航天器中精密器件布局的保结构优化

航天器中精密器件的稳定性和工作精度决定于器件布置位置的局部结构振动特性,而航天器局部振动特性又受到精密器件布局的影响.因此,航天器中精密器件的布局优化是确保其稳定高效工作的前提条件.该文建立了粘接精密器件的航天器局部柔性薄板结构的动力学模型,发展保结构分析方法模拟了薄板结构的局部振动特性.考虑精密器件形状和尺寸、散热间...     

加权幂平均复合判断矩阵的群体AHP一致性研究

判断矩阵一致性是群体综合评价的重要内容。一致性可以反映专家群体就所有可能的替代方案达成完全一致的意见,利用一致性测度可以衡量评价者之间的差异,也是共识判断的基础。文章针对加权幂平均复合判断矩阵中存在的一致性问题进行研究,从幂平均次数对复合判断矩阵影响的角度,分析幂平均次数对一致性比率的影响程度,揭示两者之间的变化规律;研究专家判断矩阵的阶数对一致性比率的作用;从群体专家权重的角度,研究权重对复合判断矩阵一致性比率的敏感性。结果表明:(1)幂平均的次数会影响复合判断矩阵的一致性,幂平均的次数在有限区间内保证复合判断矩阵的满意一致性,有限区间长度同时依赖于判断矩阵的阶数与幂平均的次数,且一致性比率是关于幂平均次数的凹函数;(2)判断矩阵的阶数越高,专家给出判断矩阵的难度加大,然而随着判断矩阵阶数的升高,一致性比率会呈递减趋势;(3)专家的权数对于一致性比率影响较小,即专家权数的灵敏度较低,给定权数的扰动后不会影响复合判断矩阵的满意一致性。     

Flow around an ellipsoid of revolution in a harmonic coaxial vector field

We give an integral equation defining a coaxial magnetic field near the surface of a superconductive axisymmetric body and the velocity of the liquid near the surface of an axisymmetric body situated coaxially to the flow of an ideal liquid. Using this equation in the case when the axisymmetric magnetic field before the placement of an ellipsoid of revolution coaxially to the field changed along the axis by a polynomial law, we analytically define the densities of the surface current and the force with which the magnetic field acts on the ellipsoid. Also the velocity of the liquid is determined near the surface of the ellipsoid of revolution and the force acting on the ellipsoid placed coaxially in the flow of an ideal liquid when the velocity of the liquid before the placement of the ellipsoid changed along the axis of symmetry by a polynomial law.     

目标散布区对导弹目标选择概率影响的仿真模型

当反舰导弹飞近目标散布区时,导弹搜索雷达必须开机搜索目标,导弹根据目标反射信号的几何或能量特性,利用某一算法从被探测到的,包括敌方施放的假目标在内的所有目标中选择某一目标作为导弹的攻击目标.目标散布区的外形和大小对导弹选择真实目标概率的影响是一个尚未得到深入研究的问题.推导了目标散布区对导弹正确选择目标概率的影响函数;在考虑了目标舰及时提供假目标的仿真模型的基础上,给出了七种导引头选择目标的算法及仿真模型.仿真结果表明,目标散布区影响反舰导弹雷达的开机时间,从而影响导引头选择真实目标的概率及其抗电子干扰能力.     

PPP项目中非完全利益群体的合作形成机制研究

协调政府与社会资本合作的利益分歧,进而实现个体理性向集体理性的趋同,这是纾解PPP项目合作困境的切入点之一。基于合作博弈理论,本文构建PPP项目非完全利益群体的合作形成机制,分析政府与社会资本间“合作共赢”的必要因素。研究表明,由政府与社会资本组成的PPP项目非完全利益群体,可在“理性-效用转移-有效协商”机制的协同作用下主动采取最优合作策略。其中,理性机制验证了政府与社会资本达成合作意向的前提,效用转移机制可实现二者之间的风险-收益对等,有效协商机制将达成政府与社会资本合作的帕累托均衡。     

