MOLECULAR DYNAMICS SIMULATION ON LOW ANGLE GRAIN BOUNDARIES

Molecular dynamics simulation has been performed to investigate the microstructure and properties of low angle grain boundaries, employing the embedded atom method(EAM) type interatomic potential for Ni-Al alloy. The energies of the low angle grain boundaries with different dislocation densities were calculated, and the results indicate that the low angle grain boundary energy varies as a function of misorientation angle. The simulation was found in good agreement with the calculation on the basis of the dislocation theories in the low angle scale. The low angle grain boundary energy goes up with the increase of misorientation angle and tends to go down after reaching a maximum. An energy cusp exists when the misorientation angle increases further, but in this scale the dislocation theories are invalid for energy calculation due to the strong interaction of the dislocations at the boundaries. The simulation results also indicate that the microstructure of low angle grain boundaries can still be described as dislocations when the misorientation angle is larger than 10°.     

高升阻比模型天平校准安装角误差控制要求

文章针对高升阻比类模型气动力测量的要求,对天平校准安装角误差影响进行了初步分析,天平的单元校准中,主要有两个安装角对天平校准结果产生影响,这两个安装角分别为攻角和滚转角,研究结果表明:天平的不同分量和不同校准系数对安装角误差的要求是不尽相同的,力分量以及滚转力矩校准,安装角误差可以允许在度水平上;俯仰力矩和偏航力矩校准攻角误差只能在分量级上;法向力对轴向力干扰系数校准的攻角误差,以及法向力对侧向力干扰系数校准的滚转角误差均只能允许在十分之几分或百分之几分的水平上.单纯从校准来看,法向力对轴向力的干扰系数要求攻角误差控制,以及法向力对侧向力干扰系数要求的滚转角误差控制,均非常困难;结合风洞实验测量中高升阻比模型的载荷匹配情况,这个误差控制可以适当放宽,攻角误差可以放宽到分量级上,滚转角误差仍为十分之几分量级上,天平校准时采用常规的角度测量仪器进行测量和调整均非常困难,只有配置高精度的角度测量仪器,才能满足高升阻比模型气动力测量对天平校准角度误差控制的要求.      

颗粒孔洞流的最大休止倾角和流量公式

实验测量了重力驱动下的玻璃珠颗粒样品通过不同倾角和孔径的圆形孔洞的卸载流量.发现无论孔径大小,流量均与倾角的余弦呈良好的线性关系;线性外推得到的零流量角,即流量休止临界角随颗粒粒径与孔洞直径之比的减小而线性增加;在无穷大孔径极限下,此临界角在Bagnold角的误差范围内与样品的安息角一致.这些结果表明流量随倾角余弦线性变化的经验公式能揭示临界角的行为和特性,这是参数随倾角变化的Beverloo公式所不能描述的. 关键词： 颗粒物质 倾斜孔洞流 Beverloo公式     

快电子发散角的实验测量

采用飞秒激光辐照铜靶,利用电子角分布仪和LiF热释光探测器测量了快电子发射的发散角.实验结果显示,快电子的发散角与激光入射角密切相关,随着激光入射角增加,快电子的发散角逐渐减小.在相同入射角条件下,加上预脉冲将导致快电子的发散角变小.这个结果为获取较小发散角的快电子束提供了实验参考.     

液晶盒视角对比度曲线的实验测量

设计了一种测量液晶盒视角的实验装置,通过固定的水平角度和竖直角度扭曲向列相液晶盒光透过率的测量,得到了视角-对比度曲线。不同的水平和竖直视角,其对比度也是不同的。无论竖直视角的大小,水平视角为0°时对比度最大;当对比度大于某一数值（例如50）时,随着竖直视角从20°增加到20°,水平视角的范围先增大后减小。     

Effect of oblique incidence angle of sunlight on the optimized folding angle of V-shaped organic solar cells

We numerically investigate the effect of the incidence angle of sunlight on the optimized folding angle of V-shaped organic solar cells (VOSCs) to obtain the best power conversion efficiency in a realistically operating environment. The light absorbance at the active layer is calculated based on the finite element method with respect to the incidence angle of sunlight and the folding angle of the VOSC. We calculate the generation energy density per day at each folding angle by integrating the angular response of the short-circuit current and the open-circuit voltage with the consideration of the variation of the incidence angle during daytime. We show that the optimized folding angle of the VOSC based on the variation of the generation energy density per day is close to that determined from the variation of the electric power density in normal incidence, which has been widely used to optimize the folding angle of VOSCs.     

