Emission lines from nitrogen-like ions and their diagnostic use     

P. K. Raju  B. N. Dwivedi 《Astrophysics and Space Science》1990,173(1):13-26

Line emissions from nitrogen-like ions NeIV, MgVI, and AlVII have been studied as a diagnostic probe for the emitting regions of astrophysical plasma. Line intensities from these ions have been calculated and compared, in this study, with available observational data for solar plasma.  相似文献   

On the Propagation and Dissipation of Alfvén Waves in Coronal Holes     

B. N. Dwivedi  A. K. Srivastava 《Solar physics》2006,237(1):143-152

We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts.  相似文献   

Strong and Weak Damping of Slow MHD Standing Waves in Hot Coronal Loops     

V. S. Pandey  B. N. Dwivedi 《Solar physics》2006,236(1):127-136

Slow magnetohydrodynamic (MHD) standing wave oscillations in hot coronal loops for both strong (i.e. τ_d/P∼ 1) and weak (i.e. τ_d/P≥ 2) damping are investigated taking account of viscosity, thermal conductivity and optically thin radiation. The individual effect of the dissipative terms is not sufficient to explain the observed damping. However, the combined effect of these dissipative terms is sufficient to explain the observed strong damping, as well as weak damping seen by SUMER. We find that, the ratio of decay time (τ_d) and period (P) of wave, i.e., τ_d/P (which defines the modes of damping, whether it is strong or weak) is density dependent. By varying density from 10⁸ to 10¹⁰ cm⁻³ at a fixed temperature in the temperature range 6 – 10 MK, observed by SUMER, we get two sets of damping: one for which τ _d/P∼ 1 corresponds to strong damping that occurs at lower density and another that occurs at higher density for which τ_d/P ≥ 2 corresponds to weak damping. Contrary to strong-damped oscillations, the effect of optically thin radiation provides some additional dissipation apart from thermal conductivity and viscosity in weak-damped oscillations. We have, therefore, derived a resultant dispersion relation including the effect of optically thin radiation. Solutions of this dispersion relation illustrate how damping time varies with physical parameters of loops in both strong and weak damping cases.  相似文献   

Copper Ore Identification using Spectral Similarity Measurement from Hyperion Image,Mapping of Porphyry Copper Mineralized Zone     

Krishnendu Banerjee  Manish Kumar Jain 《Journal of the Geological Society of India》2018,91(2):239-247

This work illustrates the effectiveness of hyperspectal image spectroscopy and lab spectroscopy in identification techniques of minerals in alteration zone of ore body. The adopted procedure involves testing of Hyperion image spectra, their processing for noise, spectral matching and spectral similarity measurement with selected library spectra. Average weighted spectral similarity; visual and statistical matching techniques were used to select end-members from image spectra. Minimum noise fraction and pixel purity index technique were used to retrieve end-member spectra from hyperion image. Hyperspectral image like hyperion has the capability to deliver laboratory standard spectroscopic result. This paper illustrates the capability of hyperion image spectra in copper ore identification and mapping of chalcopyrite outcrop. A systematic approach has been made in this paper. This approach describes how image end member spectra and laboratory spectra can be co-related to fetch accurate spectral form of chalcopyrite ores. Thus, statistical and graphical comparison has been carried out between image derived end member spectra and laboratory spectra of chalcopyrite for better accuracy. The visual measurements is satisfactory, R = 0.973 for fine and 0.976 for medium grained chalcopyrite ore. Excellent statistical significance levels (90–97%) are found while comparing these spectra. There are many success stories of sub-pixel and N-dimensional feature space methods to separate the hydrothermal alteration zones from iron oxide mixed ore bodies. Thus, unmixing methods are very useful for mapping of most dominating mineral parts of a pixel from hyperspectral images which have coarse spatial resolution. Finally, mapping of mineralized zone has been achieved through sub-pixel based classifiers like spectral angle mapper (SAM), constrained energy minimization (CEM) and adaptive coherence estimator (ACE) techniques.  相似文献   

Flood Frequency Analysis of Betwa River,Madhya Pradesh India     

H. K. Pandey  Shivam Dwivedi  Kamlesh Kumar 《Journal of the Geological Society of India》2018,92(3):286-290

Flood is common phenomena worldwide since time immemorial. Recently the change in climatic parameters has drastically affected the pattern and magnitude of flood. India being one of the tropical country face flood and drought situations every year, therefore it needs accurate assessment and forecast of flood for proper management of natural resources.An attempt has been made through the present study which consists frequency analysis on maximum daily discharge data in Betwa river at Basoda, Mohana and Shahijina gauging stations in Madhya Pradesh state using Gumbel’s Extreme value distribution and Log Pearson Type-3 distribution for 20 years period (1993-2012).The result shows that Log Pearson Type-3 distribution is better suited for Betwa basin. The results can be used by civil engineers for deciding the dimensions of hydraulic structures such as spillways, dams, bridges etc. Floods are forecasted for the different return periods for Betwa river.  相似文献   

Evaluation of fertility indicators associated with arsenic-contaminated paddy fields soil   总被引：1，自引：0，他引：1  

P. S. Chauhan  S. K. Mishra  S. Misra  V. K. Dixit  S. Pandey  P. Khare  M. H. Khan  S. Dwivedi  A. Lehri 《International Journal of Environmental Science and Technology》2018,15(11):2447-2458

