HTPB官能度数学模型建立

为了研究自由基型液体端羟基聚丁二烯预聚物(HTPB)体系官能度分布情况,对其化学合成中自由电子转移情况进行了分析,并通过数学统计的方法对其官能度分布进行理论数值模拟,建立了适用于自由基型HTPB官能度分布的函数关系式,并与GPC所测结果进行对比。结果显示,计算所得函数关系式与测试数据吻合结果较好,数值模拟结果准确性较高;自由基聚合生产的不同批次的HTPB官能度分布存在较大差异,单官能度分子含量可从5%~24%,二官能度分子的含量可从50%~81%;利用数学统计得到的函数关系,可将复杂的HTPB官能度测试转变为简单的分子量分布测试。     

Atmospheric reentry hemisphere prediction for prograde orbits using logical disjunction

A unique logic-based algorithm for atmospheric reentry hemisphere prediction is presented for spacecraft in low-eccentricity, prograde low Earth orbits at altitudes of 300 km and lower. Using two-line element (TLE) data for initial orbit conditions, coupled with coarse estimates for spacecraft aerodynamic characteristics, the algorithm relies on logical disjunction operations based on a dual analysis of histogram and two-weighted Gaussian probability density function (PDF) fits of predicted reentry latitude data. The algorithm requires the execution of a series of parametric simulations to determine the reentry hemisphere for variations in spacecraft aerodynamic coefficients and drag reference area. When implemented, the algorithm yields accurate hemisphere predictions on average 15 days from reentry as demonstrated by historical reentry cases from 1979 to 2018. All reentry cases were selected to demonstrate the algorithm’s ability to deliver accurate reentry hemisphere predictions for spacecraft with varying physical size and mass, and reentering during different periods of solar cycle activity.     

Contamination of short GRBs by giant magnetar flares: Significance of downward revision in distance to SGR 1806–20

We highlight how the downward revision in the distance to the star cluster associated with SGR 1806–20 by Bibby et al. (2008) reconciles the apparent low contamination of BATSE short GRBs by intense flares from extragalactic magnetars without recourse to modifying the frequency of one such flare per 30 years per Milky Way galaxy. We also discuss the variety in progenitor initial masses of magnetars based upon cluster ages, ranging from ∼50 M_⊙ for SGR 1806–20 and AXP CXOU J164710.2–455216 in Westerlund 1 to ∼17 M_⊙ for SGR 1900+14 according to Davies et al. (2009) and presumably also 1E 1841–045 if it originated from one of the massive RSG clusters #2 or #3.     

A fast pulse phase estimation method for X-ray pulsar signals based on epoch folding

X-ray pulsar-based navigation (XPNAV) is an attractive method for autonomous deep-space navigation in the future. The pulse phase estimation is a key task in XPNAV and its accuracy directly determines the navigation accuracy. State-of-the-art pulse phase estimation techniques either suffer from poor estimation accuracy, or involve the maximization of generally non-convex object function, thus resulting in a large computational cost. In this paper, a fast pulse phase estimation method based on epoch folding is presented. The statistical properties of the observed profile obtained through epoch folding are developed. Based on this, we recognize the joint prob-ability distribution of the observed profile as the likelihood function and utilize a fast Fourier transform-based procedure to estimate the pulse phase. Computational complexity of the proposed estimator is analyzed as well. Experimental results show that the proposed estimator significantly outperforms the currently used cross-correlation (CC) and nonlinear least squares (NLS) estima-tors, while significantly reduces the computational complexity compared with NLS and maximum likelihood (ML) estimators.     

Evaluation and improvement of coastal GNSS reflectometry sea level variations from existing GNSS stations in Taiwan

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1?m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10?cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7?cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.     

强不确定系统“全系数之和等于1”的实现方法

摘要： 研究强不确定系统“全系数之和等于1”的实现方法，强不确定系统指的是系统的静态增益及其界不完全确知且范围较大.“全系数之和等于1”是吴宏鑫院士20世纪80年代发现的，该原理表明，对于未知连续系统，其离散化系统的系数的和在一定条件下是1.该原理的发现对于解决闭环辨识和自适应控制的瓶颈问题具有关键作用.“全系数之和等于1”是在一定条件下成立的.为了实现系统的“全系数之和等于1”，需要对系统进行一定的变换，以满足所需条件.其中，采用静态增益的标称值的倒数进行输入变换的方法在实际中得到了广泛应用.但是，当系统的不确定性较大时，该变换将带来较大偏差.针对该问题开展了深入研究，明确给出了系统静态增益的不确定性与标称值的比值的关系对于实现“全系数之和等于1”的影响.当不确定性与标称值的比值较小时，可以近似实现“全系数之和等于1”；当比值较大时，进一步给出了通过选取合适的采样周期，近似实现“全系数之和等于1”的方法.本文的研究对于特征模型理论在实际中的应用提供了一定的基础.     

基于层次分析法的综合射频架构选取技术研究

综合射频系统是作战飞机航空电子系统的重要组成部分，它们是作战飞机通过无线电方式感知外界信息的重要系统。系统架构的选取直接影响了飞机的作战性能，针对以往架构选取依赖大量定性分析而缺乏定量对比问题，提出了基于层次分析法的综合射频架构选取技术，该技术能够有效地根据不同的任务需求和平台需求，综合考虑定量和定性因素，给出更为合理对比分析结果，为综合射频系统的系统设计提供技术支撑。该技术也可推广到航空领域其他多目标决策问题的应用。     

DME Interference mitigation for L-DACS1 based on system identification and sparse representation

L-band digital aeronautical communication system 1 (L-DACS1) is a promising candi-date data-link for future air-ground communication, but it is severely interfered by the pulse pairs (PPs) generated by distance measure equipment. A novel PP mitigation approach is proposed in this paper. Firstly, a deformed PP detection (DPPD) method that combines a filter bank, correlation detection, and rescanning is proposed to detect the deformed PPs (DPPs) which are caused by mul-tiple filters in the receiver. Secondly, a finite impulse response (FIR) model is used to approximate the overall characteristic of filters, and then the waveform of DPP can be acquired by the original waveform of PP and the FIR model. Finally, sparse representation is used to estimate the position and amplitude of each DPP, and then reconstruct each DPP. The reconstructed DPPs will be sub-tracted from the contaminated signal to mitigate interference. Numerical experiments show that the bit error rate performance of our approach is about 5 dB better than that of recent works and is closer to interference-free environment.     

基于H∞方法的控制系统作动器最优控制仿真研究

在设计控制系统模型时,首先引入了有限差分法(FDM)离散化后的波动方程,然后基于H∞最优控制原理,检查闭环控制系统的稳定性和可探测性,对控制系统传感器和作动器的位置进行优化配置.通过计算闭环反馈系统的范数,最终得到了控制系统的最优控制算法.仿真结果表明,利用波动方程来优化控制系统传感器和作动器位置的算法是可行的,可广泛应用于飞控系统的设计中.