Two-scale analysis of a filament-wound cylindrical structure and application of periodic boundary conditions

A two-scale numerical approach to predict the effective in-plane properties of helical filament-wound thin-walled cylindrical tubes is provided. A meso-scale repeated unit cell (RUC) model for a filament-wound tube is established according to the manufacturing process, in which cross-overs, undulations and overlaps of fibre bundles are described using a bottom-up solid modelling technique. An approach to implement the general periodic boundary conditions in a finite element analysis scheme is also presented. As an application example, the effective in-plane elastic constants of glass fibre/epoxy filament-wound tubes are predicted and the influences of the number of the winding circuits and the shape of the fibre bundles are analyzed and discussed. In addition, the stress/strain distribution in the RUC is obtained which provides the essential information on the stress/strain concentration due to fibre cross-over/undulation/overlap. This then indicates the location where damage will initiate.     

Vapour-liquid equilibrium of the acetone---methanol system in the presence of KSCN and comparison with other salts

The effect of KSCN at salt mole fractions of 0.01–0.05 and at saturation on the VLE of the binary acetone-methanol system has been experimentally investigated at 101.32 kPa using a modified Othmer equilibrium still. The experimental data were correlated by the electrolytic NRTL model [B. Mock, L.B. Evans and C.C. Chen, AIChE J., 32 (1986) 1655–1664], the extended UNIQUAC equation [B. Sander, A. Fredensland and P. Rasmussen, Chem. Eng. Sci., 41 (1986) 1171–1183] and the modified Wilson and NRTL models proposed by Tan [T.C. Tan, AIChE J., 31 (1985) 2083–2085; Chem. Eng. Res. Des., 65 (1987) 355–366; Trans. Inst. Chem. Eng., 68 (1990) 93–102]. The results were compared with those obtained by Tan's predictive models. A crossover between the salting-out and salting-in effects on acetone and a non-azeotropic minimum in the temperature-composition diagram were observed at low and high salt concentrations. Based on the solubility data in the mixture, comparisons with the effect of other salts on the same mixed solvent were made.     

Stereoselektive Totalsynthese von natürlichem Phytol und Phytolderivaten und deren Verwendung zur Herstellung von natürlichem Vitamin K1

Steroselective Total Synthesis of Natural Phytol and Derivatives thereof; Use of these Compounds in the Synthesis of Natural Vitamin K₁ The Li₂CuCl₄-catalyzed couplings of the easily accessible bifunctional C₅ allylic acetates (E)- 18a and (E)- 18b with racemic hexahydrofarnesylmagnesium bromide ((3 RS/RS, 7 RS/SR)- 19a ) proceed with high chemo- and stereoselectivity (≥98% (E)-retention) to give the (2E, 7 RS/RS, 11 RS/SR)-phytol derivatives 1a and 1b , respectively, in yields of 72–80% (Scheme 5). The same couplings performed with optically active hexahydrofarnesylmagnesium bromide (3 R, 7 R)- 19a yielded the (E)-phytol derivatives of the natural series (7 R, 11R)- 1a and (7 R, 11 R)- 1b. Acid-catalyzed hydrolysis of(2 E, 7 R, 11 R)- 1b gave natural phytol((2 E, 7 R, 11 R)- 1c ) Friedel-Crafts alkylation of ‘menadiol monobenzoate’ 11b with (2 E, 7 R, 11 R)- 1a or (2 E, 7 R, 11 R)- 1b gave the dihydrovitamine K₁ derivative (2 E/Z, 7′ R, 11′R)- 12b ((E/Z)≈? 9:l). Conversion of configurationally pure (2 E, 7′ R, 11′ R)- 12b (yield 73%; obtained after chromatographic removal of the (Z)-isomer) into natural vitamine K₁ ((2 E,7′ R, 11′ R)- 2 ) was achieved in the usual way by saponification and oxidation with air. Some further investigations of the coupling reactions of bifunctional C₅ allylic synthons with hexahydrofarnesylmagnesium bromide (3 RS/RS, 7 RS/SR)- 19a showed the outcome of these reactions to be critically dependent on the nature of the leaving group, the double-bond geometry and the nature and concentration of the catalyst. Thus, the Li₂CuCl₄-catalyzed couplings of (3 RS/RS,7 RS/SR)- 19a with the allylic halides 29a and 29c as well as with p-toluenesulfonate 29b yielded besides the phytol derivatives 1a and 1b - also the S_N2′-type products 30a and 30b (Scheme 8, Table 2); the same result was found for the coupling with the cis-configurated allylic acetates (Z)- 18a and (Z)- 18b (Table 3). A similar loss of chemo selectivity as well as the loss of stereoselectivity in the coupling reactions of 19 with the bifunctional (E)-olefins of type 18 was observed when the Li₂CuCl₄-catalyst concentration was increased from 0.2 to 25 mol-% or upon substitution of Li₂CuCl₄ by copper (I) chloride or iodide (Table 4).     

