Dissolution du nickel en transpassivité—I. Méthode de calcul

The behaviour of nickel has been studied in 0,5 M H₂SO₄, 25°C, in the transpassive region. The experimental polarisation curves were determined by a potentiostatic technique over the potential range 1000–1800 mV/sce; the dissolution curves were determined directly by the nickel weight loss per unit time at each potential; the oxygen discharge curves were determined by the volume of gas evolved per unit time. In the transpassive region several reactions occur simultaneously. In order to explain the nickel dissolution, and the depassivation of the metal, in this potential range, a model of the mechanism is proposed, and the method of calculation described. The experimental current voltage curves are compared and are in good accord with the calculated curves.     

Wavelet-based spectral shaping of UWB radio signal for multisystem coexistence

Although Ultra Wide Band (UWB) wireless systems supposed to coexist with other spectrally overlapping (narrowband) wireless systems, mutual interference degrades the performance of both systems. In this paper we investigate two techniques for reducing this mutual interference which do not require modification of the narrowband system. We propose to shape the spectrum of the Transmitted Reference (TR)-UWB signal using wavelet based multi-resolution technique to avoid its interference to other wireless systems. The reverse (narrowband) interference is alleviated using a notch filter at UWB receiver that could have much smaller bandwidth in this Gaussian pulse-shaped multi-resolution environment. TR simulations under AWGN and multipath channel conditions show that up to 55 dB reduction of UWB RF energy is possible at the interfering IEEE 802.11a band using the wavelet spectral shaping technique. The challenge is not to exceed the specified pulse duration while shaping the spectrum. The proposed technique does not reduce the throughput of the UWB system. It is general in the sense, it can be used for the better coexistence of any narrowband wireless system with UWB system.     

Coordination of multi-agent Euler–Lagrange systems via energy-shaping: Networking improves robustness

In this paper, the robust coordination of multi-agent systems via energy-shaping is studied. The agents are nonidentical, Euler–Lagrange systems with uncertain parameters which are regulated (with and without exchange of information between the agents) by the classical energy-based controller where the potential energy function is shaped such that, if the parameters are known, all agents converge globally to the same desired constant equilibrium. Under parameter uncertainty, the globally asymptotically stable (GAS) equilibrium point is shifted away from its desired value and this paper shows that adding information exchange between the agents to the decentralized control policy improves the steady-state performance. More precisely, it proves that if the undirected communication graph is connected, the equilibrium of the networked controller is always closer (in a suitable metric) to the desired one than that of the decentralized controller. The result holds for all interconnection gains if the potential energy functions are quadratic, else, it is true for sufficiently large gains. An additional advantage of networking is that the asymptotic stabilization objective can be achieved by using lower gains into the loop. Some experimental results (using two nonlinear manipulators) given support to the main results of the paper.     

A modeling framework for urban traffic systems microscopic simulation

In this paper a modeling framework for urban traffic systems (UTS) is presented. The model, used for agent based micro-simulation, describes both the traffic network and dynamic entities, namely vehicles, traffic lights, and pedestrians. The framework allows defining systematically the necessary components and their behavior of a model oriented to event driven simulation, which can be executed in a distributed way. In the model, the vehicles are conceived as mobile agents with decision making capabilities that interact with the environment and other entities within the traffic network, performing diverse activities according to numerous situations arisen during the simulation. A multi-level Petri net based formalism, named n-LNS is used for describing the structure of the UTS and the components behavior. The first level describes the traffic network; the second level models the behavior of diverse road network users considered as agents, and the third level specifies detailed procedures performed by the agents, namely travel plans, tasks, etc.     

Residual‐based a posteriori estimators for the potential formulations of electrostatic and time‐harmonic eddy current problems with voltage or current excitation

In this paper, we consider some potential formulations of electrostatic as well as time‐harmonic eddy current problems with voltage or current excitation sources. The well‐posedness of each formulation is first established. Then, the reliability of the corresponding residual‐based a posteriori estimators is derived in the context of the finite element method approximation. Finally, the implementation in an industrial code is performed, and the obtained theoretical results are illustrated on an academic and on an industrial benchmark. Copyright © 2015 John Wiley & Sons, Ltd.     

Chemical Compatibility between Strontium-Doped Lanthanum Manganite and Yttria-Stabilized Zirconia

Equimolar powder mixtures and multilayer pellets of single-phase Sr-doped lanthanum manganite perovskite materials La_y-xSr_xMnO₃ with La content y = 1 and 0.95 and Sr content 0 ≤ x ≤ 0.5 were annealed in air with 8 mol% Y₂O₃-ZrO₂ at 1470 K, up to 400 h and at 1670 K. up to 200 h. X-ray diffraction and electron probe microanalysis confirmed the formation of La₂Zr₂O₇ or SrZrO₃ depending on the composition of the perovskites. No reaction products could be detected for La_0.95-xSr _xMnO₃ with 0.2 ≤ x ≤ 0.4 after annealing for 400 h at 1470 K, and for the perovskite La_0.65Sr_0.3MnO₃ even after annealing for 200 h at 1670 K. The results demonstrate the improved chemical compatibility of La-deficient perovskites against reaction with zirconia and can provide a basis for the selection of a sufficiently chemically stable material for the air electrode of solid oxide fuel cells.