Ahmad  F. Frazer  G.J. Kassam  S.A. Amin  M.G. 《IEEE transactions on aerospace and electronic systems》2004,40(1):206-220

A coarray-based near-field, wideband synthetic aperture beamformer using stepped-frequency signal synthesis and post-data acquisition processing is presented. While coarray techniques offer significant reduction in the number of array elements for a given angular resolution, the hybrid subarray-stepped frequency realization of wideband systems simplifies implementations and offers flexibility in beamforming. Proof of concept is provided using real data collected in an anechoic chamber for several pulse shapes and array weightings.  相似文献   

    

Yu. F. Gortyshov  V. G. Tonkonog  A. G. Kochenkov 《Russian Aeronautics (Iz VUZ)》2007,50(3):248-252

The critical flow conditions and structural forms of a two-phase flow that is formed during water efflux from the region of moderate and low pressures into a rarefied medium are analyzed. The difference in the structural forms of a flow realized at the low-head efflux from the structure of a flow occurring in the fluid flow with moderate and high initial pressures is established. The critical pressure differential characterizing the establishment of the maximum flowrate is determined and the decisive influence of turbulence on the vapor phase generation and flow conditions of a two-phase medium is shown.  相似文献   

  总被引：1，自引：0，他引：1  

Gerten  G. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(11):3-8

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Moschopoulos  G. Mei Qiu Pinheiro  H. Jain  P. 《IEEE transactions on aerospace and electronic systems》2003,39(2):660-674

A pulsewidth modulated (PWM) full-bridge converter that simultaneously performs input power factor correction (PFC) and DC-DC conversion is proposed. The converter is the same as the standard voltage-fed PWM full-bridge converter with a diode-bridge low-pass filter front end, but with a slight modification that results in an improvement in power factor that is sufficient to satisfy the EN61000-3-2 requirements for electrical equipment. The operation of the converter is explained and analyzed, and the results of the analysis are used to determine the converter's steady-state characteristics, which are discussed in detail. A design procedure for the selection of components is then derived and demonstrated with an example. The feasibility of the converter and its ability to satisfy EN61000-3-2 requirements on electrical equipment is shown with results obtained from an experimental prototype.  相似文献   

    

Raina  G. Malik  O.P. 《IEEE transactions on aerospace and electronic systems》1985,(1):100-105

A power generation scheme using a synchronous generator with an excitation control system driven by a variable-speed wind turbine is described. The proposed scheme has been analyzed over a wide speed range and under wind gusting conditions. Performance characteristics show that it is feasible to use variable-speed fixed-pitch wind turbines to generate electric power.  相似文献   

    

R. H. D. Corbet  A. P. Smale  J. W. Menzies  G. Branduardi-Raymont  P. A. Charles  K. O. Mason 《Space Science Reviews》1985,40(3-4):415-419

We present optical spectroscopy and photometry of 4U 1258-61 obtained over the course of six years. Evidence for the evolution of a circumstellar envelope throughout the course of the observations is presented.  相似文献   

    

S. Mereghetti  G. F. Bignami  P. A. Caraveo  A. Goldwurm  G. G. C. Palumbo 《Space Science Reviews》1985,40(3-4):495-501

A new EXOSAT (LE/CMA) observation of the region in Crux (R.A. 11h 45m, Dec. -62°) where Markert et al. (1981) reported the existence of two x-ray SNR's is presented. After cleaning the CMA field from the point source component, due to the UV emission of the numerous stars in the field, the smoothed x-ray contours are compared to the 408 MHz radio map of Caswell et al. (1983). The existence of two, well-separate x-ray emission regions is confirmed by EXOSAT, and the current x-ray/radio picture is not sufficent to distinguish clearly between the assumption of one or two (possibly interacting) SNR's in the region.  相似文献   

    

Lindsey F. Smith  G. Meynet  J. -C. Mermilliod 《Space Science Reviews》1993,66(1-4):413-416

Evolutionary models allow an assignment of both a mass and a luminosity to a Wolf-Rayet (WR) star in a cluster, and hence allow a determination of the Bolometric Correction (B.C.). The B.C.'s derived for WN stars range from –4.0 to –6.0 with the expected trend of larger values (in absolute values) for stars with higher excitation spectra. For WC stars, there is little evidence for a similar trend; most observations presented here are consistent with B.C.=–4.5, as found by Smith and Maeder (1989). The convergence of B.C. values derived from evolutionary and atmospheric models is extremely satisfactory, giving increased confidence in both methods.  相似文献   

    

Trunk  G.V. Gordon  W.B. Cantrell  B.H. 《IEEE transactions on aerospace and electronic systems》1990,26(1):146-153

A technique which uses maximum-likelihood estimates (MLEs) of target Doppler and target amplitude is developed for rejecting clutter residues. Multiple estimates are made and consistency checks are applied to the estimates. Simulation results indicate that for large clutter-to-noise ratios (C/N⩾55 dB) the probability of false alarm from clutter residues is reduced from 1.0 to below 0.01  相似文献   

    

Wright  C.H.G. Delp  E.J. Gallagher  N.C.  Jr. 《IEEE transactions on aerospace and electronic systems》1990,26(1):122-145

A necessary requirement of a strategic defence system is the detection of incoming nuclear warheads in an environment that may include nuclear detonations of undetected or missed target warheads. A computer model which simulates incoming warheads as distant endoatmospheric targets is described. A model of the electromagnetic noise expected in the nuclear environment is developed. Predicted atmospheric effects are also included. The ability of nonlinear image enhancement algorithms to their ability to suppress the noise and atmospheric effects of the nuclear environment is examined. These algorithms are then tested, using the combined target and noise models, and evaluated in terms of noise removal and their ability to resolve closely spaced targets  相似文献