1,720,962 research outputs found
Identification and Simulation of a Spatial Ecological Model in a Lake with Fractal Boundary
No full textWe propose a 2D ecological model of phytoplankton dynamics accounting for the distribution and the evolution of algae in a large basin located in the Amazonian region. The model is described by a set of reaction-drift-diffusion equations and is driven by several exogenous inputs, such as wind velocity and direction, water temperature and solar radiation. Due to the roughness of the domain, a preliminary boundary extraction with a curvelet algorithm is performed. Then, the model is simulated in an approximated domain, where the contour has been reconstructed by estimating a set of Recurrent Fractal Interpolation Functions, aimed at preserving its fractal structure. Simulations are combined with time and space chlorophyll-a data in order to estimate the parameters of the model. The proposed algorithm is based on an iterative two-step identification procedure, where reaction parameters are recovered first and then used for estimating diffusion and transport parameters. Comparison results at different accuracy approximations and before and after the algorithm implementation are presented and discussed
Mathematical modelling and parameter estimation of the Serra da Mesa basin
No full textThis work concerns the development and calibration of several classes of mathematical models describing ecological and bio-geochemical aspects of aquatic systems. We focus our experimental analysis on the Serra da Mesa lake in Brazil, from which the biological information is extracted by real online measurements provided by the SIMA monitoring program of the Brazilian Institute for Space Research (INPE).
A preliminary analysis is carried out so as to define the input-output data to be accounted for by the models. Furthermore, several classes of mathematical models are considered for fitting real data of biological processes. In order to do that, a two-step parameter identification/validation procedure is applied: the first step uses the integrals of the differential equations to reduce the nonlinear estimation problem to a linear least squares one. The parameter vector resulting from the first step is used for initializing a nonlinear minimization procedure. The results are discussed to assess the fitting performances of the physical and black-box models proposed in the paper. Several simulations are presented that could be used for developing scenario analysis and managing the real system
Homogenization of multi-species reaction-diffusion systems in domains with rough boundaries
No full textWe address the problem of parametrizing the boundary data for reaction‐diffusion partial differential equations associated to distributed systems that possess rough boundaries. Using techniques from homogenization theory and multiple‐scale analysis we present the effective equation and boundary conditions that are satisfied by the homogenized solution. We present numerical simulations that validate our theoretical results
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
Linear least squares parameter estimation of nonlinear reaction diffusion equations
No full textThis paper concerns with the development of a direct parameter identification procedure for a class of nonlinear reaction-diffusion equations. We assume to know the model equations with the exception of a set of constant parameters, such as diffusivity and reaction term parameters. Using the finite element method the original partial differential equation is transformed into a set of ordinary differential equations. A linear least squares method is then applied to estimate the unknown parameters by using normal equations. The measurements errors obtained following this approach are significantly lower than the error obtained by a nonlinear least squares identification procedure. In order to better understand the differences between the two approaches, a sensitivity analysis with respect to initial conditions and mesh dimension is performed. The robustness of the method is tested on noise corrupted data, showing that the linear least square method may be sensitive to perturbations in the data. The procedure is applied to two ecological models describing the dynamics of population growth. © 2011 IMACS
Effective rough boundary parametrization for reaction-diffusion systems
No full textWe address the problem of parametrizing the boundary data for reaction-diffusion partial differential equations associated to distributed systems that possess rough boundaries. The boundaries are modeled as fast oscillating periodic structures and are endowed with Neumann or Dirichlet boundary conditions. Using techniques from homogenization theory and multiple-scale analysis we derive the effective equation and boundary conditions that are satisfied by the homogenized solution. We present numerical simulations that validate our theoretical results and compare it with the alternative approach based on solving the same equation with a smoothed version of the boundary. The numerical tests show the accuracy of the homogenized solution to the effective system vis a vis the numerical solution of the original differential equation. The homogenized solution is shown undergoing dynamical regime shifts, such as anticipation of pattern formation, obtained by varying the diffusion coefficient
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
Strumenti di simulazione per il controllo di gestione: dall’analisi dei sistemi alla System Dynamics
No full textIl contributo prende in analisi le potenzialità che gli strumenti di simulazione possono avere ai fini di una migliore comprensione e gestione di sistemi complessi, proponendo in tal senso anche un esempio relativo ad un caso operativ
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