Self-association and relative stability of the isomeric structures of acetaldoxime

The abnormal syn/anti ratio for acetaldoxime is explained, on the basis of NMR evidence, in terms of preferred self-association of the anti isomer.     

Effect of the platinum content on the microstructure and micropore size distribution of Pt/alumina-pillared clays

The aim of this work is to study the effect of the platinum content (0-1.8 wt % Pt) on the microstructure of an alumina-pillared clay. For this purpose, the nitrogen physisorption data at -196 degrees C, the micropore size distributions of the supported platinum catalysts, and the hydrogen chemisorption results at 30 degrees C have been analyzed and compared. The preparation of the catalysts has modified the textural properties of the Al-pillared clay support, giving rise to a loss of surface area and micropore volume. After reduction at 420 degrees C, the presence of dispersed metallic platinum with mean crystallite size in the 22-55 A range has been found by hydrogen adsorption. Comparison of all results reveals that the platinum species block the micropore entrances by steric hindrance to nitrogen access as the platinum content increases.     

Homomorphisms between JC＊-algebras and Lie C＊-algebras

It is shown that every almost ＊-homomorphism h ： A→B of a unital JC＊-algebra A to a unital JC＊-algebra B is a ＊-homomorphism when h（rx） = rh（x） （r 〉 1） for all x∈A, and that every almost linear mapping h ： A→B is a ＊-homomorphism when h（2^nu o y） - h（2^nu） o h（y）, h（3^nu o y） - h（3^nu） o h（y） or h（q^nu o y） = h（q^nu） o h（y） for all unitaries u ∈A, all y ∈A, and n = 0, 1,.... Here the numbers 2, 3, q depend on the functional equations given in the almost linear mappings. We prove that every almost ＊-homomorphism h ： A→B of a unital Lie C＊-algebra A to a unital Lie C＊-algebra B is a ＊-homomorphism when h（rx） = rh（x） （r 〉 1） for all x ∈A.     

Adsorption of 1-octanol at the free water surface as studied by Monte Carlo simulation

The adsorption of 1-octanol at the free water surface has been investigated by Monte Carlo computer simulation. Six different systems, built up by an aqueous and a vapor phase, the latter also containing various number of octanol molecules, have been simulated. The number of the octanol molecules has been chosen in such a way that the octanol surface density varies in a broad range, between 0.27 and 7.83 micromol/m(2) in the six systems simulated. For reference, the interfacial system containing bulk liquid octanol in the apolar phase has also been simulated. The results have shown that the formation of hydrogen bonds between the interfacial water and adsorbed octanol molecules is of key importance in determining the properties of the adsorbed layer. At low octanol surface concentration values all the octanol molecules are strongly (i.e., by hydrogen bonds) bound to the aqueous phase, whereas their interaction with each other is negligibly small. Hence, they are preferentially oriented in such a way that their own binding energy (and thus their own free energy) is minimized. In this preferred orientation the O-H bond of the octanol molecule points flatly toward the aqueous phase, declining by about 30 degrees from the interfacial plane, irrespectively from whether the octanol molecule is the H-donor or the H-acceptor partner in the hydrogen bond. Hence, in its preferred orientation the octanol molecule can form at least two low energy hydrogen bonds with water: one as a H-donor and another one as a H-acceptor. Moreover, the preferred orientation of the hydrogen bonded water partners is close to one of the two preferred interfacial water alignments, in which the plane of the water molecule is parallel with the interface. When increasing the octanol surface density, the water surface gets saturated with hydrogen bonded octanols, and hence any further octanol molecule can just simply condense to the layer of the adsorbed octanols. The surface density value at which this saturation occurs is estimated to be about 1.7 micromol/m(2). Above this surface density value the hydrogen bonded octanols and their water partners are oriented in such a way that the number of the water-octanol hydrogen bonds is maximized. Hence, the preferred alignment of the O...O axes of these hydrogen bonds is perpendicular to the interface. This orientation is far from the optimal alignment of the individual octanol molecules, which is also reflected in the observed fact that, unlike in the case of many other adsorbents, the average molecular binding energy of the adsorbed octanol molecules increases (i.e., becomes less negative) with increasing octanol surface density.     

Pi-conjugated dendrimers based on bis(enediynyl)benzene units

We have synthesized a new family of pi-conjugated dendrimers that are based on bis(enediynyl)benzene units by using both divergent and convergent approaches. The compounds at all three generations have strong bluish-green fluorescence, especially the third-generation dendrimer, which has the highest extinction coefficient and quantum efficiency in this series. [structure: see text]     

Parametric dependence of turbulent particle transport in tore supra plasmas

Steady state full noninductive current tore supra plasmas offer a unique opportunity to study the local parametric dependence of particle pinch velocity, in order to discriminate among different theories. Magnetic field shear is found to generate an inward pinch which is dominant in the gradient region (normalized radius 0.3相似文献   

$\Phi $-functions for complex 2D-objects

Within two-dimensional cutting and packing problems with irregular shaped objects, the concept of -functions has been proven to be very helpful for several solution approaches. In order to construct such -functions a previous work, in which so-called primary objects are considered, is continued. Now -functions are constructed for pairs of objects which can be represented as a finite combination (union, intersection, complement) of primary objects which allows the handling of arbitrary shaped objects by appropriate approximations of sufficient accuracy.Received: October 2002, Revised: October 2003, AMS classification: 65K05, 90C26, 90B06All correspondence to: Guntram Scheithauer     

On nonoscillating integrals for computing inhomogeneous Airy functions

Integral representations are considered of solutions of the inhomogeneous Airy differential equation . The solutions of these equations are also known as Scorer functions. Certain functional relations for these functions are used to confine the discussion to one function and to a certain sector in the complex plane. By using steepest descent methods from asymptotics, the standard integral representations of the Scorer functions are modified in order to obtain nonoscillating integrals for complex values of . In this way stable representations for numerical evaluations of the functions are obtained. The methods are illustrated with numerical results.