排序方式: 共有42条查询结果,搜索用时 15 毫秒
11.
Sensitive X-ray polarimetry in the keV energy range can be achieved by measuring the azimuthal angle distribution of emitted electrons after the photoelectric absorption of X-rays in a micropattern gas detector. However, the initial direction of the electron is not readily measurable due to the randomization of its motion during energy loss. By using the Geant4, Maxwell and Garfield packages, we simulated the detected electron tracks following photoelectric absorption, electron drift and diffusion in the gas, and proposed a technique capable of reconstructing the initial direction of the emitted photoelectron. The technique allows us to measure the angular modulation of flux predicted for a polarized X-ray beam. We calculated the modulation factors in 2-10 keV with a gas mixture of neon and CO2 , and discussed how electron diffusion along the drift will dilute the track and suppress the modulation. These results are useful for the design of the X-ray polarimeter. 相似文献
12.
新型有机非线性光学晶体-L-苹果酸脲晶体生长的初步探讨 总被引:2,自引:2,他引:0
本文初步探讨了新型非线性光学晶体-L-苹果酸脲的晶体生长,研究结果表明,L-苹果酸脲晶体在甲醇、乙醇和水三种介质中的溶解度温度系数均较大,同温度下L-苹果酸脲晶体在水中的溶解度最大,无水甲醇次之,无水乙醇中最小.L-苹果酸脲晶体在无水甲醇中的成核自由能比在无水乙醇中的低得多,因此在无水甲醇中易于成核,晶核数多,晶体尺寸小,而在无水乙醇介质中,虽然成核相对比较困难一些,但有利于制备大的单晶,且发现低温有利于大晶体的生长.因此宜选择无水乙醇为晶体生长介质.L-苹果酸脲晶体在介质中以非均匀成核方式在试管壁成核长大,晶体呈棱柱状,生长过程中呈现台阶生长的特征. 相似文献
13.
在模拟人体生理条件下,采用紫外光谱、荧光光谱和同步荧光光谱法相结合,研究槐果碱(SC)和氧化槐果碱(OSC)与溶菌酶(LYSO)的相互作用机制,并探讨其构效关系。紫外光谱显示,SC和OSC可与LYSO发生相互作用;荧光光谱表明,SC和OSC对LYSO的内源荧光均有显著的猝灭作用,猝灭机制主要为静态猝灭和非辐射能量转移。SC和OSC均可与LYSO形成1∶1复合物,在温度为310K下二者与LYSO的结合常数K分别为0.922×105、2.81×105 L·mol-1,结合距离r分别为3.81、4.39nm,其作用力主要为氢键和范德华力。OSC与LYSO的结合能力明显强于SC;同步荧光光谱表明,OSC与LYSO相互作用后,LYSO的构象发生改变,而SC与LYSO相互作用后,LYSO的构象基本不变。Fe3+、Mg2+、Cu2+、Zn2+四种金属离子的存在增强了SC和OSC与LYSO的结合能力,四种金属离子均以"离子架桥"模式介导SC和OSC与LYSO的相互作用,且其强弱顺序为:Mg2+>Cu2+>Fe3+>Zn2+。 相似文献
14.
15.
Theoretical Computation for Non-Equilibrium Air Plasma Electrical Conductivity at Atmospheric Pressure 下载免费PDF全文
Based on the Chapman-Enskog theory, we calculate the electrical conductivity of non-equilibrium air plasma in the two-temperature model. We consider different degrees of non-equilibrium, which is defined by the ratio of electronic temperature to heavy particles temperature. The method of computing the composition of air plasma is demonstrated. After calculating the electrical conductivity from electron temperature 1000 K to 15000K, the present result is compared with Murphy's study [Plasma Chem. Plasma Process 15 (1994) 279] for equilibrium case. All the calculation is completed at atmospheric pressure. The present results may have potential applications in numerical calculation of non-equilibrium air plasma. 相似文献
16.
空间相机热设计中的极端工况确定 总被引:1,自引:0,他引:1
针对具有多姿态变化特点的空间相机,提出了考虑太阳辐射的到达外热流和吸收外热流两种情况下的极端工况确定方法和计算流程。根据辐射学的基本理论,并结合相机的结构特点,推导出了相机外表面总太阳辐射流的计算公式;根据相机进出地影的情况和太阳常数分别建立了相应矩阵,并进行了有关矩阵的运算和变换;借助工具软件Matlab求解得到了投落到相机外表面的总太阳辐射外热流极值,并在此基础上确定出该相机的极端工况;将此工况输入到I-DEAS/TMG仿真环境中进行仿真分析,验证了此方法的正确性。该计算方法同样适用于其它类型的相机,具用通用价值。 相似文献
17.
18.
Improvement of elevated-temperature performance of Li1.02Cr0.1Mn1.9O4 cathode material by silicious surface modification was studied. The Li1.02Cr0.1Mn1.9O4 cathode material was treated by silanes coupling agent and then heated at 580 ℃ to remove organic material. The structures of the modified and unmodified Li1.02Cr0.1Mn1.9O4 were characterized by SpectraPlus, SEM and XRD. The results show that the surface layer of Li1.02Cr0.1Mn1.9O4 material is found to be rich in silicious compound. X-ray diffraction show that all the samples have perfect spinel structure. The electrochemical characterization of modified Li1.02Cr0.1Mn1.9O4 cathode material was tested. The cycle stability of charge/discharge at 55℃ is improved. The results of the charge/discharge curves show that the modified Li1.02Cr0.1Mn1.9O4 has better performance than those unmodified according to the inhibition of decline of reversible capacity of spinel Li1.02Cr0.1Mn1.9O4. Therefore, cycle performance is improved so obviously that 86.03% of the initial capacity is preserved after 100 cycles. 相似文献
19.
20.
采用三种低温溶胶-凝胶法制备了具有不同Fe3O4掺杂量的磁靶向纳米Fe3O4-TiO2复合物, 通过X射线衍射(XRD)、透射电镜(TEM)、傅里叶变换红外(FTIR)光谱、紫外-可见(UV-Vis)光谱、荧光光谱(FS)及磁性能分析等表征方法筛选出包覆均匀、分散性好、磁性能优异及光催化活性较高的纳米Fe3O4-TiO2复合物. 以四甲基偶氮唑蓝(MTT)法检测肝癌细胞(HepG2)的存活率, 考察纳米Fe3O4-TiO2复合物在外磁场作用下对HepG2 细胞的光催化杀伤效应. 结果表明: 采用方法三制备的5%(质量分数)Fe3O4-TiO2复合物具备核-壳结构, 在混悬液中分散性较好, 平均粒径约为50 nm, 具有较强的光催化活性和良好的磁响应性, 同时将纳米TiO2的光响应范围拓宽至444 nm; 在外磁场作用下, 紫外光和可见光激发纳米Fe3O4-TiO2复合物对HepG2细胞的杀伤效应差异不大, 且均强于纳米TiO2; 其杀伤效应在0-1.0 T范围内随着外磁场强度的增大而增强. 相似文献