基于光机集成仿真技术的摆镜特性分析

为考察相关跟踪系统摆镜在静力和动力载荷工况下面形参数是否满足工程需求,基于光机集成仿真技术对相关跟踪摆镜特性进行了分析,得到了在静力和时间历程载荷所对应的三种工况下的面形变化分布和面形表征参数,并对仿真结果的数据可靠性进行了数值角度验证。结果表明,光机集成仿真方法可以有效地消除由动力载荷产生的主动刚体位移,可得到摆镜面形参数和在动力载荷作用下不同时刻的摆镜面型变化,弥补了在实验条件下难以测得由动力载荷作用的面形参数和面形分布情况。当1g加速度载荷在摆镜光轴方向上时,静力载荷对面形的影响起主导作用;当1g加速度载荷不在摆镜光轴方向上时,动力载荷对面形的影响起主导作用。通过光机集成仿真结果对所设计的摆镜在相应工况下的面形进行有效评估,获得了有意义的设计指导数据。     

Atomic Structure of [0001] Tilt Boundaries in GaN

Crystals of GaN grown by molecular-beam epitaxi on (0001) sapphire show [0001] tilt boundaries of low and high angles (V. Potin et al., Physical Review B, 61, 5587 (2000)). The structure of these boundaries plays a role in the optoelectrical properties shown by this semiconductor. In this work we have studied the atomic structure of 7, 13 and 19 boundaries (in the coincidence side lattice notation) by means of atomic computer simulation using a modified version of the empirical Stillinger-Weber interatomic potential. For each boundary we studied the interface of lowest period and found the atomic structure of minimum energy by applying the method of quasidynamic relaxation. Special attention has been paid to the 13 where we have studied two different interfaces comparing our results with the experimental results obtained in a study of bicrystals of ZnO (A.N. Kiselev et al., Phil. Mag. A, 76, 633 (1997)). In these boundaries the atomic structure can be understood in terms of edge dislocations located along the boundary. The a edge dislocation in GaN has been studied with the same potential and the stable structures are presented here for comparison.     

Depth-dependent mosaic tilt and twist in GaN epilayer:An approximate evaluation

An approach based on depth-sensitive skew-angle x-ray diffraction （SAXRD） is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that （103） plane and （101） plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive （103）/（101） ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.     

高密度光盘径向倾斜对DPD循轨误差信号影响分析

根据高密度光盘参数 ,计算了聚焦光斑在光盘表面扫描过程中每个位置的光瞳光强分布 ,得到DPD(Differ entialPhaseDetection)循轨误差信号。考虑盘片的径向倾斜 ,在光瞳光强分布方程中引入盘片的径向倾斜角度参数 ,计算了高密度盘片产生径向倾斜时DPD循轨误差信号的变化 ,进而分析了盘片的径向倾斜引入的循轨伺服误差及其对循轨伺服的负面影响。结果表明 ,高密度盘片产生 0 .5°的径向倾斜相当于引入了 0 .0 12 μm的循轨误差     

Texture change through film thickness and off-axis accommodation of (0 0 2) planes

