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91.
92.
Ashraf A. Sediek Abeer A. Shaddy Wafaa M. Abdou 《Journal of heterocyclic chemistry》2011,48(6):1258-1263
A new and efficient conjugate addition of trimethyl and triethyl phosphites to 3‐ω‐azidoacetylcoumarin ( 1 ) has been studied. The reaction proceeded smoothly at r.t. furnishing 1,2,3,4‐triazaphosphole coumarin derivatives 4a , 4b in ~75% yields. Linear substituted triazoles 10b , 11a were also obtained from the reactions of 1 with α‐keto ylides, acetyl‐ and benzoylmethylene triphenylphosphoranes. Contrary to these results, Wittig reaction was occurred when 1 was allowed to react with α‐alkoxycarbonylmethylene‐ and cyanomethylenetriphenylphosphoranes 7c , 7d , 7e as well as with methylidene‐ and benzylidenetriphenylphosphoranes 8b , 10a resulting in the formation of the corresponding olefins either as an intermediate 14b or as final products 11b , 11c , 12a . J. Heterocyclic Chem., (2011). 相似文献
93.
Abdou M. Abdel‐Rehim Ronald B. Morgan Walter Wilcox 《Numerical Linear Algebra with Applications》2014,21(3):453-471
We consider symmetric positive definite systems of linear equations with multiple right‐hand sides. The seed conjugate gradient (CG) method solves one right‐hand side with the CG method and simultaneously projects over the Krylov subspace thus developed for the other right‐hand sides. Then the next system is solved and used to seed the remaining ones. Rounding error in the CG method limits how much the seeding can improve convergence. We propose three changes to the seed CG method: only the first right‐hand side is used for seeding, this system is solved past convergence, and the roundoff error is controlled with some reorthogonalization. We will show that results are actually better with only one seeding, even in the case of related right‐hand sides. Controlling rounding error gives the potential for rapid convergence for the second and subsequent right‐hand sides. Polynomial preconditioning can help reduce storage needed for reorthogonalization. The new seed methods are applied to examples including matrices from quantum chromodynamics. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
94.
Abdou O. Abdelhamid Mamdouh A. M. Afifi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2703-2713
2-[1,2-Diaza-3-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))prop-2-enylidene]-3-phenyl-5-substituted 1,3,4-thiadiazolines and 2-{[4-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]cyanomethylene}-3-phenyl-5-substitu- ted 1,3,4-thiadiazolines were synthesized from hydrazonoyl halides and 4-{-2-aza-2-[(methylthiothioxomethyl)amino]vinyl}-2,3-dimethyl-1-phenyl-3-pyrazoin-5-one and 2-[4-(2,3-dimethyl-5-oxo-1-phenyl-3-pyrazolin-4-yl)-1,3-thiazol-2-yl]ethane-nitrile, respectively. All synthesize compounds were elucidated by elemental analysis, spectra, and alternative synthesis routes, whenever possible. 相似文献
95.
An efficient approach to a new series of benzothiazaphosphepines and their derived phosphonates in good yields (64–75%) was reported. The strategy relied on the reactions of the easily available 2-arylmethylene-aminobenzenethiols with different types of Wadsworth–Horner–Emmons (WHE) reagents in dimethylformamide (DMF)/lithium hydride (LiH) solution. All new compounds were bioscreened and showed, in vitro, moderate to good antioxidant and antidiabetic activities. 相似文献
96.
Water-in-oil emulsion drops are formed and stabilized with phospholipids which can adhere and form a bilayer. Using microfluidics, adhesive drop pairs are then trapped and submitted to an ac electric field. We observe three distinct states as a function of the adhesion energy and the electric field intensity. The pair can be either stable, though slightly deformed, or unzip and separate, or coalesce. The frontiers between the different states directly reflect vesicle detachment forces and electroporation theories. The experimental approach that we propose for probing liquid interface wetting between monolayers allows us to finely tuned the tension in the bilayer and gives access to bilayer unzipping. 相似文献
97.
AbstractFungal endophytes are considered promising sources of new bioactive natural products. In this study, a Mucor sp. has been isolated as an endophyte from the medicinal plant Centaurea stoebe. Through bioactivity-guided fractionation, the isolation of the new bioactive terezine E in addition to the previously reported 14-hydroxyterezine D was carried out. The isolated compounds were fully characterised by HRESIMS and 1D and 2D NMR analyses. Both compounds exhibited potent antiproliferative activity against K-562 and HUVEC cell lines and antifungal efficacy against the tested fungal strains. 相似文献
98.
M. A. Abdou S. A. Mahmoud M. A. Darwish 《Journal of Applied Mathematics and Computing》1998,5(2):251-258
The numerical method is used to solve the Fredholm integral equation of the second kind with weak singular kernels using the Toeplitz matrices. The solution has a computing time requirement ofO(N 2), where 2N + 1 is the number of discretization points used. Also, the error estimate is computed. Some numerical examples are computed using the MathCad package. 相似文献
99.
Math search is a new area of research with many enabling technologies but also many challenges. Some of the enabling technologies
include XML, XPath, XQuery, and MathML. Some of the challenges involve enabling search systems to recognize mathematical symbols
and structures. Several math search projects have made considerable progress in meeting those challenges. One of the remaining
challenges is the creation and implementation of a math query language that enables the general users to express their information
needs intuitively yet precisely. This paper will present such a language and detail its features. The new math query language
offers an alternative way to describe mathematical expressions that is more consistent and less ambiguous than conventional
mathematical notation. In addition, the language goes beyond the Boolean and proximity query syntax found in standard text
search systems. It defines a powerful set of wildcards that are deemed important for math search. These wildcards provide
for more precise structural search and multi-levels of abstractions. Three new sets of wildcards and their implementation
details will also be discussed.
相似文献
100.
Sayed A. Ahmed Ahmed M. Hussein Walaa G. M. Hozayen Ahmed H. H. El‐Ghandour Abdou O. Abdelhamid 《Journal of heterocyclic chemistry》2007,44(4):803-810
Pyrazolo[1,5‐a]pyrimidines were synthesized from the appropriate 3‐aminopyrazoles with the appropriate sodium (3‐oxocycloalkylidene)methenolate, β‐diketone, β‐keto esters or 1,2‐disubstituted acrylonitrile. Elemental analyses, spectral data, alternative synthesis route and X‐ray elucidated structures of the newly synthesized compounds. 相似文献