Stochastic voltage model and experimental measurement of ocean-scattered GPS signal statistics

Information about the roughness of the ocean surface and related geophysical parameters, such as wind speed, is present in the shape of the code-correlation waveform of forward-scattered Global Positioning System (GPS) signals. A model is developed for the statistics of this waveform to be used in designing retrieval algorithms and predicting their accuracy in the estimation of geophysical parameters. One potential application of this model is to assess the feasibility of bistatic GPS measurements from satellite orbits. Time and frequency domain models for the complex "voltage" correlation waveform are developed and compared against experimental results. The voltage model can be applied to determine the upper limit for predetection integration time. The resulting temporal and spatial correlation function has a form similar to the van Cittert-Zernike theorem in that it can be expressed in terms of two-dimensional Fourier transform. The fast Fourier transform is, thus, used for efficient computation. Waveforms were generated from measurements of reflected GPS signals recorded in 1999 from an airborne receiver at an altitude of 3200 m during a flight near Puerto Rico. Complex voltage correlations were produced using the coarse-acquisition code with a 1-ms integration time over a range of code delay "bins". The Doppler compensation frequency was set equal to the Doppler frequency obtained by tracking the direct line-of-sight GPS signal. The resulting spectra and derived correlation times of the voltage signal time series in each delay bin were compared with the predictions of the model. The model agreed well with the experimental data, near the specular point, showing correlation times between 4-6 ms.     

DSS development and applications in China

This paper provides an overview of the application and development of decision support systems in China. The curriculum and research in decision support systems in major Chinese universities is introduced first, then selected recent applications of decision support systems in China is described. Finally, the main research topics and direction on decision support systems in China are discussed.     

一个改进的单抓钩周期性排序模型及其在自动化学处理线中的应用

计算机控制的抓钩广泛用于自动化学处理线的工件的运送。抓钩的排序直接影响系统的生产率,抓钩排序的目标是对运送进行排序以极大化生产率。当某工序处理时间非常长时,该工序成为瓶颈。为了去除该瓶颈,系统可以为该工序设计多个处理槽,这称为“多重处理槽”问题。本文提出一个改进的混合整数规划模型以求解有“多重处理槽”的单抓钩周期性排序问题的最优解。实例表明所提出的方法是有效的。     

基于规则的专家系统中不确定性推理的研究

提出了权值法和修正权值法两种不确定性推理算法,与常用的几种方法相比,权值法根据各证据重要程度的不同,区别对待证据的可信度信息,同时充分利用每一条信息;修正权值法除了具有权值法的优点外,又区分了可信度分布的差异。运用修正权值法已成功建造了多个实用专家系统。     

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求文针对我国天然气凝液如何利用问题,结合新技术进展,进行了初步探讨,认为原料较多的场合,应以催化脱氢或芳构化作为当前的主要加工方向。对原料较少的场合,也提出一些看法。     

Study and implementation of the virtual view in unix

The security of information systems is important. protecting them from the viewpoint of methodology has become the critical task of their planners and implementers. This article proposes a new idea about the virtual view based upon unix stemming from the usual view concept,analyzes the characteristics of the virtual view,and finally gives the way of realization of the virtual view.     

一种新颖的认证机制

识别和认证是计算机安全保密的一项重要内容。识别用于区分不同的用户,认证用于鉴别用户的身份。其中认证是实施存取控制的关键,常规的基于口令的认证机制,对于防止口令猜测的进攻显得无能为力,而本文提出的认证机制具有良好的抗猜测特性,而且易于实现。     

协作营销信息系统的研究

营销信息系统是支持企业营销管理和决策的基本工具。本文简要讨论了营销信息系统的概念和发展,认为营销信息系统在本质上是协作处理系统,在对agent属性分析的基础上,提出了协作营销信息系统的结构。