The effect of the framework structure on the chemical properties of the vanadium oxide species incorporated within zeolites

V-silicalite catalysts (VS-1 and VS-2) prepared by hydrothermal synthesis have been studied by ESR, XAFS (XANES and EXAFS) and photoluminescence spectroscopy. The in situ characterization of these V-silicalites shows that vanadium is present within the zeolitic framework as a highly dispersed tetrahedrally coordinated V-oxides, VO₄ unit, having a short V=O bond length. Photoluminescence spectroscopy in static and dynamic mode, as well as XAFS studies allow to detect in the V-silicalites different V species than that present in V-HMS or V/SiO₂, in terms of V=O bond length, vibrational energy, bond angle and lifetime of the excited triplet state. It is suggested that the combined contribution of the neighboring Si---OH group attached to the VO₄ unit and the zeolitic rigid framework structure of V-silicalites cause a more significant and pronounced effect on the chemical properties of the VO₄ unit than the flexible structure of V-HMS or V/SiO₂. Moreover, the dynamic quenching of the phosphorescence by the addition of reactant molecules such as NO or propane indicates that the V species in the excited triplet state can be expected to be the active sites for the photocatalytic reactions.     

The Future of the Refractory Industry, with a Chinese Perspective

Globalization is a reality resulting in many changes in the refractory industry. In this paper some of the threats and opportunities, which are influencing the future prosperity of the refractory industry on a worldwide basis, are being evoked. Some key technical and management issues are underlined, in terms of adjusting the productivity-quality-cost to the customers requirements ; producing unshapes versus shapes; innovations supported by research; international profile for the import-export game; training and education. Consequences for China, who does play a dominant role due to the size of its internal market （ customers demand） and the magnitude of its production capability （including raw materials availability）, are being drawn.     

The effect of reaction conditions on montmorillonite-catalysed peptide formation

Oligomerization of glycine (gly) and diglycine (gly₂) on montmorillonite was performed as cyclic, drying-wetting process at temperatures below 100°C, under varying reaction conditions. The influence of substrate/clay ratio, temperature and pH was found to be different for amino acid (AA) dimerization, cyclic anhydride (CA) formation and peptide chain elongation. High temperatures and neutral pH favour CA formation over diglycine production. An AA/catalyst ratio of 0.2 mmol/g leads to optimal yields. This supports the assumption that amino acid dimerization and CA formation take place at the edges of clay particles. Peptide chain elongation, starting from gly₂, produces higher yields at higher temperatures and neutral pH.     

Paf-acether in human skin

Paf is a phospholipid mediator present in human skin which induces inflammatory events such as neutrophil infiltration and increased vascular permeability. Recent data suggest that cutaneous cells, such as fibroblasts and keratinocytes, produce paf and that paf is released during allergic cutaneous reactions. It is tempting to speculate that paf may contribute to the development of various skin disorders with acute and chronic skin inflammation. Paf antagonists may help in bringing answers to this hypothesis and may offer new prospects for the treatment of cutaneous inflammatory diseases. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

Fractal Characteristics of Fracture Surfaces

Quantitative fractography is often used to study material failure mechanisms. During calculation of surface or profile roughness parameters, the magnification used in obtaining fractographic data is found to influence the value of the parameters. Fractal geometry has been developed into a tool capable of defining surface and profile topography without sensitivity to magnification, and several studies have related fractal dimension ( D _F) to other physical or mechanical properties. In this study, we obtained the fractal dimension of profiled fracture surfaces of one glass and three proprietary dental porcelains. The fracture toughness ( K _1c) of these materials was also measured using the indentation-strength method. Results show the surfaces to be fractal. No quantitative relationship between fractal dimension and toughness was found. Differences in K _1c were demonstrated between some materials. It is postulated that the size range within which fractal dimension can be defined as constant is dependent on the toughening mechanism, and that the relationship between K _Ic and D _F cannot be identical for all materials.     

Large-scale in vivo synthesis of the carbohydrate moieties of gangliosides GM1 and GM2 by metabolically engineered Escherichia coli

Two metabolically engineered Escherichia coli strains have been constructed to produce the carbohydrate moieties of gangliosides GM2 (GalNAcbeta-4(NeuAcalpha-3)Galbeta-4Glc; Gal = galactose, Glc = glucose, Ac = acetyl) and GM1 (Galbeta-3GalNAcbeta-4(NeuAcalpha-3)Galbeta-4Glc. The GM2 oligosaccharide-producing strain TA02 was devoid of both beta-galactosidase and sialic acid aldolase activities and overexpressed the genes for CMP-NeuAc synthase (CMP = cytidine monophosphate), alpha-2,3-sialyltransferase, UDP-GlcNAc (UDP = uridine diphosphate) C4 epimerase, and beta-1,4-GalNAc transferase. When this strain was cultivated on glycerol, exogenously added lactose and sialic acid were shown to be actively internalized into the cytoplasm and converted into GM2 oligosaccharide. The in vivo synthesis of GM1 oligosaccharide was achieved by taking a similar approach but using strain TA05, which additionally overexpressed the gene for beta-1,3-galactosyltransferase. In high-cell-density cultures, the production yields for the GM2 and GM1 oligosaccharides were 1.25 g L(-1) and 0.89 g L(-1), respectively.     

Modelling of the Nonlinear Behavior of Compatibilized Polyethylene/Polyamide Blends in Shear and Extensional Flows

We have studied the effect of the amount Φ_c of a reactive compatibilizer on the rheological properties of a polyethylene/polyamide blend, under steady shear and transient extensional flows. Here, we propose to describe the viscosity η(γ) and the first normal stress coefficient γ₁(γ) using a Carreau‐type power‐law model, which is a three‐parameter model. A single model is sufficient to express the behavior of γ₁(γ) On the other hand, the complete η(γ) curve is described by the superposition of two Carreau models, in relation to the presence of two relaxation mechanisms. Moreover, the extentional viscosity η_E(?), estimated using the end pressure drop observed in capillary flow experiments, is expressed by a two‐parameter power‐law model.     

Experimental and theoretical analysis of the operation of a natural gas cogeneration system using a polymer exchange membrane fuel cell

This paper reports experimental and numerical results of an investigation of five identical cogeneration systems using PEM (Polymer Exchange Membrane) fuel cells and running on natural gas. The natural gas is reformed locally to produce hydrogen. The accuracy of numerical results is validated by comparison with experimental data and the system performances are analysed in terms of electrical, thermal and total efficiencies. It appears that the energetic performances are low, particularly at low current. Simple solutions for enhancing the system electrical performances by modifying control laws are proposed.     

Powerful Parallel and Symmetric 3D Thinning Schemes Based on Critical Kernels

The main contribution of the present article consists of new 3D parallel and symmetric thinning schemes which have the following qualities:

They are effective and sound, in the sense that they are guaranteed to preserve topology. This guarantee is obtained thanks to a theorem on critical kernels;

They are powerful, in the sense that they remove more points, in one iteration, than any other symmetric parallel thinning scheme;

They are versatile, as conditions for the preservation of geometrical features (e.g., curve extremities or surface borders) are independent of those accounting for topology preservation;

They are efficient: we provide in this article a small set of masks, acting in the grid ?³, that is sufficient, in addition to the classical simple point test, to straightforwardly implement them.