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541.
Percec V Smidrkal J Peterca M Mitchell CM Nummelin S Dulcey AE Sienkowska MJ Heiney PA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(14):3989-4007
The synthesis of three libraries of self-assembling hybrid dendrons containing a primary structure based on the sequence (4-3,4-3,5)12G2-CO(2)CH(3) generated from benzyl ether, biphenyl-4-methyl ether, and AB(2) repeat units constructed from (AB)(y)--AB(2) combinations of benzyl ethers, is reported. The structural and retrostructural analysis of their supramolecular dendrimers facilitated the discovery of new architectural principles that lead to the assembly of functional helical pores. The self-assembly of an example of hybrid dendron containing -H, -CO(2)CH(3), -CH(2)OH, -COOH, -COOK, -CONH(2), -CONHCH(3), -CO(2)(CH(2))(2)OCH(3), -(R) and -(S)-CONHCH(CH(3))C(2)H(5) as X-groups at the apex demonstrated that these self-assembling dendrons provide the simplest strategy for the design and synthesis of porous columns containing a diversity of hydrophilic and hydrophobic functional groups in the inner part of the pore. The results reported here expand the scope and limitations of dendrons available for the self-assembly of functional pores that previously were generated mostly from dendritic dipeptides, to simpler architectures based on hybrid dendrons. 相似文献
542.
Emil Ioan Muresan Spiridon Oprea Vasile Hulea Theodor Malutan Mihai Vata 《Central European Journal of Chemistry》2008,6(3):419-428
The kinetics of the esterification reaction between acetic acid and epichlorohydrin catalysed by Purolite A-520E strong basic
anion exchange resin was studied. The effects of certain parameters such as stirring speed, particle diameter, temperature,
catalyst amount and molar ratio between reactants were experimentally determined. It was found that the overall reaction rate
is intrinsically kinetically controlled. The partial orders of reaction with respect to catalyst, acetic acid and epichlorohydrin
were determined. A reaction mechanism is proposed. Based on chromatographic data and taking into account the partial orders
of reaction, a more detailed kinetic model is suggested.
相似文献
543.
Low density open-cell foams were obtained from polylactic acid (PLA) and from blends of PLA with thermoplastic starch (TPS) using CO(2) as a blowing agent. Two unexpected features were found. First, a 2D cavitation process in the fractured cell walls was unveiled. Elliptical cavities with dimensions in the 100-300 nm range were aligned perpendicular to large cell cracks clearly exhibiting 2D crazing prior to macroscopic cell rupture. Secondly, a significant crystallization rate increase associated with the CO(2) foaming of PLA was discovered. While the PLA used in this study crystallized very slowly in isothermal crystallization, the PLA foams exhibited up to 15% crystallinity, providing evidence that CO(2) plasticization and the biaxial stretching upon foam expansion provided conditions that could increase the crystallization rate by several orders of magnitude. 相似文献
544.
Mihai Mihailescu Vicentiu Radulescu 《Proceedings of the American Mathematical Society》2007,135(9):2929-2937
We consider the nonlinear eigenvalue problem in , on , where is a bounded open set in with smooth boundary and , are continuous functions on such that , , and for all . The main result of this paper establishes that any sufficiently small is an eigenvalue of the above nonhomogeneous quasilinear problem. The proof relies on simple variational arguments based on Ekeland's variational principle.
545.
Stephan Ramon Garcia Mihai Putinar 《Transactions of the American Mathematical Society》2007,359(8):3913-3931
A bounded linear operator on a complex Hilbert space is called complex symmetric if , where is a conjugation (an isometric, antilinear involution of ). We prove that , where is an auxiliary conjugation commuting with . We consider numerous examples, including the Poincaré-Neumann singular integral (bounded) operator and the Jordan model operator (compressed shift). The decomposition also extends to the class of unbounded -selfadjoint operators, originally introduced by Glazman. In this context, it provides a method for estimating the norms of the resolvents of certain unbounded operators.
546.
Improved Halbach sensor for NMR scanning of drill cores 总被引:3,自引:0,他引:3
Anferova S Anferov V Arnold J Talnishnikh E Voda MA Kupferschläger K Blümler P Clauser C Blümich B 《Magnetic resonance imaging》2007,25(4):474-480
A lightweight Halbach magnet system for use in nuclear magnetic resonance (NMR) studies on drill cores was designed and built. It features an improved homogeneous magnetic field with a strength of 0.22 T and a maximum accessible sensitive volume. Additionally, it is furnished with a sliding table for automatic scans of cylindrical samples. This device is optimized for nondestructive online measurements of porosity and pore size distributions of water-saturated full cylindrical and split semicylindrical drill cores of different diameters. The porosity of core plugs with diameters from 20 to 80 mm can be measured routinely using exchangeable radiofrequency coils. Advanced NMR techniques that provide 2D T(1)-T(2) correlations with an average measurement time of 30 min and permeability estimates can be performed with a special insert suitable for small core plugs with diameter and length of 20 mm. 相似文献
547.
Fernández EJ Laguna A López-de-Luzuriaga JM Monge M Nema M Olmos ME Pérez J Silvestru C 《Chemical communications (Cambridge, England)》2007,(6):571-573
Complex [Au(C6F5)2][Bi(C6H4CH2NMe(2)-2)2] displays the first example of an interaction between Au(I) and Bi(III), the nature of which is shown to be consistent with the presence of a high ionic contribution (79%) and a dispersion type (van der Waals) interaction (21%). 相似文献
548.
549.
This study aims to evidence the influence of polyelectrolytes structure and the number of double layers on the properties
of some new nanostructured architectures formed by layer-by-layer self-assembly of complementary weak polyelectrolytes on
planar surfaces. For this purpose, we used chitosan and poly(allylamine hydrochloride) as polycations, and poly(acrylic acid)
and poly(2-acrylamido-2-methylpropanesulfonic acid–co-acrylic acid) as polyanions. To get a direct image on the polyelectrolyte
multilayers formation and properties, gravimetry, infrared spectroscopy, and atomic force microscopy have been used. The capacity
of the polyions to overcompensate the complementary polyions charges, and thus to influence the swelling degree in water of
thin films, was strongly influenced by the chain structure and flexibility. A special attention was paid to the responsiveness
of the new composite materials to the pH of the swelling environment. 相似文献
550.
Gabriela Sãcãrescu Nicolae Voiculescu Mihai Marcu Liviu Sãcãrescu Rodinel Ardeleanu Mihaela Simionescu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(3):509-516
Abstract Using the well known Wurtz coupling technique, polyhydrosilanes copolymers with diphenyl - and methyl(phenyl) - sequences, were synthesised. This work describes the possibility to maintain stable Si-H group and to obtain in good yields, soluble, high molecular, functional polysilanes. IR, 1-NMR, 13C, UV spectral data, quantitative elemental Si and H (from Si-H) analyses and indirect molecular weight investigation sustain the molecular structure of the copolysilanes. 相似文献