无光滤波六倍频微波信号产生的系统设计

基于两个级联偏振调制器,提出了一种高频谱纯度、稳定的六倍频微波信号产生方法。该方法通过适当调整偏振片的偏振方向、射频驱动信号电压和相位,实现无光滤波器条件下、任何波段六倍频微波信号的产生。利用Optisystem平台搭建的仿真系统,以S波段4 GHz信号为例,验证了该设计系统产生的六倍频信号质量,并分析了非理想射频驱动电压和相位对六倍频信号质量的影响,结果表明：该设计系统能产生最大光边带抑制比、射频无杂散抑制比分别为21.3,15.2 dB的六倍频微波信号;且非理想驱动电压和相位差的偏离应控制在理想值5%的范围之内。     

Spectral indices to assess the carotenoid/chlorophyll ratio from adaxial and abaxial leaf reflectance

The ratio between the carotenoid and chlorophyll concentrations can indicate the physiology and phenology of plants. Most of the vegetation indices related to the ratio between the carotenoid and chlorophyll contents only consider the reflectance from the adaxial leaf surface. In this study, it was found that the leaf reflectance from the abaxial surface is lower than that of the adaxial surface in the visible wavelength region. On the contrary, the reflectance is higher on the adaxial surface in the near-infrared wavelength region. The difference ratio index resulted in the best correlation with the carotenoid/chlorophyll ratio and was the most robust among all the spectral indices studied when the spectral information on the adaxial and abaxial surfaces was pooled. The result indicated that this index can accurately estimate the carotenoid/chlorophyll ratio because of the insensitivity to the differences between adaxial and abaxial leaf surfaces.     

Partial electrical potential distribution around nanospheres in metallic nanostructured films

In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals.     

制冷系统的广义预测控制方法研究

制冷系统的蒸发器过热度的控制对于制冷系统稳定、高效运行具有重要作用。文中通过实验辨识了基于过热度和蒸发温度的制冷系统多输入多输出模型,并采用广义模型预测控制方法,针对制冷系统的变负荷运行工况下进行了实验研究。结果表明,该方法很好的适应了制冷系统变过热度、变蒸发温度的控制要求,相比常规的单输入单输出PID控制,跟踪性能良好、动态控制精度高,可以适应制冷系统负荷大范围变动的控制需求。     

Micro‐Raman study of exfoliated Bi2Sr2CaCu2O8+δ single crystals with different thicknesses

Exfoliated Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) single crystals were prepared by micromechanical cleavage of bulk Bi‐2212 single crystals on SiO₂/Si substrates. Room temperature micro‐Raman spectra were collected using a 532‐nm laser source. The evolutions of the spectra of A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) Raman modes with different thicknesses of the samples were studied. The refractive index of Bi‐2212 single crystal was obtained by studying the intensity evolutions based on the interference effect. The observed wavenumber shifts of the A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

阻抗障碍物声散射的反问题

研究了从声散射场的远场分布的信息来再现声阻抗障碍物形状的反问题,建立了求解这类反问题的一种非线性最优化模型,并提出了数值实现该非线性最优化模型的一种两步调整迭代算法.两步过程的应用使在确定未知障碍物形状的非线性最优化步中未知函数的个数达到了最少,而在调整迭代过程中,通过利用前一迭代步所得重构信息,使重构精度得到了相当大的改进.所建立的反演算法的一个特别吸引人的性质是,只需要远场分布的一个Fourier系数即可对未知声阻抗障碍物作几何物形的设别.对大量具有各种几何形状的二维障碍物的数值算例保证了本算法是实用和有效的.     

A molecular dynamics simulation of segregation behaviours of horizontally vibrated binary granular mixture

This paper performs the two-dimensional, soft-sphere molecular dynamics simulations to study the granular segregation in a binary granular mixture with the same size but different density in the container with the sawtooth base under horizontal vibration. The segregation phase diagram is presented in the acceleration-frequency space. When the acceleration is high enough to result in relative motions of the particles, the system can be in various states (mixed state, vertical and horizontal segregation state), which depend on both acceleration and frequency. Due to the sawtooth base there is stratified flow effect besides density effect. The density effect raises the light particles. The stratified flow drives the particles in the upper levels to the right and the particles in the lower particles to the left, those fact results in the appearance of the left segregation state. The left segregation state can be changed to the right segregation by changing the shape of the sawtooth. As the vibration frequency increases, the stratified flow effect becomes weaker and weaker, so at high vibration frequencies the vertical segregation state appears instead of the left segregation state.     

枪晶石变温拉曼光谱及其固液相微结构研究

枪晶石在传统冶金连铸保护渣中起着十分重要的作用。采用紫外激光光源和电荷耦合器件(CCD)探测器,测定了枪晶石晶体和高温拉曼光谱(温度范围:298~1 723 K),观察了其在变温状态(升温和降温过程)下的特征谱变化。谱图结果显示,枪晶石熔态微结构单元与固态的相比更为多元化,表明熔体状态下多种团簇结构共存。同时,利用枪晶石晶胞结构模型,通过Dmol3密度泛函(DFT)理论计算了其分子振动频率,将其与实验值相结合,确定了特征谱峰的归属,为进一步采用拉曼光谱法原位研究保护渣中枪晶石的结构变化与行为特征提供了重要依据。     

弹道导弹再入段地面红外探测仿真分析

为改善弹道导弹再入段地面红外探测效果,考虑导弹再入过程中气动加热、红外辐射的大气衰减以及背景辐射等因素,建立起弹道导弹再入段地面红外探测仿真分析模型,并估算分析了探测系统在不同状况下信噪比.分析结果表明:优选工作波段、增加系统口径及曝光时间、改善光学设计、选择晴朗无云天气观测等均有利于改进地面红外观测效果.     

基于近红外反射光谱的无损血糖分析

无损血糖监测是一种方便且无痛的血糖监测方法。目前,大部分的血糖检测方法都是有损的。提出了一种基于近红外反射光谱的无损血糖检测方法。近红外反射光谱是一种安全、简单并且有效的方法,被应用于很多领域。采用口服葡糖糖耐量试验来采集数据,用偏最小二乘回归方法来建模。使用市售血糖仪采指尖血作为参考值,同时用光谱仪提取手掌光谱,共取得42组样本。血糖浓度范围在5~12 mmol·L-1。采用留一法交叉验证,获得所有数据的交叉验证的均方根误差为1.16 mmol·L-1。通过归一化和无关变量消除的预处理方法来减少噪声并消除一些额外因素,优化的均方根误差为0.79 mmol·L-1。基于个人的数据进行建模,得到了远小于整体数据的结果：0.41 mmol·L-1。该方法在个人血糖检测的市场化方面有广阔的应用前景。