4,626 research outputs found

    The nature of X-ray spectral variability in Seyfert Galaxies

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    We use a model-independent technique to investigate the nature of the 2-15 keV X-ray spectral variability in four Seyfert galaxies and distinguish between spectral pivoting and the two-component model for spectral variability. Our analysis reveals conclusively that the softening of the X-ray continuum with increasing flux in MCG -6-30-15 and NGC 3516 is a result of summing two spectral components: a soft varying component (SVC) with spectral shape independent of flux and a constant hard component (HCC). In contrast, the spectral variability in NGC 4051 can be well described by simple pivoting of one component, together with an additional hard constant component. The spectral variability model for NGC 5506 is ambiguous, due to the smaller range of fluxes sampled by the data. We investigate the shape of the hard spectral component in MCG -6-30-15 and find that it appears similar to a pure reflection spectrum, but requires a large reflected fraction (R>3). We briefly discuss physical interpretations of the different modes of spectral variability.Comment: Accepted for publication in MNRAS letter

    Welfare Reform in Agricultural California

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    When welfare reforms were enacted in 1996, a higher than average percentage of residents in the agricultural heartland of California, the San Joaquin Valley, received cash assistance. Average annual unemployment rates during the 1990s ranged from 12% to 20%, and 15% to 20% of residents in major farming counties received cash benefits. This analysis develops and estimates a two-equation cross-sectionally correlated and timewise autoregressive model to test the hypothesis that in agricultural areas, seasonal work, low earnings, and high unemployment, as well as few entry-level jobs that offer wages and benefits equivalent to welfare benefits, promote welfare use and limit the potential of local labor markets to absorb ex-welfare recipients.cross-sectionally correlated and timewise autoregressive model, farm workers, immigration, welfare reform, Public Economics,

    Impact of Flower Harvesting on the Salt Marsh Plant \u3cem\u3eLimonium carolinianum\u3c/em\u3e

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    Because of the potentially detrimental effects of seed production on adult survivorship and growth, moderate flower harvesting may have little negative impact on population growth of long-lived perennial plants such as Limonium carolinianum (Walter) Britton. We examined this by collecting data on survivorship, growth, and fecundity of an unharvested population over a period of 5 years and conducted a controlled experiment to examine the effect of harvesting on adult survivorship and growth over a 3-year period. Data were summarized in the form of a stage structured matrix population model with a stochastic element that incorporated year-to-year variation in transition probabilities. Contrary to our original hypothesis, we found that preventing seed set through removal of flowers did not increase adult survivorship or growth. By determining the harvest level that reduced population growth rate to 1.0, we estimated the maximum sustainable harvest level to be 16%, a value that is approximately half that of reported harvest levels on accessible marshes in the study area. In spite of this, the reported harvest levels are unlikely to drive local populations to extinction in the foreseeable future. Providing the adult population size is \u3e100 and harvest levels are \u3c90%, time to local extinction will exceed 100 years. This is a function of the very high survivorship of adults in this species and the fact that harvesting has no negative impact on adult survivorship or growth. However, because of the long preadult phase in this species (8–9 years) and the fact that fecundity of young adults is low, recovery from overharvesting is extremely slow. Adult population size can be reduced to 25% of its original value in 7 years at high harvest levels, but it will take 34 years on average to recover once harvesting is terminated

    Benchmark Analyses for Fracture Mechanics Methods for Assessing Sub-Clad Flaws - NESC-VI Final Report

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    The sixth project of the Network for Evaluating Structural Integrity (NESC-VI) deals with the fracture mechanics analysis of a set of 3 tests on beam specimens with simulated sub-surface flaws, which were performed by NRI Re¿ plc for the PHARE project ¿WWER Cladded Reactor Pressure Vessel Integrity Evaluation (with Respect to PTS Events)¿. The objectives were as follows: ¿ to assess the capability to predict whether the cracks propagating into the cladding arrest or cause full fracture, and ¿ to assess the capability to predict the location of first initiation: near-surface or deep crack tip. The project was launched in December 2006 and completed in March 2009. It brought together a group of 10 organisations from NESC to perform comparative analyses of selected tests, based on a comprehensive datapack prepared by NRI. The investigations focussed almost exclusively on assessing the capability to predict the location of first initiation. The main results are as follows: ¿ Comparison of analyses performed by individual partners showed that the FE simulations produced consistent predictions of the observed force vs. load-line displacement (or crack mouth opening displacement) behaviour. However the differences in predicted crack tip stress intensity, KJ, as a function of applied loading were greater than those found in similar intercomparisons made as part of previous NESC projects. This underlines the importance of periodically performing such exercises. ¿ The influence of two modelling factors on KJ was clearly established: firstly for this type of specimen, for which the clad makes up almost 12% of the cross-section, the associated residual stresses have a significant effect in reducing KJ values and therefore need to be considered in "best-estimate" analysis. The second concerns the use of 2-D or 3-D models: in this case the 2D FE models underestimated KJ values and are considered non-conservative. ¿ For this combination of test specimen geometry and flaw, constraint loss is expected at the near-surface tip. A range of constraint parameters were evaluated (elastic T-stress, elastic-plastic T-stress and Q) to confirm this. However only in two cases these were used in quantitative analyses: constraint-modified FAD and KIeff, both using elastic T-stress. These indicate that fracture is likely to initiate at lower (deep) tip, which is consistent with the limited high-speed video camera evidence. In general more systematic application of 2- parameter approaches is needed. ¿ Both local approach models predicted initiation of cleavage fracture first from the lower crack front for medium and higher loads. Concerning the capability to predict whether the cracks propagating into the cladding arrest or cause full fracture, the two analyses performed indicate that when the load at first pop-in is low, crack arrest in the clad can be correctly predicted on the basis of the J-R curve, but that further work is needed to ensure the reliability of such approaches over the full load range.JRC.F.4-Safety of future nuclear reactor

