Abstract
The IEEE 802.15.4 standard provides a flexible communication support for low-rate wireless personal area networks) applications. When active, the beacon-enabled mode provides a real-time communication to the supported application by adopting a guaranteed time slot (GTS) mechanism. However, this mechanism permits only up to seven real-time communicating devices. One way to deal with this limitation is to share the communication opportunities among the periodic tasks, by skipping some of the task activations in a controlled way. One of the widely accepted periodic task models that allows skips in periodic activations is the (m,k)-firm model. Motivated by this problem, this paper proposes the use of a dynamic GTS scheduling approach based on the (m,k)-firm task model, to deal with the GTS starvation problem. The proposed scheduling approach is based on pre-defined spins of the originally defined (m,k)-firm pattern. The use of an exact schedulability analysis test ensures that for each admitted message stream, at least m messages will be transmitted within each window of k consecutive deadlines. The schedulability analysis may be executed in polynomial time and therefore can be used as an online admission test for GTS requests. The effectiveness of the approach has been assessed both by a set of simulations and an experimental evaluation.

Abstract
An important feature for the design of algorithms for Wireless Sensor Networks is the estimation of its lifetime. To design communication protocols and data collection algorithms with low power consumption, a key factor is the ability to measure the actual consumption in the sensor node. This ability enables the verification of theoretical/simulated models, allowing an accurate estimation of the network longevity. This paper proposes a system for measuring the energy consumption levels of sensor nodes in normal operation, allowing the estimation of the real lifetime for each node, enabling the optimization of energy aware protocols. Presented data is related to the energy consumption of a MicaZ node and to the behavior of the full discharge of a battery pack. A set of polynomial functions describing this energy discharge are also presented that can be easily inserted into the battery models of network simulators to obtain a more realistic behavior.

Abstract
In the last decade refractometric sensors have attracted an increasing interest by the scientific community due to their ability to perform ambient monitoring, to assess food quality and safety, and also to the fact that they enable the development of label free sensors in the biomedical area. These advances result, namely, from the use of long period fibre gratings in the turning points and/ or with thin films in the transition region that allows resolutions of 10(-6) to changes in the refractive index of the surrounding medium. Resolutions exceeding 10(-8) can also be achieved when long period fibre gratings are combined with evanescent field based devices. This paper reviews the recent path towards the development of ultrahigh sensitive optical fibre refractometric sensors.

Abstract
The effect on permanent magnet synchronous generator (PMSG) wind turbines due to grid voltage decrease and fifth harmonic is studied in this paper by computer simulations. A multilevel power converter topology and two control strategies, namely fractional and integer-order controllers, are considered in order to evaluate that effect. A comparison between the two control strategies is presented. Finally, conclusions are duly drawn.

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