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Publications

2009

Efficiency analysis accounting for internal and external non-discretionary factors

Authors
Camanho, AS; Portela, MC; Vaz, CB;

Publication
COMPUTERS & OPERATIONS RESEARCH

Abstract
This paper develops a method based on data envelopment analysis (DEA) for efficiency assessments taking into account the effect of non-discretionary factors. A typology that classifies the non-discretionary factors into two groups is proposed: the factors that characterize the external conditions where the decision making units (DMUs) operate (external factors), and the factors that are internal to the production process but cannot be controlled by the decision makers (internal factors). This paper proposes an enhanced DEA model that accommodates non-discretionary inputs and outputs and treats them differently depending on their classification as internal or external to the production process. This generalized model integrates the previous approaches for dealing with non-discretionary variables described in the DEA literature. The model defines the efficient frontier based exclusively on the discretionary variables and internal non-discretionary factors, but the potential peers of each DMU are restricted to other units facing comparable external conditions (represented by the external non-discretionary factors). The peer selection criteria implemented in the DEA model is informed by decision makers' opinion, The applicability of the model developed is illustrated with a real-world assessment of retailing stores.

2009

Radar Based Collision detection developments on USV ROAZ II

Authors
Almeida, C; Franco, T; Ferreira, H; Martins, A; Santos, R; Almeida, JM; Carvalho, J; Silva, E;

Publication
OCEANS 2009 - EUROPE, VOLS 1 AND 2

Abstract
This work presents the integration of obstacle detection and analysis capabilities in a coherent and advanced C&C framework allowing mixed-mode control in unmanned surface systems. The collision avoidance work has been successfully integrated in an operational autonomous surface vehicle and demonstrated in real operational conditions. We present the collision avoidance system, the ROAZ autonomous surface vehicle and the results obtained at sea tests. Limitations of current COTS radar systems are also discussed and further research directions are proposed towards the development and integration of advanced collision avoidance systems taking in account the different requirements in unmanned surface vehicles

2009

ESTIMATION OF RF PA NONLINEARITIES AFTER CROSS-CORRELATING POWER SUPPLY CURRENT AND OUTPUT VOLTAGE

Authors
Veiga, R; Mota, P; da Silva, JM;

Publication
2009 IEEE 15TH INTERNATIONAL MIXED-SIGNALS, SENSORS, AND SYSTEMS TEST WORKSHOPS

Abstract
The present paper describes developments carried-out on estimating 1 dB compression and third-order intercept points after the cross-correlation between power supply dynamic current and output voltage of radio-frequency power amplifier. The underlining theory and a circuit that allows implementing this measurement on-chip are presented. Simulation results, including the analysis of optimum stimuli amplitudes and the Monte Carlo analysis to circuits' process variations are presented. These show that good accuracy can be obtained with relatively simple measurement conditions.

2009

Fractal Monopole Antenna Design Using Minkowski Island Geometry

Authors
Luo, Q; Salgado, HM; Pereira, JR;

Publication
2009 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM AND USNC/URSI NATIONAL RADIO SCIENCE MEETING, VOLS 1-6

Abstract
In this paper, two printed multiband fractal monopole antennas using the 1(st) and 2(nd) iteration of Minkowski Island geometry are proposed for WLAN communications. The monopole antennas have compact size of 28 x 18 mm(2) and 21.5 x 18 mm(2), respectively. The proposed antennas with different sizes of the ground plane have also been studied through numerical simulations in Ansoft HFSS. It is found that without using any impedance matching method, both of the proposed antennas exhibit good impedance match at both 2.4 and 5.2 GHz band, which is confirmed by the measurement results. It is also observed that the monopole antenna with the geometry of the 1(st) iteration Minkowslci Island can also operate at 3.5 and 5.8 GHz, which means that it almost covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. The simulation shows that both antennas exhibit high radiation efficiency and the measured radiation patterns show that both antennas have similar radiation patterns at each resonant frequency.

2009

Distributed, Modular HTL

Authors
Henzinger, TA; Kirsch, CM; Marques, ERB; Sokolova, A;

Publication
2009 30TH IEEE REAL-TIME SYSTEMS SYMPOSIUM, PROCEEDINGS

Abstract
The Hierarchical Timing Language (HTL) is a real-time coordination language for distributed control systems. HTL programs must be checked for well-formedness, race freedom, transmission safety (schedulability of inter-host communication), and time safety (schedulability of host computation). We present a modular abstract syntax and semantics for HTL, modular checks of well-formedness, race freedom, and transmission safety, and modular code distribution. Our contributions here complement previous results on HTL time safety and modular code generation. Modularity in HTL can be utilized in easy program composition as well as fast program analysis and code generation, but also in so-called runtime patching, where program components may be modified at runtime.

2009

Autonomous Bathymetry for Risk Assessment with ROAZ Robotic Surface Vehicle

Authors
Ferreira, H; Almeida, C; Martins, A; Almeida, J; Dias, N; Dias, A; Silva, E;

Publication
OCEANS 2009 - EUROPE, VOLS 1 AND 2

Abstract
The use of unmanned marine robotic vehicles in bathymetric surveys is discussed. This paper presents recent results in autonomous bathymetric missions with the ROAZ autonomous surface vehicle. In particular, robotic surface vehicles such as ROAZ provide an efficient tool in risk assessment for shallow water environments and water land interface zones as the near surf zone in marine coast. ROAZ is an ocean capable catamaran for distinct oceanographic missions, and with the goal to fill the gap were other hydrographic surveys vehicles/systems are not compiled to operate, like very shallow water rivers and marine coastline surf zones. Therefore, the use of robotic systems for risk assessment is validated through several missions performed either in river scenario (in a very shallow water conditions) and in marine coastlines.

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