The photovoltaic effect and charge carrier mobility in layered compositions of bithiophene or related rotaxane copolymer with C<Subscript>70</Subscript> fullerene derivative

Organic photovoltaic cells with a bulk heterojunction have been manufactured in which the photoactive layer consists of a mixture of bithiophene copolymer or related rotaxane with a fullerene derivative (PC₇₀BM). The mobility of charge carriers in photoactive layers has been determined, the current–voltage characteristics of photovoltaic cells have been measured, and the energy level diagram of cell components has been constructed. It is established that the polyrotaxane component (macrocycle) insulates a part of thiophene fragments of the macromolecule, thus hindering the transport of carriers and leading to large energy losses for exciton dissociation, which results in a decreasing photovoltaic effect.     

Long-term performance and binder chemical structure evolution of elastomeric bituminous geomembranes

This paper presents the results of uniaxial tensile tests, flow-rate measurements, and size-exclusion chromatography (SEC), which are used to evaluate the ageing of elastomeric bituminous geomembranes (BGMs) that were installed 6, 10, 15, 20, and 30 years ago in ponds at two different sites in France. SEC was used to detect oxidation and the absence of polymer in the bitumen at the surface of the 20- and 30-year-old BGMs. The results indicate that, for BGMs exposed less than 20 years, there was no oxidation or degradation of the polymer at the core. However, the elastomeric polymer was altered at the core of the 30-year-old BGM, resulting in an embrittlement of the bitumen, but this did not affect the mechanical properties of the glass veil and nonwoven polyester geotextile in the BGM core. Lastly, the flow rates through the BGM measured according to EN 14150 are still below 10^?6 m³ m^?2 d^?1, which indicates that the elastomeric bituminous GM is still watertight after 30 years of exposure.     

Chemical synthesis of some Schiff base-type polymers containing pyrrole units

Summary The synthesis of three Schiff-base type monomers containing pyrrole units was performed. Their polymerization was carried out by chemical oxidation with (NH₄)₂S₂O₈. Some preliminary thermal and electrical properties were determined.     

Synthesis and characterization of a fully aromatic polyazomethine with rotaxane architecture

This paper reports the preparation and characterization of a new aromatic polyazomethine with rotaxane architecture. The complex of β‐cyclodextrin and 1,4‐phenylenediamine was treated with N‐n‐butyl‐3,6‐diformylcarbazole, which is large enough to prevent dethreading. The polycondensation reaction was performed in N,N‐dimethylformamide leading to polyazomethine soluble in polar solvents. Measurements made by gel permeation chromatography of the dimethylformamide‐soluble (DMF) soluble polyazomethine show the presence of high molecular weight material. The structure and thermal properties of the resulting polymer were characterized by IR, ¹H NMR, TGA and DSC techniques. Copyright © 2003 Society of Chemical Industry     

The dual reciprocity boundary element method for solving Cauchy problems associated to the Poisson equation

This paper presents an application of the dual reciprocity method (DRM) to a class of inverse problems governed by the Poisson equation. Here the term inverse refers to the fact that the boundary conditions are not fully specified, i.e. they are not known for the entire boundary of the solution domain. In order to investigate the ability of the DRM to reconstruct the unknown boundary conditions using overspecified conditions on the accessible part of the boundary we consider some test problems involving circular, annular and square domains. Due to the ill-posed nature of the problem, i.e. the instabilities in the solution of these problems, the DRM is combined with the Tikhonov regularization method.     

Background subtraction via incremental maximum margin criterion: a discriminative subspace approach

Background subtraction is one of the basic low-level operations in video analysis. The aim is to separate static information called “background” from the moving objects called “foreground”. The background needs to be modeled and updated over time to allow robust foreground detection. Recently, reconstructive subspace learning models, such as principal component analysis (PCA) have been used to model the background by significantly reducing the data’s dimension. This approach is based on the assumption that the main information contained in the training sequence is the background meaning that the foreground has a low contribution. However, this assumption is only verified when the moving objects are either small or far away from the camera. Furthermore, the reconstructive representations strive to be as informative as possible in terms of well approximating the original data. Their objective is mainly to encompass the variability of the training data and so they give more effort to model the background in an unsupervised manner than to precisely classify pixels as foreground or background in the foreground detection. On the other hand, discriminative methods are usually less adapted to the reconstruction of data; although they are spatially and computationally much more efficient and often give better classification results compared with the reconstructive methods. Based on this fact, we propose the use of a discriminative subspace learning model called incremental maximum margin criterion (IMMC). The objective is first to enable a robust supervised initialization of the background and secondly a robust classification of pixels as background or foreground. Furthermore, IMMC also allows us an incremental update of the eigenvectors and eigenvalues. Experimental results on different datasets demonstrate the performance of this proposed approach in the presence of illumination changes.     

Structure and morphology of nanoporous zno and dark current‐Voltage characteristics of the glass/(TCO)/zno/poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5'‐bithiophene)/ag structure

The hybrid organic‐inorganic structure based on glass/(TCO)/nanoporous ZnO/poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5′‐bithiophene)]/Ag that was prepared by physical deposition has been investigated. The structure of the nanostructured ZnO obtained by magnetron sputtering was confirmed by X‐ray diffractometry (XRD) and energy dispersive X‐ray spectroscopy (EDX). Scanning electron microscopy (SEM) analysis proved the existence of short and interconnected zinc oxide (ZnO) fibers, which form a continuous porous network with pores having an average diameter of 100 nm. Current‐voltage (I‐V) curves of the glass/TCO/ZnO/PF‐BT/Ag hybrid structure are similar to those of typical p‐n junctions and stable until 90°C temperature. According to the I‐V characteristics, the dominant mechanism of current flow is based on the generation‐recombination of carriers in the depletion region at low direct biases and also on the injection of carriers at high biases. The reverse branch of the I‐V characteristic, calculated in log‐log scale, shows one segment with a power coefficient of 3/2 at room temperature. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42415.     

The boundary-element method for the determination of a heat source dependent on one variable

This paper investigates the inverse problem of determining a heat source in the parabolic heat equation using the usual conditions of the direct problem and a supplementary condition, called an overdetermination. In this problem, if the heat source is taken to be space-dependent only, then the overdetermination is the temperature measurement at a given single instant, whilst if the heat source is time-dependent only, then the overdetermination is the transient temperature measurement recorded by a single thermocouple installed in the interior of the heat conductor. These measurements ensure that the inverse problem has a unique solution, but this solution is unstable, hence the problem is ill-posed. This instability is overcome using the Tikhonov regularization method with the discrepancy principle or the L-curve criterion for the choice of the regularization parameter. The boundary-element method (BEM) is developed for solving numerically the inverse problem and numerical results for some benchmark test examples are obtained and discussed     

Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressure

Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80°C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 × 10^?3 mol L^?1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 × 10^?3 mol L^?1. The results indicate the existence of a direct phenol‐oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build‐up and stabilizer consumption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Bearing grease deterioration

About 80% of bearing mountings are grease lubricated. This has many advantages, such as eliminating complicated oil cooling systems, and better organisation of the available space in machine tools and aircraft. However, the bearing service life is reduced by grease deterioration. Many papers give recommendations concerning regreasing intervals but information concerning grease deterioration and service life is poor. This paper presents theoretical and experimental work concerning grease film thickness estimation and its deterioration. An equation relating grease service life to the main influencing factors is proposed. We measured grease film thickness by the global electrical resistance method. Grease deterioration is illustrated by electron microscopy.