高斯光束在单轴挛晶界面上的反射与折射

给出了高斯光束入射到挛晶结构的电磁场分布,解出了反射系数和透射系数。根据晶体的色散关系解出了入射角、反射角和折射角关于晶体参量及波矢的方程,并根据角度方程给出了在一定参量下反射角和折射角关于入射角变化的关系图,以图示的方法显示了光束在界面处的异常性质。根据角度关系和反射、透射系数分析了异常光束在界面处能够出现二性折射、负反射、全透射和全反射等光束的奇特性质;分析了出现这些奇特性质对晶体参量和入射角所要求的条件。根据时间平均的能流密度公式,用数值模拟的方法给出了二性折射、全透射和全反射在特定参量下的高斯光束在挛晶内的能流密度分布图及当发生全反射时不同宽度光束在界面处关于入射角的古斯-亨兴(Goos-Hanchen)位移。     

倾斜入射楔形薄膜滤光片的透射光谱研究

角度调谐薄膜滤光片因较大的波长调谐特性和良好的矩形度在密集波分复用系统中得到了广泛的应用。在倾斜入射时薄膜滤光片透射光谱的透射率和半宽不仅受到入射角度的影响,还跟滤光片两端面间的非平行度即楔角的大小有关。详细分析了楔角对对滤光片透射率以及半宽的影响,发现适当的楔角和角度取向能够改善倾斜入射状态下滤光片的透射光谱特性。设计制备了楔角为0.8°的楔形薄膜角度调谐滤光片,实验结果证明保持该楔角的方向与倾斜入射角度相同时会严重的劣化透射光谱的透射率和矩形度,方向相反时则可以提高光谱的透射率以及矩形度,并使器件的波长调谐范围增大约10 nm。     

基于空间光调制器的光束大角度扫描技术研究

为实现一束激光在90°锥形范围内的扫描，利用液晶空间光调制器在光束偏转控制时精度高、无机械惯性等优点，研究并建立了基于液晶空间光调制器的光束偏转和角放大光路系统。提出了空间光调制器的可编程相位调制算法和角放大光路结构，推导了空间光调制器光束偏转角度与相位灰度驱动图的关系，设计了角度放大倍率高于22倍的角放大光路系统。在此基础上，建立了光束扫描控制实验系统，对该装置角度出射范围进行了测量，将实际的角放大倍率与设计值进行对比。实验结果表明:研制系统的出射视场角可达91.22°，并可通过畸变校正实现出射视场角范围内的规则形状扫描。该研究在光束敏捷控制、无线激光通信、目标搜索与追踪等领域具有重要的研究价值和应用前景。     

Mechanical properties of spruce wood cell walls by nanoindentation

In order to study the effects of structural variability, nanoindentation experiments were performed in Norway spruce cell walls with highly variable cellulose microfibril angle and lignin content. Contrary to hardness, which showed no statistically significant relationship with changing microfibril angle and lignin content, the elastic modulus of the secondary cell wall decreased significantly with increasing microfibril angle. While the elastic moduli of cell walls with large microfibril angle agreed well with published values, the elastic moduli of cell walls with small microfibril angle were clearly underestimated in nanoindentation measurements. Hardness measurements in the cell corner middle lamella allowed us to estimate the yield stress of the cell-wall matrix to be 0.34±0.16 GPa. Since the hardness of the secondary cell wall was statistically not different from the hardness of the cell corner middle lamella, irrespective of high variability in cellulose microfibril angle, it is proposed that compressive yielding of wood-cell walls is a matrix-dominated process. PACS 83.80.Mc     

波动方程角度域偏移成像

在共炮集数据的波动方程深度偏移成像中,利用常规的波场传播算子进行检波点波场和震源波场的向下传播,在各个深度层借助波场的窗口Fourier框架展开,得到局部角度域的检波点波场和震源波场,然后应用偏移成像原理,提出了共炮集数据的波动方程角度域偏移成像方法.通过角度域偏移成像,可以得到地下成像点处的角度域成像矩阵以及共地层倾角偏移成像剖面和共反射角偏移成像剖面.也可为基于偏移成像的后续处理方法技术,如振幅随角度变化分析处理、角度域共成像道集提取和角度域速度分析,提供基础资料.以陡倾角模型和国际标准的Marmousi模型为数值试验例子,验证了波动方程角度域偏移成像方法的正确性和有效性.     

激光角度欺骗干扰中自然地物假目标选择研究

针对激光角度欺骗干扰中自然地物假目标应用需求,在分析了干扰能量传输和干扰过程中武器威胁角、地物倾角以及入射角、反射角等角度关系的基础上,建立了自然地物假目标干扰能量分布模型。依据所建立的模型,对砂石类和建筑类地物反射干扰能量分布进行了仿真研究。仿真结果表明,在相同功率激光照射的条件下,地物倾角相同时对相同位置的激光制导武器,砂石类地物比建筑类地物干扰效果好,在实际防护中砂石类地物选择优先级要高于建筑类地物;同一种地物反射的干扰能量随地物倾角的增大而增大;对于漫反射特性较好的建筑类假目标,威胁角一定时,地物倾角在大致与威胁角互余时反射能量达到最大;对于砂石类目标,存在随入射角大小变化的镜像反射分量,使得导引头接收到地物反射能量达到最大值时威胁角和地物倾角不满足互余关系。进一步研究了在导引头接收到的砂石类地物反射能量最大值时地物倾角和武器威胁角的关系,通过数据分析,得到在实际防护过程中,砂石类自然地物的倾角选择要至少大于31°的结论。根据地物倾角和威胁角关系的散点图特征,分别采用一阶、二阶、三阶、四阶多项式对二者进行拟合,在充分考虑函数复杂度、拟合性能的前提下,确定三阶多项式为最佳拟合函数。在武器威胁角已知的情况下,可以通过三次多项式拟合得到最佳干扰效果时砂石类自然地物的倾角取值。研究结果对自然地物假目标的选择具有一定的指导意义。     

