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排序方式: 共有204条查询结果,搜索用时 15 毫秒
141.
Marie Buchotte Claudia Bello Pierre Vogel Nicolas Floquet Murielle Muzard Richard Plantier-Royon 《Tetrahedron: Asymmetry》2009,20(17):2038-2042
A series of sulfonium salts derived from 1,5-dithiopent-1-enopyranosides was prepared in a three-step sequence from protected d- and l-erythrofuranoses. The key step is the nucleophilic displacement of a leaving group by a sulfur atom of carbohydrate-derived ketene dithioacetals. Such compounds were assayed for their properties as glycosidase inhibitors. 相似文献
142.
E. Laredo M. Grimau A. Bello F. Snchez M. A. Gmez C. Marco I. Campoy J. M. Arribas 《Journal of Polymer Science.Polymer Physics》2005,43(12):1408-1420
Polypropylene (PP) and polyamide‐6 (Ny‐6) blends with a 70/30 composition have been studied by broadband dielectric spectroscopy. The unmodified blends are immiscible, and 10% of PP functionalized with maleic anhydride was added as a compatibilizer. The influence of the compatibilizer on the water sorption and on the molecular dynamics of the Ny‐6 phase is followed by the changes induced in the dielectric loss spectra of these blends in both wet and dry states. The shortest range motions are unaffected by the compatibilizer in the dry state, but a higher water sorption is observed in the unmodified blend. Higher activation energies are found for the β relaxation in the dry blends than for the Ny‐6 homopolymer, showing the existence of constraints on these longer scale motions. During increasing temperature experiments, two segmental modes are recorded, the lower temperature mode corresponding to the plasticized material; as the temperature is raised, a second cooperative mode is found, originating in the dry Ny‐6 amorphous phase, rigidized by the loss of moisture. The comparison of the dielectric strengths of the modes shows that the unmodified blend absorbs more water than the compatibilized blend. The segmental dynamics are unaffected by compatibilization. At high temperatures, the high temperature tail of the segmental mode is much higher in the absence of the compatibilizer. The contribution of a peak due to interfacial polarization is lowered by the presence of the compatibilizer, which makes the interface more diffuse and the trapping of free carriers less effective. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1408–1420, 2005 相似文献
143.
Jose Ailton Conceicao Bispo Carlos Francisco Sampaio Bonafe Maria Gabriela Bello Koblitz Carlos Geilson Santana Silva Ancelmo Rabelo de Souza 《Journal of mathematical chemistry》2013,51(1):144-152
The use of the classic Henry–Michaelis–Menten (HMM) model (or simply, Michaelis–Menten model) to study the substrate and enzyme concentration dependence of enzyme catalysis is a very important step in understanding many biochemical processes, including microbial growth. Although the HMM model has been extensively studied, the conditions in which the substrate concentration is not in excess have still not been adequately defined mathematically. This lack of definition occurs despite at the cellular and molecular levels most systems generally do not operate in a state of substrate excess. In the present work, we describe an approach for studying enzyme reactions in which substrate concentrations are not in excess. Our results show that the use of extent of reactions and numerical simulation of the velocities of reaction provides an important advance in this field and furnishes results not obtained in previous studies involving these aspects. This approach, in association with knowledge of the rate constants, provides a direct and easy means of examining the single substrate–enzyme profile during product formation at any enzyme–substrate ratio. This approach is more direct than previous models that required the use of empirical equations with arbitrary constants. 相似文献
144.
J. Y. Bello Cruz G. Bouza Allende 《Journal of Optimization Theory and Applications》2014,162(2):371-391
In some applications, the comparison between two elements may depend on the point leading to the so called variable order structure. Optimality concepts may be extended to this more general framework. In this paper, we extend the steepest descent-like method for smooth unconstrained vector optimization problems under a variable order structure. Roughly speaking, we see that every accumulation point of the generated sequence satisfies a necessary first order condition. We discuss the consequence of this fact in the convex case. 相似文献
145.
146.
A. Antonello G. Brusatin M. Guglielmi V. Bello G. Mattei G. Zacco A. Martucci 《Journal of nanoparticle research》2011,13(4):1697-1708
A sol–gel route for TiO2 nanocrystals (NCs) synthesis has been developed at low temperature without surfactants. Synthetic and processing parameters
have been optimized to maximize particles’ colloidal stability and crystallinity. The obtained TiO2 NCs can be homogeneously dispersed in a sol–gel derived organic–inorganic hybrid material, resulting in homogeneous composite
films when prepared by spin coating. High refractive index films were obtained with high TiO2 NCs loading and good transparency. Furthermore, TiO2 colloidal solutions can be used for depositing porous crystalline films, whose structural evolution has been followed under
different annealing treatments. Nanocrystals were characterized by UV–Vis absorption, TEM, FT-Raman, and XRD techniques, while
nanocomposite and TiO2 films were analyzed by SEM, TEM, and spectroscopic ellipsometry. 相似文献
147.
We propose two restricted memory level bundle-like algorithms for minimizing a convex function over a convex set. If the memory is restricted to one linearization of the objective function, then both algorithms are variations of the projected subgradient method. The first algorithm, proposed in Hilbert space, is a conceptual one. It is shown to be strongly convergent to the solution that lies closest to the initial iterate. Furthermore, the entire sequence of iterates generated by the algorithm is contained in a ball with diameter equal to the distance between the initial point and the solution set. The second algorithm is an implementable version. It mimics as much as possible the conceptual one in order to resemble convergence properties. The implementable algorithm is validated by numerical results on several two-stage stochastic linear programs. 相似文献
148.
In this article, we propose a strongly convergent variant on the projected subgradient method for constrained convex minimization problems in Hilbert spaces. The advantage of the proposed method is that it converges strongly when the problem has solutions, without additional assumptions. The method also has the following desirable property: the sequence converges to the solution of the problem which lies closest to the initial iterate. 相似文献
149.
J. Y. Bello Cruz P. S. M. Santos S. Scheimberg 《Journal of Optimization Theory and Applications》2013,159(3):562-575
We introduce an explicit algorithm for solving nonsmooth equilibrium problems in finite-dimensional spaces. A particular iteration proceeds in two phases. In the first phase, an orthogonal projection onto the feasible set is replaced by projections onto suitable hyperplanes. In the second phase, a projected subgradient type iteration is replaced by a specific projection onto a halfspace. We prove, under suitable assumptions, convergence of the whole generated sequence to a solution of the problem. The proposed algorithm has a low computational cost per iteration and, some numerical results are reported. 相似文献
150.
W.J. Zhang C.Y. Chan K.M. Chan I. Bello Y. Lifshitz S.T. Lee 《Applied Physics A: Materials Science & Processing》2003,76(6):953-955
Large-area, 1-μm-thick cubic boron nitride (cBN) films were deposited on (001) silicon substrates by electron-cyclotron-resonance-enhanced
microwave-plasma chemical vapor deposition (ECR-MP CVD) in a mixture of He-Ar-N2-BF3-H2 gases. With the assistance of fluorine chemistry in the gas phase and substrate reactions, the phase purity of the sp3-configuration was improved to over 85% at a reduced substrate bias voltage of -40 V. The grown films show clear Raman transversal
optical (TO) and longitudinal optical (LO) phonon vibration modes, characteristic of cBN. Such Raman spectral characteristics
are the first ever observed in cBN films prepared under ECR-MP CVD conditions.
Received: 3 May 2002 / Accepted: 7 May 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +852-2788/7830, E-mail: apwjzh@cityu.edu.hk 相似文献