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排序方式: 共有211条查询结果,搜索用时 171 毫秒
111.
M. Rafi M. Latif S. Mahmood I. A. Khan M. R. Husain 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,25(2):153-156
The absorption spectra of Bi2 molecule has been obtained in the region 3166–3380 Å in the second order of a 3.4 m Ebert Spectrograph with a reciprocal dispersion of 2.6 Å/mm. The bands obtained are found to belong to two new systems named G-X and J-X. Vibrational analysis is performed and computer methods have been used to determine the molecular constants. 相似文献
112.
Fawi M. Abd El Latif Eman A. El Rady Dietrich Dupp 《Journal of heterocyclic chemistry》2003,40(1):57-60
Ethyl 2‐cyano‐3‐(5‐chloro‐1,3‐diphenylpyrazol‐4‐yl)acrylate ( 1 ) undergoes both conjugate addition of a number of methylene‐active ethanenitriles and direct addition of other active methylene donors to the cyano carbon atom. These additions are the starting events of cascades of subsequent reactions eventually forming (i) novel polyfunctional pyrazolyl‐substituted monocyclic pyridines ( 4a , b and 6 ), (ii) 1,3‐benzothiazole and benzimidazole‐fused pyridines ( 11, 13 ) and (iii) pyrazolo[5,4‐b]pyridines ( 19b, 20 ) in one‐pot reactions in ethanolic solution containing catalytic amounts of piperidine. 相似文献
113.
Changes in the structure of nylon 6 fibers annealed in dry and wet atmospheres were studied by small-and wide-angle x-ray diffraction. In the presence of water or saturated steam, fibers can be annealed to the same strucutral state at temperatures 70°C lower than in dry atmosphere. This is due to the enhanced mobility of the molecular segments in the amorphous region, a mechanism which is also known to lower the Tg by the same amount. Upon annealing under unconstrained conditions, lamellar spacing, crystallite size in the equatorial plane, crystalline as well as fiber density, and the chain-axis repeat increase with annealing-temperature; whereas crystalline orientation and the Van der Waals separation of the hydrogen-bonded sheets decrease. The monoclinic angle 8 remains constant at 66.7° (σ = 0.3°) and might depend on the starting fiber rather than on the treatment of the fiber. Most of these changes occur above a critical temperature of 170°C if dry, or 100°C if wet; rate of crystallization is also the highest under these conditions in nylon. The effect of these changes on such fiber properties as dyeing and the role of micro voids in dye diffusion and in dye uptake are discussed. Surface premelting and the accompanying changes in the surface structure of the lamellae, selective melting, and more importantly, the longitudinal motion of the nylon 6 chains and the resulting folding of interfibrillar extended amorphous chains are invoked to explain the shrinkage of the fiber, disorientation of the crystallites, increase in crystalline perfection, and the increase in lamellar spacing. 相似文献
114.
Minimization of the auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene
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Andrey E. Rudenko Alia A. Latif Barry C. Thompson 《Journal of polymer science. Part A, Polymer chemistry》2015,53(12):1492-1499
In this work, we present a powerful set of synthetic strategies aimed at minimization of auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene. As such, we report efficient lowering of Pd(OAc)2 catalyst loading as well as loading of other auxiliary reagents, such as neodecanoic acid and N,N‐dimethylacetamide. Unprecedented low loadings of catalyst down to 0.0313% (313 ppm) were achieved, while producing polymer in high yield (91% after Soxhlet extraction), with a high molecular weight (24.2 kDa) and carefully controlled chemical structure thus making the optimized DArP protocol significantly more cost‐effective, convenient, sustainable, and environmentally friendly. The resulting polymer samples were thoroughly investigated in terms of their chemical structure as well as optical, thermal, chain ordering and electronic properties using GPC analysis, 1H NMR, MALDI, UV–vis, GIXRD spectroscopy, DSC, and SCLC hole mobility measurements. The results demonstrate that the reagent lowering strategies increase the polymer regioregularity from 94.6 to 96.5% as evidenced by 1H NMR spectra and corroborated by GIXRD, DSC, and UV–vis measurements. Additionally, polymer samples obtained at low reagent loading are more uniformly proton‐terminated as evidenced by 1H NMR and MALDI end‐group analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1492–1499 相似文献
115.
