The Effect of Integrator Pole Position on the Performance of an Adaptive Array

The LMS adaptive array requires an integrator in each weight feedback control loop. In practice the integrator is often replaced by a low-pass filter, i.e., by a filter with a single pole at s = - ? (where s is complex frequency). The effect of this pole position on array performance is examined. It is shown that to obtain optimal performance from the array, ? must be less than k?2, where k is the loop gain and ?2 is the thermal noise power per element. When at exceeds k?2, the output signal-to-inter ference-plus-noise ratio from the array is degraded for intermediate values of interference power.     

鲁棒Kalman滤波及其在水下组合导航中的应用

在水下捷联惯导(SINS)/多普勒计程仪(DVL)组合导航系统中,当外部辅助信息受到野值等非高斯噪声污染时,选取调节因子γ为固定值将会降低基于Huber方法的鲁棒Kalman滤波(HRKF)算法的精度和鲁棒性。针对此问题,提出了一种基于马氏距离(MD)算法的调节因子自适应的鲁棒Kalman滤波(HRAKF)算法。首先利用MD算法对正常/异常的观测量进行辨识;进而建立γk递推关系式,并根据量测噪声特性对γ值进行实时调整;最后利用γk求取Huber权函数,并对量测噪声阵进行修正。选取8000s船载实测数据,分别利用Kalman滤波(KF)、HRKF及HRAKF算法进行水下组合导航半物理仿真试验。试验结果初步表明:在观测量受到野值或混合高斯分布噪声污染时,相较于KF和HRKF,HRAKF可实现更高精度、更加稳定的组合导航。     

战略储备系统备件最优储备量计算的解析方法

 首先简要介绍了战略储备系统及其寿命过程。然后从分析系统的寿命过程入手,将其寿命过程分为两个阶段,每个阶段分别用一连续时间马尔可夫链来描述系统的动态过程,在此基础上给出了战略储备系统最优战略储备量计算的解析方法,并针对不可修的情况给出了简化的计算公式。     

Design and analysis of new p(n,k) polyphase pulse compression codes

P(n,k) codes as a new class of polyphase pulse compression codes are introduced and analyzed in detail. The P(n,k) codes are conceptually derived by step approximation of the phase function of a nonlinear-frequency modulated (NLFM) Chirp signal with a favorable energy density spectrum. The significant advantages of P(n,k) codes over conventional polyphase codes are lower autocorrelation sidelobes and an improved tolerance of low Doppler shifts and precompression bandwidth limitations. The primary disadvantage of the P(n,k) codes over conventional codes is a loss in range resolution. The uniform P(n,k) codes are especially attractive for radars employing digital signal professing because their favorable correlation properties also remain when quantization effects are taken into account     

不含短环的（n，3，k）LDPC码的几何构造方法

提出了基于不含短环的(n,2,k)规则低密度奇偶校验(LDPC)码的一种最短环长为8的(n,3,k)规则LDPC码的几何构造方法。该方法简单直观而有效。仿真结果显示,在AWGN信道中该码具有明显优于随机构造的规则LDPC码的性能。     

液态碳氢燃料热辐射物性参数反演方法

基于光线跟踪法建立了玻璃-液态碳氢燃料-玻璃3层平板总透射比的正问题模型,给出了反演液态碳氢燃料热辐射物性参数(光谱吸收指数 k 和光谱折射指数 n)的反问题模型,采用Monte-Carlo(M-C)法结合区间逼近法求解.通过将已知文献中庚烷的热辐射物性参数作为“真实值”,采用正问题模型计算总透射比作为“实验测量值”,然后利用反问题模型计算 n 和 k ,并分析实验偏差对反演计算的影响.研究结果表明:①模型反演 k 计算误差的标准差小于0.003%,而 n 的标准差高于21%.②实验偏差对反演计算影响较大,且偏差达到1.0%时个别反演数据明显“失真”.③ k 反演计算误 差的标准差 y 与实验偏差 γ 满足 y =2285.2 γ2- 10.484 γ +0.0037的关系式; n 反演计算误差的标准差受实验偏差影响较小,但偏差导致反演 n 误差均超过20%.      