非对称信息证券交易的跨期动态博弈均衡解析

揭示了不对称信息条件下证券市场均衡的基本特征.Grossman和Stiglitz模型依据不知情交易者的弱理性,解析了证券交易的静态均衡状态.O'Hara模型增强了不知情交易者的理性,强调了市场均衡时的风险定价,但其命题的成立条件是相互矛盾的.认为不知情交易者信息收集和处理能力的提高会使决策更为理性,证券市场的均衡本质上是交易者的动态博弈均衡.依此思路,运用不完美信息的跨期动态博弈模型解析了非对称信息条件下证券交易者的精炼贝叶斯纳什均衡.结论显示出,市场失效的主要原因是交易者之间的信息分析能力不平衡,而不是信息不对称;市场流动性的决定因素不是信息不对称风险而是知情交易者与不知情交易者所研判的无风险收益率的差别.     

彩信图像监测技术在河道冰-水情远程无人监测中的应用

针对黄河中上游冰凌灾害预报系统的建设,设计研制了黄河河道冰、水情图像远程无人自动监测系统.该系统基于GPRS移动通信中彩信图像数据传输技术,利用单片机控制摄像探头采集和压缩黄河河道现场冰情图像信息,通过GPRS网络以彩信格式发送到用户手机,实现了对黄河河道冰情图像的无线远程实时监测.该系统可以使冰情检测人员在移动过程中随时获取河道实时冰情图像信息,更加适合野外环境下冰凌灾害预防的监测与预报,具有较大的工程应用价值.     

企业雇佣下残疾人就业行为研究——基于就业促进政策的演化博弈分析

融合就业是残疾人可持续发展的关键途径。基于演化博弈理论和残疾人就业促进政策,建立残疾人与用人单位(企业)行为交互过程的动态演化模型,用数值实验展示了初始条件改变和决策变量不同取值对系统演化结果的影响。研究发现,残疾人就业行为路径演化系统收敛于良好状态和“锁定”状态两种模式;调控模型中的参数收敛于不同模式的概率发生显著变化或变化不明显,揭示了现实中残疾人就业治理效果不理想的深层次原因;通过提高残疾人的工资待遇、心理收益、为企业创造的价值,减少残疾人的社会补助与就业付出的人力和社会资本,增加残疾人就业法定比例、企业雇佣残疾人的声誉收益、增值税退税优惠(企业符合退税条件)与雇佣残疾人数量,减少企业支持残疾人的就业投入等均能使系统演化到良好状态的概率增加。这为制定灵活有效的残疾人就业制度、政策与措施提供了较大的操作空间,多元主体协同治理,利益共享,良性互动,以跳出不良“锁定”状态,实现残疾人就业行为良序发展,破解就业难题。     

裂纹面分布加载裂尖SIFs分析的广义参数Williams单元北大核心CSCD

带裂缝服役是工程结构的常态,由于流体侵入到裂缝内部,裂纹面直接受荷,使得裂缝进一步扩展,甚者影响结构的安全性.广义参数Williams单元(简记W单元)在分析断裂问题中,利用Williams级数建立裂尖奇异区的位移场,通过求解广义刚度方程可直接获得应力强度因子(stress intensity factors,SIFs),具有高精高效性;但W单元需满足奇异区内裂纹面自由的边界条件,故在分析裂纹面加载的问题中受限.该文基于SIFs互等,在等效奇异区范围中,将裂纹面的荷载等效为奇异区外围边界裂纹面上的集中力,避免奇异区内裂纹面受荷,故采用W单元即可简便计算.算例分析表明:等效奇异区尺寸取裂纹长度的1/20,等效荷载系数P建议取2.0,W单元计算精度均满足1%的误差限,证明该文在奇异区裂纹面受荷等效处理方法上具有合理性、通用性,克服了W单元在分析裂纹面加载问题的局限性.     

