Clump lifetimes and the initial mass function     

Paul C. Clark  Ralf S. Klessen  Ian A. Bonnell 《Monthly notices of the Royal Astronomical Society》2007,379(1):57-62

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Passage through India: the Mozambique Ocean suture,high‐pressure granulites and the Palghat‐Cauvery shear zone system     

Alan S. Collins  Chris Clark  K. Sajeev  M. Santosh  David E. Kelsey  Martin Hand 《地学学报》2007,19(2):141-147

The Mozambique Ocean closed as Gondwana formed. Its suture has been identified in Madagascar (Betsimisaraka suture), but its continuation, into India, is controversial. The Palghat‐Cauvery shear system appears an ideal candidate as it: (i) lies along strike of the Betsimisaraka suture in Gondwana; (ii) forms a high‐pressure granulite belt; and (iii) separates crustal domains with different geological histories. However, existing age constraints have been used to suggest that the structure is Archaean/Palaeoproterozoic. Here we date metamorphic zircons using secondary ion mass spectrometry (535.0 ± 4.9 Ma) and monazites using electron probe micro‐analysis (537 ± 9, 532 ± 8, 525 ± 10 Ma). No evidence for an earlier metamorphic event was found. The identification of Palghat‐Cauvery high‐pressure metamorphism as Cambrian, and recognition that it bounds crustal domains of contrasting origin, points to it being the southern continuation of the Betsimisaraka suture and southern margin of Neoproterozoic India.  相似文献   

Coca-Cola granite     

Roger Mason 《Geology Today》2002,18(5):200-200

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Electromagnetic Models of Compact Radio Sources and Circular Polarisation     

Roger Blandford 《Astrophysics and Space Science》2003,288(1-2):155-160

An electromagnetic model of relativistic jets is outlined. It is suggested that these jets be interpreted as current flows and that they owe their persistence and collimation to the pinching action of the magnetic field. Such structures are unstable and it is suggested that the nonlinear development of these instabilities involves the formation of an electromagnetic turbulence spectrum. This turbulence may be responsible for the acceleration of relativistic electrons and positrons. It may also provide the electromagnetic field in which these electrons and positrons radiate. Some mechanisms through which circular polarisation may be created in this environment are outlined.  相似文献   

Formation of jets in Comet 19P/Borrelly by subsurface geysers     

Roger V Yelle  Laurence A Soderblom 《Icarus》2004,167(1):30-36

Observations of the inner coma of Comet 19P/Borrelly with the camera on the Deep Space 1 spacecraft revealed several highly collimated dust jets emanating from the nucleus. The observed jets can be produced by acceleration of evolved gas from a subsurface cavity through a narrow orifice to the surface. As long as the cavity is larger than the orifice, the pressure in the cavity will be greater than the ambient pressure in the coma and the flow from the geyser will be supersonic. The gas flow becomes collimated as the sound speed is approached and dust entrainment in the gas flow creates the observed jets. Outside the cavity, the expanding gas loses its collimated character, but the density drops rapidly decoupling the dust and gas, allowing the dust to continue in a collimated beam. The hypothesis proposed here can explain the jets seen in the inner coma of Comet 1P/Halley as well, and may be a primary mechanism for cometary activity.  相似文献   

Geophysical surveys for identifying saline groundwater in the semi‐arid region of the central Altiplano,Bolivia     

Roger Gurin  Marc Descloitres  Anne Coudrain  Amal Talbi  Robert Gallaire 《水文研究》2001,15(17):3287-3301

In the central part of the Bolivian Altiplano, the shallow groundwater presents electrical conductivities ranging from 0·1 to 20 mS/cm. In order to study the origin of this salinity pattern, a good knowledge is required of the geometry of the aquifer at depth. In this study, geophysics has been used to complement the sparse data available from drill holes. One hundred time‐domain electromagnetic (TDEM) soundings were carried out over an area of 1750 km². About 20 geological logs were available close to some of the TDEM soundings. Three intermediate results were obtained from the combined data: (i) the relationship between the electrical conductivity of the groundwater and the formation resistivity, (ii) geoelectrical cross‐sections and (iii) geoelectrical maps at various depths. The limited data set shows a relationship between resistivity and the nature of the rock. From the cross‐sections, a conductive substratum with a resistivity of less than 1 Ω·m was identified at most of the sites at depths ranging from 50 to 350 m. This substratum could be a clay‐rich formation containing brines. Using derived relationships, maps of the nature of the formation (sandy, intermediate and clayey sediments) were established at depths of 10 and 50 m. Discrimination between sand and clays was impossible where groundwater conductivity is high (>3 mS/cm). In the central part of the area, where the groundwater conductivity is low, sandy sediments are likely to be present from the surface to a depth of more than 200 m. Clayey sediments are more likely to be present in the south‐east and probably constitute a hydraulic barrier to groundwater flow. In conclusion, the study demonstrates the efficiency of the TDEM sounding method to map conductive zones. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Interpretation of cone penetration results in multilayered soils     

