A new approach to the initial value problem

5th Portuguese Conference on Automatic Control, September, 5-7, 2002, Aveiro, Portugal

On the initial conditions in continuous-time fractional linear systems

Signal Processing, Vol. 83, nº 11

Factorization of elliptic boundary value problems by invariant embedding and application to overdetermined problems

Dissertação para obtenção do Grau de Doutor em Matemática

Factorization by invariant embedding of elliptic problems: circular and star-shaped domains

Dissertação apresentada para obtenção do grau de Doutor em Matemática na especialidade de Equações Diferenciais, pela Universidade Nova de Lisboa,Faculdade de Ciências e Tecnologia

Evolution of reputation in networks: A mean field game approach

This work models the competitive behaviour of individuals who maximize their own utility managing their network of connections with other individuals. Utility is taken as a synonym of reputation in this model. Each agent has to decide between two variables: the quality of connections and the number of connections. Hence, the reputation of an individual is a function of the number and the quality of connections within the network. On the other hand, individuals incur in a cost when they improve their network of contacts. The initial value of the quality and number of connections of each individual is distributed according to an initial (given) distribution. The competition occurs over continuous time and among a continuum of agents. A mean field game approach is adopted to solve the model, leading to an optimal trajectory for the number and quality of connections for each individual.

Molecular diversity of bla genes in Klebsiella pneumoniae and Escherichia coli isolates

Dissertation presented to obtain a Ph.D. degree in Biology, speciality Microbiology, by Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia

Incapacidade auto-reportada e retorno à actividade profissional em utentes com dor crónica lombar

RESUMO: O absentismo à actividade profissional devido à condição de Dor Lombar apresenta-se como um problema de saúde pública com elevados custos económicos nas sociedades ocidentais. É estimado que cerca de 20% a 47% dos utentes com Dor Lombar não retornam à sua actividade profissional no período de 3 meses, sendo responsáveis por 75% a 90% de todos os custos e baixas médicas associadas à condição. Objectivo: O objectivo deste estudo foi analisar a capacidade de retorno à actividade profissional em utentes com Dor Crónica Lombar (DCL), que procuraram a Fisioterapia em situação de agudização dos seus sintomas, e averiguar a sua relação com os níveis de Incapacidade auto-reportados. Secundariamente pretendemos avaliar a influência das Crenças de medo-evitamento, nos níveis de Incapacidade auto-reportados. Metodologia: Foi efectuado um estudo correlacional prospectivo no qual se observou uma amostra de 56 utentes com DCL que tivessem apresentado novos episódios de agudização dos seus sintomas. Após 3 meses de follow-up (n=42) foi avaliado o “regresso ao trabalho em boas condições” e a sua relação com os níveis de Incapacidade iniciais, bem como o contributo das Crenças de medo-evitamento para essa Incapacidade funcional. Resultados: Foi verificada uma correlação negativa entre os níveis de Incapacidade funcional e o Sucesso no “regresso ao trabalho em boas condições” (ρ = -0.369; p =0.016), sendo que os scores mais elevados da Incapacidade correspondem à Falha nesse regresso. Verificámos também uma correlação positiva entre a existência das Crenças de medo-evitamento relativas ao Trabalho e a Incapacidade (r =0.511; p =0,001), apresentando estas Crenças um valor preditivo (β= 0.533; p =0.001) na Incapacidade auto-reportada. Conclusões: A capacidade de retorno à actividade profissional nos utentes com DCL, após um novo episódio de agudização dos seus sintomas, está relacionada com níveis de Incapacidade funcional. Os factores psicossociais, nomeadamente as Crenças de medo-evitamento relativas ao Trabalho apresentam um valor preditivo para essa Incapacidade auto-reportada.------------------------------ABSTRACT:Work-absenteeism due to the condition of Low Back Pain (LBP) presents itself as a public health problem with high economic costs in Western societies. It is estimated that 20% to 47% of patients with LBP not returned to their work-activity in period of 3 months, accounting for 75% to 90% of all medical costs and sickness compensation associated. Objective: The aim of the present study was to assess the ability to return to work on patients with chronic LBP, who searched for physical therapy in a situation of worsening of their symptoms, and examine their relationship with levels of self-reported disability. Secondly we intend to evaluate the influence of fear-avoidance beliefs to the levels of self-reported disability. Methods: We conducted a prospective cross-sectional study in which we observed 56 patients chronic LBP with new episodes of exacerbation of their symptoms. After a 3 months follow-up (n = 42) we evaluated the “return to work in good health” and its relationship with initial levels of disability and the contribution of fear-avoidance beliefs for that disability. Results: There was a negative correlation between levels of disability and “return to work in good health” success (ρ = -0.369, p = 0.016), with the highest scores correspond to the failure in the work-return. We also found a positive correlation between the existence of fear-avoidance beliefs for work and disability (r = 0.511; p = 0.001), with a predictive value of these fear-avoidance beliefs (β = 0.533; p = 0.001) in self-reported disability. Conclusions: The ability to return to work in chronic LBP patients, after a new episode of exacerbation of symptoms is related to the levels of functional disability. Psychosocial factors, including fear-avoidance beliefs for work showed a predictive value for the self-reported disability.

