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661.
J Birn M Hesse K Schindler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1763-1771
Magnetic reconnection in traditional, two-dimensional theory can be closely associated with topological properties of the magnetic field, separatrices, neutral lines, or separators. Such well-defined topological properties may no longer exist, or become hopelessly complicated, in more general three-dimensional configurations, that otherwise behave physically quite similarly to the two-dimensional configurations. We discuss generalized definitions of reconnection applied to such situations and illustrate typical properties with simulations of three-dimensional reconnection in the magnetotail. 相似文献
662.
663.
Tuley M.T. Ralston J.M. Rotondo F.S. Andrews A.M. Rosen E.M. 《Aerospace and Electronic Systems Magazine, IEEE》2002,17(5):10-12
Previously, K. Bakhtar and E. Sagal [ibid. vol. 17, pp. 4-11, 2002] made remarkable claims for the performance of the Bakhtar Associates ground-penetrating radar (GPR) in detecting and classifying buried unexploded ordnance (UXO). In this article, we report the results of the series of blind tests on the EarthRadar carried out during the Fall of 2000 and Spring of 2001, which led to very different conclusions regarding the radar's performance. The contents of this article are excerpted from the final report on the testing, prepared by the Institute for Defense Analyses 相似文献
664.
F J Burns Y Jin S J Garte S Hosselet 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):507-519
In the multistage theory of carcinogenesis, cells progress to cancer through a series of discrete, irreversible, heritable genetic alterations or mutations. However data on radiation-induced cancer incidence in rat skin suggests that some part of an intermediate repairable alteration may occur. Data are presented on cancer induction in rat skin exposed to the following radiations: 1. an electron beam (LET=0.34 keV/um, 2. a neon ion beam (LET=25 keV/um and 3. an argon ion beam (LET=125 keV/um. The latter 2 beams were generated by the Bevalac at the Lawrence Berkeley Laboratory, Berkeley, CA. About 6.0 cm2 of skin was irradiated per rat. The rats were observed every 6 weeks for at least 78 weeks and tumors were scored at first occurrence. Several histological types of cancer, including squamous and basal cell carcinomas, were induced. The cancer yield versus radiation dose was fitted by the quadratic equation (Y(D)=CLD+BD2), and the parameters C and B were estimated for each type of radiation. Analysis of the DNA from the electron-induced carcinomas indicated that K-ras and/or c-myc oncogenes were activated in all tumors tested, although only a small proportion of neon-induced tumors showed similar activation. In situ hybridization indicated that the cancers contain subpopulations of cells with differing amounts of c-myc and H-ras amplification. The results are consistent with the idea that ionizing radiation produces carcinogenically relevant lesions via 2 repairable events at low LET and via a non-repairable, linked event pathway at high LET; either pathway may advance the cell by 1 stage in the multistage model. The model, if validated, permits the direct calculation of cancer risk in rat skin in a way that can be subjected to experimental testing. 相似文献
665.
666.
Gholdston E. Hartung J. Friefeld J. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(2):25-30
The Electric Power System (EPS) being built for the International Space Station has undergone several significant changes over the last year, as major design decisions have been made for the overall station. While the basic topology and system elements have remained the same, there are important differences in connectivity, assembly sequence, and start-up. The key drivers for these changes in architecture have been the goal to simplify verification, and most significantly, the introduction of extensive Russian participation in the program. Having the Russians join the international community in this project has resulted in an expanded station size, larger crew, and almost doubled the observable surface of the Earth covered by the station. For the power system it has meant additional interfaces for power transfer, and new challenges for solar tracking at the higher inclination orbit. This paper reviews the current architecture and emphasizes the new features that have evolved, as the design for the new, larger station has developed. Additionally, the possible application of developing technology to the station, and other future missions is considered 相似文献
667.
This paper describes an approach for incorporating a neural network with real-time learning capability in a flight control architecture. The architecture is also applicable, in general, for the control of processes described by nonlinear differential equations of motion in which there exists a control for each degree of freedom. The main features are that the defining equations of motion for the process to be controlled are poorly known with respect to their functional forms, and that the functional forms, themselves, may undergo sudden and unexpected variation. It is well known that such systems are difficult to control, particularly when the effect of the control action enters nonlinearly. Numerical results based on 6DOF simulations of a high performance aircraft are presented to illustrate the potential benefits of incorporating neural networks as a part of a flight control system architecture 相似文献
668.
A Gaussian sum estimation algorithm has previously been developed to deal with noise processes that are non-Gaussian. Inherent in this algorithm is a serious growing memory problem that causes the number of terms in the Gaussian sum to increase exponentially at each iteration. A modified Gaussian sum estimation algorithm using an adaptive filter is developed that avoids the growing memory problem of the previous algorithm while providing effective state estimation. The adaptive filter is comprised of a fixed set of estimators operating in parallel with each individual estimate possessing its own corresponding weighting term. A simulation example illustrates the new non-Gaussian estimation technique 相似文献
669.
Several major fuel cell projects and their status are described. The fuel cell types discussed are phosphoric acid, molten carbonate, solid oxide, and polymer. One of the technologies is very close to commercialization. Two others offer the possibility for higher efficiency and large capacity electric generation using coal. Still another may be the answer to the key issues facing the transportation sector 相似文献
670.
Morgan C.J. Moyer L.R. Wilson R.S. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(3):41-43
A technique is presented for determining the ideal detection threshold when Gaussian noise and Weibull distributed clutter returns are present on a radar receiver and neither is dominant. Quantitative data is presented for several clutter types and false alarm probabilities 相似文献