On the thermal degradation of cellulose in cotton fibers

Thermal decomposition of cellulose has been widely studied for the past several years. It has been reported that the source of cellulose and its composition greatly affect its pyrolysis. One of the most widely used analytical tools for the study of cellulose pyrolysis is thermogravimetric (TG) analysis. Several model-fitting methods have been employed to study cellulose pyrolysis kinetics. An alternative to the model-fitting approach is the so-called model-free method developed by Vyazovkin. This isoconversional technique calculates the activation energy as a function of the degree of the conversion. In this article, the pyrolysis of cellulose in cotton fibers compared to microcrystalline cellulose (Avicel, PH 105) was investigated. TG curves were acquired as a function of the heating rates (4, 5, 8, 10, and 16 °C min^?1) and the model-free method was used to analyze the data. Activation energies of cotton fibers and Avicel were obtained, and compared to the data reported in the literature. In addition, models for isothermal decomposition were calculated and compared with experimental data at the same temperature.     

P/S ligands derived from carbohydrates in Rh-catalyzed hydrosilylation of ketones

Reported is the synthesis of a number of diastereomerically pure cationic Rh(I)-complexes I starting from phosphinite thioglycosides. These complexes were used in the asymmetric hydrosilylation of prochiral ketones. The reactivity and enantioselectivity of the reaction was shown to be dependent on the pyranose ring, the substituent at the sulfur atom, the hydroxylic protective groups and most significantly on the alkene co-ligand.     

Structural and optical properties of a-Si1−xCx:H films synthesized by dc magnetron sputtering technique

Hydrogenated amorphous SiC films (a-Si_1−xC_x:H) were prepared by dc magnetron sputtering technique on p-type Si(1 0 0) and corning 9075 substrates at low temperature, by using 32 sprigs of silicon carbide (6H-SiC). The deposited a-Si_1−xC_x:H film was realized under a mixture of argon and hydrogen gases. The a-Si_1−xC_x:H films have been investigated by scanning electronic microscopy equipped with an EDS system (SEM-EDS), X-ray diffraction (XRD), secondary ions mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR), UV-vis-IR spectrophotometry, and photoluminescence (PL). XRD results showed that the deposited film was amorphous with a structure as a-Si_0.80C_0.20:H corresponding to 20 at.% carbon. The photoluminescence response of the samples was observed in the visible range at room temperature with two peaks centred at 463 nm (2.68 eV) and 542 nm (2.29 eV). In addition, the dependence of photoluminescence behaviour on film thickness for a certain carbon composition in hydrogenated amorphous SiC films (a-Si_1−xC_x:H) has been investigated.     

A unified framework of multi-objective cost functions for partitioning unstructured finite element meshes

Good performance of parallel finite element computations on unstructured meshes requires high-quality mesh partitioning. Such a decomposition task is normally done by a graph-based partitioning approach. However, the main shortcoming of graph partitioning algorithms is that minimizing the so-called edge cut is not entirely the same as minimizing the communication overhead. This paper thus proposes a unified framework of multi-objective cost functions, which take into account several factors that are not captured by the graph-based partitioning approach. Freely adjustable weighting parameters in the framework also promote a flexible treatment of different optimization objectives. A greedy-style post-improvement procedure is designed to use these cost functions to improve the quality of subdomain meshes arising from the graph-based partitioning approach. Both serial and parallel implementation of the post-improvement procedure have been done. Numerical experiments show that communication overhead can indeed be reduced by this improvement procedure, thereby increasing the performance of parallel finite element computations.     

Introduction

No Abstract.       

Les α et β-Cetophosphonates,des Precurseurs de Pyrrolidines et de Quinoleines Phosphonatees

The condensation of primary amines on α- or β-ketophosphonates affords the corresponding iminophosphonates. The reaction was found to be highly stereoselective, affording the E isomer exclusively. These phosphonylimines were then treated in basic media to give pyrrolidines and quinolines through intramolecular cyclization. The structures of all obtained products were confirmed by NMR spectroscopy (¹H, ³¹P, ¹³C), and in some cases by mass spectrometry.     

Mixed S/P Ligands from Carbohydrates: Synthesis and Utilization in Asymmetric Catalysis

Abstract

New chiral mixed sulfur/phosphorus ligands derived from carbohydrates are reported. These ligands were found to be efficient catalyst precursors for palladium-catalyzed asymmetric substitution of 1,3-diphenylpropenyl acetate with dimethyl malonate or benzylamine (up to 96% ee), and for rhodium-catalyzed methyl acetamidocinnamate hydrogenation (up to 92% ee).     

Structural and electrochemical characterization of polyaniline/LiCoO2 nanocomposites prepared via a Pickering emulsion

Polyaniline (PANI)/LiCoO₂ nanocomposite materials are successfully ready through a solid-stabilized emulsion (Pickering emulsion) route. The properties of nanocomposite materials have been put to the test because of their possible relevance to electrodes of lithium batteries. Such nanocomposite materials appear thanks to the polymerization of aniline in Pickering emulsion stabilized with LiCoO₂ particles. PANI has been produced through oxidative polymerization of aniline and ammonium persulfate in HCl solution. The nanocomposite materials of PANI/LiCoO₂ could be formed with low amounts of PANI. The morphology of PANI/LiCoO₂ nanocomposite materials shows nanofibers and round-shape-like morphology. It was found that the morphology of the resulting nanocomposites depended on the amount of LiCoO₂ used in the reaction system. Ammonium persulfate caused the loss of lithium from LiCoO₂ when it was used at high concentration in the polymerization recipe. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide evidence to well-ordered layered structure of the PANI/LiCoO₂ nanocomposite materials with high LiCoO₂ content. The ratios of the intensities of 003 and 104 peaks were found to be higher than 1.2 indicating no pronounced mixing of the lithium and cobalt cations. The electrochemical reactivity of PANI/LiCoO₂ nanocomposites as positive electrode in a lithium battery was examined during lithium ion deinsertion and insertion by galvanostatic charge–discharge testing; PANI/LiCoO₂ nanocomposite materials exhibited better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiCoO₂ cathode. The best advancement has been observed for the PANI/LiCoO₂ nanocomposite 5 wt.% of aniline.     

Structural and nanomechanical properties of porous silicon: Cheap substrate for CMOS process industry

The surface topology of porous silicon (PSi) is a relevant parameter that decides the compatibility of such substrate with CMOS process. Using standard resistivity (1–10 Ω·cm) of Si substrate to fabricate PSi-S is a low cost solution for the industry. In this paper, through an atomic force microscopy (AFM) analysis, the root mean square (RMS) roughness, the power spectral density and the correlation length were determined for different PSi layers. Furthermore, the measured hardness, Young's modulus, and stress have been made for different thicknesses of PSi: 5, 10, 50, and 200 μm. The obtained results demonstrated that very interesting properties have been achieved with the 50 μm-thick PSi-S layer with a maximum porosity around 65%, a surface roughness less than 1 nm and a hardness value of (~1 GPa). The realized results encourage the utilization the PSi-based substrate into the industry process and thus the development of a Systems-on-Chip (SoC).