ENIDH – EEM - Comunicações, Congressos, Seminários, Encontros, etc.
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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.
- 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.
- 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.
- Indoor Position Method Using Wi-FiPublication . Fernandes, Luís; Barata, Fábio; Chaves, PauloThe main objective of this paper is to present an indoor position method, developed for museums and hospitals, in order to known the position of persons and equipments. The method is composed by a particle filter algorithm to be embedded in smartphones or tags. The main goal is to develop a light method to run by not very powerful microprocessors, energized by batteries. The position method presented is based on a Wi-Fi structure, to lighten the use of the communication network, the position is generated by each device from raw data received locally.
- Optimization of fibers orientation in a composite specimenPublication . Monte, Sara M. C.; Infante, Vírginia; Moleiro, Filipa; Madeira, J. F. A.The main purpose of this study was to optimize the fibers orientation in a composite specimen with the objective to minimize the displacement. This composite specimen can be used in aerospace or mechanical structures. The objective function was performed with static analysis by altering the fibers orientation in a finite element solid model, computed using the ANSYS program. A recent method for global optimization GLODS (Global and local optimization using direct search) was used for the optimization process. In the sequence, specimens were manufactured and experimental tested, in o order to validate the numerical results obtained.
- Features of the European Maritime ClustersPublication . Simões, Abel; Salvador, Regina; Soares, Carlos GuedesThe paper analyses the national and regional European maritime clusters according to the sea basin division proposed by the European Union Integrated Maritime Policy: Atlantic and Arctic oceans; Baltic, Black, Mediterranean and North seas. In line with Wijnolst, Jensen & Sødal (2003) that propose a maritime sector benchmarking - the “Global Maritime Benchmarking” – which should allow evaluating the maritime clusters evolution and strength - the paper start to estimate nine indicators: 1. structural indicators (no. of clusters, no. of companies, no. of employees, no. of sectors, technological level, location); 2. economic indicators (Gross Added Value, production, productivity, profit and rentability rates); 3. internationalisation (exports and imports, major clients and suppliers, international average prices, EU and third countries markets shares); 4. critical mass (agglomerations and scale economies by maritime sector) and leader firms; 5. level playing-field (free-competition, monopolistic, oligopolistic markets); 6. innovation (major universities and R&D centres, no. patents, regional innovation systems); 7. institutional framework (governance, connection with regional and national governments)and business networks; 8. labour market (unemployment rate, average wages) and education (major schools and courses by different grades, training centres); and 9. Image and communication. The comparison between sea basins will allow characterizing “Maritime Europe’, identifying the location of the main excellence centres and the major beneficiaries of the Integrated Maritime Policy decisions. The paper also suggest public strategies that would support clusters development – or “cluster enablers” – that include, among others, the definition of an industrial policy, strengthening of demand pull sectors or the promotion of innovation, R&D and leader firms. The needed conditions in order that Europe could organise itself has a “vast continental maritime cluster” are also under scrutiny
- A 1.1 µA voltage reference circuit with high PSRR and temperature compensationPublication . Pereira, M. Silva; Costa, João E. N.; Santos, M.; Vaz, J. CaldinhasThis paper presents a low-power and a low output voltage CMOS Bandgap Reference Generator topology with high PSRR and a novel temperature curvature compensation method. The proposed design was implemented in a standard 0.13 μm CMOS process. The main circuit is based in an opamp based β-multiplier bandgap circuit with resistive division. The compensation method cancels out up to 2nd order non-linear terms of the BJT voltage by using the MOSFET leakage current effect. The performance of the circuit was verified by post-layout simulations. Simulated results have shown temperature coefficients as low as -4.4 ppm/°C over a temperature range of 140°C (-40°C to 100°C). In addition the circuit demonstrated a PSSR of -100 dB at low frequencies and -73 dB at 1 MHz. The current consumption is 1.1 μA at 27°C.