Emplacement of Amba Dongar carbonatite-alkaline complex at Cretaceous/Tertiary boundary: Evidence from40Ar-39Ar chronology     

Jyotiranjan S. Ray  Kanchan Pande  T. R. Venkatesan 《Journal of Earth System Science》2000,109(1):39-47

  相似文献   

Spatial Patterns in Surface Energy Balance Components Derived from Remotely Sensed Data     

Karen S. Humes  Ray Hardy  William P. Kustas 《The Professional geographer》2000,52(2):272-288

A relatively simple modeling approach for estimating spatially distributed surface energy fluxes was applied to two small watersheds, one in a semi‐arid climate region and one in a sub‐humid region. This approach utilized a combination of ground‐based meteorological data and remotely sensed data to estimate ‘instantaneous’ surface energy fluxes at the time of the satellite or aircraft overpasses. The spatial resolution in the watershed grid cells, which was on the order of 100‐400 km, was selected to be compatible with ground measurements used for validation. The model estimates of surface energy fluxes compared well with ground‐based measurements of surface flux (typically within approximately 40 Wm^?2). The model accuracy may be slightly less for bare soil surfaces due to an overestimation of the soil heat flux. In addition to demonstrating the feasibility of computing spatially distributed values of surface energy fluxes, these maps were used to qualitatively infer the dominant factors controlling the energy fluxes for the time period shortly following precipitation events in the basins. For the semi‐arid watershed, values of sensible heat flux varied considerably over the watershed and displayed a pattern very similar to that of the spatially variable cumulative precipitation for at least one to eight days prior to the image acquisition. Due to the large fraction of exposed bare soil in a semi‐arid ecosystem, even very small precipitation events had a strong influence on the pattern of sensible heat fluxes observed shortly after the event (less than 24 hours). For the sub‐humid watershed, the fluxes tended to be more uniform across the watershed, and were influenced by a combination of precipitation total and land cover type.  相似文献   

Hot moments and hot spots of nutrient losses from a mixed land use watershed   总被引：1，自引：0，他引：1  

Qing Zhu  John P. Schmidt  Ray B. Bryant 《Journal of Hydrology》2012

  相似文献   

Projected entrainment of fish resulting from aggregate dredging     

Drabble R 《Marine pollution bulletin》2012,64(2):373-381

Previous research to assess impacts from aggregate dredging has focussed on infaunal species with few studies made of fish entrainment. Entrainment evidence from hydraulic dredging studies is reviewed to develop a sensitivity index for benthic fish. Environmental monitoring attendant with the granting of new licences in the Eastern Channel Region (ECR) in 2006 offers a unique opportunity to assess the effects of dredging upon fish. Projected theoretical fish entrainment rates are calculated based upon: abundance data from 4m beam trawl sampling of fish species over the period 2005-2008; sensitivity data; and dredging activity and footprint derived from Electronic monitoring System (EMS) data. Results have been compared with actual entrainment rates and also against summary results from independent analysis of the changes in fish population over the period 2005-2008 (Drabble, 2012). The case is made for entrainment surveys to form part of impact monitoring for marine aggregate dredging.  相似文献   

Relativistic anisotropic charged fluid spheres with varying cosmological constant     

Saibal Ray  Sumana Bhadra  G. Mohanti 《Astrophysics and Space Science》2008,315(1-4):341-346

Static spherically symmetric anisotropic source has been studied for the Einstein-Maxwell field equations assuming the erstwhile cosmological constant Λ to be a space-variable scalar, viz., Λ=Λ(r). Two cases are examined out of which one reduces to isotropic sphere. The solutions thus obtained are shown to be electromagnetic in origin as a particular case. It is also shown that the generally used pure charge condition, viz., ρ+p=0 is not always required for constructing electromagnetic mass models.  相似文献   

3- to 14-μm Spectroscopy of Comet C/1999 T1 (McNaught-Hartley)     

David K. Lynch  Ray W. Russell  Michael L. Sitko 《Icarus》2002,159(1):234-238

We report spectroscopy of Comet C/1991 T1 (McNaught-Hartley) at 3-13 μm on January 31.62 and February 1.7 2001 UT (delta=1.29 AU, r=1.40 AU) using the broadband array spectrograph system on the IRTF. The spectrum showed a silicate emission feature extending about 20% above the continuum. Two emission features at 10.3 and 11.2 μm appeared above the silicate band, the latter seemingly indicative of crystalline olivine. The 10.3-μm feature is only a 1-2 sigma detection but if real could indicate the presence of hydrated silicates. The color temperature at 8-13 μm was 260±10 K, approximately 6% above the blackbody radiative equilibrium temperature of 235 K. The magnitude at [N] was 3.13±0.02. On the second night, the comet had brightened slightly ([N]=2.98±0.02) and the two prominent emission features were absent, although the silicate emission feature maintained its trapezoidal shape with shoulders at 9.5 and 11.2 μm.  相似文献   

