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31.
This is the first of two papers presenting a systematic development of a continuum model of a porous medium and of transport
processes occurring in it. The concept of a Representative Elementary Volume (REV) as opposed to any arbitrary volume of averaging
quantities at the micro-scale, is quantified. A universal criterion for selecting the size of an REV as a function of measurable
characteristics of a porous medium and selected tolerance levels of estimation errors, is developed. The rules of spatial
averaging are extended by including the effects of both the configuration of the solid matrix and of interphase transfer phenomena
within an REV. 相似文献
32.
We study subgradient methods for computing the saddle points of a convex-concave function. Our motivation comes from networking
applications where dual and primal-dual subgradient methods have attracted much attention in the design of decentralized network
protocols. We first present a subgradient algorithm for generating approximate saddle points and provide per-iteration convergence
rate estimates on the constructed solutions. We then focus on Lagrangian duality, where we consider a convex primal optimization
problem and its Lagrangian dual problem, and generate approximate primal-dual optimal solutions as approximate saddle points
of the Lagrangian function. We present a variation of our subgradient method under the Slater constraint qualification and
provide stronger estimates on the convergence rate of the generated primal sequences. In particular, we provide bounds on
the amount of feasibility violation and on the primal objective function values at the approximate solutions. Our algorithm
is particularly well-suited for problems where the subgradient of the dual function cannot be evaluated easily (equivalently,
the minimum of the Lagrangian function at a dual solution cannot be computed efficiently), thus impeding the use of dual subgradient
methods. 相似文献
33.
34.
研究了二维Sinai台球系统的经典与量子的对应关系,运用定态展开法和Gutzwiller的周期轨道理论对Sinai台球系统的态密度经傅里叶变换得到的量子长度谱进行分析,并把量子长度谱中峰的位置与其所对应的经典体系的周期轨道长度做对比,发现两者之间存在很好的对应关系.观察到了一些量子态局域在短周期轨道附近形成量子scarred态或量子superscarred态.还研究了同心与非同心Sinai台球系统的能级最近邻间距分布,发现同心Sinai台球系统是近可积的,非同心Sinai台球系统在θ=3π/8下,随两中心间距离的增加,能级最近邻间距分布将由近可积向维格那分布过渡. 相似文献
35.
A simple genetic algorithm is implemented to perform multi parameter optimization of Raman Fiber Amplifier for 100 channel S band dense wavelength division multiplexed system at 25 GHz interval. A cost effective system using single Raman pump is investigated aiming at maximum average gain. The single counter propagating pump is optimized to frequency of 211.528 THz and 652.93 mW power level with optimum Raman fiber length of 44.064 Km. There is evidence to show that the optimum solution presents a small gain variation (less than 3 dB) over an effective bandwidth covering 197–199.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q-factor (19.52 dB) and BER (1.46 × 10−21). 相似文献
36.
A laser image system for investigating the influence of orifice spacing on twin bubbles formation in shear-thinning fluid was established. The bubbles formation process at two orifices could be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technology. The shape and size of bubbles generating in carboxymethylcellulose (CMC) aqueous solutions were studied experimentally at the orifices spacing 1Do, 2Do and 3Do (Do orifice diameter). The results reveal that the minute bubbles can be imaged clearly and amplified without distortion in the higher concentration solutions, and therefore the shape and size of bubbles are obtained accurately. With the increase of orifice spacing, bubble instantaneous volume in shear-thinning fluid decreases at the radial expansion stage but then increases at vertical elongation period, and the deformation and deviation of bubbles forming goes down due to the reduced interaction of adjacent bubble. 相似文献
37.
38.
Yi-Ching Yao 《Annals of the Institute of Statistical Mathematics》1987,39(1):377-383
Summary The problem of testing for constant hazard against a change-point alternative is considered. It is shown that this problem
is related to another one in quality control. Based on this relationship, a test is proposed. The main advantages of this
test are its computational simplicity and the ready availability of small and large sample distribution theory. 相似文献
39.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
40.
提出并实验研究了一种2μm波段全光纤间隔可调双波长光纤激光器.该激光器采用传统的环形腔设计,以最大输出功率33dBm的1 565nm光纤激光器为泵浦源,4m单模掺铥光纤为增益介质,腔内为嵌入多模干涉滤波器的Sagnac环的复合滤波结构.该复合滤波器可实现间隔可调谐,高边模抑制比的双波长激光信号输出.通过泵浦功率的控制和对复合滤波器中偏振控制器的调节,实现双波长3nm到80nm间隔可调的激光输出,边模抑制比为60dB,线宽为0.2nm,功率稳定度为±1.5dB/h,双峰能量差小于4dB. 相似文献