Gel’fand三元组上多分数Lévy过程(英文)

本文研究了Gel’fand三元组上多分数Lévy过程.通过将分数Lévy过程的参数替换为依赖于时间t的函数,从而定义了Gel’fand三元组上的多分数Lévy过程以及其一维边际分布和协方差函数.     

高速大容量光纤光栅解调仪的研究

采用半导体光放大器和可调谐法布里-珀罗滤波器,以环路结构组成高速扫描激光器,结合光耦合器、光环路器和光电二极管等,形成4通道大容量高速光纤光栅解调仪。系统采用2kHz的类三角波调制信号,驱动法布里-珀罗滤波器在50nm的光谱范围内进行快速扫描。通过引入光纤梳状滤波器和单峰滤波器组成的参考通路,消除法布里-珀罗滤波器的非线性效应和扫描波长漂移问题,使得解调仪具有很好的稳定性和线性度。高速光纤光栅解调仪的稳定性为2pm,分辨率为1pm,线性度为0.99957,测量精度为5pm,解调频率为2kHz。     

An extended queueing control model for facilities with front room and back room operations and mixed-skilled workers

Three related problems arising in retail facilities with front room and back room operations, and cross-trained workers, are considered. In the first problem, the goal is to determine an optimal policy for switching workers between the two rooms. In the second and third problems, the goal is to determine the minimum number of workers that should be hired by the facility such that a satisfactory switching policy exists. We analyze two questions arising from previous work on these problems. Firstly, we demonstrate that the previously proposed policy definition is sub-optimal and cannot represent a set of solutions that are reasonable in practice, and propose an alternative definition. Secondly, we examine the problem of finding the optimal combination of cross-trained and specialized workers under a complete set of assumptions regarding worker costs. This analysis shows that the structure of the optimal solution depends on the policy definition that is employed. Moreover, under some assumptions the cost of the ‘optimal’ solution with the original policy definition will be greater than the cost of the optimal solution with the new one.     

两条Bézier样条的光滑连接

研究了用一条样条曲线把两条不相连接的样条曲线光滑连接起来的问题,给出了连接两条一元n次参数样条曲线为一条新的一元n次参数样条曲线的条件,适用于参数样条曲线添加控制顶点的情形,进一步得到了两条一次、二次、三次Bézier样条曲线在几何连续性下实现自然光滑连接的条件.     

Spatiotemporal measurements of flame stretch and propagation rates for lean and rich CH4/air premixed flames interacting with a turbulent-wake

A 1.5 m long turbulent-wake combustion vessel with a 0.15 m × 0.15 m cross-sectional area is proposed for spatiotemporal measurements of curvature, strain, dilatation and burning rates along a freely downward-propagating premixed flame interacting with a parallel row of staggered vortex pairs having both compression (negative) and extension (positive) strains simultaneously. The wanted wake is generated by rapidly withdrawing an electrically-controlled, horizontally-oriented sliding plate of 5 mm thickness for flame–wake interactions. Both rich and lean CH₄/air flames at the equivalence ratios  = 1.4 and  = 0.7 with nearly the same laminar burning velocity are studied, where flame–wake interactions and their time-dependent velocity fields are obtained by high-speed, high-resolution DPIV and laser-tomography. Correlations among curvature, strain, stretch, and dilatation rates along wrinkled flame fronts at different times are measured and thus their influences on front propagation rates can be analyzed. It is found that strain-related effects have significant influence on front propagation rates of rich CH₄/air (diffusionally stable) flames even when the curvature weights more in the total stretch than the strain rate does. The local propagation rates along the wrinkled flame front are more intense at negative strain rates corresponding to positive peak dilatation rates but the global propagation rate averaged along the rich flame front remains constant during all period of flame–wake interaction. For lean CH₄/air (diffusionally unstable) flames, the curvature becomes a dominant parameter influencing the structure and propagation of the wrinkled flame front, where both local and global propagation rates increase significantly with time, showing unsteady flame propagation. These experimental results suggest that the theory of laminar flame stretch can be applicable to a more complex flame–wake interaction involving unsteadiness and multitudinous interactions between vortices.     

