组合夹具复杂等级确定方法

我厂组合夹具室成立于１９６８年，在军品及民品生产中，尤其是在型号研制中广泛使用了组合夹具，仅在型号研制生产中使用的各种组合夹具就达２０００余套，其中有钻、铣（刨插）、镗、磨等各种机床夹具，检验夹具，焊接夹具，装配夹具。实践证明，组合夹具是一种先进的不...     

The turbo PMHT

The PMHT (probabilistic multihypothesis tracker) uses "soft" a posteriori probability associations between measurements and targets. Its implementation is a straightforward iterative application of a Kalman smoother operating on "synthetic" (i.e., modified) measurements, and of recalculation of these synthetic measurements based on the current track estimate. In this correspondence, we first discuss the basic PMHT and some of the older PMHT variants that have been used to enhance convergence. We then introduce the new turbo PMHT, which is informed by the recent success of turbo decoding in the digital communication context. This new PMHT has performance substantially improved versus any of the previous versions.     

Detection of hidden Markov model transient signals

Addressed here is the quickest detection of transient signals which can be represented as hidden Markov models (HMMs), with the application of detection of transient signals. Relying on the fact that Page's test is equivalent to a repeated sequential probability ratio test (SPRT), we are able to devise a procedure analogous to Page's test for dependent observations. By using the so-called forward variable of an HMM, such a procedure is applied to the detection of a change in hidden Markov modeled observations, i.e., a switch from one HMM to another. Performance indices of Page's test, the average run length (ARL) under both hypotheses, are approximated and confirmed via simulation. Several important examples are investigated in depth to illustrate the advantages of the proposed scheme.     

NOx羽烟引起的局部电离层电子密度扰动

通过空间飞行器抛出羽烟的球状近似，研究白天ＮＯ和ＮＯ２羽烟在Ｅ层的扩散，光化学过程及它们对电子密度的影响。由于光致电离和郭解复合反应，抛出的ＮＯ羽烟在Ｅ层造成电子密度最大７．５倍的瞬时增加，而ＮＯ２羽烟可以使Ｅ层下部电子密度瞬时升高达２４倍。     

Robust detection of small stochastic signals

We consider the problem of detecting a stochastic signal in white not-necessarily-Gaussian noise, using vector valued observations. The locally optimal detector is presented and its performance evaluated. The least-favorable signal spectrum and noise density (over specified classes) are found, and it is shown that the detector using these least-favorable assumptions is minimax robust. The class of spectra is that of any stochastic signal of specified power whose spectrum can be bounded from above and from below by two given positive functions. The class of densities is the ε-contamination model. We present examples of the performance achievable with the robust detector in one of these the spectral uncertainty class corresponds to the unknown Doppler shift of a radar return signal. It is demonstrated that the standard matched-filter's performance degradation with increasing Doppler shift can be avoided almost entirely through use of the robust processor     

Correlation between horizontal and vertical monopulse measurements

Many radar systems use the monopulse ratio to extract angle of arrival (AOA) measurements in both azimuth and elevation angles. The accuracies of each such measurement are reasonably well known: each measurement is, conditioned on the sum-signal return, Gaussian-distributed with calculable bias (relative to the true AOA), and variance. However, we note that the two monopulse ratios are functions of basic radar measurements that are not entirely independent, specifically in that the sum signal is common to both. The effect of this is that the monopulse ratios are dependent, and a simple explicit expression is given for their correlation; this is of considerable interest when the measurements are supplied to a tracking algorithm that requires a measurement covariance matrix. The system performance improvement when this is taken into account is quantified: while it makes little difference for a tracking radar with small pointing errors, there are more substantial gains when a target is allowed to stray within the beam, as with a rotating (track-while-scan) radar or when a single radar dwell interrogates two or more targets at different ranges. But in any case, the correct covariance expression is so simple that there is little reason not to use it. We additionally derive the Cramer-Rao lower bound (CRLB) on joint azimuth/elevation angle estimation and discover that it differs only slightly from the covariance matrix corresponding to the individual monopulse ratios. Hence, using the individual monopulse ratios and their simple joint accuracy expression is an adequate and quick approximation of the optimal maximum likelihood procedure for single resolved targets.     

The case for like-sensor predetection fusion

There has been a great deal of theoretical study into decentralized detection networks composed of similar (often identical), independent sensors, and this has produced a number of satisfying theoretical results. At this point it is perhaps worth asking whether or not there is a great deal of point to such study-certainly two sensors can provide twice the illumination of one, but what does this really translate to in terms of performance? We take as our metric the ground area covered with a specified Neyman-Pearson detection performance. To be fair, the comparison will be of a multisensor network to a single-sensor system where both have the same aggregate transmitter power. The situations examined are by no means exhaustive but are, we believe, representative. Is there a case? The answer, as might be expected, is “sometimes.” When the statistical situation is well behaved there is very little benefit to a fused system; however, when the environment is hostile the gains can be significant. We see, depending on the situation, gains from colocation, gains from separation, optimal gains from operation at a “fusion range,” and sometimes no gains at all     

航天器姿态控制的一种自适应方法

针对航天器转动惯量参数未知恒定或缓慢时变,以及外部扰动力矩未知恒定或缓慢时变,基于非线性系统的无源性理论,给出了姿态控制的一种自适应方法.事先不需要不确定性的任何信息,控制过程中可根据自适应律给出其估值.理论分析和数值仿真都表明,该方法在保证参数估计误差有界的同时实现航天器对姿态角指令的快速无静差跟踪.     

测定应力强度因子的守恒积分┐光弹性法

提出了测定断裂力学中应力强度因子的守恒积分－光测弹性力学方法,推导了守恒积分中位移梯度的应力分量表达式,从而可由应力光图所提供的信息计算守恒积分,并确定应力强度因子．本方法克服了单参数法与双参数法固有缺点．由此所得结果与由边界配置法所得结果非常一致．     

嵌入式软件仿真测试环境软件体系结构研究

利用嵌入式软件仿真测试环境(ESSTE,Embedded Software Simulation Testing Environment)对实时嵌入式软件进行系统测试是国内外公认的、行之有效的方法.基于UML和"4+1"视图模型,系统地对ESSTE的软件体系结构进行了描述.各个视图之间保持了良好的一致性,特别地,在设计视图中将ESSTE软件分为两大组件-实时组件和非实时组件,并按照"管道-过滤器"的软件体系结构模式组织,分别给出了它们的关键类.非实时组件的关键类是配置工具类,实时组件的关键类是模型类、实时变量类和调度器类.据此设计和实现的ESSTE-Basic体现了较好的质量特性,如可更改性、可移植性等,其成功地对多个软件进行了系统测试,高效地发现了大量潜藏的软件错误,验证了ESSTE软件体系结构的正确性和有效性.