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Search Results: 1 - 10 of 193673 matches for " Howard D Bondell "
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A nonparametric Bayesian test of dependence
Yimin Kao,Brian J Reich,Howard D Bondell
Statistics , 2015,
Abstract: In this article, we propose a new method for the fundamental task of testing for dependence between two groups of variables. The response densities under the null hypothesis of independence and the alternative hypothesis of dependence are specified by nonparametric Bayesian models. Under the null hypothesis, the joint distribution is modeled by the product of two independent Dirichlet Process Mixture (DPM) priors; under the alternative, the full joint density is modeled by a multivariate DPM prior. The test is then based on the posterior probability of favoring the alternative hypothesis. The proposed test not only has good performance for testing linear dependence among other popular nonparametric tests, but is also preferred to other methods in testing many of the nonlinear dependencies we explored. In the analysis of gene expression data, we compare different methods for testing pairwise dependence between genes. The results show that the proposed test identifies some dependence structures that are not detected by other tests.
Environmental, Institutional, and Demographic Predictors of Environmental Literacy among Middle School Children
Kathryn T. Stevenson, M. Nils Peterson, Howard D. Bondell, Angela G. Mertig, Susan E. Moore
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0059519
Abstract: Building environmental literacy (EL) in children and adolescents is critical to meeting current and emerging environmental challenges worldwide. Although environmental education (EE) efforts have begun to address this need, empirical research holistically evaluating drivers of EL is critical. This study begins to fill this gap with an examination of school-wide EE programs among middle schools in North Carolina, including the use of published EE curricula and time outdoors while controlling for teacher education level and experience, student attributes (age, gender, and ethnicity), and school attributes (socio-economic status, student-teacher ratio, and locale). Our sample included an EE group selected from schools with registered school-wide EE programs, and a control group randomly selected from NC middle schools that were not registered as EE schools. Students were given an EL survey at the beginning and end of the spring 2012 semester. Use of published EE curricula, time outdoors, and having teachers with advanced degrees and mid-level teaching experience (between 3 and 5 years) were positively related with EL whereas minority status (Hispanic and black) was negatively related with EL. Results suggest that school-wide EE programs were not associated with improved EL, but the use of published EE curricula paired with time outdoors represents a strategy that may improve all key components of student EL. Further, investments in teacher development and efforts to maintain enthusiasm for EE among teachers with more than 5 years of experience may help to boost student EL levels. Middle school represents a pivotal time for influencing EL, as improvement was slower among older students. Differences in EL levels based on gender suggest boys and girls may possess complementary skills sets when approaching environmental issues. Our findings suggest ethnicity related disparities in EL levels may be mitigated by time spent in nature, especially among black and Hispanic students.
Web 2.0 Sites for Collaborative Self-Access: The Learning Advisor vs. Google
Craig D. Howard
Studies in Self-Access Learning Journal , 2011,
Abstract: While Web 2.0 technologies provide motivated, self-access learners with unprecedented opportunities for language learning, Web 2.0 designs are not of universally equal value for learning. This article reports on research carried out at Indiana University Bloomington using an empirical method to select websites for self-access language learning. Two questions related to Web 2.0 recommendations were asked: (1) How do recommended Web 2.0 sites rank in terms of interactivity features? (2) How likely is a learner to find highly interactive sites on their own? A list of 20 sites used for supplemental and self-access activities in language programs at five universities was compiled and provided the initial data set. Purposive sampling criteria revealed 10 sites truly represented Web 2.0 design. To address the first question, a feature analysis was applied (Herring, The international handbook of internet research. Berlin: Springer, 2008). An interactivity framework was developed from previous research to identify Web 2.0 design features, and sites were ranked according to feature quantity. The method used to address the second question was an interconnectivity analysis that measured direct and indirect interconnectivity within Google results. Highly interactive Web 2.0 sites were not prominent in Google search results, nor were they often linked via third party sites. It was determined that, using typical keywords or searching via blogs and recommendation sites, self-access learners were highly unlikely to find the most promising Web 2.0 sites for language learning. A discussion of the role of the learning advisor in guiding Web 2.0 collaborative self-access, as well as some strategic short cuts to quick analysis, conclude the article.
An upper bound on $P$-wave charmonium production via the color-octet mechanism
Howard D. Trottier
Physics , 1993,
Abstract: A factorization theorem for $P$-wave quarkonium production, recently derived by Bodwin, Braaten, Yuan and Lepage, is applied to $\Upsilon \to \chi_{cJ} + X$, where $\chi_{cJ}$ labels the ${}^3 P_J$ charmonium states. The widths for $\chi_{cJ}$ production through color-singlet $P$-wave and color-octet $S$-wave $c \bar c$ subprocesses are computed each to leading order in $\alpha_s$. Experimental data on $\Upsilon \to J / \psi + X$ is used to obtain an upper bound on a nonperturbative parameter (related to the probability for color-octet $S$-wave $c \bar c$ hadronization into $P$-wave charmonium) that enters into the factorization theorem.
