基于Tophat变换和文字纹理的车牌定位算法

针对车牌自动识别系统的应用场景越来越广泛,提出一种新的基于Tophat滤波和文字纹理特征的车牌定位算法.首先,利用形态学Tophat滤波抑制背景、消除不均匀光照,然后对图像进行二值化操作和连通域分析;其次,扫描图像得到区域的垂直投影图(VPM, Vertical Projection Map),对VPM进行离散余弦变换(DCT, Discrete Cosine Transformation),利用中低频描绘子重构VPM,重构后的VPM更为平滑,不受噪声影响,其波峰波谷数量、统计量更能描绘区域纹理的本质属性;最后,结合部分中低频描绘子和统计量组成描述区域纹理的模式向量,输入支持向量机归类.实验表明,算法适用于自然场景中的车牌定位问题,具有较强的适应性.      

A comprehensive numerical model investigating the thermal-dynamic performance of scientific balloon

The increase of balloon applications makes it necessary for a comprehensive understanding of the thermal and dynamic performance of scientific balloons. This paper proposed a novel numerical model to investigate the thermal and dynamic characteristics of scientific balloon in both ascending and floating conditions. The novel model consists of a dynamic model and thermal model, the dynamic model was solved numerically by a computer program developed with Matlab/Simulink to calculate the velocity and trajectory, the thermal model was solved by the Fluent program to find out the balloon film temperature distribution and inner Helium gas velocity and temperature field. These models were verified by comparing the numerical results with experimental data. Then the thermal and dynamic behavior of a scientific balloon in a real environment were simulated and discussed in details.     

Simulation analysis for effects of bone loss on acceleration tolerance of human lumbar vertebra

The purpose of the present study was to analyze and predict the changes in acceleration tolerance of human vertebra as a result of bone loss caused by long-term space flight. A human L3–L4 vertebra FEM model was constructed, in which the cancellous bone was separated, and surrounding ligaments were also taken into account. The simulation results demonstrated that bone loss has more of an effect on the acceleration tolerance in x-direction. The results serve to aid in the creation of new acceleration tolerance standards, ensuring astronauts return home safely after long-term space flight. This study shows that more attention should be focused on the bone degradation of crew members and to create new protective designs for space capsules in the future.     

Rapid design and optimization of low-thrust rendezvous/interception trajectory for asteroid deflection missions

Asteroid deflection techniques are essential in order to protect the Earth from catastrophic impacts by hazardous asteroids. Rapid design and optimization of low-thrust rendezvous/interception trajectories is considered as one of the key technologies to successfully deflect potentially hazardous asteroids. In this paper, we address a general framework for the rapid design and optimization of low-thrust rendezvous/interception trajectories for future asteroid deflection missions. The design and optimization process includes three closely associated steps. Firstly, shape-based approaches and genetic algorithm (GA) are adopted to perform preliminary design, which provides a reasonable initial guess for subsequent accurate optimization. Secondly, Radau pseudospectral method is utilized to transcribe the low-thrust trajectory optimization problem into a discrete nonlinear programming (NLP) problem. Finally, sequential quadratic programming (SQP) is used to efficiently solve the nonlinear programming problem and obtain the optimal low-thrust rendezvous/interception trajectories. The rapid design and optimization algorithms developed in this paper are validated by three simulation cases with different performance indexes and boundary constraints.     

Stability of relative equilibria of the full spacecraft dynamics around an asteroid with orbit–attitude coupling

The full dynamics of spacecraft around an asteroid, in which the spacecraft is considered as a rigid body and the gravitational orbit–attitude coupling is taken into account, is of great value and interest in the precise theories of the motion. The spectral stability of the classical relative equilibria of the full spacecraft dynamics around an asteroid is studied with the method of geometric mechanics. The stability conditions are given explicitly based on the characteristic equation of the linear system matrix. It is found that the linearized system decouples into two entirely independent subsystems, which correspond to the motions within and outside the equatorial plane of the asteroid respectively. The system parameters are divided into three groups that describe the traditional stationary orbit stability, the significance of the orbit–attitude coupling and the mass distribution of the spacecraft respectively. The spectral stability of the relative equilibria is investigated numerically with respect to the three groups of system parameters. The relations between the full spacecraft dynamics and the traditional spacecraft dynamics, as well as the effect of the orbit–attitude coupling, are assessed. We find that when the orbit–attitude coupling is strong, the mass distribution of the spacecraft dominates the stability of the relative equilibria; whereas when the orbit–attitude coupling is weak, both the mass distribution and the traditional stationary orbit stability have significant effects on the stability. We also give a criterion to determine whether the orbit–attitude coupling needs to be considered.     

