Abstract

Abstract
The integration of larger and larger amounts of wind power is a major target of the European Union, however it represents a challenge for power system planning and operation. The paper analyses stability aspects concerning the operation of Multi-Terminal HVDC networks connecting offshore wind farms to the AC systems. Modelling issues are tackled, relevant to control schemes needed for a secure operation of the overall AC-DC system in case of contingencies both on the AC side and on the DC side. First, power flow control principles are described for the "backbone" HVDC grid topology (consisting of point-to-point connections between offshore wind farms and mainland grid, linked by a DC connection). Second, dynamic converter models suitable to investigate electromechanical transients are illustrated and some stability issues connected to the network performance under contingencies/disturbances are pointed out. The need both to survive severe disturbances and to provide ancillary services calls for the adoption of advanced control schemes. Some simulations are described to illustrate the behaviour of the mixed AC-DC network under contingencies concerning both faults on DC cables and faults on AC lines. The work has been carried out within Working Package 5 of EU co-founded Project TWENTIES.

Abstract
Permanent semi-natural grassland meadows (lameiros) are characteristic of the mountain rural landscapes in northeast Portugal and represent the main fodder resource for livestock production. Furthermore, these meadows are recognized for their environmental, historical, cultural and visual landscape value. A monitoring study based on remote-sensing data was implemented to understand the impacts of management practices on the lameiros vegetation dynamics and to analyse changes in vegetation dynamics over the period 1998-2008 in response to inter-annual climatic variability. Ten-day SPOT-VEGETATION (VGT) image composites from this period were used to examine the annual temporal profile using the normalized difference vegetation index (NDVI) and their relationship with ground-based observation of vegetation growth and reflectance inferred with a spectroradiometer. Results show that the NDVI profile fits well the characteristic vegetation growth dynamics and associated management practices in the region. For the period from July 2007 to December 2008, the variation in vegetation height explains 46 to 52% of the variation in NDVI derived respectively from spectroradiometer and VGT data. NDVI referring to dates of specific stages of the vegetation dynamics and management practices in lameiros was tested against climatic variables, for the period 1998-2008. More than 57% of the inter-annual variability of the average NDVI during the lameiros development period can be explained by the mean temperature, and 53% of the variability on the date of occurrence of maximum vegetation development (MVD) can be explained by the mean temperature during the spring period. These results support the analysis of lameiros responses to different scenarios of climate and water management and may support the implementation of more efficient farm activities.

Abstract
During the last two decades the research and development of legged robots has grown steadily. Legged systems present major advantages when compared with "traditional" vehicles, because they allow locomotion in terrain inaccessible to vehicles with wheels and tracks. However, the robustness of legged robots, and specially its energy consumption, among other aspects, still lag being mechanisms that use wheels and tracks. Therefore, in the present state of development, there are several aspects that need to be improved and optimized. One of these aspects relates to the optimum parameters that these machines should adopt in order to minimize the energy consumption. Due to the large number of parameters involved in this optimization process, one way to achieve meaningful results is using evolutionary strategies. Genetic Algorithms are a way to "imitate nature" replicating the process that nature designed for the generation and evolution of species. This paper presents a genetic algorithm, running over a simulation application of legged robots, which allows the optimization of several parameters of a quadruped robot model.

Abstract
This paper describes and compares several approaches applied to compute the inverse kinematics of a 10 degrees of freedom hyper-redundant robot. The proposed approaches are based on an exhaustive method and several error optimization algorithms. The algorithms' performance was evaluated based on two criteria: computing time and final actuator positioning error. The mentioned hyper-redundant robot was projected to be used in biomedical applications. © 2012 IEEE.

Abstract
The present work describes and compares several approaches applied to compute the inverse kinematics of a ten degrees of freedom hyper-redundant robot. The proposed approaches are based on an exhaustive method and several error-optimization algorithms. The algorithms' performance was evaluated based on two criteria: computational processing time and final actuator positioning error. The results obtained show that for a small number of modules (less or equal to four), the exhaustive method provides the best problem solution: acceptable computational processing time as well as minimum error. However, for larger number of modules, the error-optimization approach has far better performance regarding the error to processing time ratio. The mentioned hyper-redundant robot was projected to be used in biomedical applications.