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Search Results: 1 - 10 of 191317 matches for " D. Poulson "
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Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant
Bryan Poulson
International Journal of Nuclear Energy , 2014, DOI: 10.1155/2014/423295
Abstract: Flow accelerated corrosion (FAC) of carbon steels in water has been a concern in nuclear power production for over 40 years. Many theoretical models or empirical approaches have been developed to predict the possible occurrence, position, and rate of FAC. There are a number of parameters, which need to be incorporated into any model. Firstly there is a measure defining the hydrodynamic severity of the flow; this is usually the mass transfer rate. The development of roughness due to FAC and its effect on mass transfer need to be considered. Then most critically there is the derived or assumed functional relationship between the chosen hydrodynamic parameter and the rate of FAC. Environmental parameters that are required, at the relevant temperature and pH, are the solubility of magnetite and the diffusion coefficient of the relevant iron species. The chromium content of the steel is the most important material factor. 1. Introduction Flow accelerated corrosion (FAC) of carbon steels in water has been a major concern in civil nuclear power production for over 40 years [1, 2]. The important features of FAC are the linear or increasing rate with time and the generation of a scalloped surface. Its effects have been unique in two important ways. Firstly it has affected nearly every reactor type worldwide and sometimes in more than one location; Figure 1 shows some examples [3–6]. Secondly it is probably the only corrosion mechanism that has led to accidents that have caused fatalities. There have been pipe ruptures leading to a release of steam and deaths of workers, but it must be emphasized that such fatalities are not unique to nuclear plants. Figure 1: Examples of FAC in nuclear power plants. The occurrence of FAC, or erosion corrosion as it is sometimes known, is critically dependent on the following: the temperature and chemistry of the environment (pH and oxygen content), the hydrodynamics of the system, and the composition of the steel particularly the chromium content; this is shown schematically in Figure 2. Figure 2: Factors influencing FAC. There are various approaches to predicting the possibility and the rate of flow accelerated corrosion. Testing has involved either actual components or a chosen specimen. In addition there are theoretical or empirical models, some computer based, available to allow the prediction of attack. It is readily apparent that any review must be very selective; other reviews are available [7–10]. This review has tried to cover areas that the author has been involved with over the last 40 years that have been neglected
Randomized controlled trial of anterior-chamber intraocular lenses in Nepal: long-term follow-up
Evans,J.R.; Hennig,A.; Pradhan,D.; Foster,A.; Lagnado,R.; Poulson,A.; Johnson,G.J.; Wormald,R.P.L.;
Bulletin of the World Health Organization , 2000, DOI: 10.1590/S0042-96862000000300013
Abstract: most of the estimated 20 million people who are blind with cataracts live in rural areas of developing countries, where expert surgical resources are scarce. we have studied the use of multiflex open-loop anterior-chamber intraocular lenses (aciol) in high-volume low-cost surgery. between 1992 and 1995, a total of 2000 people attending lahan eye hospital, nepal, with bilateral cataracts reducing vision to < 6/36 were randomly allocated to receive intracapsular extraction (icce) with aphakic spectacles, or icce with an aciol. we re-examined the cohort (1305/2000, 65%) between november 1996 and april 1997 and report the findings in this article. there were 13 new cases of poor visual outcome (best corrected vision <6/60) arising after one year: 9 in the aciol group and 4 in the control group; odds ratio 2.1 (95% confidence interval, 0.59-9.55). the causes of poor outcome were as follows: aciol group - retinal detachment (4 cases), cystoid macular oedema (2), epiretinal membrane (1), age-related macular degeneration (1), and late endophthalmitis (1); control group - retinal detachment (2 cases), late endophthalmitis (1), and primary open-angle glaucoma with age-related macular degeneration (1). in rural areas of developing countries, well-manufactured multiflex open-loop aciols can be implanted safely by experienced ophthalmologists after routine icce, avoiding the disadvantages of aphakic spectacle correction.
Genomic Characterization of H14 Subtype Influenza A Viruses in New World Waterfowl and Experimental Infectivity in Mallards (Anas platyrhynchos)
Andrew M. Ramey, Rebecca L. Poulson, Ana S. González-Reiche, Daniel R. Perez, David E. Stallknecht, Justin D. Brown
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0095620
Abstract: Recent repeated isolation of H14 hemagglutinin subtype influenza A viruses (IAVs) in the New World waterfowl provides evidence to suggest that host and/or geographic ranges for viruses of this subtype may be expanding. In this study, we used genomic analyses to gain inference on the origin and evolution of H14 viruses in New World waterfowl and conducted an experimental challenge study in mallards (Anas platyrhynchos) to evaluate pathogenicity, viral replication, and transmissibility of a representative viral strain in a natural host species. Genomic characterization of H14 subtype IAVs isolated from New World waterfowl, including three isolates sequenced specifically for this study, revealed high nucleotide identity among individual gene segments (e.g. ≥95% shared identity among H14 HA gene segments). In contrast, lower shared identity was observed among internal gene segments. Furthermore, multiple neuraminidase subtypes were observed for H14 IAVs isolated in the New World. Gene segments of H14 viruses isolated after 2010 shared ancestral genetic lineages with IAVs isolated from wild birds throughout North America. Thus, genomic characterization provided evidence for viral evolution in New World waterfowl through genetic drift and genetic shift since purported introduction from Eurasia. In the challenge study, no clinical disease or lesions were observed among mallards experimentally inoculated with A/blue-winged teal/Texas/AI13-1028/2013(H14N5) or exposed via contact with infected birds. Titers of viral shedding for mallards challenged with the H14N5 IAV were highest at two days post-inoculation (DPI); however shedding was detected up to nine DPI using cloacal swabs. The distribution of viral antigen among mallards infected with H14N5 IAV was largely restricted to enterocytes lining the villi in the lower intestinal tract and in the epithelium of the bursa of Fabricius. Characterization of the infectivity of A/blue-winged teal/Texas/AI13-1028/2013(H14N5) in mallards provides support for similarities in viral replication and shedding as compared to previously described waterfowl-adapted, low pathogenic IAV strains in ducks.
