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排序方式: 共有424条查询结果,搜索用时 31 毫秒
131.
132.
Sushobhan Chowdhury Tanmoy Chanda Suvajit Koley B. Janaki Ramulu Keshav Raghuvanshi Maya Shankar Singh 《Tetrahedron》2014
β-Allyl-β-hydroxy dithioesters have been employed in the synthesis of hitherto unreported and synthetically demanding 2H-thiopyrans via regioselective intramolecular annulation strategy. Lewis acid BF3·Et2O efficiently mediates the regioselective dehydration followed by intramolecular thioannulation at room temperature. The attractive features of this protocol include mild conditions, high atom-economy and excellent yields with the elimination of water as the only by-product. 相似文献
133.
Grassberger P Christensen C Bizhani G Son SW Paczuski M 《Physical review letters》2011,106(22):225701
We study four Achlioptas-type processes with "explosive" percolation transitions. All transitions are clearly continuous, but their finite size scaling functions are not entirely holomorphic. The distributions of the order parameter, i.e., the relative size s(max)/N of the largest cluster, are double humped. But-in contrast to first-order phase transitions-the distance between the two peaks decreases with system size N as N(-η) with η>0. We find different positive values of β (defined via (s(max)/N)~(p-p(c))β for infinite systems) for each model, showing that they are all in different universality classes. In contrast, the exponent Θ (defined such that observables are homogeneous functions of (p-p(c))N(Θ)) is close to-or even equal to-1/2 for all models. 相似文献
134.
Ran Y. Suckeveriene Ron Rahman Maya Ovadia Daniela Szczupak Guy Mechrez Moshe Narkis 《先进技术聚合物》2014,25(1):4-8
This paper describes a study on emulsifier‐free ultrasonically assisted in‐situ copolymerization method of acrylamide and styrene in the presence of CNT, resulting in stable and uniform dispersions. The dispersions prepared were found stable for several months. Thermogravimetric analysis (TGA) curves and conversion measurements provided an insight regarding the polymerization mechanism and the nanocomposites structure. Films prepared of the polymerization products resulted in some clear and transparent coatings. The polymerization method described is simple and very fast compared with the other literature reported methods. TGA was extensively used as an analytical tool for determination of the composition of acrylamide–styrene copolymers. TGA and differential scanning calorimetry indicate that the polymerization product is largely a poly(styrene‐co‐acrylamide), where the acrylamide fraction is attached to the CNT surfaces. The copolymer produced, with and without CNT, is essentially a block copolymer, where each block contains small amounts of the other comonomer. To the authors' best knowledge, this report is the first one describing the production of stable dispersions of CNT in surfactant‐free poly(styrene‐co‐acrylamide) emulsion. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
135.
Maya L. Chen C.H. Stevenson K.A. Kenik E.A. Allman S.L. Thundat T.G. 《Journal of nanoparticle research》2002,4(5):417-422
Batches of water-soluble gold nanoclusters of nominal 2.0 or 3.5-nm diameter were prepared to evaluate particle size determinations by a number of techniques such as transmission electron microscopy or atomic force microscopy and to validate estimates derived by mass spectrometric analysis using matrix-assisted laser desorption ionization (MALDI). Good agreement was found and MALDI lends itself to analyses even in the presence of aggregates. 相似文献
136.
A well‐known conjecture of Erd?s states that given an infinite graph G and sets A, ? V(G), there exists a family of disjoint A ? B paths ?? together with an A ? B separator X consisting of a choice of one vertex from each path in ??. There is a natural extension of this conjecture in which A, B, and X may contain ends as well as vertices. We prove this extension by reducing it to the vertex version, which was recently proved by Aharoni and Berger. © 2005 Wiley Periodicals, Inc. J Graph Theory 50: 199–211, 2005 相似文献
137.
