Interaction of coeval felsic and mafic magmas from the Kanker granite,Pithora region,Bastar Craton,Central India

Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes.     

Elemental variations in glacier cryoconites of Indian Himalaya and Spitsbergen,Arctic

Cryoconite samples were collected from two different climatic domains i.e., the Sutri Dhaka glacier, western Himalaya India and Svalbard glaciers, the Spitsbergen, Arctic, to understand the elemental source and elemental deposition patterns. The data of geochemical analysis suggest that the Himalayan cryoconite samples accumulate higher concentrations as compared to the cryoconite samples of the Arctic glaciers. The concentration of lithophile elements (Cs, Li, Rb and U) was recorded higher in the cryoconite holes of the Himalayas, especially, in the lower to the higher parts of the glacier, whereas, lower concentrations were recorded in the Arctic samples. Chalcophile elements in the Himalayan cryoconites are enriched in As and Bi while the Arctic cryoconite samples show a higher concentration of Bi, Pb and As. The higher concentrations are responsible for influencing the ecosystem and in human health related issues. Siderophile elements (Co, Fe, Mn and Ni) show high concentrations in the Himalayan samples, whereas, the Arctic samples show minor variations and low elemental concentration in these elements, respectively. In addition, a few elements, such as Ag, Mg, and Ca show higher concentration in the Himalayan glacier samples. Ca also occurs in high concentrations in Arctic glacier samples. R-mode factor analysis of the Himalayas (Arctic) samples indicate that the elements are distributed in four (three) factors, explaining 89% (90%) of the variance in their elemental distribution. The Factor 1 suggests statistically significant positive loadings for most of the lithophile, chalcophile and siderophile elements of the “Himalayan” and the Arctic cryoconite samples. The sample-wise factor score distribution shows a considerable variation in the sampling locations along the glaciers of both the regions. Factors 2 and 3, demonstrate insignificant loading for most of the elements, except statistically significant positive loading in some of the elements of the both, Himalayan and Arctic “cryoconites”. The higher elemental concentration in the cryoconites of the Himalayan region may be an indicator of the natural processes and/or attributed to the rapid industrialization in the Asian countries.     

Removal of NO3– from Drinking Water by Electrocoagulation – An Alternate Approach

The present study provides an electrocoagulation method, for the removal of NO₃^– from drinking water using magnesium as the anode and cathode. The experiments are carried out as a function of pH, temperature, and current density. The results show that the maximum removal efficiency of 95.8% was achieved at a current density of 0.25 A/dm², at a pH of 7.0. The adsorption of NO₃^– preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of the adsorbed molecules. The adsorption process follows a second‐order kinetics model. Thermodynamic studies show that the adsorption was exothermic and spontaneous in nature.     

Simulation of accelerograms from simplified deterministic approach for the 23rd October 2004 Niigata-ken Chuetsu,Japan earthquake

A simple hybrid approach for the simulation of strong ground motion is presented in this paper. This approach is based on the deterministic modelling of rupture plane initially started by Midorikawa, Tectonophysics 218:287–295, (1993) and further modified by Joshi, Pure Appl Geophys (PAGEOPH) 8:161, (2004). In this technique, the finite rupture plane of the target event is divided into several subfaults, which satisfy scaling relationship. In this paper, simulation of strong ground motion due to a rupture buried in a earth medium consisting of several layers of different velocities and thicknesses is made by considering (1) transmission of energy at each layer; (2) frequency filtering properties of medium and earthquake source; (3) correction factor for slip of large and small magnitude earthquakes and (4) site amplification ratio at various stations. To test the efficacy of the developed technique, strong motion records were simulated at different stations that have recorded the 2004 Niigata-ken Chuetsu, Japan earthquake (M _s 7.0). Comparison is made between the simulated and observed velocity and acceleration records and their response spectra. Distribution of peak ground acceleration, velocity and displacement surrounding the rupture plane is prepared from simulated and observed records and are compared with each other. The comparison of synthetic with the observed records over wide range of frequencies shows that the present technique is effective to predict various strong motion parameters from simple deterministic model which is based on simple regression relations and modelling parameters.     

