Image reconstruction based on total-variation minimization and alternating direction method in linear scan computed tomography

Linear scan computed tomography (LCT) is of great benefit to online industrial scanning and security inspection due to its characteristics of straight-line source trajectory and high scanning speed. However, in practical applications of LCT, there are challenges to image reconstruction due to limited-angle and insufficient data. In this paper, a new reconstruction algorithm based on total-variation (TV) minimization is developed to reconstruct images from limited-angle and insufficient data in LCT. The main idea of our approach is to reformulate a TV problem as a linear equality constrained problem where the objective function is separable, and then minimize its augmented Lagrangian function by using alternating direction method (ADM) to solve subproblems. The proposed method is robust and efficient in the task of reconstruction by showing the convergence of ADM. The numerical simulations and real data reconstructions show that the proposed reconstruction method brings reasonable performance and outperforms some previous ones when applied to an LCT imaging problem.     

登陆我国大陆热带气旋的纬度分布特征

登陆点位置是热带气旋研究的重要课题.为消除因资料单一产生的误差, 本文采用1951-2010年中国、美国、日本三套热带气旋最佳路径资料, 分析了登陆我国大陆热带气旋频数的年际变化规律, 并研究了登陆纬度的分布和变化特征. 本文以总结三套资料一致反映的现象为主, 得到以下一些有意义的结果: 从总体上看, 中国资料集内的登陆频数比其他两套资料平均每年约多1个. 1970年后三套资料的登陆频数基本保持不变, 登陆纬度有较一致的北移, 而1970年前两者在三套资料内的变化不太一致. 从单位纬度登陆频数上看, 登陆数绝大部分集中在北纬30° 以下, 且总体上随纬度增加而减少, 其中北纬21°-23° 登陆数偏多, 北纬20°-21° 和北纬23°-24° 登陆数偏少.     

XFEL飞秒同步与定时系统中光纤长度变化的数字化监测(英)

分析了X射线自由电子激光装置对飞秒同步定时系统的技术需求。系统中采用光纤来传输定时/相位信息。而光纤的光长度会随温度的慢漂而改变,因此通过对比实验研究了温度慢漂对光纤长度变化的影响。研制了基于现场可编程门阵列（FPGA）的数字化相位和幅度检测器对光纤长度变化进行数据监测。百米光纤在典型昼夜温差下导致的时间延迟约6 ps。结果显示此数字化相位和幅度检测器可以用于飞秒同步定时系统的长度变化监测和稳定控制系统当中。     

“空气比热容比”教学中的物理思想与测定的关键问题分析

该实验从诸多气体状态变化中选取了3个关键的状态,实验设计巧妙,整个实验中涉及的理论分析过程复杂,实验操作有很多不可控因素,因此如何在实验教学中把握实验的设计思想,找到测量的关键点显得尤为重要.本文旨在分析实验过程的基础上,利用力学中“回复力”的概念,使学生快速掌握实验过程的变化规律,并以“压强”为控制因素,进行数据记录,从而使学生把握了实验测量的关键点,提高了实验的教学效率.     

批到达M/G/1重试排队的队长的尾渐近

用随机分解法研究成批到达服务时间为次指数分布的重试排队中队长的尾行为,得到了该系统与其相应的标准排队系统队长尾分布的关系;对次指数尾,结果也能用于正则变化尾,进而得到正则变化尾渐近．     

Comparative experimental study of laser-induced transitions in crystalline silicon by femtosecond,picosecond, and millisecond laser ablation

In order to study laser-induced transitions of the crystalline silicon, comparative ablation experiments by femtosecond-, picosecond-, and millisecond-pulsed laser were carried out on<111>crystalline silicon wafers in this study. For each laser ablating process, final chemical composition and microstructural state of ablated material on sample surface were analyzed by X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. Then the influences of laser pulse duration variation on the composition and microstructure of ablated material were also discussed. Therefore, the experimental results were considered to provide more completed and further understandings of laser-induced transitions of crystalline silicon, which may have some contribution to the development of laser-semiconductors micromachining.     

Right and Left Matrix-Valued Stochastic Exponentials and Explicit Solutions to Systems of SDEs

We study the properties of the right and left matrix-valued stochastic exponentials by their quadratic variation processes between two matrices of semimartingales. We obtain explicit solutions of linear and some nonlinear systems of stochastic differential equations by expressing the right and left stochastic exponentials in a closed-form formula.     

Solutions to the 1-harmonic flow with values into a hyper-octant of the N-sphere

We announce existence results for the 1-harmonic flow from a domain of ${\mathbb{R}}^m$ into the first hyper-octant of the $N$-dimensional unit sphere, under homogeneous Neumann boundary conditions. The arguments rely on a notion of “geodesic representative” of a BV-vector field on its jump set.