SciELO Brasil - Scientific Electronic Library Online
(53.052 recursos)
SciELO (Scientific Electronic Library Online) is an electronic library covering a selected collection of Brazilian scientific journals. The objective of the site is to implement an electronic virtual library, providing full access to a collection of serial titles, a collection of issues from individual serial titles, as well as to the full text of articles. The project envisages the development of a common methodology for the preparation, storage, dissemination and evaluation of scientific literature in electronic format.
Mostrando recursos 1 - 20 de 26
1.
Finding the closest Toeplitz matrix - Eberle,Maria Gabriela; Maciel,Maria Cristina
The constrained least-squares n × n-matrix problem where the feasibility set is the subspace of the Toeplitz matrices is analyzed. The general, the upper and lower triangular cases are solved by making use of the singular value decomposition. For the symmetric case, an algorithm based on the alternate projection method is proposed. The implementation does not require the calculation of the eigenvalue of a matrix and still guarantees convergence. Encouraging preliminary results are discussed.
2.
A weighted projection centering method - Moretti,Antonio Carlos
An iterative method for finding the center of a linear programming polytope is presented. The method assumes that we start at a feasible interior point and each iterate is obtained as a convex combination of the orthogonal projection on the half spaces defined by the linear inequalities plus a special projections on the same half spaces. The algorithm is particularly suitable for implementation on computers with parallel processors. We show some examples in two dimensional space to describe geometrically how the method works. Finally, we present computational results on random generated polytopes and linear programming polytopes from NetLib to compare...
3.
On the convergence properties of the projected gradient method for convex optimization - Iusem,A. N.
When applied to an unconstrained minimization problem with a convex objective, the steepest descent method has stronger convergence properties than in the noncovex case: the whole sequence converges to an optimal solution under the only hypothesis of existence of minimizers (i.e. without assuming e.g. boundedness of the level sets). In this paper we look at the projected gradient method for constrained convex minimization. Convergence of the whole sequence to a minimizer assuming only existence of solutions has also been already established for the variant in which the stepsizes are exogenously given and square summable. In this paper, we prove the...
4.
A mathematical formulation of the boundary integral equations for a compressible stokes flow - Cunha,Francisco Ricardo; Sousa,Aldo João de; Loewenberg,Michael
A general boundary integral formulation for compressible Stokes flows is theoretically described within the framework of hydrodynamic potentials. The integral equation is implemented numerically to the study of drop expansion in compressible viscous flows. Marker point positions on the drop interface are involved by using the boundary integral method for calculation of fluid velocity. Surface discretization is adaptive to the instantaneous drops shapes. The interplay between viscous and surface tension and its influence on the evolving emulsion microstructure during its expansion is fundamental to the science and technology of foam processing. In this article the method is applied for 3D...
5.
Optimal design of a plate of variable thickness: a variational approach in dimension one - Pedregal,Pablo; Donoso,Alberto
For a typical design problem of a plate of variable thickness, we analyze the one-dimensional situation through a variational reformulation to discover that, in contrast with the higher dimensional case, there are optimal solutions. Another typical interpretation of this simplification is that of the optimal shape of a bending beam. The mechanism employed for the existence issue is the direct method for the new formulation. Optimality conditions are then pursued.
6.
Generalized line criterion for Gauss-Seidel method - Garcia,M.V.P.; Humes Jr.,C.; Stern,J.M.
We present a module based criterion, i.e. a sufficient condition based on the absolute value of the matrix coefficients, for the convergence of Gauss-Seidel method (GSM) for a square system of linear algebraic equations, the Generalized Line Criterion (GLC). We prove GLC to be the ''most general'' module based criterion and derive, as GLC corollaries, some previously know and also some new criteria for GSM convergence. Although far more general than the previously known results, the proof of GLC is simpler. The results used here are related to recent research in stability of dynamical systems and control of manufacturing systems.
7.
Finite element approximation of bipolar viscous fluids - Manouzi,H.; Brahmi,A.; Farhloul,M.
A bipolar viscous fluid model is assumed to regularise the solution of Newtonian and quasi-Newtonian flows. In this article, a mixed finite element approximation of the bipolar viscous fluids is proposed. In this approximation the velocity of the fluid together with its laplacian are the most relevant unknowns. An existence and uniqueness results are proved. A mixed finite element approximation is derived and numerical results are presented.
8.
Approximate controllability for the semilinear heat equation in RN involving gradient terms - Menezes,Silvano Bezerra de
We prove the approximate controllability of the semilinear heat equation in R N, when the nonlinear term is globally Lipschitz and depends both on the state u and its spatial gradient Ñu. The approximate controllability is viewed as the limit of a sequence of optimal control problems. In order to avoid the difficulties related to the lack of compactness of the Sobolev embeddings, we work with the similarity variables and use weighted Sobolev spaces.
9.
Treatment of geophysical data as a non-stationary process - Rocha,Marcus P.C.; Leite,Lourenildo W.B.
The Kalman-Bucy method is here analized and applied to the solution of a specific filtering problem to increase the signal message/noise ratio. The method is a time domain treatment of a geophysical process classified as stochastic non-stationary. The derivation of the estimator is based on the relationship between the Kalman-Bucy and Wiener approaches for linear systems. In the present work we emphasize the criterion used, the model with apriori information, the algorithm, and the quality as related to the results. The examples are for the ideal well-log response, and the results indicate that this method can be used on a...
10.
