Fourier变换在非参数统计上的一个应用

非参数统计的一个重要研究方向是概率密度估计,密度估计的核心问题是求最优窗宽.基于Fourier变换及其性质给出了待估计的密度函数二阶导数的平方的积分的一个估计式,与传统的估计式相比,该式是对密度函数修正得到的.     

数列题的探究

通过对历年高考数学试题的深入研究,发现高考数学试题主要来源于以下五个方面：即将课本中的例题与习题、历年的高考试题、历年的初、高中数学竞赛试题、高等数学试题进行加工、改造、演变成为高考试题,还有个别的创新试题．下面举个例子来说明高考数学试题来源于历年的高考试题．     

DURATION OF NEGATIVE SURPLUS FOR A TWO STATE MARKOV-MODULATED RISK MODEL

We consider a continuous time risk model based on a two state Markov process, in which after an exponentially distributed time, the claim frequency changes to a different level and can change back again in the same way. We derive the Laplace transform for the first passage time to surplus zero from a given negative surplus and for the duration of negative surplus. Closed-form expressions are given in the case of exponential individual claim. Finally, numerical results are provided to show how to estimate the moments of duration of negative surplus.     

高功率激光装置大口径光学元件侧面清洗实验

针对高功率激光装置内部最易产生受激布里渊散射(SBS)效应的大口径取样光栅(BSG)元件,测试了经过化学刻蚀、紫外激光清洗作用处理后,大口径光学元件BSG侧面在355 nm激光辐照下的损伤阈值、损伤形态以及产生的石英颗粒气溶胶对环境污染程度的分析。结果表明:经过化学刻蚀,BSG侧面的损伤阈值提高78%,基本与通光面的损伤阈值相当,而经过紫外激光处理后的损伤阈值提升不高,仅为通光面损伤阈值的56%。侧面对比分析了相同激光能量辐照下样片侧面产生的气溶胶污染状况,结果表明紫外激光处理同样可以提高光学元件侧面产生污染物的阈值,且对光学元件性能没有影响。通过微观形貌和对通光口径影响分析表明,紫外激光清洗处理比化学刻蚀具有更好的安全性和适用性。     

神光-Ⅲ主机装置下装模块空间对接关键技术北大核心CSCD

初步分析了在建神光-Ⅲ主机装置下装模块空间对接过程,指出"对中"和"碰撞"问题是下装模块空间对接监测的关键技术。"对中"监测技术主要是将三维问题转换为二维问题,利用机器视觉扑捉特征点下装模块进行位置和姿态的判断。"碰撞"监测技术主要是利用下装模块装校过程发生碰撞必然产生"力"的作用的原理,监测碰撞点上各个方向作用力,间接反映碰撞发生程度,并将测量数据分析后反馈至对接平台执行,及时修正下装模块空间对接运动轨迹,实现了下装模块全过程的"轻碰撞"对接。     

大口径KDP晶体角度相位匹配离线测量精度研究

为满足惯性约束聚变(ICF)实验对激光驱动器高效三倍频能力的要求, 对离线测量晶体角度相位匹配方案进行了优化。采取的主要优化措施是:提高晶体准直技术能力;降低模拟小口径激光输出变化对测量不稳定性的影响。通过理论分析和对实际测量结果的系统分析,得到了晶体离线测量的不确定度:其中二倍频相位匹配角测量扩展不确定度为15.94 rad,三倍频相位匹配角测量扩展不确定度为27.8 rad,达到了较高的晶体离线测量精度要求。     

初发系统性红斑狼疮患者外周血清IL-17的表达

目的探讨IL-17在初发系统性红斑狼疮（SLE）患者外周血清中的表达水平及其临床意义。方法选择42例初次诊断、未经治疗的SLE患者（SLE组）及26例同期健康志愿者（对照组）,采用双抗体夹心酶联免疫吸附试验（ELISA）方法测定外周血清IL-17水平,同时检测外周血抗ds- DNA等抗体及免疫球蛋白、补体等水平并进行相关分析。结果活动期和缓解期SLE患者血清IL-17水平均较对照组明显升高,差异均有统计学意义（均P＜0.05）。活动期和缓解期SLE患者间血清IL-17水平的差异无统计学意义（P＞0.05）。具有皮肤损害的SLE患者血清IL-17水平较无皮肤损害者高,使用环磷酰胺的SLE患者血清IL-17水平较未使用环磷酰胺者高,差异有统计学意义（P＜0.05）。SLE患者血清IL-17水平与SLEDAI、血沉、CRP、IgG、C3、C4均无相关性（均P＞0.05）。19例SLE活动期患者治疗1个月后血清IL-17水平较治疗前明显下降,差异有统计学意义（P＜0.05）。结论 IL-17与狼疮患者的皮肤损害密切相关;IL-17在SLE的发病中起到重要作用并与疾病严重性有关。     

用祖暅原理求平面图形面积的探索

我们知道：能用初等方法求出面积的平面图形有圆与多边形（可分割成三角形来求）,除此以外就屈指可数了．本文与同学们一起探索用祖暅 原理求平面图形的面积,直到推导出椭圆的面积公式,一起来吧,其乐无穷。     

Effects of prism beam expander and slits on excimer laser linewidth narrowing module

Theoretical simulation and experiments based on a prism beam expander and an echelle grating are conducted to study the dependence of linewidth and pulse energy on incidence angle and slit width. With a larger prism incident angle or narrower slit width, the linewidth becomes narrower while the laser pulse energy becomes lower. However, the pulse energy can be improved by optimally designing the prism beam expander. In addition, a subpicometer linewidth ArF laser is obtained with a double-prism beam expander and an echelle grating.     

Effect of fused silica subsurface defect site density on light intensification

The effect of defect density on the modulation of incident laser waves is investigated. First, based on the actual defect distribution in the subsurface of fused silica, a three-dimensional (3D) grid model of defect sites is constructed. The 3D finite-difference time-domain method is developed to solve the Maxwell equations. Then the electrical field intensity in the vicinity of the defect sites in the subsurface of fused silica is numerically calculated. The relationships between the maximal electrical field intensity in fused silica and the geometry of the defect sites are given. The simulated results reveal that the modulation becomes more remarkable with an increase of the defect density. In addition, the effect of the distribution mode of defects on modulation is discussed. Meanwhile, the underlying physical mechanism is analyzed in detail.