Atomic processes in astrophysics     

John C. Raymond  Nancy S. Brickhouse 《Astrophysics and Space Science》1996,237(1-2):321-340

We review the atomic processes responsible for astrophysical emission line spectra, paying particular attention to the reliability of the rates used to determine the physical conditions in the emiting gas. We discuss particular cases where often-neglected processes play important roles.  相似文献   

The deepening of the wind-Mixed layer     

Raymond T. Pollard  Peter B. Rhines  Rory O. R. Y. Thompson 《地球物理与天体物理流体动力学》2013,107(1):381-404

Abstract

A simple model is given that describes the response of the upper ocean to an imposed wind stress. The stress drives both mean and turbulent flow near the surface, which is taken to mix thoroughly a layer of depth h, and to erode the stably stratified fluid below. A marginal stability criterion based on a Froude number is used to close the problem, and it is suggested that the mean momentum has a strong role in the mixing process. The initial deepening is predicted to obey

where u. is the friction velocity of the imposed stress, N the ambient buoyancy frequency, and t the time.

After one-half inertial period the deepening is arrested by rotadeon at a depth h = 2^2/4 u.{(Nf)⁺

where f is the Coriolis frequency. The flow is then a “mixed Ekman” layer, with strong inertial oscillations superimposed on it. Three quarters of the mean energy of the deepening layer is found to be kinetic, and only one-quarter potential.

Heating and cooling are included in the model, but stress dominates for time-scales of a day or less. Non-uniform stratification and currents existing prior to the onset of the wind are easily included.

Agreement between the first formula above and laboratory experiments of Kato and Phillips is very satisfactory; the second formula is consistent with observations of Francis and Stommel, though a more thorough test is needed. Oceanic observations in general support the assumption of slab-like mean profiles and direct response of the fluid to local winds.  相似文献   

First Results from the Soho Ultraviolet Coronagraph Spectrometer     

J. L. Kohl  G. Noci  E. Antonucci  G. Tondello  M. C. E. Huber  L. D. Gardner  P. Nicolosi  L. Strachan  S. Fineschi  J. C. Raymond  M. Romoli  D. Spadaro  A. Panasyuk  O. H. W. Siegmund  C. Benna  A. Ciaravella  S. R. Cranmer  S. Giordano  M. Karovska  R. Martin  J. Michels  A. Modigliani  G. Naletto  C. Pernechele  G. Poletto  P. L. Smith 《Solar physics》1997,175(2):613-644

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe the extended solar corona from 1.25 to 10 R⊙ from Sun center. Initial observations of polar coronal holes and equatorial streamers are described. The observations include measurements of spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å, Mgx 625 Å, Fexii 1242 Å and several others. Intensities for Mgx 610 Å, Sixii 499 Å, and 520 Å, Sx 1196 Å, and 22 others have been observed. Preliminary results for derived H⁰, O⁵⁺, Mg₉₊, and Fe¹¹⁺ velocity distributions and initial indications of outflow velocities for O⁵⁺ are described. In streamers, the H⁰ velocity distribution along the line of sight (specified by the value at e^-1, along the line of sight) decreases from a maximum value of about 180 km s^-1 at 2 R⊙ to about 140 km s^-1 at 8 R⊙. The value for O⁵⁺ increases with height reaching a value of 150 km s^-1 at 4.7 R⊙. In polar coronal holes, the O⁵⁺ velocity at e^-1 is about equal to that of H⁰ at 1.7 R⊙ and significantly larger at 2.1 R⊙. The O⁵⁺ in both streamers and coronal holes were found to have anisotropic velocity distributions with the smaller values in the radial direction.  相似文献   

Memorial for Edward L. Fireman     

Raymond Davis  Ursula B. Marvin  John A. Wood 《Meteoritics & planetary science》1991,26(2):171-171

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Vector magnetic fields in prominences     

R. Grant Athay  Charles W. Querfeld  Raymond N. Smartt  Egidio Landi Degl'innocenti  Veronique Bommier 《Solar physics》1983,89(1):3-30

