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941.
R. Z. Sagdeev G. A. Avanesov I. V. Barinov A. I. Debabov V. A. Kvasikov V. I. Moroz V. A. Shamis V. I. Tarnapolski D. A. Usikov Ya. L. Ziman B. S. Zhukov B. A. Smith S. Larson F. Szabo K. Szeg A. Kondor L. Vrhalmi E. Mernyi L. Szabo I. Toth P. Cruvellier A. Abergel J. -L. Bertaux J. E. Blamont M. Danz D. Mhlmann H. Stiller H. P. Zapfe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(12):95-104
The VEGA-1 and VEGA-2 spacecraft made their closest approach to Comet Halley on 6 and 9 March, respectively. In this paper those results of the onboard imaging experiment which were obtained around closest approach are discussed. The nucleus of the comet was clearly identifiable as an irregularly shaped object, with overall dimensions of (16±1)×(8±1)×(8±1) km. The nucleus rotates in the prograde sense about an axis nearly perpendicular to the orbital plane with a period of 53±2 hours. Its albedo is only Many of the jet features observed during the second fly-by have been spatially reconstructed. Their sources form a quasi-linear structure on the surface. The dust above the surface is shown to be generally optically thin with the exception of certain specific dust jets. Brightness features on the surface are clearly seen. Correlating our data with other measurements, we conclude that the dirty snow-ball model will probably need to be revised. 相似文献
942.
Chiang S.J. Liaw C.M. Ouyang J.H. Chiang C.C. 《IEEE transactions on aerospace and electronic systems》1995,31(1):257-266
The design and implementation of a multimodule parallel series-loaded resonant (SLR) converter system is presented. The SLR converter to be paralleled is operated in the n=2 discontinuous mode (DCM). Its dc analysis and dynamic modeling are made. In parallel operation, an average control technique is proposed to compensate the mismatch in current control characteristics of each parallel converter. Good dynamic and static current sharing characteristics are obtained. In addition, to obtain good output voltage regulating control performance, a design procedure is presented to find the parameters of feedback voltage controller according to the prescribed specifications 相似文献
943.
Raghavan R.S. Qiu H.F. McLaughlin D.J. 《IEEE transactions on aerospace and electronic systems》1995,31(2):647-657
We develop a constant false-alarm rate (CFAR) approach for detecting a random N-dimensional complex vector in the presence of clutter or interference modeled as a zero mean complex Gaussian vector whose correlation properties are not known to the receiver. It is assumed that estimates of the correlation properties of the clutter/interference may be obtained independently by processing the received vectors from a set of reference cells. We characterize the detection performance of this algorithm when the signal to be detected is modeled as a zero-mean complex Gaussian random vector with unknown correlation matrix. Results show that for a prescribed false alarm probability and a given signal-to-clutter ratio (to be defined in the text), the detectability of Gaussian random signals depends on the eigenvalues of the matrix Rc-1Rs. The nonsingular matrix Rc and the matrix Rs are the correlation matrices of clutter-plus-noise and signal vectors respectively. It is shown that the “effective” fluctuation statistics of the signal to be detected is determined completely by the eigenvalues of the matrix Rc-1Rs. For example the signal to be detected has an effective Swerling II fluctuation statistics when all eigenvalues of the above matrix are equal. Swerling I fluctuation statistics results effectively when all eigenvalues except one are equal to zero. Eigenvalue distributions between these two limiting cases correspond to fluctuation statistics that lie between Swerling I and II models 相似文献
944.
Thomopoulos S.C.A. Bougoulias D.K. Chin-Der Wann 《IEEE transactions on aerospace and electronic systems》1995,31(1):21-38
Dignet is a self-organizing artificial neural network (ANN) that exhibits deterministically reliable behavior-to-noise interference, when the noise does not exceed a prespecified level of tolerance. The complexity of the proposed ANN, in terms of neuron requirements versus stored patterns, increases linearly with the number of stored patterns and their dimensionality. The self-organization of Dignet is based on the idea of competitive generation and elimination of attraction well in the pattern space. Dignet is used for detection and distributed decision fusion. Analytical and numerical results are included 相似文献
945.
