Exact Formulation of Window Functions for Analog Network Spectral Analyzers

An equation for the spectral window function for analog network analyzers is derived without assumptions on length of data interval available. The equation, given in terms of filter pole-zero locations for both the filter-bank and heterodyned-input type analyzers, can be programmed on a digital computer without difficulty. As an illustration, the "growth" of a spectral window with increasing length of available data is shown for a special case: a single-tuned circuit followed by a squaring circuit and perfect integrator. The error in using the usual approximation also is indicated. Use of the derived equation for quantitative comparisons of analog and digital analyzers is noted.     

英航的转危为机和全球航空业的结构性变革——专访英国航空公司首席执行官威利·沃尔什

刚过去的2009年在许多航空业人士心中可能是永远无法过去的一年。这一年50多家航空公司倒闭,逾2800架商用飞机停场,全球航空运输能力缩减4%-5%,全球航空业哀鸿遍     

Parabolic Drag-Free Flight, Actuation with Kicks, Spectral Analysis with Gaps

The LISA Pathfinder Drift Mode is an experimental mode proposed for the LISA Pathfinder drag free space mission. The Drift Mode’s specificity is to switch off a possibly noisy actuator periodically in order to minimize the actuation noise. The experiment delivers a measurement that includes data segments virtually free of any actuation force noise. The corresponding acceleration data is then used to estimate the experiment disturbance spectrum, using a calibrating and gap-filling algorithm. This article focuses on two points to demonstrate the feasibility and interest of such an experiment: a first part is dedicated to experiment control and dynamics, whereas the second part explains how to solve the challenging problem posed by the data analysis.     

金属光谱发射率的仿真与分析

 在研究物体的辐射特性时,需要用到物体表面的发射率等物性参数作为输入参数。实验测量发射率数据的适用范围受到一定限制,不能满足所有情况的数值仿真需要。从电磁波传播的基础理论着手,结合金属自由电子气模型,考虑光学参数的色散关系和空气入射到金属内折射角的复数关系,并在随机模拟金属粗糙表面的基础上,模拟并讨论了不同影响因素下实际金属表面的光谱发射率变化趋势。将本文的数值仿真与其他相关的实验和仿真数据进行对比,结果表明,该方法从本质理解并计算金属实际表面光谱发射率数值,结果可信,并具有普遍适应性。     

Spectral Analysis of Optimal and Suboptimal Gyro Monitoring Filters

Gyro monitoring filters are used to estimate and correct gyro drift rates of local-level inertial navigation systems. Conventional gyro monitoring filters are usually designed based on a simplified model of gyro drift rate. Furthermore, the effectiveness of these filters-and of many filters of the "Kalman" type-is often measured in terms of the root mean square (rms) criterion in contrast to the spectral content criterion typical of classical Wiener filtering theory. This paper has two objectives: to propose a gyro monitoring filter which is based on a more detailed model of gyro drift rate; and to propose a method of filter performance evaluation which uses as criterion a measure of the spectral content of the error process. The proposed gyro monitoring filter is shown to have improved spectral contents resulting in superior navigation performance for the gyro error models used in the calculations (comparable to commercial-grade aircraft gyros).     

Spectral Analysis and Subtraction of Noise in Radar Signals

A new method of maximum entropy spectral estimation called the revised maximum entropy method (MEM) is formulated and is applied to the spectral analysis of the echo signals from atmospheric turbulence observed by an incoherent scatter radar. The revised MEM is shown free from many demerits of the other methods for spectral analysis. Further it makes it possible to subtract the white noise usually contained in the data during the processing. Some examples of spectral estimation are shown for the actual radar signals and the simulated data. Another application of the revised MEM is the subtraction of the clutter component which is difficult to do by linear filtering. The method is successfully applied to several data abounding with the clutter to obtain the spectra of the echo signals with less clutter distortion.     

Spectral Analysis of ELT Signals for SARSAT

Search and rescue satellite-aided tracking (SARSAT) relays the emergency locator transmitter (ELT) signals of distressed aircraft to an earth station for spectral analysis. Of considerable importance are the characteristics of the spectrum of the ELT signal since the probability of locating the downed aircraft is closely related to the quality of the ELT signal spectrum itself. In this paper, it is shown that the spectrum can be adversely affected by a number of factors including the phase and frequency characteristics of the carrier and their interaction with the amplitude modulation. Two new models are proposed which greatly reduce the self-generated interference produced by ELT units presently being used.     

基于Walsh基和二值离散余弦基单像素成像的对比分析

为提升单像素成像的测量效率,对Walsh基和二值离散余弦基单像素成像进行了对比研究。针对Walsh变换和抖动二值化后的离散余弦变换,提出了一种借鉴机器学习的排序方法,即通过分别统计80000幅图像的Walsh测量基和离散余弦测量基各自相应测量权重绝对值,按权重由大到小排序得到了两种具有先验知识的测量基优化排序。按两种测量基优化排序,研究了在相同压缩采样下的单像素成像。利用随机选取的500幅图像,定量分析了成像的峰值信噪比和结构相似度。研究发现,两类测量基在压缩采样为5%时,500幅图像平均峰值信噪比可达20dB,平均结构相似度达0.5以上;在采样率1%~10%的区间,二值化的离散余弦基重建结果占优;在采样率10%~20%的区间,两种测量基效果相当;在采样率大于20%时,Walsh基占优。该结论为单像素成像技术实现快速、高信噪比成像提供了一种方法,对推进单像素成像测量基的选取具有较好的参考价值。     