Periodicities of solar electron flare occurrence: analysis of cycles 21–23     

Partha Chowdhury  P. C. Ray 《Monthly notices of the Royal Astronomical Society》2006,373(4):1577-1589

  相似文献   

Evolution of massive binary stars in the LMC and its implications for radio pulsar population     

N. Rathnasree  A. Ray 《Journal of Astrophysics and Astronomy》1992,13(1):3-52

The Hertzsprung-Russell diagram of the Large Magellanic Cloud compiled recently by Fitzpatrick & Garmany (1990) shows that there are a number of supergiant stars immediately redward of the main sequence although theoretical models of massive stars with normal hydrogen abundance predict that the region 4.5 ≤ logT _eff ≤ 4.3 should be un-populated (“gap”). Supergiants having surface enrichment of helium acquired for example from a previous phase of accretion from a binary companion, however, evolve in a way so that the evolved models and observed data are consistent — an observation first made by Tuchman & Wheeler (1990). We compare the available optical data on OB supergiants with computed evolutionary tracks of massive stars of metallicity relevant to the LMC with and without helium-enriched envelopes and conclude that a large fraction (≈ 60 per cent) of supergiant stars may occur in binaries. As these less evolved binaries will later evolve into massive X-ray binaries, the observed number and orbital period distribution of the latter can constrain the evolutionary scenarios of the supergiant binaries. The distributions of post main sequence binaries and closely related systems like WR + O stars are bimodal-consisting of close and wide binaries in which the latter type is numerically dominating. When the primary star explodes as a supernova leaving behind a neutron star, the system receives a kick and in some cases can lead to runaway O-stars. We calculate the expected space velocity distribution for these systems. After the second supernova explosion, the binaries in most cases, will be disrupted leading to two runaway neutron stars. In between the two explosions, the first born neutron star’s spin evolution will be affected by accretion of mass from the companion star. We determine the steady-state spin and radio luminosity distributions of single pulsars born from the massive stars under some simple assumptions. Due to their great distance, only the brightest radio pulsars may be detected in a flux-limited survey of the LMC. A small but significant number of observable single radio pulsars arising out of the disrupted massive binaries may appear in the short spin period range. Most pulsars will have a low velocity of ejection and therefore may cluster around the OB associations in the LMC.  相似文献   

The development of volcanic hosted massive sulfide and barite–gold orebodies on Wetar Island, Indonesia     

Philip M. Scotney  Stephen Roberts  Richard J. Herrington  Adrian J. Boyce  Ray Burgess 《Mineralium Deposita》2005,40(1):76-99

Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves precious metal-rich volcanogenic massive sulfide and barite deposits, which produced approximately 17 metric tonnes of gold. The polymetallic massive sulfides are dominantly pyrite (locally arsenian), with minor chalcopyrite which are cut by late fractures infilled with covellite, chalcocite, tennantite–tetrahedrite, enargite, bornite and Fe-poor sphalerite. Barite orebodies are developed on the flanks and locally overly the massive sulfides. These orebodies comprise friable barite and minor sulfides, cemented by a series of complex arsenates, oxides, hydroxides and sulfate, with gold present as <10 m free grains. Linear and pipe-like structures comprising barite and iron-oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization. Hydrothermal alteration around the orebodies is zoned and dominated by illite–kaolinite–smectite assemblages; however, local alunite and pyrophyllite are indicative of late acidic, oxidizing hydrothermal fluids proximal to mineralization. Altered footwall volcanic rocks give an illite K–Ar age of 4.7±0.16 Ma and a ⁴⁰Ar/³⁹Ar age of 4.93±0.21 Ma. Fluid inclusion data suggest that hydrothermal fluid temperatures were around 250–270°C, showed no evidence of boiling, with a mean salinity of 3.2 wt% equivalent NaCl. The ³⁴S composition of sulfides ranges between +3.3 and +11.7 and suggests a significant contribution of sulfur from the underlying volcanic edifice. The ³⁴S barite data vary between +22.4 and +31.0, close to Miocene seawater sulfate. Whole rock ⁸⁷Sr/⁸⁶Sr analyses of unaltered volcanic rocks (0.70748–0.71106) reflect contributions from subducted continental material in their source region. The ⁸⁷Sr/⁸⁶Sr barite data (0.7076–0.7088) indicate a dominant Miocene seawater component to the hydrothermal system. The mineral deposits formed on the flanks of a volcanic edifice at depths of ~2 km. Spectacular sulfide mounds showing talus textures are localized onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks. The orebodies were covered and preserved by post-mineralization chert, gypsum, Globigerina-bearing limestone, lahars, subaqueous debris flows and pyroclastics rocks.  相似文献   

Wellhead Protection Area Delineation Using the Analytic Element Method of Ground-Water Modeling   总被引：2，自引：0，他引：2  

Ray W. Wuolo  David J. Dahlstrom  Mark D. Fairbrother 《Ground water》1995,33(1):71-83

  相似文献