DSpace Collection:http://hdl.handle.net/10362/10472014-04-20T11:16:39Z2014-04-20T11:16:39ZRevision based total semantics for extended normal logic programsAbrantes, Mário António Rodrigues Grandehttp://hdl.handle.net/10362/113152014-02-05T14:51:58Z2013-01-01T00:00:00ZTitle: Revision based total semantics for extended normal logic programs
Authors: Abrantes, Mário António Rodrigues Grande
Description: Dissertação para obtenção do Grau de Doutor em
Matemática - Lógica e Fundamentos da Matemática2013-01-01T00:00:00ZParameter estimation in the presence of auxiliary informationSousa, Rita Cristina Pinto dehttp://hdl.handle.net/10362/112952014-02-04T12:07:14Z2013-01-01T00:00:00ZTitle: Parameter estimation in the presence of auxiliary information
Authors: Sousa, Rita Cristina Pinto de
Abstract: In survey research, there are many situations when the primary variable of interest is sensitive. The sensitivity of some queries can give rise to a refusal to answer or to false answers given intentionally. Survey can be conducted in a variety of settings, in part dictated
by the mode of data collection, and these settings can differ in how much privacy
they offer the respondent. The estimates obtained from a direct survey on sensitive questions would be subject to high bias. A variety of techniques have been used to improve reporting by increasing the privacy of the respondents.
The Randomized Response Technique (RRT), introduced byWarner in 1965, develops a random relation between the individual’s response and the question. This technique
provides confidentiality to respondents and still allows the interviewers to estimate the
characteristic of interest at an aggregate level.
In this thesis we propose some estimators to improve the mean estimation of a sensitive
variable based on a RRT by making use of available non-sensitive auxiliary information.
In the first part of this thesis we present the ratio and the regression estimators as
well as some generalizations in order to study the gain in the estimation over the ordinary RRT mean estimator. In chapters 4 and 5 we study the performance of some exponential type estimators, also based on a RRT. The final part of the thesis illustrates an approach to mean estimation in stratified sampling. This study confirms some previous results for a different sample design. An extensive simulation study and an application to a real dataset are done for all the study estimators to evaluate their performance. In the last chapter we present a general discussion referring to the main results and conclusions as well as showing an application to a real dataset which compares the performance of study estimators.
Description: Dissertação para obtenção do Grau de Doutora em
Estatística e Gestão de Risco, Especialidade em Estatística2013-01-01T00:00:00ZModelação de matrizes estocásticas simétricas operadores do tipo vecSalvador, Dina Maria Morgadohttp://hdl.handle.net/10362/110892014-01-21T14:30:07Z2013-01-01T00:00:00ZTitle: Modelação de matrizes estocásticas simétricas operadores do tipo vec
Authors: Salvador, Dina Maria Morgado
Description: Dissertação para obtenção do Grau de Doutor em
Estatística e Gestão do Risco2013-01-01T00:00:00ZFactorization of elliptic boundary value problems by invariant embedding and application to overdetermined problemsOrey, Maria de Serpa Salema Reis dehttp://hdl.handle.net/10362/86772013-02-01T11:59:39Z2011-01-01T00:00:00ZTitle: Factorization of elliptic boundary value problems by invariant embedding and application to overdetermined problems
Authors: Orey, Maria de Serpa Salema Reis de
Abstract: The purpose of this thesis is the factorization of elliptic boundary value problems defined in cylindrical domains, in a system of decoupled first order initial value problems. We begin with the Poisson equation with mixed boundary conditions, and use the method of invariant embedding: we embed our initial problem in a family of similar problems, defined in sub-domains of the initial domain, with a moving boundary, and an additional condition in the moving boundary. This factorization is inspired by the technique of invariant temporal embedding used in Control Theory when computing the optimal feedback, for,
in fact, as we show, our initial problem may be defined as an optimal control problem. The
factorization thus obtained may be regarded as a generalized block Gauss LU factorization.
From this procedure emerges an operator that can be either the Dirichlet-to-Neumann or
the Neumann-to-Dirichlet operator, depending on which boundary data is given on the
moving boundary. In any case this operator verifies a Riccati equation that is studied
directly by using an Yosida regularization. Then we extend the former results to more
general strongly elliptic operators. We also obtain a QR type factorization of the initial
problem, where Q is an orthogonal operator and R is an upper triangular operator. This
is related to a least mean squares formulation of the boundary value problem.
In addition, we obtain the factorization of overdetermined boundary value problems, when
we consider an additional Neumann boundary condition: if this data is not compatible
with the initial data, then the problem has no solution. In order to solve it, we introduce a perturbation in the original problem and minimize the norm of this perturbation, under the hypothesis of existence of solution. We deduce the normal equations for the overdetermined problem and, as before, we apply the method of invariant embedding to factorize the
normal equations in a system of decoupled first order initial value problems.
Description: Dissertação para obtenção do Grau de Doutor em
Matemática2011-01-01T00:00:00Z