Dynamos on stream surfaces of a highly conducting fluid     

Andrew D. Gilbert  Yannick Ponty 《地球物理与天体物理流体动力学》2013,107(1-2):55-95

Abstract

This paper discusses dynamo action in generalisations of the Ponomarenko dynamo at large magnetic Reynolds number. The original Ponomarenko dynamo consists of a spiralling flow in which the stream surfaces are concentric cylinders of circular cross section, and the flow depends only on distance from the axis in cylindrical polar coordinates.

In this study, the stream surfaces are allowed to be cylinders of arbitrary cross section, and the flow is only required to be independent of the coordinate along the cylinder axes. For smooth flows alpha and eddy diffusion effects are identified, in terms of the geometry of the stream surfaces, and asymptotic formulae for growth rates in the limit of large magnetic Reynolds number are obtained. Numerical support for these results is presented using direct simulation of dynamo action in selected flows at high conductivity. Finally the case is considered when in spherical polar coordinates the flow is independent of the azimuthal coordinate and the stream surfaces, which are tori, have arbitrary cross sections.  相似文献   

Influence of bioturbation by the polychaete Nereis diversicolor on the structure of bacterial communities in oil contaminated coastal sediments   总被引：1，自引：0，他引：1  

Cuny P  Miralles G  Cornet-Barthaux V  Acquaviva M  Stora G  Grossi V  Gilbert F 《Marine pollution bulletin》2007,54(4):452-459

Patterns of change in the structure of bacterial communities monitored by ribosomal intergenic spacer analysis (RISA) in oil contaminated sediments inhabited or not by the marine polychaete Nereis diversicolor were studied during 45 days under laboratory conditions. Results supported by principal component analysis showed a marked response of the bacterial communities to the oil contamination and to the presence of N. diversicolor. Phylogenetic affiliation of specific RISA bands showed that, in the contaminated sediments, the presence of the marine polychaetes favoured the development of bacteria which may play an active role in natural bioremediation processes of oil polluted environments.  相似文献   

Hydrocarbons in coastal sediments from the Mediterranean sea (Gulf of Fos area, France)   总被引：2，自引：0，他引：2  

Mille G  Asia L  Guiliano M  Malleret L  Doumenq P 《Marine pollution bulletin》2007,54(5):566-575

Sedimentary hydrocarbons have been studied quantitatively and qualitatively in 11 coastal stations located in the Gulf of Fos (French Mediterranean coast). Hydrocarbon levels ranged from 10 to 260 mg kg(-1) sed. dry weight. A new parameter "NAR" (Natural n-alkane ratio) is proposed to evaluate the contribution of terrestrial inputs of hydrocarbons in the sediments. The origins of hydrocarbons are multiple: terrestrial inputs, biogenic, pyrolytic (industry emissions mainly steel and iron industries, ship and road traffic). Generally, the main source of contamination is not petroleum. Several ratios between parent polycyclic aromatic hydrocarbons show that the sources of hydrocarbons in the sediments are generally much more pyrolytic than petrogenic.  相似文献   

Book reviews     

D. J. Gilbert  Geoff Hicks  B. H. McArdle  Philip Tortell  Alex Gilmour 《新西兰海洋与淡水研究杂志》2013,47(1):93-101

Theory and management of tropical fisheries. Edited by D. Pauly and G. I. Murphy. Proceedings of the ICLARM/CSIRO Workshop on the Theory and Management of Tropical Multispecies Stocks. 12–21 January 1981, Cronulla, Australia. 1982. 360 p. $US21.50 surface; hardbound.

Animals of the estuary shore : illustrated guide and ecology. By Malcolm B. Jones, 1983. University of Canterbury publication No. 32. 162p., 140 figures, 11 keys. ISBN 0900–392–32–0 (soft cover, spiral bound). Price NZ$7.50.

Numerical ecology. By L. Legendre and P. Legendre, 1983. Elsevier Scientific Publishing Company, Amsterdam. $US83.00.

The control of oil pollution (revised edition). Edited by J Wardley‐Smith. Graham & Trot‐man Limited, London. 1983. 285 p., 98 figures, 17 tables. ISBN 0.86010 3382. £19.00/$US35.00.

