Validation tests of the full-discontinuous Galerkin/extrinsic cohesive law framework of Kirchhoff-Love shells

Due to its ability to account for discontinuities, the discontinuous Galerkin (DG) method presents two main advantages for modeling crack initiations and propagation. On the one hand, it provides an easy way to insert the cohesive elements during the simulation and therefore avoids the drawbacks inherent to the use of an extrinsic cohesive law. On the other hand, the capture of complex crack path requires very thin meshes, and the recourse to a parallel implementation of DG formulations exhibits a high scalability of the resolution scheme. Recently, the authors developed such a DG-fracture framework for Kirchhoff-Love shells in the linear and non-linear ranges. They proved that this framework dissipates, during the fracture process, an amount of energy equal to the fracture energy of the material and that the model is able to propagate the crack with the right speed. In this paper, novel numerical benchmarks are presented to validate the method in various fracture conditions. The two first ones include an initial notch and study the fracture propagation under two different dynamic loadings (impact and blast). The two other ones focus on the fragmentation of initially unbroken specimens due to uniform expansion, in order to demonstrate the ability of the new framework to model crack initiations. Results are in all cases in agreement with the ones reported in the literature.     

A least‐squares coupling method between a finite element code and a discrete element code

This paper presents a coupling method between a discrete element code CeaMka3D and a finite element code Sem. The coupling is based on a least‐squares method, which adds terms of forces to finite element code and imposes the velocity at coupling particles. For each coupling face, a small linear system with a constant matrix is solved. This method remains conservative in energy and shows good results in applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of Cu off-stoichiometry on wide band gap CIGSe solar cells

The electric properties of solar cells based on co-evaporated Cu(In,Ga)Se₂ (CIGSe) thin film show a good tolerance regarding the absorber Cu content (y = [Cu]/([In] + [Ga])) for standard Ga concentration, i.e. x = [Ga] / ([In] + [Ga]) ~ 0.3. In the present contribution, we show that this tolerance is lost when the gallium content is increased. Wide bandgap CIGSe samples (x ~ 0.55) with a variation in y from 0.97 to 0.84 have been grown. The efficiency of the cells decreases from 12.6% to 6.5% for y = 0.97 and 0.84 respectively. For the lowest y, the efficiency is harmed because of a low short-circuit current density (J_sc), an increased voltage dependency in the current collection, which affects the fill factor (FF), and a decrease of the open-circuit voltage (V_oc). For y = 0.97 and 0.84 respectively, the decrease of the activation energy (E_a) from 1.36 to 1.24 eV indicates a shift of the area of the dominant recombination from the space charge region towards the interface. There seems to be evidence that reducing the Cu-content in the CIGSe thin film will cause a decrease in the width of the space charge region. Solar cells based on Cu-rich CIGSe (1.03 < y < 1.09) have also been fabricated and characterized. A strong deterioration of their electrical properties is observed despite the KCN etch of the segregated Cu_2 − xSe binary phases at the surface, suggesting the presence of residual Cu_2 − xSe precipitates within the layer.     

Characterization of the atrazine's bound (nonextractable) residues using fractionation techniques for soil organic matter

Atrazine's bound residues (BR), in the range of 10-40% of the applied atrazine,were obtained by laboratory incubation (56 d) of four soils having different capacities to degrade atrazine in relation to the presence or absence of a microflora able to mineralize the triazinic ring. Soil size fractionation followed by alkaline extraction, before and after HF treatment, and then acid hydrolysis with 2 M HCl in reflux conditions was applied to the soils containing BR. Most of the BR were in the finest fraction (<20 microm) that contained the humified organic matter (from 61 to 77% of the total BR), and between 78 and 89% was made soluble during the different steps of the chemical fractionation procedure. From 20 to 50% of the BR of the fraction <20 microm was identified as the intact atrazine and its main derivatives, indicating that this proportion of the BR was probably formed by entrapment in voids of the soil organic matter. Between 13 and 30% of the BR was associated to humic acids (HA); they were not dialyzable and were released by acid hydrolysis with HCl, indicating that these BR were chemically bound to HA by an heteroatomic bond after the substitution of the chlorine atom of atrazine. Comparison of the results obtained for the four soils indicated that (i) an important activity of microorganisms able to mineralize the triazinic ring favors the formation of highly degraded products that can form BR; (ii) a soil pH <6 favors the formation and stabilization of hydroxylated derivatives of atrazine, and (iii) a high content of humic acids favors the formation of chemically bound residues.     

