Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

In this work, we study biharmonic surfaces that are parameterized by biharmonic coordinate functions. We study a class of biharmonic surfaces called graph-type biharmonic surfaces. Also, we define a class of surfaces associated to two harmonic functions (FH2A-surfaces), these surfaces satisfy a relation between the Gaussian curvature, the projection of the Gauss map on a fixed plane and two harmonic functions. We show that a particular class of graph-type biharmonic surfaces are FH2A-surfaces. Finally, we classify the FH2A-surfaces of rotation.

The goal of this paper is to show explicitly the construction of a Cartan-Eilenberg system for the twisted equivariant K-theory groups of a finite G-CW complex, with G a finite group. Such a system defines a spectralsequence, whose second page is given by the Cˇech cohomology of a presheaf associated to projective representations of isotropy groups.

The quotient of an algebraic variety by action of an algebraic group does not always has a variety structure. The aim of this work is to describe a methodfor constructing good quotients, in the sense of Geometric invariant theory, in algebraicgeometry.

In this paper, we present a characterization of the convergence on the n-th order Grassmannian that permits us to show in a direct way that this set is compact and every vector bundle is measurable. Finally, we obtain a criterion to induce measurable bundles.

In this work, maximum flows observed in the Paranapanema river basin are modeled by a mixture of two GEV distributions whose components correspond to the summer and winter subpopulations. The nonlinear discriminant function allowed to confirm the assumption of mixture model.The proposed model is then used to determine probabilities of exceedance and return periods associated with extreme flows, which are of fundamental importance for hydraulic projects. The results show significant differences when a mixture model is used and therefore an approach more coherent with the observed data.

This paper presents a literature review of the Vehicle Routing Problem (VRP) applied to natural disasters in South America. The review focuses on the last ten years (2009 - 2019), in free access and paid databases.83% are in Spanish and 17% in English. Most of the investigations deal with shipping and delivery of products, but there are also papers on programming and routing of personnel, such as volunteers, humanitarian logistics specialists, medical personnel, and military personnel. In the review, several characteristics of the problem have been taken into account, such as, the type of disaster, the VRP model used, the solution method employed, the use or not of parameters with uncertainty. The 65 % of investigations were found in databases of free access, 83 % are deterministic models, the most used model is the classic VRP, the exact solution methods are the most used, followed by the metaheuristics (mainly the genetic algorithms). It is hoped that this work will serve to give a general perspective on the application of VRP to disaster problems, as well as to serve as a background for work in this area.

In this work, a basic epidemiological model is used to determine the evolution of COVID-19 in each of the regions of Peru. For determining the parameters of the model which characterize a certain epidemic, the reports of infected, deceased and recovered people provided by the Regional Health Management of Peru are used. As a result, we obtained the configuration of the infected, susceptible and removed which are consistent with the existing bibliography, thus we also obtain a time interval in which there is a considerable number of infected, the maximum number of infected and the date on which it occurs.

The present study proposes the use of a segmented SIR-D mathematical model to predict the evolution of epidemiological populations of interest in the COVID-19 pandemic (Susceptible [S], Infected [I], Recovered [R] and dead [D]), information that is often key to guiding decision-making in the fight against epidemics. In order to obtain a better model calibration and a lower prediction error in the short term, we performed the model segmentation in 6 stages of periods of 14 days each. At each stage, the epidemiological  that define the system of equations are empirically estimated by linear regression of the epidemiological surveillance data that the Peruvian Ministry of Health collects and reports daily. This strategy showed better model calibration compared to an unsegmented SIR-D model.

In this paper analyzed the stability of linear systems with continuous Markovian jumps. Firstly, the conditions for the Markov chain to be homogeneous and the state space is finite are imposed. Then the types of stability are presented, for example quadratic average stability, stochastic stability, exponential stability and almost certain stability. Stability in quadratic mean is analyzed by the real part of the eigenvalues of a certain matrix. Finally, an equation of Lyapunov is presented.

In this work we gather works from the literature that present the qualitative study via linear semigroups to the Timoshenko Beams System with dissipative mechanisms. Such problems do not have an analytical solution, but with the use of the exponentials theory of non-limited operators and Functional Analysis tools, it is possible to perform the asymptotic analysis for the models presented. Therefore, the objective of the work is accomplish a numerical analysis, using finite difference methods. We show that the qualitative results, proven by the semigroup theory, are verified for beam with concrete material and aluminum material.