Electric vehicles that can't reach trolley wires need batteries. In the early 1900's electric cars disappeared when owners found that replacing the car's worn-out lead-acid battery costs more than a new gasoline-powered car. Most of today's electric cars are still propelled by lead-acid batteries. General Motors in their prototype Impact, for example, used starting-lighting-ignition batteries, which deliver lots of power for demonstrations, but have a life of less than 100 deep discharges. Now promising alternative technology has challenged the world-wide lead miners, refiners, and battery makers into forming a consortium that sponsors research into making better lead-acid batteries. Horizon's new bipolar battery delivered 50 watt-hours per kg (Wh/kg), compared with 20 for ordinary transport-vehicle batteries. The alternatives are delivering from 80 Wh/kg (nickel-metal hydride) up to 200 Wh/kg (zinc-bromine). A Fiat Panda traveled 260 km on a single charge of its zinc-bromine battery. A German 3.5-ton postal truck traveled 300 km with a single charge in its 650-kg (146 Wh/kg) zinc-air battery. Its top speed was 110 km per hour 相似文献
946.
An up-to-date assessment of adaptive control technology as applied to robotics is presented. Although the field is relatively new and does not yet represent a mature discipline, considerable attention for the design of sophisticated robot controllers has occurred. In this presentation, adaptive control methods are divided into model reference adaptive systems and self-tuning regulators with further definition of various approaches given in each class. The similarity and distinct features of the designed controllers are delineated and tabulated to enhance comparative review 相似文献
947.
Blachman N.M. Mousavinezhad S.H. 《IEEE transactions on aerospace and electronic systems》1986,(1):2-7
Bessel functions, used extensively in mathematical physics, electromagnetics, and communication-system theory, must often be approximated by appropriate formulas. The functions J?(x) and I?(x) for integer values of p are well approximated by the sum of a small number of circular and hyperbolic sines or cosines, respectively, when x is not too large, e.g., less than 10, and convenient expressions are obtained for their errors. These approximations are especially convenient for use on personal computers (PCs) and pocket calculators and in analytically evaluating integrals. 相似文献
948.
Controlled-root formulation for digital phase-locked loops 总被引:4,自引:0,他引:4
In a new formulation for digital phase-locked loops, loop-filter constants are determined from loop roots that can each be selectively placed in the s-plane on the basis of a new set of parameters, each with single and direct physical meaning in terms of loop noise band, width root-specific decay rate, or root-specific damping. Loops of first to fourth order are treated in the continuous-update approximation (BL T→0) and in a discrete-update formulation with arbitrary B LT. Deficiencies of the continuous-update approximation in large-BLT applications are avoided in the new discrete-update formulation. A new method for direct, transient-free acquisition with third- and fourth-order loops can improve the versatility and reliability of acquisition with such loops 相似文献
949.
Stright J.R. Rogers S.K. Quinn D.W. Fielding K.H. 《IEEE transactions on aerospace and electronic systems》1996,32(2):768-774
The theory of embedded time series is shown applicable for determining a reasonable lower bound on the length of test sequence required for accurate classification of moving objects. Sequentially recorded feature vectors of a moving object form a training trajectory in feature space. Each of the sequences of feature vector components is a time series, and under certain conditions, each of these time series has approximately the same fractal dimension. The embedding theorem may be applied to this fractal dimension to establish a sufficient number of observations to determine the feature space trajectory of the object. It is argued that this number is a reasonable lower bound on test sequence length for use in object classification. Experiments with data corresponding to five military vehicles (observed following a projected Lorenz trajectory on a viewing sphere) show that this bound is indeed adequate 相似文献
950.
M. M. Shvarts S. M. Grach E. N. Sergeev V. L. Frolov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):59-62
Results of computer simulations of the broad continuum (BC) feature of stimulated electromagnetic emissions (SEE) of the ionosphere are presented. The simulations were performed using the model of BC generation based on the double transformation of electromagnetic waves to upper hybrid (UH) waves and back with artificial small scale irregularities (ASI) of plasma density. An induced scattering of the UH waves by thermal ions provided a wide spectrum of SEE. For the simulations an empirical model of the ASI spectrum, development and decay was used. 相似文献