Abstract
In this paper we make a comparative assessment between the RT-WiFi and HCCA approaches to handle real-time traffic in IEEE 802.11 networks operating in open communication environments. The main focus will be on the assessment of the admission control mechanism proposed for the RT-WiFi upper layer, that is based on a non-preemptive EDF scheduling algorithm combined with a mechanism that measures the blockage times on medium access of real-time stations due to retransmissions and delays. The goal is to achieve a good compromise between medium utilization and timeliness. This proposal is compared with HCCA, and the results show that RT-WiFi offers a significantly better behavior in what concerns the maximum number of admitted streams.

Abstract
The supercontinum generation has been achieved mainly by two different approaches, namely, with femtosecond intense pulses or using a continuous wave laser or larger pulses centered on the anomalous dispersion region. In order to improve temporal coherence, it has been suggested the introduction of a pulse seed or the propagation of both a large pulse pump and a small weaker continuous wave to control the soliton fission. Here we propose supercontinuum generation using a hybrid input, we pump with a continuous laser and copropagate a picosecond signal. We compare the bandwidth of the supercontinuum using only the continuous pump or the hybrid setup. Simulations of the generalized Schrodinger equation, using an adequate input-noise model to reproduce the spectrum of the continuous signal, are performed in order to investigate the supercontinuum generation in the optical communication window under different dispersion regimes.

Abstract
In the last years, the electric power systems have been restructured, moving from a vertical integrated model to a market oriented environment. The new paradigms associated with the restructuring of the electricity sector made it critical to develop new efficient and reliable methodologies to study and analyze the security of the power networks. In this paper it is proposed a method to evaluate the impact of external elements on the responsibility area of a Transmission System Operator (TSO) using the influence factor method. This approach offers a concrete support in the determination of the observability area, which at the end remains in the responsibility of the single TSO. The influence factor is a numerical value used to quantify the greatest effect of the outage of an external network component on any internal network branch. The developed methodology was applied to study the IEEE 118 bus test power network. All simulations of the transmission systems of the IEEE 118 bus were performed using the PSS®E software package from Siemens PTI, making the division of the network in two countries (areas). From the simulation results, some conclusions that provide a valuable contribution to understanding the influence factor method are pointed out. © 2012 IEEE.

Abstract
In this work, an in-depth analysis concerning the transmission performance of IEEE802.11g/n WiFi signals in a radio-over-fiber system is presented. Low-cost optical/electrical transceivers based on 850 nm vertical cavity surface emitting lasers (VCSELs) and PIN photodiodes are considered. System modelling includes the impact of noise generated in the optical path, such as relative intensity noise (RIN), shot noise, photodetector thermal noise, clipping and intermodulation distortion. Analytic results based on Volterra series analysis for the performance of the system in terms of SNR and EVM for several optical modulation index values are obtained. The theoretical analysis is also compared with experimental results. Among several conclusions, it is observed that the laser intermodulation distortion, clipping and RIN are the most relevant factors.

Abstract
Dragonflies show unique and superior flight performances than most of other insect species and birds. They are equipped with two pairs of independently controlled wings granting an unmatchable flying performance and robustness. In this paper, it is presented an adaptive scheme controlling a nonlinear model inspired in a dragonfly-like robot. It is proposed a hybrid adaptive (HA) law for adjusting the parameters analyzing the tracking error. At the current stage of the project it is considered essential the development of computational simulation models based in the dynamics to test whether strategies or algorithms of control, parts of the system (such as different wing configurations, tail) as well as the complete system. The performance analysis proves the superiority of the HA law over the direct adaptive (DA) method in terms of faster and improved tracking and parameter convergence.

Abstract
Voltage stability is predominantly a load stability phenomenon and solutions to voltage stability can be found by control of the load as seen from the bulk power network. A delay of the load restoration gives time for other corrective actions. The load restoration may be delayed and/or limited by certain countermeasures, such as blocking of Under Load Tap Changers (ULTC). In this paper it was studied the impact of the ULTC on the dynamic voltage collapse of an electric power system with large scale wind generation. It is used the Cigré Electric Power Network with 32 bus and three wind farms equipped with wind turbines, including pitch control coupled with a Fixed Speed Induction Generator (FSIG) and a shunt capacitor bank. The automatic voltage regulators (AVR) of the generating units and the turbine speed governors were modelled. Different load models were used and the ULTC were taken into account. Several significant disturbances were simulated in the test power network, such as the increase of the wind speed, the tripping of an overhead transmission line and three-phase short-circuits. The simulation results were obtained using the EUROSTAG software package. Finally, some conclusions that provide a better understanding of the ULTC effect on the dynamic voltage stability in a system with a large amount of wind power generation are pointed out. © 2012 IEEE.