Beacon scheduling in cluster-tree IEEE 802.15.4/ZigBee wireless sensor networks

The recently standardized IEEE 802.15.4/Zigbee protocol stack offers great potentials for ubiquitous and pervasive computing, namely for Wireless Sensor Networks (WSNs). However, there are still some open and ambiguous issues that turn its practical use a challenging task. One of those issues is how to build a synchronized multi-hop cluster-tree network, which is quite suitable for QoS support in WSNs. In fact, the current IEEE 802.15.4/Zigbee specifications restrict the synchronization in the beacon-enabled mode (by the generation of periodic beacon frames) to star-based networks, while it supports multi-hop networking using the peer-to-peer mesh topology, but with no synchronization. Even though both specifications mention the possible use of cluster-tree topologies, which combine multi-hop and synchronization features, the description on how to effectively construct such a network topology is missing. This report tackles this problem, unveils the ambiguities regarding the use of the cluster-tree topology and proposes two collisionfree beacon frame scheduling schemes.

A sensitivity study of the WRF model in wind simulation for an area of high wind energy

The performance of the Weather Research and Forecast (WRF) model in wind simulation was evaluated under different numerical and physical options for an area of Portugal, located in complex terrain and characterized by its significant wind energy resource. The grid nudging and integration time of the simulations were the tested numerical options. Since the goal is to simulate the near-surface wind, the physical parameterization schemes regarding the boundary layer were the ones under evaluation. Also, the influences of the local terrain complexity and simulation domain resolution on the model results were also studied. Data from three wind measuring stations located within the chosen area were compared with the model results, in terms of Root Mean Square Error, Standard Deviation Error and Bias. Wind speed histograms, occurrences and energy wind roses were also used for model evaluation. Globally, the model accurately reproduced the local wind regime, despite a significant underestimation of the wind speed. The wind direction is reasonably simulated by the model especially in wind regimes where there is a clear dominant sector, but in the presence of low wind speeds the characterization of the wind direction (observed and simulated) is very subjective and led to higher deviations between simulations and observations. Within the tested options, results show that the use of grid nudging in simulations that should not exceed an integration time of 2 days is the best numerical configuration, and the parameterization set composed by the physical schemes MM5–Yonsei University–Noah are the most suitable for this site. Results were poorer in sites with higher terrain complexity, mainly due to limitations of the terrain data supplied to the model. The increase of the simulation domain resolution alone is not enough to significantly improve the model performance. Results suggest that error minimization in the wind simulation can be achieved by testing and choosing a suitable numerical and physical configuration for the region of interest together with the use of high resolution terrain data, if available.

Calculation of fractional derivatives of noisy data with genetic algorithms

This paper addresses the calculation of derivatives of fractional order for non-smooth data. The noise is avoided by adopting an optimization formulation using genetic algorithms (GA). Given the flexibility of the evolutionary schemes, a hierarchical GA composed by a series of two GAs, each one with a distinct fitness function, is established.

Anotação colaborativa de conteúdos utilizando jogos com propósito

Com o crescimento da informação disponível na Web, arquivos pessoais e profissionais, protagonizado tanto pelo aumento da capacidade de armazenamento de dados, como pelo aumento exponencial da capacidade de processamento dos computadores, e do fácil acesso a essa mesma informação, um enorme fluxo de produção e distribuição de conteúdos audiovisuais foi gerado. No entanto, e apesar de existirem mecanismos para a indexação desses conteúdos com o objectivo de permitir a pesquisa e acesso aos mesmos, estes apresentam normalmente uma grande complexidade algorítmica ou exigem a contratação de pessoal altamente qualificado, para a verificação e categorização dos conteúdos. Nesta dissertação pretende-se estudar soluções de anotação colaborativa de conteúdos e desenvolver uma ferramenta que facilite a anotação de um arquivo de conteúdos audiovisuais. A abordagem implementada é baseada no conceito dos “Jogos com Propósito” (GWAP – Game With a Purpose) e permite que os utilizadores criem tags (metadatos na forma de palavras-chave) de forma a atribuir um significado a um objecto a ser categorizado. Assim, e como primeiro objectivo, foi desenvolvido um jogo com o propósito não só de entretenimento, mas também que permita a criação de anotações audiovisuais perante os vídeos que são apresentados ao jogador e, que desta forma, se melhore a indexação e categorização dos mesmos. A aplicação desenvolvida permite ainda a visualização dos conteúdos e metadatos categorizados, e com o objectivo de criação de mais um elemento informativo, permite a inserção de um like num determinado instante de tempo do vídeo. A grande vantagem da aplicação desenvolvida reside no facto de adicionar anotações a pontos específicos do vídeo, mais concretamente aos seus instantes de tempo. Trata-se de uma funcionalidade nova, não disponível em outras aplicações de anotação colaborativa de conteúdos audiovisuais. Com isto, o acesso aos conteúdos será bastante mais eficaz pois será possível aceder, por pesquisa, a pontos específicos no interior de um vídeo.

