Spectra: Robust Estimation of Distribution Functions in Networks

Distributed aggregation allows the derivation of a given global aggregate property from many individual local values in nodes of an interconnected network system. Simple aggregates such as minima/maxima, counts, sums and averages have been thoroughly studied in the past and are important tools for distributed algorithms and network coordination. Nonetheless, this kind of aggregates may not be comprehensive enough to characterize biased data distributions or when in presence of outliers, making the case for richer estimates of the values on the network. This work presents Spectra, a distributed algorithm for the estimation of distribution functions over large scale networks. The estimate is available at all nodes and the technique depicts important properties, namely: robust when exposed to high levels of message loss, fast convergence speed and fine precision in the estimate. It can also dynamically cope with changes of the sampled local property, not requiring algorithm restarts, and is highly resilient to node churn. The proposed approach is experimentally evaluated and contrasted to a competing state of the art distribution aggregation technique.Comment: Full version of the paper published at 12th IFIP International Conference on Distributed Applications and Interoperable Systems (DAIS), Stockholm (Sweden), June 201

Desenvolvimento de software modular para análise pelo método dos elementos finitos em incompressibilidade

The importance of numerical simulation in the engineering field makes relevant the development of computational tools, based on the Finite Element Method, to solve structural problems. However, the application of the classical Finite Element approach to incompressible (or near-incompressible) situations has been a source of numerical problems, such as volumetric locking. This Dissertation describes several formulations used in the analysis of incompressible problems, with focus on the four-node bi-linear quadrilateral element. Over the last decades special attention has been given to improve the performance of this element under incompressibility due to its computational effectiveness, making it attractive to be used in complex problems. The devised solutions are often targeted at treating the effects of volumetric locking, although some of them were originally targeted at the treatment of shear locking. In this context, the studied formulations were the selective integration approach, the B-bar method, the mixed (u/p) method and the enhanced strain method, which includes compatible and incompatible mode elements. In order to computationally implement these finite element formulations, a revision of the fundamental concepts and basic formulas of the classical method, and for each alternative formulation, is carried out. In the context of incompressibility, the underlying concept is presented and the problem of locking is described. The development of an in-house software, also in the context of this Dissertation, targeted at solving incompressible problems is discussed. Some important sub-routines and programming approaches are referred to with code examples. Finally, the quality of implementation and efficiency of the finite element formulations is evaluated by analyzing a series of benchmark tests, using the developed in-house software and comparing the results against the ones coming from a commercial finite element software.A importância da simulação numérica no campo da engenharia torna relevante o desenvolvimento de ferramentas computacionais, baseadas no Método dos Elementos Finitos, destinadas à resolução de problemas estruturais. Contudo, a aplicação do Método dos Elementos Finitos a problemas incompressíveis ou (quasi-incompressíveis) apresenta tipicamente uma série de problemas, nomeadamente de retenção numérica. Nesta dissertação são descritas várias formulações destinadas à análise de problemas incompressívies com enfoque no elemento finito quadrilátero (bilinear) de quatro nós. Nas últimas décadas, este elemento tem vindo a receber especial atenção no sentido de melhorar a sua performance em problemas de incompressibilidade, devido à sua elevada eficiência em termos computacionais, o que o torna atractivo para ser utilizado em problemas mais complexos. Geralmente, as soluções desenvolvidas passam por estratégias de minimização dos efeitos de retenção volumétrica, embora algumas dessas formulações se destinassem originalmente a resolver problemas de retenção associados às componentes de deformação de corte. Neste contexto, as formulações estudadas foram a integração selectiva, o método B-bar, o método misto deslocamento/pressão e o método das deformações acrescentadas, o qual inclui formulações de modos compatíveis e incompatíveis. Tendo em vista a implementação computacional destas formulações de elementos finitos, efectua-se uma revisão dos conceitos básicos fundamentais do método clássico e das formulações alternativas. No contexto da incompressibilidade, apresenta-se o conceito básico e uma breve referência ao problema da retenção. No contexto desta dissertação foi desenvolvido um software destinado a resolver problemas de incompressibilidade. Algumas sub-rotinas são apresentadas fazendo referência a algumas abordagens de programação com exemplificação de código. Finalmente, avalia-se a qualidade da implementação e a eficiência das formulações implementadas através da análise de resultados de diversos benchmarks, usando o software desenvolvido e comparando os resultados obtidos com aqueles provenientes de um software comercial.Mestrado em Engenharia Mecânic

Enhanced two-phase contention window MAC protocol for wireless sensor networks applications

