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11.
Nicholas I. M. Gould Dominique Orban Annick Sartenaer Phillipe L. Toint 《4OR: A Quarterly Journal of Operations Research》2005,3(3):227-241
In this paper, we examine the sensitivity of trust-region algorithms on the parameters related to the step acceptance and
update of the trust region. We show, in the context of unconstrained programming, that the numerical efficiency of these algorithms
can easily be improved by choosing appropriate parameters. Recommended ranges of values for these parameters are exhibited
on the basis of extensive numerical tests.
MSC classification:
65K05, 90C26, 90C30 相似文献
12.
Dominique Arlettaz 《manuscripta mathematica》1989,64(4):431-443
The classical extension problem is to determine whether or not a given mapg:AY, defined on a given subspaceA of a spaceX, has an extensionXY. The present paper examines this question in the special case where thek-invariants ofY are cohomology classes of finite order (for instance ifY is an infinite loop space). 相似文献
13.
Dominique Dehareng Georges Dive Josette Lamotte-Brasseur Jean-Marie Ghuysen 《Theoretical chemistry accounts》1989,76(2):85-94
Summary The electrostatic interaction energy between methanol and the dyad water-imidazole has been computed numerically at three levels of approximation from 3D grids of the charge density of one partner and the electrostatic potential of the other. The minimum positions and energy values thus obtained compare well with those calculated analytically. The numerical procedure is especially interesting for the prediction of the stable conformers. 相似文献
14.
Cyclic and acyclic beta-ketoesters were efficiently trifluoromethylated with 5-trifluoromethyldibenzothiophenium tetrafluoroborate in the presence of a phase-transfer catalyst to afford the corresponding alpha-substituted alpha-trifluoromethyl beta-ketoesters in good to excellent yields. In a second approach, 5-trifluoromethyldibenzothiophenium tetrafluoroborate and tetrabutylammonium difluorotriphenylstannate were used for efficient electrophilic trifluoromethylation of various silyl enol ethers leading to the corresponding alpha-trifluoromethyl ketones in good to high yields. 相似文献
15.
Polypeptides containing a basic amino acid close to their single tryptophan residue were irradiated with monochromatic 302 nm radiation. Tryptophan photolysis was monitored by absorption and fluorescence spectroscopy. Amino acid loss was evaluated by amino acid analysis. Only the protonated residues adjacent to tryptophan in the sequence were destroyed upon tryptophan excitation. This reaction is probably due essentially to direct interaction between the excited tryptophan and the neighbouring residue without electron solvation. 相似文献
16.
Tessore F Roberto D Ugo R Pizzotti M Quici S Cavazzini M Bruni S De Angelis F 《Inorganic chemistry》2005,44(24):8967-8978
Coordination of 4'-(C6H4-p-X)-2,2':6',2'-terpyridines [X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning of the ancillary ligands. 相似文献
17.
The 2-(diphenylphosphino) ethyl group (DPPE) as a new carboxyl-protecting group in peptide chemistry
Dominique Chantreux Jean-Paul Gamet Robert Jacquier Jean Verducci 《Tetrahedron》1984,40(16):3087-3094
The use of the 2-(diphenylphosphino)ethyl group for carboxyl-protection of amino acids or peptides is described. This group is easily introduced by esterification using 2-(diphenylphosphino) ethanol in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. These Dppe esters are stable under the standard conditions for peptide synthesis. Deprotection is carried out under mild conditions by quaternisation using methyl iodide followed by a β-elimination induced by fluoride ion or potassium carbonate. 相似文献
18.
Hirel C Luneau D Pécaut J Ohrström L Bussière G Reber C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(14):3157-3161
The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m space group with a=7.4050(7), c=8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two-dimensional square array of spin S=1/2 antiferromagnetically coupled (J=-10 cm(-1) and g=2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively. 相似文献
19.
E. Peter Kündig Chantal Dupr Bernadette Bourdin Allan Cunningham Dominique Pons 《Helvetica chimica acta》1994,77(2):421-428
Two new C2 chiral bidentate phosphorous ligands have been prepared in enantiomerically pure form. The two phosphorous centers bear electron-withdrawing groups ((CF3)2CH? O, C6F5) and are linked by a trans-cyclopentane-1,2-diol-derived bridge. Photolysis of [Cr(η6-C6H6)(CO)3] in the presence of these two new ligands and of two previously reported bidentate phosphites, and fluorophosphinites (L) afforded [Cr(η6-C6H6)(CO)L] complexes. IR Spectral comparison of the complexes shows the new ligands to be intermediate in their bonding properties between alkyl phosphites and CO. 相似文献
20.
Atomic force microscopy imaging of hair: correlations between surface potential and wetting at the nanometer scale 总被引:2,自引:0,他引:2
Dupres V Camesano T Langevin D Checco A Guenoun P 《Journal of colloid and interface science》2004,269(2):329-335
We report investigations of hair surface potential under wetting at the nanometric scale by atomic force microscopy (AFM). Surface potential imaging was used to characterize the electrostatic properties of the hair samples. We found that the surface potential noticeably increases along the edges of the cuticles. These results are correlated with wetting behavior of different liquids performed using AFM in noncontact mode. 相似文献