Minimizing metastabilities in Cu(In,Ga)Se2/(CBD)Zn(S,O,OH)/i‐ZnO‐based solar cells

Chemical bath deposited (CBD)Zn(S,O,OH) is among the alternatives to (CBD)CdS buffer layers in Cu(In,Ga)Se₂(CIGSe)‐based devices. Nevertheless, the performances reached by devices buffered with (CBD)Zn(S,O,OH) vary strongly from one sample to another and from one laboratory to another, indicating that parameters of minority impact with (CBD)CdS‐buffered devices have major influence when buffered with (CBD)Zn(S,O,OH). Moreover, the literature reports, but not systematically, the requirement of substituting the standard resistive intrinsic ZnO by (Zn,Mg)O and/or soaking the devices in ultraviolet‐containing light in order to reach optimal device operation. The present study investigates the impact of the three following parameters on the optoelectronic behavior of the Cu(In,Ga)Se₂/(CBD)Zn(S,O,OH)/i‐ZnO‐based solar cells: (i) CIGSe surface composition; (ii) (CBD)Zn(S,O,OH) layer thickness; and (iii) i‐ZnO layer resistivity. The first conclusion of this study is that all of these parameters are observed to influence the electrical metastabilities of the devices. The second conclusion is that the light soaking time needed to achieve optimal photovoltaic parameters is decreased by (i) using absorbers with Cu content close to stoichiometry, (ii) increasing the buffer layer thickness, and (iii) increasing the resistivity of i‐ZnO. By optimizing these trends, stable and highly efficient Zn(S,O,OH)‐buffered CIGSe solar cells have been fabricated. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxidation Mechanisms and Kinetics of 1D-SiC/C/SiC Composite Materials: II, Modeling

A model, based on a simple axisymmettical fiber/interphase/ matrix assembly, is derived to depict the oxidation behavior of ID-SiC/C/SiC composites within the temperature range 900–1300°C and for 10 < P _O2 < 100 kPa. It takes into account (i) the changes versus time of the geometry of the annular pore resulting from the consumption by oxidation of the carbon interphase, (ii) the may transfers by diffusion along the pore of the reactant and products, and (iii) the chemical reactions with oxygen of both the pore walls (yielding silica) and the pore bottom (consisting of carbon). The model gives the gaseous species concentration and silica thickness profiles along the pore, the length of carbon consumed by oxidation, and the relative weight change. The model depicts in a satisfactory manner the features of the TGA curves recorded on actual composites and it is in excellent agreement with the measurements of the carbon interphase lengths consumed by oxidation. It shows that the oxidation resistance of ID-SiC/C/SiC composites is better at high temperatures ( T 1100°C) and for thin carbon interphases ( e 0.1 μm). Under such conditions, the materials exhibit a self-healing behavior.     

Synthesis and photopolymerization of acrylic acrylate copolymers

Acrylate‐functionalized copolymers were synthesized by the modification of poly(butyl acrylate‐co‐glycidyl methacrylate) (BA/GMA) and poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate). ¹³C‐NMR analyses showed that no glycidyl methacrylate block longer than three monomer units was formed in the BA/GMA copolymer if the glycidyl methacrylate concentration was kept below 20 mol %. We chemically modified the copolymers by reacting the epoxy group with acrylic acid to yield polymers with various glass‐transition temperatures and functionalities. We studied the crosslinking reactions of these copolymers by differential scanning calorimetry to point out the effect of chain functionality on double‐bond reactivity. Films formed from acrylic acrylate copolymer precursors were finally cured under ultraviolet radiation. Network heterogeneities such as pendant chains and highly crosslinked microgel‐like regions greatly influenced the network structure and, therefore, its viscoelastic properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 753–763, 2002     

Job mobility, its determinants, and its effects: Longitudinal data from the Maastricht cohort study.

This prospective study of 12,140 employees examined the effects of work characteristics and situational, psychological, and health aspects on job mobility. Before job change, the mobility group reported significantly more conflicts with the supervisor, higher physical and emotional strain, higher degree of job insecurity, lower job satisfaction, and lower degree of commitment compared with employees who did not change jobs. After job change, the mobility group reported improved autonomy, task diversity, decreased occurrence of conflicts with the supervisor, decreased physical and emotional strain, and improved training possibilities and job security than before the change. Changing jobs had a positive effect on employees with respect to job perception and job satisfaction and led to reduced fatigue and need for recovery. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alfred Binet and higher education.

At the beginning of the 20th century, Alfred Binet sought teaching positions at the Colfte de France and the Sorbonne. Binet wanted to develop experimental psychology in France, but the strong psychopathological orientation of French psychology blocked his ambition. The 1st part of this article relates the history of the introduction of psychology, via Théodule Ribot, to the Sorbonne and the Coll6ge de France. Ribot's premature retirement from the Collège de France in 1901 triggered a battle that led to Binet's repeated failure to gain access to these institutions of higher education and the success in 1902 of Ribot's students: Pierre Janet at the Colfte de France and Georges Dumas at the Sorbonne. (PsycINFO Database Record (c) 2010 APA, all rights reserved)