This work was supported by the PhD FCT grant SFRH/BD/38356/2007 and IT grant PEst-OE/EEI/ LA0008/2011. I also acknowledge several projects where I was involved in: COST IC1004, COST 2100, MobileMAN, OPPORTUNISTIC-CR, PROENERGY-WSN, Smart-Clothing, and INSYSMNowadays, the user of Wireless Sensor Networks (WSNs) is becoming more and more demanding in terms of choice and diversity of applications. As a consequence, as the diversity of applications continues to grow there is a need to identify and classify the set of detailed characterization parameters that facilitates to sketch up a taxonomy for WSN applications. The proposed taxonomy identi es the services offered by each application makes a tool available to better understand the services and requirements of each application, along with a holistic overview of the WSN proposed application taxonomy. The research also involved the actual development of WSN applications within different research projects, namely in the elds of healthcare (Smart Clothing), civil engineering structure monitoring (INSYSM) and precision agriculture. Different medium access control mechanisms employ different collision avoidance schemes to cope with packet collision and retransmission, trading-off complexity, energy inef ciency and control of packet overhead. In particular, this PhD thesis addresses the study the packet collision probability for a MAC protocol that employs a collision avoidance mechanism with two contention window and consequent proposal of a model for the collision probability. Simulation results validate the model for saturated traf c. For unsaturated traf c and with a small number of nodes, the accuracy of the model is limited by numerical rounding. It is shown that, by using our analytical model, we have been able to obtain performance metrics such as network throughput and average service time for the successful transmissions. In addition, the Enhanced Reliability Decision Algorithm in the physical layer has been proposed. The frame capture effect (FC) feature has been implemented in the IEEE 802.15.4 compliant physical layer of the MiXiM framework. The proposed decision algorithm utilizes the Signal to Noise-plus-Interference ratio (SNIR) and the size of the packet to guarantee the delivery with certain reliability to the MAC layer, of a packet received at the PHY layer. A gain of more than 10 % has been achieved in the delivery ratio. Promising results have also been obtained for the SCP-MAC protocol with the FC effect enabled, for different values of reliability. As one of the main contributions of this thesis, an innovative ef cient multi-channel MAC protocol, based on SCP-MAC, was proposed, the so-called Multi-Channel Scheduled Channel Polling (MC-SCP-MAC) protocol. The in uential range concept, denial channel list (which considers the degradation metric of each slot channel), extra resolution phase algorithm and frame capture effect have been explored to achieve the maximum performance in terms of delivery ratio and energy consumption. It has been shown MC-SCP-MAC outperforms SCP-MAC and MC-LMAC in denser scenarios, with improved throughput fairness. Considering the in uential range concept reduces the redundancy level in the network facilitating to reduce the energy consumption whilst decreasing the latency. The conclusions from this research reveal the importance of an appropriate design for the MAC protocol for the desired WSN application. Depending on the objective or mission of the WSN application, different protocols are required. Therefore, the overall performance of a WSN application certainly depends on the appropriate development and application of the appropriate communication protocols (e.g., MAC, network layer)

A comparison about the predictive ability of FCGARCH, facing EGARCH and GJR

In order to study the volatility of a stock market, several volatility models have been created, studied and improved throughout the time. Due to the extreme and actual situation in international stock market’s volatility, the main objective of this thesis is to focus on the FCGARCH model created by Medeiros and Veiga (2009), and compare it with some of the most popular asymmetric autoregressive conditional heteroskedasticity models, such as EGARCH and GJR. Using the daily returns of 5 most important international stock market indexes, such as S&P500 (USA), FTSE100 (UK), Nikkei225 (Japan), DAX30 (Germany) and PSI20 (Portugal), and using the Harvey-Newbold test, we are going to check which of these models is the best one to fit the conditional heteroskedastic volatilities of the returns of the indexes under study. In order to make the thesis possible, I have created the FCGARCH, EGARCH and GJR models’ codes in Matlab, with the help of my co-supervisor, Doctor Renato Costa, as well as used the Harvey-Newbold test in E-views, created by my supervisor, Professor José Dias Curto. According to the estimation results, in the in-sample analysis, when looking at the Quasi-Maximum-Log likelihood goodness-of-fit measure, the FCGARCH fits most of the indexes’ returns under study, where, in the out-of-sample analysis, according to the Harvey-Newbold test for multiple forecasts encompassing, the results show that the GJR seems to encompass the other two models in most of the indexes, thus concluding that GJR seems to be the best model to forecast the volatility.Para que possamos estudar a volatilidade de uma ação, muitos foram os modelos criados, estudados e melhorados ao longo do tempo. Devido à extrema e atual situação da volatilidade nos mercados acionistas internacionais, o principal objetivo desta tese é focar no modelo FCGARCH, criado por Medeiros e Veiga (2009), e compará-lo com alguns dos mais importantes modelos heterocedásticos, autorregressivos e assimétricos, como o EGARCH e o GJR. Utilizando os retornos diários de 5 dos índices mais importantes a nível internacional, tais como S&P500 (EUA), FTSE100 (RU), Nikkei225 (Japão), DAX30 (Alemanha) e PSI20 (Portugal), e usando o teste de Harvey-Newbold, vamos descobrir qual dos modelos apresentados é o que melhor descreve o comportamento das variâncias condicionais heterocedásticas dos retornos dos índices sob estudo. Para que a criação desta tese fosse possível, tive de criar os códigos dos modelos do FCGARCH, EGARCH e GJR no Matlab, com a ajuda do meu co-orientador, o Doutor Renato Costa, assim como usar o teste de Harvey-Newbold no E-views, criado pelo meu orientador, o Professor José Dias Curto. De acordo com os resultados estimados, na análise in-sample, ao olharmos para a medida de quase-máxima-verosimilhança, o FCGARCH descreve bem a maioria dos retornos sob estudo, enquanto, na análise out-of-sample, de acordo com o teste de Harvey-Newbold para a abrangência de previsões, os resultados demonstram que o GJR parece abranger os outros dois modelos na maioria dos índices, desta forma concluindo que o GJR parece ser o melhor modelo para prever a volatilidade

