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991.
Poriel C Ferrand Y Le Maux P Rault-Berthelot J Simonneaux G 《Inorganic chemistry》2004,43(16):5086-5095
Anodic oxidation of free base and manganese complexes of tetraspirobifluorenylporphyrins leads to the coating of the working electrode by insoluble electroactive poly(9,9'-spirobifluorene-free and manganese porphyrin) films which electrochemical behavior and physicochemical properties are described. After removal from the electrode, the manganese-complexed polymers were evaluated as catalysts for the oxidation of alkenes by iodobenzene diacetate or iodosylbenzene. The results show that the reactions proceeded very efficiently at room temperature with good yields. The electrosynthesized polymer catalysts can be recycled by simple filtration and reused even up to the eighth cycle without loss of activity and selectivity. These results represent an important improvement over those previously described for manganese-porphyrin-catalyzed epoxidation reactions. 相似文献
992.
993.
Mancini I Guella G Sauvain M Debitus C Duigou AG Ausseil F Menou JL Pietra F 《Organic & biomolecular chemistry》2004,2(5):783-787
We report here on new 6-hydroxy-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidinium alkaloids, belonging to the phloeodictyne family, isolated from the haplosclerid sponge Oceanapia[=Phloeodictyon]fistulosa(Bowerbank, 1873) from New Caledonian shallow waters. Online LC-ESI-MS analysis, coupled to tandem fragmentation experiments on the crude alkaloid mixture, allowed us to clarify their flat structures, including structural isomers. At least 25 different components, of which 17 are new members with variable terminus and length chains, were characterised, besides less abundant analogues bearing a thioethylguanidine side chain. Crude mixtures and HPLC enriched fractions proved active against chloroquine-resistant Plasmodium falciparum, with IC(50) values ranging from 0.6 to 6 microM, while cytotoxicity against human A-549 cell line was low. This makes these alkaloids a good prospect as leads for novel antimalarial agents. 相似文献
994.
Studies of CO-dissociative substitution reactions of the complexes Ru(CO)4L (L = a wide variety of P-donor ligands) have been extended and analysis of the results by the QALE methodology has been refined (QALE = quantitative analysis of ligand effects). Rates increase substantially with increasing size of L, mainly as a consequence of increasingly favourable activation entropies. These can be associated with increasing Ru-CO bond breaking that is compensated enthalpically by increasing Ru-P bond making allowed by release of steric strain. Explicit allowance for pi-acidity shows that these effects are just significant while sigma-donor and aryl effects are negligible. However, pendent hydrogen atoms, attached directly to the phosphorus atoms, have a pronounced and unique positive effect on the rates, with significant kinetic isotope effects (KIE). This is associated with the novel occurrence of direct Ru-H or incipient Ru-(eta2-P-H) agostic bond making as the CO ligand departs. 相似文献
995.
996.
In earlier papers the authors studied finite pseudorandom binary sequences, and they constructed sequences with strong pseudorandom properties. In these earlier constructions multiplicative characters were used. In this paper a new construction is presented which utilizes properties of additive characters. These new sequences can be computed fast, they are well-distributed relative to arithmetic progressions and their correlations of small order are small, but the price paid for the fast computation is that the correlations of large order can be large. 相似文献
997.
Summary. We are concerned with efficient numerical simulation of the radiative transfer equations. To this end, we follow the Well-Balanced approachs canvas and reformulate the relaxation term as a nonconservative product regularized by steady-state curves while keeping the velocity variable continuous. These steady-state equations are of Fredholm type. The resulting upwind schemes are proved to be stable under a reasonable parabolic CFL condition of the type tO(x2) among other desirable properties. Some numerical results demonstrate the realizability and the efficiency of this process.Mathematics Subject Classification (1991): 82C70, 65M06, 35B25Work partially supported by EEC network #HPRN-CT-2002-00282.Revised version received July 21, 2003 相似文献
998.
Raúl Ferreira Pablo Groisman Julio D. Rossi 《Numerical Methods for Partial Differential Equations》2004,20(4):552-575
We study numerical approximations of positive solutions of the porous medium equation with a nonlinear source, where m > 1, p > 0 and L > 0 are parameters. We describe in terms of p, m, and L when solutions of a semidiscretization in space exist globally in time and when they blow up in a finite time. We also find the blow‐up rates and the blow‐up sets, proving that there is no regional blow‐up for the numerical scheme. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2004 相似文献
999.
Roy?SmithEmail author Robert?VarleyEmail author 《Annali di Matematica Pura ed Applicata》2004,183(3):401-419
The Prym map
factors through a space ={X} of intrinsically polarized varieties, namely
, where
is a connected étale double cover of a smooth curve C of genus g,
consists of the set of even precanonical effective divisors on
, and (P,) is the principally polarized Prym variety associated to . X is a connected, reduced local complete intersection of (pure) dimension g-1, and when C is non hyperelliptic X is normal and irreducible. By analogy with the proofs of the classical Torelli theorem for curves by Andreotti and by Andreotti-Mayer and Green, which factor the Jacobi map through a symmetric product of the curve, the present factorization may be used to attack the Torelli problem for Prym varieties. In [19] we have shown that X determines the Prym variety (P,), as the Albanese variety of X, and that X also determines the double cover
, at least when C is non hyperelliptic and the codimension of sing in P is at least 5. The next challenge in this approach to the Torelli problem is to analyze the infinitesimal structure of these maps.The goal of the present paper is to show the first map
is unramified when C is non hyperelliptic, i.e. that a first order deformation of
which induces the trivial first order deformation of X, is already trivial on
. (This question was studied for g=3 by H. Yin [23].) We do this as follows for g3. There is a map
from
to a curve of effective Cartier divisors on X. We prove that if C is non hyperelliptic, this map is an isomorphism from
onto a smooth connected component
of the Hilbert scheme of X. This is an analogue of Prop. 4.1. b), p.334, in [7], (that the set
, is a connected component of Hilb(C(g-1)) isomorphic to C).Then we deduce that if a first order deformation of
induces the trivial deformation of X, the deformation of
is isomorphic to the trivial deformation of the curve
in Hilb(X). It follows that the original deformation of
is trivial. The complementary question of whether every first order deformation of X comes from a first order deformation of
, analogous to Thm. 3.6 of [7], is proved in [23] for g=3 and C non hyperelliptic, but remains open for g4 at the time of writing. We will work throughout over the complex numbers, and will generally assume the base curve C is smooth and non hyperelliptic, although some results are true more generally. Dedicated in memory of Fabio BardelliMathematics Subject Classification (2000) 14H40, 14K 相似文献
1000.
Raúl?E.?CurtoEmail author Lawrence?A.?Fialkow 《Integral Equations and Operator Theory》2004,50(2):169-196
Given real numbers
with 00 >0 , the truncated parabolic moment problem for entails finding necessary and sufficient conditions for the existence of a positive Borel measure , supported in the parabola p(x, y) = 0, such that
We prove that admits a representing measure (as above) if and only if the associated moment matrix
is positive semidefinite, recursively generated and has a column relation p(X, Y) = 0, and the algebraic variety () associated to satisfies card
In this case, admits a rank
-atomic (minimal) representing measure.Submitted: August 25, 2003 相似文献