PLASTIC ANALYSIS OF THIN PLATES WITH ANISOTROPIC HARDENING

In this paper we discuss the adoption of the anisotropic hardening model due to theexistence of Bauschinger effect when thin plate is applied by repeated loading.The loadingcondition of thin plates for linear kinematic hardening has been deduced in terms ofgeneralized forces and generalized plastic deformation.And it can be extended to nonlinearkinematic hardening and mixed hardening.Finally as an example the numerical results areobtained for a circular plate.     

“阳”加速器钼丝X-pinch初步实验研究

 在“阳”加速器上进行了直径分别为10, 15, 20 μm, 交叉角为32°,45°,60°的钼（Mo）丝X-pinch实验。“阳”加速器产生的电流峰值约520 kA，上升时间80 ns。实验中通过X射线功率谱仪和纳秒分幅相机等仪器对Mo丝X-pinch辐射特性进行了诊断。实验表明：Mo丝X-pinch过程中会出现多次X射线爆发，箍缩过程中产生的热点辐射出能量超过3 keV的X射线，探测到的最小热点直径小于30 μm。     

一种可在线更新的PET实时查找表电路的设计与实现

介绍了一种正电子发射断层成像术实时查找表电路。该电路接收符合电路输出的位置信号和能量信号,用查表的方法完成重心法中的除法运算,然后再第二次查表得到该γ光子所入射到的晶格的离散化坐标值和能量阈值,并完成能量甄别以剔除部分散射事件。此外,该电路还结合了呼吸门控和心电门控功能。查找表存储在flash器件中,由CPLD控制读写。本设计的特点是利用硬件电路来完成查找表功能,效率更高,每次事件的查表寻址的延迟时间小于100ns,并且可以在线更新查找表的内容,使用方便。另外,还说明了用CPLD来读写NORflash的方法,以及该电路与系统中其它模块间的数据通信方法。     

利用凸晶摄谱仪获取Z箍缩等离子体X辐射单色图像

考虑晶体摇摆曲线的影响,用光线追迹方法讨论了凸晶摄谱仪的能谱分辨率、单色图像径向空间分辨本领以及晶体与X射线源之间的距离对它们的影响.根据讨论建立了云母凸晶摄谱仪,在"强光一号"装置上对系统进行了成功地测试,获得铝丝阵负载Z箍缩等离子体X辐射单色图像.时间积分图像表明,Z箍缩Al等离子体K壳层Lya和Heβ线辐射来自等离子体核心直径约2.3 mm的区域.     

CVD金刚石薄膜探测器性能研究

通过实验测量和理论分析, 从载流子动力学角度研究了用于脉冲辐射探测的CVD金刚石薄膜探测器的适用结构、电荷收集效率和时间响应性能. 结果表明, CVD金刚石薄膜可以制成均匀型结构的探测器; 薄膜中的缺陷会降低探测器的电荷收集效率, 探测器的电荷收集效率随场强增大而增大直至饱和. 已研制的CVD金刚石探测器电荷收集时间可达719ps, 在2.5V/μm场强下达到饱和, 电荷收集效率 达60.5%; 晶格散射是影响探测器时间响应的主要因素, 选用大晶粒甚至单晶金刚石薄膜可以提高探测器时间响应.     

A FINITE ELEMENT—MATHEMATICAL PROGRAMMING METHOD FOR ELASTOPLASTIC PROBLEMS BASED ON THE PRINCIPLE OF VIRTUAL WORK

By expanding the yielding function according to Taylor series and neglecting the high order terms, the elastoplastic constitutive equation is written in a linear complementary form. Based on this linear complementary form and the principle of virtual work, a finite element-complementary method is derived for elastoplastic problem. This method is available for materials which satisfy either associated or nonassociated flow rule. In addition, the existence and uniqueness of solution for the method are also discussed and some useful conclusions are given. The project is supported by the National Natural Science Foundation of China     

Z箍缩等离子体高分辨X辐射谱诊断

 为了获取丝阵Z箍缩等离子体高能谱分辨的X辐射图像,建立了云母球面弯晶X光摄谱仪,根据色散平面内球面弯晶诊断空间分布X光源的几何模型分析了摄谱仪的能谱分辨,计算结果与光线追迹方法得到的结果吻合。当探测器位于罗兰圆上时,系统具备最优能谱分辨。在“强光一号”装置上,利用该摄谱仪诊断了镀镁铝丝阵负载Z箍缩等离子体的X辐射图像,结果表明,该球面弯晶摄谱仪的能谱分辨率高于1 000。     

基于Boltzmann输运方程的SPECT系统解析建模方法

在单光子发射断层成像(SPECT)中, 为了校正劣化因素的影响, 提高图像质量, 需要对SPECT成像的物理过程进行准确建模. 本文提出了基于Boltzmann输运方程及其Neumann级数解理论的SPECT系统解析建模方法, 并采用数论高维数值积分算法对解析建模公式进行数值求解. 分别对点源、均匀圆柱体模型和NCAT模型进行SPECT投影过程计算, 将其结果与传统的Monte Carlo建模方法进行比较. 结果表明解析建模方法的计算速度和精度综合性能优于Monte Carlo建模方法, 且具有不受统计噪声影响的优点, 因而更适于进行SPECT成像过程的建模.     

SHAKEDOWN ANALYSIS OF SHELL STRUCTURES OF KINEMATIC HARDENING MATERIALS

It is of great practical importance to analyze the shakedown of shell structures undercyclic loading,especially of those made of strain hardening matericls.In this paper,some further understanding of the shakedown theorem for kinematichardening materials has been made,and it is applied to analyze the shakedown of shellstructures.Though the restdual stress of a real state is related to plastie strain.the time-independent residual stress field(?),as we will show in the theorem may be unrelated to thetime-independent kinematically admissible plastic strain field(?)For the engineeringapplication,it will be much more convenient to point this out clearly and definitely,otherwise it will be very difficult Also we have proposed a new method of proving thistheorem.The above theorem is applied to the shak edown analysis of a cylindrical shell withhemspherical ends.According to the elastic solution,various possible residual stress andplastic strain fields,the shakedown analysis of the structure can be reduced to a     

A CVD diamond film detector for pulsed proton detection

A chemical vapour deposition （CVD） diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo （MC） simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.