Effect of aging on the reinforcement efficiency of carbon nanotubes in epoxy matrix

The reinforcement efficiency of carbon nanotubes (CNTs) in epoxy matrix was investigated in the elastic regime. Cyclic uniaxial tensile tests were performed at constant strain amplitude and increasing maximum strain. Post-curing of the epoxy and its composite at a temperature close to the glass transition temperature allowed us to explore the effect of aging on the reinforcement efficiency of CNT. It is found that the reinforcement efficiency is compatible with a mean field mixture rule of stress reinforcement by random inclusions. It also diminishes when the maximum strain increased and this effect is amplified by aging. The decrease of elastic modulus with increasing cyclic maximum strain is quite similar to the one observed for filled elastomers with increasing strain amplitude, a phenomenon often referred as the Payne effect

Different experimental ways to minimize the preforming defects of multi-layered interlock dry fabric

International audienceThis study presents a strategy to improve the quality of a dry fabric’s preforms. Preforming tests were realized with one and two-layers of interlock carbone fabric at different configurations. Initial results led to preforms with several defects. For one-layer preforming, a new blank holder geometry and an increase of the pressure applied on the fabric allowed to improve the quality of the preforms. On the other hand, for two-layer preforming, the insertion of a mat fabric in the interface of the two preformed layers allowed to decrease the friction and to improve the preforms quality, significantly

The electronic transport properties and microstructure of carbon nanofiber/epoxy composites

Carbon nanofibres (CNF) were dispersed into an epoxy resin using a combination of ultrasonication and mechanical mixing. The electronic transport properties of the resulting composites were investigated by means of impedance spectroscopy. It was found that a very low critical weight fraction (pc = 0.064 wt %) which may be taken to correspond to the formation of a tunneling conductive network inside the matrix. The insulator-to-conductor transition region spanned about one order of magnitude from 0.1 to 1 wt %. Far from the transition, the conductivity increased by two orders of magnitude. This increase and the low value of the conductivity were explained in terms of the presence of an epoxy film at the contact between CNF. A simple model based on the CNF-CNF contact network inside the matrix was proposed in order to evaluate the thickness of that film.Comment: 7 page

Fault diagnosis of power converters in a grid connected photovoltaic system using artificial neural networks

Introduction. The widespread use of photovoltaic systems in various applications has spotlighted the pressing requirement for reliability, efficiency and continuity of service. The main impediment to a more effective implementation has been the reliability of the power converters. Indeed, the presence of faults in power converters that can cause malfunctions in the photovoltaic system, which can reduce its performance. Novelty. This paper presents a technique for diagnosing open circuit failures in the switches (IGBTs) of power converters (DC-DC converters and three-phase inverters) in a grid-connected photovoltaic system. Purpose. To ensure supply continuity, a fault-diagnosis process is required throughout all phases of energy production, transfer, and conversion. Methods. The diagnostic approach is based on artificial neural networks and the extraction of features corresponding to the open circuit fault of the IGBT switch. This approach is based on the Clarke transformation of the three-phase currents of the inverter output as well as the calculation of the average value of these currents to determine the exact angle of the open circuit fault. Results. This method is able to effectively identify and localize single or multiple open circuit faults of the DC-DC converter IGBT switch or the three-phase inverter IGBT switches.Вступ. Широке використання фотоелектричних систем у різних застосуваннях висунуло на перший план нагальні вимоги до надійності, ефективності та безперервності обслуговування. Основною перешкодою для ефективнішого застосування була надійність силових перетворювачів. Справді, наявність несправностей у силових перетворювачах може спричинити збої в роботі фотоелектричної системи, що може знизити її продуктивність. Новизна. У цій статті представлена методика діагностики обриву кола в перемикачах (IGBT) силових перетворювачів (перетворювачів постійного струму та трифазних інверторів) у фотоелектричній системі, підключеній до мережі. Мета. Для забезпечення безперервності постачання потрібен процес діагностики несправностей на всіх етапах виробництва, передачі та перетворення енергії. Методи. Діагностичний підхід заснований на штучних нейронних мережах та вилучення ознак, що відповідають обриву кола IGBT-перемикача. Цей підхід ґрунтується на перетворенні Кларка трифазних струмів на виході інвертора, а т акож розрахунку середнього значення цих струмів для визначення точного кута обриву кола. Результати. Цей метод дозволяє ефективно ідентифікувати та локалізувати одиночні або множинні несправності розімкнутого кола IGBT-перемикача DC-DC перетворювача або IGBT-перемикача трифазного інвертора

Purifying Performance of the STEP of Mrirt (Natural lagoon)

AbstractThe purifying system of the domestic lagoon sewage remains one of the most widely used processes in Morocco (81% of lagoon-type wastewater treatment plants) since it is the most technical solution which is suited to the economic and climatic conditions of our country.Throughout this work, we tended to study the purifying performance of the wastewater treatment plant in the town of Mrirt, by measuring the parameters, which indicate the pollution degree, namely BOD5, COD and TSS. According to the results obtained from those parameters, we determined the causes of the non-conformity of rejection for the global parameters of pollution with respect to the unfiltered samples and proposed the solutions for the good purification of the STEP with a tertiary treatment, which is based on the physicochemical methods of the water discharged into the natural environments.In the light of this work, the monthly results throughout the last two years (2012-2013) concerning the parameters of the raw and purified wastewater studied and discharged from the town of Mrirt have shown that:* The average BOD5 which is recorded at the inlet and the outlet of the STEP is respectively 575 mg O2 / l and 159 mg O2 / l.* The average TSS which is recorded at the inlet is 450 mg / l and at the outlet is 169 mg / l* The average COD, which is recorded at the inlet and the outlet, is respectively 1015 mg O2 / l and 169 mg O2 / l.On the basis of the obtained results, it can be said that the most suitable kind of the natural lagooning process in Morocco (the town of Mrirt) remains very sensitive to the various factors influencing the effluent yield of the STEP such as the accumulation of sludge at the level of the anaerobic basins, the climate change out of the seasons (temperature variation), residence period, volumetric and superficial load, the algal development ...etc. 

Boundedness of the Hilbert transform on Besov spaces

The Hilbert transform along curves is of a great importance in harmonic analysis. It is known that its boundedness on $L^p(\mathbb{R}^n)$ has been extensively studied by various authors in different contexts and the authors gave positive results for some or all $p,10$ (i.e. $B^{s}_{p,q}(\mathbb{R}^n) \hookrightarrow L^p(\mathbb{R}^n), s>0)$. Thus, our result may be viewed as an extension of known results to the Besov spaces $B^{s}_{p,q}(\mathbb{R}^n)$ for general values of $s$ in $\mathbb{R}$