Landscape structure and use,climate, and water movement in the Mekong River basin

In this article the relative roles of precipitation and soil moisture in influencing runoff variability in the Mekong River basin are addressed. The factors controlling runoff generation are analysed in a calibrated macro‐scale hydrologic model, and it is demonstrated that, in addition to rainfall, simulated soil moisture plays a decisive role in establishing the timing and amount of generated runoff. Soil moisture is a variable with a long memory for antecedent hydrologic fluxes that is influenced by soil hydrologic parameters, topography, and land cover type. The influence of land cover on soil moisture implies significant hydrologic consequences for large‐scale deforestation and expansion of agricultural land. Copyright © 2007 John Wiley & Sons, Ltd.     

Evaluation of reservoir temperatures and local utilization of geothermal waters of the Konkan Coast, India

Geochemical studies on fifteen geothermal manifestations (38–70°C) from the Konkan coast geothermal province of India have been used to evaluate the reservoir temperatures. Activity studies of the minerals and the waters present in the reservoirs suggest that the thermal waters are in equilibrium with montmorillonite, kaolinite and quartz at about 100°C. Reservoir temperatures of these geothermal systems as estimated by geochemical thermometers, are 88 to 128°C, and thus too low for economic electricity production.     

Diagnostics of solar ions: Ne VI,Mg VI,Si VIII and Mg VIII observed by SERTS

Diagnostics of solar ions Nevi, Mgvi, Siviii, and Mgviii in an active region observed by SERTS have been presented. Density, temperature, and electron pressure in the emitting source have been derived from theoretical line-ratio curves and its EUV spectrum obtained by SERTS. The variation of neon-to-magnesium and silicon-to-magnesium abundances has been discussed in the interpretation of the active region spectrum obtained by SERTS.     

Equilibrium Structures of Differentially Rotating Primary Components of Binary Stars

In this paper a method is proposed for computing the equilibrium structures and various other observable physical parameters of the primary components of stars in binary systems assuming that the primary is more massive than the secondary and is rotating differentially about its axis. Kippenhahn and Thomas averaging approach (1970) is used in a manner earlier used by Mohan, Saxena and Agarwal (1990) to incorporate the rotational and tidal effects in the equations of stellar structure. Explicit expressions for the distortional terms appearing in the stellar structure equations have been obtained by assuming a general law of differential rotation of the typeω² = b ₀+b ₁ s ²+b ₂ s ⁴, where ω is the angular velocity of rotation of a fluid element in the star at a distance s from the axis of rotation, and b ₀, b ₁, b ₂ are suitably chosen numerical constants. The expressions incorporate the effects of differential rotation and tidal distortions up to second order terms. The use of the proposed method has been illustrated by applying it to obtain the structures and observable parameters of certain differentially rotating primary components of the binary stars assuming the primary components to have polytropic structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of central condensation on the modes of nonradial oscillations of stellar models

Modes of nonradial oscillations of six composite polytropic models have been investigated numerically to study the effect of central condensation parameter being the density at the centre and the mean density of a stellar model) on the modes of nonradial oscillations of stellar models.     

Local Contrast Based Adaptive SAR Speckle Filter

In this paper, we propose an adaptive filtering technique for Synthetic Aperture Radar (SAR) images. A new windowing technique is introduced where the total window is divided into five equal sized overlapping sub-windows. The pixel to be filtered is a part of each of these sub-windows. A weighted mean of all sub-windows is computed for the pixel under consideration. The weights are accounted from a measure of heterogeneity calculated for each sub-windows. The filter is able to adapt automatically and adjust the speckle suppression strength based on local statistics. This allows the filter to preserve edges while strongly suppressing speckle over homogeneous areas. The proposed filter was compared with some well known SAR filtering techniques in terms of speckle suppression and edge preservation ability. Several experiments were performed on datasets acquired from both air-borne and space-borne SAR platforms. Some well known indices were used for quantitative comparison with other filters. Among the filters compared, the proposed filter shows good speckle suppression ability while still exhibiting reasonable edge preservation ability.