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161.
Alabaster C.M. Hughes E.J. Matthew J.H. 《IEEE transactions on aerospace and electronic systems》2003,39(3):990-1001
Evolutionary algorithms are applied to the optimization of pulse repetition frequency (PRF), for both eight-and nine PRFs, in medium PRF radar while considering the detailed effects of sidelobe clutter and many other technical factors. The algorithm presented also ensures that all the solutions produced are fully decodable and have no blind velocities. The evolutionary algorithm was able to identify near-optimum PRF sets for a realistic radar system with only a modest computational effort. 相似文献
162.
The main goal of the paper is to demonstrate the presence of chaotic trajectories in the gaseous disk of a real spiral galaxy. As an example we have chosen NGC 3631. First, we show the stationarity of the 3-D velocity field restored from the observed line-of-sight velocity field of the gaseous disk. That allows to analyse behaviour of the trajectories of the fluid particles (gas clouds) in the disk, calculating the corresponding observed streamlines. We estimate the Lyapunov characteristic numbers using their independence of the metrics and show the existence of chaotic trajectories outside the vortices which are present in the velocity field, and in the vicinity of the saddle point. Related spectra of the stretching numbers for some trajectories are also calculated. 相似文献
163.
Semenov Vladimir S. Kubyshkin Igor V. Kiendl Michael T. Biernat Helfried K. Rijnbeek Richard P. Besser Bruno P. 《Space Science Reviews》1997,82(3-4):451-461
In this article we address several criticisms of Petschek-type reconnection models which have recently been raised by Heikkila. We discuss features of the time-dependent Petschek-type models in the context of the solar wind-magnetosphere interaction, and point out that such models can incorporate and reproduce observed features at the magnetopause, such as plasma jets and erosion of the current sheet. We argue that some of Heikkila's criticisms can be attributed to weaknesses in the analysis due to incomplete experimental information, rather than to flaws in the concept of reconnection per se; in this category we include the question of which instability leads to the localised breakup of the magnetopause current sheet. Other criticisms are based on an adherence to steady-state models, and cannot be sustained within the extended time-dependent theory. We discuss, for example, how the time-dependent model can provide a consistent picture of how energy from the incoming solar wind is transferred and converted as it enters the magnetosphere. 相似文献
164.
Multiposition alignment of strapdown inertial navigation system 总被引:3,自引:0,他引:3
Lee J.G. Park C.G. Park H.W. 《IEEE transactions on aerospace and electronic systems》1993,29(4):1323-1328
The authors demonstrate that the stationary alignment of strapdown inertial navigation system (SDINS) can be improved by employing the multiposition/technique. Using an observability analysis, it is shown that an optimal two-position alignment not only satisfies complete observability conditions but also minimizes alignment errors. This is done by analytic rank testing of the stripped observability matrix and numerical calculation of the error covariance. It is also shown that an optimal three-position alignment accelerates the convergence of the alignment error compared with two-position alignment 相似文献
165.
A two-pole filter is proposed as a detector for a scanning radar. The optimum values of the filter coefficients are found and are approximated by a simple expression. The optimum two-pole filter requires a 0.15-dB increase in signal-to-noise ratio in order to provide the same detection capability as the optimum detector, and yields azimuth estimates whose standard deviation are within 15 percent of the Cramér-Rao lower bound. The estimator is simple to implement, avoiding the storage requirements of the moving window detector and the bias complications of the feedback integrator. 相似文献
166.
V. A. Grigoriev 《Space Science Reviews》1989,49(1-2):151-155
The scintillation time-of-flight triggering system of the Gamma-1 gamma-ray telescope provides for both the time-of-flight discrimination and the pulse height discrimination of the secondary particles. The paper gives some experimental results for energy dependence of the instrument efficiency in 30–300 MeV energy range for different trigger logics. 相似文献
167.
168.
Krishna M. V. Apparao 《Space Science Reviews》1994,69(3-4):255-329
Observations of X-ray emission from Be star/X-ray binaries are reviewed. Some optical characteristics of these binaries are also presented. Theoretical aspects pertaining to the X-ray emissions are given. 相似文献
169.
Parameters of expanding magnetic loops and arches and of mass flows generated by them in the corona have been computed in a 1D two-fluid approximation. Two possible trigger mechanisms of the coronal transients have been considered: (i) sudden increase of the background magnetic field strength, and (ii) heating and compression plasma inside these magnetic structures. We discuss the formation of shock waves and their dependence on dynamics and geometry of the magnetic structures. 相似文献
170.
Magnetic Position and Orientation Tracking System 总被引:3,自引:0,他引:3
Raab F.H. Blood E.B. Steiner T.O. Jones H.R. 《IEEE transactions on aerospace and electronic systems》1979,(5):709-718
Three-axis generation and sensing of quasi-static magneticdipole fields provide information sufficient to determine both the position and orientation of the sensor relative to the source. Linear rotation transformations based upon the previous measurements are applied to both the source excitation and sensor output vectors, yielding quantities that are linearly propotional to small changes in the position and orientation. Changes are separated using linear combinations of sensor output vectors, transformed to the desired coordinate frame, and used to update the previous measurements. Practical considerations for a head-tracking application are discussed. 相似文献