A geometric factor calculation method based on the isotropic flux assumption

One of the instruments onboard the China Seismic Electromagnetic Satellite （CSES） is the Low Energy Particle Detector （LEPD）. The primary objective of LEPD is to provide measurements of the fluxes, energy spectra and pitch angles of 100 keV to 10 MeV electrons and protons from 2 to 50 MeV in the Earth＇s magnetosphere. The geometric factor is one of the principle parameters of a detector, which converts the physical quantity-count rate to the particle quantity-flux. In this paper, we calculated the geometric factor of LEPD via computer modeling of an isotropic radiation environment. It was first demonstrated that the radiation intensity related should obey a cosine-law, then a general sampling method of generating this distribution via GPS of GEANT4 was explained. Furthermore, combined with flux normalization, a comparison of the geometric factor calculation of a set of 2-layer detectors with different shapes （cylinder, truncated cone and rectangle） was performed. Results show a generally good agreement between simulation and analytical calculations for the cylinder and truncated cone detectors, and the result of the rectangular one, for which there is no accurate analytical formula, is consistent with the previous simulated results by others. As a practical instance of the 2-layer rectangle detector, the geometric factor of LEPD is 10.336±0.036 m cm2·sr for 10 MeV proton and 8.211±0.032 m cm2·sr for 8 MeV electron.     

瞬发中子密度衰减法计算中子代时间

采用蒙特卡罗程序MCNP计算了西安脉冲堆中子代时间。使用MCNP程序模拟了反应堆瞬发中子通量密度衰减,基于忽略缓发中子项的点堆动力学方程计算出中子代时间。在微次临界下,研究了次临界度、源的分布、计数区域等对西安脉冲堆中子代时间计算结果的影响。计算分析表明:采用瞬发中子密度衰减法计算中子代时间时,微次临界度、源分布、计数区域等对计算结果影响都很小;误差产生的主要原因是忽略缓发中子项的点堆动力学方程并不能较好地反应瞬发中子通量密度的衰减规律。     

等截面引射器启动性能数值研究

采用雷诺平均方程和SST k-ω湍流模型,空间离散采用二阶精度的Roe FDS方法,限制器采用Min-Mod方法,时间迭代采用隐式方法,研究了等截面引射器长度、引射器与喷管的间隙对其启动性能的影响。结果表明:等截面引射器存在启动、临界、不启动三种状态;在引射器长度一定的情况下,引射器与喷管之间的间隙越小,引射器的启动压比越小;在引射器与喷管之间间隙一定的情况下,对于本文所计算的工况,当引射器长度小于3m时,引射器所需的启动压比会很大,当引射器长度小于2m,则引射器很难启动;当引射器长度超过7m时,会对引射器的加工、安装、冷却带来诸多不利影响。     

Depolarization and Electrical Response of Porous PZT 95/5 Ferroelectric Ceramics under Shock Wave Compression

The release of bound charges by shock wave loading of poled lead zirconate titanate （PZT 95/5） ferroelectric ceramics can result in a high-power electrical energy output. In this study, a theoretical formulation describing the depolarization and electrical response of porous PZT 95/5 ceramics in the normal mode to shock wave compression loading perpendicular to the polarization direction is developed. The depoling process in porous poled PZT 95/5 ceramics is analyzed by using a parallel circuit consisting of a current source, capacitance, conductance and a circuit load. This modeling takes the effects of porosity on wave velocity and remanent polarization and dielectric constant into account, and the effects of variations in dielectric constant and conductivity in the shocked region are assessed. The output current characteristics of porous PZT 95/5 ceramics under short-circuit and resistive load conditions are analyzed and compared with the experiment, with the results showing that theoretical predictions taking into consideration the porosity of ferroelectric ceramics are in close agreement with the experimentally measured electrical response of porous PZT 95/5 under shock wave compression loading.     

Cu,Zn离子注入SiO_2纳米颗粒合成及氧气氛围下的热稳定性研究

通过45 keV,1.0×1017cm-2的Cu离子注入SiO2基底合成了嵌入式的Cu纳米颗粒,采用不同剂量的50 keV Zn离子对Cu纳米颗粒进行后续辐照,详细研究了Zn离子后续辐照对Cu纳米颗粒结构、光学性质的影响及其氧气气氛下的热演变规律.研究结果表明,Cu和0.5×1017cm-2的Zn离子顺次注入可在SiO2基底中形成Cu-Zn合金纳米颗粒,它们可以在516 nm附近引起独特的表面等离子共振(SPR)吸收峰.后续O2气氛中450?C退火可以导致Cu-Zn合金纳米颗粒分解,并在基体中形成了ZnO和Cu纳米颗粒.研究结果还表明后续Zn离子的辐照可以有效地提高Cu纳米颗粒的抗氧化能力;同时基体中Cu的存在也会加速Zn向样品表面的扩散,从而促进了ZnO的形成.     

船-冰作用中海冰典型破坏模式的离散元数值模拟

在破冰船破冰过程中,冰排主要表现为挤压与弯曲两种破坏模式.本文基于黏结离散单元法对船-冰作用中的这两种典型破坏模式进行数值模拟.海冰离散元数值试样采用随机排布方式生成,采用单轴压缩试验与三点弯曲试验相结合的方式标定模型中的细观参数.将船-冰碰撞中的挤压和弯曲作用方式简化为直立或倾斜 平板与海冰的作用模式,构建挤压与弯曲破坏的海冰离散元数值试样,分析了挤压破坏模式中不同加载方位以及冰厚和加载速率对破坏模式的影响,以及弯曲破坏模式中不同冰排夹角以及冰厚和加载速率对破坏模式的影响.计算结果表明,离散元海冰数值模型可以很好地对冰排挤压与弯曲破坏现象进行模拟,可揭示冰排在不同破坏模式下的破坏机理.     

基于三维光谱角统计的光谱图像信息提取方法

提出了一种新的基于三维光谱角统计的光谱图像信息提取方法。通过对影像上横向、竖向和对角方向相邻像元间采用光谱角计算相似度,构成一个三维的信息统计模型。该模型反映了相邻像元间所代表物质的相似度,通过在统计模型中设置不同的阈值和提取不同轴向的切片,可以从影像中提取代表同种物质的均匀区域和边缘信息,用于监督分类中训练样本的采集。该统计方法与直方图、散点图等传统统计工具相比,鲁棒性和可靠性更高,提取的信息更丰富。     

Irradiation hardening behaviors of tungsten-potassium alloy studied by accelerated 3-MeV W^2+ ions

Tungsten-potassium(WK)alloy with ultrafine/fine grains and nano-K bubbles is fabricated through spark plasma sintering(SPS)and rolling process.In this study,3-MeV W^2+ ion irradiation with a tandem accelerator is adopted to simulate the displacement damage caused by neutrons.As the depth of irradiation damage layer is limited to only 500 nm,the hardening behaviors of WK alloy and ITER(International Thermonuclear Experimental Reactor)-W under several damage levels are investigated through Bercovich tip nanoindentation test and other morphological characterizations.The indenter size effect(ISE),soft substrate effect(SSE),and damage gradient effect(DGE)are found to influence the measurement of nano-hardness.Few or no pop-ins in irradiated samples are observed while visible pop-in events take place in unirradiated metals.Extensive pile-up with different morphology features around the indentation exists in both WK and ITER-W.The WK shows a smaller hardness increment than ITER-W under the same condition of displacement damage.This study provides beneficial information for WK alloy serving as a promising plasma facing materials(PFMs)candidate.