The redistribution functionR IV     

Sean J. McKenna  William Nelson 《Astrophysics and Space Science》1986,125(1):103-114

In this paper we address comments made in a recent paper by Hubený and Heinzel (1986). By use of an identity which they report, the photon redistribution function appropriate for scattering transitions between two radiation broadened atomic levels is derived using the simpler Voigt functions. The behaviour of the redistribution function relative to complete redistribution is then examined. It is important to note that the conclusions originally arrived at by McKenna (1984a) are reinforced by this examination. In particular, for most scattering angles, there exists a significant cohrently scattered component of the redistribution function, and the deviations from complete redistribution are large over most outgoing frequencies for a given incoming frequency.  相似文献   

The Kuroshio Extension and its recirculation gyres     

Steven R. Jayne  Nelson G. Hogg  Stephanie N. Waterman  Luc Rainville  Kathleen A. Donohue  D. Randolph Watts  Karen L. Tracey  Julie L. McClean  Mathew E. Maltrud  Bo Qiu  Shuiming Chen  Peter Hacker 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2088-2099

This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of these recirculations gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program (June 2004–June 2006) and include current meters, pressure and current recording inverted echo sounders, and subsurface floats. The position and strength of the recirculation gyres simulated by a high-resolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio's transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current's transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.  相似文献   

Timing eclipses of the Galilean moons with a CCD photometer     

Jim Park  Peter Nelson 《Experimental Astronomy》1994,5(1-2):171-174

The use of an Optec SSP/Lynxx (tradename) CCD imaging photometer for the recording of the Galilean satellite phenomena, with software supplied by Mallama (1992) is described. An example data set (for lo) and least squares reduction is presented.  相似文献   

COMPUTERIZED PERSONAL BIBLIOGRAPHY MANAGEMENT     

Frederick E. Nelson 《The Professional geographer》1991,43(2):205-211

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Radio and visible-light observations of a coronal arcade transient     

T. E. Gergely  M. R. Kundu  F. T. Erskine III  C. Sawyer  W. J. Wagner  R. Illing  L. L. House  M. K. McCabe  R. T. Stewart  G. J. Nelson  M. J. Koomen  D. Michels  R. Howard  N. Sheeley 《Solar physics》1984,90(1):161-176

We discuss simultaneous visible-light and radio observations of a coronal transient that occurred on 9 April, 1980. Visible-light observations of the transient and the associated erupting prominence were available from the Coronagraph/Polarimeter carried aboard SMM, the P78-1 coronagraph, and from the Haleakala Observatory. Radio observations of the related type III-II-IV bursts were available from the Clark Lake and Culgoora Observatories. The transient was extremely complex; we suggest that an entire coronal arcade rather than just a single loop participated in the event. Type III burst sources observed at the beginning of the event were located along a nearby streamer, which was not disrupted, but was displaced by the outmoving loops. The type II burst showed large tangential motion, but unlike such sources usually do, it had no related herringbone structure. A moving type IV burst source can be associated with the most dense feature of the white-light transient.  相似文献   

The Fifth International Geological Congress, Washington, 1891     

Clifford M. Nelson 《《幕》》2006,29(4):279-286

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Cluster infall in the concordance ΛCDM model     

Maximiliano C. Pivato  Nelson D. Padilla  Diego G. Lambas 《Monthly notices of the Royal Astronomical Society》2006,373(4):1409-1415

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9969 Braille: Deep Space 1 infrared spectroscopy, geometric albedo, and classification     

B.J. Buratti  D.T. Britt  M.D. Hicks  R.H. Brown  R.M. Nelson  T.C. Owen  B.R. Sandel  N. Thomas 《Icarus》2004,167(1):129-135

Spectra of Asteroid 9969 Braille in the 1.25-2.6 μm region returned by the Deep Space 1 (DS1) Mission show a ∼10% absorption band centered at 2 μm, and a reflectance peak at 1.6 μm. Analysis of these features suggest that the composition of Braille is roughly equal parts pyroxene and olivine. Its spectrum between 0.4 and 2.5 μm suggests that it is most closely related to the Q taxonomic type of asteroid. The spectrum also closely matches that of the ordinary chondrites, the most common type of terrestrial meteorite. The geometric albedo of Braille is unusually high (p_v=0.34), which is also consistent with its placement within the rarer classes of stony asteroids, and which suggests it has a relatively fresh, unweathered surface, perhaps due to a recent collision.  相似文献   

Composition of Titan''s surface from Cassini VIMS     

T.B. McCord  G.B. Hansen  B.J. Buratti  R.N. Clark  D.P. Cruikshank  E. D&#x;Aversa  C.A. Griffith  E.K.H. Baines  R.H. Brown  C.M. Dalle Ore  G. Filacchione  V. Formisano  C.A. Hibbitts  R. Jaumann  J.I. Lunine  R.M. Nelson  C. Sotin  the Cassini VIMS Team 《Planetary and Space Science》2006,54(15):1524-1539

Titan's bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite's dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan's solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan's history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission's visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 μm were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan T_a encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79 μm in the poorly understood 2.8-μm methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-μm methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8 μm that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface.  相似文献   

COCORP: new perspectives on the deep crust   总被引：7，自引：0，他引：7  

L. Brown  D. Wille  L. Zheng  B. DeVoogd  J. Mayer  T. Hearn  W. Sanford  C. Caruso  T.-F. Zhu  D. Nelson  C. Potter  E. Hauser  S. Klemperer  S. Kaufman  J. Oliver 《Geophysical Journal International》1987,89(1):47-54

Summary. Relict sutures from colliding continents, regions characterized by a "young" Mono, layering and faulting throughout the crust, mid-crustal magma traps, and seismic "bright spots" which suggest deep crustal fluids are among recent COCORP findings. In addition, new studies of signal penetration, noise mitigation, recording geometry, and coherency filtering have yielded better understanding of, and substantial improvements in, data quality. Amplitude anomalies, or "bright spots", in the Basin and Range may be due to magma at mid-crustal levels; in one case, a normal fault appears to link the deep magma with young surface volcanics. Another bright spot. 15 km deep in southeastern Georgia, has a flat geometry that suggests a gas/liquid interface, perhaps within fluids underthrust along an Appalachian suture. The Mono continues to appear relatively undisturbed in many regions of past deformation, suggesting that its formation post-dates these major tectonic episodes. The diversity of reflection patterns from the U.S. Cordillera casts further doubt on the generality of the common model of a reflective, layered lower crust underlying a transparent upper crust.  相似文献