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131.
132.
Summary Cysteamine is proposed as a user-friendly thiol donor with application to the analysis of proanthocyanidins by thiolysis.
Oligomeric proanthocyanidins are potent antioxidants and disease-preventing agents. The efficiency of which depends on their
composition and size. The degree of polymerization of proanthocyanidins is usually estimated by thiolysis then reversedphase
high-performance liquid chromatography. The new derivatization procedure is an alternative to the use of toluene-α-thiol as
thiol donor. In addition to enabling the direct chromatographic analysis of curude material, the amino function introduced
facilitates prior discrimination between terminal and extension flavanoid moieties by means of cation-exchange chromatography. 相似文献
133.
134.
We provide necessary and sufficient conditions for the existence of T-periodic solutions of a system of second-order ordinary differential equations that models the motion of two or three collinear charged particles of the same sign. 相似文献
135.
Simon J. Garden Christopher Glidewell John N. Low Susan A. McWilliam Angelo C. Pinto Janet M. S. Skakle Jose C. Torres James L. Wardell 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(10):1212-1214
In the title compound, C7H7IN2O2, the O atoms of the nitro group are disordered over two sets of sites and there is evidence that the intramolecular I⃛nitro interaction is repulsive. In the crystal structure, there are neither strong hydrogen bonds, nor intermolecular I⃛nitro interactions, nor aromatic π–π-stacking interactions. 相似文献
136.
G. F. Torres del Castillo 《General Relativity and Gravitation》1987,19(7):699-705
The Weyl neutrino equation is integrated in flat space-time assuming that the energy-momentum tensor of the neutrino field vanishes. It is shown that the flux vector of the neutrino field is tangent to a twist-free and shear-free congruence of null geodesics, which is a special Robinson congruence and constitutes a geometrical representation of a null twistor. It is also shown that, conversely, given such a congruence, a ghost neutrino field can be constructed. 相似文献
137.
138.
Gerardo G. Naumis A. Bazán M. Torres R. Quintero-Torres 《Physica B: Condensed Matter》2008,403(18):3179-3184
One of the few examples in which the physical properties of an incommensurable system reflect an underlying higher dimensionality is presented. Specifically, we show that the reflectivity distribution of an incommensurable one-dimensional cavity is given by the density of states of a tight-binding Hamiltonian in a two-dimensional triangular lattice. Such effect is due to an independent phase decoupling of the scattered waves, produced by the incommensurable nature of the system, which mimics a random noise generator. This principle can be applied to design a cavity that avoids resonant reflections for almost any incident wave. An optical analogy, by using three mirrors with incommensurable distances between them, is also presented. Such array produces a countable infinite fractal set of reflections, a phenomena which is opposite to the effect of optical invisibility. 相似文献
139.
P. P. Parekh A. Bari T. M. Semkow M. A. Torres 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(2):321-325
It is imperative to use a leak-proof container for counting liquid sample to prevent contamination of costly gamma detectors. We report in this technical note a sealant that ensures no leak. It is a vinyl adhesive sealant used for household purposes, marketed by Gloucester Co., Inc, Franklin, MA under the trade name of Phenoseal (translucent variety). This sealant was superior to other sealants studied because it cures quickly, peels off easily after counting, and contains no detectable radioactivity. We have thoroughly tested this sealant in our laboratory and successfully employed it in the routine analysis of environmental liquid samples. 相似文献
140.
G. F. Torres Del Castillo 《Letters in Mathematical Physics》1986,12(2):149-155
By using the expressions for the solutions of the Einstein-Maxwell equations in terms of potentials, valid in the case where the spacetime admits a shear-free geodesic null congruence and the electromagnetic field is aligned to it, we show that a pair of complex potentials generates simultaneous perturbations of the gravitational and the electromagnetic fields. We also show that if the background electromagnetic field is null, then the pair of complex potentials is determined by a pair of coupled, linear, second-order differential equations. 相似文献