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621.
A microscopic model for the excitation and relaxation processes in photochemistry at surfaces is developed. Our study is based on ab initio calculations and the surrogate Hamiltonian method treating surface electron-hole pairs as a bath of two-level systems. Desorption probabilities and velocities in the experimentally observed range are obtained. The excited state lifetime is calculated, and a dependence of observables on pulse length is predicted. 相似文献
622.
Christiane Takacs 《Journal of Theoretical Probability》2001,14(3):699-715
We consider a random walk on
in a stationary and ergodic random environment, whose states are called types of the vertices of
. We find conditions for which the speed of the random walk is positive. In the case of a Markov chain environment with finitely many states, we give an explicit formula for the speed and for the asymptotic proportion of time spent at vertices of a certain type. Using these results, we compare the speed of random walks on
in environments of varying randomness. 相似文献
623.
624.
Hassane Boumchita Michel Legraverend Emile Bisagni Christiane Huel 《Journal of heterocyclic chemistry》1990,27(6):1815-1819
The synthesis of 1-amino-3,3-bis(benzyloxymethyl)cyclobutane has been performed from 3,3-bis(benzyloxymethyl)cyclobutanone, via the corresponding oxime which was reduced with lithium aluminum hydride. The amine thus obtained led to two new cyclobutyl analogs of adenosine and guanosine which were devoid of antiviral activity against HSV-1, HCMV and HIV in cell culture. 相似文献
625.
626.
Detlev Joachimi Peter R. Ashton Christiane Sauer Neil Spencer Carsten Tschierske Kerstin Zab 《Liquid crystals》1996,20(3):337-348
Various paracyclophane derivatives incorporating 4,4'-biphenyl, 2,5-diphenyl-1,3,4-thiadiazole, phenyl benzoate and 2,6-disubstituted naphthyl rigid cores were synthesized and their mesomorphic behaviour was studied using polarizing microscopy, DSC and X-ray diffraction. Most of these macrocyclic compounds possess liquid crystalline properties with unexpectedly high clearing temperatures compared to those of conventional calamitic mesogens. In this way, the coupling of two appropriate rigid units using flexible chains to form a macrocycle constitutes a new and powerful approach towards mesophase induction and stabilization. The types of mesophase formed by these macrocycles do not depend only on the nature of the bridging chains, but also strongly on the structure of the rigid aromatic system. The smectic A phase and the E phase are formed by polyetherbiphenylophanes. Poly-ethercyclophanes incorporating the 2,5-diphenylthiadiazole rigid core form nematic and smectic C phases. The nematic phase is the only mesophase when the rigid core is the phenyl benzoate unit. No mesomorphic properties could be detected for macrocycles which featured either the benzyl phenyl ether moiety or the 2,6-disubstituted naphthalene unit in their constitution. 相似文献
627.
Christiane Takacs 《Probability Theory and Related Fields》1998,111(1):123-139
Summary. We define directed rooted labeled and unlabeled trees and find measures on the space of directed rooted unlabeled trees which
are invariant with respect to transition probabilities corresponding to a biased random walk on a directed rooted labeled
tree. We use these to calculate the speed of a biased random walk on directed rooted labeled trees. The results are mainly
applied to directed trees with recurrent subtrees, where the random walker cannot escape.
Received: 12 March 1997/ In revised form: 11 December 1997 相似文献
628.
Christiane Lefevre-Percsy 《Journal of Geometry》1980,15(1):93-98
We determine all sets Q of points of any finite dimensional protective space P such that each line intersecting Q in more than one point, either is contained in Q or contains exactly one point not on Q. If P is a finite protective space of order q, these sets are the so called sets of class (0, 1, q, q + 1). 相似文献
629.