    Exact Numerical Solution of the BCS Pairing Problem

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    We propose a new simulation computational method to solve the reduced BCS Hamiltonian based on spin analogy and submatrix diagonalization. Then we further apply this method to solve superconducting energy gap and the results are well consistent with those obtained by Bogoliubov transformation method. The exponential problem of 2^{N}-dimension matrix is reduced to the polynomial problem of N-dimension matrix. It is essential to validate this method on a real quantumComment: 7 pages, 3 figure

    Mark-Recapture and Stochastic Population Models for Polar Bears of the High Arctic

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    We used mark-recapture data and population viability analysis (PVA) to estimate demographic parameters, abundance, and harvest risks for two adjacent populations of polar bears (Ursus maritimus) inhabiting Lancaster Sound and Norwegian Bay, Canada. Analyses were based on data from 1871 bears that were uniquely marked during the period 1972–97. Our best-fitting mark-recapture model specified sex and age effects on probabilities of survival and an effect of prior recapture (dependence) on capture probability. The most parsimonious solution in our analysis of survival was to assume the same rate for the Lancaster Sound and Norwegian Bay populations. Total (harvested) annual survival rates (mean ± 1 SE) for females included: 0.749 ± 0.105 (cubs), 0.879 ± 0.050 (ages 1–4), 0.936 ± 0.019 (ages 5– 20), and 0.758 ± 0.054 (ages 21+). Mean litter size was 1.69 ± 0.01 cubs for females of Lancaster Sound and 1.71 ± 0.08 cubs for females of Norwegian Bay. By age six, on average 0.31 ± 0.21 females of Lancaster Sound were producing litters (first age of reproduction was five years); however, females of Norwegian Bay did not reproduce until age seven or more. Total abundance (1995–97) averaged 2541 ± 391 bears in Lancaster Sound and 203 ± 44 bears in Norwegian Bay. The finite rate of increase (lambda) during the study period was estimated to be 1.001 ± 0.013 for bears of Lancaster Sound and 0.981 ± 0.027 for bears of Norwegian Bay. We incorporated demographic parameters into a harvest-explicit PVA to model short-term (15 yr) probabilities of overharvesting (i.e., 1997–2012). Our harvest simulations suggest that current levels of kill are approaching and perhaps exceeding the sustainable yield in both populations.Nous avons recouru aux données obtenues par marquage et recapture ainsi qu’aux analyses de viabilité de population pour estimer les paramètres démographiques, l’abondance et les risques liés à la récolte de deux populations adjacentes d’ours polaires (Ursus maritimus) évoluant dans le détroit de Lancaster et la baie Norwegian, au Canada. Les analyses reposaient sur les données relatives à 1 871 ours marqués de manière unique pendant la période allant de 1972 à 1997. Notre modèle de marquage et recapture le mieux ajusté tenait compte des effets du sexe et de l’âge sur les probabilités de survie, ainsi que de l’effet d’une recapture antérieure (dépendance) sur la probabilité de capture. La solution la plus parcimonieuse de notre analyse de survie consistait à assumer le même taux pour les populations du détroit de Lancaster et de la baie Norwegian. Les taux totaux de survie annuels (récoltés) (moyenne ± 1 SE) chez les femelles s’établissaient comme suit : 0,749 ± 0,105 (oursons), 0,879 ± 0,050 (âges 1-4), 0,936 ± 0,019 (âges 5-20), et 0,758 ± 0,054 (âges 21+). La grosseur moyenne des portées était de 1,69 ± 0,01 ourson dans le cas des femelles du détroit de Lancaster, et de 1,71 ± 0,08 ourson dans le cas des femelles de la baie Norwegian. Avant l’âge de six ans, en moyenne 0,31 ± 0,21 femelle du détroit de Lancaster produisait des portées (l’âge de reproduction le plus jeune était de cinq ans); cependant, les femelles de la baie Norwegian ne se reproduisaient pas avant l’âge de sept ans ou plus. L’abondance totale (1995-1997) atteignait en moyenne 2 541 ± 391 ours au détroit de Lancaster, et 203 ± 44 ours dans la baie Norwegian. Le taux fini d’augmentation (lambda) pendant la période d’étude était estimé à 1,001 ± 0,013 dans le cas des ours du détroit de Lancaster, et de 0,981 ± 0,027 dans le cas des ours de la baie Norwegian. Nous avons intégré les paramètres démographiques à une analyse de viabilité de population de récolte explicite pour modéliser les probabilités à court terme (15 ans) de surrécolte (i.e. 1997-2012). Nos simulations de récolte laissent croire que les taux d’ours tués approchent et peuvent même dépasser le rendement admissible des deux populations

