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2003

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Articles 331 - 360 of 3876

Full-Text Articles in Physical Sciences and Mathematics

An Inconsistency Sensitive Arrangement Algorithm For Curve Segments, Victor Milenkovic, Elisha Sacks Nov 2003

An Inconsistency Sensitive Arrangement Algorithm For Curve Segments, Victor Milenkovic, Elisha Sacks

Department of Computer Science Technical Reports

No abstract provided.

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Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look Nov 2003

Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look

Physics Faculty Publications

We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (Eel=2   MeV, fluence 6×1017   cm-2) ZnO samples. The Zn vacancies are identified at concentrations of [VZn]≃2×1015   cm-3 in the as-grown material and [VZn]≃2×1016   cm-3 in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.

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Reducing Redundancy In The Hypertree Decomposition Scheme, Peter Harvey, Aditya K. Ghose Nov 2003

Reducing Redundancy In The Hypertree Decomposition Scheme, Peter Harvey, Aditya K. Ghose

Faculty of Informatics - Papers (Archive)

Hypertree decomposition is a powerful technique for transforming near-acyclic CSPs into acyclic CSPs. Acyclic CSPs have efficient, polynomial time solving techniques, and so these conversions are of interest to the constraints community. We present here an improvement on the opt-k-decomp algorithm for finding an optimal hypertree decomposition.

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Mantle Layering Across Central South America, Kelly H. Liu, Stephen S. Gao, Paul G. Silver, Yongkai K. Zhang Nov 2003

Mantle Layering Across Central South America, Kelly H. Liu, Stephen S. Gao, Paul G. Silver, Yongkai K. Zhang

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

Imaging of seismic velocity discontinuities along a 3000 km profile across central South America at 20°S suggests that the depth variations of the 410-km (d410) and 660-km (d660) discontinuities are closely associated with the high-velocity Nazca slab and juxtaposed low-velocity oceanic mantle beneath the slab. The mantle transition zone thickness ranges from 220 km in the oceanic mantle to 270 km in a 600-km-wide area occupied by the deflected Nazca slab. The slab deflection has also been suggested by previous studies of seismic tomography and seismicity. This 50 km difference in the thickness corresponds to a lateral temperature variation of …

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P* Index Of Segregation: Distribution Under Reassignment, Charles F. Bond, F. D. Richard Nov 2003

P* Index Of Segregation: Distribution Under Reassignment, Charles F. Bond, F. D. Richard

Journal of Modern Applied Statistical Methods

Students of intergroup relations have measured segregation with a P* index. In this article, we describe the distribution of this index under a stochastic model. We derive exact, closed-form expressions for the mean, variance, and skewness of P* under random segregation. These yield equivalent expressions for a second segregation index: η2. Our analytic results reveal some of the distributional properties of these indices, inform new standardizations of the indices, and enable small-sample significance testing. Two illustrative examples are presented.

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A Critical Examination Of The Use Of Preliminary Tests In Two-Sample Tests Of Location, Kimberly T. Perry Nov 2003

A Critical Examination Of The Use Of Preliminary Tests In Two-Sample Tests Of Location, Kimberly T. Perry

Journal of Modern Applied Statistical Methods

This paper explores the appropriateness of testing the equality of two means using either a t test, the Welch test, or the Wilcoxon-Mann-Whitney test for two independent samples based on the results of using two classes of preliminary tests (i.e., tests for population variance equality and symmetry in underlying distributions).

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Confidence Intervals For P(X Less Than Y) In The Exponential Case With Common Location Parameter, Ayman Baklizi Nov 2003

Confidence Intervals For P(X Less Than Y) In The Exponential Case With Common Location Parameter, Ayman Baklizi

Journal of Modern Applied Statistical Methods

The problem considered is interval estimation of the stress - strength reliability R = P(Xθ and λ respectively and a common location parameter μ . Several types of asymptotic, approximate and bootstrap intervals are investigated. Performances are investigated using simulation techniques and compared in terms of attainment of the nominal confidence level, symmetry of lower and upper error rates, and expected length. Recommendations concerning their usage are given.