Jonathan Breuer Sergey Denisov Latif Eliaz 《Mathematical Physics, Analysis and Geometry》2018,21(4):33
It is known that the essential spectrum of a Schrödinger operator H on \(\ell ^{2}\left (\mathbb {N}\right )\) is equal to the union of the spectra of right limits of H. The natural generalization of this relation to \(\mathbb {Z}^{n}\) is known to hold as well. In this paper we generalize the notion of right limits to general infinite connected graphs and construct examples of graphs for which the essential spectrum of the Laplacian is strictly bigger than the union of the spectra of its right limits. As these right limits are trees, this result is complemented by the fact that the equality still holds for general bounded operators on regular trees. We prove this and characterize the essential spectrum in the spherically symmetric case. 相似文献
116.
Disperse Dyes Based on 5‐Arylazo‐thiazol‐2‐ylcarbamoyl‐thiophenes: Synthesis,Antimicrobial Activity and Their Application on Polyester
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A series of novel 5‐arylazo‐thiazol‐2‐ylcarbamoyl‐thiophene derivatives was synthesized, and their chemical structures were secured by elemental and spectroscopic analyses. Their versatility for pharmaceutical purposes and textile dyeing as disperse dyes were reported. The synthesized dyes were applied to polyester fabrics by using high temperature dyeing method at 130°C. The dyed polyester fabrics displayed very good washing and perspiration fastness and moderate light fastness. Finally, the synthesized compounds showed biological activities against Bacillus subtilis, Staphylococcus aureus (Gram positive bacteria), Escherichia coli, and Pseudomonas aeruginosa (Gram‐negative bacteria), while no effect had been reported against fungi. The minimum inhibitory concentration of the most active compound was evaluated. 相似文献
117.
Abbas Sayadi-bander Latif Pourkarimi Refail Kasimbeyli Hadi Basirzadeh 《Journal of Global Optimization》2017,69(3):587-606
In multi-parametric programming an optimization problem is solved as a function of certain parameters, where the parameters are commonly considered to be bounded and continuous. In this paper, we use the case of strictly convex multi-parametric quadratic programming (mp-QP) problems with affine constraints to investigate problems where these conditions are not met. Based on the combinatorial solution approach for mp-QP problems featuring bounded and continuous parameters, we show that (i) for unbounded parameters, it is possible to obtain the multi-parametric solution if there exists one realization of the parameters for which the optimization problem can be solved and (ii) for binary parameters, we present the equivalent mixed-integer formulations for the application of the combinatorial algorithm. These advances are combined into a new, generalized version of the combinatorial algorithm for mp-QP problems, which enables the solution of problems featuring both unbounded and binary parameters. This novel approach is applied to mixed-integer bilevel optimization problems and the parametric solution of the dual of a convex problem. 相似文献
118.
Siddiqui HL Zia-Ur-Rehman M Ahmad N Weaver GW Lucas PD 《Chemical & pharmaceutical bulletin》2007,55(7):1014-1017
Different dimeric disulfides, having the basic skeleton of bis[2-amino-4-phenyl-5-thiazolyl] disulfides were synthesized in a straightforward manner from acetophenones. 2-Amino-4-phenyl-1,3-thiazoles were prepared by the reaction of thiourea with substituted acetophenones in the presence of iodine which were then converted to the title compounds. All the compounds were subjected to preliminary evaluation for their biological activity against Gram positive and Gram negative bacteria. Some of the assayed compounds showed marked activity against Bacillus cereus and Pseudomonas aeruginosa. 相似文献
119.
DURAN Celal SENTURK H. Basri GUNDOGDU Ali BULUT V. Numan ElCi Latif SOYLAK Mustafa TUFEKCI Mehmet UYGUR Yaprak 《中国化学》2007,25(2):196-202
A procedure for preconcentration of Mn(Ⅱ), Fe(Ⅱ), Co(H), Cu(Ⅱ), Cd(Ⅱ), Zn(Ⅱ), Pb(Ⅱ) and Ni(Ⅱ) based on retention of their complexes with 8-hydroxyquinoline (HQ) on Amberlite XAD-2000 resin in a column was proposed for the analysis of environmental samples by flame AAS. Various parameters such as pH, eluent type, volume, concentration, flow rate and volume of sample solution, and matrix interference effect on the retention of the metal ions were investigated. The optimum pHs for the retention of metal complexes in question were about 6 except for Mn^2+ for whose value is 8. The loading capacity of the adsorbent for these metals and their recoveries from the resin under the optimum conditions were in the range 6.82-9.26 mg·g^-1 and 95%-101%, respectively. The enrichment factor was calculated as 100 and the limit of detection was in the range 0.3-2.2 μg·L^-1 (n=20, blank+ 3s). The proposed enrichment method was applied to tap water, stream water and vegetable samples. The validation of the procedure was carried out by analysis of certified reference material and standard addition. The analytes were determined with a relative standard deviation lower than 6% in all samples. 相似文献
120.