Polymer deformation in various flows

Using a Langevin-like approach, the deformation of a polymer, modelled as a bead-spring chain, is calculated in simple shear, elongational and Kramers potential flow. Analytic expressions for the mean-square end-to-end distance, radius of gyration, segment-segment distance, static structure factor up to O(q⁴) and the intrinsic elongational viscosity are given. Near equilibrium, preaveraged hydrodynamic interaction is taken into account.     

Morphological analysis of physically reconstructed capillary hybrid silica monoliths and correlation with separation efficiency

We report an experimental study on the structural (especially radial) heterogeneity of eleven 100 μm i.d. capillary tetramethoxysilane-methyltrimethoxysilane hybrid silica monoliths with different pore and skeleton sizes, which were imaged by an optimized confocal laser scanning microscopy method. This method allows the optical sectioning of the monoliths, which is a prerequisite for quantitative morphological image analysis. Both radial porosity profiles and chord length distributions were calculated in the macropore domain for each column from at least 100 complete cross-sectional views along the column axis. The statistical approach visualized radial heterogeneities on different length scales in the monolithic structures. Chord length distributions followed a simplified k-gamma function, and a structural parameter obtained from this function is introduced to provide a scalar measure of column heterogeneity. It enables the comparison of monoliths with different pore sizes and helps to establish correlations between the microscopic properties of a column, eddy dispersion, and its separation efficiency.     

On the presence of fictitious solar neutrino flux variations in radiochemical experiments

Journal of Experimental and Theoretical Physics - The currently available data on solar neutrino flux variation in radiochemical experiments and Cherenkov measurements have so far defied a simple...     

Feasibility of diffusion-NMR surface-to-volume measurements tested by calculations and computer simulations

It has been demonstrated previously that the surface-to-volume ratio S/V can be determined from the derivative of the time-dependent diffusion coefficient D(t), in the limit t --> 0. Several questions arise concerning the practicality of determining S/V by NMR. In particular, how large are the errors generated by (1) working outside the t --> 0 limit and (2) measuring D outside the b --> 0 limit, both for narrow and full-width gradient pulses? Here b is gamma2G2delta2Delta for narrow pulses and gamma2G2t3/12 for broad pulses. These questions are addressed by random-walk computer simulations and numerical calculations in geometries relevant to small-airways of lung. The results demonstrate that one can work well outside the t --> 0 and b --> 0 limits, provided 10-20% accuracy in the measured S/V is sufficient. Emphasis is placed on the useful range of times t for which NMR determinations of lung S/V are feasible.     

The first three anisotropy constants of nickel

The technique of ferromagnetic resonance at 23 GHz has been used to determine the first three anisotropy constants of pure Ni down to 4.2K. A temperature and orientation dependent linewidth has also been observed.     

Distributivität und subdirekte Zerlegbarkeit vollständiger Verbände

Ohne Zusammenfassung     

Über die Gestalt von Polymermolekülen

Zusammenfassung Mit Hilfe von Monte-Carlo-Methoden wurden die mittleren Quadrate der Hauptträgheitsachsen von ungestörten und gestörten Ketten berechnet, deren Baueinheiten im kontinuierlichen Raum erzeugt worden sind. Die Ketten besaßen dabei bis zuN=1024 Bindungen. Die auf 1/N=0 extrapolierten Werte verhielten sich wie 1:2,7:11,9 im ungestörten, wie 1:3,0:14,3 im gestörten Falle.

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Summary Monte-Carlo-methods were employed to generate off-lattice random chains and chains with excluded volume up toN=1024 steps. The principal moments of the mean square radius of gyration were calculated and extrapolated to 1/N–0. Their ratios are as 1:2.7:11.9 for random chains, and as 1:3.0:14.3 for perturbed chains.