部分相干光在大气湍流中的到达角起伏

研究了部分相干高斯谢尔光束在大气湍流中的到达角起伏.主要采用湍流内外尺度的修正Von Karmon谱模型及广义惠更斯-菲涅尔原理和交叉谱密度函数推导出了部分相干光在大气湍流中的到达角起伏表达式.对比分析了湍流内外尺度、湍流强度、传输距离、源相干参数以及波长等参数对部分相干光在大气湍流水平路径上传输时的到达角起伏的影响.结果表明:随着传输距离的增加,到达角起伏越来越小;随着大气湍流内外尺度和源相干参数的增加,到达角起伏也越来越大;与部分相干光相比,完全相干光的到达角起伏受湍流影响很小;随着波长和湍流强度的减小,到达角起伏越来越小.     

开口角度对二维颗粒流稀疏流-密集流转变的影响

用计算机模拟的方法研究了开口角度对二维颗粒流稀疏流—密集流转变的影响.在固定入口流量和固定颗粒数两种条件下,均发现当开口角度大于零时,开口角度的增大可以提高颗粒流由稀疏流向密集流转变的最大出口流量.在稀疏流状态下,出口流量与开口角度无关;而在密集流状态下,出口流量随开口角度的增大而增大.进一步的计算还发现增加开口角度可以提高颗粒流出开口的流动速度,且最大出口流量与颗粒的流动速度呈线性关系. 关键词： 颗粒物质 颗粒流 分子动力学模拟     

光学观测中太阳夹角的分析与计算

对影响光学观测效果的太阳夹角计算方法进行了研究。首先给出了太阳夹角的定义及计算公式。然后重点研究了太阳视位置的计算方法,比较了几种赤纬角计算方法,给出了一种改进的时角计算方法,实现了高精度的太阳视位置计算,并对其计算精度进行了分析。最后提出了在实际光学观测应用中的太阳夹角计算算法。实验表明,太阳视位置计算精度比传统数值近似方法高一个数量级,能够满足光学观测中太阳光照分析的需要。     

Measurement of angular-dependent hysteresis loops in perpendicular magnetic recording media

The intrinsic angular-dependent hysteresis loops in perpendicular recording media have been measured by iteratively correcting the demagnetization effect in order to maintain the internal total field at a fixed angle. Both the angle and the magnitude of the applied field are adjusted simultaneously to compensate for the demagnetization field change. Significant differences have been observed between the conventional angular-dependent hysteresis loop with a constant applied field angle and the intrinsic angular-dependent hysteresis loop with a fixed total field angle. Without demagnetization corrections, the field range in which irreversible magnetization occurs changes as a function of the field angle, whereas it remains constant if proper demagnetization field corrections are applied.     

Non-contact measurement of angle of view between the inspected surface and the thermal imager

The angle of view between inspected object and thermal imager influences the values of temperature measured by infrared thermography. This happens because the emissivity depends on the angle of radiation, and because the apparent temperature measured is influenced by that angle of view combined to thermal imager’s field of view. Therefore, it is necessary to know the angle of view during thermographic inspection, which is generally not feasible due to safety reasons. This paper develops a method of measuring the angle of view with no contact with the inspected object, by employing laser distance meters, commonly available in the market.     

Tip splittings and phase transitions in the dielectric breakdown model: mapping to the diffusion-limited aggregation model

We show that the fractal growth described by the dielectric breakdown model exhibits a phase transition in the multifractal spectrum of the growth measure. The transition takes place because the tip splitting of branches forms a fixed angle. This angle is eta dependent but it can be rescaled onto an "effectively" universal angle of the diffusion-limited aggregation branching process. We derive an analytic rescaling relation which is in agreement with numerical simulations. The dimension of the clusters decreases linearly with the angle and the growth becomes non-ractal at an angle close to 74 degrees (which corresponds to eta = 4.0+/-0.3).     

Angle step selection for geometrical-optics approximation in light scattering

On the basis of the Shannon sampling theorem, we present a relationship between the maximal scattering angle step and the radius of particles in the calculation of light scattering intensity distribution. For the first rainbow intensity application, the relationship between the maximal scattering angle step and radius of particles is derived from that between the ripple frequency and radius and refractive index of particles using this method. For the geometrical-optics approximation, the incident angle is used to calculate the scattering intensity distribution. To get the highest speed, the maximal incident angle step is necessary. The relationship between the maximal step of incident angle and radius of particles is deduced from the maximal scattering angle step equation. As indicated by our result, the maximal step of the incident angle is not a constant and it varies with incident angle.     

倾斜均质表面上非等径液滴的聚合特性

对倾斜均匀表面上非等径液滴的聚合过程及特性进行了可视化实验研究,获得了液滴半径和表面倾角等参数对液滴聚合过程中液滴液桥半径、接触角和接触线变化特性的影响规律,进一步说明了倾斜表面上液滴聚合可以加快液滴的运动.