Augmented interface systems for the Darcy-Stokes problem

In this paper we study interface equations associated to the Darcy-Stokes problem using the classical Steklov-Poincaré approach and a new one called augmented. We compare these two families of methods and characterize at the discrete level suitable preconditioners with additive and multiplicative structures. Finally, we present some numerical results to assess their behavior in presence of small physical parameters

Numerical approximation of a steady MHD problem

We consider a magnetohydrodynamic (MHD) problem which models the steady flow of a conductive incompressible fluid confined in a bounded region and subject to the Lorentz force exerted by the interaction of electric currents and magnetic fields. We present an iterative method inspired to operator splitting to solve this nonlinear coupled problem, and a discretization based on conforming finite elements

Changing Landscapes: The Provincial Text in Russian-Soviet Culture. Introduction

Introduction to the monographic section “Changing Landscapes: the Provincial Text in Russian-Soviet Culture.”Introduction to the monographic section “Changing Landscapes: the Provincial Text in Russian-Soviet Culture.

Presença de 20% ou mais de clue cells como um criterio diagnostico de vaginose bacteriana em esfregaços de Papanicolaou

Orientador: Jose Antonio SimõesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias MedicasResumo: Objetivo: Avaliar a acurácia da presença de pelo menos 20% de clue cells nos esfregaços de Papanicolaou para o diagnóstico de vaginose bateriana (VB), avaliar a reprodutibilidade interobservador deste critério padronizado e comparar a acurácia das amostras cervicais e vaginais para este diagnóstico. Métodos: Foi realizado um estudo de validação de teste diagnóstico envolvendo 135 mulheres em idade reprodutiva atendidas no ambulatório de Planejamento Familiar da Universidade Estadual de Campinas. As mulheres foram submetidas a um exame ginecológico, no qual foram coletadas amostras cervicais e do fundo de saco vaginal para o exame de Papanicolaou, e também amostras do fundo de saco vaginal para realização do exame bacterioscópico corado pelo método de Gram e a para o exame a fresco. Avaliaram-se também os quatro critérios clínicos de Amsel para diagnóstico de VB. As lâminas de Gram foram analisadas utilizando os critérios bacterioscópicos de Nugent, método considerado padrão-ouro, no qual uma pontuação = 7 foi considerada positiva para VB. Nos esfregaços de Papanicolaou a presença de 20% ou mais de clue cells foi considerada positiva para VB, sendo este critério avaliado por dois observadores de laboratórios diferentes. Resultados: A freqüência de VB foi de 22% quando diagnosticada pelo método de Nugent, 24% pelo método de Papanicolaou e 29% pelos critérios de Amsel. O exame de Papanicolaou para o diagnóstico de VB utilizando como o critério a presença de pelo menos 20% de clue cells nos esfregaços, apresentou sensibilidade de 87%, especificidade de 94%, valor preditivo positivo de 81% e valor preditivo negativo de 96%. Este critério resultou em uma excelente concordância entre as amostras cervicais e vaginais (Kappa: 0,92) e também em uma excelente concordância entre os dois observadores (Kappa: 0,87). Conclusão: A presença de 20% ou mais de clue cells nos esfregaços de Papanicolaou é um critério acurado e reprodutível para o diagnóstico de VB, podendo ser utilizado para o diagnóstico presuntivo desta infecção sem a necessidade de coleta adicional de amostra vaginalAbstract: Objective: To evaluate the accuracy of the presence of at least 20 % of clue cells to diagnose bacterial vaginosis (BV) in Pap-smear, to asses the reproducibility of this criterion for the diagnosis of BV between different observers and to compare the accuracy of samples collected from cervical and vaginal sites to perform the diagnosis of BV. Methods: This is a diagnostic test validation study of 135 women of reproductive age attending at the Family Planning Out-patient Clinic of the Universidade Estadual de Campinas. A pelvic examination was performed to collect samples from cervical and vaginal sites for Pap-smear. Swabs were also collected for Gram¿s stain and wet mount. Amsel¿s criteria were also used for the presence of BV. The Gram stained slides were evaluated and graded for the presence of BV using Nugent¿s criteria. A score = 7 was defined as BV and considered as gold standard. The presence of = 20% of clue cells in Pap-smears was defined as positive for BV. These Pap-smears were analysed by two cytologists from different laboratories. Results: The frequency of BV was 22% by Nugent¿s criteria, 29% by Amsel¿s criteria and 24% by Pap-smear criterion. The use of the presence of at least 20% of clue cells in the Pap-smear for the diagnosis of BV showed a sensitivity of 87%, specificity of 94%, positive predictive value of 81% and negative predictive value of 96%. The concordance among the cervical and vaginal samples for the diagnosis of BV by Pap-smear was excellent (Kappa: 0.92). In addition, the concordance between the observers for diagnosis of BV by Pap-smear was also excellent (Kappa: 0.87). Conclusion: Our findings support the accuracy and reproducibility of Pap-smear for presumptive diagnosis of BV using the presence of 20% of clue cells as a diagnosis criterion. Furthermore, the results suggest that the screening of BV by Pap's can be made without an additional vaginal sample collectionMestradoCiencias BiomedicasMestre em Tocoginecologi