深埋隧洞围岩应力的精确解与近似解的对比分析

对不同断面形状的深埋隧洞进行了分析,比较了隧洞围岩应力解析解与通过当量半径方法得到的近似解之间的差别.首先,应用复变函数的基本理论,给出圆形、椭圆、矩形、直墙拱形等几种常见深埋隧洞围岩应力的解析表达式.其次,应用当量半径的折算形式,将其任意形状的边界转化为标准圆形断面,利用Lamé解答得到了各围岩应力分量.最后,考虑隧洞断面形状参数的变化,通过数值算例对精确解和近似解进行了比较,分析了当量半径折算形式的精确度.在此基础上,应用有限元方法验证了复变函数解析解的精确性,以椭圆、矩形和直墙拱形的复变函数解验证当量半径精确度.结果表明,当量半径的折算形式解答与精确解答之间相似程度与隧洞的断面形状和几何参数之间有着密切的关系.     

On the evaluation of some distributions that arise in simultaneous tests for the equality of the latent roots of the covariance matrix

In this paper, the authors consider the evaluation of the distribution functions of the ratios of the intermediate roots to the trace of the real Wishart matrix as well as the ratios of the individual roots to the trace of the complex Wishart matrix. In addition, the authors consider the evaluation of the distribution functions of the ratios of the extreme roots of the Wishart matrix in the real and complex cases. Some applications and tables of the above distributions are also given.     

基于动态参照点的鲁棒投资组合模型及其拓展

鲁棒投资组合模型是一种适用于收益不确定条件下寻求最优决策的方法。首先考虑投资者对底线的重视,根据当收益触及底线时,激进者和保守者在参照点上的不同变化情况,建立动态参照点模型。接着,一方面将动态参照点作为划分获益和损失的界限值,改进现有的Worst-case Omega(WOmega)模型。另一方面结合投资者对下侧风险更为厌恶的特点,以动态参照点作为下侧风险的基准,改进现有的Relative Robust Portfolio Optimization(RRPO)模型。实证研究中,对于WOmega类模型,结果表明激进行为模型在样本内表现较好,而保守行为模型在样本外表现较好。对于RRPO类模型,结果显示激进行为的收益表现良好,保守行为对标准差及最大损失值的控制较好。随着约束的放松,所有模型的收益都能得到可观提升。     

THE RELATIONSHIP BETWEEN PROJECTIVE GEOMETRIC AND RATIONAL QUADRATIC B-SPLINE CURVES

For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments.     

Boundary Shape Control of the Navier-Stokes Equations and Applications

In this paper, the geometrical design for the blade's surface in an impeller or for the profile of an aircraft, is modeled from the mathematical point of view by a boundary shape control problem for the Navier-Stokes equations. The objective function is the sum of a global dissipative function and the power of the fluid. The control variables are the geometry of the boundary and the state equations are the Navier-Stokes equations. The Euler-Lagrange equations of the optimal control problem are derived, which are an elliptic boundary value system of fourth order, coupled with the Navier-Stokes equations. The authors also prove the existence of the solution of the optimal control problem, the existence of the solution of the Navier-Stokes equations with mixed boundary conditions, the weak continuity of the solution of the Navier-Stokes equations with respect to the geometry shape of the blade's surface and the existence of solutions of the equations for the Gateaux derivative of the solution of the Navier-Stokes equations with respect to the geometry of the boundary.     

