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81.
Ali Emrouznejad Abdel Latef Anouze Emmanuel Thanassoulis 《European Journal of Operational Research》2010
Data Envelopment Analysis (DEA) is a nonparametric method for measuring the efficiency of a set of decision making units such as firms or public sector agencies, first introduced into the operational research and management science literature by Charnes, Cooper, and Rhodes (CCR) [Charnes, A., Cooper, W.W., Rhodes, E., 1978. Measuring the efficiency of decision making units. European Journal of Operational Research 2, 429–444]. The original DEA models were applicable only to technologies characterized by positive inputs/outputs. In subsequent literature there have been various approaches to enable DEA to deal with negative data. 相似文献
82.
对基于矩形阵列的高功率微波二维密集阵阵列合成进行了研究。仿真分析了均匀矩形栅格阵列的远场方向图,结果表明采用密集阵可以实现高效的、具有确定主波束的空间功率合成。并分析了阵元间距及阵元初相位对阵列空间功率合成的影响,结果表明:阵元间距越小,栅瓣越少,主波束宽度越宽,具有确定主波束的临界距离越小;当目标高度超过阵临界距离时,阵元初相位相差越小合成效率越高,阵列初相位分布范围超过/2时,阵列得不到确定的主波束,进行阵列设计时应充分考虑阵元间距及初相位对阵列合成的影响。 相似文献
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85.
Despite the importance of a complete characterization of dendritic patterns in castings, the availability of studies on the development of tertiary dendrite arms is scarce in the literature. In the present study, the tip cooling rate, local solidification time, primary and tertiary dendrite arm spacings have been determined in Pb–Sb alloys castings directionally solidified under unsteady-state heat flow conditions. The alloys compositions experimentally examined are widely used in the as-cast condition for the manufacture of positive and negative grids of lead-acid batteries. The initial growth of tertiary dendritic arms from the secondary branches was found to occur only for a Pb–3.5 wt% Sb alloy at cooling rates in the range 0.4–0.2?K/s, with no evidence of this spacing pattern for Pb–Sb alloys having lower solute content. Tertiary dendritic branches have been observed along the entire casting lengths for alloys of the Pb–Sb hypoeutectic range having compositions higher than 4.0 wt% Sb. It is shown that a power function experimental law with a characteristic ?0.55 exponent is able to characterize the tertiary spacing evolution with the solidification cooling rate for alloys compositions ≥4.0 wt% Sb. The only exception was the Pb–3.5 wt% Sb alloy for which λ 3 exhibited significant lower values when compared with the experimental values obtained for the other Pb–Sb alloys for a same solidification cooling rate. 相似文献
86.
The microstructure of a composite containing a quasicrystal phase, i.e. so-called crystal–quasicrystal (CQ) composite, was studied. The CQ composite was obtained by the Bridgman method via solidification of Al61Cu27Fe12 alloy (numbers indicate at%). The process was conducted at a pull out rate of v = 0.07 mm/min. The average temperature gradient in the heating zone was 43 K/cm. The composite matrix consisted of cubic β phase Al(Fe, Cu), with reinforcement of λ-phase rod-shaped fibres surrounded by a quasicrystal icosahedral ψ phase, which also existed in the fibre core. The fibres were rhomboidal in cross-section. The composite was studied using X-ray and electron diffraction, light-optical and scanning electron microscopy (SEM), X-ray topography and Laue diffraction. 相似文献
87.
This paper presents a new design for an insensitive-polarization all-optical switch using 2 × 2 multimode interference (MMI) couplers. The switching structure can operate at central operating wavelength 1550 nm for both polarizations. A nonlinear directional coupler is used to realize the phase shifter and therefore switching mechanism is obtained. The transfer matrix method and beam propagation method are used to design and optimize the whole device structure. 相似文献
88.
Pranabendu Ganguly Juran Chandra Biswas Samir Kumar Lahiri 《Fiber and Integrated Optics》2013,32(6):511-520
Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO 3 curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple. 相似文献
89.
Min Jin Jiayue Xu Xinhua Li Hui Shen Qingbo He 《Crystal Research and Technology》2008,43(10):1074-1077
Novel relaxor ferroelectric crystal 0.93Pb(Zn1/3Nb2/3)O3‐0.07PbTiO3 (PZNT93/7) with dimensions about Ø40× 70 mm3 was obtained by directional solidification technique. The growth defects of the crystal were investigated. Rocking curve analysis revealed the crystalline quality of PZNT93/7 crystal was not perfect and the FWHM value was measured to be about 0.7°. Some pits and oxide particles in micro‐size were formed in the crystal due to the growth conditions. A series of growth steps parallel to (001) face were observed which were attributed to the growth behavior. Moreover, it was found the average chemical composition of the crystal was deviated slightly to the stoichiometric value of PZNT93/7. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.
The split-step Fourier method is used to study the energy switching characteristics of fiber nonlinear directional couplers with the third-order dispersion. The effects of the third-order dispersion increases with the third-order dispersion coefficient and input power and result in pulse shift and energy decreases. Adding high-order nonlinear can partly overcomes these effects. 相似文献