Free boundary viscous flows at micro and mesolevel during liquid composites moulding process

Numerical simulation aspects, related to low Reynolds number free boundary viscous flows at micro and mesolevel during the resin impregnation stage of the liquid composite moulding process (LCM), are presented in this article. A free boundary program (FBP), developed by the authors, is used to track the movement of the resin front accurately by accounting for the surface tension effects at the boundary. Issues related to the global and local mass conservation (GMC and LMC) are identified and discussed. Unsuitable conditions for LMC and consequently GMC are uncovered at low capillary numbers, and hence a strategy for the numerical simulation of such flows is suggested. FBP encompasses a set of subroutines that are linked to modules in ANSYS. FBP can capture the void formation dynamics based on the analysis developed. We present resin impregnation dynamics in two dimensions. Extension to three dimensions is a subject for further research. Several examples are shown and efficiency of different stabilization techniques are compared. Copyright © 2004 John Wiley & Sons, Ltd.     

Studies on Radical Cations I. Molecular and electronic structure of [3]radialene cation produced by γ-irradiation in condensed phase

γ-Irradiation of tris (methylidene)-cyclopropane (‘[3]radialene’) 1 in a rigid electron scavenging matrix (butylchoride/i-pentane, 1:1) at 77 K leads to formation of its molecular cation 1 ⁺. Slight softening of the matrix by a temperature increase of 3–5 K results in formation of a newly absorbing species, tentatively assigned arising from structrral relaxation of 1 ⁺ by π-bond rotation:      

Electrophoretic analysis of oxidatively modified eye lens proteins in vitro: implications for diabetic cataract

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of eye lens proteins showed that both progression of diabetic cataract in rats in vivo and precipitation of soluble eye lens proteins stressed by free radicals in vitro were accompanied by significant protein cross-linking. There was a noticeable contribution of disulfide bridges to protein cross-linking in diabetic eye lens in vivo. In contrast, under conditions in vitro, when eye lens proteins were exposed to hydroxyl or peroxyl radicals, we showed that the participation of reducible disulfide linkages in the formation of high molecular mass products was markedly lower. These in vivo--in vitro differences indicate that the generally accepted role of reactive oxygen species in diabetic cataractogenesis may be overestimated in connection with the processes of protein cross-linking.     

Stereoselective synthesis of (R)-(+)-1-methoxyspirobrassinin, (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether and their enantiomers or diastereoisomers

Stereoselective synthesis of cruciferous indole phytoalexin (R)-(+)-1-methoxyspirobrassinin and its unnatural (S)-(−)-enantiomer was achieved by spirocyclization of 1-methoxybrassinin in the presence of (+)- and (−)-menthol and subsequent oxidation of the obtained menthyl ethers. Methanolysis of menthyl ethers in the presence of TFA afforded (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether as well its unnatural (2S,3S)-, (2R,3S)-, and (2S,3R)-isomers.     

Studies on Radical Cations,III. The Type C Valence-Isomeric System Quadricyclane Radical Cation/Norbornadiene Radical Cation

The previously discussed principles involved in electrocyclic reactions of openshell ions are exemplified for a type C system, the radical cation couple quadricyclane⁺ ( Q ⁺)/norbornadiene⁺ ( NBD ⁺). Exhaustive calculations (MINDO/3) for the various states of the ions support the general predictions for such types of systems. The barrier of interconversion Q ⁺ → NBD ⁺ is estimated to be significantly lower than that for the corresponding neutrals. Experimental support to this prediction is obtained by γ-irradiation of Q or NBD in an electron scavenging matrix. In both cases only NBD ⁺ is observed, indicating that Q ⁺ is not stable at 77 K. Previous observations and propositions referring to the system Q ⁺/ NBD ⁺ are discussed in view of the present findings.     

