NO dissociation pathways on Rh(1 0 0), (1 1 0), and (1 1 1) surfaces: A comparative density functional theory study

The chemisorption and dissociation pathways of NO on the Rh(1 0 0), (1 1 0), and (1 1 1) surfaces are studied by the plane-wave density functional theory (DFT) with CASTEP program. In addition, the electronic and geometrical effects that affect the NO dissociation reactions have been investigated in detail. The calculation results are presented as following: The effective activation energies of the best NO dissociation pathways on the Rh(1 0 0), the Rh(1 1 0), and the Rh(1 1 1) are 0.63, 0.66 and 1.77 eV, respectively. The activity of the Rh planes for NO dissociation is in the order of Rh(1 0 0) ≈ Rh(1 1 0) > Rh(1 1 1). The low dissociation barrier for Rh(1 0 0) and Rh(1 1 0) is associated with the existence of a lying-down NO structure which acts as a precursor for dissociation. By Mulliken population analysis and structure analysis, both electronic and geometrical effects are found to affect the NO dissociation reactions, but the geometrical effect exceed the electronic. The energy decomposition scheme has been used to provide further insight into the NO dissociation reactions. Based on the calculations, the interaction energy between N and O in the transition state on the Rh(1 1 1) is found much larger than that on the Rh(1 0 0) and the Rh(1 1 0). The major differences of should originate from the variation of the bonding competition effect.     

Two-Phase Image Segmentation by Nonconvex Nonsmooth Models with Convergent Alternating Minimization Algorithms

Two-phase image segmentation is a fundamental task to partition an image into foreground and background. In this paper, two types of nonconvex and nonsmooth regularization models are proposed for basic two-phase segmentation. They extend the convex regularization on the characteristic function on the image domain to the nonconvex case, which are able to better obtain piecewise constant regions with neat boundaries. By analyzing the proposed non-Lipschitz model, we combine the proximal alternating minimization framework with support shrinkage and linearization strategies to design our algorithm. This leads to two alternating strongly convex subproblems which can be easily solved. Similarly, we present an algorithm without support shrinkage operation for the nonconvex Lipschitz case. Using the Kurdyka-Łojasiewicz property of the objective function, we prove that the limit point of the generated sequence is a critical point of the original nonconvex nonsmooth problem. Numerical experiments and comparisons illustrate the effectiveness of our method in two-phase image segmentation.     

双重网络嵌入对公司IPO后市场表现的影响研究

将社会网络嵌入理论从单一网络拓展至双重网络,分析上市公司同时嵌入风险投资网络和承销商网络对公司IPO上市后市场表现的影响。利用2004～2017年有风险投资支持的IPO公司数据,实证检验结果表明：(1)单独嵌入风险投资网络中心位置、单独嵌入承销商网络中心位置,均会提高公司IPO后市场表现;(2)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后短期市场表现的正向影响会相互替代;(3)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后长期市场表现的正向影响会互相补充。     

船用惯性导航系统姿态测量误差辨识及其补偿方法研究

本文分析了某型号船用惯性导航系统（ＳＩＮＳ）的试验数据，结果表明，ＳＩＮＳ的姿态误差主要来源于水平测姿传感器。据此，本文对该ＳＩＮＳ水平姿态测量误差的辨识及其补偿方法进行了研究，并建立了水平测姿误差的回归数学模型，以提高ＳＩＮＳ姿态精度     

弱形式方程中分片函数奇异性的光滑化分析

研究弱形式方程中的分片光滑函数因求导数出现的奇异性问题，意在为得到离散格式时正确处理这一问题提供依据。在不改变拟合性质的情况下，将分片函数光滑化，则分步积分公式仍然有效。通过光滑后的函数讨论其积分的性质，总结出了几条计算规则。文中的典型例子说明这些计算规则是合理而有效的。     

应变硬化水泥基复合材料(SHCC)本构关系逆向分析研究

水泥基复合材料的高脆性是导致其性能退化和结构不耐久的主要原因之一.脆性的直观表现为应力-应变曲线具有明显的软化段.添加高模量聚乙烯醇纤维的水泥基材料的韧性性能可得到显著改善,受拉破坏和受弯破坏时呈现出应变硬化和多微缝开裂特征,导致其本构关系异于普通水泥基材料.通过直拉试验可直接得到σ-ε曲线,但该试验技术上难于实现而且造价高、耗时长.四点弯曲试验易于实现但需要将力-变形曲线转换成σ-ε曲线.本文通过CONHARD软件,采用逆向分析法,模拟变形和裂缝开展,反复迭代以求得试验曲线与数值计算结果的最佳拟合.该方法以弹性宏单元模型预处理未裂区域,以多层单元模型模拟裂缝扩展区域,假定初始σ-ε曲线,通过进化运算法则进行迭代和修正,最终可获得多线性应力应变曲线.数值计算结果与试验曲线吻合较好.     