Approximating fractional derivatives in the perspective of system control

The theory of fractional calculus goes back to the beginning of the theory of differential calculus, but its application received attention only recently. In the area of automatic control some work was developed, but the proposed algorithms are still in a research stage. This paper discusses a novel method, with two degrees of freedom, for the design of fractional discrete-time derivatives. The performance of several approximations of fractional derivatives is investigated in the perspective of nonlinear system control.

Analysis of the Van der Pol oscillator containing derivatives of fractional order

In this paper a modified version of the classical Van der Pol oscillator is proposed, introducing fractional-order time derivatives into the state-space model. The resulting fractional-order Van der Pol oscillator is analyzed in the time and frequency domains, using phase portraits, spectral analysis and bifurcation diagrams. The fractional-order dynamics is illustrated through numerical simulations of the proposed schemes using approximations to fractional-order operators. Finally, the analysis is extended to the forced Van der Pol oscillator.

Extending the learning object definition to represent programming problems

The present generation of eLearning platforms values the interchange of learning objects standards. Nevertheless, for specialized domains these standards are insufficient to fully describe all the assets, especially when they are used as input for other eLearning services. To address this issue we extended an existing learning objects standard to the particular requirements of a specialized domain, namely the automatic evaluation of programming problems. The focus of this paper is the definition of programming problems as learning objects. We introduce a new schema to represent metadata related to automatic evaluation that cannot be conveniently represented using existing standards, such as: the type of automatic evaluation; the requirements of the evaluation engine; or the roles of different assets - tests cases, program solutions, etc. This new schema is being used in an interoperable repository of learning objects, called crimsonHex.

Defining programming problems as learning objects

Standards for learning objects focus primarily on content presentation. They were already extended to support automatic evaluation but it is limited to exercises with a predefined set of answers. The existing standards lack the metadata required by specialized evaluators to handle types of exercises with an indefinite set of solutions. To address this issue we extended existing learning object standards to the particular requirements of a specialized domain. We present a definition of programming problems as learning objects that is compatible both with Learning Management Systems and with systems performing automatic evaluation of programs. The proposed definition includes metadata that cannot be conveniently represented using existing standards, such as: the type of automatic evaluation; the requirements of the valuation engine; and the roles of different assets - tests cases, program solutions, etc. We present also the EduJudge project and its main services as a case study on the use of the proposed definition of programming problems as learning objects.

Tecnologias multimédia no apoio ao ensino aprendizagem de suporte básico de vida

A sociedade moderna encontra-se numa evolução progressiva e vertiginosa nomeadamente no que respeita às novas tecnologias. Independentemente da área de conhecimento, é de senso comum que cada vez mais é necessária uma formação sólida, sendo fundamental a preparação e a consolidação das futuras gerações na utilização das novas tecnologias. As plataformas de e-learning são hoje em dia uma realidade mais que afirmada e com aplicação em todos os setores de atividade. Na área da saúde, e mais concretamente no que diz respeito ao tema de Suporte Básico de Vida (SBV), foi-nos possível verificar que a maioria das pessoas revela falta de conhecimentos sobre o tema e, não obstante existirem cursos sobre este tema, a disponibilidade para a sua frequência nem sempre é possível pela distância, falta de tempo e disponibilidade para a sua frequência, bem como pelos custos envolvidos. O presente estudo pretende contribuir para uma análise e investigação sobre o potencial de utilização das novas Tecnologias Multimédia, aplicando-as ao ensino concreto de primeiros socorros e especialmente de Suporte Básico de Vida, num recurso educativo digital com o formato de Objeto de Aprendizagem. Para o efeito, será construído um Objeto de Aprendizagem temático, focalizando o tema de SBV. O repositório MERLOT foi utilizado como meio de distribuição global, no sentido de aferir o potencial e facilidade de distribuição e catalogação com metadados. Foi ainda colocado on-line o “SBVOA” (Objeto de Aprendizagem desenvolvido no presente estudo), numa página criada apenas para o efeito. Esta dissertação apresenta o estudo desenvolvido para investigação do potencial de aprendizagem proporcionado pelo Objeto de Aprendizagem desenvolvido, validando se pode ser uma alternativa interativa de educação em SBV, contribuindo deste modo para a diminuição de eventuais perdas de vida.

