Etude du marqueur MxA pour la compréhension de la physiopathologie des pyélonéphrites aiguës de l'enfant

LILLE2-BU Santé-Recherche (593502101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Experimental diagnostic and numerical simulation of an internal arc fault in a medium voltag cell

Internal arc faults are extremely rare phenomena characterized by a powerful non-controlled electric arc due to a dysfunction. Internal arc faults on medium voltage (MV) cells are a focal area where experimental tests are carried out to set the switchgear in conformity with IEC standards [1]. In order to limit the internal arc effects, a new protection filter constituted of a porous medium [2] was recently used providing better performance as compared with traditional filter technologies. The arcing fault process can be chronologically summarized as follows: • An internal arc fault involves a pressure rise in the initially sealed metal enclosure of a medium voltage cell due to an increase in the temperature and the vaporized mass (plastic and metal vapours). • To avoid explosion of the metal enclosure containing the insulating gas, a safety valve located at the bottom of the internal metal enclosure bursts when the pressure reaches a critical value. • After the valve has burst, the gas releases and a shock wave is generated: the hot gas flow is ejected towards the buffer area, then it penetrates into the porous filter. • The porous medium's aim is to absorb the shock wave generated at the valve opening and to cool the hot gas flow by heat exchange with the grains composing the protective filter. The final role of the filter is to obtain a gaseous outflow which is not harmful to the equipment and the people located in the MV cell vicinity. In order to simulate the process and to enhance the protection technology, several experimental investigations, and numerical simulation on the arcing fault in a MV cell have been carried out, and are presented in this paper

How to reveal latent degradation of coatings provoked by UV-light

International audienceThis paper deals with predictions of the service life of the two main technologies used for automotive clearcoats: acrylic-melamine and acrylic-urethane. This work demonstrates that the UV-light irradiation leads to chain scissions and crosslinking for the unstabilised and stabilised formulations. Mechanisms are proposed to explain the dramatic increase in the values of the mechanical properties for the two technologies as a function of the ageing time. For a determined critical value of the mechanical properties, water acts to reveal the latent damage by leading to the formation of cracks. Moreover, when the polymer reaches a certain level of network densification due to UV-light irradiation, the system cannot accept the stress induced by the water inflation/deflation and cracks will occur. Other solvents were also tested to understand the effects of polarity on the formation of the cracks

Numerical simulation of a pressure wave interacting with a protection filter during an internal arc fault in a medium voltage cell

International audienceWe present a two-dimensional mathematical model and a specific numerical method to study the interaction of a pressure shock wave, due to an internal arc fault, with a protection filter in a medium voltage cell. The model is based on Euler equations in porous medium taking into account the porosity variation. Calculation results are compared to experimental measurements of the pressure performed on apparatus specially adapted for tests

Two-dimensional modelling of internal arc effects in an enclosed MV cell provided with a protection porous filter

International audienceMedium voltage (MV) cells have to respect standards (for example IEC ones (IEC TC 17C 2003 IEC 62271-200 High Voltage Switchgear and Controlgear—Part 200 1st edn)) that define security levels against internal arc faults such as an accidental electrical arc occurring in the apparatus. New protection filters based on porous materials are developed to provide better energy absorption properties and a higher protection level for people. To study the filter behaviour during a major electrical accident, a two-dimensional model is proposed. The main point is the use of a dedicated numerical scheme for a non-conservative hyperbolic problem. We present a numerical simulation of the process during the first 0.2 s when the safety valve bursts and we compare the numerical results with tests carried out in a high power test laboratory on real electrical apparatus

Numerical simulation of the porous filter properties for the internal arc mollifying effects

