基于水平集方法的数字胸片图像分割

水平集方法能有效地解决曲线演化过程中的拓扑变化问题，基于全局特性的活动轮廓模型采用水平集方法给出的迭代解，能有效进行分割。用这种方法对CR胸片图像进行分割研究，并根据CR图像的特点，给出了只需一次演化的方法：直接针对原图像可以得到肺部大致区域；而针对CR的局部标准偏差图像可以得到肋骨的边缘图像。实验结果表明，该方法能很好地对CR图像进行分割。     

一种应用改进符号序列熵与滑动窗奇异值的退化特征提取方法

为了准确跟踪岸桥关键部件的性能退化状态,提出一种基于改进符号序列熵与滑动窗奇异值的在线退化特征提取方法.针对岸桥工况特殊、振动随机冲击频繁的特点,引入阈值因子并改进序列符号化方法,在保留方向变化信息的同时兼顾"粗粒化"的幅值变化信息,从而提高符号序列熵滤除随机冲击、刻画振动信号复杂度大小的能力.在线计算振动信号的改进符...     

基于Hoek-Brown破坏准则深埋硐室围岩结构可靠度分析

为了研究不同参数对深埋硐室围岩稳定性的影响,基于"楔形塌落体+圆弧转动体"的计算模型,将极限分析上限定理与可靠度理论相结合,构建了Hoek-Brown破坏准则下深埋硐室围岩结构可靠度模型,分析了相关参数对深埋硐室围岩结构可靠度的影响规律.结果表明:侧压系数K会引起深埋硐室顶板和两帮的失效概率发生显著差异.Hoek-Br...     

基于马尔可夫过程的混流装配线缓冲区容量研究

为研究混流装配线缓冲区容量,基于马尔可夫过程原理,建立了通用的混流装配线模型,分析了模型中工作站和缓冲区状态,绘制了工作站与缓冲区的状态图,建立了状态转移矩阵,分析了工作站与缓冲区在不同状态下装配线正常运转的概率,推导出了装配线可用度与缓冲区容量之间的关系。用可用度计算公式分析混流装配线缓冲区设置对提高装配线可用度的影响,并以两级系统为例计算缓冲区容量,分析了缓冲区容量与可用度、费用之间的关系。     

孔隙水压力作用下盾构隧道开挖面支护力上限研究

基于极限分析上限定理和空间离散技术,构建了适用于在饱和土体中掘进的盾构隧道开挖面上限破坏机制。在此基础上,将孔隙水压力做的功率作为一个外力功率引入上限定理的虚功率方程,通过优化计算,得到了孔隙水压力作用下盾构隧道开挖面支护力的上限解。为了证明上限解的有效性,基于数值模拟技术计算了孔隙水压力作用下隧道开挖面极限支护力的数值解,并将得到的数值解和上限解进行了对比分析,结果表明,上限解和数值解非常接近。最后,分析了参数变化对开挖面支护力和破坏面的影响,分析结果表明:孔隙水压力对支护力上限解影响明显而对开挖面破坏范围的影响不大。     

沿空留巷巷旁充填体支护结构可靠性分析

针对沿空留巷巷旁充填体力学参数中有许多为随机变量的特征,根据沿空留巷巷旁充填体支护结构稳定性极限状态方程,运用工程结构可靠性理论建立了沿空留巷巷旁充填体支护结构可靠性模型.采用蒙特卡罗法在Matlab环境下计算了其结构可靠度,编程过程简化,计算速度快,精度高,且不受极限状态方程非线性、随机变量非正态的限制,并指出了提高沿空留巷巷旁充填体支护结构可靠度的方法和措施,为沿空留巷巷旁充填体支护参数设计和优化提供了科学依据.     

当代大学生价值观念的嬗变与新时期高校的德育工作

针对高校大学生价值观念教育这一问题,分析了当代大学生观念嬗变的原因与特点,指出了德育对侪值观念的引导作用,探讨了新时期德育工作的新内容和新举措。     

Influence of pore water pressure on upper bound analysis of collapse shape for square tunnel in Hoek-Brown media

To investigate the effective shape of collapsing block in square tunnel subjected to pore water pressure, the analytical solution of detaching curve was derived using upper bound theorem of limit analysis with Hoek-Brown failure criterion. The work rate of pore water pressure, which was regarded as an external rate of work, was taken into account in the framework of limit analysis. Taking advantages of variational calculation, the objective function with respect to detaching curve was optimized to obtain the effective shape of collapsing block for square tunnel. According to the numerical results, it is found that the varying pore water pressure coefficient only affects the height and width of the collapsing block, whereas the shape of collapsing block remains unchanged.     

Reliability analysis of retaining walls with multiple failure modes

In order to reduce the errors of the reliability of the retaining wall structure in the establishment of function, in the estimation of parameter and algorithm, firstly, two new reliability and stability models of anti-slipping and anti-overturning based on the upper-bound theory of limit analysis were established, and two kinds of failure modes were regarded as a series of systems with multiple correlated failure modes. Then, statistical characteristics of parameters of the retaining wall structure were inferred by maximal entropy principle. At last, the structural reliabilities of single failure mode and multiple failure modes were calculated by Monte Carlo method in MATLAB and the results were compared and analyzed on the sensitivity. It indicates that this method, with a high precision, is not only easy to program and quick in calculation, but also without the limit of nonlinear functions and non-normal random variables. And the results calculated by this method which applies both the limit analysis theory, maximal entropy principle and Monte Carlo method into analyzing the reliability of the retaining wall structures is more scientific, accurate and reliable, in comparison with those calculated by traditional method.