Showrooming : a look into the Portuguese electronics market

The Internet made information widely available to every person with a connection. Furthermore, the increasing popularity of tablets and smartphones in the 2000s made the Internet connection more accessible and mobile. Nowadays, the combination of the facilitated access to the Internet and the growing number of online retailers generates transparency on the consumers’ minds that wasn’t possible before. We can check the price of an iPhone on a country on the other side of the world just by tapping a few times on the screen. Therefore, there’s a risk that brick-and-mortar stores turn into showrooms as consumers use them to see and touch the products but they never actually make the purchase offline. Although online vs. offline behavior has been widely studied in the past, the research about showrooming is insufficient. Plus, showrooming has many times been addressed from a negative standpoint, where authors try to identify and quantify the adverse effects for retailers.A Internet tornou a informação amplamente disponível para qualquer pessoa com uma conexão. Para além disso, a popularidade crescente dos tablets e smartphones nos anos 2000 fez com que esta conexão se tornasse fácil e móvel. Hoje em dia, a combinação do acesso à Internet com o número crescente de retalhistas online criou uma transparência para os consumidores que não era possível até agora. Qualquer consumidor pode ver o preço de um produto num país que fica do outro lado do mundo ao clicar duas ou três vezes num ecrã. Existe então o risco das lojas tradicionais se tornarem em lojas de exposição que os consumidores usam apenas para ver os produtos. Embora o comportamento online vs. offline já tenha sido extensivamente estudado no passado, há uma quantidade limitada de investigação no que diz respeito ao showrooming. Para além disso, o fenómeno tem sido muitas vezes estudar ode uma perspetiva negativa em que os autores tentam identificar e quantificar os efeitos negativos para os retalhistas

Internationalization plan of NMusic to Angola

Field lab: Entrepreneurial and innovative venturesThe work project hereby presented consists in the internationalization plan of the Portuguese start-up NMusic to the Angolan market. It starts by going through the literature review, background of the company and the analysis of its business model, where the stakeholders and the competitive advantages of the firm are identified. Then, there is the analysis of the business environment and market research supported by semi structured interviews, followed by the recommendation for NMusic’s entry mode and implementation plan. A qualitative risk assessment was conducted and final recommendations were provided to ensure the internationalization to Angola succeeds. Given that the technology infrastructure and the digital music industry in Angola are still underdeveloped the internationalization to Angola must be perceived as a stake in the future when this industry will be at its full potential. The main recommendation is to position the service as premium and target the high income consumers. This way it will be possible to gain market experience and step by step increasing the brand awareness and market share

Álvaro Siza and Carlos Castanheira’s China Design Museum: Form, Contemporary City and Design Method

Portuguese architects, Álvaro Siza and Carlos Castanheira’s China Design Museum of the China Academy of Art in Hangzhou (2012-2018) calls for a problematization of the theme of the “boundary” at different levels. In this essay the project is compared with other relevant works in regards to form, the contemporary city and design method. Formed by two bars and a partly sunken volume enclosing a triangular courtyard, the building is immediately reminiscent of other L and U plans by Siza that question private/public and interior/exterior relationships. After Rem Koolhaas published “The Generic City” in 1994, the Chinese city became the epitome of the contemporary city. Since Siza’s architecture has been discussed in terms of its continuity with the city and tradition, the project of the China Design Museum raises the question: How does Siza work in the Chinese city? Siza and Castanheira’s building is at the same time part of a large campus planned by the well-known local architects Wang Shu and Lu Wenyu/Amateur Architecture, whose experimental approach to drawing and craft skills suggests yet another set of comparisons. To sum up, Siza and Castanheira avoid easy solutions: the siting and massing, scale, spatial organization and material expression of the China Design Museum provide a measure between realities – open/closed, traditional/contemporary, local/universal – that first appeared incommensurable