Browsing by Issue Date, starting with "2012-02"
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- Modelação e simulação: uma aplicação ao problema da ruína do jogadorPublication . Pedro, Salomé da SilvaEm 1657, é publicado o primeiro livro sobre cálculo de probabilidades, de Christiaan Huygens. Esta pequena coletânea de problemas relativos a jogos de azar, baseada na correspondência entre Blaise Pascal e Pierre de Fermat em 1654, permitiu despertar a atenção de numerosos matemáticos durante os séculos XVII, XVIII e XIX para esta temática, razão pela qual surgiram variadas generalizações de alguns dos problemas propostos. O último desafio apresentado neste opúsculo de Huygens, e porventura um dos mais célebres problemas em probabilidades, é o problema da ruína do jogador. A autoria deste problema foi durante muitos séculos atribuída a Huygens, no entanto, o seu verdadeiro autor é Pascal. Ao longo dos séculos, foram apresentadas diversas versões deste problema e diferentes formas de o resolver, algumas dessas resoluções utilizam equações às diferenças. Neste trabalho, apresentaremos alguns resultados relativos a equações às diferenças de primeira e segunda ordem e abordaremos algumas das suas aplicações. Faremos uma resenha histórica acerca da origem do cálculo de probabilidades, do problema da ruína do jogador e das suas diferentes versões. Apresentaremos algumas soluções exatas para algumas dessas variantes, com recurso à modelação do problema através de equações às diferenças. Far-se-á a apresentação de algumas caraterísticas do jogo da ruína e apresentaremos metodologias de obtenção de soluções aproximadas do problema da ruína do jogador, recorrendo à simulação Monte Carlo (via software R) e à Lei dos Grandes Números. Por fim, far-se-á uma análise crítica à possibilidade de utilização deste problema na disciplina de Matemática no ensino secundário, nomeadamente no que se refere à utilização de simulação no ensino das probabilidades, através da construção e utilização de simuladores adequados no software R e na folha de cálculo Microsoft Excel, e de uma tarefa para este nível de ensino sobre este problema.
- Can Phlorotannins Purified Extracts Constitute a Novel Pharmacological Alternative for Microbial Infections with Associated Inflammatory Conditions?Publication . Lopes, Graciliana; Sousa, Carla; Silva, Luís R.; Pinto, Eugénia; Andrade, Paula B.; Bernardo, João; Mouga, Teresa; Valentão, Patrícia; Mande HolfordBacterial and fungal infections and the emerging multidrug resistance are driving interest in fighting these microorganisms with natural products, which have generally been considered complementary to pharmacological therapies. Phlorotannins are polyphenols restricted to brown seaweeds, recognized for their biological capacity. This study represents the first research on the antibacterial, antifungal, anti-inflammatory and antioxidant activity of phlorotannins purified extracts, which were obtained from ten dominant brown seaweeds of the occidental Portuguese coast. Phlorotannins content was determined by the specific dimethoxybenzaldehyde (DMBA) method and a yield between 75 and 969 mg/Kg phloroglucinol units (dry matter) was obtained. Fucus spiralis ranked first, followed by three Cystoseira species. The anti-inflammatory potential of the purified extracts was assessed via inhibitory effect on nitric oxide (NO) production by lipopolysaccharide-stimulated RAW 264.7 macrophage cells, Cystoseira tamariscifolia being the one showing promising activity for the treatment of inflammation. NO scavenging ability was also addressed in cell free systems, F. spiralis being the species with highest capacity. The antimicrobial potential of the extracts was checked against five Gram-positive and four Gram-negative bacteria and three fungi strains, that commonly colonize skin and mucosa and are responsible for food contamination. The different extracts were more effective against Gram-positive bacteria, Staphylococcus epidermidis being the most susceptible species. Concerning antifungal activity, Trichophyton rubrum was the most sensitive species. Although the molecular mechanisms underlying these properties remain poorly understood, the results obtained turn phlorotannins purified extracts a novel and potent pharmacological alternative for the treatment of a wide range of microbial infections, which usually also present an inflammatory component. In addition to the biological properties demonstrated herein, phlorotannins extracts may also be preferred, in order to avoid side effects and allergic reactions commonly associated with synthetic drugs.
- Fuzzy logic based approach for object feature trackingPublication . Lopes, Nuno Vieira; Melo-Pinto, Pedro; Couto, Pedro M.This thesis introduces a novel technique for feature tracking in sequences of greyscale images based on fuzzy logic. A versatile and modular methodology for feature tracking using fuzzy sets and inference engines is presented. Moreover, an extension of this methodology to perform the correct tracking of multiple features is also presented. To perform feature tracking three membership functions are initially defined. A membership function related to the distinctive property of the feature to be tracked. A membership function is related to the fact of considering that the feature has smooth movement between each image sequence and a membership function concerns its expected future location. Applying these functions to the image pixels, the corresponding fuzzy sets are obtained and then mathematically manipulated to serve as input to an inference engine. Situations such as occlusion or detection failure of features are overcome using estimated positions calculated using a motion model and a state vector of the feature. This methodology was previously applied to track a single feature identified by the user. Several performance tests were conducted on sequences of both synthetic and real images. Experimental results are presented, analysed and discussed. Although this methodology could be applied directly to multiple feature tracking, an extension of this methodology has been developed within that purpose. In this new method, the processing sequence of each feature is dynamic and hierarchical. Dynamic because this sequence can change over time and hierarchical because features with higher priority will be processed first. Thus, the process gives preference to features whose location are easier to predict compared with features whose knowledge of their behavior is less predictable. When this priority value becomes too low, the feature will no longer tracked by the algorithm. To access the performance of this new approach, sequences of images where several features specified by the user are to be tracked were used. In the final part of this work, conclusions drawn from this work as well as the definition of some guidelines for future research are presented.
- Distributed Coding/Decoding Complexity in Video Sensor NetworksPublication . Cordeiro, Paulo J.; Assunção, PedroVideo Sensor Networks (VSNs) are recent communication infrastructures used to capture and transmit dense visual information from an application context. In such large scale environments which include video coding, transmission and display/storage, there are several open problems to overcome in practical implementations. This paper addresses the most relevant challenges posed by VSNs, namely stringent bandwidth usage and processing time/power constraints. In particular, the paper proposes a novel VSN architecture where large sets of visual sensors with embedded processors are used for compression and transmission of coded streams to gateways, which in turn transrate the incoming streams and adapt them to the variable complexity requirements of both the sensor encoders and end-user decoder terminals. Such gateways provide real-time transcoding functionalities for bandwidth adaptation and coding/decoding complexity distribution by transferring the most complex video encoding/decoding tasks to the transcoding gateway at the expense of a limited increase in bit rate. Then, a method to reduce the decoding complexity, suitable for system-on-chip implementation, is proposed to operate at the transcoding gateway whenever decoders with constrained resources are targeted. The results show that the proposed method achieves good performance and its inclusion into the VSN infrastructure provides an additional level of complexity control functionality.