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Search Results: 1 - 10 of 406480 matches for " Diana M. Stone "
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Exposure to Zoonotic Abortifacients among Sheep and Goats in Grenada
Diana M. Stone,Sachin Kumthekar,Alfred Chikweto,Derek Thomas
International Journal of Animal and Veterinary Advances , 2012,
Abstract: The aim of this study was to determine the prevalence of exposure to the zoonotic abortifacients Brucella spp, Coxiella burnetii and Chlamydophila abortus among sheep and goats in the Caribbean Tri-Island state of Grenada. Documentation of exposure to these important bacterial pathogens will facilitate instituting appropriate prevention and control measures. Serum samples were collected from 582 animals from the islands of Grenada and Carriacou during 2009-2010. Sera were tested by enzyme-linked immunosorbent assay (ELISA) for determination of antibodies to smooth lipopolysaccharides (s-LPS) of B. abortus strain S-99, inactivated C. abortus antigens and to C. burnetii phase I and II purified antigens. None of the animals examined tested positive for antibody to C. burnetii. Evidence of Brucella exposure was noted in 13 (3.6%) of 362 sheep, representing animals from both islands of Grenada and Carriacou, whereas none of the 220 goats examined tested positive. Exposure to either Brucella abortus or B. melitensis could account for the detected antibody to Brucella s-LPS antigens. Antibody to C. abortus was detected in 6.0% of animals tested (24 sheep and 10 goats), representing animals from Carriacou and all 6 parishes of Grenada. Taken together, our results indicate moderate widespread exposure of small ruminants to the zoonotic abortifacients Brucella spp and Chlamydophila abortus in the tri-island state of Grenada and is the first report documenting such exposures in any animal species in this region of the Caribbean.
Stone.,M 杜小勇
计算机科学 , 1991,
Abstract: 我们将早期的层次和网状数据库系统称做第一代数据库系统,现在的这些关系系统称做第二代数据库系统。本文将讨论我们称做第三代数据库系统的下一代数据管理系统所应具有的特征。文中提出的3条基本原则和13个详述的命题集中反映了我们的要求。
Transient Population Dynamics of Mosquitoes during Sterile Male Releases: Modelling Mating Behaviour and Perturbations of Life History Parameters
Christopher M. Stone
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0076228
Abstract: The release of genetically-modified or sterile male mosquitoes offers a promising form of mosquito-transmitted pathogen control, but the insights derived from our understanding of male mosquito behaviour have not fully been incorporated into the design of such genetic control or sterile-male release methods. The importance of aspects of male life history and mating behaviour for sterile-male release programmes were investigated by projecting a stage-structured matrix model over time. An elasticity analysis of transient dynamics during sterile-male releases was performed to provide insight on which vector control methods are likely to be most synergistic. The results suggest that high mating competitiveness and mortality costs of released males are required before the sterile-release method becomes ineffective. Additionally, if released males suffer a mortality cost, older males should be released due to their increased mating capacity. If released males are of a homogenous size and size-assortative mating occurs in nature, this can lead to an increase in the abundance of large females and reduce the efficacy of the population-suppression effort. At a high level of size-assortative mating, the disease transmission potential of the vector population increases due to male releases, arguing for the release of a heterogeneously-sized male population. The female population was most sensitive to perturbations of density-dependent components of larval mortality and female survivorship and fecundity. These findings suggest source reduction might be a particularly effective complement to mosquito control based on the sterile insect technique (SIT). In order for SIT to realize its potential as a key component of an integrated vector-management strategy to control mosquito-transmitted pathogens, programme design of sterile-male release programmes must account for the ecology, behaviour and life history of mosquitoes. The model used here takes a step in this direction and can easily be modified to investigate additional aspects of mosquito behaviour or species-specific ecology.
The Wardle Instability in Interstellar Shocks: I. Nonlinear Dynamical Evolution
James M. Stone
Physics , 1997, DOI: 10.1086/304595
Abstract: The nonlinear evolution of unstable C-type shocks in weakly ionized plasmas is studied by means of time-dependent magnetohydrodynamical simulations. This study is limited to shocks in magnetically dominated plasmas (in which the Alfven speed in the neutrals greatly exceeds the sound speed), and microphysical processes such as ionization and recombination are not followed. Both two-dimensional simulations of planar perpendicular and oblique C-type shocks, and fully three-dimensional simulation of a perpendicular shock are presented.