Hermite spectral and pseudospectral methods for nonlinear partial differential equation in multiple dimensions - Cheng-Long,Xu; Ben-Yu,Guo
Hermite approximation in multiple dimensions is investigated. As an example, a spectral scheme and a pseudospectral scheme for the Logistic equation are constructed, respectively. The stability and the convergence of the proposed schemes are proved. Numerical results show the high accuracy of this new approach.
11.
Bounds for the subsistence of a problem of heat conduction - Barrea,Andrés; Turner,Cristina
In this paper, we consider a slab represented by the interval 0 < x < 1, at the initial temperature u0(x) > 0 and having a heat flux q(t) on the left face and a nonlinear condition on the right face x = 1. We consider the corresponding heat conduction problem and we assume that the phase-change temperature is 0ºC. We prove that certain conditions on the data are necessary and sufficient in order to obtain estimations of the occurrence of a phase-change in the material.
12.
A mathematical model for virus infection in a system of interacting computers - Gondar,J. López; Cipolatti,R.
We introduce a simplified theoretical model to describe a virtual virus propagation process in a set of interacting computers. The propagation mechanisms considered here are those related to the reception of messages through internet as well as the ones concerning the simple exchange of files using recording devices as compact disks or the commonly used floppy disks. In spite of its inherent simplicity, this model provides a good idea of the infection process and trends. From the mathematical point of view, the nonlinear delay integral equation that we obtain here presents certain interesting features which are explored and enlightened in...
13.
Alternant and BCH codes over certain rings - Andrade,A.A.; Interlando,J.C.; Palazzo Jr.,R.
Alternant codes over arbitrary finite commutative local rings with identity are constructed in terms of parity-check matrices. The derivation is based on the factorization of x s - 1 over the unit group of an appropriate extension of the finite ring. An efficient decoding procedure which makes use of the modified Berlekamp-Massey algorithm to correct errors and erasures is presented. Furthermore, we address the construction of BCH codes over Zm under Lee metric.
14.
Simultaneous exact control of piezoelectric systems in multilayered media - Kapitonov,Boris V.; Raupp,Marco Antonio
This paper considers a pair of transmission problems for the system of piezoelectricity having piecewise constant coefficients. Under suitable monotonicity conditions on the coefficients and certain geometric conditions on the domain and the interfaces where the coefficients have a jump discontinuity, results on simultaneous boundary observation and simultaneous exact control are established.
15.
Fuzzy Ostrowski type inequalities - Anastassiou,George A.
We present optimal upper bounds for the deviation of a fuzzy continuous function from its fuzzy average over [a,b] Ì R, error is measured in the D-fuzzy metric. The established fuzzy Ostrowski type inequalities are sharp, in fact attained by simple fuzzy real number valued functions. These inequalities are given for fuzzy Hölder and fuzzy differentiable functions and these facts are reflected in their right-hand sides.
16.
Exact solutions for drying with coupled phase-change in a porous medium with a heat flux condition on the surface - Santillan Marcus,Eduardo A.; Tarzia,Domingo A.
Exact solutions for the problem of drying with coupled phase change in a porous medium with a heat flux condition on x = 0 of the type - q0/ , with q0 > 0, for any value of the Luikov number Lu is obtained. This solution can be only obtained when q0 verifies a certain inequality. Besides, for large Luikov number (more precisely, Lu > ), we obtain that the temperature distribution t2 reaches to a minimum value which is smaller than its initial temperature or limit value reached at +¥.
17.
Damage theory: microscopic effects of vanishing macroscopic motions - Bonetti,Elena; Frémond,Michel
This paper deals with a mechanical model describing the evolution of damage in elastic and viscoelastic materials. The state variables are macroscopic deformations and a microscopic phase parameter, which is related to the quantity of damaged material. The equilibrium equations are recovered by refining the principle of virtual powers including also microscopic forces. After proving an existence and uniqueness result for a regularized problem, we investigate the behavior of solutions, in the case when a vanishing sequence of external forces is applied. By use of a rigorous asymptotics analysis, we show that macroscopic deformations can disappear at the limit, but...
18.
Infinite horizon differential games for abstract evolution equations - Shaiju,A.J.
Berkovitz's notion of strategy and payoff for differential games is extended to study two player zero-sum infinite dimensional differential games on the infinite horizon with discounted payoff. After proving dynamic programming inequalities in this framework, we establish the existence and characterization of value. We also construct a saddle point for the game.
19.
Steam injection into water-saturated porous rock - Bruining,J.; Marchesin,D.; Van Duijn,C.J.
We formulate conservation laws governing steam injection in a linear porous medium containing water. Heat losses to the outside are neglected. We find a complete and systematic description of all solutions of the Riemann problem for the injection of a mixture of steam and water into a water-saturated porous medium. For ambient pressure, there are three kinds of solutions, depending on injection and reservoir conditions. We show that the solution is unique for each initial data.
20.
A convergence result for an outer approximation scheme - Burachik,R.S.; Lopes,J.O.
In this work we study the variational inequality problem in finite dimensional spaces. The constraint set we consider has the structure of semi-infinite programming. Standard convergence analysis for outer approximation methods includes boundedness of the constraint set, or, alternatively, coerciveness of the data. Using recession tools, we are able to replace these assumptions by the hypotheses of boundedness of the solution set and that the domain of the operator contains the constraint set.
1.
, with q0 > 0, for any value of the Luikov number Lu is obtained. This solution can be only obtained when q0 verifies a certain inequality. Besides, for large Luikov number (more precisely, Lu > 
), we obtain that the temperature distribution t2 reaches to a minimum value which is smaller than its initial temperature or limit value reached at +¥. 