聚四氟乙烯对齿轮润滑成膜膏润滑性能的影响

作者以聚四氟乙烯(PTFE)为固体润滑剂填料对GM型齿轮润滑成膜膏进行了改进,并且研制出了两种新的成膜膏系列产品。经四球试验机、动静摩擦系数精密测定仪和SRV试验机评价的结果表明,添加PTFE的GM-2型成膜膏的承载能力和减磨性能都明显地比未添加的好;以PTFE为主要固体润滑剂填料的GM-3和MFC-1型两种润滑成膜膏也都具有良好的润滑性能,其中后者的性能与含PTFE的GM-2型成膜膏的接近。通过对摩擦轨迹的电子探针检测发现,PTFE在摩擦过程中于摩擦表面形成了转移膜,因而改善了润滑成膜膏的摩擦学性能。     

SYMPLECTIC STRUCTURE OF POISSON SYSTEM

When the Poisson matrix of Poisson system is non-constant, classical symplectic methods, such as symplectic Runge-Kutta method, generating function method, cannot preserve the Poisson structure. The non-constant Poisson structure was transformed into the symplectic structure by the nonlinear transform.Arbitrary order symplectic method was applied to the transformed Poisson system. The Euler equation of the free rigid body problem was transformed into the symplectic structure and computed by the midpoint scheme. Numerical results show the effectiveness of the nonlinear transform.     

水和水蒸汽热力学物性参数及导数的计算与应用

本文针对现代换热设备设计、两相流动与传热研究的需要,介绍了可供科研使用的水和水蒸汽物性计算方法,完善了计算程序。根据超临界锅炉设计中的超临界水的物性计算,两相流研究和换热设备动态特性研究中对物性导数计算的需要,提供了两个算例,并进行了定性分析。     

A 3D LIF system for turbulent buoyant jet flows

A Laser-Induced Fluorescence (LIF) system for mapping the three dimensional tracer concentration field in turbulent flows is described. The system is particularly suited to studies of single or multiple buoyant jets discharged into unstratified and stratified flowing environments for conditions typical of wastewater discharges into surface water bodies. A laser beam is scanned through the flow and LIF images are obtained in parallel planes with a high-speed synchronized CCD camera. Refractive index matching is used to minimize refractive index variations due to local density gradients. An application to vertical round buoyant jets discharging into unstratified and stratified cross flows is presented. The three-dimensional system can obtain vastly more data than is possible with probe-based techniques and can yield far more insight into the flow and mixing processes.Abbreviations a Combined attenuation coefficient, cm^-1 - a_w Attenuation coefficient for fresh water, cm^-1 - B Buoyancy flux of buoyant jet, cm⁴/s³ - c Tracer concentration, g/l - C _salt, C _eth Salt and ethanol concentrations, g/l - d Port diameter, cm - g Acceleration due to gravity, cm/s² - Modified acceleration due to gravity at source, cm/s² - Q Volume flux of buoyant jet, cm³/s - I Image gray scale level, DN - l _a,l _Q , l _M , l _s, l _t Buoyant jet length scales, cm (Eq. 8) - L _y Distance from camera to image plane, cm - M Momentum flux of buoyant jet, cm⁴/s² - M _y Image scale factor - N Buoyancy frequency, s^-1 - u _a Ambient flow velocity, cm/s - u _j Jet exit velocity, cm/s - P Laser power, W - S ₀ Lowest dilution on the vertical center-plane through the nozzle - S _m Minimum dilution: lowest dilution in a vertical plane perpendicular to the flow - x, y, z Coordinates, cm - z _m Maximum rise height of buoyant jets, cm - z _e Equilibrium rise height of buoyant jets, cm - Image calibration constant - ₀ Effluent density, g/cm³ - _a Ambient density, g/cm³