A novel target detection approach based on adaptive radar waveform design

To resolve problems of complicated clutter, fast-varying scenes, and low signal-clutterratio (SCR) in application of target detection on sea for space-based radar (SBR), a target detection approach based on adaptive waveform design is proposed in this paper. Firstly, complicated sea clutter is modeled as compound Gaussian process, and a target is modeled as some scatterers with Gaussian reflectivity. Secondly, every dwell duration of radar is divided into several sub-dwells. Regular linear frequency modulated pulses are transmitted at Sub-dwell 1, and the received signal at this sub-dwell is used to estimate clutter covariance matrices and pre-detection. Estimated matrices are updated at every following sub-dwell by multiple particle filtering to cope with fast-varying clutter scenes of SBR. Furthermore, waveform of every following sub-dwell is designed adaptively according to mean square optimization technique. Finally, principal component analysis and generalized likelihood ratio test is used for mitigation of colored interference and property of constant false alarm rate, respectively. Simulation results show that, considering configuration of SBR and condition of complicated clutter, 9 dB is reduced for SCR which reliable detection requires by this target detection approach. Therefore, the work in this paper can markedly improve radar detection performance for weak targets.     

Acceleration of Solar-Energetic Particles by Shocks

Our current understanding of the acceleration of solar-energetic particles is reviewed. The emphasis in this paper is on analytic theory and numerical modeling of the physics of diffusive shock acceleration. This mechanism naturally produces an energy spectrum that is a power law over a given energy interval that is below a characteristic energy where the spectrum has a break, or a rollover. This power law is a common feature in the observations of all types of solar-energetic particles, and not necessarily just those associated with shock waves (e.g. events associated with impulsive solar flares which are often described in terms of resonant stochastic acceleration). Moreover, the spectral index is observed to have remarkably little variability from one event to the next (about 50%). Any successful acceleration mechanism must be able to produce this feature naturally and have a resulting power-law index that does not depend on physical parameters that are expected to vary considerably. Currently, only diffusive shock acceleration does this.     

应用激光相位-多普勒系统测量雾化液滴颗粒和流动特性

在几何光学近似理论的基础上分析了相位多普勒方法的理论模型和相位 粒径特性关系 ,分析了实验应用的光纤型激光相位多普勒系统的原理和组成 ,并应用此系统对雾化喷嘴的流动和颗粒特性进行了测量 ,得到了液滴的二维速度与粒径的相关和统计特性。     

Laboratory investigation of physical mechanisms of auroral charged particle acceleration in the field-aligned current layers

One of the major topics of space weather research is to understand auroral structure and the processes that guide, accelerate, and otherwise control particle precipitation and during substorms. The problem is that it is not clear the structure of the magnetic field-aligned electric fields and how they are supported in the magnetospheric plasma. The objective of this research is to study the physical mechanisms of these phenomena in a laboratory experiment. It should be achieved by simulating the charged particle acceleration due to field-aligned electrical field generation in all totality of the interconnected events: generation of a plasma flow, its evolution in the magnetic field, polarization of plasma, generation of the field-aligned currents, development of instabilities in the plasma and current layers, double layers or anomalous resistance regions appearance, electron acceleration. Parameters of the laboratory simulation and preliminary results of the experiment are discussed.     

Impact effects from small size meteoroids and space debris

When the impact risk from meteoroids and orbital debris is assessed the main concern is usually structural damage. With their high impact velocities of typically 10–20 km/s millimeter or centimeter sized objects can puncture pressure vessels and other walls or lead to destruction of complete subsystems or even whole spacecraft. Fortunately chances of collisions with such larger objects are small (at least at present). However, particles in the size range 1–100 μm are far more abundant than larger objects and every orbiting spacecraft will encounter them with certainty. Every solar cell (8 cm² area) of the Hubble Space Telescope encountered on average 12 impacts during its 8.25 years of space exposure. Most were from micron sized particles.     

基于离线状态监测的复杂装备预知维修决策及优化

基于免疫粒子群优化算法,对可进行离线状态监测故障呈现渐发特性的复杂装备预知维修决策问题进行了研究。分析了维修决策的必备条件,包括研究对象的前提假设、决策内容、剩余维修时间预测以及维修相关费用;将复杂装备维修决策问题转化为带有约束条件的目标函数求最小解的问题,并构建了数学模型;运用结合粒子群优化算法明确方向性搜索和免疫系统多样性保持能力优势的免疫粒子群算法,对模型进行求解;通过某航空机电设备的实例应用验证,该方法可以有效地解决复杂装备预知维修决策的问题,结果与实际情况基本一致。     

Experiment of gas plasma plume deflection by magnetic control

To investigate the deflection effect of gas plasma plume controlled by magnetic field, a novel experimental scheme was presented. The Cs2CO3 catalytic ionization seeds were injected into the combustion chamber to obtain gas plasma on a high temperature magneto hydrodynamic (MHD) experiment rig. The plasma jet was deflected under the action of an external magnetic field, resulting in a thrust-vector effect. Particle image velocimetry (PIV) collected two-dimensional images of jet flow field. Through image processing and velocity vector analysis, the jet deflection angle can be obtained quantitatively. At 1800-2500K, the jet deflection was verified experimentally under the condition of 0.45T magnetic field strength. The results indicate that the jet deflection angle increases gradually with the increase of gas temperature, and above 2200K, the jet deflection angle increase obviously. In the process of gas plasma jet, it is feasible to realize the jet deflection controlled by MHD by adding an external magnetic field.     

基于PSO-RWE的自适应小波阈值函数滚动轴承振动信号去噪方法

针对现有小波去噪方法存在阈值函数中未知参数选取依赖经验,导致去噪不充分或去噪后信号失真的问题。提出了一种基于相对小波熵(RWE)的粒子群优化(PSO)算法,用于小波阈值函数中未知参数的自适应寻优,达到滚动轴承振动信号自适应降噪目的。改进了一种含两未知参数的小波阈值函数;以相对小波熵为优化算法的适应度函数对未知参数进行自适应寻优,得到最优小波阈值函数;通过对模拟仿真信号和试验采集的滚动轴承振动信号进行分析。结果表明:优化后的小波去噪方法能够更好地将噪声从染噪信号中滤除,去噪后信号波形的平滑度更好,信噪比相较硬阈值去噪提高294%,而且保留了原始信号更多的细节特征,具有更好的去噪性能和应用实用价值。     

基于CPHD的双层粒子滤波目标跟踪算法

常规基于势概率假设密度滤波(Cardinalized Probability Hypothesis Density,CPHD)的粒子滤波(Particle Fil? ter,PF)跟踪算法应用于多目标跟踪时,容易遇到因粒子数量增加而带来的运算效率下降、目标数目估计不准的问题。文章基于常规粒子滤波 CPHD跟踪算法,通过部署双层粒子,提出基于势概率假设密度滤波的双层粒子滤波 (Two-Layer Particle Filter-CPHD,TLPF-CPHD)算法,以便提高目标数目及状态估计精度。仿真实验结果证明,相比于常规 PF-CPHD算法,新算法具有更好的目标数目和状态估计准确性。