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Wolfram Neutsch Herbert Kalisch Horst Fichtner S. Ranga Sreenivasan Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408
The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical
integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory,
orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis
of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives
for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical
grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper
by Kalish et al.(2002).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Population growth worldwide leads to an increasing pressure on the land. Recent studies reported that many areas covered by badlands are decreasing because parts of badlands are being levelled and converted into arable land. It is important to monitor these changes for environmental planning. This paper proposes a remote-sensing-based detection method which allows mapping of badland dynamics based on seasonal vegetation changes in the lower Chambal valley, India. Supervised classification was applied on three Landsat (Thematic Mapper) images, from 3 different seasons; January (winter), April (summer) and October (post-monsoon). Different band selection methods were applied to get the best classification. Validation was done by ground referencing and a GeoEye-1 satellite image. The image from January performed best with overall accuracy of 87% and 0.69 of kappa. This method opens the possibilities of using semi-automatic classification for the Chambal badlands which is so far mapped with manual interpretations only. 相似文献
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G. Narasimhulu Naidu M. P. Ranga Rao Hira Lal Yadav 《Astrophysics and Space Science》1983,89(1):77-87
Self-similar unsteady flows with zero temperature gradient behind strong spherical shocks propagating in non-uniform perfect gas at rest are investigated. The total energy of the flow is assumed to be varying with the shock radius obeying a power law. Approximate solutions in a closed analytical form are obtained using the integral method. Also these solutions are shown to be useful to calculate easily and quickly the shock temperature, X-ray surface brightness and luminosity which are important in astrophysical problems. It is found that these approximate solutions are in close agreement with numerical solutions. 相似文献
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This study assesses the origin and pollution of trace metals in surface soils in a region with contrasting land uses (urban
vs. rural). Principal component analysis (PCA) reveals that Cr and Ni are predominantly of geogenic origin. These two trace
metals are also the only ones with statistically significant correlations with soil particle size and organic matter content.
Copper, Pb and Zn, and possibly Hg, are of anthropogenic origin, but their concentrations rarely reach levels described as
strongly polluted by pollution indexes. The concentrations of these anthropogenic trace metals are statistically not different
in urban and rural areas, except for Pb that is higher in the urban area. This general lack of a difference between the two
land uses indicates that the influence of this small urban area on trace metal concentrations in soils is minor. Lead and
Zn have the most, but still a modest number, of strongly polluted sites, mainly in an industrial part of the city. GIS analysis
shows that, based on the pollution load index (PLI), overall concentrations of trace metals also reach their highest levels
in that industrial area. These observations indicate that the influence of industry on trace metal pollution in soil exceeds
that of other urban activities in the region. Local background concentrations were found to be very different from general
crustal background concentrations. This demonstrates the importance of the careful selection of a background type in studies
like this. 相似文献
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It has been suggested that the distribution functions characterizing the constituents of the solar coronal plasma are non-Maxwellian. If so, an accurate treatment of the collisional momentum and energy exchange between the plasma constituents within the framework of hydrodynamic models requires a re-evaluation of the general transfer integrals in multi-component plasmas. We have evaluated these integrals numerically for both Maxwellian and non-Maxwellian distribution functions of the plasma species avoiding the standard approximation for the collision cross sections frequently employed in the literature. Significant differences are shown to exist in the energy exchange rates for different distributions. We also demonstrate the inadequacy of the assumption of thermodynamic equilibrium in the innermost solar wind and reveal the importance of an accurate evaluation of the transfer integrals for the solar coronal plasma based on more realistic velocity distributions.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994. 相似文献
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Most rural areas in the developing countries lack access to qualified out-patient (OPD) care. The gap in health services provision arises, due to lack of qualified doctors and is oftentimes filled by unqualified doctors who are also known as private non-degree practitioners (PNDPs). Despite their dominance, their presence is often neglected in access to health care studies. This leaves a scenario which lacks informal, but predominant, care. This paper uses a mix-method approach, combining exhaustive quantitative census of all health care providers along with location details in Geographic Information System to address the accessibility to PNDP. Longitudinal quantitative as well as spatial surveys were conducted for 3 years (2010, 2012 and 2013) in districts of Pratapgarh and Kanpur Dehat in state of Uttar Pradesh and Vaishali in Bihar state. The results of this study show that PNDPs account for 25 % of the all health care providers active across the study areas. The PNDPs are active in a radius of 2–5 km and are main workforce for the OPD care. Considering all health care providers PNDPs provide best potential accessibility to OPD care. If the PNDPs are removed from the scenario; remote areas will be the most affected ones, leaving them with almost no OPD care. 相似文献
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The effects of barite (94–96% BaSO4), a major constituent of drilling muds used in marine oil drilling operations, on meiofauna were studied in an experimental flow-through system. Aquaria containing sand or varying proportions of barite and sand received a continuous supply of unfiltered seawater from Santa Rosa Sound, Florida, for ten weeks. At the end of this period the composition, biomass and vertical distribution of the meiofauna were determined. Most of the meiofauna (>99%) occurred in the highly aerobic upper 2 cm portion of the substratum. Rotifera, Foraminifera, Hydrozoa, Turbellaria, Ostracoda, Polychaeta and Bivalvia did not exhibit significant differences between control and experimental aquaria. However, the densities of Nematoda, Copepoda and Copepoda nauplii varied with the substrate composition. The meiofaunal densities in the aquaria containing 1:10 or 1:3 mixtures of barite and sand were greater than that in aquaria containing sand alone. A marked decrease in meiofaunal density was evident in aquaria containing 5·5 cm of sand covered with a 0·5 cm layer of barite. 相似文献
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Elaborate experiments were performed in a 30 m long, 0.5 m deep and 0.2 m wide laboratory flume to study the process of infiltration of fine sediment into the pores of coarse sediment forming the channel bed material. Different concentrations of suspended load of fine sediment of size 0.064 mm were passed over the channel bed made up of three different types of coarse sediments; two uniform and one nonuniform. The proportion of fine sediment infiltrated into the pores of bed material for each equilibrium concentration of suspended load of fine sediment in the flow was studied during several experimental runs. The proportion of fine sediment within the pores of bed material increased with an increase in the equilibrium concentration of suspended load of fine sediment in the flow. This process continued till the pores within the coarse sediment bed were filled up to the capacity with the fine sediment transported by the flow in suspension. The theoretical value was identified for limit for maximum proportion of fine sediment that can be present within the pores of bed material. On further increase in the concentration of suspended load of fine sediment in the flow, deposition of fine sediment occurs on the surface of the flume bed in the form of ripples of the fine sediment. This condition is defined as 'depositional condition'. Experimental observations on these and related aspects are presented herein. 相似文献