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On weekly variations of the ionospheric foF2-frequency possibly caused by anthropogenic activity
(1996)
Liquid crystalline side group polymers with azo-chromophores and fluorinated tails of varying length
(1996)
Consequences of current generation in the ionosphere caused by neutral wind action on Es-clouds
(1996)
On the Balmer line problem
(1996)
An attempt to introduce finite diffusion regions into magnetohydrodynamic reconnection models
(1996)
Herstellung und Charakterisierung geordneter ultradünner Poly(arylen- 1,3,4-oxadiazol) Schichten
(1996)
Ionospheric currents and turbulence caused by the influence of neutral winds on sporadic E-layers
(1996)
For bilayer stacks of non-centrosymmetrical molecules, formed by the Langmuir-Blodgett (LB) technique (Y deposition), 00l peaks for the bilayer period are usually observed in the X-ray specular reflectivity curve, in this study, we show that the introduction of stacking disorder at lower transfer ratios and the subsequent partial repair of defects by a parallel shift of oppositely oriented molecules into the vacancies may result in the formation of antiphase domains and in an increase in the average monolayer symmetry followed by quenching of the bilayer peaks. The X-ray reflectivity data, obtained for multilayers of penta-alkynes, are used to demonstrate this real structural effect, which is expected to be of general importance for X-ray and neutron reflectivity data reduction and for the structural modelling of multilayers.
In this second paper we describe the comprehensive structure investigations on multilayers of uranyl arachidate formed by Langmuir-Blodgett deposition from subphases of different pH on solid substrates by means of a combination of infrared spectroscopy, X-ray specular reflection, ellipsometry, and scanning force microscopy, The structure of these multilayers and their stability are obviously influenced by the subphase pH. The pH range of the acid to salt conversion determined for the Langmuir films is confirmed by the infrared spectroscopic data of the multilayers. While arachidic acid films, deposited from an uranyl acetate subphase of low pH, are found to have strongly distorted rough surface, the films of uranyl structure, The influence of the counterions on the alkyl chain conformation, chain packing, reorganization probability, and stability of the multilayer is discussed.
We report on bifurcation studies for the incompressible magnetohydrodynamic equations in three space dimensions with periodic boundary conditions and a temporally constant external forcing. Fourier representations of velocity, pressure and magnetic field have been used to transform the original partial differential equations into systems of ordinary differential equations (ODE), to which then special numerical methods for the qualitative analysis of systems of ODE have been applied, supplemented by the simulative calculation of solutions for selected initial conditions. In a part of the calculations, in order to reduce the number of modes to be retained, the concept of approximate inertial manifolds has been applied. For varying (increasing from zero) strength of the imposed forcing, or varying Reynolds number, respectively, time-asymptotic states, notably stable stationary solutions, have been traced. A primary non- magnetic steady state loses, in a Hopf bifurcation, stability to a periodic state with a non-vanishing magnetic field, showing the appearance of a generic dynamo effect. From now on the magnetic field is present for all values of the forcing. The Hopf bifurcation is followed by further, symmetry-breaking, bifurcations, leading finally to chaos. We pay particular attention to kinetic and magnetic helicities. The dynamo effect is observed only if the forcing is chosen such that a mean kinetic helicity is generated; otherwise the magnetic field diffuses away, and the time-asymptotic states are non-magnetic, in accordance with traditional kinematic dynamo theory.
PG 1159 stars
(1996)