CFAR detection of distributed targets in non-Gaussian disturbance

The subject of detection of spatially distributed targets in non-Gaussian noise with unknown statistics is addressed. At the design stage, in order to cope with the a priori uncertainty, we model noise returns as Gaussian vectors with the same structure of the covariance matrix, but possibly different power levels (heterogeneous environment). We also assume that a set of secondary data, free of signal components, is available to estimate the correlation properties of the disturbance The proposed detector assumes no a priori knowledge about the spatial distribution of the target scatterers and ensures the constant false alarm rate (CFAR) property with respect to both the structure of the covariance matrix and the power levels. Finally, the performance assessment, conducted modeling the disturbance as a spherically invariant random process (SIRP), confirms its validity to operate in real radar scenarios     

Semidetached systems: Evolutionary viewpoints and observational constraints

The present knowledge on the evolution of semidetached systems is reviewed. Characteristics of observed systems are discussed and general properties tested by the behaviour of theoretical models. New models of mass accreting companion stars are computed. The accretion phase is divided into a fast and slow phase with an accretion rate depending on the initial mass of the mass losing star and on the initial mass ratio, assuming the systems are undergoing a case B of mass transfer. The results are compared with observed systems with masses of the gainers located within the theoretical range. Up to now no computations exist for the evolution of medium mass close binaries including overshooting of the convective core. However some of the influences of extended convective mixing on the interaction of close binaries are investigated. A larger probability for the occurrence of case A of mass exchange and a larger remnant mass at the end of the process are the most important results. Finally the investigation into the origin of individual systems (in mass, mass ratio and period) is discussed, showing that progress both in observations and in theoretical models result in a more detailed and more restricted determination of the initial parameters of the individual systems.Research associate, NFWO, Belgium.     

Deep space environments for human exploration.

Mission scenarios outside the Earth's protective magnetic shield are being studied. Included are high usage assets in the near-Earth environment for casual trips, for research, and for commercial/operational platforms, in which career exposures will be multi-mission determined over the astronaut's lifetime. The operational platforms will serve as launching points for deep space exploration missions, characterized by a single long-duration mission during the astronaut's career. The exploration beyond these operational platforms will include missions to planets, asteroids, and planetary satellites. The interplanetary environment is evaluated using convective diffusion theory. Local environments for each celestial body are modeled by using results from the most recent targeted spacecraft, and integrated into the design environments. Design scenarios are then evaluated for these missions. The underlying assumptions in arriving at the model environments and their impact on mission exposures within various shield materials will be discussed.     

Deep and Shallow Solid-Earth Structures Reconstructed with Sequential Integrated Inversion (SII) of Seismic and Gravity Data

In this paper, the possibility of using simultaneously seismic and gravity data, for the reconstruction of solid-Earth structures, has been investigated through the use of an algorithm which allows joint efficient and reliable optimisation of compressional velocity and mass density parameters. We view the measured data as a realisation of a stochastic process generated by the physical parameters to be sought and we construct a “probability density function” which includes three kinds of information: information derived from gravity measurements; information derived from seismic travel time inversion and information on the physical correlation among density and velocity parameters. We show that combining data has a beneficial effect on the inversion since: it makes the problem more stable and as a consequence, providing that the quality of data is sufficiently high, enables more accurate and reliable reconstruction of the unknown parameters. In this context, we look forward the GOCE mission, which promises high spatial resolution (100–200 km) and accurate (1–2 mGals) gravity data. We show results obtained from data sets calculated for a lateral inhomogeneous earth synthetic model and from seismic and gravity field data analysed: — in the framework of TOMOVES (TOMOgraphy of Mt. VESuvius) experiment, an European project aiming at reconstructing the 3-D image of Mt. Vesuvius volcano and the crust underneath. using high resolution seismic tomography techniques and other geophysical methods; — for a profile inserted in a project aiming at reconstructing the crustal structure between Corsica and the Northern Appennines which crosses the Ligurian Sea and cuts the Ligurian Appennines W of La Spezia, extending up to Parma. This revised version was published online in August 2006 with corrections to the Cover Date.     

高比冲双组元液体远地点火箭发动机研究

综述了国内外研制的双组元液体远地点火箭发动机的性能、特点和发展趋势。在分析了液体远地点发动机提高比冲的各种技术途径后，提出可通过改进喷注器设计、减少边区液膜冷却流量、采用扰流环二次燃烧和使用新型耐更高温材料等措施，以提高远地点发动机的比冲。     

喷管性能计算的软件实现

基于化学平衡和化学动力学理论，用C^ 和FORTRAN编写了液体火箭发动机喷管性能一维计算软件，软件建立了相关的推进剂数据和化学反应数据库，使计算很简便，针对某型号发动机进行计算，得到了特定条件下发动机的性能参数和化学动力学损失等。     

PLC在立体车库中的应用

以一座 2层 44车位立体车库为例 ,介绍了可编程控制器 (PLC)在立体车库中的应用 ,用PLC实现对车库系统的自动化控制。叙述了立体车库的设计、PLC控制系统的构成和程序设计。     

顾及多路径误差改正的GNSS大坝形变监测研究

在GPS短基线相对定位中,可以根据多路径误差周期约为1天的重复性特点建立误差模型,采用坐标域或观测值域滤波的方法进行多路径误差改正.北斗系统由GEO、IGSO和MEO三种卫星类型组成,其中MEO卫星类型接近7天的轨道周期与GEO和IGSO约为1天的轨道周期差异较大,因此对北斗观测值进行多路径误差改正时只能采用观测值域滤波方法.本文以某水库大坝形变监测网为例,对GPS和BDS观测值分别建立多路径误差模型,根据各自卫星轨道周期进行多路径误差改正,结果表明经改正后大坝形变监测精度有较大提高.