A comprehensive theoretical investigation of the electronic states of Ca2 up to the Ca(4s(2) 1S) + Ca(4s5p 1P) dissociation limit

A theoretical survey of the electronic structure of Ca(2) is presented using two-electron pseudopotentials complemented by core-polarization operators on Ca atoms and multireference configuration interaction/quasidegenerate perturbation theory (MRCI/QDPT) treatment of molecular excited states. The spectroscopic constants of 70 electronic states up to 30,000?cm(-1) above the ground state are determined. This implies all Ca(2) states dissociating up to the Ca(4s(2) (1)S) + Ca(4s5p (3,1)P) dissociation limits. All spin states (singlet, triplet, and quintet) are investigated. The work emphasizes the variety of interactions implying singly valence and lowest Rydberg excited states, doubly excited states generated by atom pairs (3)P(4s4p) + (3)P(4s4p), or (3)P(4s4p) + (3)D(4s3d), 4p3d double excitations asymptotically localized on a single-atom. Zwitterionic Ca(+) + Ca(-) configurations are evidenced and shown to induce specific electronic patterns in (1)Σ(g)(+), (3)Σ(g)(+), (1)Σ(u)(+), (3)Σ(u)(+), (1)Π(g), (3)Π(g), (1)Π(u), and (3)Π(u) symmetry manifolds. They also provide insight for qualitative features (barriers) found for the lower electronic states already investigated in previous publications by other authors.     

Comparison of nine different real-time PCR chemistries for qualitative and quantitative applications in GMO detection

Several techniques have been developed for detection and quantification of genetically modified organisms, but quantitative real-time PCR is by far the most popular approach. Among the most commonly used real-time PCR chemistries are TaqMan probes and SYBR green, but many other detection chemistries have also been developed. Because their performance has never been compared systematically, here we present an extensive evaluation of some promising chemistries: sequence-unspecific DNA labeling dyes (SYBR green), primer-based technologies (AmpliFluor, Plexor, Lux primers), and techniques involving double-labeled probes, comprising hybridization (molecular beacon) and hydrolysis (TaqMan, CPT, LNA, and MGB) probes, based on recently published experimental data. For each of the detection chemistries assays were included targeting selected loci. Real-time PCR chemistries were subsequently compared for their efficiency in PCR amplification and limits of detection and quantification. The overall applicability of the chemistries was evaluated, adding practicability and cost issues to the performance characteristics. None of the chemistries seemed to be significantly better than any other, but certain features favor LNA and MGB technology as good alternatives to TaqMan in quantification assays. SYBR green and molecular beacon assays can perform equally well but may need more optimization prior to use.     

Characterization of soil particle surfaces using adsorption excess isotherms

Measurement of adsorption excess isotherms of methanol-benzene mixtures was applied to the characterization of soil particle surfaces. The sorption capacity and Gibbs energy of sorption of the solid-liquid interface were determined for montmorillonite, three types of soil, and their humin fractions. The soils were found to be less polar or less hydrophilic than the clay, and the humin fraction of soils was found to be less hydrophilic than the whole soils. The soil and humin samples have heterogeneous surfaces which can be divided in two regions on the basis of their relative polarity. The x-axis intersection of the straight section of isotherm assigns the relative proportions of the hydrophilic and hydrophobic regions of the surface.     

Synthesis and characterization of nanoheterostructures based on oligothiophene functionalized Ru nanoparticles

Monodisperse ruthenium nanoparticles functionalized by electroactive oligothiophenes have been prepared and characterized. Using TEM, UV-visible and FTIR we established that the organization of these nanoparticles into nanospheres can be directly controlled via modulation of the pi-pi interaction between the organic components adsorbed on the surface. This finding also shows that the self-assembled nanoheterostructures may be switched from monodisperse nanoparticles to ordered nanospheres by tuning the pH.     

A new method for recycling asymmetric catalysts via formation of charge transfer complexes

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity.