Search results for "modeling"
showing 10 items of 4489 documents
A Multidisciplinary Approach to the Analysis of Multifactorial Land Mammal Colonization of Islands
2013
A highly debated question that engages paleontologists, zoogeographers, and zoologists is how terrestrial mammals colonize islands. The question’s oversimplification and the subjective and partial responses to it have led to reductionist models. Insular faunas and fossil assemblages result from a complex interaction of geological, biological (in a broad sense), climatic, eustatic, taphonomic, and historical processes. Insular assemblages and their accompanying variables should be investigated on a case-by-case basis. In this article, we discuss not only common misconceptions and their potential origins but also the key issues that should be addressed when dealing with the colonization of is…
Molecular analysis of the fungal microbiome associated with the olive fruit fly Bactrocera oleae
2015
Abstract A molecular approach was used to investigate the fungal microbiome associated with Bactrocera oleae a major key pest of Olea europea , using the ITS2 region of the ribosomal DNA (rDNA) as barcode gene. Amplicons were cloned and a representative number of sequenced fragments were used as barcode genes for the identification of fungi. The analysis of the detected sequence types (STs) enabled the identification of a total of 34 phylotypes which were associated with 10 fungal species, 3 species complexes and 8 genera. Three phylotypes remained unresolved within the order Saccharomycetales and the phylum Ascomycota because of the lack of closely related sequences in GenBank. Cladosporiu…
Effect of attitudes toward Physical Education on motives to sport practice outside school hours
2016
[Resumen] La literatura especializada destaca la relación entre la participación de los adolescentes en actividades físicas y diversos beneficios físicos y psicosociales. Sin embargo, la actividad física de los adolescentes está por debajo de lo necesario para disfrutar de una buena salud física y psicológica. Existe consenso en que la Educación Física puede ayudar a los adolescentes a implicarse en actividades físicas y promover estilos de vida saludables. Por ello, el objetivo de este trabajo ha sido analizar la relación entre las actitudes hacia la Educación Física y los motivos para la práctica deportiva fuera del horario escolar. Han participado 428 alumnos de Educación Secundaria y 1º…
Effects of nonlinearity and substrate’s deformability on modulation instability in NKG equation
2017
International audience; This article investigates combined effects of nonlinearities and substrate's deformability on modulational instability. For that, we consider a lattice model based on the nonlinear Klein-Gordon equation with an on-site potential of deformable shape. Such a consideration enables to broaden the description of energy-localization mechanisms in various physical systems. We consider the strong-coupling limit and employ semi-discrete approximation to show that nonlinear wave modulations can be described by an extended nonlinear Schrodinger equation containing a fourth-order dispersion component. The stability of modulation of carrier waves is scrutinized and the following …
Backbone of credit relationships in the Japanese credit market
2016
We detect the backbone of the weighted bipartite network of the Japanese credit market relationships. The backbone is detected by adapting a general method used in the investigation of weighted networks. With this approach we detect a backbone that is statistically validated against a null hypothesis of uniform diversification of loans for banks and firms. Our investigation is done year by year and it covers more than thirty years during the period from 1980 to 2011. We relate some of our findings with economic events that have characterized the Japanese credit market during the last years. The study of the time evolution of the backbone allows us to detect changes occurred in network size,…
Spanning Trees and bootstrap reliability estimation in correlation based networks
2007
We introduce a new technique to associate a spanning tree to the average linkage cluster analysis. We term this tree as the Average Linkage Minimum Spanning Tree. We also introduce a technique to associate a value of reliability to links of correlation based graphs by using bootstrap replicas of data. Both techniques are applied to the portfolio of the 300 most capitalized stocks traded at New York Stock Exchange during the time period 2001-2003. We show that the Average Linkage Minimum Spanning Tree recognizes economic sectors and sub-sectors as communities in the network slightly better than the Minimum Spanning Tree does. We also show that the average reliability of links in the Minimum …
Volatility Effects on the Escape Time in Financial Market Models
2008
We shortly review the statistical properties of the escape times, or hitting times, for stock price returns by using different models which describe the stock market evolution. We compare the probability function (PF) of these escape times with that obtained from real market data. Afterwards we analyze in detail the effect both of noise and different initial conditions on the escape time in a market model with stochastic volatility and a cubic nonlinearity. For this model we compare the PF of the stock price returns, the PF of the volatility and the return correlation with the same statistical characteristics obtained from real market data.
A Phenomenological Operator Description of Dynamics of Crowds: Escape Strategies
2015
Abstract We adopt an operatorial method, based on creation, annihilation and number operators, to describe one or two populations mutually interacting and moving in a two-dimensional region. In particular, we discuss how the two populations, contained in a certain two-dimensional region with a non-trivial topology, react when some alarm occurs. We consider the cases of both low and high densities of the populations, and discuss what is changing as the strength of the interaction increases. We also analyze what happens when the region has either a single exit or two ways out.
On the equivalence between the Scheduled Relaxation Jacobi method and Richardson's non-stationary method
2017
The Scheduled Relaxation Jacobi (SRJ) method is an extension of the classical Jacobi iterative method to solve linear systems of equations ($Au=b$) associated with elliptic problems. It inherits its robustness and accelerates its convergence rate computing a set of $P$ relaxation factors that result from a minimization problem. In a typical SRJ scheme, the former set of factors is employed in cycles of $M$ consecutive iterations until a prescribed tolerance is reached. We present the analytic form for the optimal set of relaxation factors for the case in which all of them are different, and find that the resulting algorithm is equivalent to a non-stationary generalized Richardson's method. …
A computational method for the Helmholtz equation in unbounded domains based on the minimization of an integral functional
2012
Abstract We study a new approach to the problem of transparent boundary conditions for the Helmholtz equation in unbounded domains. Our approach is based on the minimization of an integral functional arising from a volume integral formulation of the radiation condition. The index of refraction does not need to be constant at infinity and may have some angular dependency as well as perturbations. We prove analytical results on the convergence of the approximate solution. Numerical examples for different shapes of the artificial boundary and for non-constant indexes of refraction will be presented.