall Wilson

Faculty Publications

In order to be useful, a learning algorithm must be able to generalize well when faced with inputs not previously presented to the system. A bias is necessary for any generalization, and as shown by several researchers in recent years, no bias can lead to strictly better generalization than any other when summed over all possible functions or applications. This paper provides examples to illustrate this fact, but also explains how a bias or learning algorithm can be “better” than another in practice when the probability of the occurrence of functions is taken into account. It shows how domain knowledge …

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