Observations of linear polarization in two resolved components of HeI D₃ are interpreted using the Hanle effect to determine vector magnetic fields in thirteen prominences. As in all vector magnetic field measurements, there is a two-fold ambiguity in field direction that is symmetric to a 180° rotation about the line-of-sight. The polar angles of the fields show a pronounced preference to be close to 90° from the local solar radius, i.e., the field direction is close to horizontal. Azimuth angles show internal consistency from point to point in a given prominences, but because of the rotational symmetry, the fields may be interpreted, in most cases, as crossing the prominence either in the same sense as the underlying photospheric fields or in the opposite sense. An exceptionally well observed large prominence of approximately planar geometry exhibits no measurable change in the vector magnetic field either with height or with location along the prominence axis. A second well observed large prominence overlying a sharply curved magnetic neutral line, when interpreted assuming that the prominence field has the same sense as the photospheric field, shows a rotation in the azimuth angle of the field relative to the observer by about 150° and relative to the local plane of the prominence by about 65°. In the alternative interpretation in which the prominence field has the opposite sense of the photospheric field, the field still rotates by 150° relative to the observer but remains essentially constant with respect to the plane of the prominence. This prominence erupted shortly after the extended observations. One good quality observation during the course of the eruption gives a vector field fully consistent with the pre-eruption field in the same segment of the prominence.  相似文献   

Latitudinal variation of wind erosion of crater ejecta deposits on Mars     

Raymond E. Arvidson  Marcello Coradini  A. Carusi  A. Coradini  M. Fulchignoni  C. Federico  R. Funiciello  M. Salomone 《Icarus》1976,27(4):503-516

Wind erosion seems to be the dominant process eroding crater ejecta deposits and sorrounding materials on Mars. In the equatorial zone, ejecta deposits are eroded back by scarp recession, where scarp heights appear to be approximately equivalent to ejecta thickness. In mantled areas, escarpments develop by relatively rapid deflation of sorrounding aeolian debris, leaving the ejecta deposit (continuous deposit and zone of high density of secondary craters) standing high above sorrounding terrain. If the rate of scarp recession is controlled by the rate of aeolian undercutting of escarpment bases, then recession rates may scale roughly as the inverse with respect to scarp height. Thus, preferential preservation of ejecta deposits emplaced in thickest aeolian debris may occur. An empirical model developed for wind erosion of ejecta deposits in nonmantled areas suggests that removal of ejecta materials on the average is exceedingly slow (～10^?5m/yr for 10m high scarp). On the other hand, rapid deflation of aeolian debris around crater ejecta is implied. Results suggest high differential aeolian erosion rates that are a function of both grain sizes and large-scale surface roughness. Aeolian activity on Mars has probably been dominated by rapid recycling of fine-grained debris, the bulk of which formed under more erosive conditions prevalent in the early history of Mars.  相似文献   

Craters and associated aeolian features on mariner 9 photographs: an automated data gathering and handling system and some preliminary results     

Raymond E. Arvidson  Thomas A. Mutch  Kenneth L. Jones 《Earth, Moon, and Planets》1974,9(1-2):105-114

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Vector magnetic fields in prominences     

Charles W. Querfeld  Raymond N. Smartt  Veronique Bommier  Egidio Landi Degl'innocenti  Lewis L. House 《Solar physics》1985,96(2):277-292

The Stokes components of He i D₃ emission in two quiescent prominences, using full spectral profile measurements, are analyzed to derive vector magnetic fields. Two independently developed schemes, based on the Hanle effect, are used for interpretation. They involve solutions of the statistical equilibrium equations for the He i D₃ multiplet, including the effect of coherency and full level crossing, which predict the magnetic field dependence of the observed polarization. Derived magnetic field vector solutions for each pair of linear polarization Stokes profiles corresponding to an observational point in the prominence are, intrinsically, not uniquely determined, and a set of possible solutions is usually obtained. However, mutual consistency of these solutions with those independently predicted by the form of the circular polarized component, allow, in almost all cases, rejection of all solutions of a set except one symmetrical pair. Of such a pair, a unique solution can be determined with a high confidence level by reference to independent potential field information. Field vectors are found usually to be close to horizontal and normal to the prominence surface, but extreme exceptions are found. Field values range from 6 G to 60 G. The derived vectorfield configurations and their magnitudes are briefly discussed relative to these prominences and to different quiescent prominence models.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.  相似文献   

News and notes     

N. Purnachandra Rao  Sukanta Roy  Kusumita Arora  B. K. Rastogi  Suman Sarkar  M. Venkataswamy  Raymond A. Duraiswami 《Journal of the Geological Society of India》2013,81(5):722-730

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Reply to “Superior techniques for disposal of highly radioactive waste (HLW)” by R. Pusch and R. Weston     

Raymond Munier 《Environmental Earth Sciences》2013,69(1):297-303

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