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The synthesizing of pseudorandom signals which possess an odd crosscorrelation function of useful characteristics is presented. The characteristics are applicable for signal tracking systems such as those associated with ranging instrumentation and spread-spectrum communication. Another property of these signals is that they possess a zero dc component which may be applied for radiating useful carrierless signals. 相似文献
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Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide
Lanfang H. Levine Hirokazu Kasahara Joachim Kopka Alexander Erban Ines Fehrl Fatma Kaplan Wei Zhao Ramon C. Littell Charles Guy Raymond Wheeler John Sager Aaron Mills Howard G. Levine 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The metabolic consequence of suboptimal (400 μmol mol−1 or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO2] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO2]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO2] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO2] and physiological age. In general, plants grown under high [CO2] exhibited a metabolite profile characteristic of older plants under ambient CO2. Elevated [CO2] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO2] to a much greater extent at 10,000 ppm CO2 than at 1500 ppm CO2. The percentage increase of starch content resulting from CO2 enrichment declined as plants develope. In contrast, elevated [CO2] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO2] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO2] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO2-grown plants, both elevated CO2 levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO2] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO2 on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO2 levels. 相似文献
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It has been noted that signal aperture radar (SAR) imagery of clutter exhibits Rayleigh multiplicative noise due to speckle. We use a database of MSTAR target chips to verify that the noise is multiplicative rather than additive for all regions in the chip. Then, by examining histograms corresponding to the noise residuals, we show that a Weibull distribution that is almost Rayleigh best fits the data. However, when we restrict the analysis over the target region, the log-normal and Rayleigh models fit the noise equally as well. This can be attributed to scattering mechanisms that are unstable over five degrees of aspect angle 相似文献
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Kaplan L.J. Ormsby J.F.A. Fowle E.N. Johnson K.R. Bates R.H.T. Bickel S.H. 《IEEE transactions on aerospace and electronic systems》1969,(4):654-660
A satellite has been designed for application to radar calibration. Electromagnetic and mechanical characteristics of the satellite and their influence on the selection of shape and other parameters are discussed. Theoretical and experimental scattering data are included. 相似文献
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The difference in viscous properties of proton and electron gases in fully ionized hydrogen plasma is shown to result in a possibility of generation in this plasma of the magnetic field, even if initially there was no field. As an example, a simplified planar stationary model of a magnetohydrodynamic process of the eddy sink type is considered. It is demonstrated that the intensity of the generated magnetic field strongly depends on plasma temperature, so that the range T = 100000–500000 K corresponds to the range of maximum magnetic induction B = 50–2700 G. Such values are frequently observed in ordinary stars, in particular, in solar flares. 相似文献
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Kaplan L.M. McClellan J.H. Seung-Mok Oh 《IEEE transactions on aerospace and electronic systems》2002,38(1):74-88
Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image 相似文献
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The complex video compression methods in the process of being standardized, which are designed to reduce transmission needs by detecting and coding image redundancy temporally and spatially between frames, are examined. Methods involving fractals, and wavelets may achieve more efficient coding by defining spatial formats and equations more applicable to the specific image than the more general-purpose transforms of the standards. A newer method involves the capture of an entire database of image characteristics and identifies and stores the 3-D motion in the image field. The image can be reproduced at high compression rates at remote locations. Telecommunication products that facilitate the operation and use of video compression systems are presented 相似文献
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This work considers the problem of selecting the best nodes for localizing (in the mean squared (MS) position error sense) a target in a distributed wireless sensor network. Each node consists of an array of sensors that are able to estimate the direction of arrival (DOA) to a target. Different computationally efficient node selection approaches that use global network knowledge are introduced. Performance bounds based on the node/target geometry are derived, and these bounds help to determine the necessary communication reach of the active nodes. The resulting geolocation performance and energy usage, based on communication distance, is evaluated for a decentralized extended Kalman filter (EKF) that is exploiting the different selection approaches. 相似文献
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