International audienceA mathematical model and numerical experiments of pressure wave impacts with a porous medium are presented to simulate the valve burst out of a medium voltage switchgear and to evaluate the protection filter efficiency. A simplified one-dimensional gas flow model in porous medium with variable porosity is used. To solve numerically the governing equations, we employed the numerical method presented in Rochette et al. (2005) [18] to take into account the non-conservative term P(∂phi/∂x). Three sets of test are performed to study several filter prototypes. The objective is to provide a filter which does not produce a high reflected wave and cools enough the ejected hot gas. We first consider filters with variable porosity and simulate the interaction with an incident pressure wave, then we consider two types of granular material to characterize their incidence on the flow and finally, we simulate two different fluid flows (air and SF6) going through the porous medium

Photooxidation of polymers: Relating material properties to chemical changes

International audienceThis paper is devoted to a comprehensive study of the photo-oxidation of polymeric materials with the goal of correlating modifications of the polymer properties at the molecular and macroscopic levels. Several techniques were used to characterise the modifications of the chemical properties and mechanical behaviour over time under UV light. The methodology was developed on materials used as organic coatings; initially, a well-characterised phenoxy resin (PKHJ ) was chosen as a model and then the approach was applied to an acrylate-melamine thermoset currently used as a topcoat in the automotive industry. Analysis of degraded samples by IR spectroscopy allowed us to propose a photooxidation mechanism. This mechanism suggested that chain scission occurred under photo-oxidation. To entirely understand the degradation of the polymers, gel fraction, thermoporosimetry, DMA, AFM nanoindentation and micro-hardness determinations were performed. The results showed that crosslinking reactions occurred in competition with chain scission and explained for the first time why crosslinking reactions were quite prevalent. Based on the obtained results, quantitative correlations were made between the various criteria of degradation, thus relating the chemical structure changes to the mechanical property modifications

Chemical structure evolution of acrylic-melamine thermoset upon photo-ageing

International audienceThis article reports a study of the influence of UV light irradiation in the presence of oxygen on both the chemical structure evolution and mechanical properties of an acrylicmelamine (AM) thermoset. Photo-oxidation of the thermoset was investigated by several techniques, such as IR spectroscopy, DMA, headspace-SPME and atomic force microscopy (AFM). The measurements by infrared spectroscopy combined with gas analysis allowed us to elucidate details of the reaction mechanisms that are difficult to detect by only spectroscopic measurements. This approach was used to probe mechanistic aspects of the photo-oxidation of acrylic-melamine (AM) thermoset and was completed by dynamic-mechanical measurements combined with AFM and micro-hardness measurements, which revealed the effect of photo-oxidation on the mechanical properties of the thermoset

Photochemical Behavior of Polylactide/ZnO Nanocomposite Films

International audienceThis study reports the effect of light on PLA/ ZnO nanocomposites films produced by melt-extrusion. The attention focused on the discrimination between the photocatalytic degradation of PLA provoked by ZnO and the UV screening effect of the ZnO nanoparticles. The chemical modifications of PLA induced by UV light irradiation were analyzed using infrared spectroscopy and completed through the analysis of the low-molecular-weight photoproducts using IC and SPME and the characterization of chain scissions with SEC. A comprehensive mechanism for the photooxidation of PLA was then proposed. The results indicated that the photocatalytic activity of ZnO nanoparticles induces the oxidation of PLA. Because ZnO limits the penetration of light inside the samples, this effect mainly concerns the first micrometers at the surface of the exposed samples. Cross-sectional analysis using micro-IR and ATR-IR spectroscopies was performed to highlight the degradation profile in the PLA/ZnO nanocomposites

Correlation between water uptake and loss of the insulating properties of PE/ATH composites used in cables applications.

International audiencePE/ATH composites are known to lose insulating properties in use condition. The known reason for that behaviour seems to be the water uptake due to two major reasons: hydrophilic behaviour of ATH and degradation of the polymer matrix with the accumulation of oxidation products that lead to create an hydrophilic matrix. This study aims to identify the synergetic or antagonistic effects of the thermo-oxidation on the water absorption and mostly/above all to correlate the modification of the chemical structure with the loss of the functional properties