Tests of cosmic ray radiography for power industry applications
J. M. Durham,E. Guardincerri,C. L. Morris,J. Bacon,J. Fabritius,S. Fellows,K. Plaud-Ramos,D. Poulson,J. Renshaw
Physics , 2015,
Abstract: In this report, we assess muon multiple scattering tomography as a non-destructive inspection technique in several typical areas of interest to the nuclear power industry, including monitoring concrete degradation, gate valve conditions, and pipe wall thickness. This work is motivated by the need for radiographic methods that do not require the licensing, training, and safety controls of x-rays, and by the need to be able to penetrate considerable overburden to examine internal details of components that are otherwise inaccessible, with minimum impact on industrial operations. In some scenarios, we find that muon tomography may be an attractive alternative to more typical measurements.
Efeitos da radia??o ultravioleta-B sobre a morfologia foliar de Arabidopsis thaliana (L.) Heynh. (Brassicaceae)
Boeger, Maria Regina Torres;Poulson, Mary;
Acta Botanica Brasilica , 2006, DOI: 10.1590/S0102-33062006000200008
Abstract: reduction of the ozone layer results in the increase in ultraviolet radiation reaching the earth's surface, especially the ultraviolet-b (uv-b). the increase of radiation may induce structural and physiological changes in plants, influencing their growth and development. this paper evaluates the effects of ambient uv-b radiation upon to the leaf morphology of arabidopsis thaliana developed under controlled conditions. the seeds of a. thaliana grown in environmental chamber, with 300 μmol m-2s-1 de photosynthetically active radiation (par) with and without 6 kj m-2 s-1 of radiation uv-bbe (uv-bbe; uv-b biologically effective). after 21 days, ten leaves of each treatment (with and without uv-b radiation) were collected to measure leaf area, fresh and dry mass, aef, stomata and trichome densities of both leaf surfaces, leaf thickness and concentration of phenolic compounds and total chlorophyll, and chlorophyll a and b. leaves treated with uv-b radiation presented smaller leaf area, fresh and dry weight, hair density, and stomata density on the adaxial epidermis. however, leaves treated with uv-b presented higher mean values for total thickness, mesophyll thickness, higher concentration of total chlorophyll, chlorophyll a and b, and phenolic compounds when compared to leaves without uv-b radiation. these significant morphological differences (p < 0.05) between leaves treated with and without uv-b radiation indicate that a. thaliana is not insensible to uv-b radiation and possess mechanisms that minimize the negative effects on leaf development and growth. although, the plant responses to uv-b radiation involves several physiological mechanisms, that need more detailed investigation.
Detecting Special Nuclear Material Using Muon-Induced Neutron Emission
E. Guardincerri,J. D. Bacon,K. Borodzin,J. M. Durham,J. M. Fabritius II,A. Hecht,E. C. Milner,H. Miyadera,C. L. Morris,J. O. Perry,D. Poulson
Physics , 2014, DOI: 10.1016/j.nima.2015.03.070
Abstract: The penetrating ability of cosmic ray muons makes them an attractive probe for imaging dense materials. Here, we describe experimental results from a new technique that uses neutrons generated by cosmic-ray muons to identify the presence of special nuclear material (SNM). Neutrons emitted from SNM are used to tag muon-induced fission events in actinides and laminography is used to form images of the stopping material. This technique allows the imaging of SNM-bearing objects tagged using muon tracking detectors located above or to the side of the objects, and may have potential applications in warhead verification scenarios. During the experiment described here we did not attempt to distinguish the type or grade of the SNM.
