European intercomparison on electron spin resonance identification of irradiated foodstuffs

The results of a co-trial organized by the Community Bureau of Reference on the use of Electron Spin Resonance spectroscopy for the identification of irradiated food in 21 laboratories are presented. The trial was qualitative on beef and trout bones, sardine scales, pistachio nut shells, dried grapes, and papaya, and quantitative on poultry bones. There was no difficulty in identifying irradiated meat bones, dried grapes, and papaya. In the case of fish bones there is a need for further kinetic study on different species. Identification of irradiation in pistachio nuts is more complicated and additional research is needed before further trials. All laboratories were able to distinguish between chicken bones irradiated at 1 to 3 kGy or 7 to 10 kGy although there was a partial overlap between the results.     

Two- or three-stage least squares?

Two elements enter the choice between 2 and 3SLS for full-system estimation: statistical efficiency and computational cost. 2SLS always has the computational edge, but 3SLS can be more efficient, a relative advantage that increases with the strength of the interrelations among the error terms. A measure of these interrelations is thus helpful in making the choice, and, when there are only two equations, this has suggested using a high pairwise error correlation as an indicator of when to use 3SLS. In larger systems of equations, however, these pairwise correlations can remain small even though more general interrelations give 3SLS the relative advantage. More general indicators are therefore needed, and this paper suggests three such and demonstrates their efficacy.Professor of Economics, Boston College, and Principal Research Associate, Center for Computational Research in Economics and Management Science, MIT. All computation was done on the TROLL system at MIT. My thanks go to Josh Charap for his able research assistance. This research was sponsored in part by the National Science Foundation under grant #IST-8420614.     

调质状态下40Cr钢的焊接

在合理制定焊接工艺的基础上，采用R307珠光体耐热钢焊条成功地进行40Cr钢在调质状态下的焊接，解决了通常采用25—13型奥氏体焊条焊接出现的焊缝强度低、焊接接头性能差的问题。     

Improved Estimates for the Accuracy of Small Disjuncts

Learning systems often describe a target class as a disjunction of conjunctions of conditions. Recent work has noted that small disjuncts, i.e., those supported by few training examples, typically have poor predictive accuracy. One model of this accuracy is provided by the Bayes-Laplace formula based on the number of training examples covered by the disjunct and the number of them belonging to the target class. However, experiments show that small disjuncts associated with target classes of different relative frequencies tend to have different error rates. This note defines the context of a disjunct as the set of training examples that fail to satisfy at most one of its conditions. An empirical adaptation of the Bayes-Laplace formula is presented that also makes use of the relative frequency of the target class in this context. Trials are reported comparing the performance of the original formula and the adaptation in six learning tasks.     

The stability robustness determination of state space models with real unstructured perturbations

This paper considers the robust stability of a linear time-invariant state space model subject to real parameter perturbations. The problem is to find the distance of a given stable matrix from the set of unstable matrices. A new method, based on the properties of the Kronecker sum and two other composite matrices, is developed to study this problem; this new method makes it possible to distinguish real perturbations from complex ones. Although a procedure to find the exact value of the distance is still not available, some explicit lower bounds on the distance are obtained. The bounds are applicable only for the case of real plant perturbations, and are easy to compute numerically; if the matrix is large in size, an iterative procedure is given to compute the bounds. Various examples including a 46th-order spacecraft system are given to illustrate the results obtained. The examples show that the new bounds obtained can have an arbitrary degree of improvement over previously reported ones. This work has been supported by the Natural Sciences and Engineering Research Council of Canada under Grant No. A4396.     

最大似然反褶积软件包的研制与应用

本文简明地介绍最大似然反褶积的基本原理、软件包的研制过程和应用效果。 最大似然反褶积是美国80年代研究出的一种地震资料处理新方法,它有效地解决了传统褶积模型中无法进行信噪分离的矛盾。经松辽盆地实践证明,它可以求出高分辨率和高信噪比的反射系数、最小相位化子波、合成记录、相对层速度和绝对层速度。与国外的VELOG和SEISLOG处理软件的处理结果相比,分辨率和信噪比均有很大的提高。 在软件包的研制过程中,我们主要解决了数学模型复杂和运算速度慢的问题,使最大似然反褶积在CYBER-855S计算机上成为可实用的数字处理技术。 该项技术在大庆油田朝阳沟地区进行了初步应用,结果表明,对薄层地震响应的分辨能力有明显的提高。与井岩性柱状图对比,6m以上的砂层都可以分辨出来,并且对应得比较准确。有些3m的薄层也可以找到。 该软件包的研制成功并在地震资料处理中得到应用,这在国内是首创。     

Spectral estimation of video signals

Spectrum analyzers are ubiquitous in laboratory work concerning one dimensional signals. This is because linear operators are best examined in the frequency domain. Linear operators, such as linear filters, DCT coders, line shufflers, etc., dominate also the video systems scenario. Their frequency domain study is as appropriate and informative as it is in the case of their one-dimensional counterparts. This paper considers the problems associated with the introduction of two well-known spectral estimation techniques, the periodogram and AR estimates, to the context of television signals. The potential for application of spectral estimation to video problems is exemplified by a number of applications related to the fields of enhanced quality television and HDTV. Special attention is paid to the computational aspects, whose effective solution conditions the practical applicability of the proposed spectral estimation techniques.R. Rinaldo is currently at the Department of Electrical and Computer Engineering of the University of California, Berkeley.     

非平稳ARMA信号自校正滤波器及其应用

本文处理带白色观测噪声的非平稳ARMA信号估计问题.应用状态空间方法和现代时 间序列分析方法[1],基于ARMA新息模型,提出了非平稳ARMA信号自校正滤波器,推广了 Hagander和Wittenmafk的结果[2],并给出了在雷达跟踪系统和检测数据数字滤波方面的应 用.仿真结果说明了本文结果的实用性和有效性.