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151.
152.
Vendeuvre C Bertoncini F Thiébaut D Martin M Hennion MC 《Journal of separation science》2005,28(11):1129-1136
Modeling the retention in comprehensive two-dimensional gas chromatography (GC x GC) was achieved using retention indices obtained in conventional GC. Predicted results were compared with experimental data obtained in the two-dimensional separation of a synthetic hydrocarbon mixture. This proved to be helpful in optimizing the operating conditions of GC x GC separation of a complex petroleum sample and in identifying chemical families. 相似文献
153.
In this paper we formulate power systems as nonlinear nearly Hamiltonian systems. Using the invariance principle for ordinary differential equations, necessary and sufficient conditions for asymptotic stability are established and a new method of estimating the domain of attraction of the stable equilibrium point is developed. The present results constitute a novel approach to stability analysis and involve the following three steps:
- Given a system with dissipation, the stability of its equilibrium is ascertained by determining the stability of the associated conservative system.
- Attractivity of the stable equilibrium of the entire system (with dissipation) is determined from the system topology.
- An estimate of the domain of attraction of the asymptotically stable equilibrium is obtained by making use of results obtained in (a) and (b).
154.
Antoine R Broyer M Dugourd P Breaux G Hagemeister FC Pippen D Hudgins RR Jarrold MF 《Journal of the American Chemical Society》2003,125(30):8996-8997
Molecular beam electric deflection measurements have been used to determine electric susceptibilities for small unsolvated alanine-based peptides. The electric susceptibility provides information about the charge distribution within the peptide and can be used to distinguish between zwitterionic and canonical forms. Measured electric susceptibilities for WAn peptides (n = 1-5) are similar to those for capped Ac-WAn-NH2 peptides (which cannot form zwitterions). Susceptibilities calculated using a simulated tempering-based approach are substantially larger for the zwitterionic form than for the canonical form. The measured susceptibilities are in good agreement with those calculated for the canonical form. For the larger peptides, the lowest potential energy structure found in the simulations is hairpin-like, while the lowest free energy structure found at room temperature is extended. The zwitterionic form is constrained by intramolecular interactions which make it entropically unfavorable. 相似文献
155.
Elisabeth Seguin Michel Koch Evelyne Chenu Marcel Hayat 《Helvetica chimica acta》1980,63(5):1335-1346
Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and Tubulosine Pseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described. 相似文献
156.
To test the eventual involvement of sterols with a cyclopropane containing side chain in bio-methylation processes, 24,25-methanocholest-5-en-3β-ol ( 5 ) and 24,25-methano-26-methylcholest-5-en-3β-ol ( 6 ) were synthesized. Together with the naturally occurring cyclopropane petrosterol ( 1 ), they were submitted to acid isomerization to provide chemical models for some of their potential metabolites. 相似文献
157.
Jakubowicz K Wong YS Chiaroni A Bénéchie M Marazano C 《The Journal of organic chemistry》2005,70(19):7780-7783
[reaction: see text] 3-Alkyl-1,4-dihydropyridines dimerize in acidic medium, at low temperature, to give polycyclic imminium salts derivatives that were reduced to afford new polycyclic diamine scaffolds. The reaction can be extended to enantiopure series starting from R-(+)- or S-(-)-1-phenylethylamine. Long exposure of the polycyclic imminium salt intermediates to air moisture at 20 degrees C resulted in formation of new amide derivatives. This is probably due to the addition of water followed by an intramolecular oxido-reduction process. 相似文献
158.
Kolen'ko YV Kovnir KA Gavrilov AI Garshev AV Meskin PE Churagulov BR Bouchard M Colbeau-Justin C Lebedev OI Van Tendeloo G Yoshimura M 《The journal of physical chemistry. B》2005,109(43):20303-20309
Mesoporous nanosized TiO2 and Zn(x)Ti(1-x)O(2-x) solid solution having a Zn content below 10 mol % with a particles size between 13 and 17 nm are prepared by a template-free sol-gel method followed by high-temperature supercritical drying in 2-propanol. The structural, textural, and electronic properties of the obtained nanomaterials are methodically investigated by using XRD, SEM, TEM, ED, HREM, EDX, ICP-OES, N(2) adsorption-desorption, Raman spectroscopy, and diffuse reflectance UV-vis spectroscopy. It is shown that the proposed synthesis technique leads to the formation of a Zn(x)Ti(1-x)O(2-x) solid solution based on the anatase crystal structure rather than a two-phase sample. High-resolution electron microscopy and electron diffraction indicate that the distribution of zinc atoms over the anatase structure does not lead to a considerable deformation of the crystal structure. 相似文献
159.
The finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results. The influence of the computational parameters is discussed. An alternative scheme has also been implemented, for inner check, that consists of applying a static electric field to a slab of increasing thickness in the direction orthogonal to the surface; the dielectric response at the center of the slab is shown to converge rapidly to the bulk value evaluated with the sawtooth field. The method is accurate and permits the determination of nonlinear corrections to the dielectric constant. When used in conjunction with the local density approximation (LDA) scheme, it provides for the dielectric constant of the three above-mentioned compounds values close to those recently obtained with a time-dependent density functional theory approach. 相似文献
160.
Christian Deshayes Michel Chabannet Suzanne Gelin 《Journal of heterocyclic chemistry》1986,23(5):1595-1598
The title compounds were prepared by acid-catalyzed cyclization of aryloxymethyl- or (2-arylethyl)-4-carboxymethylisoxazoles which in turn were synthesized from aryloxymethyl- or (2-arylethyl)isoxazole-4-carboxylic acids by Arndt-Eistert homologation. 相似文献