What is the value of value-at-risk after all?: A conditional approach using quantile regressions

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Finance from the NOVA – School of Business and Economics

Continente Choose&Drive

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Management from the NOVA – School of Business and Economics

A technology diffusion perspective of Enterprise Resource Planning across European Small and Medium Enterprises: from determinants to Use to Value

Tese apresentada como requisito parcial para obtenção do grau de Doutor em Gestão de Informação

Business model analysis of Mobitto: How to solve the chicken and egg problem of a multi-sided platform?

A Work Project, presented as part of the requirements for the Award of a Masters Degree in Management from the NOVA – School of Business and Economics

Constraint reasoning with local search for continuous optimization

Optimization is a very important field for getting the best possible value for the optimization function. Continuous optimization is optimization over real intervals. There are many global and local search techniques. Global search techniques try to get the global optima of the optimization problem. However, local search techniques are used more since they try to find a local minimal solution within an area of the search space. In Continuous Constraint Satisfaction Problems (CCSP)s, constraints are viewed as relations between variables, and the computations are supported by interval analysis. The continuous constraint programming framework provides branch-and-prune algorithms for covering sets of solutions for the constraints with sets of interval boxes which are the Cartesian product of intervals. These algorithms begin with an initial crude cover of the feasible space (the Cartesian product of the initial variable domains) which is recursively refined by interleaving pruning and branching steps until a stopping criterion is satisfied. In this work, we try to find a convenient way to use the advantages in CCSP branchand- prune with local search of global optimization applied locally over each pruned branch of the CCSP. We apply local search techniques of continuous optimization over the pruned boxes outputted by the CCSP techniques. We mainly use steepest descent technique with different characteristics such as penalty calculation and step length. We implement two main different local search algorithms. We use “Procure”, which is a constraint reasoning and global optimization framework, to implement our techniques, then we produce and introduce our results over a set of benchmarks.

A type system for value-dependent information flow analysis

Information systems are widespread and used by anyone with computing devices as well as corporations and governments. It is often the case that security leaks are introduced during the development of an application. Reasons for these security bugs are multiple but among them one can easily identify that it is very hard to define and enforce relevant security policies in modern software. This is because modern applications often rely on container sharing and multi-tenancy where, for instance, data can be stored in the same physical space but is logically mapped into different security compartments or data structures. In turn, these security compartments, to which data is classified into in security policies, can also be dynamic and depend on runtime data. In this thesis we introduce and develop the novel notion of dependent information flow types, and focus on the problem of ensuring data confidentiality in data-centric software. Dependent information flow types fit within the standard framework of dependent type theory, but, unlike usual dependent types, crucially allow the security level of a type, rather than just the structural data type itself, to depend on runtime values. Our dependent function and dependent sum information flow types provide a direct, natural and elegant way to express and enforce fine grained security policies on programs. Namely programs that manipulate structured data types in which the security level of a structure field may depend on values dynamically stored in other fields The main contribution of this work is an efficient analysis that allows programmers to verify, during the development phase, whether programs have information leaks, that is, it verifies whether programs protect the confidentiality of the information they manipulate. As such, we also implemented a prototype typechecker that can be found at http://ctp.di.fct.unl.pt/DIFTprototype/.

The antecedents of post-initial adoption behavior in a S-D logic context

Repercussions of innovation adoption and diffusion studies have long been imperative to the success of novel introductions. However, perceptions and deductions of current innovation understandings have been changing over time. The paradigm shift from the goods-dominant (G-D) logic to the service-dominant (S-D) logic potentially makes the distinction between product (goods) innovation and service innovation redundant as the S-D logic lens views all innovations as service innovations (Vargo and Lusch, 2004; 2008; Lusch and Nambisan, 2015). From this perspective, product innovations are in essence service innovations, as goods serve as mere distribution mechanisms to deliver service. Nonetheless, the transition to such a broadened and transcending view of service innovation necessitates concurrently a change in the underlying models used to investigate innovation and its subsequent adoption. The present research addresses this gap by engendering a novel model for the most crucial period of service diffusion within the S-D logic context – the post-initial adoption phase, which demarcates an individual’s behavior after the initial adoption decision of a service. As a wellfounded understanding of service diffusion and the complementary innovation adoption still lingers in its infancy, the current study develops a model based on interdisciplinary domains mapping. Here fore, knowledge of the relatively established viral source domain is mapped to the comparatively undetermined target domain of service innovation adoption. To assess the model and test the importance of the explanatory variables, survey data from 750 respondents of a bank in Northern Germany is scrutinized by means of Structural Equation Modeling (SEM). The findings reveal that the continuance intention of a customer, actual usage of the service and the customer influencer value all constitute important postinitial adoption behavior that have meaningful implications for a successful service adoption. Second, the four constructs customer influencer value, organizational commitment, perceived usefulness and service customization are evidenced to have a differential impact on a iv customer’s post-initial adoption behavior. Third, this study indicates that post-initial adoption behavior further underlies the influence of a user’s age and besides that is also provoked by the internal and external environments of service adoption. Finally, this research amalgamates the broad view of service innovation by Nambisan and Lusch (2015) with the findings ensuing this enquiry’s model to arrive at a framework that it both, generalizable and practically applicable. Implications for academia and practitioners are captured along with avenues for future research.