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Approximate Bayesian Confidence Intervals For The Variance Of A Gaussian Distribution, Vincent A. R. Camara Nov 2003

Approximate Bayesian Confidence Intervals For The Variance Of A Gaussian Distribution, Vincent A. R. Camara

Journal of Modern Applied Statistical Methods

The aim of the present study is to obtain and compare confidence intervals for the variance of a Gaussian distribution. Considering respectively the square error and the Higgins-Tsokos loss functions, approximate Bayesian confidence intervals for the variance of a normal population are derived. Using normal data and SAS software, the obtained approximate Bayesian confidence intervals will then be compared to the ones obtained with the well known classical method. The Bayesian approach relies only on the observations. It is shown that the proposed approximate Bayesian approach relies only on the observations. The classical method, that uses the Chi-square statistic, does …

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Random Regression Models Based On The Elliptically Contoured Distribution Assumptions With Applications To Longitudinal Data, Alfred A. Bartolucci, Shimin Zheng, Sejong Bae, Karan P. Singh Nov 2003

Random Regression Models Based On The Elliptically Contoured Distribution Assumptions With Applications To Longitudinal Data, Alfred A. Bartolucci, Shimin Zheng, Sejong Bae, Karan P. Singh

Journal of Modern Applied Statistical Methods

We generalize Lyles et al.’s (2000) random regression models for longitudinal data, accounting for both undetectable values and informative drop-outs in the distribution assumptions. Our models are constructed on the generalized multivariate theory which is based on the Elliptically Contoured Distribution (ECD). The estimation of the fixed parameters in the random regression models are invariant under the normal or the ECD assumptions. For the Human Immunodeficiency Virus Epidemiology Research Study data, ECD models fit the data better than classical normal models according to the Akaike (1974) Information Criterion. We also note that both univariate distributions of the random intercept and …

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Type I Error Rates Of Four Methods For Analyzing Data Collected In A Groups Vs Individuals Design, Stephanie Wehry, James Algina Nov 2003

Type I Error Rates Of Four Methods For Analyzing Data Collected In A Groups Vs Individuals Design, Stephanie Wehry, James Algina

Journal of Modern Applied Statistical Methods

Using previous work on the Behrens-Fisher problem, two approximate degrees of freedom tests, that can be used when one treatment is individually administered and one is administered to groups, were developed. Type I error rates are presented for these tests, an additional approximate degrees of freedom test developed by Myers, Dicecco, and Lorch (1981), and a mixed model test. The results indicate that the test that best controls the Type I error rate depends on the number of groups in the group-administered treatment. The mixed model test should be avoided.

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A Nonparametric Fitted Test For The Behrens-Fisher Problem, Terry Hyslop, Paul J. Lupinacci Nov 2003

A Nonparametric Fitted Test For The Behrens-Fisher Problem, Terry Hyslop, Paul J. Lupinacci

Journal of Modern Applied Statistical Methods

A nonparametric test for the Behrens-Fisher problem that is an extension of a test proposed by Fligner and Policello was developed. Empirical level and power estimates of this test are compared to those of alternative nonparametric and parametric tests through simulations. The results of our test were better than or comparable to all tests considered.

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Example Of The Impact Of Weights And Design Effects On Contingency Tables And Chi-Square Analysis, David A. Walker, Denise Y. Young Nov 2003

Example Of The Impact Of Weights And Design Effects On Contingency Tables And Chi-Square Analysis, David A. Walker, Denise Y. Young

Journal of Modern Applied Statistical Methods

Many national data sets used in educational research are not based on simple random sampling schemes, but instead are constructed using complex sampling designs characterized by multi-stage cluster sampling and over-sampling of some groups. Incorrect results are obtained from statistical analysis if adjustments are not made for the sampling design. This study demonstrates how the use of weights and design effects impact the results of contingency tables and chi-square analysis of data from complex sampling designs.