Analytical Results for the x, y Kalman Tracking Filter

A two-dimensional x, y Kalman tracking filter is analyzed for a track-while-scan (TWS) operation when the radar sensor measures range and bearing (r, ?) at uniform sampling intervals T seconds apart. This development explicitly considers the coupling between the quantities measured by the sensor (r, ?) and the Cartesian x, y coordinate system selected for the tracking operation. The steadystate components of the gain and error covariance matrixes are analytically determined under the assumption of a white noise maneuver acceleration model in two dimensions. These results are verified by computer calculation of the Kalman filter matrix equations.     

Primordial Helium and ΔY/ΔZ from H II Regions and from Fine Structure in the Main Sequence Based on Hipparcos Parallaxes

The primordial helium abundance YP is important for cosmology and the ratio Y/Z of the changes relative to primordial abundances constrains models of stellar evolution. While the most accurate estimates of YP come from emission lines in extragalactic H II regions, they involve an extrapolation to zero metallicity which itself is closely tied up with the slope Y/Z. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of Y/Z from fine structure in the main sequence of nearby stars. We derive such an estimate from Hipparcos data for stars with Z Z and find values between 2 and 3, which are consistent with stellar models, but still have a large uncertainty.     

二分图中哈密顿[k,k+1]因子

主要研究了在均衡二分图G中哈密顿[k,k 1]因子的存在性.设G=(X,Y,E),|X|=1Y1=2/n≥4(k-2)-3,k≥2且n≥2,δ(G)≥k,若G中每一对不相邻的顶点u,v有max{dG(x),dG(x)}≥4/n 2,则G有包含哈密顿圈C的[k,k 1]因子.在此基础上,进一步给出结论:二分图G=(X、Y、E),|x|=|Y|=2/n≥4(k-2)且n≥2,δ(G)≥k,若G中每一对不相邻的顶点u,v有dG(v)≥2/n 4,则G有包含哈密顿圈C的[k,k 1]因子.结论在很大程度上改进了已有的包含哈密顿圈的度条件,进一步完善了包含哈密顿圈的因子理论.     

域k上三次一般方程式的解的计算

我们已经研究了域k上的n（n≥5）次一般方程在特征标为0的情形下关于幂根是不可解的，而对于n≤4是可解的。本文利用n次循环域的拉格朗日分解式及循环群σ∈G（K/k）的结构，推出域k上的三次一般方程在特征标为0的情形下一般解的计算公式。     

On detection using filter banks and higher order statistics

We suggest a method, based on the use of filter bank and higher order statistics (cumulants), for detection of transient signals. The method first uses a bandpass filter bank, which separates the spectrum of the observed signal into narrow frequency bands. Each subfilter of the filter bank is then followed by a cumulant estimator, and thereby suppressing colored noise. By selecting those subfilters that have large output energies, the filter bank can approximate the behavior of a matched filter. Moreover, no a priori information about the waveform of the signal is needed. The performance of the detector is evaluated by using a simulated signal as well as a measured signal. The presented detector is compared with the optimal matched filter detector.     

多渐消因子Kalman滤波器在SINS初始对准中的应用(英文)

针对系统模型和统计信息不能精确已知的条件下Kalman滤波无法给出最优解这一问题,单一渐消因子Kalman滤波算法对于简单的系统是有效的,但是对于复杂的多变量系统,仅仅利用单个的渐消因子是不够的。本文提出了一种多渐消因子滤波算法,通过利用开窗法计算新息序列协方差的无偏估计获得渐消因子矩阵。利用渐消因子矩阵调节一步预测均方误差矩阵k|k1P,对不同的滤波通道提供不同的渐消速率。将该方法应用于SINS的初始对准中,仿真和试验结果表明:当真实系统噪声统计特性同设定参数不一致时,对准精度明显高于其他滤波算法。其对不确定性噪声具有较低的敏感度,对系统参数具有较好的滤波效果。因而,在实际应用中具有重要的参考价值。     

