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91.
For a given set M of positive integers, a problem of Motzkin asks for determining the maximal density μ(M) among sets of nonnegative integers in which no two elements differ by an element of M. The problem is completely settled when |M|?2, and some partial results are known for several families of M for |M|?3, including the case where the elements of M are in arithmetic progression. We consider some cases when M either contains an arithmetic progression or is contained in an arithmetic progression. 相似文献
92.
Retailers often conduct non-overlapping sequential online auctions as a revenue generation and inventory clearing tool. We build a stochastic dynamic programming model for the seller’s lot-size decision problem in these auctions. The model incorporates a random number of participating bidders in each auction, allows for any bid distribution, and is not restricted to any specific price-determination mechanism. Using stochastic monotonicity/stochastic concavity and supermodularity arguments, we present a complete structural characterization of optimal lot-sizing policies under a second order condition on the single-auction expected revenue function. We show that a monotone staircase with unit jumps policy is optimal and provide a simple inequality to determine the locations of these staircase jumps. Our analytical examples demonstrate that the second order condition is met in common online auction mechanisms. We also present numerical experiments and sensitivity analyses using real online auction data. 相似文献
93.
计及管道边界条件滑移的影响,研究微极流体蠕动泵,经由圆柱形管道输运的Stokes流动.壁面运动的控制方程为正弦波方程.使用润滑理论,得到了轴向速度、微转动向量、流函数、压力梯度、摩擦力和机械效率的解析数值解.用图形表示出构成参数,如像耦合参数、微极参数和表征蠕流泵特性的滑移参数、摩擦力和俘获现象的影响.数值计算表明,当耦合参数较大时,需要蠕动泵的压力更大,而微极参数和滑移参数正相反.俘获团块的大小随耦合参数和微极参数的减小而缩小,而随滑移参数的增大而缩小. 相似文献
94.
In the present paper, photovoltaic studies of dye-sensitized solar cells (DSSCs) based on betacyanin/TiO2 and betacyanin/WO3–TiO2 have been done. The cell performances were compared through I–V curves and wavelength dependant photocurrent measurements for the two new types of DSSCs. The TiO2-coated DSSC showed the photovoltage and photocurrent of 300 mV and 4.96 mA/cm2, whereas the cell employing WO3–TiO2 photoelectrode showed the values 435 mV and 9.86 mA/cm2, respectively. The conversion efficiency of TiO2 based dye-sensitized solar cell was found to be 0.69 %, while WO3–TiO2-based cell exhibited a higher conversion efficiency of 2.2 %. The better performance of the WO3–TiO2 dye-sensitized solar cell photoelectrode is thought to be due to an inherent energy barrier at the electrode/electrolyte interface leading to the reduced recombination of photoinduced electrons. 相似文献
95.
G. K. Singh A. P. Singh V. K. Sharma A. Kapoor K. N. Tripathi 《Optics & Laser Technology》2002,34(3):219-223
A general expression for the change in extraordinary refractive index of the annealed proton exchanged LiNbO3 waveguide has been deduced. The expression deduced explains the experimental results of decrease in change of extraordinary refractive index with annealing. The effect of annealing time has also been incorporated following Cao's model (Cao, Ramaswamy, Srivastava, J. Lightwave Technol. 10 (1992) 1302–1313). The concentration profile of protons in the annealed waveguide has been deduced theoretically, which is consistent with the previous results. The spontaneous polarization has been considered as the central mechanism for change in extraordinary refractive index due to proton exchange with annealing. 相似文献
96.
H. P. Singh D. D. Tripathi R. B. Mishra 《International Journal of Theoretical Physics》1987,26(9):861-872
The equations of magnetohydrodynamics of a perfect fluid are classified with respect to the Coriolis parameter, and all essentially different solutions of rank one are indicated. The geometry of streamlines is discussed. 相似文献
97.
Tripathi V.K. Liu C.S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(3):466-471
The introduction of a plasma and a strong guide magnetic field in a free electron laser (FEL) slows down the phase velocity of radiation, significantly reducing the requirements on beam energy for generating frequencies below the electron-cyclotron frequency (ω1≲ωc). Around plasma resonance (ω1~ωp), the FEL mode couples to two-stream instability (TSI), attaining a large growth rate, comparable to that of the wiggler-free TSI. At plasma densities comparable to beam density, the beam-induced local depression in the electron density of the plasma acts as a waveguide for guiding any high-frequency radiation when the beam current is ≳17 kA 相似文献
98.
Brajesh Pandey Amita Tripathi R. P. Tripathi H. C. Verma 《Hyperfine Interactions》2005,166(1-4):537-542
Mössbauer spectroscopic studies of two sedimentary layers from Petriccio section in Gubbio formation are presented. It is found that these layers have almost the same iron phases nanophase hematite and phyllosilicate and with the same compositions as those in the Cretaceous-Tertiary Boundary (KTB) in Petriccio. The two layers also show enhancement in the siderophile elements such as Cr, Ni, Fe, Ca etc. to that found in the KTB layer. The two layers are well separated from the KTB layer, 128 and 149 cm below this layer, and show no enhancement of iridium. From the data it is suggested that the two layers also represent some kind of impact by extraterrestrial (ET) bolides. 相似文献
99.
An efficient fast Fourier transform method has been employed to determine correlation function [g(r*)] using the structure factor [S(Q*)] calculated with the rescaled mean spherical approximation (RMSA) and the DLVO potential. Based on this function a parametric
(size and charge) study of the ordering in a highly charged and concentrated macroions (an ideal colloid) has been made. The
strength of the correlation increases with the increase in the charge on macroions and it saturates after acertain value.
Similarly, a critical diameter of the particle depending on the charge on it has been found at which normal feature of the
ordering disappears. 相似文献
100.
The Anderson-Grüneisen parameter δ has been computed theoretically from a general expression developed by Sharma and Tripathi[6]. The δ-γ (Grüneisen parameter) curves have been plotted to find a relation for the best fitted yielding curves by the method of least squares. The relation developed can be put as δ = AγB and it can be inferred that chang's[3] relation is a particular case of this general equation. 相似文献