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91.
Michael Sawodny Albert Schmidt Manfred Stamm Wolfgang Knoll Claus Urban Helmut Ringsdorf 《先进技术聚合物》1991,2(3):127-136
Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water–air interface by slow compression at room temperature. From the area per monomer unit of A0≈0.25 nm2 a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir–Blodgett–Kuhn (LBK) multilayer assemblies of varying thicknesses (from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of d0 = 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated. Photo-isomerization by UV-irradiation (at λ = (360±30)nm) was examined by UV-VIS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order–disorder transition for optical information storage. 相似文献
92.
93.
Y. Marandet H. Capes L. Godbert-Mouret M. Koubiti J. Rosato R. Stamm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(2):247-260
In this work we investigate the influence of low
frequency turbulence on Doppler spectral line shapes in magnetized
plasmas. Low frequency refers here to fluctuations whose typical
time scale is much larger than those characterizing the atomic
processes, such as radiative decay, collisions and charge exchange.
This ordering is in particular relevant for drift wave turbulence,
ubiquitous in edge plasmas of fusion devices. Turbulent fluctuations
are found to affect line shapes through both the spatial and time
averages introduced by the measurement process. The profile is
expressed in terms of the fluid fields describing the plasma.
Assuming the spectrometer acquisition time to be much larger than
the turbulent time scale, an ordering generally fulfilled in
experiments, allows to develop a statistical formalism. We proceed
by successively investigating the effects of density, fluid velocity
and temperature fluctuations on the Doppler profile of a spectral
line emitted by a charge exchange population of neutrals. Line
shapes, and especially line wings are found to be affected by ion
temperature or fluid velocity fluctuations, and can in some cases
exhibit a power-law behavior. These effects are shown to be
measurable with existing techniques, and their interpretation in
each particular case would rely on already existing tools. From a
fundamental point of view, this study gives some insights in the
appearance of non-Boltzmann statistics, such as Lévy statistics,
when dealing with averaged experimental data. 相似文献
94.
Fernanda Patrício 《BIT Numerical Mathematics》1978,18(3):342-347
A numerical process is presented which provides a cubic spline function approximation for the solution of initial value problems in ordinary differential equations. With interpolate cubic spline functions we can achieveO(h
4) convergence. 相似文献
95.
Hellmuth Stamm und Margot Goehring 《Fresenius' Journal of Analytical Chemistry》1940,120(7-8):230-232
Ohne ZusammenfassungMitt. III.: Diese Ztschrft.115, 1 (1938/39). 相似文献
96.
This paper extends prior work by the authors on solving nonlinear least squares unconstrained problems using a factorized
quasi-Newton technique. With this aim we use a primal-dual interior-point algorithm for nonconvex nonlinear programming. The
factorized quasi-Newton technique is now applied to the Hessian of the Lagrangian function for the transformed problem which
is based on a logarithmic barrier formulation. We emphasize the importance of establishing and maintaining symmetric quasi-definiteness
of the reduced KKT system. The algorithm then tries to choose a step size that reduces a merit function, and to select a penalty
parameter that ensures descent directions along the iterative process. Computational results are included for a variety of
least squares constrained problems and preliminary numerical testing indicates that the algorithm is robust and efficient
in practice. 相似文献
97.
98.
E. W. Fischer K. Hahn J. Kugler U. Struth R. Born M. Stamm 《Journal of Polymer Science.Polymer Physics》1984,22(8):1491-1513
A new method for the evalution of neutron scattering data from semicrystalline polymers is proposed for small and intermiediate q [q = (4π/λ)sinθ/2]. It is based on the assumption that, in general, a molecule cryustallizes in various lamellae. Within one lamella the crystalline stems connected by loop or folds from intramolecular “clusters,” which are connected by tie molecules. Without further assumptions the method yields in a straightforward manner the following quantities: (i) the average number of clusters per molecule, from which the number of tie molecules can be estimated; (ii) the radius of gyration <R> of the centers of the stems belonging to one cluster; and (iii) the radius of gyration <R> of the cluster centers with respect to the center of the molecule the method was successfully tested using experimental data obtained from poly(ethylene oxide), polyethylene, and isotactic polypropylene. 相似文献
99.
100.