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Wide-angle one-way wave equations 总被引:3,自引:0,他引:3
A one-way wave equation, also known as a paraxial or parabolic wave equation, is a differential equation that permits wave propagation in certain directions only. Such equations are used regularly in underwater acoustics, in geophysics, and as energy-absorbing numerical boundary conditions. The design of a one-way wave equation is connected with the approximation of (1-s2)1/2 on [-1,1] by a rational function, which has usually been carried out by Padé approximation. This article presents coefficients for L2, L infinity, and other alternative classes of approximants that have better wide-angle behavior. For theoretical results establishing the well posedness of these wide-angle equations, see the work of Trefethen and Halpern ["Well-posedness of one-way wave equations and absorbing boundary conditions," Math. Comput. 47, 421-435 (1986)]. 相似文献
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Marc Halpern Yoel Sasson Itamar Willner Mordecai Rabinovitz 《Tetrahedron letters》1981,22(18):1719-1722
The effects of water molecules and quat structure are shown to be significant in determining the behavior of alkylation reactions of weakly acidic carbon acids under PTC/OH? conditions. 相似文献
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The emission Mössbauer spectra of 125I labeled iodobenzene, methyl iodide, and of their dilute solutions in benzene and hexane, were computer analyzed. Two species were observed, in one of which tellurium is presumably attached to two organic moieties, while in the other, tellurium is attached to a single organic moiety. 相似文献
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Tsai P Ichikawa K Mailer C Pou S Halpern HJ Robinson BH Nielsen R Rosen GM 《The Journal of organic chemistry》2003,68(20):7811-7817
Apparent rate constants, at acidic pH and neutral pH for the reaction of a family of ester-containing 5-carboxyl-5-methyl-1-pyrroline N-oxides with superoxide (O2*-) were estimated, using ferricytochrome c as a competitive inhibitor. It was of interest to note that the rate constants were similar among the different nitrones and not that significantly different from that found for 5-(diethoxyphosphoryl)-5-dimethyl-1-pyrroline N-oxide. At acidic pH, the rate constant for spin trapping O2*- was 3-fold greater than that at physiological pH. Subsequent experiments determined the half-life of aminoxyls, derived from the reaction of these nitrones with O2*-. The EPR spectra were modeled by using a global analysis method. The results clearly demonstrated that EPR spectra of all the aminoxyls were inconsistent with a model that included a single gamma-hydrogen splitting. A better interpretation modeled them as two diastereomers with identical nitrogen splittings and slightly different beta-hydrogen splittings. Detailed line width analyses slightly favored an equal line width-unequal population ratio for the two diastereomers. 相似文献
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M. Mikoŀajczyk J. Michalski A. Halpern R. Sochaxcka 《Monatshefte für Chemie / Chemical Monthly》1969,100(4):1266-1273
Zusammenfassung An den Modellverbindungen Dialkylchlorthiophosphat (RO)2P(S)Cl (R=Me, Et, n-Pr) und Diphenylchlorthiophosphat (PhO)2P(S)Cl wurde der Austausch Chlorid—Radiochlorid am Thiophosphorylzentrum untersucht. Die bimolekularen Geschwindigkeitskonstanten, die Aktivierungsenergien und Aktivierungsentropien wurden berechnet. Der Einfluß von Substituenten auf bimolekulare Substitutionsreaktionen am vierfach koordinierten Phosphoratom wurde diskutiert.
Mit 3 Abbildungen 相似文献
Chlorine isotopic exchange at phosphorus atoms, I.: Chloridothiophosphates
The chloride—radiochloride ion exchange at the thiophosphoryl centre has been studied using dialkylchloridothiophosphates (RO)2P(S)Cl (R=Me, Et, n-Pr) and diphenylphosphorochloridothionate, (PhO)2P(S)Cl, as model compounds. The bimolecular rate constants, energies and entropies of activation have been calculated. Effects of the substituents in the bimolecular displacement reaction on four-coordinated phosphorus atom have been discussed.
Mit 3 Abbildungen 相似文献
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Neomethymycin (I) has been transformed into “anhydrocycloneomethynolide” (V) which could be degraded via (−)--methyllevulinic acid to (−)--methylsuccinic acid, thus establishing the absolute configuration of positions 4 and 6 in the lactonic acid (XIII). This acid is a common degradation product of methymycin, neomethymycin, pikromycin and narbomycin and there is thus available a standard of absolute configuration for these macrolide antibiotics. By a different sequence of reactions, erythromycin (XXIII) has been converted into (+)--methyllevulinic acid and (+)--methylsuccinic acid. Coupled with earlier results reported in the literature, it is now possible to assign absolute configurations to positions 10 (R) and 8 (R) of erythromycin and this applies most likely also to positions 4 (R) and 2 (S). Attention is called to the biogenetic significance of these observations. 相似文献
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