Roger Vreugdenhil  Rob Davis  John Berrill 《国际地质力学数值与分析法杂志》1994,18(9):585-599

A simple approximate analysis is presented for interpretation of cone penetration results when the cone resistance is affected by layering of soils with different stiffnesses. It is argued that the cone resistance senses the presence of a nearby layer elastically, and an approximate elastic analysis is developed to quantify the effect. Good comparisons with calibration chamber experimental results are found.  相似文献   

Maralinga,a metamorphosed carbonaceous chondrite found in Australia   总被引：1，自引：0，他引：1  

Lindsay P. Keller  James C. Clark  Charles F. Lewis  Carleton B. Moore 《Meteoritics & planetary science》1992,27(1):87-91

Abstract— The Maralinga meteorite was found near the village of Maralinga, South Australia (30°18′S, 131°16′E) in 1974, but was not recognized as a meteorite until 1989. One weathered individual was recovered with a total mass of 3.38 kg. The bulk composition and petrography of Maralinga indicate that it is a metamorphosed (petrographic type 4) carbonaceous chondrite with major similarities to the Vigarano-subtype. However, recent trace element data from the literature suggest that Maralinga should be included with the CK (Karoonda-type) carbonaceous chondrites. We classify Maralinga as an anomalous CK4 chondrite because of its abundant chondrules and refractory inclusions relative to other known members of the CK group. Maralinga contains homogeneous silicates, including Ni-bearing olivines (Fa₃₄), high-Ca clinopyroxene, and rare orthopyroxene. Plagioclase is chemically heterogeneous and falls into two distinct compositional groups one of ～ An₂₀ and an ～ An₈₀ group. Highly oxidizing conditions during metamorphism of Maralinga are indicated by the abundance of magnetite and the paucity of Fe-Ni metal.  相似文献   

The SAURON project – X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the  (V/σ, ɛ)  diagram with integral-field stellar kinematics     

Michele Cappellari  Eric Emsellem  R. Bacon  M. Bureau  Roger L. Davies  P. T. de Zeeuw  Jesús Falcón-Barroso  Davor Krajnovi&#;  Harald Kuntschner  Richard M. McDermid  Reynier F. Peletier  Marc Sarzi  Remco C. E. van den Bosch  Glenn van de Ven † 《Monthly notices of the Royal Astronomical Society》2007,379(2):418-444

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Tracer release in melting snow: Diurnal and seasonal patterns     

Roger C. Bales  Robert E. Davis  Mark W. Williams 《水文研究》1993,7(4):389-401

Time sequences of tracer release from an alpine snowpack were investigated at Mammoth Mountain, California in 1989. Lysimeter discharge and conductivity were recorded at 30 minute intervals. Three separate applications of chemical tracers were added to the snow surface to provide an ionic signal with known origins in the snowpack. Grab samples of meltwater and snow from snow pits were analysed for chemical composition. There were three distinct discharge periods, each characterized by diurnal fluctuations in discharge and conductivity. An inverse relation between discharge and conductivity was interpreted as the combination of a concentrated signal from regions in the pack less subject to leaching and a relatively dilute signal from near the snow surface where the snow was actively melting Conductivity peaks were highest and diurnal changes greatest immediately following periods of freezing. Grab samples showed little correlation with either 30 minute or daily average conductivity. Relative concentrations of individual ions in meltwater were similar between samples. Non-systematic grab sampling of snowpack meltwater is shown to be potentially misleading because of multiple ionic pulses over the ablation season and strong diurnal fluctuations in chemical concentrations. Continuous measurements of discharge conductivity are a good indicator of diurnal and seasonal changes in the rate of ion release from the snowpack, and should be used to guide sampling. Composite, or time-integrated samples rather than grab samples may be required to estimate daily and weekly rates of ion release in melting snow.  相似文献