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491.
492.
A two-special dimension electronic system characterized by a plasma parameter Γ 1 is analyzed; then, by using a rigorous non-equilibrium statistical mechanical theory, the evolution of distribution function is considered. A generalized Vlasov equation (GVE) is derived. Compared to the usual Vlasov equation, GVE presents an additional velocity-dependent correlation term. Taking as a starting point the GVE, the phenomenological approximation to two-particles function, ƒ2(r1r2p1p2; t) = ƒ1(r1p1;t)f1(r2p2;t)g(r1−r2), proposed by Singwi, Tosi, Landi and Sjolander is analyzed. 相似文献
493.
After proving a generalized version of Garkavi's theorem, we give as applications proofs of existence results on best approximation by polynomials, and fractional linear and holomorphic operators between Banach spaces. We also obtain theorems on best approximation by some types of rational functions defined in open subsets of Banach spaces. By considering a natural non-normable distance we prove that every mapping bounded on the bounded subsets of a Banach space has best approximation by polynomials of degree less than or equal to a fixed natural number n. 相似文献
494.
MC-INDO calculations of LiF, NaC, LiC and NaF crystals were performed in order to verify the generality of the parametrisation scheme is proposed. Results indicate that crystalline properties is proposed. Results indicate that the scheme is sufficiently general and an appropriate scaling of the STO's is suggested to improve the agreement with experimental data. 相似文献
495.
J Ortega J.S Matos M.I Paz Andrade E Jimenez 《The Journal of chemical thermodynamics》1985,17(12):1127-1132
Excess molar volumes VmE were determined over the entire composition range at 298.15 K for ethyl formate or ethyl acetate + hexan-1-ol, +2-methylpentan-1-ol, +3-methylpentan-2-ol, +2-methylpentan-3-ol, +3-methylpentan-3-ol, +2-methylpentan-2-ol, +4-methyl-pentan-2-ol, and +hexan-2-ol. Excess volumes were determined from density measurements made with a vibrating-tube densimeter. The VmE values were all positive, decreasing with the n value of the ester: Cn?1H2n?1CO2C2H5. 相似文献
496.
497.
A simple, rapid and precise amperometric method has been developed for quantification of ascorbic acid (AA) in pharmaceutical formulations using flow-injection analysis (FIA). A slice of recordable compact disc (CD) modified by electrodeposition of platinum was employed as the working electrode. The proposed flow system allows determinations in the 1 mumol l(-1) of the analyte and enables 90 determinations per h, employing only 150-mul sample. The method permits the direct quantification of ascorbic acid in many pharmaceutical products, avoiding cumbersome processes as previous separations, solvent extraction or sample filtration. This new procedure was applied to commercial pharmaceutical tablets and the results obtained were identical than the ones obtained by the classical iodometric method. The calibration plots for freshly prepared ascorbic acid standards were highly linear in the concentration range of 1-10 mumol l(-1) with a relative standard deviation (R.S.D.) <1%. For all real samples studied, the deviations were situated between 0.5 and 8.7%. 相似文献
498.
Ana C. Matos 《Numerische Mathematik》2001,89(3):535-560
Summary. In this paper, after recalling the two definitions of the generalizations of the Padé approximants to orthogonal series,
we will define the Padé–Legendre approximants of a Legendre series. We will propose two algorithms for the recursive computation
of some sequences of these approximants. We will also estimate the speed of convergence of the columns of the Padé–Legendre
table from the asymptotic behaviour of the coefficients of the Legendre series. Finally we will illustrate these results with
some numerical examples.
Received June 20, 1998 / Published online March 20, 2001 相似文献
499.
Oscar Martínez Matos María L. Calvo Siegfried Janz José A. Rodrigo André Delâge 《Optics Communications》2007,270(1):31-40
We propose a new type of arrayed waveguide grating (AWG) multiplexer/demultiplexer based on modified group refractive index. This device is composed by an array of straight and parallel waveguides of equal length and each waveguide consist of two sections with different width. The length of the two sections are changed from a waveguide to the adjacent one following a linear dependence resulting in a wavelength dispersive waveguide array. An example of the device design for silicon-on-insulator (SOI) platform is provided and numerical simulations have been carried out for various arrayed waveguide parameters. We demonstrate that the group index modification can be used for tailoring device dispersion properties, and that it can also result in new dispersion characteristics predicted numerically not observed in conventional AWGs. Additional advantages are that the demultiplexer does not necessarily require bending waveguide sections as in a conventional AWG (de)multiplexers, and thus yields highly compact devices with potentially very low insertion loss. Channel spacing of 1 nm have been predicted for sub-micron waveguides sizes. In this paper it is also proposed a novel wavefront converter based on waveguide array lens-like element with waveguides broadened sections. Numerical results for different input/output geometries are analized. 相似文献
500.
AbstractIn this paper, the simple dynamic facility location problem is extended to uncertain realizations of the potential locations for facilities and the existence of customers as well as fixed and variable costs. With limited knowledge about the future, a finite and discrete set of scenarios is considered. The decisions to be made are where and when to locate the facilities, and how to assign the existing customers over the whole planning horizon and under each scenario, in order to minimize the expected total costs. Whilst assignment decisions can be scenario dependent, location decisions have to take into account all possible scenarios and cannot be changed according to each scenario in particular. We first propose a mixed linear programming formulation for this problem and then we present a primal-dual heuristic approach to solve it. The heuristic was tested over a set of randomly generated test problems. The computational results are provided. 相似文献