Physical oceanography in Australia. Edited by J. Imberger. Reprinted from the Australian Journal of Marine and Freshwater Research, Volume 34, 1–230, 1983. CSIRO, Melbourne 1983.  相似文献   

The formation and evolution of massive stellar clusters in IC4662     

Andrea M. Gilbert  William D. Vacca 《Astrophysics and Space Science》2009,324(2-4):147-154

We present a multiwavelength study of the formation of massive stellar clusters, their emergence from cocoons of gas and dust, and their feedback on surrounding matter. Using data that span from radio to optical wavelengths, including Spitzer and Hubble Space Telescope ACS observations, we examine the population of young star clusters in the central starburst region of the irregular Wolf–Rayet galaxy IC4662. We model the radio-to-infrared (IR) spectral energy distributions of embedded clusters to determine the properties of their Hii regions and dust cocoons (sizes, masses, densities, temperatures), and use near-IR and optical data with mid-IR spectroscopy to constrain the properties of the embedded clusters themselves (mass, age, extinction, excitation, abundance). The two massive star-formation regions in IC4662 are excited by stellar populations with ages of ～4 Myr and masses of ～3×10⁵ M_⊙ (assuming a Kroupa initial mass function). They have high excitation and subsolar abundances, and they may actually be comprised of several massive clusters rather than the single monolithic massive compact objects known as ‘super star clusters’ (SSCs). Mid-IR spectra reveal that these clusters have very high extinction values, A _V ～20–25 mag, and that the dust in IC4662 is well mixed with the emitting gas, not in a foreground screen.  相似文献   

The effect of spacecraft radiation sources on electron moments from the Cassini CAPS electron spectrometer     

Christopher S. Arridge  Linda K. Gilbert  Gethyn R. Lewis  Edward C. Sittler  Dhiren O. Kataria  David T. Young 《Planetary and Space Science》2009,57(7):854-869

Data from the Cassini plasma spectrometer (CAPS) electron spectrometer (ELS) have been found to be contaminated with an energy-independent background count rate which has been associated with radiation sources on Cassini. In this paper we describe this background radiation and quantitatively assess its impact on numerically integrated electron moments. The general properties of such a background and its effects on numerical moments are derived. The properties of the ELS background are described and a model for the background presented. A model to generate synthetic ELS spectra is presented and used to evaluate the density and temperature of pure noise and then extended to include ambient distributions. It is shown that the presence of noise produces a saturation of the electron density and temperature at quasi-constant values when the instrument is at background, but that these noise level moments are dependent on the floating spacecraft potential and the orientation of the ELS instrument with respect to the spacecraft. When the ambient distribution has a poor signal-to-noise ratio (SNR) the noise determines the density and temperature; however, as the SNR increases (increasing primarily with density) the density and temperature tend to those of the ambient distribution. It is also shown that these noise effects produce highly artificial density-temperature inverse correlations. A method to subtract this noise is presented and shown to correct for the presence of the noise. Simulated error estimates for the density and temperature are also presented. The analysis described in this paper not only applies to weak background noise, but also to more significant penetrating backgrounds such as those in radiation belt regions of planetary magnetospheres.  相似文献   

Modified Newton-Raphson methods for preliminary orbit determination     

Edward T. Pitkin  Gilbert C. Carpenter 《Celestial Mechanics and Dynamical Astronomy》1969,1(1):72-90

Preliminary orbit determination is a multipoint boundary value problem which may be solved by the generalized Newton-Raphson iteration. When applied formally the method suffers from extensive computer storage requirements, fairly long execution times and in some cases, insufficient accuracy. In this work we seek to remove these practical difficulties via modification of the computational algorithm in such a way that solution storage is eliminated for the most part and computational speed and tolerance to imprecise integration algorithms is improved. The modified methods are applied to nine typical preliminary orbit determination problems to demonstrate fast convergence and short computation times, even with very poor starting values for the iteration. Excellent precision of the resulting solution is also demonstrated as well as the algorithm's ability to handle circular, elliptic, parabolic and hyperbolic orbits.  相似文献   

Geochemistry of the shawmere anorthosite complex,kapuskasing structural zone,Ontario     

