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131.
A simple and fast zero tracking algorithm for adaptive arrays with large look direction errors is presented and investigated. Basically, the algorithm is based on adjusting the complex zeroes of a power inversion array in a time-multiplexed manner to track all the sources in the environment. To preserve the desired signal which is supposed to be closest to the look direction of 0°, the algorithm removes the zero with the shortest distance to ej0 so that the directional response consists of only nulls steered at the jammers. When compared with the least mean square (LMS) algorithm employing zeroth and first-order look direction constraints, the new algorithm has about the same implementation complexity, is considerably faster, and possesses a much better signal-to-noise ratio (SNR) performance when the look direction is erroneous 相似文献
132.
Geiss J. Bühler F. Cerutti H. Eberhardt P. Filleux Ch. Meister J. Signer P. 《Space Science Reviews》2004,110(3-4):307-335
Space Science Reviews - The Apollo Solar Wind Composition (SWC) experiment was designed to measure elemental and isotopic abundances of the light noble gases in the solar wind, and to investigate... 相似文献
133.
We present preliminary results from high resolution observations obtained with the Michelson Doppler Imager (MDI) instrument
on the SOHO of two large solar flares of 14 July 2000 and 24 November 2000. We show that rapid variations of the line-of-sight
magnetic field occured on a time scale of a few minutes during the flare explosions. The reversibility/irreversibility of
the magnetic field of both active regions is a very good tool for understanding how the magnetic energy is released in these
flares. The observed sharp increase of the magnetic energy density at the time of maximum of the solar flare could involve
an unknown component which deposited supplementary energy into the system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
134.
Israel G. Cabane M. Brun J-F. Niemann H. Way S. Riedler W. Steller M. Raulin F. Coscia D. 《Space Science Reviews》2002,104(1-4):433-468
ACP's main objective is the chemical analysis of the aerosols in Titan's atmosphere. For this purpose, it will sample the
aerosols during descent and prepare the collected matter (by evaporation, pyrolysis and gas products transfer) for analysis
by the Huygens Gas Chromatograph Mass Spectrometer (GCMS). A sampling system is required for sampling the aerosols in the
135'32 km and 22'17 km altitude regions of Titan's atmosphere. A pump unit is used to force the gas flow through a filter.
In its sampling position, the filter front face extends a few mm beyond the inlet tube. The oven is a pyrolysis furnace where
a heating element can heat the filter and hence the sampled aerosols to 250 °C or 600 °C. The oven contains the filter, which
has a thimble-like shape (height 28 mm). For transferring effluent gas and pyrolysis products to GCMS, the carrier gas is
a labeled nitrogen 15N2, to avoid unwanted secondary reactions with Titan's atmospheric nitrogen.
Aeraulic tests under cold temperature conditions were conducted by using a cold gas test system developed by ONERA. The objective
of the test was to demonstrate the functional ability of the instrument during the descent of the probe and to understand
its thermal behavior, that is to test the performance of all its components, pump unit and mechanisms.
In order to validate ACP's scientific performance, pyrolysis tests were conducted at LISA on solid phase material synthesized
from experimental simulation. The chromatogram obtained by GCMS analysis shows many organic compounds. Some GC peaks appear
clearly from the total mass spectra, with specific ions well identified thanks to the very high sensitivity of the mass spectrometer.
The program selected for calibrating the flight model is directly linked to the GCMS calibration plan. In order not to pollute
the two flight models with products of solid samples such as tholins, we excluded any direct pyrolysis tests through the ACP
oven during the first phase of the calibration. Post probe descent simulation of flight results are planned, using the much
representative GCMS and ACP spare models.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
135.
An optimum filter for direct A/D conversion 总被引:1,自引:0,他引:1
The author describes a design procedure to find the optimum finite-impulse-response (FIR) filter coefficients when the characteristics of the bandpass filter preceding the analog-to-digital (A/D) converter are known. A simulation of direct A/D conversion performance shows the improvement over the filter coefficients designed to minimize the maximum error over a specified band of frequencies. DC cancellation may be added to the process with very little change in the coefficients of the optimum FIR filter or its performance.<> 相似文献
136.
Lee M.H. Kolodziej W.J. Mohler R.R. 《IEEE transactions on aerospace and electronic systems》1985,(5):594-600
The control of a linear system with random coefficients is studied here. The cost function is of a quadratic form and the random coefficients are assumed to be partially observable by the controller. By means of the stochastic Bellman equation, the optimal control of stochastic dynamic models with partially observable coefficients is derived. The optimal control is shown to be a linear function of the observable states and a nonlinear function of random parameters. The theory is applied to an optimal control design of an aircraft landing in wind gust. 相似文献
137.
Ning Hsing Lu Eisenstein B.A. 《IEEE transactions on aerospace and electronic systems》1984,(6):830-834
An adaptive threshold detector to test for the presence of a weak signal in additive non-Gaussian noise of unknown level is discussed. The detector consists of a locally optimum detector, a noise level estimator, and a decision device. The detection threshold is made adaptive according to the information provided by the noise level estimator in order to keep a fixed false-alarm probability. Asymptotic performance characteristics are obtained indicating relationships among the basic system parameters such as the reference noise sample size and the underlying noise statistics. It is shown that, as the reference noise sample size is made sufficiently large, the adaptive threshold detector attains the performance of a corresponding locally optimum detector for detecting the weak signal were the noise level known. 相似文献
138.
Rijsdijk F.B. van der Spek G.A. 《IEEE transactions on aerospace and electronic systems》1978,(2):226-236
For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm. 相似文献
139.
S. J. Bauer L. H. Brace D. M. Hunten D. S. Intriligator W. C. Knudsen A. F. Nagy C. T. Russell F. L. Scarf J. H. Wolfe 《Space Science Reviews》1977,20(4):413-430
The current state of knowledge of the chemistry, dynamics and energetics of the upper atmosphere and ionosphere of Venus is reviewed together with the nature of the solar wind-Venus interaction. Because of the weak, though perhaps not negligible, intrinsic magnetic field of Venus, the mutual effects between these regions are probably strong and unique in the solar system. The ability of the Pioneer Venus Bus and Orbiter experiments to provide the required data to answer the questions outstanding is discussed in detail. 相似文献
140.
Space Science Reviews - The two isotopes of nitrogen, 14N and 15N, have relative abundances extremely variable among solar system reservoirs such as planets and their atmospheres, primitive and... 相似文献