Analysis of fiber Bragg grating with exponential–linear and parabolic taper profiles for dispersion slope compensation in optical fiber links

In this paper, the effect of various taper profiles on dispersion slope compensation in optical fiber links is studied. Theoretical and numerical investigation of the linear and nonlinear group delays of tapered fiber Bragg grating's (T-FBG) under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equation using transfer matrix method. Our study shows that the linear tapered FBG profile provide the best result than the linear-exponential profile which can compensate up to 500 km. As result, the spectral characteristics of tapered grating allow them to be used efficiently in high bit rates WDM and long-haul optical communication systems for chromatic dispersion of single-mode fiber.     

横波速度径向层析成像方法及应用研究

近来三维声波成像技术的一个重要进展是利用偶极子弯曲波反演地层径向横波速度剖面。确定地层径向横波速度变化对评价井壁稳定性、估算地应力和优化油藏生产等有着重要的意义。偶极横波测井激发的弯曲波低频探测较深,高频探测较浅,本文根据偶极弯曲波的频散特征,采用约束反演的方法求取地层径向横波速度变化。在实际测井中,经常会遇到偶极子弯曲波的频散曲线在高频时缺失或者不准确的情况,这会使约束反演方法产生误差。针对这一现象,本文提出利用理论频散数据进行高频约束,并通过数值模拟验证了改进后约束反演方法的正确性。本文给出了一个致密气层的横波速度径向剖面综合应用实例,发现地层径向横波速度变化程度与岩石脆性有很好的对应关系,最终的压裂效果由压前、压后正交偶极横波各向异性的变化得到了印证,压裂后油气产量提高。     

相位补偿算法对提高太赫兹雷达距离像分辨率的研究

介绍了0.2 THz频率步进雷达系统以及获得一维距离像的方法,并利用0.2 THz雷达对角反射器进行距离像分辨率实验,分析了频率步进信号相位不一致对一维距离像以及分辨率的影响,提出了回波相位补偿的方法.经过相位补偿后,目标距离像分辨率和信噪比都显著提高,分辨率达到了厘米量级.仿真和实验结果表明,宽带太赫兹频率步进雷达经过相位补偿,可以对目标进行高分辨率成像,从而为太赫兹雷达二维和三维成像奠定了基础.     

基于光学成像的束流截面分布诊断系统

为了准确测量加速器氘离子的束流截面分布,开展了光学成像系统的设计研究。根据截面分布测量的要求,设计了光学成像系统的指标参数。采用光学设计软件ZEMAX进行了光学成像系统的设计,并通过标准白光光源和线对率板对成像效果进行检验。设计和检验的结果表明,该光学成像系统的总体成像质量较好,畸变小于0.05%,在光学分辨率为30lp/mm的条件下,中心和边缘视场的调制传递函数(MTF)值均大于0.7。将完成设计加工的光学成像系统应用于氘离子束流截面分布测量实验,实验结果初步表明,基于荧光屏的光学方法测量束流截面分布是可行的。     

相位拼接技术在数字全息中的应用

在确保较高分辩率的前提下,提出了一种相位拼接技术以解决数字全息技术中扩大测量面积的瓶颈问题.在全息数字图记录过程中,确保相邻子孔径间具有重叠区域|拼接中采用相关算法确定重叠区域,并利用再现像重叠区域具有相同信息的特点使用最小二乘方法消除由于孔径的移动所产生的倾斜误差| 相关计算和最小二乘反复迭代把相邻再现像精确统一到一个坐标系下,从而实现测量面积的扩展.以平面物体的测量为例建立了数字全息相位拼接技术的理论模型,完成了对相位物体的2×2拼接模拟,并在对标准相位板2×2的拼接实验中获得了较好的拼接效果.     

A CFD model of frost formation based on dynamic meshes technique via secondary development of ANSYS fluent

To simulate the non-uniform frost growth in flow direction for humid air flowing through a freezing channel, a 2D numerical frosting model based on dynamic meshes technique is developed in the current work via the secondary development of commercial ANSYS Fluent. The computation domain consists of both frost layer and humid air regions, and the local heat and vapor fluxes at the surface of frost layer are determined by numerical temperature and vapor fraction fields in the humid air region rather than by empirical correlations. The frost layer is treated as a growing packed bed with heat and mass transfer dominated by molecular diffusion, where local absorption coefficient of vapor desublimation and local vapor fraction are both determined by solving the pseudo steady vapor diffusion equation with a source term theoretically. The interface of frost layer and humid air regions is treated as two walls for the iteration of its temperature, of which the humid air side is specified with the temperature equal to the frost-side counterpart and the frost side takes the heat flux including the extra latent heat caused by vapor deposit. User-defined functions are compiled to implement the above treatments to ANSYS Fluent. Frosting experiments in the literature are simulated with the current model for validation. How the profile of frost layer evolves with time in the frosting process is explored. The contours and profiles of velocity, temperature and vapor fraction are presented to discuss the effects of heat and mass transfer on frost formation. Numerical results demonstrate that the proposed CFD model can predict the frost growth and densification with a relative deviation less than 5% compared with experiments. Besides, the computation load of current model is small due to no solution of complex multiphase flow. In addition, dynamic meshes help current model to capture the interface of frost layer and humid air regions accurately.     