Influenza-A Viruses in Ducks in Northwestern Minnesota: Fine Scale Spatial and Temporal Variation in Prevalence and Subtype Diversity
Benjamin R. Wilcox, Gregory A. Knutsen, James Berdeen, Virginia Goekjian, Rebecca Poulson, Sagar Goyal, Srinand Sreevatsan, Carol Cardona, Roy D. Berghaus, David E. Swayne, Michael J. Yabsley, David E. Stallknecht
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024010
Abstract: Waterfowl from northwestern Minnesota were sampled by cloacal swabbing for Avian Influenza Virus (AIV) from July – October in 2007 and 2008. AIV was detected in 222 (9.1%) of 2,441 ducks in 2007 and in 438 (17.9%) of 2,452 ducks in 2008. Prevalence of AIV peaked in late summer. We detected 27 AIV subtypes during 2007 and 31 during 2008. Ten hemagglutinin (HA) subtypes were detected each year (i.e., H1, 3–8, and 10–12 during 2007; H1-8, 10 and 11 during 2008). All neuraminidase (NA) subtypes were detected during each year of the study. Subtype diversity varied between years and increased with prevalence into September. Predominant subtypes during 2007 (comprising ≥5% of subtype diversity) included H1N1, H3N6, H3N8, H4N6, H7N3, H10N7, and H11N9. Predominant subtypes during 2008 included H3N6, H3N8, H4N6, H4N8, H6N1, and H10N7. Additionally, within each HA subtype, the same predominant HA/NA subtype combinations were detected each year and included H1N1, H3N8, H4N6, H5N2, H6N1, H7N3, H8N4, H10N7, and H11N9. The H2N3 and H12N5 viruses also predominated within the H2 and H12 subtypes, respectively, but only were detected during a single year (H2 and H12 viruses were not detected during 2007 and 2008, respectively). Mallards were the predominant species sampled (63.7% of the total), and 531 AIV were isolated from this species (80.5% of the total isolates). Mallard data collected during both years adequately described the observed temporal and spatial prevalence from the total sample and also adequately represented subtype diversity. Juvenile mallards also were adequate in describing the temporal and spatial prevalence of AIV as well as subtype diversity.
Heterogeneous Feeding Patterns of the Dengue Vector, Aedes aegypti, on Individual Human Hosts in Rural Thailand
Laura C. Harrington ,Andrew Fleisher,Diego Ruiz-Moreno,Francoise Vermeylen,Chrystal V. Wa,Rebecca L. Poulson,John D. Edman,John M. Clark,James W. Jones,Sangvorn Kitthawee,Thomas W. Scott
PLOS Neglected Tropical Diseases , 2014, DOI: 10.1371/journal.pntd.0003048
Abstract: Background Mosquito biting frequency and how bites are distributed among different people can have significant epidemiologic effects. An improved understanding of mosquito vector-human interactions would refine knowledge of the entomological processes supporting pathogen transmission and could reveal targets for minimizing risk and breaking pathogen transmission cycles. Methodology and principal findings We used human DNA blood meal profiling of the dengue virus (DENV) vector, Aedes aegypti, to quantify its contact with human hosts and to infer epidemiologic implications of its blood feeding behavior. We determined the number of different people bitten, biting frequency by host age, size, mosquito age, and the number of times each person was bitten. Of 3,677 engorged mosquitoes collected and 1,186 complete DNA profiles, only 420 meals matched people from the study area, indicating that Ae. aegypti feed on people moving transiently through communities to conduct daily business. 10–13% of engorged mosquitoes fed on more than one person. No biting rate differences were detected between high- and low-dengue transmission seasons. We estimate that 43–46% of engorged mosquitoes bit more than one person within each gonotrophic cycle. Most multiple meals were from residents of the mosquito collection house or neighbors. People ≤25 years old were bitten less often than older people. Some hosts were fed on frequently, with three hosts bitten nine times. Interaction networks for mosquitoes and humans revealed biologically significant blood feeding hotspots, including community marketplaces. Conclusion and significance High multiple-feeding rates and feeding on community visitors are likely important features in the efficient transmission and rapid spread of DENV. These results help explain why reducing vector populations alone is difficult for dengue prevention and support the argument for additional studies of mosquito feeding behavior, which when integrated with a greater understanding of human behavior will refine estimates of risk and strategies for dengue control.
An Examination of Traditional and Nontraditional Students’ Evaluations of Professorial Leadership Styles: Transformational Verses Transactional Approach
John Hood,Ronald L. Poulson,Sylvia A. Mason,Tyrone Walker
The Journal of Scholarship of Teaching and Learning , 2009,
Abstract:
A parallel sweeping preconditioner for heterogeneous 3D Helmholtz equations
Jack Poulson,Bj?rn Engquist,Siwei Li,Lexing Ying
Computer Science , 2012, DOI: 10.1137/120871985
Abstract: A parallelization of a sweeping preconditioner for 3D Helmholtz equations without large cavities is introduced and benchmarked for several challenging velocity models. The setup and application costs of the sequential preconditioner are shown to be O({\gamma}^2 N^{4/3}) and O({\gamma} N log N), where {\gamma}({\omega}) denotes the modestly frequency-dependent number of grid points per Perfectly Matched Layer. Several computational and memory improvements are introduced relative to using black-box sparse-direct solvers for the auxiliary problems, and competitive runtimes and iteration counts are reported for high-frequency problems distributed over thousands of cores. Two open-source packages are released along with this paper: "Parallel Sweeping Preconditioner (PSP)" and the underlying distributed multifrontal solver, "Clique".
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