Roberto Martínez Rubn C. Espinosa Rubn A. Toscano J. Antonio Cogordn María Del Rosario Arellano Enrique Angeles María Eugenia Posada Beatriz Maya Luisa Martínez 《Journal of heterocyclic chemistry》1996,33(3):715-718
With the aim to find new compounds with superior tranquilizer-antidepressant activity theoretical studies, synthesis, X-ray characterization and pharmacological test of the title compound were carried out. Theoretical studies suggested both tranquilizer and antidepressant activity and pharmacological tests proved it. 相似文献
138.
M.?ElzainEmail author A.?Gismelseed A.?Al-Rawas A.?Yousif H.?Widatallah Maya?Al-Azri M.?Al-Barwani 《Hyperfine Interactions》2016,237(1):8
The hyperfine properties at Fe site in iron-gallium alloy are calculated using the full-potential linear-augmented-plane-waves method. We have calculated the Fermi contact field (Bhf) and isomer shift (δ) at the Fe site versus the number of neighbouring Ga atoms. We found that Bhf decrease whereas δ increases with increasing number of neighbouring G atom. In addition we have calculated the hyperfine properties of FeGa system with DO3 structure, where various distributions of 4 the Ga atoms in the conventional unit cell are considered (including the regular DO3 structure). We found that the DO3 structure has the lowest energy as compared to the other configurations. The two distinct A and D sites of the ordered DO3 conventional unit cell have two distinct values for Bhf and δ. On changing the atomic arrangement of the Ga atoms within the conventional unit cell, the configuration of the A site is maintained whereas that of the D site becomes imperfect. The contact magnetic hyperfine fields of the D-like sites in the imperfect structures are lower than that of the DO3D site. 相似文献
139.
Spectrophotometric determination of chloride in waters using a multisyringe flow injection system 总被引:1,自引:0,他引:1
A multisyringe flow injection system (MSFIA) with spectrophotometric detection is proposed as a fast, robust and low-reagent consumption system for the determination of chloride (Cl−) in waters. The system is based in the classic reaction of Cl− with Fe3+ and Hg(SCN)2, but due to the hazardous properties of this last reagent, the proposed methodology has been developed with the aim to minimize the consumption of this one, consuming less than 0.05 mg of Hg for a Cl− determination, being the system of this type with the lowest Hg consumption. The linear working range was between 1 and 40 mg L−1 Cl− and the detection limit was 0.2 mg L−1 Cl−. The repeatability (RSD) was 0.8% for a 10 mg L−1 Cl− solution, and the injection throughput was 130 h−1. The proposed system is compared with other chloride monitoring flow systems, this comparison is realized with a point of view of the equilibrium between the obtained analytical features and produced residues toxicity. The proposed system was applied to the determination of Cl− in mineral, tap and well water. 相似文献
140.
Sarkar P Bharill S Gryczynski I Gryczynski Z Nair MP Lacko AG 《Journal of photochemistry and photobiology. B, Biology》2008,92(1):19-23
The solvatochromic fluorescent probe 8-anilino-1-naphthalenesulfonate (ANS) has been used to study the hydrophobicity and conformational dynamics of lecithin:cholesterol acyltransferase (LCAT). The ANS to LCAT binding constant was estimated from titrations with ANS, keeping a constant concentration of LCAT (2 microM). Apparent binding constant was found to be dependent on the excitation. For the direct excitation of ANS at 375 nm the binding constant was 4.7 microM(-1) and for UV excitation at 295 nm was 3.2 microM(-1). In the later case, not only ANS but also tryptophan (Trp) residues of LCAT is being excited. Fluorescence spectra and intensity decays show an efficient energy transfer from tryptophan residues to ANS. The apparent distance from Trp donor to ANS acceptor, estimated from the changes in donor lifetime was about 3 nm and depends on the ANS concentration. Steady-state and time-resolved fluorescence emission and anisotropies have been characterized. The lifetime of ANS bound to LCAT was above 16 ns which is characteristic for it being in a hydrophobic environment. The ANS labeled LCAT fluorescence anisotropy decay revealed the correlation time of 42 ns with a weak residual motion of 2.8 ns. These characteristics of ANS labeled LCAT fluorescence show that ANS is an excellent probe to study conformational changes of LCAT protein and its interactions with other macromolecules. 相似文献