墙体绕墙顶转动情况下挡土墙主动土压力分布

根据库仑土压力理论的假设,挡土墙上的土压力是由墙后填土在极限平衡状态下出现的滑动楔体产生,给出了墙体绕墙顶转动变位模式下土压力强度、土压力合力和土压力合力作用点的理论公式,并与库仑土压力理论、墙体平动变位模式下土压力和有关实验结果进行了比较．结果表明,墙体绕墙顶转动变位模式下土压力合力与墙体平动变位模式下土压力合力相等,且等于库仑理论计算结果,但土压力合力作用点和土压力分布有显著差别．     

Parametric analysis of the oscillatory solutions to stochastic differential equations with the Wiener and Poisson components by the Monte Carlo method

Using the Monte Carlo method, we address the influence of the Wiener and Poisson random noises on the behavior of oscillatory solutions to systems of stochastic differential equations (SDEs). For the linear and Van der Pol oscillators, we study the accuracy of estimates of the functionals of numerical solutions to SDEs obtained by the generalized explicit Euler method. For a linear oscillator, we obtain the exact analytical expressions for the mathematical expectation and the variance of the SDE solution. These expressions allow us to investigate the dependence of the accuracy of estimates of the solution moments on the values of SDE parameters, the size of meshsize, and the ensemble of simulated trajectories of the solution. For the Van der Pol oscillator, we study the dependence of the frequency and the damping rate of the oscillations of the mathematical expectation of SDE solution on the values of parameters of the Poisson component. The results of the numerical experiments are presented.     

Symmetry structure of the hyperbolic bifurcation without reflection of periodic orbits in the standard map

For the area preserving maps, the linearized tangent map determines the stability of the fixed point. When the trace of the tangent map is less than −2, the fixed point is inversion hyperbolic, thus the subsequent points of mapping alternate across the destabilized fixed point. That is to say, the fixed point undergoes periodic doubling bifurcation. While for the trace of the tangent map is larger than +2, the fixed point undergoes the hyperbolic bifurcation without reflection. Here, the processes of the hyperbolic bifurcation without reflection in the standard map have been examined in terms of the higher order symmetry in the momentum inversion. It is shown that the higher order symmetry lines approach asymptotically to the separatrix of the hyperbolic fixed point, and the existing symmetry lines cannot determine the structure of the periodic islands born after the hyperbolic bifurcation without reflection.     

考虑翻箱的场桥调度和提箱集卡数量的集成优化

在集装箱码头的进口箱堆场中,码头预约机制、待提箱的实时位置和场桥作业调度方案是制约堆场作业效率和堵塞情况的关键。为缓解进口箱堆场的拥塞情况并提高作业效率,在固定的预约时段内,考虑实时压箱量最少的翻箱规则,兼顾场桥间不可跨越和保持安全间距等现实约束,以场桥最长完工时间最小为目标,构建数学优化模型,设计了嵌入修复算子的改进遗传算法用于求解;通过算例实验验证了算法的有效性和方案的优越性,可为堆场实际作业提供决策参考。     

Grassmann image of non-isotropic surface of pseudo-Euclidean space

We consider submanifolds of non-isotropic planes of the Grassman manifold of the pseudo-Euclidean space. We prove a theorem about the unboundedness of the sectional curvature of the submanifolds of the two-dimensional non-isotropic planes of the four-dimensional pseudo-Euclidean space with the help of immersion in the six-dimensional pseudo-Euclidean space of index 3. We also introduce a concept of the indicatrix of normal curvature and study the properties of this indicatrix and the Grassman image of the non-isotropic surface of the pseudo-Euclidean space. We find a connection between the curvature of the Grassman image and the intrinsic geometry of the plane. We suggest the classification of the points of the Grassman image.     

连续区间数的中位算子及其灵敏度分析

研究决策信息以区间数形式给出的方案决策问题。考虑到区间数非均匀分布的特点,为避免区间极端值在区间数确定中产生较大误差,本文将中位数概念运用到区间数的确定上,提出OIP(Ordered Interval Point)有序中位算子。取单位区间单调函数(BUM函数)为二分之一所表示的值为权重,将区间数确定为一个实数,并研究算子单调性和有界性的初等运算性质。通过比较OIP算子与COWA算子对态度参数和区间长度的反应灵敏度,获得了在一定条件下OIP算子对态度参数反应更稳健,对区间长度反应更灵敏的结论。最后用算例证明该算子的可行性和有效性。