Quarkonium spin structure in lattice NRQCD
Howard D. Trottier
Physics , 1996, DOI: 10.1103/PhysRevD.55.6844
Abstract: Numerical simulations of the quarkonium spin splittings are done in the framework of lattice nonrelativistic quantum chromodynamics (NRQCD). At leading order in the velocity expansion the spin splittings are of $O(M_Q v^4)$, where $M_Q$ is the renormalized quark mass and $v^2$ is the mean squared quark velocity. A systematic analysis is done of all next-to-leading order corrections. This includes the addition of $O(M_Q v^6)$ relativistic interactions, and the removal of $O(a^2 M_Q v^4)$ discretization errors in the leading-order interactions. Simulations are done for both S- and P-wave mesons, with a variety of heavy quark actions and over a wide range of lattice spacings. Two prescriptions for the tadpole improvement of the action are also studied in detail: one using the measured value of the average plaquette, the other using the mean link measured in Landau gauge. Next-to-leading order interactions result in a very large reduction in the charmonium splittings, down by about 60% from their values at leading order. There are further indications that the velocity expansion may be poorly convergent for charmonium. Prelimary results show a small correction to the hyperfine splitting in the Upsilon system.
$Υ$ decay into charmonium and the color octet mechanism
Howard D. Trottier
Physics , 1993, DOI: 10.1016/0370-2693(94)90838-9
Abstract: A factorization theorem for $P$-wave quarkonium production, recently derived by Bodwin, Braaten, Yuan and Lepage, is applied to $\Upsilon \to \chi_{cJ} + X$, where $\chi_{cJ}$ labels the ${}^3 P_J$ charmonium states. The widths for $\chi_{cJ}$ production through color-singlet $P$-wave and color-octet $S$-wave $c \bar c$ subprocesses are computed each to leading order in $\alpha_s$. Experimental data on $\Upsilon \to J / \psi + X$ is used to obtain an upper bound on a nonperturbative parameter (related to the probability for color-octet $S$-wave $c \bar c$ hadronization into $P$-wave charmonium) that enters into the factorization theorem. The bound obtained here adds to the limited information so far available on the color-octet mechanism for $P$-wave quarkonium production.
Adjoint ``Quarks'' and the Physics of Confinement
Howard D. Trottier
Physics , 1995, DOI: 10.1016/0920-5632(96)00058-8
Abstract: The quark-antiquark potential and the chromoelectric fields generated by ``quarks'' in the adjoint representation of SU(2) color are analyzed in the scaling region of the theory. New results with interesting implications for our understanding of the confinement mechanism are presented. In particular, the formation of color-electric flux-tubes between adjoint quarks is demonstrated in four-dimensional SU(2) color. The flux-tubes for fundamental and adjoint representation quarks are shown to have very similar cross-sections. This result could imply that the QCD vacuum is dual to a type I superconductor.
ADJOINT "QUARK" COLOR FIELDS IN FOUR-DIMENSIONAL LATTICE GAUGE THEORY: VACUUM SCREENING AND PENETRATION
Howard D. Trottier
Physics , 1995, DOI: 10.1016/0370-2693(95)00902-W
Abstract: The fields generated by ``quarks'' in the adjoint representation of SU(2) color are analyzed in the scaling region of the four-dimensional lattice theory. Evidence of vacuum screening of adjoint quarks is obtained from a comparison of quark-antiquark ($Q \bar Q$) flux-tubes for quarks in the adjoint (``isospin'' $j=1$) and fundamental ($j=1/2$) representations. The component ${\cal E}_j$ of the color-electric field strength in the direction parallel to the $Q \bar Q$ axis is calculated. Near the quarks the ratio of fields ${\cal E}_{j=1} / {\cal E}_{j=1/2}$ approaches the value 8/3, which is equal to the ratio of SU(2) Casimirs. In between the quarks, the ratio falls well below 8/3 at large $R$. ${\cal E}_j$ also falls off rapidly as a function of distance $x_\perp$ perpendicular to the $Q \bar Q$ axis. However, the ratio ${\cal E}_{j=1} / {\cal E}_{j=1/2}$ depends very weakly on $x_\perp$. The flux-tubes in the two representations thus appear to have very similar cross-sections. This result could imply that the QCD vacuum is dual to a type I superconductor.
Higher-order perturbation theory for highly-improved actions
Howard D. Trottier
Physics , 2003, DOI: 10.1016/S0920-5632(03)02515-5
Abstract: I review techniques and applications of higher-order perturbation theory for highly-improved lattice actions.
Improvement, dynamical fermions, and heavy quark screening in QCD_3
Howard D. Trottier
Physics , 1998, DOI: 10.1016/S0920-5632(99)85248-7
Abstract: First results from simulations of improved actions for both gauge fields and staggered fermion fields in three dimensional QCD are presented. This work provides insight into some issues of relevance to lattice theories in four dimensions. In particular, the renormalization of the bare lattice coupling is dramatically reduced when the tree-level $O(a^2)$ improved action is used. Naik improvement of the staggered fermion action produces little reduction in scaling violations of the rho meson mass. String breaking in the heavy quark potential in the unquenched theory is also clearly resolved, using Wilson loops to bound the ground state energy.
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