对数周期偶极子天线的设计、制造和测试     

耿立红 《天文研究与技术》1997,(1)

文中所作的主要工作是为云南天文台十米抛物面设计、制造一付好的对数周期偶极子天线（ＬＰＤＡ）作馈源。工作有：（１）设计一对交叉的ＬＰ－ＤＡ；（２）分析ＬＰＤＡ特性；（３）估算抛物面的电特性；（４）讨论线极化向园极化转换的问题；（５）天线测量。ＬＰＤＡ的测量结果比较满意。该天线的方向图、平均输入阻抗、三分贝和十分贝波瓣宽度都在从０．５－１．５ＧＨｚ的频率范围内比较一致和稳定，变化很小。天线理论上的许多成就都是与数子计算机有关的。在文中，我们充分利用了计算机的功能来设计天线，分析天线特性，并从测量所得的所有数据文件中计算天线的参数。所编ＦＯＲＴＲＡＮ程序使这一切工作变得容易。最后，我们还讨论了用功率合成器实现线极化向园极化转换的各种情况  相似文献   

Book review     

D. W. Connell  Thomas M. Baugh 《Estuaries and Coasts》1992,15(2):255-255

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Isolation of resonance in acoustic backscatter from elastic targetsusing adaptive estimation schemes     

Azimi-Sadjadi  M.R. Wilbur  J. Dobeck  G.J. 《Oceanic Engineering, IEEE Journal of》1995,20(4):346-353

It has been shown that at certain frequencies the acoustic backscatter from elastic targets exhibits certain resonance behavior which closely relates to the physical properties of the target such as dimension, thickness, and composition. The purpose of this paper is to develop an automated approach for identifying the presence of resonance in the acoustic backscatter from an unknown underwater target by isolating the resonance part from the specular contribution. An adaptive transversal filter structure is used to estimate the specular part of the backscatter and consequently the error signal would provide an estimate of the resonance part. An important aspect of this scheme lies in the fact that it does not require an underlying model for the elastic return. The adaptation rule is based upon fast recursive least squares (RLS) learning. The approach taken in this paper is general in the sense that it can be applied to targets of unknown geometry and thickness and, further, does not require any a priori information about the target and/or the environment. Test results on acoustic data are presented which indicate the effectiveness of the proposed approach  相似文献   

Radial velocity searches for other planetary systems:Current status and future prospects     

W. D. Cochran  A. P. Hatzes 《Astrophysics and Space Science》1996,241(1):43-60

Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years.  相似文献   

An expansion of the Voigt function     

H. A. Harutyunian 《Astrophysics》1996,39(4):370-374

The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996.  相似文献   

Boundary Conditions and Efficient Solution Algorithms For the Potential Function Formulation of the 3-D Viscous Flow Equations     

G. A. Houseman 《Geophysical Journal International》1990,100(1):33-38

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Collisionless analogs of Riemann S ellipsoids with halo     

M. G. Abramyan 《Astrophysics》1986,25(2):563-569

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Cluster lensing of quasars as a probe of ΛCDM and dark energy cosmologies     

Ana M. Lopes  Lance Miller 《Monthly notices of the Royal Astronomical Society》2004,348(2):519-528

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The MPE X-ray test facility PANTER: Calibration of hard X-ray (15–50 kev) optics     

M. J. Freyberg  H. Bräuninger  W. Burkert  G. D. Hartner  O. Citterio  F. Mazzoleni  G. Pareschi  D. Spiga  S. Romaine  P. Gorenstein  B. D. Ramsey 《Experimental Astronomy》2005,20(1-3):405-412

The Max-Planck-Institut für extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (< 15keV). Moreover, measurements with mirror test samples for new missions like ROSITA and XEUS have been carried out at PANTER. Here we report on an extension of the energy range, enabling calibrations of hard X-ray optics over the energy range 15–50 keV. Several future X-ray astronomy missions (e.g., Simbol-X, Constellation-X, XEUS) have been proposed, which make use of hard X-ray optics based on multilayer coatings. Such optics are currently being developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA. These optics have been tested at the PANTER facility with a broad energy band beam (up to 50 keV) using the XMM-Newton EPIC-pn flight spare CCD camera with its good intrinsic energy resolution, and also with monochromatic X-rays between C-K (0.277 keV) and Cu-Kα (8.04 keV). PACS: 95.55.Ka, 95.55.Aq, 41 50.+h, 07.85.Fv  相似文献   

Pulsar Wind Nebulae in Egret Error Boxes     

Mallory S. E. Roberts  Crystal L. Brogan  Bryan M. Gaensler  Jason W. T. Hessels  C.-Y. Ng  Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100

A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM.  相似文献