排序方式： 共有20条查询结果，搜索用时 193 毫秒
1.
Elvis A. Shukla Jagdish Prasad M. S. S. Nagaraju Rajeev Srivastava D. L. Kauraw 《Journal of the Indian Society of Remote Sensing》2009,37(1):129-137
Soil resource characterization of Dhamni micro-watershed in Chandrapur district of Maharashtra was carried out using IRS-1D
LISS-III data in conjunction with field survey and ancillary data. The study indicates that nearly 84.2 per cent of the total
geographical area of the watershed is under cultivation. Forest (mainly degraded) occupy only 4.5 per cent area Whereas wasteland
with scrub cover 9.4 per cent area of the watershed. Nine soil series were tentatively identified and mapped as soil series
association in to five mapping units. These soils belong to order Inceptisol, Vertisol and Mollisol. Except the soils of wasteland
with scrub, other soils are moderately suitable for pigeonpea and soybean and have average to good productivity. 相似文献
2.
This paper summarises the X-ray properties of NGC 1068 from the observers perspective and reports new observations with the ROSAT HRI. Below ? 2 keV, the spectrum is steep and probably represents thermal emission from gas with temperature kT ? 0.1 - 0.6 keV. Above ? 2 keV, the spectrum is much flatter and may be described by a power-law with energy index α ? 0.3. Images with the ROSAT HRI reveal that about half the X-ray flux in the 0.1 - 2.4 keV band is extended on scales > 5″ (360 pc). Recent ROSAT PSPC observations of starburst galaxies show integrated soft X-ray spectra which are very similar to that of NGC 1068 below 2 keV. The spatially extended, steep, soft X-ray emission of NGC 1068 probably originates through thermal emission from a hot wind driven by the disk starburst, the Seyfert nucleus or a combination of the two. On the other hand, the hard emission above 2 keV is almost certainly dominated by the Seyfert nucleus. 相似文献
3.
Boris Chako Tchamabé Dieudonné Youmen Sébastien Owona Issa Takeshi Ohba Károly Németh Moussa Nsangou Ngapna Asobo N. E. Asaah Festus T. Aka Gregory Tanyileke Joseph V. Hell 《Central European Journal of Geosciences》2013,5(4):480-496
his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U1, U2 and U3. Interpretation of these features indicates that U1 consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U2, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U2 and U3, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin. 相似文献
4.
5.
6.
P. J. Humphrey G. Fabbiano M. Elvis M. J. Church M. Ba&#;uci&#;ska-Church 《Monthly notices of the Royal Astronomical Society》2003,344(1):134-148
We present results of a Chandra survey of the ultraluminous X-ray sources (ULX) in 13 normal galaxies, in which we combine source detection with X-ray flux measurement. 22 ULX were detected, i.e. with L x > 1 × 1039 erg s−1 ( L 10 ) and 39 other sources were detected with L x > 5 × 1038 erg s−1 ( L 5 ) . We also use radial intensity profiles to remove extended sources from the sample. The majority of sources are not extended, which for a typical distance constrains the emission region size to less than 50 pc. X-ray colour–colour diagrams and spectral fitting results were examined for indicators of the ULX nature. In the case of the brighter sources, spectral fitting generally requires two-component models. In only a few cases do colour–colour diagrams or spectral fitting provide evidence of a black hole nature. We find no evidence of a correlation with stellar mass, however, there is a strong correlation with star formation as indicated by the 60-μm flux as found in previous studies. 相似文献
7.
A new method, based on automatic differentiation technique, has been proposed in this paper to compute the derivatives of the gravity potential. Using this method we can obtain derivatives up to any order. Instead of explicit expressions of the derivatives we use an iterative scheme to simultaneously compute the value of all the desired derivatives. The algorithm here presented can be easily parallelized by using OpenMP with the consequent improvement in CPU-time efficiency. 相似文献
8.
Ribeiro AP Figueira RC Martins CC Silva CR França EJ Bícego MC Mahiques MM Montone RC 《Marine pollution bulletin》2011,62(1):192-196
Admiralty Bay (Antarctica) hosts three scientific stations (Ferraz, Arctowski and Macchu Picchu), which require the use of fossil fuel as an energy source. Fossil fuels are also considered the main source of pollution in the area, representing important inputs of major pollutants (organic compounds) and trace metals and metalloids of environmental interest. Accordingly, this work presents the results of As, Cd, Cr, Cu, Ni, Pb and Zn in sediment profiles from Admiralty Bay. The sediment results from Ferraz station were slightly higher than the other sampling sites. The highest contents were observed for Cu and Zn (from 44 to 89 mg kg−1). Otherwise, by using enrichment factors and geochronology analysis, the most relevant enrichment was observed for As in the samples collected close to the Ferraz station, indicating that increasing As content may be associated with the activities associated with this site. 相似文献
9.
F. Fiore G. Matt M. Cappi M. Elvis K. M. Leighly F. Nicastro L. Piro A. Siemiginowska & B. J. Wilkes 《Monthly notices of the Royal Astronomical Society》1998,298(1):103-113
Steep soft X-ray (0.1–2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2–10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of ∼ 2 in 10 ks), despite a factor of ∼ 10 difference in the 0.5–10 keV luminosity (7.3 × 1043 erg s−1 for PG 1244 + 026 and 6.4 × 1044 erg s−1 for NAB 0205 + 024, assuming isotropic emission, H 0 = 50.0 and q 0 = 0.0). The X-ray continuum of the two quasars flattens by 0.5–1 going from the 0.1–2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centred at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3–0.6 c ). 相似文献
10.
Susmita Chakravorty Ajit K. Kembhavi Martin Elvis Gary Ferland 《Monthly notices of the Royal Astronomical Society》2009,393(1):83-98
Signatures of warm absorbers are seen in soft X-ray spectra of about half of all type 1 Seyfert galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular, we find the following results: (i) the warm absorber exists only if the spectral index of the X-ray power-law ionizing continuum α > 0.2 and has a multiphase nature if α∼ 0.8 , which interestingly is the spectral index for most of the observed type 1 Seyfert galaxies; (ii) thermal and ionization states of highly dense warm absorbers are sensitive to their density if the ionizing continuum is sufficiently soft, i.e. dominated by the ultraviolet; (iii) absorbing gas with super-solar metallicity is more likely to have a multiphase nature and (iv) the nature of the warm absorber is significantly influenced by the absence of iron and associated elements which are produced in the later stages of star formation history in Type Ia supernovae. 相似文献