ENIDH – EEM - Engenharia Eletrotécnica Marítima
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- Description logics, rules and multi‐context systemsPublication . L. Cruz‐Filipe, l.; Henriques, R.; Nunes, I.The combination of rules and ontologies has been a fertile topic of research in the last years, with the proposal of several different systems that achieve this goal. In this paper, we look at two of these formalisms, Mdl-programs and multi-context systems, which address different aspects of this combination, and include different, incomparable programming constructs. Despite this, we show that every Mdl-program can be transformed in a multi-context system, and this transformation relates the different semantics for each paradigm in a natural way. As an application, we show how a set of design patterns for multi-context systems can be obtained from previous work on Mdl-programs.
- Lumped Model for CMOS Interconnections linesPublication . Assunção, Mário; Santos, Pedro; Freire, João CostaA study on CMOS interconnections lines up to 40GHz is presented. The lines propagation constant γ and impedance characteristic Z0 are obtained from the measured S parameters up to 40 GHz, on test structures with different lengths, with or without metal ground plane. The values of the well-defined transmission line RLGC lumped model elements per unit length for each measured test interconnection lines are obtained. Although, the RLGC elements values are frequency dependent, we show that using constant values in a wideband, from 5 GHz to 40 GHz, the interconnections model is in good agreement with the experimental S parameters, validating the modelling technique. As expected, for shorter lines, one RLGC section is adequate to attain a good agreement with measured values. However, for longer lines, the number of RLGC sections must be increased. For low frequencies the accuracy is better for interconnections lines with metal ground plane. However, for high frequencies (f > 15 GHz) the accuracy is good for both type of interconnection lines.
- Computing Repairs from Active Integrity ConstraintsPublication . Cruz-Filipe, L.; Engrácia, P.; Nunes, I.; Gaspar, G.Repairing an inconsistent knowledge base is a well known problem for which several solutions have been proposed and implemented in the past. In this paper, we start by looking at databases with active integrity constraints - consistency requirements that also indicate how the database should be updated when they are not met - as introduced by Caroprese et al.We show that the different kinds of repairs considered by those authors can be effectively computed by searching for leaves of specific kinds of trees. Although these computations are in general not very efficient (deciding the existence of a repair for a given database with active integrity constraints is NP-complete), on average the algorithms we present make significant reductions on the number of nodes in the search tree. Finally, these algorithms also give an operational characterization of different kinds of repairs that can be used when we extend the concept of active integrity constraints to the more general setting of knowledge bases.
- Patterns for Interfacing between Logic Programs and Multiple OntologiesPublication . Cruz‐Filipe, L.; Nunes, I.; Gaspar, G.Originally proposed in the mid-90s, design patterns for software development played a key role in object-oriented programming not only in increasing software quality, but also by giving a better understanding of the power and limitations of this paradigm. Since then, several authors have endorsed a similar task for other programming paradigms, in the hope of achieving similar benefits. In this paper we discuss design patterns for hybrid semantic web systems combining several description logic knowledge bases via a logic program. We introduce eight design patterns, grouped in three categories: three elementary patterns, which are the basic building blocks; four derived patterns, built from these; and a more complex pattern, the study of which can shed some insight in future syntactic developments of the underlying framework. These patterns are extensively applied in a natural way in a large-scale example that illustrates how their usage greatly simplifies some programming tasks, at the level of both development and extension. We work in a generalization of dl-programs that supports several (possibly different) description logics, but the results presented are easily adaptable to other existing frameworks such as multi-context systems.
- Tighter integration in dl-programsPublication . Cruz-Filipe, L.; Engrácia, P.; Gaspar, G.; Henriques, R.; Nunes, I.; Santos, D.We introduce a mechanism called lifting to share predicates between the two components of a dl-program, integrating them in a tighter way. Using lifting, one can reason about the predicates being shared both via the description logic knowledge base and via Datalogstyle rules, and the deductions one makes are automatically reflected globally on both components. This is a capability not directly present in dl-programs, since changes to the knowledge base only affect the queries where they occur. We show that lifting has nice theoretical properties, making it suitable for modular design of dl-programs. Furthermore, dlprogram processors can easily incorporate lifting as a new operator, and we have extended dlvhex to work with dl-programs with lifting.
- Voltage Spikes in Integrated CMOS Buck DC-DC Converters: Analysis for Resonant and Hard Switching TopologiesPublication . Rocha, José F. da; Santos, Marcelino B. dos; Costa, J. M. DoresIn an integrated DC-DC converter, voltage spikes are generated during the commutation of the power switches and they may cause the device malfunction if its magnitude is excessive. That occurs when, targeting high efficiency, very fast switching is implemented in a low voltage CMOS process, with higher impact when the converter output current is high. These conditions that cause spikes of significant magnitude, in the order of Volts, are common in modern DC-DC converters for portable equipment powered by batteries. Magnitude limitation of voltage spikes in hard switching converters is a hot research topic and the known solutions are surveyed here. Resonant switches topologies are frequently mentioned as an alternative to overcome voltage spikes in a DC-DC converter, but generally this solution is dismissed in integrated implementations. This paper investigates if the resonant topologies are an effective solution to overcome voltage spikes during the switches commutation in a buck converter. Two buck DC-DC converters using resonant switches are analyzed, namely a QR-ZCS topology and a QSW- ZVS topology. The analysis proceeds in two steps that can be easily applied to other resonant converters. Results show that resonant DC-DC converters also generate voltage spikes which magnitude is sometimes higher than that generated in a hard switching converter, and is superimposed to the overvoltage occurring in the resonant phase. This is an important result since resonant, or soft switching, converters are occasionally mistakenly mentioned as free of voltage spikes.
