Strategic Project - UI 212 - 2011-2012

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Publications

Stable weakly shadowable volume-preserving systems are volume-hyperbolic

Publication . Bessa, Mário; Lee, Manseob; Vaz, Sandra

We prove that any C1-stable weakly shadowable volume-preserving diffeomorphism defined on a compact manifold displays a dominated splitting E ⊕ F. Moreover, both E and F are volume-hyperbolic. Finally, we prove the version of this result for divergence-free vector fields. As a consequence, in low dimensions, we obtain global hyperbolicity.

2014-05-15Journal article

Open access

Estimation in Models with Commutative Orthogonal Block Structure, Imbedded Orthogonality

Publication . Ferreira, Sandra S.; Ferreira, Dário; Nunes, Célia; Mexia, João T.

As a branch of Block Designs, research on Balanced Incomplete Block Designs (BIBD) arose several interesting and defying problems within Combinatory Mathematics. Hadamard Matrices are present in our daily life and it give rise to a class of block designs named Hadamard configurations. It is easy and current to find different applications of it based on new technologies and codes of figures such as Quick Response Codes (QR Codes). These are bi-dimensional barcodes that can be easily read by common devices which have image capture function, such as mobile phones. Risk is the potential of losing something of value, weighed against the potential to gain something of value. There are several types of risk and we will focus on information security risk, namely on the information loss for QR Codes. Connections between the various methodologies and QR Codes will be discussed.

2016Book part

Restricted access

Chisquared and related inducing pivot variables: an application to orthogonal mixed models

Publication . Ferreira, Dário; Ferreira, Sandra S.; Nunes, Célia; Fonseca, Miguel; Mexia, João T.

We use chi-squared and related pivot variables to induce probability measures for model parameters, obtaining some results that will be useful on the induced densities. As illustration we considered mixed models with balanced cross nesting and used the algebraic structure to derive confidence intervals for the variance components. A numerical application is presented.

2019Journal article

Open access

Estimation and Orthogonal Block Structure

Publication . Ferreira, Sandra S.; Nunes, Célia; Ferreira, Dário; Moreira, Elsa; Mexia, João T.

Estimators with good behaviors for estimable vectors and variance components are obtained for a class of models that contains the well known models with orthogonal block structure, OBS, see [15], [16] and [1], [2]. The study observations of these estimators uses commutative Jordan Algebras, CJA, and extends the one given for a more restricted class of models, the models with commutative orthogonal block structure, COBS, in which the orthogonal projection matrix on the space spanned by the means vector commute with all variance-covariance matrices, see [7].

2015Journal article

Open access

Inducing pivot variables and non-centrality parameters in elliptical distributions

Publication . Ferreira, Dário; Ferreira, Sandra S.; Nunes, Célia; Inácio, Sónia

We used inducing pivot variables to derive confidence intervals for the non-centrality parameters of samples with elliptical errors. A numerical application is presented.

2013Journal article

Open access