Active contours for video object tracking using region, boundary and shape information

In this paper, we propose a robust model for tracking in video sequences with non-static backgrounds. The object boundaries are tracked on each frame of the sequence by minimizing an energy functional that combines region, boundary and shape information. The region information is formulated by minimizing the symmetric Kullback–Leibler (KL) distance between the local and global statistics of the objects versus the background. The boundary information is formulated using a color and texture edge map of the video frames. The shape information is calculated adaptively to the dynamic of the moving objects and permits tracking that is robust to background distractions and occlusions. Minimization of the energy functional is implemented using the level set method. We show the effectiveness of the approach for object tracking in color, infrared (IR), and fused color-infrared sequences.     

太赫兹波应用于临近空间高速飞行器测控研究

临近空间高速飞行器测控需要解决“黑障”、超视距时空连续覆盖和多目标等难题,根据太赫兹电磁波可以穿透等离子体而大气传输损耗大的特点,研究以飞机和飞艇为主要平台的空基太赫兹测控系统,提出采用扩频体制实现对高速飞行器进行测距、测速、遥测和遥控的综合测控以及多目标测控,采用 nRR(n≥3)测量体制实现高速飞行器的外弹道测量,分析表明空基太赫兹扩频测控系统技术可行,但离工程应用还有较大差距。     

Mathematical modelling of single and multi-strand tundish for inclusion analysis

In the present work a numerical study was carried out to investigate the inclusion behaviour in a four strand asymmetric billet caster tundish. A parameter called separation efficiency was used to compare inclusion behaviour quantitatively. An open source CFD code called OpenFOAM was used to model the inclusions through Lagrangian Particle Tracking approach. First, the Lagrangian particle class was defined in the existing simpleFoam solver of the OpenFOAM and the same customized solver was used to track particles in the already obtained velocity field. Inclusions were modelled as spheres and various forces acting were also considered. Present numerical results were validated using available experimental results and found to be in good agreement. Further, such inclusion behaviour was also extended for a real industrial case tundish. Inclusion flotation characteristics in thermally induced flow was analyzed in detail. This is, perhaps, for the first time such an exhaustive study on inclusion analysis being reported considering the forces acting on the inclusions particles and with OpenFOAM.     

Asynchronous particle filter for tracking using non-synchronous sensor networks

This paper deals with the problem of tracking using a sensor network when the sensors are not synchronised. We propose a new algorithm called the asynchronous particle filter that, with much less computational burden than the traditional particle filter, has a slightly poorer performance. Thus, it is a good solution to real-time applications with non-synchronised sensors when high performance is required. The low computational burden of the method lies in the fact that we do not predict and update the state every time a measurement is collected. Its high performance is due to the fact that we account for the time instant at which each measurement was taken.     

The Local Front Reconstruction Method for direct simulation of two- and three-dimensional multiphase flows

We present a new interface reconstruction technique, the Local Front Reconstruction Method (LFRM), for incompressible multiphase flows. This new method falls in the category of Front Tracking methods but it shares automatic topology handling characteristics of the previously proposed Level Contour Reconstruction Method (LCRM). The LFRM tracks the phase interface explicitly as in Front Tracking but there is no logical connectivity between interface elements thus greatly easing the algorithmic complexity. Topological changes such as interfacial merging or pinch off are dealt with automatically and naturally as in the Level Contour Reconstruction Method. Here the method is described for both two- and three-dimensional flow geometries. The interfacial reconstruction technique in the LFRM differs from that in the LCRM formulation by foregoing using an Eulerian distance field function. Instead, the LFRM uses information from the original interface elements directly to generate the new interface in a mass conservative way thus showing significantly improved local mass conservation. Because the reconstruction procedure is independently carried out in each individual reconstruction cell after an initial localization process, an adaptive reconstruction procedure can be easily implemented to increase the accuracy while at the same time significantly decreasing the computational time required to perform the reconstruction. Several benchmarking tests are performed to validate the improved accuracy and computational efficiency as compared to the LCRM. The results demonstrate superior performance of the LFRM in maintaining detailed interfacial shapes and good local mass conservation especially when using low-resolution Eulerian grids.     

Reconfigurable photonic differentiators based on all-optical phase modulation and linear filtering

We theoretically propose a novel scheme to implement two types of optical differentiators using all-optical phase modulation and linear filtering. Differences between the two differentiators rely on whether the differentiated signals are formed on the optical intensity or optical field of the output signal, which in turns depends on the relative shift between the probe wavelength and the closest notches of a linear filter. A proof-of-concept experiment is carried out using a semiconductor optical amplifier and a fiber-based delay interferometer (DI). Both differentiators are obtained for periodical Gaussian pulses and pseudo random non-return-to-zero signals at various data rates. Defined as the mean absolute deviation of the measured waveform from the ideal one, total average errors of less than 18% are observed in all cases. The impact of probe wavelength on the total average errors is investigated. Due to periodical feature of the DI spectrum, we also demonstrate the capability of multi-channel differentiation.     

Enhanced performance analysis of inter-satellite optical-wireless communication (IsOWC) system

In this paper, we have reported the improved performance by usage of a square root module. By simulation in OPTISYSTEM™ a distance of 5000 km with 1.25 Gbps was achieved with the same performance representing an enhancement of 48% when compared to the traditional detection.     

月基对地观测跟踪转台设计与分析

针对登月过程严酷的力学条件、月球表面复杂的环境特征以及严格的重量要求,设计了一种可适用于月基观测的跟踪转台.该转台主要由水平轴系及驱动机构和竖直轴系及驱动机构组成,采用霍耳元件作为位置检测元件,其综合指向准确度≤0.1°.基于有限元分析方法确定转台结构方案、优化主要支撑件结构及合理选材,并对驱动机构与轴系对转台刚度、温度适应性和指向准确度的影响做了深入分析与计算.同时进行了整机的力学模拟试验和运动机构的高低温试验,一阶谐振频率为49 Hz,在-40 ℃ ～+80 ℃温度范围内工作正常.结果表明转台各项性能指标满足工程任务要求,具有结构紧凑、可靠性高、重量轻的特点.     

大气激光通信中稳定跟踪技术研究

 为了研究大气激光通信中稳定跟踪所采用的器件及有效跟踪方法,分析了光束定位探测器件(电荷耦合器件和四象限光电探测器)的灵敏度特性,结合影响大气激光通信跟踪系统性能的五种大气湍流效应,分别讨论了光束漂移、光强起伏、光斑弥散、到达角起伏及光束扩展的原理.对质心跟踪算法和形心跟踪算法定位准确度的影响进行分析,得到在大气条件下形心算法的跟踪误差小于质心误差的结论,并通过实验进行了验证.