FCT: DM - Documentos de conferências internacionais
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- Spatial Modelling of Black Scabbardfish Fishery Off the Portuguese CoastPublication . André, Lídia Maria; Figueiredo, Ivone; Carvalho, M. Lucília; Simões, Paula; Natário, Isabel; CMA - Centro de Matemática e Aplicações; DM - Departamento de MatemáticaThe Black Scabbardfish is a deep-water fish species that lives at depths greater than 700 m. In Portugal mainland, this is an important commercial resource which is exploited by longliners that operate at specific fishing grounds located off the coast. The monitoring of the population status mainly relies on the fishery data as no independent scientific surveys take place. The present work focus on modelling the spatial distribution of the BSF species relative biomass. Georeferenced data given by the location of the fishing hauls and the corresponding catches are available for a set of different vessels that belong to the longline fishing fleet. A classical geostatistical approach was applied to fit a variogram and evaluate the isotropy of the data. Then, different regression models with fixed, structured and unstructured random effects were fitted under a Bayesian framework, considering the Stochastic Partial Differential Equation (SPDE) methodology under the Integrated Nested Laplace Approximation (INLA), addressing some practical implementation issues. The models with spatial effects seemed to perform better, although some practical constraints related to the considered covariates hindered the choice.
- Synchronisation of Weakly Coupled OscillatorsPublication . Martins, Rogério; CMA - Centro de Matemática e Aplicações; DM - Departamento de MatemáticaThe synchronization phenomenon was reported for the first time by Christiaan Huygens, when he noticed the strange tendency of a couple of clocks to synchronise their movements. More recently this phenomena was shown to be ubiquitous in nature and it is broadly studied by its applications, for example in biological cycles. We consider the problem of synchronization of a general network of linearly coupled oscillators, not necessarily identical. In this case the existence of a linear synchronization space is not expected, so we present an approach based on the proof of the existence of a synchronization manifold, the so-called generalised synchronization. Based on some results developed by R. Smith and on Wazewski’s principle, a general theory on the existence of invariant manifolds that attract the solutions of the system that are bounded in the future, is presented. Applications and estimates on parameters for the existence of synchronization are presented for several examples: systems of coupled pendulum type equations, coupled Lorenz systems of equations, and oscillators coupled through a medium, among many others.
- A Recursion-Theoretic Characterization of the Probabilistic Class PPPublication . Dal Lago, Ugo; Kahle, Reinhard; Oitavem, Isabel; CMA - Centro de Matemática e Aplicações; DM - Departamento de MatemáticaProbabilistic complexity classes, despite capturing the notion of feasibility, have escaped any treatment by the tools of so-called implicit-complexity. Their inherently semantic nature is of course a barrier to the characterization of classes like BPP or ZPP, but not all classes are semantic. In this paper, we introduce a recursion-theoretic characterization of the probabilistic class PP, using recursion schemata with pointers.
- The impact of technology on the teachers’ use of different representationsPublication . Rocha, Helena; UIED - Unidade de Investigação Educação e Desenvolvimento; DM - Departamento de MatemáticaThe potential of using different representations is widely recognized, but not much is known about how teachers use them nor about the impact of the technology on such use. The goal of this study is to characterize the teachers’ representational fluency when teaching functions at high school level, discussing, at the same time, the impact in the use of representations resulting from the use of technology. Adopting a qualitative approach, I analyze one teacher’s practice. The results suggest that algebraic and graphical representations are seen as more important, that tabular representation is assumed as irrelevant and that the access to technology impacts the representations used and how they are used.
- On the equilibrium of the egyptian game SenetPublication . Nogueira, Joaquim Eurico Anes Duarte; Rodrigues, Fátima; Trabucho, Luis; DM - Departamento de Matemática; CMA - Centro de Matemática e AplicaçõesIn this work we compute the probabilities of obtaining the values associated with the throwing of four rods in the Egyptian game Senet. Our purpose is to, among several sets of rules obtained by some historians and archeologists, deduce which ones provide the most balanced game. In the course of this study it was also possible to infer the most likely format for the rod’s cross section.
- Near permutation semigroupsPublication . André, Jorge Manuel Leocádio; DM - Departamento de MatemáticaA transformation semigroup over a set X with N elements is said to be a near permutation semigroup if it is generated by a group of permutations on N elements and by a set of transformations of rank N −1. In this paper we make a summary of the author’s thesis, in which are exhibited ways of checking whether those specific transformation semigroups belong to various structural classes of semigroups, just by analysis of the generators and without first having to generate them.
- Multi-treatment regression analysis: the unbalanced casePublication . Moreira, Elsa Estevão; Mexia, João Tiago; CMA - Centro de Matemática e Aplicações; DM - Departamento de MatemáticaUnder multi-treatment regression analysis, instead of a sample for each treatment of a linear model, there is a linear regression in the same variables. Then, instead of the action of the treatments on the sample mean values, the action on regression coefficients is studied. When data is unbalanced, the regression matrices differs between regressions. This problem is solved through the use of a block-wise diagonal covariance matrix in the ANOVA procedures. The methodology was then applied to data obtained from experiments of electrodialtic removal of 3 heavy metals from contaminated wood. First, polynomial regressions of the 4th and 3rd were fitted to each metal concentration in the electrolytes through time. Then the unbalanced case of multi-treatment regression analysis was applied aiming to choose the best treatment in jointly removing the 3 metals. Results pointed to the choice of treatment 1 as the most efficient.
- Genetic and statistical study of HIV integration in the human genomePublication . Sequeira, Inês J.; Gonçalves, Juliana; Moreira, Elsa; Mexia, João T.; Rueff, José; Brás, Aldina; DM - Departamento de Matemática; NOVA Medical School|Faculdade de Ciências Médicas (NMS|FCM)Integration of the human immunodeficiency virus (HIV) DNA into human genome is essential for HIV-induced disease. The human genome is organized into chromosomes and within these we can define the chromosomal fragile sites. Our aim is to contribute to help clarifying the integration sites preferences of HIV1 and HIV2 in fragile or non-fragile regions. Here we apply statistical techniques, namely non-parametric tests and analysis of variance for analyzing two sets of data of HIV1 and HIV2 integrations in the human genome. The results show that the integrations occur significantly with more intensity in the non-fragile regions of the human genome and that the HIV1 in particular has the major contribution to this fact. This study could have implications in human disease.
- Model validation and vec operatorsPublication . Dias, Cristina; Santos, Carla; Varadinov, Maria; Mexia, João Tiago; CMA - Centro de Matemática e Aplicações; DM - Departamento de MatemáticaWe use the vec and other relater operators to carry out inference for structured families of symmetric stochastic matrices M. These are obtained through the sum of the respective mean matrix and a symmetric stochastic matrix with null mean. We consider that the vec operator of the matrix E is normal homoscedastic. The matrices on these families correspond to the treatments of a base design, and the inference is centered on model validation and the action of the factors in the base model on mean matrices.
- Structure and StructuresPublication . Kahle, Reinhard; DM - Departamento de Matemática; CMA - Centro de Matemática e AplicaçõesIn this paper we critically evaluate the notion of the structure of the natural numbers with respect to the question how the internal structure of such a structure might be specified.