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Comparison Of Viral Trajectories In Aids Studies By Using Nonparametric Mixed-Effects Models, Chin-Shang Li, Hua Liang, Ying-Hen Hsieh, Shiing-Jer Twu Nov 2003

Comparison Of Viral Trajectories In Aids Studies By Using Nonparametric Mixed-Effects Models, Chin-Shang Li, Hua Liang, Ying-Hen Hsieh, Shiing-Jer Twu

Journal of Modern Applied Statistical Methods

The efficacy of antiretroviral therapies for human immunodeficiency virus (HIV) infection can be assessed by studying the trajectory of the changing viral load with treatment time, but estimation of viral trajectory parameters by using the implicit function form of linear and nonlinear parametric models can be problematic. Using longitudinal viral load data from a clinical study of HIV-infected patients in Taiwan, we described the viral trajectories by applying a nonparametric mixed-effects model. We were then able to compare the efficacies of highly active antiretroviral therapy (HAART) and conventional therapy by using Young and Bowman’s (1995) test.

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Jmasm8: Using Sas To Perform Two-Way Analysis Of Variance Under Variance Heterogeneity, Scott J. Richter, Mark E. Payton Nov 2003

Jmasm8: Using Sas To Perform Two-Way Analysis Of Variance Under Variance Heterogeneity, Scott J. Richter, Mark E. Payton

Journal of Modern Applied Statistical Methods

We present SAS code to implement the method proposed by Brunner et al. (1997) for performing two-way analysis of variance under variance heterogeneity.

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Statistical Pronouncements Ii, Jmasm Editors Nov 2003

Statistical Pronouncements Ii, Jmasm Editors

Journal of Modern Applied Statistical Methods

No abstract provided.

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Water Quality Monitoring Of Moore's Creek Above Lincoln Lake, M. A. Nelson, L. W. Cash, G. K. Trost Nov 2003

Water Quality Monitoring Of Moore's Creek Above Lincoln Lake, M. A. Nelson, L. W. Cash, G. K. Trost

Technical Reports

No abstract provided.

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Water Quality Sampling, Analysis And Annual Load Determinations For Tss, Nitrogen And Phosphorus At The Washington County Road 76 Bridge On Ballard Creek, Marc A. Nelson, Ron Redman, L. Wade Cash, G. Keith Trost Nov 2003

Water Quality Sampling, Analysis And Annual Load Determinations For Tss, Nitrogen And Phosphorus At The Washington County Road 76 Bridge On Ballard Creek, Marc A. Nelson, Ron Redman, L. Wade Cash, G. Keith Trost

Technical Reports

The Illinois River Basin has experienced water quality impairment from non-point source pollution for many years. This fact was well documented in the State of Arkansas' Water Quality Assessment report, the Soil Conservation Service River Basin Study, and several University of Arkansas, Fayetteville studies. Thirty-seven sub-watersheds have been identified by the SCS in the Arkansas portion of the Illinois River basin. In the Arkansas portion of the Basin, the Illinois River, Evansville Creek, Baron Fork, Cincinnati Creek, Muddy Fork, Moores Creek, Clear Creek, Osage Creek and Flint Creek were all classified as not supporting their designated use as primary contact …

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Effect Of External Electric Field On The Bulk And Interfacial Properties Of Weakly Dipolar Fluid In Slab-Shaped And Sphere-Shaped Systems, V.B. Warshavsky, Xiao Cheng Zeng Nov 2003

Effect Of External Electric Field On The Bulk And Interfacial Properties Of Weakly Dipolar Fluid In Slab-Shaped And Sphere-Shaped Systems, V.B. Warshavsky, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

