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31.
Ramírez-López P de la Torre MC Asenjo M Ramírez-Castellanos J González-Calbet JM Rodríguez-Gimeno A de Arellano CR Sierra MA 《Chemical communications (Cambridge, England)》2011,47(37):10281-10283
Reported herein is the discovery of a novel family of "clicked" estradiol-based LMWGs whose gelation ability highly depends on the gelator symmetry. These LMWGs that gel different organic solvents in the presence of H(2)O even at concentrations as low as 0.04 wt% are readily accessible using "click" chemistry. 相似文献
32.
Palacios D Wladimirsky A D'Antonio MC González-Baró AC Baran EJ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):1145-1148
The infrared and Raman spectra of Na2Cu(C2O4)(2)·2H2O, K2Cu(C2O4)(2)·2H2O and (NH4)2Cu(C2O4)(2)·2H2O were recorded and briefly discussed on the basis of their structural peculiarities and by comparison with the vibrational spectra of other metallic oxalates. 相似文献
33.
Low-frequency conductivity measurements have been performed in solid polymer electrolyte composites based on the anhydrous PVOH–LiH2PO4–Al2O3 system. A typical power law dependency in the real part of the conductivity, at higher frequencies, of the form ω n is observed, with an exponent n that depends on the alumina content and nearly independent of temperature. An analysis of the frequency dependence of the electrical susceptibility is conducted to obtain relaxation functions of the form exp[?(t/τ) β ], with an exponent β?≈?n???1. Correlation times, τ, and parameters characterizing the electrical relaxation in time and frequency domains are compared to show the equivalence of these representations. The anhydrous dc conductivity of the electrolytes increases with increasing lithium salt content, becoming of the order of 10?5 S/cm for a salt molar fraction of x?=?0.14. This conductivity value increased by about one order of magnitude by addition of nanoporous particles of Al2O3. The temperature dependence of the samples conductivity was well described by the Vogel–Tammann–Fulcher’s equation indicating the effect of the polymer chains flexibility on ion migration. Although all membranes exhibited a “universal dynamic response” associated to the random hopping of the mobile carriers, variations in the measured relaxation parameters with alumina content indicate an increase of ionic correlations when adding the nonporous particles to the polyelectrolyte. 相似文献
34.
José A. Zapata 《General Relativity and Gravitation》1998,30(8):1229-1245
The canonical quantization of diffeomorphism invariant theories of connections in terms of loop variables is revisited. Such theories include general relativity described in terms of Ashtekar-Barbero variables and extension to Yang-Mills fields (with or without fermions) coupled to gravity. It is argued that the operators induced by classical diffeomorphism invariant or covariant functions are respectively invariant or covariant under a suitable completion of the diffeomorphism group. The canonical quantization in terms of loop variables described here, yields a representation of the algebra of observables in a separable Hilbert space. Furthermore, the resulting quantum theory is equivalent to a model for diffeomorphism invariant gauge theories which replaces space with a manifestly combinatorial object. 相似文献
35.
Marcos Ghislandi Luis Antonio Sanchez de A. Prado Alejandra de la Vega Oyerviedes Hans Wittich Karl Schulte Ana Barros‐Timmons 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3326-3335
Vapor‐grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (t‐BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert‐butyl acrylate) (poly(t‐BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t‐BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326–3335, 2008 相似文献
36.
Silvia Jerez Galiano Miguel Uh Zapata 《Journal of Computational and Applied Mathematics》2010,234(5):1395-1403
We develop a new flux-limiter method based on the Richtmyer two-step Lax-Wendroff (R2LW) method coupled with a conservative upwind method and a nonconventional flux-limiter function. The proposed method is TVD stable and preserves the linear stability condition of the R2LW method. The numerical results show that this method improves on the approximations obtained by standard first-order and second-order TVD schemes. The new method provides accurate results for nonlinear hyperbolic equations with discontinuous solutions. 相似文献
37.
The cycloaddition reactions of 9-substituted anthracenes and levoglucosenone were investigated under microwave irradiation and conventional heating conditions. Considering time, yields, and regioselectivity, microwave technology has proven to be an ideal tool to achieve this chemical transformation. [reaction: see text]. 相似文献
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Gustavo Corach Alejandra Maestripieri 《Numerical Functional Analysis & Optimization》2013,34(6):659-673
A generalization with singular weights of Moore–Penrose generalized inverses of closed range operators in Hilbert spaces is studied using the notion of compatibility of subspaces and positive operators. 相似文献