Resumo em Inglês:

We introduce a weak formulation for a system of electrostatic and hydrodynamic equations modelling the electrophoretic motion of charged particles in ionized fluids. We obtain a local in time existence theorem, using the results established in [11] and properties of the solutions of the Poisson-Boltzmann equation. These properties follows from singular integral operators techniques.

Resumo em Inglês:

We study the Riemann problem with forward combustion due to injection of air into a porous medium containing solid fuel. We neglect air compressibility and heat loss to the rock formation. Given initial reservoir and injection conditions, we prove that there is a unique time asymptotic wave sequence for combustion with complete oxygen consumption. The sequence consists of a region of unburned air at injection temperature, a warming discontinuity, a hot region with unburned air, a combustion wave and a region with burned air and unburned fuel at the initial reservoir temperature. The waves have very different speeds, and therefore they cannot be detected in laboratory experiments that focus on the combustion wave. However, they should occur in field scale. By introducing a cut-off in Arrhenius' law, the reaction rate vanishes at reservoir temperature, and two types of wave sequences are possible. One was already described. The other occurs for incomplete oxygen consumption. In this case, the wave sequence contains another wave, i.e., there is another region ahead of the combustion wave containing incompletely burned air at reservoir temperature, and a gas composition discontinuity that moves fast. However, instead of a unique solution for each Riemann data, there is a one parameter family of wave speeds and strengths. This multiplicity of solutions may to be due to the cut-off.

Resumo em Inglês:

Acid injection in porous medium is a process widely used for stimulation of petroleum wells and leads to the formation of highly conductive channels called wormholes. Two different transport-reaction models have been developed in Part I to describe the phenomenon at the core-scale. The possible existence of core-scale effective properties which appear in these models is discussed here on the basis of Darcy-scale numerical experiments. The advantages and drawbacks of one-equation and two-equation models are investigated by reference to averaged fields computed from Darcy-scale simulations.

Resumo em Inglês:

The versatility of a robot to perform a task is limited principally by the flexibilityof its end-effector. In the last years, research has been focused on the development of a hand with several fingers since these devices are capable of manipulating and grasping objects of different forms. A dexterous manipulation system, composed of a robot hand with several fingers and an object that will be held or manipulated, could be modeled as a set of rigid bodies in contact. The dynamics of several rigid bodies in contact tries to predict the accelerations and forces at the contact points of the set of rigid bodies with Coulomb friction. The calculation of such forces allows us to determine if the contact is maintained or disappears and to plan a determined action. The equations that describe the problem form a system of differential algebraic equations. In this contribution the problem is reformulated as a mixed nonlinear complementarity problem (MNCP). Then, an optimization problem with box constraints associated to the MNCP is presented using an adequate merit function. Conditions about the equivalence between the problems are established. Finally, the optimization problem is solved using a robust and efficient algorithm. Encouraging numerical results are reported.

Resumo em Inglês:

In this paper, we describe a new primal-dual path-following method to solve a convex quadratic program (QP). The derived algorithm is based on new techniques for finding a new class of search directions similar to the ones developed in a recent paper by Darvay for linear programs. We prove that the short-update algorithm finds an epsilon-solution of (QP) in a polynomial time.

Resumo em Inglês:

We study the effect of the nonlinear dependence of the iterate x k of Conjugate Gradients method (CG) from the data b in the GCV procedure to stop the iterations. We compare two versions of using GCV to stop CG. In one version we compute the GCV function with the iterate x k depending linearly from the data b and the other one depending nonlinearly. We have tested the two versions in a large scale problem: positron emission tomography (PET). Our results suggest the necessity of considering the nonlinearity for the GCV function to obtain a reasonable stopping criterion.