硬X光光电成像系统面密度分辨能力

针对基于将X光转换成可见光接收的硬X光光电成像系统,研究了系统面密度分辨能力的理论模型,获得了系统面密度分辨能力的上下限的表达式;建立了对硬X光成像系统对面密度分辨能力的测量方法。利用自制面密度分辨率板,实验测量了由射频X光机、转换屏、光纤锥耦合和CCD相机组成的硬X光光电成像系统在不同照射量下的面密度极限分辨能力的上下限值。实验结果与理论分析模型分析趋势一致,在未饱和条件下面密度分辨力上限随着照射量的增加而不断增加,而面密度分辨力下限随着照射量的增加将减小。     

基于模式搜索的渴求函数法在多响应优化中的应用

渴求函数法是处理多响应参数优化的常用方法之一,它通过最大化总体渴求值获得因子的最佳水平组合.然而,随着因子个数和响应个数的增加,渴求函数往往变得多约束、多峰分布、高度非线性,传统的基于梯度的优化算法不适用.根据因子及响应个数等问题复杂程度不同,提出了以模式搜索算法为基础,用重叠等值线图或遗传算法设定模式搜索的起始点,对总体渴求函数进行寻优的新方法.算例验证了该方法的有效性.     

X射线散射对面密度测量结果影响的数值模拟研究

定性分析了X射线散射对面密度测量结果的影响,给出了面密度测量结果偏差的评估表达式。利用蒙特卡罗方法数值模拟了不同照相布局、不同光源能量和不同材料类型情形下X射线散射对测量结果的影响。模拟结果表明：在无防护窗情形下,被测物自身散射将导致测量结果偏小;在有防护窗情形下,前窗散射对测量结果的影响不大,后窗散射对测量结果的影响与接收介质离被测物的距离有关,具体表现为距离越小影响越大;在一定光子能量范围内,光源能量越低散射导致的测量偏差越大;被测物的原子序数和密度越大,散射导致的测量偏差越大。     

Time-Resolved Visualization of Laser-Induced Heating of Gold with MeV Ultrafast Electron Diffraction

Time-resolved electron diffraction employing MeV electron beams is demonstrated experimentally at the center for ultrafast diffraction and microscopy of Shanghai Jiao Tong University. A high-quality diffraction pattern is recorded by a single shot of electron pulse. Synchronization between the pump laser and the probe electron beam is achieved through measurement of electron deflection caused by the laser-induced plasmas in a metal tip. We study the ultrafast structural dynamics of the gold lattice excited by a femtosecond laser through tracing the change of Bragg peaks intensity at different time delays. It is expected that the combination of MeV ultrashort electron beams and femtoseeond laser pulses will open many new opportunities in the ultrafast and ultrasmall world.     

基于标记中子方法检测墙体爆炸物扣除本底方法

利用电磁等技术确定墙体内可疑区域,采用标记中子方法检测可疑区域是否含有爆炸物,是快速、准确、可靠的技术手段.为了降低高密度墙体的影响,更准确判断墙体内是否存在爆炸物,分别采用全能峰面积(TPA)法,科沃尔(Covell)峰面积法,沃森(Wasson)峰面积法对2种元素C、O的特征峰进行本底扣除.采用扣除本底后的C、O特征峰计数比(C/O)值来确定墙体内是否存在爆炸物,与不扣除本底计数时的C/O值相比,其适用性得到较大提高.     

铁掺杂TiO2/膨润土光催化剂的制备及表征

以溶胶-凝胶法制备了过渡金属铁掺杂的Fe-TiO2/膨润土复合光催化剂,通过XRD、FTIR技术对该系列催化剂的结构进行了表征,并以亚甲基蓝染料废水为模型,考察了紫外光和日光下铁掺杂量对催化剂性能的影响。结果表明,催化剂中有锐钛矿型TiO2生成,铁掺杂TiO2进入了膨润土的蒙脱石层间,改变了蒙脱石层间的有序性,生成了Ti—O—Si键,实现了TiO2粒子与膨润土的复合;适量Fe3+的掺杂降低了TiO2粒子的粒径,并且部分Fe3+还可能进入了TiO2的晶格,形成了缺陷位,拓宽了TiO2的光谱利用范围,提高了光催化活性。     

Strain Tunable Berry Curvature Dipole,Orbital Magnetization and Nonlinear Hall Effect in WSe_2 Monolayer

The electronic topology is generally related to the Berry curvature,which can induce the anomalous Hall effect in time-reversal symmetry breaking systems.Intrinsic monolayer transition metal dichalcogenides possesses two nonequivalent K and K’ valleys,having Berry curvatures with opposite signs,and thus vanishing anomalous Hall effect in this system.Here we report the experimental realization of asymmetrical distribution of Berry curvature in a single valley in monolayer WSe₂ via applying uniaxial strain to break C_3v symmetry.As a result,although the Berry curvature itself is still opposite in K and K’ valleys,the two valleys would contribute equally to nonzero Berry curvature dipole.Upon applying electric field E,the emergent Berry curvature dipole D would lead to an out-of-plane orbital magnetization M ∝ D·E,which further induces an anomalous Hall effect with a linear response to E²,known as nonlinear Hall effect.We show the strain modulated transport properties of nonlinear Hall effect in monolayer WSe₂ with moderate hole-doping by gating.The second-harmonic Hall signals show quadratic dependence on electric field,and the corresponding orbital magnetization per current density M/J can reach as large as 60.In contrast to the conventional Rashba-Edelstein effect with in-plane spin polarization,such current-induced orbital magnetization is along the out-of-plane direction,thus promising for high-efficient electrical switching of perpendicular magnetization.     

用于红外光谱分析的溴化钾的提纯

分析纯溴化钾的红外光谱中通常含有杂质产生的强干扰吸收带,不能直接作为红外光谱分析用的试剂。以乙二胺四乙酸（EDTA）为螯合剂,与分析纯溴化钾中的杂质生成水溶性络合物,通过重结晶、高温焙烧,去除了溴化钾中的杂质,得到了高纯度的溴化钾。实验结果表明,该溴化钾的光谱纯度优于市面上价格昂贵的光谱纯溴化钾,获得了更高质量的红外光谱图,降低了红外光谱实验的成本。     

Cu-ZnO/膨润土光催化氧化降解甲基橙废水

以膨润土为载体,采用溶胶-凝胶法制备了Cu-ZnO/膨润土光催化剂,通过XRD对其结构进行了表征,研究了该催化剂光催化降解甲基橙染料废水的性能.结果表明:ZnO插入了膨润土层间并与之成功复合,Cu2+渗入了ZnO晶格,拓宽了其光谱响应范围,提高了催化剂对太阳光和可见光的利用率.该催化剂易于回收,经高温活化后,可重复多次使用.     

双面金属铝包覆介质波导测量介质厚度和折射率

利用双面金属铝包覆波导的测量方法,测量了硅片的厚度和折射率。这种方法利用双面金属铝包覆波导的超高阶模的偏振不灵敏和对金属层要求较低的特点,降低了对仪器的要求和测量的成本。同时,由于应用高灵敏的超高阶导模为探针,测量精度较高,结果显示测量精度在1%以内。