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991.
Guido Schneider 《Communications in Mathematical Physics》1996,178(3):679-702
We are interested in the nonlinear stability of the Eckhaus-stable equilibria of the Swift-Hohenberg equation on the infinite line with respect to small integrable perturbations. The difficulty in showing stability for these stationary solutions comes from the fact that their linearizations possess continuous spectrum up to zero. The nonlinear stability problem is treated with renormalization theory which allows us to show that the nonlinear terms are irrelevant, i.e. that the fully nonlinear problem behaves asymptotically as the linearized one which is under a diffusive regime. 相似文献
992.
Gerhard Herzberg 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(3-4):187-187
993.
Carsten Beta Kai Schneider Marie Farge 《Communications in Nonlinear Science & Numerical Simulation》2003,8(3-4):537
This paper presents the application of coherent vortex simulation (CVS) filtering, based on an orthogonal wavelet decomposition of vorticity, to study mixing in 2D homogeneous isotropic turbulent flows. The Eulerian and Lagrangian dynamics of the flow are studied by comparing the evolution of a passive scalar and of particles advected by the coherent and incoherent velocity fields, respectively. The former is responsible for strong mixing and produces the same anomalous diffusion as the total flow, due to transport by the coherent vortices, while mixing in the latter is much weaker and corresponds to classical diffusion. 相似文献
994.
995.
996.
Laura Kovalenko Martin W. Schr der R. Amaranatha Reddy Siegmar Diele Gerhard Pelzl Wolfgang Weissflog 《Liquid crystals》2005,32(7):857-865
New five-ring bent-core mesogens derived from 4-cyanoresorcinol as the central core have been synthesized. The mesophases were assigned by polarizing microscopy, X-ray diffraction and electro-optical measurements. It was found that the mesophase behaviour clearly depends on the direction of the carboxyl linking groups between the aromatic rings. If the outer and inner ester linking groups of a wing are in the same direction then nematic phases and, for long chain members, SmC and SmCPA phases are observed. If the outer and inner linking groups are in opposing directions a dimorphism, SmA-SmAPA, is observed and the clearing temperatures are increased by about 55 K. It is remarkable that in the SmCPA phases of the first series, polar switching preferably takes place through a collective rotation of the molecules around their long axes which is accompanied by the inversion of the chirality of the smectic layers. 相似文献
997.
Gerhard J. Woeginger 《Operations Research Letters》2005,33(2):210-215
This paper is a comparative review of three related books:Giorgio Ausiello, Pierluigi Crescenzi, Giorgio Gambosi, Viggo Kann, Alberto Marchetti-Spaccamela, Marco Protasi, Complexity and Approximation (Combinatorial Optimization Problems and Their Approximability Properties), second printing, Springer, Berlin, 2003, ISBN 3-540-65431-3, 524 pp., €53.45 (first printing 1999).Juraj Hromkovi?, Algorithmics for Hard Problems (Introduction to Combinatorial Optimization, Randomization, Approximation, and Heuristics), second edition, Springer, Berlin, 2003, ISBN 3-540-44134-4, 544 pp., €53.45 (first printing 2001).Vijay Vazirani, Approximation Algorithms, second printing, Springer, Berlin, 2002, ISBN 3-540-65367-8, 380 pp., €37.40 (first printing 2001). 相似文献
998.
Gerhard Lischke 《Mathematical Logic Quarterly》2005,51(3):299-304
The square of a language L is the set of all words pp where p ∈ L. The square of a regular language may be regular too or context‐free or none of both. We give characterizations for each of these cases and show that it is decidable whether a regular language has one of these properties. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
Gerhard Quinkert Stefan Scherer Dietmar Reichert Hans-Peter Nestler Helma Wennemers Andreas Ebel Klaus Urbahns Klaus Wagner Klaus-Peter Michaelis Gerhard Wiech Günter Prescher Bernd Bronstert Bernd-Jürgen Freitag Ilka Wicke Dietmar Lisch Pavel Belik Thorsten Crecelius Dirk Hrstermann Gottfried Zimmermann Jan W. Bats Gerd Dürner Dieter Rehm 《Helvetica chimica acta》1997,80(6):1683-1772
The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction). 相似文献
1000.
C.M. Marian F. Schneider M. Kleinschmidt J. Tatchen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):357-367
Electronic spectra of uracil in its diketo (lactam) form and five enol (lactim) tautomeric forms have been investigated by
means of combined density functional and configuration interaction methods. We have simulated the effects of hydrogen bonding
with a protic solvent by recomputing the spectrum of uracil in the presence of two, four, or six water molecules. Geometries
of the electronic ground state and several low-lying excited states have been optimized. Spin-orbit coupling has been determined
for correlated wavefunctions employing a non-empirical spin-orbit mean-field approach. In accord with experiment, we find
the diketo tautomer to be the most stable one. The calculations confirm that the first absorption band arises from the 1( π↦π*) S
0↦S
2 excitation. The experimentally observed vibrational structure in this band originates from a breathing mode of the six ring.
Complexation with water molecules is seen to cause a significant blue shift of n↦π* excitations while leaving π↦π* excitations nearly uninfluenced. Computed radiative lifetimes are presented for the experimentally known weak phosphorescence
from the π↦π* excited T1 state. Among the uracil lactim tautomers, one is particularly interesting from a spectroscopic point of view. In this tautomer,
the π↦π* excitation gives rise to the S1 state.
Received 18 February 2002 / Received in final form 5 June 2002 Published online 13 September 2002 相似文献