A Statistical Mechanical Analysis on the Bound State Solution of an Energy-Dependent Deformed Hulthén Potential Energy *

In this article, we investigate the bound state solution of the Klein Gordon equation under mixed vector and scalar coupling of an energy-dependent deformed Hulthén potential in D dimensions. We obtain a transcendental equation after we impose the boundary conditions. We calculate energy spectra in four different limits and in arbitrary dimension via the Newton-Raphson method. Then, we use a statistical method, namely canonical partition function, and discuss the thermodynamic properties of the system in a comprehensive way. We find out that some of the thermodynamic properties overlap with each other, some of them do not.     

基于太赫兹时域光谱技术的光学参数提取方法的研究进展

光学参数是宏观上表征材料光学性质的物理量,间接反映了材料的微观特性,对光学参数准确的提取可以研究材料的微观性质和机理。近年来,太赫兹时域光谱技术作为一种新兴的光谱分析手段已经成为研究的热点。由于太赫兹辐射能量低并且脉冲宽度窄(皮秒量级),太赫兹时域光谱技术在提取光学参数方面具有无损伤和高时间分辨率的特点。本文总结了基于太赫兹透射和反射时域光谱技术的光学参数提取方法的研究进展,着重阐述了几种经典方法,分析了每种方法的优缺点,并讨论了太赫兹时域光谱技术用于提取材料光学参数的挑战。研究结果表明,透射法适用于对太赫兹波吸收较弱的物质,而反射法则适用于对太赫兹波有强烈吸收的材料。     

Locally risk-minimizing hedging strategies for unit-linked life insurance contracts under a regime switching L��vy model

This paper extends the model and analysis in that of Vandaele and Vanmaele [Insurance: Mathematics and Economics, 2008, 42: 1128–1137]. We assume that parameters of the Lévy process which models the dynamic of risky asset in the financial market depend on a finite state Markov chain. The state of the Markov chain can be interpreted as the state of the economy. Under the regime switching Lévy model, we obtain the locally risk-minimizing hedging strategies for some unit-linked life insurance products, including both the pure endowment policy and the term insurance contract.     

基于时域位相分析的云纹法形貌测量技术研究

采用影像云纹法和时域相位分析技术研究了物体形貌测量的新方法.通过研制高精度旋转平台,利用栅线旋转的方式使栅线的空间频率以一定的规律变化,使物体的离面高度与该点的灰度变化率有关.在利用FFT确定灰度变化频率时,采用补零的方法提高了频率的确定精度,从而有效地提高了物面形貌测量的精度.实验发现:当补零倍数达到原始长度的128倍时,使用空间频率为5 l/mm的栅线精度可以达到0.02mm.本文讨论了该方法相关技术参数的选取方法,给出了标定实验和利用该测量系统实际测量门齿生长发育沟的实例,阐述了牙齿表面形貌数字化在牙科修复手术中的意义.通过具体标定过程与应用实例,证明了本文提出的测量方法提高了测量精度,简化了测量过程,在云纹干涉形貌测量领域有了新的突破.     

Numerical study on the dynamics of droplet passing through a cylinder obstruction in confined microchannel flow

The droplet dynamics passing through a cylinder obstruction was investigated with direct numerical simulations with FE-FTM (Finite Element-Front Tracking Method). The effect of droplet size and capillary number (Ca) was studied for both Newtonian and viscoelastic fluids. In the case of Newtonian droplet immersed in Newtonian medium, the droplet breakup induced by the geometric hindrance depends on the droplet size. As Ca increases, the short droplets (1.3 times longer than the channel width) break up while passing through the obstruction. However, the breakup does not occur for longer droplets (1.8 times longer than the channel width). When the viscoelastic fluid characterized by the Oldroyd-B model is considered, the Newtonian droplet immersed in viscoelastic medium breaks up into two smaller droplets while passing through the cylinder obstruction with increasing De_m (Deborah number of the medium). We also show that the normal stress difference plays a key role on the droplet breakup and the droplet extension. The normal stress difference is enhanced in the negative wake region due to the droplet flow, which also promotes droplet extension in that region. This numerical study provides information not only on underlying physics of the droplet flows passing through a cylinder obstruction but also on the useful guidelines for microfluidic applications.