排序方式: 共有22条查询结果,搜索用时 15 毫秒
1.
Richard I. Klein Maxwell T. Sandford II Rodney W. Whitaker 《Space Science Reviews》1980,27(3-4):275-282
Two-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.Authors listed alphabetically 相似文献
2.
Maxwell W. Hunter II 《Space Science Reviews》1967,6(5):601-654
Velocity requirements for scientific probe vehicles operating throughout the entire solar system are presented. Both direct flights and those using planetary swingby modes are considered. Launch-vehicle and payload sizes necessary to perform useful scientific missions are examined. Scientific investigation of the solar system is shown to be much less difficult than is commonly believed. 相似文献
3.
Cadzow J.A. Wilkes D.M. Peters R.A. II Li X. 《IEEE transactions on aerospace and electronic systems》1993,29(4):1110-1122
A synthesis-by-analysis model for texture replication or simulation is presented. This model can closely replicate a given textured image or produce another image that although distinct from the original, has the same general visual characteristics and the same first and second-order gray-level statistics as the original image. The texture synthesis algorithm, proposed contains three distinct components: a moving-average (MA) filter, a filter excitation function, and a gray-level histogram. The analysis portion of the texture synthesis algorithm derives the three from a given image. The synthesis portion convolves the MA filter kernel with the excitation function, adds noise, and modifies the histogram of the result. The advantages of this texture model over others include conceptually and computationally simple and robust parameter estimation, inherent stability, parsimony in the number of parameters, and synthesis through convolution. The authors describe a procedure for deriving the correct MA kernel using a signal enhancement algorithm, demonstrate the effectiveness of the model by using it to mimic several diverse textured images, discuss its applicability to the problem of infrared background simulation, and include detailed algorithms for the implementation of the model 相似文献
4.
Napolitano M.R. Cnsanova J.J. Windon D.A. II. Seanor B. Martinelli D. 《IEEE transactions on aerospace and electronic systems》1999,35(1):61-71
The results are presented of a comparative study evaluating the performance of neural network (NN) and fuzzy logic reconstructors (FLRs) for the development of a virtual flight data recorder (VFDK). Typical flight data recorders (FDRS) on commercial airliners do not record the aircraft control surface deflections. These dynamic parameters are critical in the investigation of an accident or an uncommanded maneuver. The results are shown relative to a VFDR based on a neural network simulator (NNS) along with a neural network reconstructor (NNR) or a FLR The NNS is trained off-line, using available flight data for the particular aircraft, for the purpose of simulating any desired dynamic output recorded in current FDRs. The NNS is then interfaced with the NNR or with the FLR. The output of the two reconstructors are the control surface deflections which minimize a performance index based on the differences between the available data from the FDR and the output from the NNS. The study tested with night data from a B737-300 shows that both schemes, the one with the NNR and the one with the FLR, provide accurate reconstructions of the control surface deflections time histories 相似文献
5.
建立了一种普遍的解析理论用于研究确定性载荷作用下轴向受载的单对称Bernoulli—Euler薄壁梁的弯扭耦合动力响应。首先通过直接求解轴向受载的单对称均匀Bernoulli-Euler薄壁梁单元弯扭耦合振动的运动偏微分方程,给出了计算其自由振动的精确方法,并导出了轴向受载的Bernoulli—Euler薄壁梁自由振动主模态的正交条件。然后利用简正模态法研究了确定性载荷作用下轴向受载的Bernoulli—Euler薄壁梁的弯扭耦合动力响应,该梁所受到的载荷可以是集中载荷或分布载荷。最后假定确定性载荷是谐波变化的,得到了各种激励下封闭形式的解,并针对具体算例讨论了动力弯曲位移和扭转位移的数值结果。 相似文献
6.
Napolitano M.R. Silvestri G. Windon D.A. II Casanova J.L. Innocenti M. 《IEEE transactions on aerospace and electronic systems》1998,34(2):456-468
The objective of this document Is to show the capabilities of parallel hardware-based on-line learning neural networks (NNs). This specific application is related to an on-line estimation problem for sensor validation purposes. Neural-network-based microprocessors are starting to be commercially available. However, most of them feature a learning performed with the classic back-propagation algorithm (BPA). To overcome this lack of flexibility a customized motherboard with transputers was implemented for this investigation, The extended BPA (EBPA), a modified and more effective BPA, was used for the on-line learning, These parallel hardware-based neural architectures were used to implement a sensor failure detection, identification, and accommodation scheme in the model of a night control system assumed to be without physical redundancy in the sensory capabilities. The results of this study demonstrate the potential for these neural schemes for implementation in actual flight control systems of modern high performance aircraft, taking advantage of the characteristics of the extended back-propagation along with the parallel computation capabilities of NN customized hardware 相似文献
7.
Gleason D. Andrisani D. II. 《IEEE transactions on aerospace and electronic systems》1989,25(5):768-771
An analysis of a discrete constant-gain α-β-γ tracking filter is presented. Steady-state tracking filter gains are determined without solving a discrete matrix Ricatti equation. Explicit closed-form gain solutions are found as a function of the roots to a cubic equation. Gain variations as a function of process noise, measurement noise, and sampling time are investigated 相似文献
8.
E. D. Feigelson S. Casanova T. Montmerle J. Guibert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):311-314
Two soft X-ray images of the Chamaeleon I star forming cloud obtained with the ROSAT Position Sensitive Proportional Counter are presented. Seventy reliable, and perhaps 19 additional, X-ray sources are found. Up to Ninety percent of these sources are certainly or probably identified with T Tauri stars formed in the cloud. Twenty to 35 are probably previously unrecognized ‘weak’ T Tauri (WTT) stars. T Tauri X-ray luminosities range from log
, or 102 – 104 times solar levels, with mean
in the 0.2–2.5 keV band. The X-ray luminosities of well-studied Chamaeleon cloud members are correlated with a complex of four stellar properties: effective temperature, mass, radius and bolometric luminosity. The spatial distribution, H-R diagram locations of the stars indicate WTT and CTT are coeval. The total premain sequence population of the cloud is likely to be > 100 stars, with WTT stars outnumbering ‘classical’ T Tauri (CTT) stars by 2:1. 相似文献
9.
10.
Philip P. Chandler II 《Space Policy》1985,1(1):7-9
This article contrasts the political motivations behind the US space station initiative with those underlying the European Space Agency's Long Term Plan. Philip Chandler concludes that European cooperation in NASA's space station programme (SSP) will serve three needs: to buy time; to allow European users to undertake longer, manned experiments; and, to keep the Spacelab teams intact. However, in itself the SSP holds little value for Europe. 相似文献