    radR: an open-source platform for acquiring and analysing data on biological targets observed by surveillance radar

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    <p>Abstract</p> <p>Background</p> <p>Radar has been used for decades to study movement of insects, birds and bats. In spite of this, there are few readily available software tools for the acquisition, storage and processing of such data. Program radR was developed to solve this problem.</p> <p>Results</p> <p>Program radR is an open source software tool for the acquisition, storage and analysis of data from marine radars operating in surveillance mode. radR takes time series data with a two-dimensional spatial component as input from some source (typically a radar digitizing card) and extracts and retains information of biological relevance (i.e. moving targets). Low-level data processing is implemented in "C" code, but user-defined functions written in the "R" statistical programming language can be called at pre-defined steps in the calculations. Output data formats are designed to allow for future inclusion of additional data items without requiring change to C code. Two brands of radar digitizing card are currently supported as data sources. We also provide an overview of the basic considerations of setting up and running a biological radar study.</p> <p>Conclusions</p> <p>Program radR provides a convenient, open source platform for the acquisition and analysis of radar data of biological targets.</p

    Community pharmacists’ attitudes towards, and experiences of, providing medication reviews after hospital discharge: a questionnaire survey

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    ObjectivesTo investigate the attitudes and experiences of community pharmacists providing medicines-use review (MUR) and post-discharge medicines-use review (PD-MUR) services.MethodsAn online survey for community pharmacists who had experience providing the MUR service.Key findingsIn total, 495 community pharmacists responded to the survey. A total of 89% (n = 382) of community pharmacists wanted to receive the patient’s full discharge summary and 79% (n = 363) preferred electronic communication. Community pharmacists thought they could build trusted relationships with patients and felt that patients were willing to discuss post-discharge medicines-related issues with them. Less experienced pharmacists conducted more MURs than more experienced pharmacists (P = 0.004), and pharmacists working in large multiples (&gt;50 pharmacies) conducted more MURs than those working in independent pharmacies (ConclusionsCommunity pharmacists believe they have a vital role in supporting patients after hospital discharge. They can build long-lasting, trusted relationships with patients and patients are willing to discuss medication issues with them. By providing community pharmacists in all locations with timely access to accurate discharge information, they could use their knowledge and skills to better support patients after hospital discharge

    Treatment recommendations for psoriatic arthritis

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    Objective: To develop comprehensive recommendations for the treatment of the various clinical manifestations of psoriatic arthritis (PsA) based on evidence obtained from a systematic review of the literature and from consensus opinion. Methods: Formal literature reviews of treatment for the most significant discrete clinical manifestations of PsA (skin and nails, peripheral arthritis, axial disease, dactylitis and enthesitis) were performed and published by members of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA). Treatment recommendations were drafted for each of the clinical manifestations by rheumatologists, dermatologists and PsA patients based on the literature reviews and consensus opinion. The level of agreement for the individual treatment recommendations among GRAPPA members was assessed with an online questionnaire. Results: Treatment recommendations were developed for peripheral arthritis, axial disease, psoriasis, nail disease, dactylitis and enthesitis in the setting of PsA. In rotal, 19 recommendations were drafted, and over 80% agreement was obtained on 16 of them. In addition, a grid that factors disease severity into each of the different disease manifestations was developed to help the clinician with treatment decisions for the individual patient from an evidenced-based perspective. Conclusions: Treatment recommendations for the cardinal physical manifestations of PsA were developed based on a literature review and consensus between rheumatologists and dermatologists. In addition, a grid was established to assist in therapeutic reasoning and decision making for individual patients. It is anticipated that periodic updates will take place using this framework as new data become available
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