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21.
In many natural environments, such as in underwater hot springs and hydrothermal vents, thermal gradients are accompanied with changes in the concentration of chemical compounds transported to the seawater, causing the so-called double-diffusive, mixed convection. To study the physical scenarios in such systems, a vertical channel filled with a porous medium saturated with saline water is considered. The motion in the sediment-filled channel is induced by two buoyancy forces and an external pressure gradient, similar to the situation in a vent with an upward flow direction. The fluid flow has been modeled by an extended Darcy model, and the flow instability mechanisms have been studied numerically. The linear stability analysis is performed considering a wide range of Darcy number (Da = 10−5 -10−8). The instability boundary curve showed three distinct dynamic regimes: (i) Rayleigh-Taylor (R-T), (ii) log-log non-linear variation, and (iii) log-log linear variation. The domain of different regimes were sensitive to external pressure gradient as well as permeability. Similar to cross-diffusive natural convection in pure viscous fluids, a linear relationship between logarithmic absolute values of critical thermal Rayleigh number (∣RaT∣) and solute Rayleigh number (RaC) is found in the third regime. Based on the permeability, for any solute Rayleigh number (RaC), there existed a minimum value of Reynolds number (Re), below which R-T type of instability appeared. Above this minimum value, the instability was due to two buoyancy forces, known as buoyant instability. Simulations of secondary flow via energy analysis demonstrated the development of complex dynamics at the critical state in all three regimes characterized by transition of multi to uni-cellular structures and vice verse. 相似文献
22.
Different extractants were used to determine various forms of Fe and Al in three soil profiles developed under a tropical environment in India. The average contents of Fe and Al, extracted by different extracting reagents were found to be in descending order, as follows:
Analysis of pyrophosphate (pyr), oxalate (oxa) and dithionate (dith) extractable Fe and Al showed that with increasing soil age, the crystalline Fe and Al oxides increased at the expense of the poorly crystalline forms. The mean content of amorphous Fe and Al, crystalline Fe and Al and their ratio values in the three different soil series estimated the degree of soil development and were found to be in the following descending order: Ghoradanga >Kanchanpur >Lachimpur. Correlation between different forms of Fe and Al and selected soil properties were examined. Multiple regression equations were formulated to show the relation among soil properties and different forms of Fe and Al. 相似文献
23.
Sagar S Salunkhe A K Bera S S Rao V Raghu Venkataraman Uday Raj Y V N Krishna Murthy 《Journal of Earth System Science》2018,127(8):116
Desertification has emerged as a major economic, social and environmental problem in the western part of India. The best way of dealing with desertification is to take appropriate measures to arrest land degradation, especially in areas prone to desertification. This requires an early warning system for desertification based on scientific inputs. Hence, in the present study, an attempt has been made to develop a comprehensive model for the assessment of desertification risk in the Jodhpur district of Rajasthan, India, using 23 desertification indicators. Indicators including soil, climate, vegetation and socio-economic parameters were integrated into a GIS environment to get environmental sensitive areas (ESAs) to desertification. Desertification risk index (DRI) was calculated based on ESAs to desertification, the degree of land degradation and significant desertification indicators obtained from the stepwise multiple regression model. DRI was validated by using independent indicators such as soil organic matter content and cation exchange capacity. Multiple regression analysis shows that 16 indicators out of 23 were found to be significant for assessing desertification risk at a 99% confidence interval with \(R^{2}=0.83\). The proposed methodology provides a series of effective indicators that would help to identify where desertification is a current or potential problem, and what could be the actions to alleviate the problem over time. 相似文献
24.
Subir Bera Sudha Gupta Mahasin Ali Khan Aniruddha De Radhanath Mukhopadhyay 《Journal of Earth System Science》2014,123(6):1433-1438
A part of the compressed tree fern axis with leaf and adventitious root scars in unusual arrangement from Plio–Pleistocene sediments of Arunachal Pradesh, India is described as Cyathea siwalika sp. nov. This record suggests that Cyathea was an important component of tropical evergreen forest in the area during the Plio–Pleistocene and this group subsequently declined in importance within the local vegetation. 相似文献