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991.
992.
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
993.
Structures for radar detection in compound Gaussian clutter 总被引:1,自引:0,他引:1
Sangston K.J. Gini F. Greco M.V. Farina A. 《IEEE transactions on aerospace and electronic systems》1999,35(2):445-458
The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance 相似文献
994.
L. Ofman M. Romoli G. Noci G. Poletto J. L. Kohl R. A. Howard C. St. Cyr C. E. Deforest 《Space Science Reviews》1999,87(1-2):287-290
In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness
(pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is
the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes.
In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new
data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power
spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
995.
Al/SiC复合材料的准分子激光表面改性 总被引:1,自引:0,他引:1
利用KrF准分子激光对SiC晶须增强铝基复合材料进行表面改性。借助于显微镜及X射线衍射技术,对激光处理前后试件表层的显微组织及化学结构进行了分析。结果表明,准分子激光处理后,试件表面形成了一个几微米厚的铝层。该薄层中基本上不含金属间化合物,SiC增强相的数量也显着减少。腐蚀测试结果表明,准分子激光表面处理后,材料的抗腐蚀性能得到了显着提高。 相似文献
996.
采用X射线衍射技术测定了冷轧Inconel718合金在860℃加热温度下的δ相和γ″相含量,研究了冷轧变形对δ相和γ″相析出行为的影响。结果表明,冷轧变形影响δ相的析出形貌,随冷轧变形量增加,δ相由针状向颗粒状转变。δ相析出的重量百分数与时间的关系符合Avrami方程,随冷轧变形量增加,n值减小,α值增加。在860℃加热温度下,等温15min时已有γ″相析出,随时间增加,γ″相含量增加,达到最大值后又降低。在试验中给定的时间条件下,随冷轧变形量增加,γ″相含量降低,而δ相含量增加。 相似文献
997.
K. Miyamoto M. Oka R. Yamamoto Y. Masuda T. Hoson S. Kamisaka J. Ueda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):2033-2036
Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth. 相似文献
998.
A Sato T Hamazaki T Oomura H Osada M Kakeya M Watanabe T Nakamura Y Nakamura N Koshikawa I Yoshizaki S Aizawa S Yoda A Ogiso M Takaoki Y Kohno H Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(6):807-813
The paper summarizes the data on proliferation and gravity-related gene expression of osteoblasts that were obtained from an experiment conducted under simulated and real microgravity conditions. Simulated microgravity conditions obtained in a clinostat depress proliferation of both osteoblast-like MC3T3-E1 and HeLa carcinoma cells. This depression of proliferation occurs in a collagen gel culture in which the flow of culture medium by rotation may be reduced. Interestingly, MC3T3-E1 cells which are probably one of target cells to microgravity are more sensitive than the HeLa cells. Simulated microgravity inhibited the epidermal growth factor (EGF)-induced c-fos gene expression in the MC3T3-El cells. To examine in detail the effect of real microgravity on the EGF signal transduction cascade in osteoblasts, MC3T3-E1 cells were cultured in the Cell Culture Experiment Module of the sounding rocket TR-1A6. The EGF-induced c-fos expression in cells was depressed under short-term microgravity conditions in the sounding rocket, while the phosphorylation of mitogen-activated protein kinase (MAPK) was not affected compared with the controls grown on the ground. These results suggest that an action site of microgravity in the signal transduction pathway may be downstream of MAPK. 相似文献
999.
M R Sims C T Pillinger I P Wright J Dowson S Whitehead A Wells J E Spragg G Fraser L Richter H Hamacher A Johnstone N P Meredith C de la Nougerede B Hancock R Turner S Peskett A Brack J Hobbs M Newns A Senior M Humphries H U Keller N Thomas J S Lingard T C Ng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(11):1925-1928
The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies. 相似文献
1000.