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Model Algorithm (model + algorithm)
Selected AbstractsOn scientists' discomfort in fisheries advisory science: the example of simulation-based fisheries management-strategy evaluationsFISH AND FISHERIES, Issue 2 2010Sarah B M Kraak Abstract Scientists feel discomfort when they are asked to create certainty, where none exists, for use as an alibi in policy-making. Recently, the scientific literature has drawn attention to some pitfalls of simulation-based fisheries management-strategy evaluation (MSE). For example, while estimates concerning central tendencies of distributions of simulation outcomes are usually fairly robust because they are conditioned on ample data, estimates concerning the tails of distributions (such as the probability of falling below a critical biomass) are usually conditional on few data and thus often rely on assumptions that have no strong knowledge base. The clients of scientific advice, such as the European Commission, are embracing the mechanization of the evaluation of proposed Harvest Control Rules against the precautionary principle and management objectives. Where the fisheries management institutions aim for simple answers from the scientists, giving ,green/red light' to a proposed management strategy, the scientists are forced into a split position between satisfying the demands of their advisory role and living up to the standards of scientific rigour. We argue against the mechanization of scientific advice that aims to incorporate all relevant processes into one big model algorithm that, after construction, can be run without circumspection. We rather encourage that fisheries advice should be a dynamic process of expert judgement, incorporating separate parallel concurrent, lines of scientific evidence, from quantitative and qualitative modelling exercises and factual knowledge of the biology and the fishery dynamics. This process can be formalized to a certain degree and can easily accommodate stakeholder viewpoints. [source] Fire disturbance disrupts co-occurrence patterns of terrestrial vertebrates in Mediterranean woodlandsJOURNAL OF BIOGEOGRAPHY, Issue 5 2006Maurizio Sarà Abstract Aim, This paper uses null model analysis to explore the pattern of species co-occurrence of terrestrial vertebrate fauna in fire-prone, mixed evergreen oak woodlands. Location, The Erico,Quercion ilicis of the Mediterranean belt (50,800 m a.s.l.) in the Madonie mountain range, a regional park in northern Sicily (37°50, N, 14°05, E), Italy. Methods, The stratified sampling of vertebrates in a secondary succession of recent burned areas (BA, 1,2 years old), intermediate burned areas (INT, 4,10 years old) and ancient burned areas (CNB, > 50 years old), plus forest fragments left within burned areas (FF, 1,2 years old) permitted the comparison of patterns of species co-occurrence using a set of separate presence/absence matrices. First, the breeding avifauna derived from standardized point counts was analysed using Stone & Roberts'C -score, and by a null model algorithm (fixed/equiprobable). Secondly, the analysis was repeated using all vertebrate species recorded in the succession. Results, Sixty-five species were recorded in the 2-year study period in the four sample treatments. Birds were found to make up the largest component (63%) of the recorded assemblage. The BA treatment had the lowest species richness, followed in order by the small, medium and large FFs, and then by the CNBs. For both analyses (birds and total vertebrates), the C -scores were quite small and not significantly different from those that could be expected by chance in the BA and INT burned areas; this indicates a random co-occurrence among vertebrates of those assemblages. Contrariwise, for both analyses in the CNBs, the C -scores were large and significantly different from the simulated indices, thereby indicating a non-random co-occurrence pattern (segregation) of vertebrates in the undisturbed woodlands. In addition, C -score values for the surviving FFs show a significant aggregation of species. Main conclusions, The null model analyses highlighted a new aspect of fire disturbance in Mediterranean woodland ecosystems: the disruption in patterns of co-occurrence in the terrestrial vertebrate community. Wildfire alters community organization, inducing, for at least 10 years, a random aggregate of species. Communities re-assemble themselves, showing the occurrence of species segregation at least 50 years after fire. [source] Optimal foraging on the roof of the world: Himalayan langurs and the classical prey modelAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010Ken Sayers Abstract Optimal foraging theory has only been sporadically applied to nonhuman primates. The classical prey model, modified for patch choice, predicts a sliding "profitability threshold" for dropping patch types from the diet, preference for profitable foods, dietary niche breadth reduction as encounter rates increase, and that exploitation of a patch type is unrelated to its own abundance. We present results from a 1-year study testing these predictions with Himalayan langurs (Semnopithecus entellus) at Langtang National Park, Nepal. Behavioral