Emerging environmental issues related to heavy metal contamination in rice draw great concern about the soil quality of paddy farming lands irrigated with groundwater. Investigating the functioning of soil microorganisms exposed to heavy metal contamination is imperative for agricultural soil manipulations. The current study accentuates the influence of heavy metals on microbial activity and community composition in arable soil of West Bengal State of India. The result revealed that the fertility indicators (activity of all soil enzymes) and growth-limiting factors (soil N and P) were negatively correlated with the heavy metal stress except the soil total organic content which demonstrated significant positive correlation with the heavy metals. In case of functional diversity of soil, all the considered diversity indices exhibited no specific pattern along with the availability of heavy metals. Further, despite the heavy metal contamination, we observed a very complex and indifferent pattern of bacterial community composition along the heavy metal contamination sites. Overall, we found that γ-Proteobacteria had been the most abundant bacterial community followed by Actinobacteria, Firmicutes, β-Proteobacteria and α-Proteobacteria. Commemorating all the results, we can infer that arsenic and other heavy metal contamination is deteriorating the soil quality and hence warrants immediate attention of concerned soil scientist and agronomists.  相似文献   

Stability assessment of jointed rock slope with different crack infillings under various thermomechanical loadings     

Pushpendra Sharma  Amit Kumar Verma  Anil Negi  Manish Kumar Jha  Pradeep Gautam 《Arabian Journal of Geosciences》2018,11(15):431

Thermoelastic deformation of rock significantly affects the stability of rock slope because thermoelastic strains may cause fracture propagation under favorable condition of failure. Rock slope stability depends on the balance between shear stress and shear resistance along the plane of weakness. Due to warming of rock slopes by heat transfer phenomena, viz. conduction and convection, considerable change in induced stresses (normal and shear) and resistance takes place which further causes instability in rock slope. In this paper, a two-dimensional finite element model has been used to simulate the stability of jointed rock slope containing crack in its upper surface. Four different cases have been simulated on the basis of infilling material (air, water, ice, water and ice) in the crack. Stability of rock slope is examined in terms of shear displacement and factor of safety for different thermal conditions of slope surface. A comparative study has been done for the four cases of infilling material in the crack. The various affecting parameters, viz. shear displacement, factor of safety, shear strength along the joint, and different surface temperature conditions, are illustrated by means of graphs. It has been found that the values of horizontal and vertical displacements are in the range of millimeters. The maximum values of horizontal and vertical displacements are 2.17 mm. Moreover, the maximum values of vertical compressive and tensile stresses are 15.4 MPa and 4.45 MPa respectively for the said four cases. According to the infilling material in the crack, the stability of the rock slope for the given geometry of slope is found in the following order: crack filled with ice < crack filled with ice and water < crack filled with water < empty crack. Validations of numerical results have been done from previous studies, and it has been found that the trends of normal stress, shear strength, and shear displacement along the joint are well matched.  相似文献   

The vorticity axis flip and its control on mineralization     

Manish A. Mamtani 《Journal of the Geological Society of India》2013,81(1):27-30

This paper discusses the possible role of vorticity axis flip in controlling fluid flow and consequent development of hydrothermal deposits. Structural, kinematic and vorticity data from the vicinity of the Singhbhum Shear Zone (SSZ) are used to propose a two stage model to explain hydrothermal mineralization. It is suggested that in the initial stage, fractures, weak planes, foliations and/or shear zones develop. Fracture permeability is weak at this stage, as a consequence of which fluid pressure builds up. Variation in stress orientation during a later stage of deformation results in enhancement of fracture network, fracture permeability and its anisotropy. If a significant vorticity axis flip accompanies this variation in stress orientation, then it pumps the fluids into the fracture network, thus yielding hydrothermal mineral deposits. In the case of SSZ, the vorticity axis flip is envisaged to have taken place from steeply plunging (anticlockwise) during the early stage, to sub-horizontal during the late stage. The SSZ became a northerly dipping thrust at this late stage and the rotation around the sub-horizontal vorticity axis was such that the rocks comprising the northern block were thrust over southern block (Singhbhum granitoid). According to the author, this vorticity axis flip must have been critical in pumping up the fluids along the SSZ to form quartz veins that host mineral deposits.  相似文献   

Aquifer system response to intensive pumping in urban areas of the Gangetic plains,India: the case study of Patna     

Dipankar Saha  S. N. Dwivedi  Raj K. Singh 《Environmental Earth Sciences》2014,71(4):1721-1735

A significant component of domestic demand for water of urban areas located in the Gangetic plains is met by heavy pumping of groundwater. The present study is focused on the Patna municipal area, inhabited by 17 million people and spanning over 134 km², where entire urban water demand is catered from pumping by wells of various capacities and designs. The present study examines the nature of the aquifer system within the urban area, the temporal changes in the water/piezometric level and the recharge mechanism of the deeper aquifers. The aquifer system is made up of medium-to-coarse unconsolidated sand, lying under a ~40-m-thick predominantly argillaceous unit holding 8- to 13-m-thick localised sand layers and continues up to 220 m below ground. Groundwater occurs under semi-confined condition, with transmissivity of aquifers in 5,500–9,200 m² day^?1 range. Hydraulic head of the deeper aquifer remains in 9–19 m range below ground, in contrast to 1–9 m range of that of the upper aquitard zone. The estimated annual groundwater extraction from the deeper aquifer is ~212.0 million m³, which has created a decline of 3.9 m in the piezometric level of the deeper aquifer during the past 30 years. Unregulated construction of deep tube wells with mushrooming of apartment culture may further exacerbate the problem. The sand layers within the aquitard zone are experiencing an annual extraction of 14.5 million m³ and have exhibited stable water level trend for past one and half decades. This unit is recharged from monsoon rainfall, besides contribution from water supply pipe line leakage and seepage from unlined storm water drains.  相似文献   

Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon,Garhwal Himalaya (India)   总被引：2，自引：0，他引：2  

Amit Kumar  Akshaya Verma  Dwarika Prasad Dobhal  Manish Mehta  Kapil Kesarwani 《Journal of Earth System Science》2014,123(1):109-120

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