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991.
Mitchell R. L. Rihaczek A. W. 《IEEE transactions on aerospace and electronic systems》1968,(6):822-828
A common but troublesome requirement on radar sensors is the detection of a target in the interference from undesired scatterers, or clutter. Systems with coherent processing of pulse trains are uniquely suited for the purpose because, with pulse trains, it is possible to concentrate the receiver output for particular values of Doppler and thus suppress the clutter by Doppler filtering. This paper discusses to what degree the effectiveness of the method can be enhanced by tapering, or weighting, of the pulse amplitudes. The general results are illustrated by computer-plotted response functions for weighted pulse trains. The clutter suppression efficiency of weighting is calculated both for unilateral weighting in the receiver and for bilateral weighting in both receiver and transmitter. The significance of additional phase weighting is discussed and the results for pure amplitude weighting are compared with publishedwork on phase and amplitude weighting. 相似文献
992.
L Lamotte B Saugier D T Smernoff M Andre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(3):303-308
A simplified closed system consisting of a plant growth chamber coupled to a decomposition chamber was used to study carbon exchange dynamics. The CO2 produced via the decomposition of wheat straw was used for photosynthetic carbon uptake by wheat plants. The atmosphere of the two chambers was connected through a circuit of known flow rate. Thus, monitoring the CO2 concentrations in both compartments allowed measurement of the carbon exchange between the chambers, and estimation of the rate of respiration processes in the decomposition chamber and photosynthetic rate in the producer chamber. The objective for CELSS research was to simulate a system where a compartment producing food via photosynthesis, would be supplied by CO2 produced from respiration processes. The decomposition of biomass by the decomposer simulated both the metabolism of a crew and the result of a recycling system for inedible biomass. Concerning terrestrial ecosystems, the objective was to study organic matter decomposition in soil and other processes related to permanent grasslands. 相似文献
993.
Early in the sixties when President Kennedy announced the goal to land a man on the Moon and return him safely to Earth, there was no way to gauge, accurately and reliably, the millions of pounds of fuel and oxidizer in the proposed rocket. Late in the sixties, when Phillips Petroleum and Marathon Oil contracted to provide large-scale, long term, ocean transport of Liquefied Natural Gas, no system existed to satisfactorily gauge this stream of high value cargoes for commercial transactions. The adventure in solving these related problems led to a worldwide market for LNG Custody Transfer Systems, a successful transfer of technology from a NASA program to commercial use 相似文献
994.
995.
996.
Increasingly, digital computers are being incorporated as major hard-ware subsystems in today's large support and operational systems. As a result, computer programs and complex operational procedures, software, are also becoming major system elements. Contrary to much current practice, software must be managed, engineered, and controlled in the same manner as hardware if past pitfalls are to be avoided. NASA's NPC 500-1 and the USAF 375 series establish a basis for an effective hardware/software systems development methodology that must be adopted by both hardware and software engineers and managers. 相似文献
997.
This paper describes an SHF receiver capable of demodulating analog or digital information rates of up to 50 Mc/s. The receiver is a dual conversion superheterodyne design having a first IF of 1660 Mc/s and a second IF of 445 Mc/s. The model was developed as part of an Air Force contract to study and evaluate design techniques aimed at increasing reliability of aerospace SHF communication equipment. Semiconductor circuitry is used throughout, in addition to numerous deposited thin film circuits for reliability enhancement. The second IF amplifier design is unique in that all circuit components, with the exception of the semiconductors, are deposited, whereas more conventional microelectronics approaches to date have employed externally connected, discrete-component, frequency-selective devices, such as tunable IF coils or filter networks. 相似文献
998.
Johnson R. L. Mason J. L. Petrou N. V. Woll H. J. Hansen G. L. Regan D. C. 《IEEE transactions on aerospace and electronic systems》1966,(1):121-136
A panel session held at the 1965 Aerospace Conference, Houston,Tex., June 23, 1965. Panelists discussed Life-Suppport interfaces with Electric Power; Communications; Navigation; System Integration for Future Space Programs; and Reliability. 相似文献
999.
Integrated electronics or microelectronics is one of today's major technical frontiers. Possibilities offered to the designer of avionics subsystems, for aerospace vehicles, by these techniques, are almost limitless, from the point of view of performance capabilities as well as reliability and maintainability. Application will change current engineering practices in avionics design. Some changes will be easy; in others, problems will appear. This paper discusses these changes, indicating potential gains to be expected as well as potential problem areas. The rise in the application of integrated electronics is expected to be high for the next 10 to 15 years. By 1980, integrated circuitry will have largely replaced the use of discrete components, and the rate-of-increase-of-application curves will level off. 相似文献
1000.
We compare the results of analyzing the stress strain state for the tubular skid landing gear with regard for the physically and geometrically nonlinear scheme of deformation; the analysis is carried out by the finite element method and with the aid of a special beam-type design model. The analysis has been performed for a real helicopter design. The peculiarities of deforming the aircraft structures of the type under study are shown based on the comparison results. 相似文献