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261.
B. R. Johnson M. E. Abroe P. Ade J. Bock J. Borrill J. S. Collins P. Ferreira S. Hanany A. H. Jaffe T. Jones A. T. Lee L. Levinson T. Matsumura B. Rabii T. Renbarger P. L. Richards G. F. Smoot R. Stompor H. T. Tran C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress. 相似文献
262.
263.
A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143 总被引:1,自引:0,他引:1
K. A. Pounds J. N. Reeves A. R. King K. L. Page P. T. O'Brien M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713
We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s−1 . The highest energy lines require a column density of N H ∼ 5 × 1023 cm−2 , at an ionization parameter of log ξ∼ 3.4 . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143. 相似文献
264.
Introducing a concept of equivalent mass depth of flow, this study describes the phenomenon of non‐point source pollutant (metal) transport for pavement (or overland) flow in analogy with wave propagation in wide open channels. Hysteretic and normal mass rating curves are developed for runoff rate and mass of 12 dissolved and particulate‐bound metal elements (pollutants) using the rainfall‐runoff and water quality data of the 15 × 20 m2 instrumented pavement in Cincinnati, USA. Normal mass rating curves developed for easy computation of pollutant load are found to be of a form similar to Manning's, which is valid for open channel flows. Based on the hysteresis analysis, wave types for dissolution and mixing of particulate‐bound metals are identified. The analysis finds that the second‐order partial‐differential equation normally used for metal transport does not have the efficacy to describe fully the strong non‐linear phenomena such as is described for various metal elements by dynamic waves. In addition, the proportionality concept of the popular SCS‐CN concept is extended for determining the potential maximum metal mass Mp of all the 12 elements transported by a rain storm and related to the antecedent dry period (ADP). For the primary metal zinc element, Mp is found to increase with the ADP and vice versa. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
265.
Lance B. Morrissey Philippe Janvier Simon J. Braddy John P. Bennett Susan B. Marriott Peter R. Tarrant 《Geology Today》2006,22(2):66-67
Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle. 相似文献
266.
A. D. Biggs D. Rusin I. W. A. Browne A. G. de Bruyn N. J. Jackson L. V. E. Koopmans J. P. McKean S. T. Myers R. D. Blandford K.-H. Chae C. D. Fassnacht M. A. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088
267.
268.
Abstract— The Morávka (Czech Republic) meteorite fall occurred on May 6, 2000, 11:52 UT, during the daytime. Six H5–6 ordinary chondrites with a total mass of 1.4 kg were recovered. The corresponding fireball was witnessed by thousands of people and also videotaped by 3 casual witnesses. Sonic booms were recorded by 16 seismic stations in the Czech Republic and Poland and by one infrasonic station in Germany. A total of 2.5% of the fireball eyewitnesses reported electrophonic sounds. Satellites in Earth orbit detected part of the fireball light curve. In this first paper from a series of 4 papers devoted to the Morávka meteorite fall, we describe the circumstances of the fall and determine the fireball trajectory and orbit from calibrated video records. Morávka becomes one of only 6 meteorites with a known orbit. The slope of the trajectory was 20.4° to the horizontal, the initial velocity was 22.5 km/s, and the terminal height of the fireball was 21 km. The semimajor axis of the orbit was 1.85 AU, the perihelion distance was 0.982 AU, and the inclination was 32.2°. The fireball reached an absolute visual magnitude of ?20 at a height of 33 km. 相似文献
269.
270.
E. García L. De Haro C. O'Sullivan G. Cahill J. A. López Fernández F. Tercero B. Galocha J. L. Besada 《Experimental Astronomy》2003,15(3):173-193
A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower
the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes
modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the
horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on
the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME).
Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical
Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct
application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for
the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献