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151.
We report on the integration of the kinematic dynamo problem in a spherical domain forced by velocity fields that are convective
fluid flows resulting from a bifurcation analysis of the spherical Bénard problem. We derive a code based on generalized spherical
harmonics that ensures a divergence-free magnetic field. We determine the growth or decay of a magnetic field in the kinematic
dynamo equation for various physically relevant velocity fields which are stationary as well as time-periodic and chaotic.
Velocity signals that are produced by heteroclinic cycles are used as an input to an energy-saturated kinematic dynamo equation
that limits the growth of the linearly unstable modes. Preliminary calculations indicate the possibility of reversals of the
magnetic field for this case of forcing.
Received 8 October 1996 and accepted 28 April 1997 相似文献
152.
B. Griepink E. A. Maier P. Quevauviller H. Muntau 《Fresenius' Journal of Analytical Chemistry》1991,339(9):599-603
Summary The Community Bureau of Reference (BCR) has undertaken the production of a wide range of certified reference materials (CRMs) for the improvement of accuracy and measurement harmony in various areas of concern at European Community level. This paper provides an overview of the sectors of the BCR-programme in the field of environment i.e. for water systems (water, sediment, biota), soil analysis (soil, fertiliser, waste), plant analysis (aquatic and terrestrial plants), analysis related to animals (e.g. muscle or liver) or man (e.g. industry and food). 相似文献
153.
154.
A method is proposed for evaluating the resistance of a flywheel rim to radial stresses in free rotation. The method is based on loading a rim segment in pure bending and calculating the limiting moment and the corresponding limiting angular velocity. Applicability of the method is substantiated theoretically by investigating the similarity of the radial stress diagrams in rotation and pure bending. The method is verified experimentally for the strained state of a rim segment in pure bending.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 521–526, July–August, 1993. 相似文献
155.
Images of the surface ordering of 4-n-octyl-4'-cyanobiphenyl, a room temperature smectic liquid crystal deposited upon graphite, have been obtained by scanning tunnelling microscopy. The microscope was operated in air using the constant-current mode. Under certain tunnelling conditions it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported conformations have been observed: an overlapping bilayer structure with spacing 3.7 nm, and a monolayer structure with spacing 2.4 nm. The latter structure may represent the first visual evidence for a surface polar ordered structure. 相似文献
156.
J. H. Koolen 《European Journal of Combinatorics》2002,23(8):987
Bannai and Ito conjectured in a 1987 paper that there are finitely many distance-regular graphs with fixed degree that is greater than two. In a series of papers they showed that their conjecture held for distance-regular graphs with degrees 3 or 4. In this paper we prove that the Bannai–Ito conjecture holds for degrees 5–7. 相似文献
157.
In this study we report the levels of 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, homovallinic acid, tryptophan, 5-hydroxyindole-3-acetic acid and serotonin in lumbar cerebrospinal fluid (CSF) from patients with multiple sclerosis, cerebrovascular disease and muscular tension headache the later, as healthy controls. The separation of these substances was performed on a reversed phase column by ion pair high performance liquid chromatography and detection was made by a glassy carbon electrode set at +900 mV vs Ag+/AgCl. The whole separation was achieved within 25 min. Concentrations of all substances (10-1000 pmole/L) were linearly proportional to areas obtained. The system is sensitive, stable and reproducible. The significance of CSF levels of these metabolites from patients groups compared with healthy controls are discussed. 相似文献
158.
159.
Recent studies have established that side chain polymeric liquid crystals composed of mesogenic and non-mesogenic side groups keep their liquid-crystalline properties even for a low proportion of mesogens. We show that the detailed structures of three kinds of new diluted liquid crystal polysiloxanes depend on the nature of the co-substituent as well as on the proportion of the silicon sites occupied by the mesogenic groups. Mixtures of these systems with low molar mass liquid crystals were also investigated in terms of compatibility and/or stabilization of smectic A phases. 相似文献
160.