Is minimising the convergence rate the best choice for efficient Optimized Schwarz preconditioning in heterogeneous coupling? The Stokes-Darcy case

Optimized Schwarz Methods (OSM) are domain decomposition techniques based on Robin-type interface condition that have became increasingly popular in the last two decades. Ensuring convergence also on non-overlapping decompositions, OSM are naturally advocated for the heterogeneous coupling of multi-physics problems. Classical approaches optimize the coefficients in the Robin condition by minimizing the effective convergence rate of the resulting iterative algorithm. However, when OSM are used as preconditioners for Krylov solvers of the resulting interface problem, such parameter optimization does not necessarily guarantee the fastest convergence. This drawback is already known for homogeneous decomposition, but in the case of heterogeneous decomposition, the poor performance of the classical optimization approach becomes utterly evident. In this paper, we highlight this drawback for the Stokes/Darcy problem and we propose a more effective alternative optimization procedure.European Union Seventh Framework Programme (FP7/2007-2013; grant 294229) to M. Discacciat

Optimized Schwarz Methods in the Stokes-Darcy Coupling

This article studies optimized Schwarz methods for the Stokes–Darcy problem. Robin transmission conditions are introduced, and the coupled problem is reduced to a suitable interface system that can be solved using Krylov methods. Practical strategies to compute optimal Robin coefficients are proposed, which take into account both the physical parameters of the problem and the mesh size. Numerical results show the effectiveness of our approach.European Union Seventh Framework Programme (FP7/2007-2013; grant 294229) to M. Discacciat

Modeling dimensionally-heterogeneous problems: analysis, approximation and applications

In the present work a general theoretical framework for coupled dimensionally-heterogeneous partial differential equations is developed. This is done by recasting the variational formulation in terms of coupling interface variables. In such a general setting we analyze existence and uniqueness of solutions for both the continuous problem and its finite dimensional approximation. This approach also allows the development of different iterative substructuring solution methodologies involving dimensionally-homogeneous subproblems. Numerical experiments are carried out to test our theoretical result

Numerical analysis of the Navier-Stokes/Darcy coupling

We consider a differential system based on the coupling of the Navier-Stokes and Darcy equations for modeling the interaction between surface and porous-media flows. We formulate the problem as an interface equation, we analyze the associated (nonlinear) Steklov-Poincaré operators, and we prove its well-posedness. We propose and analyze iterative methods to solve a conforming finite element approximation of the coupled proble

Navier-Stokes/Forchheimer models for filtration through porous media

Modeling the filtration of incompressible fluids through porous media requires dealing with different types of partial differential equations in the fluid and porous subregions of the computational domain. Such equations must be coupled through physically significant continuity conditions at the interface separating the two subdomains. To avoid the difficulties of this heterogeneous approach, a widely used strategy is to consider the Navier–Stokes equations in the whole domain and to correct them introducing suitable terms that mimic the presence of the porous medium. In this paper we discuss these two different methodologies and we compare them numerically on a sample test case after proposing an iterative algorithm to solve a Navier–Stokes/Forchheimer problem. Finally, we apply these strategies to a problem of internal ventilation of motorbike helmets