真空退火对L1_0-CoPt薄膜结构、磁性及表面形貌的影响

本文利用磁控溅射的方法制备了L1_0-CoPt薄膜,研究了不同退火条件对薄膜结构、磁性以及表面形貌的影响.通过优化退火温度、保温时间以及升温速率,制备出了具有大矫顽力、高矩形比、粗糙度小的垂直各向异性L1_0-CoPt薄膜.实验发现,较高的退火温度有利于克服CoPt薄膜有序化转变所需要的能量,同时适当延长退火时间可以提高CoPt薄膜的扩散系数,从而促使无序相fcc转化为L1_0有序相fct结构.此外,退火过程中减缓升温速率可以有效减小薄膜粗糙度,从而形成平整连续膜.     

基于灰色马尔科夫模型的团簇数量演变预测方法

本文以分子动力学方法模拟液态Si的凝固过程为基础,首次建立基于马尔科夫修正的灰色预测模型对不同团簇的演变过程进行分析,利用该模型对液态Si降温过程中团簇数量的变化进行预测.结果证实应用灰色马尔科夫模型在对团簇结构的演变预测是可行的,采用马尔科夫链预测方法能提高预测结果的准确性,该方法能有效描述凝固过程中团簇的形成和演变的整体变化规律,为研究材料微观结构演变提供了一种新的思路和方法 .     

基于模糊PID的助行机器人调速系统的研究

助行机器人对系统的动态特性要求较高,而且在其爬楼的过程中有诸多不确定的因素,基于传统控制策略的单闭环负反馈控制系统调速效果难以令人满意。在这种情况下建立了系统的数学模型,设计了基于模糊PID的双闭环调速控制系统,并和传统的PID控制进行了对比。为了保证助行机器人爬楼过程的平稳性和乘坐者的舒适性,参考电梯运行的速度曲线,设计了正弦速度给定曲线。仿真结果表明：在助行机器人调速系统中,模糊PID控制比传统PID控制启动和制动过程更平稳,舒适性更高,误差更小,精度更高。     

Electrically controlled transfer of spin angular momentum of light in an optically active medium

Spin is an intrinsic property of the photon. A method for using an externally applied dc electric field to manipulate the transfer of spin angular momentum of light in an optically active medium is presented. To discuss this, we first develop a wave coupling theory of the mutual action of natural optical activity and the linear electro-optic effect. Besides being used for analyzing the electrically controlled transfer of spin angular momentum of light, the theory can also be used to describe the propagation of light traveling along an arbitrary direction in any optically active medium with an external dc electric field along an arbitrary direction.     

边界元法循环平稳近场声全息理论研究

循环平稳声场是工程中经常遇到的一种特殊非平稳声场,声压信号受到调制作用,导致频谱出现边带现象,经典的近场声全息技术重建得到的声场无法反映声场的调制特性。在平面循环平稳近场声全息基础上,提出一种边界元法的循环平稳近场声全息技术,用二阶循环统计量理论代替传统的傅里叶分析,并以声压的循环谱密度取代其频谱及功率谱密度作为重建量,可用于循环平稳声场中具有复杂表面声源的辐射声场。由于循环谱密度对循环平稳信号具有解调功能,用该方法重建得到的循环谱密度能有效地反映调制和载波信号的信息。仿真分析与实验表明了本理论的有效性和精度能满足工程要求。     

1,3,5-三氮杂苯－水簇氢键结构性质

在B3LYP/6-31 G**和MP2/6-31 G**水平上对1,3,5-三氮杂苯-(H2O)n(n=2,3)复合物的基态氢键结构进行几何优化和性质计算,结果表明复合物之间存在较强的氢键相互作用,所有稳定复合物结构中形成一个N…H-O氢键并终止于弱O…H-C氢键的氢键水链构型最稳定.氢键的形成是水分子中H-O键振动频率减小(红移).NBO分析表明,最稳定的1:2和1:3复合物发生分子问电荷转移总量分另q为0.02501 e和0.02777 e.     

全息光栅光刻胶掩模槽形演化及其规律研究

为了控制全息光栅光刻胶掩模槽形,运用曝光模型和显影模型模拟了掩模的槽形形成过程和变化规律。实验对比了不同曝光量,不同显影浓度,不同空频条件下的掩模槽形,特别是占宽比(光栅齿宽度与光栅周期的比)的情况。实验结果表明,实际槽形与模拟槽形很接近。模拟和实验均发现,在大曝光量、高浓度显影、高空频的光栅条件下所得槽形占宽比较小,槽深主要由原始胶厚决定。     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上,提出一种基于波叠加法的循环平稳近场声全息技术,可以对具有复杂表面的声源进行全息重建,重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况,可由此确定调制信号源的产生位置.仿真分析和实验验证表明,基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点,无需计算边界奇异积分,计算效率高、精度好. 关键词： 近场声全息 循环平稳信号 波叠加     

Structure and optical damage resistance of near-stoichiometric Zn:Fe:LiNbO3 crystals

A series of near-stoichiometric Zn:Fe:LiNbO₃ crystals were grown by the high-temperature top-seed solution growth (HTTSSG) method from stoichiometric melts doped with 6 mol% K₂O. Infrared (IR) transmission spectra were measured and discussed in terms of the defect structure of the near-stoichiometric Zn:Fe:LiNbO₃ crystals. The results of the transmitted beam pattern distortion method show that the optical damage resistance of the near-stoichiometric Zn:Fe:LiNbO₃ crystals increases rapidly when the ZnO concentration exceeds a threshold value. The threshold value concentration of ZnO of the near-stoichiometric Zn:Fe:LiNbO₃ crystals is much lower than that of the congruent LiNbO₃ crystals. The dependence of the optical damage resistance on the defect structure of the near-stoichiometric Zn:Fe:LiNbO₃ crystals are discussed, and the holographic recording properties of the near-stoichiometric Zn:Fe:LiNbO₃ crystals are investigated.     

Coherent Scattering of Light by Bose-Einstein Condensation in a Tight Confinement

We have observed strong scattering of a probe light by dilute Bose-Einstein condensate （BEC） ^87Rb gas in a tight magnetic trap. The scattering light forms fringes at the image plane. It is found that we can infer the real size of the condensation and the number of the atoms by modelling the imaging system. We present a quantitative calculation of light scattering by the condensed atoms. The calculation shows that the experimental results agree well with the prediction of the generalized diffraction theory, and thus we can directly observe the phase transition of BEC in a tight trap.