1,721,500 research outputs found
An effective strategy for combining variance- and distribution-based global sensitivity analysis
Full text linkWe present a new strategy for performing global sensitivity analysis capable to estimate main and interaction effects from a generic sampling design. The new strategy is based on a meaningful combination of variance- and distribution-based approaches. The strategy is tested on four analytic functions and on a hydrological model. Results show that the analysis is consistent with the state-of-the-art Saltelli/Jansen formula but to better quantify the interaction effect between the input factors when the output distribution is skewed. Moreover, the estimation of the sensitivity indices is much more robust requiring a smaller number of simulations runs. Specific settings and alternative methods that can be integrated in the new strategy are also discussed. Overall, the strategy is considered as a new simple and effective tool for performing global sensitivity analysis that can be easily integrated in any environmental modelling framework
A general probabilistic framework for uncertainty and sensitivity analysis of deterministic models
No full textUncertainty and sensitivity analysis are valuable tools for the assessment of model applications and several methods were developed in the last decades. However, the applicability of these methods is limited to scalar parameters and in many cases the analysis is still made by One-A-Time methods. These severely constrain the ability of a general assessment of the model in practical applications. In this study a general probabilistic framework for uncertainty and sensitivity analysis of deterministic models is presented. The approach is able to consider all the sources of uncertainty i.e., input, distributed parameters and model structure. In this context a global uncertainty analysis is used as a tool to evaluate the performance of the model. A global sensitivity analysis based on Sobol's method is then used as complementary tool to find the most important sources of uncertainty. The framework is used in a loop to optimize the further activities and improve the performance of the model in a goal-oriented approach. The effectiveness of the framework is demonstrated with an example with SWAP model, a 1D physicalbased hydrological model. The procedure is applied in a cropped field in Northern Germany for the year 2011. The simulation results are compared with the soil moisture detected in the root zone and considering the variance of evapotranspiration and bottom fluxes below the root zone simulated by the model. The results show that the errors in the estimation of evapotranspiration and bottom fluxes are negatively correlated. In this way the evaluation of the soil moisture alone can not be seen as a good assessment of the model performance. Finally, the sources of uncertainty are different for each process and improvement of the performance of the model strictly depends on the output considered
Nonalcoholic Fatty Liver Disease: Basic Pathogenetic Mechanisms in the Progression from NAFLD to NASH
No full textNonalcoholic fatty liver disease (NAFLD) represents a growing cause of chronic liver injury, especially in western countries, where it is becoming the most frequent indication for liver transplantation. Nonalcoholic fatty liver disease encompasses a spectrum of diseases that from simple steatosis (pure NAFLD) can progress to nonalcoholic steatohepatitis (NASH), cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD and the mechanisms behind its progression to NASH have been extensively studied. However, although the processes that determine fat accumulation are mostly clear, the mechanisms associated with the progression of the disease are not fully characterized. In predisposed patients, lipid accumulation can promote lipotoxicity and mitochondrial dysfunction, thus triggering hepatocyte death, inflammation and fibrosis. The specific role of different lipids has been identified and free fatty acids as well as free cholesterol have been identified as toxic species. To make the picture more complex, the pathogenesis of NAFLD involves pathological connections between several organs, including the adipose tissue and the gut, with the liver. The "inflamed" adipose tissue plays a key role in the release of toxic lipids, whereas alterations in the gut-liver axis have been associated with the progression from NAFLD to NASH mediated by dysbiosis, alteration of intestinal barrier, and finally bacterial translocation, which can trigger proinflammatory and profibrogenetic pathways, finally leading to cirrhosis development
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mild impact of SARS-CoV-2 infection on the entire population of liver transplant recipients: the experience of an Italian Centre based in a high-risk area
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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