Adaptive detection threshold optimization for tracking in clutter

The adaptive optimization of detection thresholds for tracking in clutter is investigated for the probabilistic data association (PDA) filter. Earlier work on this problem by T.E. Fortmann et al. (1985) involved an approximate steady-state analysis of the state error covariance and is only suitable for time-invariant systems. Furthermore, the method requires numerous assumptions and approximations about the error covariance update equation, and uses a cumbersome graphical optimization algorithm. In this work we propose two adaptive schemes for threshold optimization, namely prior and posterior optimization algorithms which minimize the mean-square state estimation error over detection thresholds which depend on data up to the previous and current time-step, respectively. These algorithm are suitable for real-time implementation in time-varying systems. Some simulation results are presented     

Nonlinear Kinetic Theory of Cosmic-ray Acceleration in Supernova Remnants

A review of kinetic nonlinear theory for cosmic-ray (CR) acceleration and subsequent -ray production due to CR nuclear component in supernova remnants (SNRs) is presented. The correspondence of the expected spectrum and composition of CRs produced inside SNRs in the Galaxy with the experimental data is discussed. Possible explanations of negative results in searching high energy -ray emission from nearby SNRs are analyzed.     

A new adaptive Kalman filter for navigation systems of carrier-based aircraft

The features of carrier-based aircraft’s navigation systems during the approach and landing phases are investigated. A new adaptive Kalman filter with unknown state noise statistics is proposed to improve the accuracy of the INS/GNSS integrated navigation system. The adaptive filtering algorithm aims to estimate and adapt the unknown state noise covariance Q in high dynamic conditions, when the measurement noise covariance R is assumed to be known empirically in advance. The new adaptive Kalman ...     

GPS／SINS姿态组合系统空间一致性研究

在基于卡尔曼滤波器并引入了姿态观测量的GPS/SINS组合导航系统中,GPS天线体坐标系与IMU所在的载体坐标系由于安装误差或其他原因不能完全重合,两个坐标系间存在失准角,导致多天线GPS与SINS输出的姿态信息在空间不能同步,这将影响卡尔曼滤波的效果。本文针对这一问题进行了深入的研究,分析了两个坐标系空间不一致的机理,给出了静态和动基座情况下标定两个坐标系位置关系的方法并进行仿真分析验证了其可行性。     

Ureilites

Ureilites are a rare group of five stony meteorites — feldsparless achondrites containing diamonds of preterrestrial origin the total weight of them being 315 carats. The whole carbon content in ureilites makes up 1.5–4.1%. Ureilites substantially differ from the other stony meteorites. In comparison with chondrites they are enriched in Mg but depleted in metal, troilite, alkaline elements. All ureilites are very similar by their structure. They contain elongated cavities generally stretched in the same direction. The structure of ureilites is an achondritic porphyric one. These meteorites consist of large olivine grains, there is less clinopyroxene (pigeonite). They contain kamacite (Ni content being 1.5–4%), troilite FeS, chromite. Carbon material is represented by diamond, graphite and organic material being present in a disequilibrium state. Two ureilites (North Haig and Dingo Pup Donga) were considerably oxidized during terrestrial weathering and contain secondary iron oxides.Diamonds are present in ureilites in thin intergrowths with graphite being disposed between silicate grains more or less evenly in the meteorite. The sizes of such black diamond-graphite aggregates are 0.3–0.9 mm. The sizes of the micromonocrystals of diamond and graphite are less than 1. The diamond-graphite aggregates contain dispersed particles of kamacite, troilite, chromite, nickelchrome, being present in very thin intergrowths with one another. Besides the usual diamond there is an admixture of lonsdaleite in the aggregates representing a hexagonal diamond with a würtzite-like structure. Lonsdaleite has been identified in the ureilites Novo Urei, Goalpara, North Haig. The diamonds of ureilites are characterized by inhomogeneities in the crystalline structure which are at least partly caused by the presence of donor nitrogen. According to the isotopic carbon composition the diamond in the meteorite Novo Urei has the value C¹³ = -5.7.The structure peculiarities of ureilites bear witness of the fact that these meteorites had been subject to the action of dynamic pressure about 300–600 kbar. The impact had taken place in cosmic space. All ureilites subdivide into two types: the first type are Novo Urei, Dyalpur, Dingo Pup Donga, the second type are Goalpara, North Haig according to the following signs: (1) olivine grains are finer in ureilites of the second type; (2) twinning is more typical of clinopyroxenes of ureilites belonging to the first type; (3) in ureilites of the first type a net-like iron distribution is observed, in ureilites of the second type kamacite plates are chiefly present between silicate grains; (4) the size of diamondgraphite intergrowths in ureilites of the first type does not exceed 0.3 mm, in ureilites of the second type it reaches 0.9 mm. Ureilites of the first type have undergone a less intensive impact than ureilites of the second type. Certain similarity of the material composition of ureilites and of the material composition of carbonaceous chondrites, the distinction of these two groups of meteorites from all other meteorites bear witness of the fact that ureilites have formed from carbonaceous chondrites during a collision of asteroid bodies in cosmic space, diamonds having been formed from the carbon material of carbonaceous chondrites.     

