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Chakhchoukh Y.,TU Darmstadt | Panciatici P.,French Electricity Transmission Network | Mili L.,Virginia Polytechnic Institute and State University
IEEE Transactions on Power Systems | Year: 2011

In this paper, the stochastic characteristics of the electric consumption in France are analyzed. It is shown that the load time series exhibit lasting abrupt changes in the stochastic pattern, termed breaks. The goal is to propose an efficient and robust load forecasting method for prediction up to a day-ahead. To this end, two new robust procedures for outlier identification and suppression are developed. They are termed the multivariate ratio-of-medians-based estimator (RME) and the multivariate minimum-Hellinger- distance-based estimator (MHDE). The performance of the proposed methods has been evaluated on the French electric load time series in terms of execution times, ability to detect and suppress outliers, and forecasting accuracy. Their performances are compared with those of the robust methods proposed in the literature to estimate the parameters of SARIMA models and of the multiplicative double seasonal exponential smoothing. A new robust version of the latter is proposed as well. It is found that the RME approach outperforms all the other methods for normal days and presents several interesting properties such as good robustness, fast execution, simplicity, and easy online implementation. Finally, to deal with heteroscedasticity, we propose a simple novel multivariate modeling that improves the quality of the forecast. © 2011 IEEE. Source

Doquet M.,French Electricity Transmission Network
IEEE Transactions on Power Systems | Year: 2015

In development studies carried out on large power systems, a need may arise for a reduction in which whole regions are seen as the nodes of a simplified graph whose edges replace the inter-regional links. The property required from this kind of backbone representation may be that reduced load flows stay close to their physical counterpart on the full grid. In the dc approximation, such a model can consist of a set of impedances attached to each edge, along with a flow characterizing a particular state of the system. The identification of the model accommodating best a large sample of flows, representative of all of their possible diversity, is a nonconvex problem for which two partially convex reformulations are proposed. Simple ad hoc algorithms are introduced as a way to find approximate solutions satisfying first-order optimality conditions. © 2014 IEEE. Source

Faller P.,French Electricity Transmission Network | Hureau C.,National Polytechnic Institute of Toulouse | Berthoumieu O.,National Polytechnic Institute of Toulouse
Inorganic Chemistry | Year: 2013

Aggregation of amyloid-β (Aβ) by self-assembly into oligomers or amyloids is a central event in Alzheimer's disease. Coordination of transition-metal ions, mainly copper and zinc, to Aβ occurs in vivo and modulates the aggregation process. A survey of the impact of CuII and ZnII on the aggregation of Aβ reveals some general trends: (i) ZnII and CuII at high micromolar concentrations and/or in a large superstoichiometric ratio compared to Aβ have a tendency to promote amorphous aggregations (precipitation) over the ordered formation of fibrillar amyloids by self-assembly; (ii) metal ions affect the kinetics of Aβ aggregations, with the most significant impact on the nucleation phase; (iii) the impact is metal-specific; (iv) CuII and ZnII affect the concentrations and/or the types of aggregation intermediates formed; (v) the binding of metal ions changes both the structure and the charge of Aβ. The decrease in the overall charge at physiological pH increases the overall driving force for aggregation but may favor more precipitation over fibrillation, whereas the induced structural changes seem more relevant for the amyloid formation. © 2013 American Chemical Society. Source

Dalle B.,French Electricity Transmission Network | Admirat P.,French Electricity Transmission Network
Cold Regions Science and Technology | Year: 2011

This article deals with the accretion mechanisms of wet snow observed both on a stranded conductor sample in wind tunnel conditions and on real power lines in natural weather conditions. It summarizes the theory and practical observations. Report of experience from France are given in order to demonstrate the efficiency of this passive preventive method based on the increase of torsional stiffness of conductors and to introduce wet snow risk map and countermeasures in France. © 2010 Elsevier B.V. Source

Cazacliu B.,French Electricity Transmission Network | Ventura A.,French Electricity Transmission Network
Journal of Cleaner Production | Year: 2010

Current environmental and economical circumstances accelerate the developments of new concrete constituents. Whereas the process technology impacts the mix-design strategy, it seems obvious that manufacturing process is prone to evolutions. This article presents a method to compare environmental and economical consequences of different technological solutions on the basis of the influence on the cement consumption needed for a given concrete performance. Case study is the choice of dry batch or central mixed concrete production systems for a ready mixed concrete production. The theoretical difference in cement consumption is estimated by considering that the water content fluctuation is by far the dominant factor governing the truck to truck variation. The addition of a mixer is effectively found to contribute to cement reduction. Environmental comparison is performed using an EADT indicator (Environmental Amortization Duration Time) defined in the article, and testing various environmental data. The EADT for energy consumption, released CO 2 and particles are found below 6 years, in the whole range of tested environmental data for an annual production of 40,000 m3 yr -1, with 2 m3 mixer for the central mixed concrete plant. The NOx and SO2 EADT results are found sensitive to the releases of the steel plant. The financial amortization duration time corresponding to the purchase of a mixer, is found less than 2 years. Although the chosen application case is simplified, these results encourage further research. © 2010 Elsevier Ltd. All rights reserved. Source

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