1,720,963 research outputs found
HDG methods and data-driven techniques for the van Roosbroeck model and its applications
Full text linkNoninvasive estimation of doping inhomogeneities in semiconductors is relevant for many industrial applications.
The goal is to estimate experimentally the unknown doping profile of a semiconductor by means of reproducible, indirect and non--destructive measurements.
A number of technologies (such as LBIC, EBIC and LPS) have been developed which allow the indirect detection of doping variations via photovoltaic effects. The idea is to illuminate the sample at several positions while measuring
the resulting voltage drop or current at the contacts.
These technologies lead to inverse problems for which we still do not have a complete theoretical framework.
In this thesis, we present three different data-driven approaches based on least squares, multilayer perceptrons, and residual neural networks.
We compare the three strategies after having optimized the relevant hyperparameters and we measure the robustness
of our approaches with respect to noise.
The methods are trained on synthetic data sets (pairs of discrete doping profiles and corresponding photovoltage signals at different illumination positions) which are generated by a numerical solution of the forward problem using a physics-preserving finite volume method stabilized using the Scharfetter--Gummel scheme.
In view of the need of generating larger datasets for trainings, we study the possibility to apply high-order Discontinuous Galerkin methods to the forward problem, preserving the stability properties of the Scharfetter--Gummel scheme.
We prove that the Hybridizable Discontinuous Galerkin methods (HDG), a family of high-order DG methods, are equivalent to the Scharfetter--Gummel scheme on uniform unidimensional grids for a specific choice of the HDG stabilization parameter.
This result is generalized to two and three dimensions using an approach based on weighted scalar products, and on local Slotboom changes of variables. We show that the proposed numerical scheme is well-posed, and numerically validate that it has the same properties of classical HDG methods, including optimal convergence
and superconvergence of postprocessed solutions. For polynomial degree zero, dimension one, and vanishing HDG
stabilization parameter, W-HDG coincides with the Scharfetter-Gummel stabilized finite volume scheme (i.e., it produces the same system matrix)
A weighted Hybridizable Discontinuous Galerkin method for drift-diffusion problems
Full text linkIn this work we propose a weighted hybridizable discontinuous Galerkin method
(W-HDG) for drift-diffusion problems. By using specific exponential weights
when computing the product in each cell of the discretization, we are
able to mimic the behavior of the Slotboom variables, and eliminate the drift
term from the local matrix contributions, while still solving the problem for
the primal variables. We show that the proposed numerical scheme is well-posed,
and validate numerically that it has the same properties as classical HDG
methods, including optimal convergence, and superconvergence of postprocessed
solutions. For polynomial degree zero, dimension one, and vanishing HDG
stabilization parameter, W-HDG coincides with the Scharfetter-Gummel finite
volume scheme (i.e., it produces the same system matrix). The use of local
exponential weights generalizes the Scharfetter-Gummel scheme (the
state-of-the-art for finite volume discretization of transport dominated
problems) to arbitrary high order approximations.Comment: 28 pages, 4 figures, 4 table
Stochastic effects on plankton dynamics: Insights from a realistic 0-dimensional marine biogeochemical model
Full text linkMarine ecosystems exist in a noisy and uncertain environment, not governed by deterministic laws. The development of ecological communities is significantly influenced by variability, and the interaction between nonlinearity and stochastic processes can lead to phenomena that deterministic models cannot explain. Plankton, forming the base of the marine food web, are highly affected by stochastic fluctuations due to their short reproductive timescales. Investigating the effects of noise on plankton growth is essential for accurately describing and predicting marine health. We present a realistic biogeochemical model where multiplicative white noise represents environmental stochasticity affecting plankton. The model suggests ergodic properties in the presence of stochastic fluctuations, with temporal and ensemble distributions being coherent. Analytical and numerical analyses reveal that, given sufficiently low noise intensity, dynamics near equilibrium resemble an Ornstein-Uhlenbeck additive process. With higher noise intensities, resonance occurs, particularly when endogenous dynamics are periodic. The results indicate that low noise intensity can positively influence plankton persistence with an higher number of species coexisting, while higher noise intensity can establish a new equilibrium in the system
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
Variations 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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