A general procedure for the dynamic analysis of finite and infinite beams on piece-wise homogeneous foundation under moving loads

Transversal vibrations induced by a load moving at a constant speed along a finite or an infinite beam resting on a piece-wise homogeneous visco-elastic foundation are studied. Special attention is paid to the amplification of the vibrations which arise as the point load traverses a foundation discontinuity. The governing equations of the problem are solved by the normal-mode analysis. The solution is expressed in the form of an infinite sum of orthogonal natural modes multiplied by the generalized displacements. The natural frequencies are obtained numerically exploiting the concept of the global dynamic stiffness matrix. This ensures that the frequencies obtained are accurate. The methodology is neither restricted by load velocity nor damping and is simple to use, though obtaining the numerical expression of the results is not straightforward. A general procedure for numerical implementation is presented and verified. There is no restriction for finite structures, however, for infinite structures, validity of the results is restricted to a “region of interest” of finite length. To illustrate the methodology, the probability of exceeding an admissible upward displacement is determined when the load travels at a certain velocity according to the normal distribution. In this problem, the given structure has an intermediate part of adaptable foundation stiffness, which is optimized in a parametric way, enabling to draw important conclusions about the optimum intermediate stiffness. The results obtained have direct application on the analysis of railway track vibrations induced by high-speed trains crossing regions with significantly different foundation stiffness.     

Offline and online capillary electrophoresis enzyme assays of β-N-acetylhexosaminidase

Enzyme assays of β-N-acetylhexosaminidase from Aspergillus oryzae using capillary electrophoresis in the offline and online setup have been developed. The pH value and concentration of the borate-based background electrolyte were optimized in order to achieve baseline separation of N,N′,N″-triacetylchitotriose, N,N′-diacetylchitobiose, and N-acetyl-d-glucosamine. The optimized method using 25 mM tetraborate buffer, pH 10.0, was evaluated in terms of repeatability, limits of detection, quantification, and linearity. The method was successfully applied to the offline enzyme assay of β-N-acetylhexosaminidase, which was demonstrated by monitoring the hydrolysis of N,N′,N″-triacetylchitotriose. The presented method was also utilized to study the pH dependence of enzyme activity. An online assay with N,N′-diacetylchitobiose as a substrate was developed using the Transverse Diffusion of Laminar Flow Profiles model to optimize the injection sequence and in-capillary mixing of substrate and enzyme plugs. The experimental results were in good agreement with predictions of the model. The online assay was successfully used to observe the inhibition effect of N,N′-dimethylformamide on the activity of β-N-acetylhexosaminidase with nanoliter volumes of reagents used per run and a high degree of automation. After adjustment of background electrolyte pH, an online assay with N,N′,N″-triacetylchitotriose as a substrate was also performed.

Need for database extension for reliable identification of bacteria from extreme environments using MALDI TOF mass spectrometry

The ability of MALDI TOF MS (matrix-assisted laser desorption ionisation time-of-flight mass spectrometry) to identify cultivable microflora from two waste disposal sites from non-ferrous metal industry was analysed. Despite the harsh conditions (extreme pH values and heavy metal content in red mud disposal site from aluminium production or high heavy metal content in nickel sludge), relatively high numbers of bacteria were recovered. In both environments, the bacterial community was dominated by Gram-positive bacteria, especially by actinobacteria. High-quality MALDI TOF mass spectra were obtained but most of the bacteria isolates could be not identified using MALDI Biotyper software. The overall identification rate was lower than 20 %; in two of the environments tested identification rates were lower than 10 %. As a dominant bacterial species, Microbacterium spp. in drainage water from an aluminium red mud disposal site near ?iar nad Hronom, Bacillus spp. in red mud samples from the same site, and Arthrobacter spp. from nickel smelter sludge near Sereï were identified by a combination of the Biolog system and 16S rRNA sequence analysis. As the primary focus of the MALDI TOF MS-based methodology is directed towards medically important bacteria, reference database spectra expansion and refinement are needed to improve the ability of MALDI TOF MS to identify environmental bacteria, especially those from extreme environments.