Constraint solving over multi-valued logics - application to digital circuits

Due to usage conditions, hazardous environments or intentional causes, physical and virtual systems are subject to faults in their components, which may affect their overall behaviour. In a ‘black-box’ agent modelled by a set of propositional logic rules, in which just a subset of components is externally visible, such faults may only be recognised by examining some output function of the agent. A (fault-free) model of the agent’s system provides the expected output given some input. If the real output differs from that predicted output, then the system is faulty. However, some faults may only become apparent in the system output when appropriate inputs are given. A number of problems regarding both testing and diagnosis thus arise, such as testing a fault, testing the whole system, finding possible faults and differentiating them to locate the correct one. The corresponding optimisation problems of finding solutions that require minimum resources are also very relevant in industry, as is minimal diagnosis. In this dissertation we use a well established set of benchmark circuits to address such diagnostic related problems and propose and develop models with different logics that we formalise and generalise as much as possible. We also prove that all techniques generalise to agents and to multiple faults. The developed multi-valued logics extend the usual Boolean logic (suitable for faultfree models) by encoding values with some dependency (usually on faults). Such logics thus allow modelling an arbitrary number of diagnostic theories. Each problem is subsequently solved with CLP solvers that we implement and discuss, together with a new efficient search technique that we present. We compare our results with other approaches such as SAT (that require substantial duplication of circuits), showing the effectiveness of constraints over multi-valued logics, and also the adequacy of a general set constraint solver (with special inferences over set functions such as cardinality) on other problems. In addition, for an optimisation problem, we integrate local search with a constructive approach (branch-and-bound) using a variety of logics to improve an existing efficient tool based on SAT and ILP.

The globalisation in the clothing sector and its implications for work organisation: a view from the Portuguese case

The clothing sector in Portugal is still seen, in many aspects as a traditional sector with some average characteristics, such as: low level of qualifications, less flexible labour legislation and stronger unionisation, very low salaries and low capability of investment in innovation and new technology. Is, nevertheless, a very important sector in terms of labour market, with increased weight in the exporting structure. Globalisation and delocalisation are having a strong impact in the organisation of work and in occupational careers in the sector. With the pressure of global competitiveness in what concerns time and prices, very few companies are able to keep a position in the market without changes in organisation of work and workers. And those that can perform good responses to such challenges are achieving a better economical stability. The companies have found different ways to face this reality according to size, capital and position. We could find two main paths: one where companies outsource a part or the entire production to another territory (for example, several manufacturing tasks), close and/or dismissal the workers. Other path, where companies up skilled their capacities investing, for example, in design, workers training, conception and introduction of new or original products. This paper will present some results from the European project WORKS – Work organisation and restructuring in the knowledge society (6th Framework Programme), focusing the Portuguese case studies in several clothing companies in what concern implications of global context for the companies in general and for the workers in particular, in a comparative analysis with some other European countries.

Protocolo Mac para acesso multi-modo em redes de sensores sem fios móveis

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Electrotécnica e de Computadores