Repositório RCAAP

A set of parameters to assess the objective quality of visualizations of a voxel based data set, producedusing a ray caster, is proposed as a first step toward the evaluation of the overall quality of these visualizations. Results obtained using synthetic data and a simple implementation of a ray caster are presented. The final goal of this evaluation will be the computation of “confidence indices” that could offer the user a “guided visualization”, i.e. allow him/her to decide what are the best visualizations of a data set.

This paper describes a high quality speech coding system based in the ITU Recommendation G.722 “7 kHzaudio coding within 64 kbit/s”. Provides a high-level description of the recommended algorithm and a briefdiscussion about the arithmetical choices, which have been made. Some performance results are provided.

In the first part of the paper some mobile satellite communication systems proposed by various entities arebriefly presented, some channel allocation techniques described and the problem caused by handovers in ICO and LEO type constellations is discussed. Afterwards the developed traffic simulator is presented along with various simulation results for a LEO and an ICO type constellation. The simulator permits the calculation of satellite traffic at footprint and/or spotbeam level in various instances of the satellite’s trajectory.

Nowadays, around 80% of local area networks are Ethernet based. However, aside from all the criticismover Ethernet technology, the market share does not tend to decrease. The growth of transmission speed, introduced with Fast Ethernet and, more recently, with Gigabit Ethernet, keeps the technology up to date, in despite of some limitations introduced by the compatibility with previous standards.

This paper reports briefly on the modular and distributed architecture adopted for the development andimplementation of a system prototype based on a palmtop computer, aiming the support of complex task routines performed by people with severe intellectual disabilities. In particular, modularity of the adopted solution and the wireless communication protocol are shortly described, together with their interrelation with the functional specification of the project. This work is part of the European project VICAID (Vocational Integration through Computer Assistance for Intellectually Disabled People).

This paper aims to present the risks associated with the use of distributed computing environments and withthe access to information systems, identifying the solutions currently available that could minimise them. At the end, some cases of study are presented, using real security implementations adopted by Universidade de Aveiro (UA).

In this paper we describe a system for automatic all night analysis of sleep, based on neural networks. Thesystem consists of a three step analysis. The first step is the recognition of elementary patterns in EEG (delta, alpha, spindle and K complex waves), EOG and EMG, and spectral analysis for background activity. The second step is the determination of sleep stages based on these parameters. Automatic sleep scoring was performed using a multilayer feedforward network. The last step, is the supervision of the automatic decision using ambiguity rejection and coherence analysis. This work presents also, an automated system for micro arousals detection based on k-means method. The system was validated with a data set including 8 recordings (20 h). Overall agreement between the computer and human judges indicates considerable reliability of the system.

This paper discusses the VHDL simulation of Hierarchical Finite State Machines. It presentes the resultsobtained with the simulation of the model described in [1], introduces a new model and shows its advantages. Both Moore and Mealy machines are being considered. The considered model provides such new facilities as flexibility, extensibility and reuse of an algorithm described by Hierarchical Graph-Schemes.

The fast evolution of mobile computing equipment and the consequent raising mobility requirements has been the major drive of research in Wireless Local Area Networks. WLANs distinguishes from cabled networks at physical layer and MAC layer. This paper focus aspects of both layers: it presents transmissions technologies and discusses the requirements of a MAC (Medium Access Control) protocol to be used in this networks. IEEE802.11 protocol is described and its development and implementation is presented. This works has been carried on under scope of the european project ESPRIT.6892 - POWER (Portable Workstation for Education in Europe).

In this paper we present an overview of the architecture, the design process and the main properties of a communication and shared memory management unit for a MIMD type multiprocessor mesh. The circuit has been completely specified and was later designed as a standard cell ASIC based on ES21 ECPD10 library of cells, for a N-Well CMOS m process. The CAD framework used was Cadence Edge (ES2 SOLO 203

In this paper we address the issue of edge detection in digital images using linear filtering and differentiation.Our main objective was to join, and in some sense unify, a significant part of the techniques that fall into this paradigm. First, we focus on the question of two-dimensional differentiation and the problems associated with its application in the discrete spatial domain. Afterwards, we review some of the most commonly used filtering techniques for edge detection.