Development of procedures for the simulation of atmospheric flows over complex terrain, using OpenFOAM

The main purpose of this work was the development of procedures for the simulation of atmospheric ows over complex terrain, using OpenFOAM. For this aim, tools and procedures were developed apart from this code for the preprocessing and data extraction, which were thereafter applied in the simulation of a real case. For the generation of the computational domain, a systematic method able to translate the terrain elevation model to a native OpenFOAM format (blockMeshDict) was developed. The outcome was a structured mesh, in which the user has the ability to de ne the number of control volumes and its dimensions. With this procedure, the di culties of case set up and the high computation computational e ort reported in literature associated to the use of snappyHexMesh, the OpenFOAM resource explored until then for the accomplishment of this task, were considered to be overwhelmed. Developed procedures for the generation of boundary conditions allowed for the automatic creation of idealized inlet vertical pro les, de nition of wall functions boundary conditions and the calculation of internal eld rst guesses for the iterative solution process, having as input experimental data supplied by the user. The applicability of the generated boundary conditions was limited to the simulation of turbulent, steady-state, incompressible and neutrally strati ed atmospheric ows, always recurring to RaNS (Reynolds-averaged Navier-Stokes) models. For the modelling of terrain roughness, the developed procedure allowed to the user the de nition of idealized conditions, like an uniform aerodynamic roughness length or making its value variable as a function of topography characteristic values, or the using of real site data, and it was complemented by the development of techniques for the visual inspection of generated roughness maps. The absence and the non inclusion of a forest canopy model limited the applicability of this procedure to low aerodynamic roughness lengths. The developed tools and procedures were then applied in the simulation of a neutrally strati ed atmospheric ow over the Askervein hill. In the performed simulations was evaluated the solution sensibility to di erent convection schemes, mesh dimensions, ground roughness and formulations of the k - ε and k - ω models. When compared to experimental data, calculated values showed a good agreement of speed-up in hill top and lee side, with a relative error of less than 10% at a height of 10 m above ground level. Turbulent kinetic energy was considered to be well simulated in the hill windward and hill top, and grossly predicted in the lee side, where a zone of ow separation was also identi ed. Despite the need of more work to evaluate the importance of the downstream recirculation zone in the quality of gathered results, the agreement between the calculated and experimental values and the OpenFOAM sensibility to the tested parameters were considered to be generally in line with the simulations presented in the reviewed bibliographic sources.

Experimental and numerical study on the evaluation of ventilation efficiency

Buildings account for 40% of total energy consumption in the European Union. The reduction of energy consumption in the buildings sector constitute an important measure needed to reduce the Union's energy dependency and greenhouse gas emissions. The Portuguese legislation incorporate this principles in order to regulate the energy performance of buildings. This energy performance should be accompanied by good conditions for the occupants of the buildings. According to EN 15251 (2007) the four factors that affect the occupant comfort in the buildings are: Indoor Air Quality (IAQ), thermal comfort, acoustics and lighting. Ventilation directly affects all except the lighting, so it is crucial to understand the performance of it. The ventilation efficiency concept therefore earn significance, because it is an attempt to quantify a parameter that can easily distinguish the different options for air diffusion in the spaces. The two indicators most internationally accepted are the Air Change Efficiency (ACE) and the Contaminant Removal Effectiveness (CRE). Nowadays with the developed of the Computational Fluid Dynamics (CFD) the behaviour of ventilation can be more easily predicted. Thirteen strategies of air diffusion were measured in a test chamber through the application of the tracer gas method, with the objective to validate the calculation by the MicroFlo module of the IES-VE software for this two indicators. The main conclusions from this work were: that the values of the numerical simulations are in agreement with experimental measurements; the value of the CRE is more dependent of the position of the contamination source, that the strategy used for the air diffusion; the ACE indicator is more appropriate for quantifying the quality of the air diffusion; the solutions to be adopted, to maximize the ventilation efficiency should be, the schemes that operate with low speeds of supply air and small differences between supply air temperature and the room temperature.