The effect of a uniform electric field on the bulk and interfacial properties of a model dipolar fluid is investigated by using a modified mean-field density functional theory. Particular attention is given to the dependence of the vapor-liquid phase coexistence in a slab-shaped system on the direction of the electric field with respect to the slab surfaces, as well as in the sphere-shaped system on the surrounding dielectric permittivity. For planar vapor-liquid interfaces, the interfacial profiles of the orientation order parameters and components of the dielectric-permittivity tensor are calculated. Analytical expressions for these interfacial profiles and their dependence on the …

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Statistics Of Transmission In One-Dimensional Disordered Systems: Universal Characteristics Of States In The Fluctuation Tails, Lev I. Deych, Mikhail V. Erementchouk, Alexander A. Lisyansky, Alexey Yamilov, Hui Cao Nov 2003

Statistics Of Transmission In One-Dimensional Disordered Systems: Universal Characteristics Of States In The Fluctuation Tails, Lev I. Deych, Mikhail V. Erementchouk, Alexander A. Lisyansky, Alexey Yamilov, Hui Cao

Physics Faculty Research & Creative Works

We numerically study the distribution function of the conductance (transmission) in the one-dimensional tight-binding Anderson and periodic-on-average superlattice models in the region of fluctuation states where single parameter scaling is not valid. We show that the scaling properties of the distribution function depend upon the relation between the system's length L and the length ls determined by the integral density of states. For long enough systems, L ≫ ls, the distribution can still be described within a new scaling approach based upon the ratio of the localization length lloc and ls. In an intermediate …

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Review Of "Liquid Crystals: Fundamentals" By S. Singh, Peter J. Collings Nov 2003

Review Of "Liquid Crystals: Fundamentals" By S. Singh, Peter J. Collings

Physics & Astronomy Faculty Works

No abstract provided.

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Ecotoxicological Research At Dit, Maria Davoren, Colm O'Dowd, Sharon Ni Shuilleabhain Nov 2003

Ecotoxicological Research At Dit, Maria Davoren, Colm O'Dowd, Sharon Ni Shuilleabhain

Articles

The term ecotoxicology first defined by Rene Truhart in 1969, essentially describes the study of the harmful effects of chemicals upon ecosystems.

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Variable Selection For Poisson Regression Model, Felix Famoye, Daniel E. Rothe Nov 2003

Variable Selection For Poisson Regression Model, Felix Famoye, Daniel E. Rothe

Journal of Modern Applied Statistical Methods

Poisson regression is useful in modeling count data. In a study with many independent variables, it is desirable to reduce the number of variables while maintaining a model that is useful for prediction. This article presents a variable selection technique for Poisson regression models. The data used is log-linear, but the methods could be adapted to other relationships. The model parameters are estimated by the method of maximum likelihood. The use of measures of goodness-of-fit to select appropriate variables is discussed. A forward selection algorithm is presented and illustrated on a numerical data set. This algorithm performs as well if …

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Correcting Publication Bias In Meta-Analysis: A Truncation Approach, Guillermo Montes, Bohdan S. Lotyczewski Nov 2003

Correcting Publication Bias In Meta-Analysis: A Truncation Approach, Guillermo Montes, Bohdan S. Lotyczewski

Journal of Modern Applied Statistical Methods

Meta-analyses are increasingly used to support national policy decision making. The practical implications of publications bias in meta-analysis are discussed. Standard approaches to correct for publication bias require knowledge of the selection mechanism that leads to publication. In this study, an alternative approach is proposed based on Cohen’s corrections for a truncated normal. The approach makes less assumptions, is easy to implement, and performs well in simulations with small samples. The approach is illustrated with two published meta-analyses.

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On Treating A Survey Of Convenience Sample As A Simple Random Sample, W. Gregory Thatcher, J. Wanzer Drane Nov 2003

On Treating A Survey Of Convenience Sample As A Simple Random Sample, W. Gregory Thatcher, J. Wanzer Drane

Journal of Modern Applied Statistical Methods

Threat of bias has kept many from using data gathered in less than optimal conditions. We maintain that when convenience sampling represents race and gender at nearly correct proportions and can be beneficial, as these two variables are quite often used as stratification variables. We compared a convenience sample with a proven sample. Race and Sex were nearly proportional as was found in the proven sample. We conclude that the convenience sample can be used as though it is simple random.