data included continuous recording of feeding bouts and between-patch travel times. Encounter rates were estimated for 55 food types, which were analyzed for crude protein, lipid, free simple sugar, and fibers. Patch types were entered into the prey model algorithm for eight seasonal time periods and differing age-sex classes and nutritional currencies. Although the model consistently underestimated diet breadth, the majority of nonpredicted patch types represented rare foods. Profitability was positively related to annual/seasonal dietary contribution by organic matter estimates, whereas time estimates provided weaker relationships. Patch types utilized did not decrease with increasing encounter rates involving profitable foods, although low-ranking foods available year-round were taken predominantly when high-ranking foods were scarce. High-ranking foods were taken in close relation to encounter rates, while low-ranking foods were not. The utilization of an energetic currency generally resulted in closest conformation to model predictions, and it performed best when assumptions were most closely approximated. These results suggest that even simple models from foraging theory can provide a useful framework for the study of primate feeding behavior. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Structural Change in U.S. Presidents' Use of ForceAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 3 2010Jong Hee Park Has there been a structural change in the way U.S. presidents use force abroad since the nineteenth century? In this article, I investigate historical changes in the use of force by U.S. presidents using Bayesian changepoint analysis. In doing so, I present an integrated Bayesian approach for analyzing changepoint problems in a Poisson regression model. To find the nature of the breaks, I estimate parameters of the Poisson regression changepoint model using Chib's (1998) hidden Markov model algorithm and Frühwirth-Schnatter and Wagner's (2006) data augmentation method. Then, I utilize transdimensional Markov chain Monte Carlo methods to detect the number of breaks. Analyzing yearly use of force data from 1890 to 1995, I find that, controlling for the effects of the Great Depression and the two world wars, the relationship between domestic conditions and the frequency of the use of force abroad fundamentally shifted in the 1940s. [source] Diagnostic Accuracy of the Gail Model in the Black Women's Health StudyTHE BREAST JOURNAL, Issue 4 2007Lucile L. Adams-Campbell PhD Abstract:, The Gail model is used to predict the risk of breast cancer in women of diverse race/ethnic groups for clinical trial protocols. However, this model has only been validated in US white women. Using a nested case-control study design, we evaluated the diagnostic accuracy of the original Gail model (GM) and that of the revised Gail model algorithm for blacks/African-Americans (GM-B) in the Black Women's Health Study (BWHS). Risk profiles were derived via a self reported questionnaire at the time of enrollment into the BWHS in 1995. Biennial questionnaires were obtained from the participants to determine the incident cases of breast cancer. The study of 725 breast cancer cases and 725 controls revealed that the 5-year risk of breast cancer based on the GM ranged from 0.2% to 15.4% among cases and 0.2% to 13.6% among the controls. Based on the GM-B, the 5-year risk of breast cancer ranged from 0.2% to 8.7% among cases and 0.2% to 7.2% among the controls. The sensitivities of the GM and GM-B model with the standard cutoff of 1.7% were 17.9% (95% CI: 15.9,19.9%) and 4.1% (95% CI: 3.0,5.2), respectively. Both the original and the modified version of the Gail model underestimate the risk of developing breast cancer in African-American women. More importantly, the modified Gail Model (GM-B) does a worse job at predicting the development of breast cancer for blacks than the original model (GM). [source] Global Model for Optimizing Crossflow Microfiltration and Ultrafiltration Processes: A New Predictive and Design ToolBIOTECHNOLOGY PROGRESS, Issue 4 2005Gautam Lal Baruah A global model and algorithm that predicts the performance of crossflow MF and UF process individually or in combination in the laminar flow regime is presented and successfully tested. The model accounts for solute polydispersity, ionic environment, electrostatics, membrane properties and operating conditions. Computer programs were written in Fortran 77 for different versions of the model algorithm that can optimize MF/UF processes rapidly in terms of yield, purity, selectivity, or processing time. The model is validated successfully with three test cases: separation of bovine serum albumin (BSA) from hemoglobin (Hb), capture of immunoglobulin (IgG) from transgenic goat milk by MF, and separation of BSA from IgG by UF. These comparisons demonstrate the capability of the global model to conduct realistic in silico simulations of MF and UF processes. This model and algorithm should prove to be an invaluable technique to rapidly design new or optimize existing MF and UF processes separately or in combination in both pressure-dependent and pressure-independent regimes. [source] | |||||||||||||