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911.
Over the last 30 years there has been a growing Australian capability in very long-range radar systems, especially over the horizon radar (OTHR) and a related technology, surface wave radar (SWR). Both operate in the high frequency (HF) band between 3 and 30 MegaHertz (MHz), which are wavelengths between 100 and 10 metres, respectively. Based on current evidence, it appears that Australia may have found the tools with which to conduct efficient long-range surface and air surveillance more effectively than by the single use of traditional surveillance forces. Given increasing success and refinement of these technologies, one can see that the SWR systems in particular could, in addition, satisfy a number of potential export requirements and earn useful export credits. 相似文献
912.
The multipath equalization time delay estimator (METDE) provides an adaptive approach for estimating the difference in arrival times of a signal received at spatially separated sensors as well as the multipath channel characteristics. However, the parameter estimates of the METDE are biased in the presence of noise. The METDE algorithm is improved for unbiased parameter estimation via minimizing a modified cost function. Convergence behaviors and variances of the system variables of the amended method are derived. Computer simulations are included to corroborate the theoretical analysis and to evaluate the adaptive multipath delay estimation performance of the proposed algorithm. 相似文献
913.
West W.C. Whitacre J.F. Brandon E.J. Ratnakumar B.V. 《Aerospace and Electronic Systems Magazine, IEEE》2001,16(8):31-33
Recent successes in the effort to miniaturize spacecraft components using MEMS technology, integrated passive components, and low power electronics have driven the need for very low power, low profile, low mass micro-power sources for micro/nanospacecraft applications. Recent work at JPL has focused upon developing thin film/micro-batteries compatible with temperature sensitive substrates. A process to prepare crystalline LiCoO2 films with RF sputtering and moderate (<700°C) annealing temperature has been developed. Thin film batteries with cathode films prepared with this process have specific capacities approaching the practical limit for LiCoO2, with acceptable rate capabilities and discharge voltage profiles. Solid-state micro-scale batteries have also been fabricated with feature sizes on the order of 50 microns 相似文献
914.
C F Johnson T W Dreschel C S Brown R M Wheeler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(4-5):239-242
The Porous Tube Plant Nutrient Delivery System (PTPNDS), a hydrophilic, microporous ceramic tube hydroponic system designed for microgravity, will be tested in a middeck locker of the Space Shuttle. The flight experiment will focus on hardware operation and assess its ability to support seed germination and early seedling growth in microgravity. The water controlling system of the PTPNDS hardware has been successfully tested during the parabolic flight of the KC-135. One challenge to the development of the space flight experiment was to devise a method of holding seeds to the cylindrical porous tube. The seed-holder must provide water and air to the seed, absorb water from the porous tube, withstand sterilization, provide a clear path for shoots and roots to emerge, and be composed of flight qualified materials. In preparation for the flight experiment, a wheat seed-holder has been designed that utilizes a cellulose acetate plug to facilitate imbibition and to hold the wheat seeds in contact with the porous tube in the correct orientation during the vibration of launch and the microgravity environment of orbit. Germination and growth studies with wheat at a range of temperatures showed that optimal moisture was 78% (by weight) in the cellulose acetate seed holders. These and other design considerations are discussed. 相似文献
915.
The Sun–Earth connection is studied using long-term measurements from the Sun and from the Earth. The auroral activity is shown to correlate to high accuracy with the smoothed sunspot numbers. Similarly, both geomagnetic activity and global surface temperature anomaly can be linked to cyclic changes in the solar activity. The interlinked variations in the solar magnetic activity and in the solar irradiance cause effects that can be observed both in the Earth's biosphere and in the electromagnetic environment. The long-term data sets suggest that the increase in geomagnetic activity and surface temperatures are related (at least partially) to longer-term solar variations, which probably include an increasing trend superposed with a cyclic behavior with a period of about 90 years. 相似文献
916.
We report new calculations of transition radiation spectra which are correct for arbitrary energy of a particle at all frequencies down to plasma frequency. The importance of the emission mechanism for solar flares are discussed. 相似文献
917.
Over 8,000 altitude deviations are reported to NASA's Aviation Safety Reporting System each year. This is almost one an hour. The narratives of pilot incidents relate how errors made in the automation-assisted altitude change task are caused by the difficulty pilots are having interacting with automatic systems. This paper discusses the impact of increased automation in glass-cockpit airliners on the altitude deviations reported by pilots. By observing the way information is processed by the cockpit system, the author suggests that the philosophies of design and training need to change in order to facilitate, not debilitate, the aircrew 相似文献
918.
C. S. Zerefos D. S. Balis P. Zanis C. Meleti A. F. Bais K. Tourpali D. Melas I. Ziomas E. Galani K. Kourtidis A. Papayannis Z. Gogosheva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(12):1955-1963
Intensive measurements of UV solar irradiance, total ozone and surface ozone were carried out during the solar eclipse of 11 August 1999 at Thessaloniki, Greece and Stara Zagora, Bulgaria, located very close to the footprint of the moon's shadow during the solar eclipse with the maximum coverage of the solar disk reaching about 90% and 96% respectively. It is shown that during the eclipse the diffuse component is reduced less compared to the decline of the direct solar irradiance at the shorter wavelengths. A 20-minute oscillation of erythemal UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20-minute fluctuation in total ozone presumably caused by the eclipse induced gravity waves. The surface ozone measurements at Thessaloniki display a decrease of around 10–15 ppbv during the solar eclipse. Similarly, ozone profile measurements with a lidar system indicate a decrease of ozone up to 2 km during the solar eclipse. The eclipse offered the opportunity to test our understanding of tropospheric ozone chemistry. The use of a chemical box model suggested that photochemistry can account for a significant portion of the observed surface ozone decrease. 相似文献
919.
920.
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