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Bootstrapping Confidence Intervals For Robust Measures Of Association, Jason E. King Nov 2003

Bootstrapping Confidence Intervals For Robust Measures Of Association, Jason E. King

Journal of Modern Applied Statistical Methods

A Monte Carlo simulation study compared four bootstrapping procedures in generating confidence intervals for the robust Winsorized and percentage bend correlations. Results revealed the superior resiliency of the robust correlations over r, with neither outperforming the other. Unexpectedly, the bootstrapping procedures achieved roughly equivalent outcomes for each correlation.

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Letters To The Editor, Jmasm Editors Nov 2003

Letters To The Editor, Jmasm Editors

Journal of Modern Applied Statistical Methods

No abstract provided.

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Test Particle Acceleration In Three-Dimensional Magnetohydrodynamic Turbulence, P. Dmitruk, W. H. Matthaeus, N. Seenu, Michael R. Brown Nov 2003

Test Particle Acceleration In Three-Dimensional Magnetohydrodynamic Turbulence, P. Dmitruk, W. H. Matthaeus, N. Seenu, Michael R. Brown

Physics & Astronomy Faculty Works

We perform numerical experiments of test particle acceleration on turbulent magnetic and electric fields obtained from pseudospectral direct numerical solutions of the compressible three-dimensional MHD equations. We find consistent acceleration of the particles to many times the plasma characteristic (Alfven) speed and extended power laws in the density distribution of energies. Scaling laws of maximum and mean energy of particles with the nominal gyrofrequency and the MHD electric field are observed and a simple estimate is presented.

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Timber Damage By Black Bears, Dale L. Nolte, Kimberly K. Wagner, Andy Trent Nov 2003

Timber Damage By Black Bears, Dale L. Nolte, Kimberly K. Wagner, Andy Trent

United States Department of Agriculture Wildlife Services: Staff Publications

Consequences of Bear Damage
Damage Management
Bear Removal
Silvicultural Practices
Alternative Food Sources
Alternative Approaches

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Towards (Semi-) Automatic Generation Of Bio-Medical Ontologies, Vipul Kashyap, Cartic Ramakrishnan, Thomas Rindflesch Nov 2003

Towards (Semi-) Automatic Generation Of Bio-Medical Ontologies, Vipul Kashyap, Cartic Ramakrishnan, Thomas Rindflesch

Kno.e.sis Publications

The design and construction of domain specific ontologies and taxonomies requires allocation of huge resources in terms of cost and time. These efforts are human intensive and we need to explore ways of minimizing human involvement and other resources. In the biomedical domain, we seek to leverage resources such as the UMLS1 Metathesaurus and NLP-based applications such as MetaMap2 in conjunction with statistical clustering techniques, to (partially) automate the process. This is expected to be useful to the team involved in developing MeSH and other biomedical taxonomies to identify gaps in the existing taxonomies, and to be able to quickly …

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Middleware Infrastructure For Parallel And Distributed Programming Models In Heterogeneous Systems, Jameela Al-Jaroodi, Nader Mohamed, Hong Jiang, David Swanson Nov 2003

Middleware Infrastructure For Parallel And Distributed Programming Models In Heterogeneous Systems, Jameela Al-Jaroodi, Nader Mohamed, Hong Jiang, David Swanson

School of Computing: Faculty Publications

In this paper, we introduce a middleware infrastructure that provides software services for developing and deploying high-performance parallel programming models and distributed applications on clusters and networked heterogeneous systems. This middleware infrastructure utilizes distributed agents residing on the participating machines and communicating with one another to perform the required functions. An intensive study of the parallel programming models in Java has helped identify the common requirements for a runtime support environment, which we used to define the middleware functionality. A Java-based prototype, based on this architecture, has been developed along with a Java Object-Passing Interface (JOPI) class library. Since this …

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