基于比较算法和单纯形法的电子枪快速设计方法

 采用比较算法快速寻找数据库中与目标导流系数相匹配的电子枪尺寸,采用缩尺法改变其尺寸到所要求的目标尺寸。考虑电子枪尺寸对注腰半径、导流系数、层流性等参数的影响,建立了评价电子注性能的目标函数,采用单纯形法优化目标函数实现最优的电子层流性,且基于比较算法和单纯形算法的设计方法具有通用性,工作效率高。     

任意阶标度分形格分抗与非正则格型标度方程

Carlson分形格电路是分抗的理想逼近情形,但仅具有负半阶运算性能,逼近效益随着电路节次数的增加逐渐降低.虽然可嵌套得到-1/2~n阶(n为大于或等于2的整数)分抗逼近电路,但结构复杂,无法实现任意分数阶运算.通过类比拓展Carlson分形格电路,获得具有高逼近效益的任意实数阶微积算子的分抗逼近电路——标度分形格分抗,并用非正则格型标度方程进行数学描述.分别探讨非正则格型标度方程的近似求解和真实解.通过调节电阻递进比α与电容递进比β的取值,可构造出具有任意运算阶的标度分形格分抗逼近电路.标度拓展极大地提高了标度分形格分抗电路的逼近效益.随着标度因子的增加,负半阶标度分形格分抗的逼近效益逐渐增大并明显高于Carlson分形格分抗.设计了基于五节Carlson分形格分抗与负半阶标度分形格分抗的半阶微分运算电路,并对周期三角波和周期方波信号进行半阶微分运算,实验测试结果与理论分析一致.     

湍流内尺度对光波起伏频谱的影响

在不同湍流内尺度情况下,对大气湍流引起的光波光强闪烁和到达角起伏的时间频谱特征进行了实验研究。由于实际大气湍流的复杂性和不可控性,利用大气湍流模拟箱来生成具有不同内尺度的大气湍流实验环境。利用位置敏感探测器对光波的光强闪烁和到达角起伏进行了同时测量,并反演得到了光传输路径上的湍流内尺度。实验结果显示：湍流内尺度为2.7~5.0 mm,对应同一湍流内尺度,闪烁频谱和到达角起伏频谱在高频段以相同的幂指数关系下降,幂指数的绝对值与湍流内尺度的大小呈线性关系,随着内尺度的增大,频谱指数变化区间逐渐向低频方向移动。     

面向单晶SiC原子级表面制造的等离子体辅助抛光技术

目前Si基半导体由于其自身材料特性的限制,已经越来越难以满足高速发展的现代电力电子技术对半导体器件的性能要求.SiC作为新一代半导体材料具有显著的性能优势,但由于其属于典型的难加工材料,实现SiC晶圆的高质量与高效率加工成为了推动其产业化应用进程的关键.本综述在回顾近年来SiC超精密加工技术研究进展的基础上,重点介绍了一种基于等离子体氧化改性的SiC高效超精密抛光技术,分析了该技术的材料去除机理、典型装置、改性过程及抛光效果.分析结果表明,该技术具有较高的去除效率,能够获得原子级平坦表面,并且不会产生亚表面损伤.同时针对表面改性辅助抛光技术加工SiC表面过程中出现的台阶现象,探讨了该台阶结构的产生机理及调控策略.最后对等离子体辅助抛光技术的发展与挑战进行了展望.     

Spatial curvature and large scale Lorentz violation

The tension between the Hubble constant values obtained from local measurements and cosmic microwave background (CMB) measurements has motivated us to consider the cosmological model beyond ΛCDM. We investigate the cosmology in the large scale Lorentz violation model with a non-vanishing spatial curvature. The degeneracy among spatial curvature, cosmological constant, and cosmological contortion distribution makes the model viable in describing the known observational data. We obtain some constraints on the spatial curvature by comparing the relationship between measured distance modulus and red-shift with the predicted one, the evolution of matter density over time, and the evolution of effective cosmological constant. The implications of the large scale Lorentz violation model with the non-vanishing spatial curvature under these constrains are discussed.     

义工旅行动机的量表开发与验证

随着义工旅行在年轻人中的普及,不少义工组织、旅行社和旅游目的地纷纷推出义工旅行项目。然而目前的项目安排大多仿照国外,对国内年轻人的需求认识尚不明晰,学术界对这一主题的研究也相对匮乏。鉴于此,以Voluntour和EASIN义工旅行组织的参与者为研究对象,严格遵循量表开发的流程,采用探索性因子分析、3次验证性因子分析和结构方程模型检验的方法,从多个角度验证了量表的信度和效度,得到了基于中国情境的义工旅行动机量表。研究结果表明：(1）由4个维度17个测量项目组成的量表,整体结构良好,具有较好的稳定性和适用性,可成为义工旅行研究的有效测量工具;(2）义工旅行的动机维度可划分为休闲逃避、深度体验、自我服务/发展与利他四类,动机中的利他维度是区分义工旅行与背包旅行、打工度假旅行的关键属性,是年轻人选择深度休闲方式的一种体现;(3）与国外研究相比,基于中国情境的量表无保护功能与宗教参与的动机维度,且社交动机表现不突出。最后,探讨了义工旅行项目在产品开发和市场营销方面的策略。     

Constraining Lorentz invariance violation from the continuous spectra of short gamma-ray bursts

In some quantum gravity theories, a foamy structure of space-time may lead to Lorentz invariance violation(LIV). As the most energetic explosions in the Universe, gamma-ray bursts(GRBs) provide an effect way to probe quantum gravity effects. In this paper, we use the continuous spectra of 20 short GRBs detected by the Swift satellite to give a conservative lower limit of quantum gravity energy scale MQG. Due to the LIV effect, photons with different energy have different velocities. This will lead to the delayed arrival of high energy photons relative to low energy ones. Based on the fact that the LIV-induced time delay cannot be longer than the duration of a GRB,we present the most conservative estimate of the quantum gravity energy scales from 20 short GRBs. The strictest constraint, M_(QG) 5.05 × 10~(14) GeV in the linearly corrected case, is from GRB 140622 A. Our constraint on MQG,although not as tight as previous results, is the safest and most reliable so far.     

Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale

This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale.     

基于数值模拟的飞行员高速气流吹袭损伤分析

研究飞行员高速气流吹袭的损伤机理,应用尺度适应模型对人椅系统外流场进行数值模拟.在马赫数为0.6,迎角为-90°~90°条件下的数值计算结果与风洞试验结果吻合较好.对不同马赫数、不同迎角的无防护状态下的人椅系统进行数值模拟,研究发现高速气流吹袭下飞行员面颈部、胸腹部、上臂内侧、小腿迎风侧压力较大;增大人椅系统的迎角可以改善飞行员身体各部分的受力情况.