Study on O2 generation and CO2 absorption capability of four co-cultured salad plants in an enclosed system

The ability to generate O₂ and absorb CO₂ of several co-cultured vegetable plants in an enclosed system was studied to provide theoretical reference for the future man-plant integrated tests. Four kinds of salad plants (Lactuca sativa L. var. Dasusheng, Lactuca sativa L. var. Youmaicai, Gynura bicolor and Cichorium endivia L.) were grown in the CELSS Integration Test Platform (CITP). The environmental factors including O₂ and CO₂ concentration were continuously monitored on-line and the plant biomass was measured at the end of the test. The changing rules of O₂ and CO₂ concentration in the system were basically understood and it was found that the O₂ generated by the plants could satisfy the respiratory needs of 1.75 persons by calculation. It was also found that the plants could absorb the CO₂ breathed out by 2 persons when the light intensity was raised to 550 mmol m⁻² s⁻¹ PPF. The results showed that the co-cultured plants hold good compatibility and excellent O₂-generating and CO₂-absorbing capability. They could also supply some fresh edible vegetable for a 2-person crew.     

On the observability of Mars entry navigation using radiometric measurements

A thorough observability analysis of the Mars entry navigation using radiometric measurements from ground based beacons is performed. This analysis involves the evaluation of the Fisher information matrix which is derived from the maximum likelihood estimation. A series of navigation cases with multiple beacons are investigated, and both range and range-rate measurements are considered. The determinant of Fisher information matrix is used to quantify the observability of navigation system, while the trace of Fisher information matrix is used to determine the lower-bound of estimation errors. For one and two beacon cases, the navigation system is unobservable. However, the eigenvectors of Fisher information matrix give the observable and unobservable component. When three or more beacon measurements are employed, the states of entry vehicle become observable. Some valuable analytic conclusions on the relationship between the geometric configuration of beacons and observability are obtained consequently. Finally, simulation results from two navigation examples indicate that our effort is useful for understanding and assessing the observability of the Mars entry navigation using radiometric measurements.     

An innovative navigation scheme of powered descent phase for Mars pinpoint landing

Pinpoint landing (within 100 m from the target) is essential for future Mars exploration missions. This paper deals with one aspect of the pinpoint landing architecture—the navigation performance improvement during the powered descent phase, and proposes an innovative navigation scheme to obtain the vehicle complete and accurate states. On the basis of dead reckoning relying on the Inertial Measurement Unit, measurements of the Integrated Doppler Radar are adopted to correct the vehicle velocity and altitude. Distance between the vehicle and one Mars Orbiter as well as their line-of-sight relative velocity is measured by a radio sensor, and integrated in the filter to correct the vehicle horizontal position. The innovative navigation system is based on an Extend Kalman Filter. Two observation schemes are developed. One considers measurements of the Integrated Doppler Radar and radio range measurement. Another further considers radio velocity measurement. The performance of the innovative navigation scheme is greatly influenced by the position of the Mars Orbiter with respect to the target. Stochastic analyses are performed to obtain optimal locations of Mars Orbiter. Finally, the innovative navigation scheme performances are assessed through stochastic simulations. Its performance improvements are demonstrated by comparison with the Integrated Doppler Radar only navigation scheme.     

对8mm微波衰减参数计量的探讨

随着现代武器装备的更新换代和新型导弹的不断发展以及电子战中电子对抗的应用,对导弹制导雷达的要求越来越高.由于毫米波具有制导精确度高,抗干扰能力强、穿透性能好以及携带的信息量大等独特性能,因此被广泛应用于雷达、射频天线、通讯卫星、导弹等许多尖端领域.为了确保雷达的各项参数满足武器试验的要求,保障试验任务的顺利进行,对雷达的各项参数的计量检定是十分必要的.目前,"全自动8mm微波功率标准”已经建立,但8mm微波衰减参数的计量在军内还是一项空白,而衰减量值的准确与否直接影响到武器和装备性能的好坏,影响试验任务的成败.因此,我们提出了一种对8mm微波衰减参数的计量方法,以供广大从事微波计量工作的同行参考.     

形状误差分离技术的统一理论——同源、统一的各种直线形状误差分离方法评述

在对国内外现行直线形状误差分离技术分析研究的基础上,论述了各种分离方法的特点和相互关系,从原理、测量准确度和工程应用方面着眼,评述了直线形状误差测量与分离的各种主流方法--"频域三点法"、"时域递推三点法"、"二点法"、"混合两点法"、"时域乱序四点法"、"精密三点法"和"最小二乘逐次多点法"等.指出了各种方法的同源性和统一性,评述了它们的应用条件及优缺点,同时讨论了随机误差和传感器调零误差的影响及消除方法.