计算有转换判定n∶k交叉贮备系统可靠度的仿真算法

给出有转换判定的ｎ∶ｋ 交叉（ｃｒｏｓｓ ｓｔｒａｐｐｉｎｇ）贮备系统可靠性仿真的通用算法。该算法能计算具有任意部件数和任意部件寿命分布类型的有转换判定的 ｎ∶ｋ 交叉贮备系统可靠度。通过完整的误差分析对该算法的结果进行解释。     

Sensitivity Functions for Linear Discrete Systems with Applications

z-transform techniques are employed to establish general symmetry and simultaneity properties of the first sensitivity functions of the phase-canonical form of single-input, nth-order, linear, constant, discrete-time, controllable systems. It is demonstrated that computation of the first sensitivity function requires one nth-order model in addition to the system model. This simultaneity property is extended to arbitrary single-input, nth-order, linear, constant, discrete systems. In complete analogy with results presented for continuous systems, symmetry and simultaneity properties may be established for the computation of the /th sensitivity function begin{equation*}^{l}beta^{y} triangleq frac{partial^{l}y_{i}}{partialalpha_{Jl}partialalpha_{Jl-1}cdotspartialalpha_{J2}partialalpha_{J1}}|_{alpha=alpha_{0}} {rm for} substack{i = 1,2,ldots,n\ J_{k} = 1,2,ldots,n\ k = 1,2,ldots,l.}end{equation*} Extension of these results to multi-input systems is also mentioned. The usefulness of the simultaneity property is illustrated by applying the results to the design of a low-sensitivity optimal control law.     

The emission mechanisms for solar radio bursts

Emission mechanisms for meter- solar radio bursts are reviewed with emphasis on fundamental plasma emission.The standard version of fundamental plasma emission is due to scattering of Langmuir waves into transverse waves by thermal ions. It may be treated semi-quantitatively by analogy with Thomson scattering provided induced scattering is unimportant. A physical interpretation of induced scattering is given and used to derive the transfer equation in a semi-quantitative way. Solutions of the transfer equation are presented and it is emphasized that standard fundamental emission with brightness temperatures 10⁹ K can be explained only under seemingly exceptional circumstances.Two alternative fundamental emission mechanisms are discussed: coalescence of Langmuir waves with low-frequency waves and direct conversion due to a density inhomogeneity. It is pointed out for the first time that the coalescence process (actually a related decay process) can lead to amplified transverse waves. The coalescence process saturates when the effective temperature T ^t of the transverse waves reaches the effective temperature T ^l of the Langmuir waves. This saturation occurs provided the energy density in the low-frequency waves exceeds a specific value which is about 10^-9 of the thermal energy density for emission from the corona at 100 MHz. It is suggested that direct emission has been dismissed as a possible alternative without adequate justification.Second harmonic plasma emission is discussed and compared with fundamental plasma emission. It also saturates at T ^t T ^l , and this saturation should occur in the corona roughly for T ^l 10¹⁵ K. If fundamental plasma emission is attributed to coalescence with low-frequency waves, then for T ^l 10¹⁵ K the brightness temperatures at the two harmonics should be equal and equal to T ^l . This offers a natural explanation for the approximate equality of the two brightness temperature often found in type II and type III bursts.Analytic treatments of gyro-synchrotron emission are reviewed. The application of the mechanism to moving type IV bursts is discussed in view of bursts with 10¹⁰ K at 43 MHz.