Stability of quaternionic systems: a determinantal approach

In this paper we propose a definition of determinant for quaternionic polynomial matrices. This definition is later used in the study of stability of linear quaternionic systems within the behavioral setting

On the determinant of quaternionic polynomial matrices and its application to system stability

In this paper, we propose a definition of determinant for quaternionic, polynomial matrices inspired by the well-known Dieudonne determinant for the constant case. This notion allows to characterize the stability of linear dynamical systems with quaternionic coefficients, yielding results which generalize the ones obtained for the real and complex cases

Global reachability of 2D structured systems

In this paper the new concept of 2D structured system is defined and a characterization of global reachability is obtained. This extends a well known result for 1D structured systems, according to which (A ,B ) is (generically) reachable if and only if the matrix [A B] is full generically row rank and irreducible

Tornando-se subitamente Cuidador Informal!

A secção UAciência é coordenada pelo Professor Universitário Armindo Rodrigues.As questões relacionadas com os cuidadores informais têm vindo a afirmar-se não só nos discursos dos profissionais dos campos da saúde e do trabalho social, como, também, nas experiências quotidianas das famílias. O foco deste crescente interesse esta, não só relacionado com o envelhecimento da população, mas também, com as alterações das estruturas familiares, com o ingresso massivo das mulheres no mundo do trabalho ou com a diminuição dos tempos de demora nos internamentos, só para citar alguns exemplos.info:eu-repo/semantics/publishedVersio

Angular Momentum of the BTZ Black Hole in the Teleparallel Geometry

We carry out the Hamiltonian formulation of the three- dimensional gravitational teleparallelism without imposing the time gauge condition, by rigorously performing the Legendre transform. Definition of the gravitational angular momentum arises by suitably interpreting the integral form of the constraint equation Gama^ik=0 as an angular momentum equation. The gravitational angular momentum is evaluated for the gravitational field of a rotating BTZ black hole.Comment: 17 pages, no figures, v2: some misprints corrected, Ref.s added, Eq.s revised, submitted to General Relativity and Gravitatio

A remark on conditioned invariance in the behavioral approach

In this paper a definition for the property of behavioral invariance is proposed with the purpose of generalizing the state space geometric approach to the behavioral setting. Based on this notion together with the well-known notion of behavioral observer, a definition of conditioned invariance is also presented. The results obtained for the characterization of the defined properties put into evidence some problems that, in our opinion, should deserve attention. This could serve as a starting point for a discussion on the foundations of an analogue of the geometric theory within the behavioral setting

In silico optimization of the production of amino-acids in Escherichia coli

The increasing need to replace chemical synthesis of compounds of interest by more environmentally friendly biological processes is driving the research for microbial cell factories. The industrial production of amino and organic acids includes several examples of success stories using microorganisms to convert inexpensive substrates into added value products. Traditionally, the design of such microbes relied on cycles of random mutagenesis followed by phenotypic selection [1], but a deeper knowledge of the microbial physiology allowed a more rational approach to this optimization problem [2,3]. However, this task is not straightforward, since the cell metabolism has proved to be highly complex and hard to predict. One of the approaches to tackle this problem is to use Systems Biology simulation tools to predict the microorganism behavior when subjected to genetic modifications. Using genome scale stoichiometric models, such as the latest iAF1260 for Escherichia coli [4] one can simulate a great diversity of possible metabolic phenotypes under steady state conditions by imposing flux-balance constrains. The use of flux balanced analysis (FBA) allows the determination of flux values through all the reactions in the network under a set of environmental conditions and genetic manipulations, by using an objective function, such as the maximization of growth [5]. In this work, we used genetic algorithms, such as OptGene [6] to search for sets of gene knockouts that result in the overproduction in silico of amino-acids in Escherichia coli. From all the proteinogenic amino-acids, glycine yielded the best results in the optimizations. A careful analysis of the in silico flux distribution in some of the mutants revealed an interesting and non-intuitive mechanism behind glycine accumulation. Furthermore, in these mutants the growth is coupled to the production of glycine, which makes them excellent candidates for in vivo implementation. We are reaching a point where bioinformatics tools are advanced enough to aid in complex tasks, such as the optimization of microbial cell factories. Here we described an effort to optimize in silico the production of amino-acids in Escherichia coli, which resulted in the discovery of a potential set of knock-outs that leads to glycine overproduction. This serves to show the increasing importance of in silico optimizations to aid in the metabolic engineering projects, especially to search for non-intuitive beneficial genome modifications

Embrapa Technological Information: a bridge between research and society

This paper presents the efforts undertaken by the Brazilian Agricultural Research Corporation regarding Science and Technology information management, through one of its Decentralized Units, Embrapa Technological Information (Scientific and Technological Information Service', SCT). The major aim of SCT is to promote and improve the processes of scientific communication - information that feeds and that results from research activities - and of science and technology dissemination - information that results from research activities and that is directed to the general publi

A behavioral approach to estimation in nD systems

In this paper we study the problem of estimation for multidimensional systems within the context of the behavioral approach. We consider the case where there are no disturbances as well as the case where the system dynamics is perturbed, and provide necessary conditions for the solvability of the corresponding estimation problems together with the construction of a solution, if it exists. Such solution is an estimator that is asymptotic, in the sense that the error trajectories are stable with respect to a pre-specified nD stability cone.publishe