闪电等离子体连续辐射谱特征分析

闪电等离子体光谱特征是在强连续辐射背景上叠加丰富的NⅡ,NⅠ,OⅠ,HⅠ线状谱,闪电回击通道温度可达万开以上,通道内氮分子和氧分子接近完全离解,分析连续谱时,不考虑各组分分子带状谱对连续谱的影响。使用摄谱范围在400~1 000 nm的无狭缝光栅摄谱仪记录云对地闪电放电光谱,在光谱可见区低频段观测到大量一价氮离子谱线,未观测到明显的其他离子谱,认为连续辐射机制主要由氮离子与自由电子相互作用产生,包括轫致辐射和复合辐射。等离子体温度在1×104 K以下时轫致辐射连续谱呈现出平谱特征,辐射强度较弱,随着等离子体温度升高在紫外段辐射强度增加,对可见段连续谱轮廓特征没有明显影响。对于复合辐射,设闪电等离子体符合局域热力学平衡和光学薄条件,以类氢离子经典辐射理论为基础,以冈特因子作量子力学修正,考虑到复合过程中自由电子被离子俘获,大概率出现在高激发状态,引入非类氢的复杂离子近似计算方法分析氮离子复合辐射过程,导出连续谱复合辐射系数与波长的函数关系,获得特定参数条件下氮等离子连续辐射谱特征曲线,与闪电连续谱轮廓观测结果比较,发现等离子体电子温度与连续辐射谱谱峰位置密切相关,认为通过对闪电连续谱轮廓拟合,能够可靠诊断闪电放电通道表面电子温度。研究认为氮离子实有效核电荷数Z*取值对连续谱特征也有显著影响,Z*取值小,连续谱跃变特征增强;Z*取值大,连续谱展宽特征增强,从而与实测谱轮廓底部背离增大。通过多次对比发现Z*取为2~4时,理论曲线与连续谱观测轮廓具有较好的一致性,Z*的取值范围由离子种类决定,引入离子有效核电荷数Z*,能够很好地解释闪电等离子体连续谱在特定波长出现跃变的特征。     

Small target detection using bilateral filter and temporal cross product in infrared images

We introduce a spatial and temporal target detection method using spatial bilateral filter (BF) and temporal cross product (TCP) of temporal pixels in infrared (IR) image sequences. At first, the TCP is presented to extract the characteristics of temporal pixels by using temporal profile in respective spatial coordinates of pixels. The TCP represents the cross product values by the gray level distance vector of a current temporal pixel and the adjacent temporal pixel, as well as the horizontal distance vector of the current temporal pixel and a temporal pixel corresponding to potential target center. The summation of TCP values of temporal pixels in spatial coordinates makes the temporal target image (TTI), which represents the temporal target information of temporal pixels in spatial coordinates. And then the proposed BF filter is used to extract the spatial target information. In order to predict background without targets, the proposed BF filter uses standard deviations obtained by an exponential mapping of the TCP value corresponding to the coordinate of a pixel processed spatially. The spatial target image (STI) is made by subtracting the predicted image from the original image. Thus, the spatial and temporal target image (STTI) is achieved by multiplying the STI and the TTI, and then targets finally are detected in STTI. In experimental result, the receiver operating characteristics (ROC) curves were computed experimentally to compare the objective performance. From the results, the proposed algorithm shows better discrimination of target and clutters and lower false alarm rates than the existing target detection methods.     

Antihyperglycemic and Lipid Profile Effects of Salvia amarissima Ortega on Streptozocin-Induced Type 2 Diabetic Mice

Salvia amarissima Ortega was evaluated to determinate its antihyperglycemic and lipid profile properties. Petroleum ether extract of fresh aerial parts of S. amarissima (PEfAPSa) and a secondary fraction (F6Sa) were evaluated to determine their antihyperglycemic activity in streptozo-cin-induced diabetic (STID) mice, in oral tolerance tests of sucrose, starch, and glucose (OSTT, OStTT, and OGTT, respectively), in terms of glycated hemoglobin (HbA1c), triglycerides (TG), and high-density lipoprotein (HDL). In acute assays at doses of 50 mg/kg body weight (b.w.), PEfAPSa and F6Sa showed a reduction in hyperglycemia in STID mice, at the first and fifth hour after of treatment, respectively, and were comparable with acarbose. In the sub-chronic test, PEfAPSa and F6Sa showed a reduction of glycemia since the first week, and the effect was greater than that of the acarbose control group. In relation to HbA1c, the treatments prevented the increase in HbA1c. In the case of TG and HDL, PEfAPSa and F6Sa showed a reduction in TG and an HDL increase from the second week. OSTT and OStTT showed that PEfAPSa and F6Sa significantly lowered the postprandial peak at 1 h after loading but only in sucrose or starch such as acarbose. The results suggest that S. amarissima activity may be mediated by the inhibition of disaccharide hydrolysis, which may be associated with an α-glucosidase inhibitory effect.     

小半径曲线科隆蛋扣件地段钢轨波磨特性

为研究小半径曲线科隆蛋扣件轨道的波磨演化特征,首先通过分析钢轨波磨实测数据,获得了波磨的典型通过频率;然后运用车辆-轨道空间耦合模型和基于摩擦功理论的钢轨材料摩擦磨损模型,对曲线段钢轨波磨特性进行了分析。结果表明:导向轮可承载的外侧蠕滑力几乎全程达到饱和,内侧蠕滑力部分达到饱和,且饱和部分呈周期性出现;当蠕滑力等于饱和蠕滑力时,磨耗深度最大,并且内轨的磨耗深度幅值大于外轨。结合钢轨磨耗预测型面可知,外轨主要发生侧磨,内轨则趋向发生波磨,从而出现内轨波磨严重而外轨波磨轻微这一现象。磨耗频域特性分析表明,内轨磨耗等级含有与实测波磨通过频率相近的特征频率,且这些频率处的磨耗增长率较大,说明对应频率的磨耗将不断发展,最终形成波磨。