Nonlinear radial oscillations of coronal loops

The behavior of radial oscillations of coronal magnetic tubes is considered in a weakly nonlinear approximation. The nonlinear Schrödinger equation, the coefficients of which are found from the tube and radial mode parameters, has been obtained for the oscillation amplitude. The coefficients have been calculated for the fundamental radial mode, which is characterized by the absence of the cutoff in the region of low frequencies. It has been shown that the modulation instability condition is satisfied in a wide range of mode parameter values, which indicates that large-amplitude radial oscillations can exist in coronal loops.     

Analyzing the effect of moving resonance on seismic response of structures using wavelet transforms

There is a complex interaction between the seismic response (i.e., peak displacements) of a nonlinear structure and the characteristics of a ground motion. One ground motion characteristic that contributes to record‐to‐record variability is spectral nonstationarity, or the variation of signal's frequency content with time. When the predominant natural periods of a nonlinear structure elongate in such a way as to match with the predominant frequency content in the ground motion, a phenomenon called moving resonance occurs. The effect of moving resonance on the response of nonlinear structures is investigated. Continuous complex wavelet transforms are used to examine the spectral nonstationarity of ground motion acceleration histories and associated structural displacement histories to identify the occurrences of moving resonance. A three‐dimensional displacement response spectrum is used to determine which combinations of initial period and strength create the largest displacements and thus are candidate configurations for experiencing moving resonance. A method is then proposed for quantifying the effect of moving resonance on structural response. The method utilizes discrete wavelet transforms to decompose a ground motion into component signals with limited frequency band and examines the structural response due to each individual component. A discussion is provided as to how these tools can be used to identify ground motion characteristics that may be conducive to moving resonance. Copyright © 2013 John Wiley & Sons, Ltd.     

Groundwater contamination in parts of Nalgonda district,Telangana, India as revealed by trace elemental studies

The present paper deals with major and trace elements geochemistry of the groundwater from Nalgonda district, Telangana. The study area is very important in terms of anthropogenic activity like rapid industrial, urban development, pesticides, pharmaceutical, granite polishing and agro based industries. Inductively coupled plasma mass spectrometer (ICPMS) was employed to determine the concentration of trace elements in collected groundwater samples (bore well). These probe elements were further categorized as toxic elements (Pb, As, Cd, and V), alkaline earths (Sr and Ba), alkali metals (Li, Rb), transition metals (Cr, Mo and Ni), metallic elements (Cu, Fe, Zn, Al, Co), and other non-metallic elements (Se and Si). The groundwater quality was examined in perspective of Indian as well as World Health Organization drinking water standards. Based on the analytical results, groundwater in the study area is found to be slightly alkaline in nature and very hard, the average abundance of the major cations and anions is in the order of Ca⁺<Na⁺<Mg⁺<K⁺ and Cl^-<HCO₃ ^?<CO₃ ^?<SO₄ ^?<NO₃ ^?<F^– respectively. The dominant hydro chemical facies of groundwater is Na⁺ - HCO ₃ ^– – Cl^– and Na⁺ - Cl^– – HCO^– ₃ types.The results of trace elements shows that concentration of Pb, As, Cd, V in collected samples exceeding the desirable limits, and in the case of alkaline, alkali, transition, non-metallic elements, seventy per cent of the samples crossed the desirable limits, but all metallic elements viz. Cu, Fe, Zn, Al, Co is within the limits as per Indian as well as World Health Organizations drinking water standards. Factor analysis results shows that seven factors emerged as a significant contributor to the groundwater contamination is about 65.32 per cent. The spatial variation maps decipher trace elemental concentrations both geogenic and anthropogenic origin, by three zones i.e. ‘low’, ‘moderate’ and ‘high’ of the study area based on environment using Arc-GIS. High concentrations of trace elements are indicative of phenomenal rise in chemical composition and likely to have its origin from silicate weathering reactions and dissolution/precipitation processes supported by rainfall and anthropogenic activities, indiscriminate use of fertilizers/pesticides, and disposal of waste and sewage, release of reactive pollutants into the atmosphere by industries. Hence, this work is of immense societal benefit in terms of prevailing human health hazards in the study area with a direct relevance to such industrially populated regions elsewhere.