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51.
22(17 → 28)abeo-Lupene derivatives 5a and 6a were obtained after the acid-catalyzed E-ring expansion of 3-acetylbetulin (1a). Glycosylation of these dehydrated triterpenoids using Schmidt's trichloroacetimidate sugar donors in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) provided the new anhydrobetulin saponins 7b7e in which the terminal olefin C-20(29) isomerizes to form a C-19 tetrasubstituted alkene. The preliminary cytotoxic evaluation revealed that saponins 7b7d exhibited a moderate cytotoxic activity against A549, DLD-1, and WS1 human cell lines with IC50 ranging from 22 to 49 μM.  相似文献   
52.
Investment projects and businesses can be entered or exited at a cost, and the theory of real option teaches us how to find optimal activity levels that should trigger entry or exit. However, in practice, different managers or owners operate under different constraints and might apply different thresholds to the same business. We are interested in the hedging of the risk related to the cost of sub-optimal entry or exit. We introduce a new class of derivative products that can hedge this risk. The pricing of these derivatives involves the joint law of a Brownian excursion and its supremum, which is calculated thanks to Bessel processes-related distribution laws.  相似文献   
53.
In this paper, we extend and complete the classification of the generic singularities of the 3D-contact sub-Riemmanian conjugate locus in a neighborhood of the origin.  相似文献   
54.
Given functions f1 and f2 meromorphic, respectively, on subsets E1 and E2 of a Riemann surface R, we seek a function meromorphic on all of R, which simultaneously approximates f1 on E1 and f2 on E2.  相似文献   
55.
Bloch constants for planar harmonic mappings   总被引:3,自引:0,他引:3  

We give a lower estimate for the Bloch constant for planar harmonic mappings which are quasiregular and for those which are open. The latter includes the classical Bloch theorem for holomorphic functions as a special case. Also, for bounded planar harmonic mappings, we obtain results similar to a theorem of Landau on bounded holomorphic functions.

  相似文献   

56.
Preface     
Jacques-Louis Lions (1928-2001) was an exceptional mathematician, whose lasting influence is still deeply felt all over the world.He was a universally recognized and admired expert in partial differential equations, to the study of which he has made outstanding contributio  相似文献   
57.
This paper is concerned with the indentation of an elastic half-space by an axisymmetric punch under a monotonically applied normal force and under the assumption of Coulomb friction with coefficient μμ in the region of contact. Within an inner (unknown) circle the contact is adhesive, while in the surrounding annulus the surface moves inwards with increasing load. In this paper it is shown how this problem is equivalent to two coupled Abel's equations with an unknown free point, the inner circumference of the annulus. It is further shown that a product integration finite difference approximation of those integral equations leads to a mixed linear complementarity problem (mixed LCP). A method based on Newton's method for solving non-smooth nonlinear equations is demonstrated to converge under restrictive assumptions on the physical parameters defining the system; and numerical experimentation verifies that it has much wider applicability. The method is also validated against the approach of Spence. The advantage of the mixed LCP formulation is that it provides the radius of the inner adhesive circle directly using the physical parameters of the problem.  相似文献   
58.
59.
An isomer of the methylterrylene molecule was adsorbed both on Cu(111) and on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). On the bare metal surface, the STM images do not reveal any intramolecular resolution and do not depend on the applied tunnel bias. On the contrary, the images acquired at specific bias voltages for the molecule on the salt layer show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.  相似文献   
60.
The Fenton-Karma model is a simplification of complex ionic models of cardiac membrane that reproduces quantitatively many of the characteristics of heart cells; its behavior is simple enough to be understood analytically. In this paper, a map is derived that approximates the response of the Fenton-Karma model to stimulation in zero spatial dimensions. This map contains some amount of memory, describing the action potential duration as a function of the previous diastolic interval and the previous action potential duration. Results obtained from iteration of the map and numerical simulations of the Fenton-Karma model are in good agreement. In particular, the iterated map admits different types of solutions corresponding to various dynamical behavior of the cardiac cell, such as 1:1 and 2:1 patterns. (c) 2002 American Institute of Physics.  相似文献   
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