Spectral Analysis of Orbits via Discrete Fourier Transforms

We give some simple and direct algorithms for deriving the Fourier series which describe the quasi-periodic motion of regular orbits from numerical integrations of those orbits. The algorithms rely entirely on discrete Fourier transforms. We calibrate the algorithms by applying them to some orbits which were studied earlier using the NAFF method. The new algorithms reproduce the test orbits accurately, satisfy constraints which are consequences of Hamiltonian theory, and are faster. We discuss the rate at which the Fourier series converge, and practical limits on the degree of accuracy that can reasonably be achieved.     

函数间数据通信方式的分析与应用

对利用全局变量和参数来实现C语言函数间数据通信问题进行了分析 ,着重阐述了参数传递中的传值方式和传地址方式的工作原理及功能 ,在此基础上讨论了传地址方式的应用———数组形参的相关问题。     

Minor Bodies: Spectral Gradients and Relationships with Meteorites

The observational evidence of a gradient in composition of the solid matter in the Solar System as a function of heliocentric distance, with more volatile elements increasingly abundant at larger heliocentric distances, is in general agreement with commonly accepted ideas about condensation of solid material in the early protoplanetary disk. In this respect, the gradual transition from regions mostly populated by S-type objects in the inner asteroid belt to the C-type dominated outer belt, and to the D-type dominated Trojan clouds has generally been interpreted as diagnostic of a zoning of the asteroid population in terms of mineralogic composition and thermal history. The situation, however, is not completely clear, and several contradictory facts still need an explanation. Another major problem concerns the origin of meteorites. Understanding the history of these bodies is critically important, since most of our ideas about the composition of the original protosolar nebula and protoplanetary matter come from meteoritic data. In this respect, very recent advances have been achieved in the knowledge of dynamical transport mechanisms. This can have important consequences for the characterization of plausible meteorite parent bodies. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analysis of Irrational Transfer Functions for Distributed-Parameter Systems

This paper is intended as an exposition of some approximation techniques on irrational transfer functions which are frequently encountered in control systems. Two algorithms for continued fraction expansion and inversion are established.     

基于光谱分析技术的磨损故障监测

采用转盘电极式原子发射光谱分析技术,监测某型燃气轮机传动润滑系统磨损状况的发展变化趋势,及时诊断早期磨损故障.为确保光谱分析技术监测的准确性,着重研究了环境温度波动、标准曲线细化、样品黏度以及磨损颗粒尺寸等主要因素对测量结果的影响,并简要阐述了光谱分析技术的基本原理.经大量研究试验表明:光谱分析技术能够提前预报燃气轮机传动润滑系统可能发生的磨损故障,是油液状态监控的1种有效手段.     

带通椭圆球面波函数能量聚集性分析

针对带通椭圆球面波函数的能量聚集性及其在通信系统中应用的有效性问题,对带通椭圆球面波函数的能量聚集性进行了理论分析,提出了带通椭圆球面波函数是具有最佳能量聚集性的时限带通函数形式,并与基带椭圆球面波函数、类椭圆球面波函数进行了比较分析,采用基于特征值分解的数值算法对函数进行了仿真分析。理论分析和仿真结果均表明,带通椭圆球面波函数可以应用于大多数现有的传输系统,并能有效地提高系统的功率利用率。     

被动型氢原子钟原子跃迁谱线测试与分析

被动型氢原子钟的原子跃迁谱线特性决定了其稳定度指标.为使其稳定度指标达到最优,通过设计数字式测试电路对氢原子钟物理部分进行探测,获得了不同参数配置下的原子跃迁谱线,并通过数据处理分析其信噪比、增益和线宽等特性,提出了一种参数优化方案,为原子钟闭环参数设置提供了依据.     

政府对培育国际竞争优势的作用分析

随着中国加入世界贸易组织 ,土生土长的国内企业该如何走向世界 ,这是摆在我们面前的一个课题 ,但这里的“走向世界”并不是地理意义上的世界 ,国内企业要在本土市场上参与国际竞争 ,政府的作用是必不可少的     

波音747—400发电机调压器功能分析

本文分析了波音747-400型飞机发电机调压器的基本功能和工作原理,并对一些电路进行了实验研究,给出了部分实验结果。     

基于二维频谱方法的直升机噪声源的分辨与提取

针对直升机飞行时其噪声中多种噪声源相互混叠难以分辨的问题,通过随机信号理论分析,结合直升机噪声信号的特点,发展了基于二维频谱分析的直升机噪声源分辨与提取模型及方法,在此基础上将该方法应用于剪刀式尾桨直升机尾桨噪声信号的频域提取与分析.本文首先推导了这种方法的理论模型,并给出相应的求解方法;然后采用该方法分别对模拟和实测的直升机总体噪声信号进行分析,计算结果表明该方法可以有效地提取出总体噪声中的各谐波成份.最后通过对剪刀式尾桨直升机噪声的分析,获得了剪刀式尾桨降噪的机理.