- Análise Qualitativa e Quantitativa do Cluster do Mar PortuguêsPublication . Simões, Abel; Ferreira, Ana Maria; Salvador, Regina; Soares, Carlos GuedesReconhecendo-se a importância de um Cluster do Mar para Portugal, procura-se identificar e analisar as principais relações intersetoriais que se processam no seu interior. Assim, na primeira parte é feita uma análise de carácter mais qualitativo, através da aplicação de inquéritos a empresas de transporte marítimo, estaleiros navais, portos, associações empresariais e instituições de ensino e investigação. Na segunda parte, utilizando a análise de input-output procede-se à quantificação das ligações existentes entre setores do Cluster marítimo português, ao cálculo dos coeficientes de interdependência e apresentam-se alguns dos efeitos multiplicadores das atividades marítimas. Algumas debilidades estruturais, que são comuns a outras áreas, como sejam a fraca cooperação e competição entre setores económicos e incipientes relações intersetoriais, refletem-se ao nível deste Cluster como uma das suas principais fragilidades, a ponto de comprometer o reconhecimento da sua existência na economia marítima nacional.
- Modular buck-boost transformerless grid-tied inverter for low voltage solar panelsPublication . Nunes, Hugo; Pimenta, Nelson; Fernandes, Luís; Chaves, Paulo; Costa, J. M. DoresThis paper deals with a transformerless AC module for low DC voltage output photovoltaic solar panels. The DC to AC converter was designed to be a single-phase grid-tied inverter, and is based on a buck-boost topology with current mode control to shape the current and to adjust delivered power. The common ground node prevents voltage fluctuations and increases people´s safety. Low power inverters tend to be less efficient than larger ones and are prone to higher harmonic distortion. To overcome these drawbacks, special care was taken in designing the power stage, and harmonic compensation was included in the control stage. The inverter has MPPT capability and operates with unity power factor. Inverter´s operation is analysed, and some simulation results are presented. A 220Wp two-stage single-phase AC module prototype, with 240V and 50Hz sine-wave output, was build and connected to a low voltage photovoltaic solar panel. Experimental results for this plug-and-play converter are here presented.
- On the SC/FDE Uplink Alternative to OFDM in a Massive MU-MIMO ContextPublication . Torres, Paulo; Charrua, Luis; Gusmão, AntónioThis paper deals with Single Carrier (SC)/Frequency Domain Equalization (FDE) as an uplink alternative to Orthogonal Frequency Division Multiplexing (OFDM) for a Multi User (MU)-Multi-Input Multi-Output (MIMO) system where a ”massive MIMO” approach is adopted. In this context, either an optimum Minimum Mean-Squared Error (MMSE) linear detector or appropriate reduced-complexity linear detection techniques are considered. Regarding performance evaluation by simulation, two semi-analytical methods are proposed - one method in the optimum (MMSE) case and the other one in the reduced-complexity cases. This paper includes performance results for uncoded 4 Quadrature Amplitude Modulation (QAM) SC/FDE transmission and a MU-MIMO channel with uncorrelated Rayleigh fading, under the assumptions of perfect power control and perfect channel estimation.The accuracy of performance results obtained through the semi-analytical simulation methods is assessed by means of parallel conventional Monte Carlo simulations. The performance results are discussed in detail and we also emphasize the achievable ”massive MIMO” effects, even for the reduced complexity detection techniques, provided that the number of BS antennas is much higher than the number of antennas which are jointly employed in the terminals of the multiple autonomous users. Appropriate ”SC/FDE vs OFDM” comparisons are also included in this discussion of performance results.
- On the uplink detection performance in MU-MIMO broadband systems with a large number of BS antennasPublication . Torres, Paulo; Charrua, Luis; Gusmão, AntónioThis paper deals with Cyclic-Prefix (CP)-assisted uplink transmission - Orthogonal Frequency Division Multiplexing (OFDM)-based or Single Carrier (SC)/Frequency Domain Equalization (FDE)-based - within a Multi-User (MU)-Multi-Input Multi-Output (MIMO) system where a large number of Base Station (BS) antennas is adopted. In this context, either a Minimum Mean-Squared Error (MMSE) optimum linear detection or reducedcomplexity linear detection techniques are considered. Regarding performance evaluation by simulation, appropriate semi-analytical methods are proposed, and their accuracy is assessed under the assumptions of perfect power control and perfect channel estimation. This paper includes a detailed evaluation of Bit Error Rate (BER) performances for uncoded 4-Quadrature Amplitude Modulation (QAM) schemes - with both OFDM and SC/FDE - and a MU-MIMO channel with uncorrelated Rayleigh fading. The accuracy of performance results obtained through the semi-analytical simulation methods is assessed by means of parallel conventional Monte Carlo simulations. The performance results are discussed in detail, with the help of selected performance bounds, and we also emphasize the achievable ”massive MIMO” effects, even for the reduced-complexity detection techniques, provided that the number of BS antennas is much higher than the number of antennas which are jointly employed in the terminals of the multiple autonomous users. Appropriate ”SC/FDE vs OFDM” comparisons are also included in this discussion of performance results.