Dynamics on the Edge: Star-Disk Interaction
James M. Stone
Physics , 1998, DOI: 10.1063/1.55943
Abstract: Our understanding of the dynamical processes which control the structure and evolution of the interaction region between an accretion disk and the central star is reviewed. If the central star is unmagnetized, this interaction is in the form of a classical boundary layer. However, if the central star is strongly magnetized, it is expected that the inner disk is truncated by the stellar field, and the accretion flow follows the stellar field lines to the magnetic poles. Several outstanding questions remain regarding this picture. It is likely that numerical MHD simulations will prove essential to answering these questions. However, in order to model the MHD turbulence, angular momentum transport, and possible dynamo action associated with the dynamics of star-disk interaction, fully three-dimensional simulations spanning long dynamical times are required.
FLECS: Planning with a Flexible Commitment Strategy
M. Veloso,P. Stone
Computer Science , 1995,
Abstract: There has been evidence that least-commitment planners can efficiently handle planning problems that involve difficult goal interactions. This evidence has led to the common belief that delayed-commitment is the "best" possible planning strategy. However, we recently found evidence that eager-commitment planners can handle a variety of planning problems more efficiently, in particular those with difficult operator choices. Resigned to the futility of trying to find a universally successful planning strategy, we devised a planner that can be used to study which domains and problems are best for which planning strategies. In this article we introduce this new planning algorithm, FLECS, which uses a FLExible Commitment Strategy with respect to plan-step orderings. It is able to use any strategy from delayed-commitment to eager-commitment. The combination of delayed and eager operator-ordering commitments allows FLECS to take advantage of the benefits of explicitly using a simulated execution state and reasoning about planning constraints. FLECS can vary its commitment strategy across different problems and domains, and also during the course of a single planning problem. FLECS represents a novel contribution to planning in that it explicitly provides the choice of which commitment strategy to use while planning. FLECS provides a framework to investigate the mapping from planning domains and problems to efficient planning strategies.
Stone.,M 杜小勇?
计算机科学 , 1991,
Stone.,M 徐宝文
计算机科学 , 1991,
Abstract: 本文为专家数据库系统应用提出一些可能的体系结构,并断言只有以紧密耦合为基础的体系结构才是普遍适用的一种结构。还探讨了规则系统与 DBMS 相集成的研究方向,认为目前规则系统的优化技术没有得到足够的重视。最后,论述了专家数据库系统的若干特性。
Propogation of Electromagnetic Waves in the Core of a String Defect in Liquid Crystals
Ajit M. Srivastava,Michael Stone
Physics , 1993,
Abstract: We investigate the propagation of electromagnetic waves in the core of a winding number one string defect with isotropic core in nematic liquid crystals. We numerically solve wave equations for the TE mode and show the existence of guided modes arising due to the variation of the refractive index as a function of the scalar order parameter.
Turbulent resistivity driven by the magnetorotational instability
Sebastien Fromang,James M. Stone
Physics , 2009, DOI: 10.1051/0004-6361/200912752
Abstract: We measure the turbulent resistivity in the nonlinear regime of the MRI, and evaluate the turbulent magnetic Prandtl number. We perform a set of numerical simulations with the Eulerian finite volume codes Athena and Ramses in the framework of the shearing box model. We consider models including explicit dissipation coefficients and magnetic field topologies such that the net magnetic flux threading the box in both the vertical and azimuthal directions vanishes. We first demonstrate good agreement between the two codes by comparing the properties of the turbulent states in simulations having identical microscopic diffusion coefficients (viscosity and resistivity). We find the properties of the turbulence do not change when the box size is increased in the radial direction, provided it is elongated in the azimuthal direction. To measure the turbulent resistivity in the disk, we impose a fixed electromotive force on the flow and measure the amplitude of the saturated magnetic field that results. We obtain a turbulent resistivity that is in rough agreement with mean field theories like the Second Order Smoothing Approximation. The numerical value translates into a turbulent magnetic Prandtl number Pm_t of order unity. Pm_t appears to be an increasing function of the forcing we impose. It also becomes smaller as the box size is increased in the radial direction, in good agreement with previous results obtained in very large boxes. Our results are in general agreement with other recently published papers studying the same problem but using different methodology. Thus, our conclusion that Pm_t is of order unity appears robust.
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