We present our recent experimental results on the formation of off-axis texture and crystallographic tilting of crystallites that take place in thin film of transition metal nitrides. For this purpose, the microstructural development of TiAlN film was studied, specially the change in texture with film thickness. Fiber texture was measured using θ-2θ and pole figure X-ray diffraction (XRD), while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure and changes in texture with thickness. The sin²ψ method was applied to determine the stresses on (1 1 1) and (0 0 2) plane. With deposition parameters chosen, the growth texture mechanism is discussed in three different stages of film growth. Surface energy minimization at low thickness leads to the development of (0 0 2) orientation. On the other hand, the competitive growth promotes the growth of (1 1 1) planes parallel to film surface at higher thickness. However, contrary to the prediction of growth models, the (0 0 2) grains are not completely overlapped by (1 1 1) grains at higher thickness. Rather the (0 0 2) grains still constitute the surface, but are tilted away from the substrate normal showing substantial in-plane alignment to allow the (1 1 1) planes remain parallel to film surface. Intrinsic stress along (1 1 1) and (0 0 2) shows a strong dependence with preferred orientation. The stress level in (0 0 2) grains which was compressive at low thickness changes to tensile at higher thickness. This change in the nature of stress allows the (0 0 2) planes to tilt away in order to promote the growth of 〈1 1 1〉 parallel to film normal and to minimize the overall energy of system due to high compressive stress stored in the (1 1 1) grains. The change in surface morphology with thickness was observed using SEM. An increase in surface roughness with film thickness was observed which indicates the development of (1 1 1) texture parallel to film surface. TEM observations support the XRD results regarding texture change. Film hardness was measured by nanoindentation and a correlation between (1 1 1) texture, stress and hardness is obtained. The results indicate that texture development is a complex interplay between thermodynamic and kinetic forces. An attempt is made to understand this phenomenon of off-axis accommodation of (0 0 2) at higher thicknesses, which is a new result not reported previously.     

Effects of Motion, Implied Direction and Displacement of a Large-Visual-Stimulus on Postural Control

Effects of motion, implied direction in a static stimulus and displacement on postural control were examined independently. In Experiment 1, rotation of a random-dot stimulus was presented. In Experiments 2 and 3, photographic slides of natural scenes were used; participants closed their eyes during stimulus rotation to eliminate motion information. In Experiment 2, the stimulus was presented upright initially, then presented again with a tilt. In Experiment 3, the order was reversed to separate the effects of implied direction and displacement. Results showed that all information of motion, implied direction, and displacement had some effect on postural control, although visual information of motion has been presumed to have a principal effect on postural control. Results suggested that the effects of implied direction might reflect an immediate processing of information. The effects of displacement and motion might reflect a continuous processing of information.     

Shear-strain induced structural relaxation of Cu Σ3 [110](112) symmetric tilt grain boundary: The role of foreign atoms and temperature

Grain boundaries (GBs) relaxation is a promising and effective strategy to improving GB stability or stabilizing nanocrystalline metals. However, previous studies mainly focused on nanocrystalline pure metals and GB behaviors therein, without considering the role of foreign atoms such as impurity or alloying atoms in GB relaxation. In this work, the shear-strain induced structural relaxation of pure Cu Σ3 [110](112) symmetric tilt GBs (STGBs), and the effects of foreign elements (Fe and Ni) and temperature on the GB relaxation were investigated in detail by molecular dynamics method. The results show that shear strain can trigger the structural relaxation of pure, Fe- and Ni-containing Cu GBs by the emission of Shockley partial dislocations from Cu GBs. Both Fe and Ni have impediment effects on the shear-strain induced GB relaxation, though the content of Fe or Ni atom (0.00165 at.%) is quite low in the GB model. The temperature cannot trigger GB relaxation independently within the considered temperature range, but play a positive role in the shear-strain induced structural relaxations of pure, Fe- and Ni-containing Cu Σ3 [110](112) STGBs. Our work might gain new insights into the mechanically induced GB relaxation in nanocrystalline copper and could be beneficial for improving the stability of Cu GBs.     

Changes in material parameters for dye-doped ferroelectric liquid crystal

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.     

Differences in voice quality between men and women: Use of the long-term average spectrum (LTAS)

The goal of this study was to determine if there are acoustical differences between male and female voices, and if there are, where exactly do these differences lie. Extended speech samples were used. The recorded readings of a text by 31 women and by 24 men were analyzed by means of the Long-term Spectrum (LTAS), extracting the amplitude values (in decibels) at intervals of 160 Hz over a range of 8 kHz. The results showed a significant difference between genders, as well as an interaction of gender and frequency level. The female voice showed greater levels of aspiration noise, located in the spectral regions corresponding to the third formant, which causes the female voice to have a more “breathy” quality than the male voice. The lower spectral tilt in the women's voices is another consequence of this presence of greater aspiration noise.     

Study on EDFA Gain Tilt and Nonlinear Distortion in an AM-VSB CATV Optical Fiber Transmission System

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