PExIL: Programming Exercises Interoperability Language

Several standards appeared in recent years to formalize the metadata of learning objects, but they are still insufficient to fully describe a specialized domain. In particular, the programming exercise domain requires interdependent resources (e.g. test cases, solution programs, exercise description) usually processed by different services in the programming exercise life-cycle. Moreover, the manual creation of these resources is time-consuming and error-prone leading to what is an obstacle to the fast development of programming exercises of good quality. This paper focuses on the definition of an XML dialect called PExIL (Programming Exercises Interoperability Language). The aim of PExIL is to consolidate all the data required in the programming exercise life-cycle, from when it is created to when it is graded, covering also the resolution, the evaluation and the feedback. We introduce the XML Schema used to formalize the relevant data of the programming exercise life-cycle. The validation of this approach is made through the evaluation of the usefulness and expressiveness of the PExIL definition. In the former we present the tools that consume the PExIL definition to automatically generate the specialized resources. In the latter we use the PExIL definition to capture all the constraints of a set of programming exercises stored in a learning objects repository.

Making programming exercises interoperable with PExIL

Several standards have appeared in recent years to formalize the metadata of learning objects, but they are still insufficient to fully describe a specialized domain. In particular, the programming exercise domain requires interdependent resources (e.g. test cases, solution programs, exercise description) usually processed by different services in the programming exercise lifecycle. Moreover, the manual creation of these resources is time-consuming and error-prone, leading to an obstacle to the fast development of programming exercises of good quality. This chapter focuses on the definition of an XML dialect called PExIL (Programming Exercises Interoperability Language). The aim of PExIL is to consolidate all the data required in the programming exercise lifecycle from when it is created to when it is graded, covering also the resolution, the evaluation, and the feedback. The authors introduce the XML Schema used to formalize the relevant data of the programming exercise lifecycle. The validation of this approach is made through the evaluation of the usefulness and expressiveness of the PExIL definition. In the former, the authors present the tools that consume the PExIL definition to automatically generate the specialized resources. In the latter, they use the PExIL definition to capture all the constraints of a set of programming exercises stored in a learning objects repository.

A survey on e-learning content standardization

eLearning has been evolved in a gradual and consistent way. Along with this evolution several specialized and disparate systems appeared to fulfill the needs of teachers and students such as repositories of learning objects, intelligent tutors, or automatic evaluators. This heterogeneity poses issues that are necessary to address in order to promote interoperability among systems. Based on this fact, the standardization of content takes a leading role in the eLearning realm. This article presents a survey on current eLearning content standards. It gathers information on the most emergent standards and categorizes them according three distinct facets: metadata, content packaging and educational design.

Fast mobility support in low-power wireless networks: smart-HOP over RPL/6LoWPAN

With the emergence of low-power wireless hardware new ways of communication were needed. In order to standardize the communication between these low powered devices the Internet Engineering Task Force (IETF) released the 6LoWPAN stand- ard that acts as an additional layer for making the IPv6 link layer suitable for the lower-power and lossy networks. In the same way, IPv6 Routing Protocol for Low- Power and Lossy Networks (RPL) has been proposed by the IETF Routing Over Low power and Lossy networks (ROLL) Working Group as a standard routing protocol for IPv6 routing in low-power wireless sensor networks. The research performed in this thesis uses these technologies to implement a mobility process. Mobility management is a fundamental yet challenging area in low-power wireless networks. There are applications that require mobile nodes to exchange data with a xed infrastructure with quality-of-service guarantees. A prime example of these applications is the monitoring of patients in real-time. In these scenarios, broadcast- ing data to all access points (APs) within range may not be a valid option due to the energy consumption, data storage and complexity requirements. An alternative and e cient option is to allow mobile nodes to perform hand-o s. Hand-o mechanisms have been well studied in cellular and ad-hoc networks. However, low-power wireless networks pose a new set of challenges. On one hand, simpler radios and constrained resources ask for simpler hand-o schemes. On the other hand, the shorter coverage and higher variability of low-power links require a careful tuning of the hand-o parameters. In this work, we tackle the problem of integrating smart-HOP within a standard protocol, speci cally RPL. The simulation results in Cooja indicate that the pro- posed scheme minimizes the hand-o delay and the total network overhead. The standard RPL protocol is simply unable to provide a reliable mobility support sim- ilar to other COTS technologies. Instead, they support joining and leaving of nodes, with very low responsiveness in the existence of physical mobility.