E. Craig Simmons  Gilbert N. Hanson  S.B. Lumbers 《Precambrian Research》1980,11(1):43-71

The Archean Shawmere Anorthosite Complex, at the southern end of the Kapuskasing Structural Zone, consists dominantly of anorthosite (An_{65 –85}) with minor gabbroic and ultramafic units, which are completely enclosed and cut by tonalites. Both the anorthosites and the tonalites are themselves cut by narrow dikes of gabbroic anorthosite. All of the rocks have undergone high grade metamorphism and are recrystallized so that few igneous textures remain.The anorthosites, gabbros and ultramafic rocks of this complex are cumulates which contain calcic plagioclase (An_65–95) and have atomic Mg/(Mg + Fe²⁺) ratios (Mg#) greater than 0.6; less than 3 ppm Rb; 150–210 ppm Sr; and less than 60 ppm Ba. REE abundanees range from 0.2 to 10 times chondritic and exhibit both light-enriched and light-depleted REE patterns. The lower Mg^# for the samples having more enriched light REE indicates substantial fractions of ferromagnesian minerals crystallized in addition to plagioclase during fractional crystallization, suggesting that the parent magma was basaltic, and not anorthositic. The ranges in Sr, Ba and REE abundances required for the magmas are typical of those for tholeiitic basalts from Archean greenstone belts. Thus the Shawmere Anorthosite Complex may represent cumulates of a crustal-level magma chamber which could have been the immediate source of basic Archean volcanics.One gabbroic anorthositic dike sample has a steeply fractionalted REE pattern with heavy REE abundances less than chondrites and a large positive Eu anomaly. The proposed interpretations is that this rock formed by partial melting of mafic cumulates, perhaps those of the Shawmere Anorthosite Complex itself.  相似文献   

Non-explosive,constructional evolution of the ice-filled caldera at Volcán Sollipulli,Chile     

J. S. Gilbert  M. V. Stasiuk  S. J. Lane  C. R. Adam  M. D. Murphy  R. S. J. Sparks  J. A. Naranjo 《Bulletin of Volcanology》1996,58(1):67-83

 A radar and gravity survey of the ice-filled caldera at Volcán Sollipulli, Chile, indicates that the intra-caldera ice has a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km³ of ice. Reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt to dacite and have identified five distinct volcanic units in the caldera walls. Pre- or syn-caldera collapse deposits (the Sharkfin pyroclastic unit) comprise a sequence which evolved from subglacial to subaerial facies. Post-caldera collapse products, which crop out along 17 of the 20 km length of the caldera wall, were erupted almost exclusively along the caldera margins in the presence of a large body of intra-caldera ice. The Alpehué crater, formed by an explosive eruption between 2960 and 2780 a. BP, in the southwest part of the caldera is shown to post date formation of the caldera. Sollipulli lacks voluminous silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence of a large-magnitude explosive eruption. Instead, lateral magma movement at depth resulting in emptying of the magma chamber may have generated the caldera. The radar and gravity data show that the central part of the caldera floor is flat but, within a few hundred metres of the caldera walls, the floor has a stepped topography with relatively low-density rock bodies beneath the ice in this region. This, coupled with the fact that most of the post-caldera eruptions have taken place along the caldera walls, implies that the caldera has been substantially modified by subglacial marginal eruptions. Sollipulli caldera has evolved from a collapse to a constructional feature with intra-caldera ice playing a major role. The post-caldera eruptions have resulted in an increase in height of the walls and concomitant deepening of the caldera with time. Received: 12 June 1995 / Accepted: 7 December 1995  相似文献   

Normal fault displacement dislocating a Roman aqueduct of Ephesos,western Turkey     

Cees W. Passchier  Gilbert Wiplinger  Talip Güngör  Paul Kessener  Gül Sürmelihindi 《地学学报》2013,25(4):292-297

A 38‐km‐long ancient aqueduct channel that served Roman Ephesos, Turkey was dislocated vertically over 3 m by a single seismic event on a normal fault. A new channel was constructed downstream from the fault in Roman times, next to and partly on top of the original channel. Archaeological investigations and study of carbonate deposits suggest a causative seismic event in the second half of the second century CE, probably in 178 CE, after the original channel had functioned for <35 years. The ?çme Tepe fault was identified as responsible for the displacement and may still constitute a seismic and tsunami hazard for the Turkish west coast, specifically for the city of Ku?adas?. Ancient aqueducts, of which more than 1400 are presently known, are a promising and almost untapped archive for archaeoseismic studies, especially in the Mediterranean area.  相似文献