In this paper the errors caused by probe loading in reflection coefficient measurements using slotted line isquantified. A method based on the theory of conformal bilinear transforms is introduced. It allows the calculation of load reflection coefficient amplitude and phase measurement errors as well as a visual inspection of the interaction between the measuring system and the probe by plotting the full reflection coefficient in a Smith Chart. A few experimental guidelines are suggested to minimise this errors.

In the last two years the University of Aveiro has participated in the Mobile Robotics International Championship in France. In this championship the robots have to autonomously follow a line among other tasks. In order to improve the performance of our participation a mathematical model has been developed that allows, through the use of simulation, to identify problems related to the stability or controlability of the robot as well as to test possible solutions before the robot is actually built. In this paper the referred mathematical model is presented as well as an implementation of a simulator based on such model using MATLAB. A case sudy is also presented.

In this work it is described a software tool implementing the Klatt synthesiser to be used on a teaching laboratory. The user interface allows an easy edition of the synthesis parameters, thus the student may quick and easily change the phonetic characteristics of a vowel and listen to the result or seeing its time or frequency properties.

Analytical models for evaluation of optical amplifiers, namely EDFA, on communications systerns are developed. Particular aspects like opical gain, ASE noise and saturated operation are given special attention. Development of a new moment generation function for the electrical decision current is reported.The model is now abLe to deal with the main stochastic processes ocurring on a digital optical receiver: optical noise, inter-symbol interference and also electricalnoise. The model is validated through comparison with loiig-established analytical expressions for particular cases and simulation. Finally the realisation and characterisation of an EDFA amplifier to serve as a 20 Gbps receiver preamplifier is also reported.

Neste trabalho, foi realizada uma implementação dum agente robótico autónomo minimalista com capacidades de navegação avançadas, as quais dependem em arquitecturas especializadas com base em redes neuronais artificiais. Pretendesemostrar que uma plataforma robótica comparativamente simples e dotada de componentes baratos é capaz de realizar tarefas complexas de navegação, tais como dead-reckorging (intuição espacial), circunscrição de pistas visuais e correspondente discriminação / reconhecimento, bem como a construção eficiente de mapas e seu uso para navegações futuras com a tomada de atalhos e voltas. São usados shaft-encoders para a implementação de uma bússola interna grosseira, bem como sensores de infravermelhos para a detecção e circunscrição de objectos. As redes neuronais utilizadas incorporam informação espacial bem como temporal. Antes de realizar a implementação filial, foi realizada unia pesquisa bibliográfica inicial, a qual permitiu saber o que existe de actual neste campo da navegação em agentes autónomos.

Ao fim de 3 anos de actividade, 7 números, cerca de 90 artigos e 800 páginas, a Comissão Editorial decidiu encerrar o 1º volume da revista Electrónica e Telecomunicações. Contámos com a colaboração da quase totalidade do corpo docente do DETUA, com numerosas contribuições de alunos de licenciatura, de mestrado e doutoramento e, ainda de alguns professores e investigadores convidados que estiveram no Departamento. (...)

This paper presents a new coding/compression algorithm for high-quality digital audio signals. The new codercomprehends a nonuniform filter bank, gain-adaptive logaritbmic quantizers, arithmetic coding, and an explicit psychoacoustic model that adapts the quantizers according to perceptual criteria. The new system differs from other perceptual coders in that its quantizers are backward-adaptive: the adaptation is not based on the original signal but on the output signal. We discuss the advantages of backward-adaptation and its application to perceptual coding. Some results are presented.

In this paper we describe the simulation environment for artificial neural networks that we have developed, and also have used, with the aim of obtaining experimental results involving this computational paradigm. This environment is based on the NSL (Neuro-simulalion lanplage), which is an interpreted language for the development and simulation of neural networks.

The objective of this paper is to explain a new technique to simulate non-linear steady-state circuits that does not use time domain, like SPICE[12], but spectral domain to do the simulations. In this paper we develop a new frequency mapping technique to use in the discretization of continuous spectrum and a new tool to do convolution and deconvolution. Finally we prove the validity of this technique.