Abstract

Abstract
Currently there is a trend for the implementation of industrial communication systems on top of wireless communications. However, keeping up with the timing constraints of real-time traffic in open medium environments is a hard task. The main source for complexity is that, if the set of communicating devices is not previously agreed, the timing constraints imposed by such devices cannot be predicted at the system setup time, nor can be effectively controlled at the system run-time. In this paper, we propose the VTP-CSMA architecture to deal with this problem. This architecture allows the coexistence of default IEEE 802.11e devices with real-time devices sharing the same communication medium, enabling the prioritization of real-time traffic. The proposed solution is based on the control of the medium access rights by means of a Virtual Token Passing procedure (VTP), complemented by an underlying traffic separation mechanism that prioritizes realtime traffic over the traffic from default IEEE 802.11 stations. The simulation analysis shows that the VTP-CSMA architecture guarantees values for both the throughput and the average access delay that significantly improves the results obtained for default IEEE 802.11e stations operating under EDCA mode.

Abstract

Abstract

Abstract
The main purpose of this work is the development of an optimization model for the design of the grounding grid in electrical substations. The problem is formulated as a mixedinteger linear programming problem, in terms of the constructive characteristics and the peculiar requirements to construct and to install the grounding grid. The model incorporates the variables that define the grid characteristics of all possible configurations including the grid geometry and the depth and conductor size. The optimization problem is subject to safety constraints related with the maximum allowed touching and step voltages. It also includes the equivalent impedance of the transmission line connected to the substation where it will be located the grounding grid to be designed. The methodology allows selecting the optimum grid of the possible configurations, so that is a very useful tool for the engineering design. The formulation and specifications used is based in IEEE Std. 80-2000.

Abstract
Third-order nonlinear and linear optical properties of nickel(II) and copper(II) complexes with salen ligands, functionalised with electron donor/acceptor groups (DA-salen), have been investigated in solution by the Z-scan technique using an Nd:YAG laser (lambda(inc) = 1064 nm) and UV/Vis spectroscopy. The [M(DA-salen)] complexes exhibit positive nonresonant nonlinear refractive indexes (net) in the range 27.0-8.50 center dot 10(-21) m(2)W(-1) and nonlinear absorption coefficients (a(2)(I)) within the range 1.80-26.0 center dot 10(-17) mW(-1). The latter values correspond to less than 10% of the overall magnitude of the third-order susceptibility, vertical bar chi(3)vertical bar, which is the result of the absence of electronic transitions near lambda(inc) = 1064 nm. For the group of N-II complexes, the highest net values are exhibited by the complexes with aromatic diimine bridges and large pi-electron delocalisation, which leads to intense electronic charge-transfer bands (epsilon > 16000 mol(-1) dm(3) cm(-1)) in the region lambda = 275-500 nm. The complexes that exhibit charge-transfer bands near lambda(inc)/2 = 532 nm, also show the highest a(2)(I) values, a consequence of multiphoton absorption processes. For the group of Cult complexes, the highest net value is also observed by the complex that exhibits the most intense charge-transfer bands in the region lambda = 275-475 nm. Between Ni-II and Cu-II complexes with the same DA-salen ligands, those of copper show always higher net values, indicating that NLO responses can also be fine-tuned by the metal centre. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)