Application of Mixture Models to Survival Data

Survival models are being widely applied to the engineering field to model time-to-event data once censored data is here a common issue. Using parametric models or not, for the case of heterogeneous data, they may not always represent a good fit. The present study relays on critical pumps survival data where traditional parametric regression might be improved in order to obtain better approaches. Considering censored data and using an empiric method to split the data into two subgroups to give the possibility to fit separated models to our censored data, we’ve mixture two distinct distributions according a mixture-models approach. We have concluded that it is a good method to fit data that does not fit to a usual parametric distribution and achieve reliable parameters. A constant cumulative hazard rate policy was used as well to check optimum inspection times using the obtained model from the mixture-model, which could be a plus when comparing with the actual maintenance policies to check whether changes should be introduced or not.

Pacote de sincronização de réplicas de bases de dados

A replicação de base de dados tem como objectivo a cópia de dados entre bases de dados distribuídas numa rede de computadores. A replicação de dados é importante em várias situações, desde a realização de cópias de segurança da informação, ao balanceamento de carga, à distribuição da informação por vários locais, até à integração de sistemas heterogéneos. A replicação possibilita uma diminuição do tráfego de rede, pois os dados ficam disponíveis localmente possibilitando também o seu acesso no caso de indisponibilidade da rede. Esta dissertação baseia-se na realização de um trabalho que consistiu no desenvolvimento de uma aplicação genérica para a replicação de bases de dados a disponibilizar como open source software. A aplicação desenvolvida possibilita a integração de dados entre vários sistemas, com foco na integração de dados heterogéneos, na fragmentação de dados e também na possibilidade de adaptação a várias situações. ABSTRACT: Data replication is a mechanism to synchronize and integrate data between distributed databases over a computer network. Data replication is an important tool in several situations, such as the creation of backup systems, load balancing between various nodes, distribution of information between various locations, integration of heterogeneous systems. Replication enables a reduction in network traffic, because data remains available locally even in the event of a temporary network failure. This thesis is based on the work carried out to develop an application for database replication to be made accessible as open source software. The application that was built allows for data integration between various systems, with particular focus on, amongst others, the integration of heterogeneous data, the fragmentation of data, replication in cascade, data format changes between replicas, master/slave and multi master synchronization.

Trans-national cooperation: an asset in the Portuguese overseas trade. Foreigners operating in the Portuguese overseas trade, 1580-1590

This paper aims to discuss the role of foreign merchants, operating from Portugal, in the Portuguese overseas trade, during the first ten years of Iberian Union. The focus is not in products or routes, but in the mechanisms of association of such merchants. Iberian Union created a legal framework which prohibited the interference and trade of Portuguese agents in the Spanish Empire and vice-versa. Due to the imperialist wars of the Habsburgs, the Portuguese Empire also suffered from Dutch and English rivalry both in the Indic and in the Atlantic and also from the embargos of Dutch and English products and ships in Iberian ports. In such conjuncture, how did merchants related with each other? What was the impact of the political union of the Portuguese and Spanish crowns in trading associations? The used data sources are the notarial contracts of Lisbon for the same period. The paper highlights the role of Castilian merchants in the Portuguese trade, but it also stresses that Iberian partnerships have prevailed before 1580. The role of other merchants, such as Flemish/Dutch, Germans, Italians and French, is also considered. The paper discusses how and why did these merchants join in trans-national partnerships and what was their role in the Portuguese trade network at the time.