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131.
Costas D. Apostolopoulos Minas P. Georgiadis Elias A. Couladouros 《Journal of heterocyclic chemistry》1996,33(3):703-708
A new procedure for the efficient synthesis of 1,4-piperazinones, 1,4-thiazinones and 1,4-diazepinones is presented. The reaction is based on a ring chain transformation of γ-keto-δ-crotonolactones induced by 1,2- or 1,3-diamino- (or thiamino-) binucleophiles. The reaction sequence of this transformation is also discussed. 相似文献
132.
133.
Nine pairs of isomeric 2,4,6-tris(halophenyl)-1,3,5-trithianes have been assayed in the crude state by n.m.r. techniques, and separated and purified by chromatography. Contrary to previous reports, the α-(cis, trans)-isomers are the major products in most cases. These compounds are shown to exist as puckered chair trithiane structures, even in the more hindered α-(cis, trans)-o-halophenyl cases, by the clear resolution of axial and equatorial trithiane ring protons in a ratio of 2:1. An o-halogen on an axial phenyl group in the α-isomers causes the aromatic group to exert an anisotropic deshielding effect on adjacent axial protons, so as to cause the axial and equatorial proton peaks to appear as a singlet in some solvents. Melting point differences, in several cases quite large, from those previously reported have been observed for six of the eighteen triaryltrithianes reported. 相似文献
134.
Maria Ochsenkühn-Petropulu Irene Vottea Rachel Argyropulu Leonidas Mendrinos Klaus-Michael Ochsenkühn 《Mikrochimica acta》1999,130(4):289-294
Coatings of the high-temperature superconductor YBa2Cu3O7–x (x = 0.1–0.2) (YBCO), were deposited on commercial Ni,Ti and stainless steel substrates, by an electrophoretic deposition technique. Sintering and annealing procedures were followed in order to get strongly adherent superconducting films. The suitability of the used substrates was tested by measuring the stoichiometry and the superconducting properties of the deposited coatings by X-ray diffraction analysis (XRD), Raman spectroscopy and magnetization measurements with a superconducting quantum interference device (SQUID). 相似文献
135.
136.
In this paper, the method of reflected caustics—which was used to evaluate Mode III SIF's in stationary cracks in isotropic plates—was extended to deal with stationary cracks in orthotropic plates. Furthermore, a correspondence between the anisotropic stationary case and the case of a Mode III dynamic crack, traversing an isotropic plate, is developed by analyzing appropriately the governing equations of the two problems. For this purpose the singulardisplacement field for rectilinearly orthotropic cracked bodies was combined with either Yoffé's model for steady-state, or Broberg's model for transient-crack propagation. Graphs are given where the equivalence between these cases can be established. In this way, the dynamic problem of the propagating crack in an isotropic medium can be readily simulated by considering the experimentally easier anisotropic stationary case. 相似文献
137.
Violetta Constantinou-Kokotou Elias A. Couladouros Minas P. Georgiadis George Kokotos 《Journal of carbohydrate chemistry》2013,32(5):749-756
ABSTRACT A simple and effective procedure for the resolution of 2,3-dideoxy-DL-2-enopyranos-4-uloses is presented. This procedure is based on column chromatographic separation of their diastereomeric O-(N-tert-butyloxycarbonyl)-L-alanyl esters, followed by mild acidic cleavage of the ester function. L-Aculose, 2,3,6-trideoxy-L-glycero-hex-2-enopyranos-4-ulose, is also prepared in satisfactory yield. 相似文献
138.
Leonidas Guibas Dmitriy Morozov Quentin Mérigot 《Discrete and Computational Geometry》2013,49(1):22-45
Distance functions to compact sets play a central role in several areas of computational geometry. Methods that rely on them are robust to the perturbations of the data by the Hausdorff noise, but fail in the presence of outliers. The recently introduced distance to a measure offers a solution by extending the distance function framework to reasoning about the geometry of probability measures, while maintaining theoretical guarantees about the quality of the inferred information. A combinatorial explosion hinders working with distance to a measure as an ordinary power distance function. In this paper, we analyze an approximation scheme that keeps the representation linear in the size of the input, while maintaining the guarantees on the inference quality close to those for the exact but costly representation. 相似文献
139.
Kalliopi Miliou Leonidas N. Gergidis Costas Vlahos 《Journal of polymer science. Part A, Polymer chemistry》2020,58(13):1757-1770
The conformation and the internal stratification of mixed brushes formed from oppositely charged Y(−) and Y(+)-shaped chains in salt free, monovalent, and divalent salt solutions were studied by means of molecular dynamics simulations using the primitive model. Scaling relations of mixed brush height with respect to the grafting surface per chain, the ratio of the total positive to the total negative charge of polyelectrolyte chains, and salt concentrations were obtained. The simulations predicted that mixed brushes show a unique response to divalent salt (1:2) solutions. For symmetric brushes having the same spacer lengths, number of chains and charged units fractions the increase of the salt concentration leads to the enrichment of the outer brush surface with Y(+) units and the lamella microphase separation. For asymmetric brushes in high salt concentration cylindrical domain microphases are formed. 相似文献
140.
Reconstruction Using Witness Complexes 总被引:1,自引:1,他引:0
We present a novel reconstruction algorithm that, given an input point set sampled from an object S, builds a one-parameter family of complexes that approximate S at different scales. At a high level, our method is very similar in spirit to Chew’s surface meshing algorithm, with one
notable difference though: the restricted Delaunay triangulation is replaced by the witness complex, which makes our algorithm
applicable in any metric space. To prove its correctness on curves and surfaces, we highlight the relationship between the
witness complex and the restricted Delaunay triangulation in 2d and in 3d. Specifically, we prove that both complexes are
equal in 2d and closely related in 3d, under some mild sampling assumptions. 相似文献