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排序方式: 共有207条查询结果,搜索用时 15 毫秒
1.
Arman Melkumyan 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):330-349
The problem of electric and acoustic waves diffraction by a half-plane crack in a transversal isotropic piezoelectric medium
is investigated. The crack is assumed to be electric permeable and free of tractions. The so-called “quasi-hyperbolic approximation”
[15] is adopted. Applying Laplace transformations and Wiener–Hopf technique a closed form solution is obtained. By the means
of Cagniard–de Hoop method a detailed dynamic full electroacoustic wavefield’s investigation is conducted. Mode conversion
between electric and acoustic waves, effect of electroacoustic head wave, Bleustein–Gulyaev surface wave and the wavefield
structure depending on the type of the incident wave (acoustic or electric) and its angle of incidence are analyzed in details.
The dynamic field intensity factors at the crack tip depending on the angle of incidence and on time are derived explicitly.
Numerical analysis is presented. 相似文献
2.
Farukh Arjmand Shamima Parveen Mala Chauhan Shaiba Parveen Sartaj Tabassum 《Transition Metal Chemistry》2006,31(2):237-245
New mononuclear and dinuclear complexes [3-hydroxyethyl-1,3,5,8,11pentaazacyclotridecane]copper(II) (1)/nickel(II) (2) perchlorate and O,O ethane bridged bis-copper(II) (3)/nickel(II) (4) macrocycles have been synthesized and characterized by various spectroscopic techniques, viz. i.r., n.m.r., e.p.r., u.v.–vis. and conductance measurements. Spectral data and conductance measurements reveal that all
the complexes are consistent with square-planar geometry and are ionic in nature. The catalytic activity of the dinuclear
Cu(II) complex (3) in the presence of pyrocatechol was determined spectrometrically by monitoring the increase of the o-benzoquinone characteristic absorption band at 25,000 cm−1 with respect to time in DMF saturated with molecular oxygen. The kinetic parameters Vmax (2.8×10−3 M s−1) and KM (1.4×10−3 mm) have been determined by Michaelis–Menten method. Electrochemistry of the dinuclear Cu(II) complex has been studied in the
presence of molecular oxygen with pyrocatechol and without pyrocatechol at a scan rate of 0.1 V s−1 by cyclic voltammetry. On addition of pyrocatechol, complex shows a shift in Epc, Epa and E1/2 values indicating the oxidation of substrate (pyrocatechol). 相似文献
3.
4.
New asymmetric ligands have been synthesized by condensing o-phenylene diamine with CS2 and PhCHO/MeCHO, and their complexes with MnII, CoII, NiII, CuII and ZnII were prepared and characterized by elemental analyses, conductivity measurements, i.r., u.v.–vis., e.p.r. and n.m.r. spectra. The transition metals in the complexes show square planar geometry and are ionic. Photokinetic studies of the DNA-metal complexes [C10H10S4N2Cu](NO3)2 and [C10H10S4N2Ni](NO3)2 were carried out and the rate constants k(DNA-complex) were calculated. The results indicate that DNA reacts with the metal complex in two steps. DNA first undergoes structural degradation and is then completely hydrolysed as indicated by spectral changes consistent with earlier results. The asymmetric N2S2 macrocyclic metal complexes show a strong propensity for DNA inhibition and can be used as an intercalating binding model. 相似文献
5.
A new template-directed chiral porphyrin [(TPP)Co(Trp)], where TPP = tetraphenylporphyrin and Trp = 1-tryptophan, was prepared and characterized by various physico-chemical methods. Interaction of [(TPP)Co(Trp)] with calf thymus DNA was studied by u.v.–vis. spectroscopy and cyclic voltammetry. The complex [(TPP)Co(Trp)], after interaction with calf thymus DNA, shows a shift in the absorption spectrum and a large hypochromicity, indicating an intercalating binding mode. This observation was further confirmed by the electrochemical behavior of [(TPP)Co(Trp)] before and after interaction with calf thymus DNA. The complex experiences a negative shift in E
1/2 and a decrease in E
p. The ratio of cathodic to anodic peak currents i
pc/i
pa was 1 for [(TPP)Co(Trp)] while for DNA bound complex i
pc/i
pa 1, suggesting that the calf thymus DNA moiety is bound strongly to the complex [(TPP)Co(Trp)]. Kinetic studies of the DNA-porphyrin complex reveal a psuedo-first order rate law as the plot of k
obs
versus calf thymus DNA is linear passing through the origin. 相似文献
6.
Shengfei Jin Hang T. Dang Graham C. Haug Viet D. Nguyen Hadi D. Arman Oleg V. Larionov 《Chemical science》2020,11(34):9101
Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.α-Branched carboxylic acids and other carbonyls are readily accessed by a metal- and base-free deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls via boron enolates, resulting in a tricomponent coupling with unconventional electrophiles. 相似文献
7.
8.
Santhosh Govindaraju Sumaiya Tabassum 《Phosphorus, sulfur, and silicon and the related elements》2017,192(3):292-299
Silica iodide catalyzed, competent synthesis of 15 novel substituted-1,4,5,6-tetrahydropyridine-3-carboxylate derivatives was achieved by a one-pot four-component cyclocondensation of Meldrum's acid, aryl aldehydes, aromatic amines and ethyl acetoacetate under ultrasonic irradiation. In comparison to the conventional methods, our protocol is convenient, eco-friendly and offers several benefits such as: mild conditions, high yields, shorter reaction time and ease in product isolation. 相似文献
9.
An efficient stereoselective three-component reaction for the synthesis of functionalized spiro[4H-pyran-3,3′-oxindole] derivatives was realized through an organocatalyzed domino Knoevenagel/Michael/cyclization reaction using a cinchonidine-derived thiourea as the catalyst. Using water as the additive was found to improve the product ee values significantly. Under the optimized conditions, the reactions between isatins, malononitrile, and 1,3-dicarbonyl compounds yield the desired spirooxindole products in good yields (71–92%) and moderate to high ee values (up to 87% ee). 相似文献
10.
A novel scheme for pressure fluctuations in turbulent flows is developed. The pressure fluctuations are sensitive parameter in some of the fluid phenomena. In the computational methods and modeling turbulence flow, the pressure fluctuations are eliminated after averaging of the Navier-Stokes equations, and only average pressure could be calculated. In this research, the Reynolds-averaged Navier-Stokes equations are computed using SIMPLE method. The Reynolds stress transport model (RSTM) is used to determine the Reynolds stresses and the flow details. The velocity fluctuations are simulated using the Kraichnan model. The Poisson equation for the pressure fluctuations is obtained by taking the divergence of the incompressible momentum equation and algebraic operations, and this equation is numerically solved by finite difference method. The effects of Reynolds number on the pressure fluctuations are studied. 相似文献