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961.
Jean Picard 《Probability Theory and Related Fields》2002,122(4):593-612
Consider the semigroup $P_t$ of an elliptic diffusion; we describe a simple stochastic method providing gradient estimates
on $P_tf$. If $N$ is a manifold endowed with a connection, the method can also be applied to the associated nonlinear semigroup
$Q_t$ acting on $N$-valued maps. With a localization technique, we deduce gradient estimates for real harmonic functions or
$N$-valued harmonic maps. Moreover, the results are extended to a class of hypoelliptic diffusions.
Received: 31 July 2000 / Revised version: 20 September 2001 / Published online: 15 March 2002 相似文献
962.
963.
964.
X Tang W Ens F Mayer K G Standing J B Westmore 《Rapid communications in mass spectrometry : RCM》1989,3(12):443-448
Daughter ions from decomposition of [M + H]+ parent ions have been observed in a time-of-flight mass spectrometer fitted with an ion mirror. Unit mass resolution is obtained for parent ions of masses up to several thousand u when the mirror voltage is set at a value determined by the usual velocity-focusing criterion for parent ions. Under this condition the daughter-ion resolution in the low-mass range suffers. Considerable improvement is obtained when the daughter-ion spectrum is examined in several segments, with the mirror voltage optimized for each segment. The daughter-ion spectrum from decay of metastable [M + H]+ parent ions in Substance P is measured using this technique. Reasons are suggested for differences between the spectrum obtained and a spectrum for the same compound recently obtained using a tandem double-focusing instrument. 相似文献
965.
Jean Mawhin 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1987,38(2):257-265
The method of upper and lower solutions and convexity arguments are used to prove sharp results for the existence and multiplicity of periodic solutions for first order ordinary differential equations depending upon a parameter.Dedicated to Professor H. W. Knobloch for his sixtieth birthday 相似文献
966.
967.
968.
Ken Hosoya Jean M. J. Frchet 《Journal of polymer science. Part A, Polymer chemistry》1993,31(8):2129-2141
Monodisperse polymer particle-based separation media were prepared by a multi-step swelling and polymerization method with two pairs of monomers and two porogenic solvents. Their chromatographic properties were compared to those of beads prepared by a corresponding suspension polymerization method without the use of seed polymer to ascertain the influence of the seed polymer on their porous structures. A large change in porous structure was observed when the swollen particle consisting of monomers and porogenic solvents contained at least one good solvent for the polystyrene seed polymer, allowing it to remain in the polymerizing medium. In contrast, when the polystyrene seed particle was excluded from the swollen oil droplets, due to its poor solubility in the monomers and the porogenic solvents, there was no difference in the chromatographic properties such as pore volume, pore size, pore size distribution, or retention selectivity between the multi-step swelling and polymerization method and the suspension polymerization method. Since the only difference between the multi-step swelling and polymerization method and the suspension method is the use of the seed polymer, it appears that a very small amount (< 1% v/v) of seed polymers in the enlarged swollen droplets plays an important role as a porogen and affects the porous structure as well as the chromatographic properties of the monodisperse polymer particle-based separation media. © 1993 John Wiley & Sons, Inc. 相似文献
969.
Jean Dolbeault Maria J. Esteban Javier Duoandikoetxea Luis Vega 《Annales Scientifiques de l'école Normale Supérieure》2007,40(6):885-900
We prove some Hardy type inequalities related to the Dirac operator by elementary methods, for a large class of potentials, which even includes measure valued potentials. Optimality is achieved by the Coulomb potential. When potentials are smooth enough, our estimates provide some spectral information on the operator. 相似文献
970.
We analyze some cases for which the Pollak–Grabert–Hänggi theory on the activated rate processes for generalized Langevin dynamics exhibits unexplained disagreements with numerical results. First we analyze carefully the PGH theory and we show that a kind of Markovian hypothesis implicitly made in the reasoning is sometimes violated. Then we propose modifications of the original theory in order to take into account the possible effects caused by this violation, and we compare the corrected results with simulations. 相似文献