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Bouguenais, France

Schoefs F.,CNRS Research Institute in Civil Engineering and Mechanics | Abraham O.,Lunam University
Transportation Research Record | Year: 2012

The aim of the study reported in this paper was to provide rational aid tools to quantify the performance of nondestructive testing (NDT) tools. This study focused on the quantification of the performance of impact-echo sources (steel balls of varied diameters), applied with a new, contactless robot, for duct void detection and thickness measurements in a reinforced concrete wall. Because of uncertainties during the testing, the data were analyzed in a probabilistic context, with the knowledge that on-site inspections were affected by uncertainties. The αδ method was used in this regard, where the probabilities of detection and false alarm rates were used to build receiver operating characteristic curves. The methodology was applied to data measured on the same wall with two steel ball diameters: 0.16 and 0.125 m. The quantity analyzed here was the impact-echo method (resonance) frequency. This methodology could be extended to other parameters of the impact-echo setup as well as to other NDT methods. Source


Antonios J.,Lunam University | Ginot N.,University of Nantes | Batard C.,University of Nantes | Scudeller Y.,University of Nantes | MacHmoum M.,Lunam University
Microelectronics Journal | Year: 2012

This paper presents a model reduction approach for constructing lumped RC thermal networks of IGBT-modules of inverters for which heat and subsequent temperature increases vary with time on different scales ranging from nanosecond to second. It was observed that the time-dependent heat and temperature profiles of transistors and diodes of IGBT-modules of inverters oscillate at two frequencies, one in the range 0.1-50 Hz corresponding to the load current modulation, and the other in the range 1-20 kHz corresponding to the switching frequency. The reduction approach consisted of decomposing the module into different elements, each being described with a number of RC cells selected according to the time-constant of the element with regard to the module. The lumped RC thermal networks were found in good agreement with the continuous model by offering a considerably lower computational time on the different time scales. For simplicity, the reduction approach is presented for one-dimensional heat flow through the cross-plane direction of the module. © 2012 Elsevier Ltd. All rights reserved. Source


Lassabatere L.,University of Lyon | Yilmaz D.,University | Yilmaz D.,Tunceli University | Peyrard X.,Lunam University | And 5 more authors.
Vadose Zone Journal | Year: 2014

In the vadose zone, preferential flow and transport are much more common than uniform water flow and solute transport. In recent decades, several models have been developed for preferential water flow and physical nonequilibrium solute transport. Among these models, the dual-permeability approach is an interesting tool for the conceptualization and modeling of preferential flow. However, this approach has been mainly studied from a numerical point of view. In this study, we developed a new analytical model for water infiltration into dual-permeability soils. The model is based on the analytical model originally proposed for single-permeability soils. The proposed model relies on the assumption that the water exchange rate at the interface between the matrix and fast-flow regions does not change cumulative infiltration at the soil surface, so that the total cumulative infiltration can be set equal to the sum of independent cumulative infiltrations into each region. This assumption was investigated using numerically generated data. The proposed analytical model was then used to evaluate the effects of fast-flow region hydraulic properties and hydraulic conditions on total cumulative infiltration for the case of single- and multi-tension water infiltration experiments. Finally, both single- and dual-permeability models were evaluated with respect to their ability to fit experimental data and associated problems of non-uniqueness in optimized parameters. The proposed model could serve as a new tool for modeling and characterizing preferential flow in the vadose zone. © Soil Science Society of America. Source


Delamain M.,Lunam University | Delamain M.,French National Center for Scientific Research | Ruban V.,Lunam University | Ruban V.,French National Center for Scientific Research | And 2 more authors.
Techniques - Sciences - Methodes | Year: 2016

The waterproofing due to the urban expansion increases runoff in cities. This phenomenon affects the ecosystems by facilitating the transfer of pollutants. The management of runoff water in urban areas is thus a real stake. The objective of this study is the identification of the sources of pollutants by being interested in the practices of maintenance of the surfaces of two sites of Nantes (the Pin Sec catchment and the ecodistrict Bottière Chénaie). It also aims at estimating the impact of the best management practices on the quality of runoff water by focusing on metals and pesticides. The results show a change of practices both by professionals and individuals resulting in a reduction of the use of pesticides for the benefit of natural gardening. In spite of the presence of best management practices (swales, vegetated roofs, retention ponds) on the ecodistrict, the quality of runoff water is rather identical to that of the Pin Sec catchment. The same elements are present mainly on both sites: zinc, Strontium and Copper. However, Strontium concentrations in runoff waters of the ecodistrict (47 - 94 μg/L) are higher than those of the Pin Sec catchment (34 μg/L). The use of pesticides by certain actors is at the origin of the quantification of the glyphosate and its product of degradation (AMPA) on both sites. Abnormal contents in Mecoprop (13 μg/L) appear in waters stemming from vegetated roofs of the ecodistrict Bottière Chénaie. They would come from an agent anti-root present in the bitumen roof coating. © ASTEE 2016. Source

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