Seismic assessment in southern Baromura hill,northeast India,considering geophysical aspects

This paper aims to assess the geophysical signatures like morphology and structure of a fault line, which is situated in a part of southern Baromura hill of Tripura, northeast India. In this work manual observations and technical applications were adopted for understanding the morphological and structural characters of the fault line. As tectonic mapping is one of the main objectives of this study, the remote sensing technique was used to prepare a tectonic map of the study area. Geothermal range of the area was measured by unsupervised classification of Landsat TM thermal infrared band (band 6). The classified thermal band was overlaid by another classified shortwave infrared band (band 7 of Landsat TM), which explains the structural evidences of the study area. In addition, an automated digital elevation model (DEM) was prepared to assess the morphological characters of the study area particularly near the confluence of R. Maharani and R. Gumti. To analyse the structural condition of the faulted zone, resistivity characters of the rocks were measured by “vertical electrical sounding” (VES) method. The electrical resistivity character of this area strongly supports that a displacement occurred in this place. Finally an attempt was made to explain the character of faulting on the basis of morphological signatures and structural evidences for future disaster management planning.     

Geophysical Log-based Coal Characterization of Middle Permian Barakar Formation from North Karanpura Coal Field,India

North Karanpura coal field is the western most marginal coal bearing segment of east-west trending Damodar valley basin. It consists of middle Permian Barakar Formation with sandstone, siltstone, coal and shale being the dominant lithofacies, deposited in a fluvial meandering environment, giving rise to repetitive fining upwards cycles. Study of geophysical logs, the drilled core holes were used to identify lithofacies, correlate coal seams with splitmerge behavior; which has been used to understand lateral and vertical facies disposition. Geophysical logs have been employed to compute various coal assay parameters–ash, fixed carbon, moisture, volatile content, cleat porosity, vitrinite reflectance seam wise. Study of log based coal assay parameters, calibrated with lab based values depicts lateral coal quality variation, i.e. decreasing ash content, higher fixed carbon from east to west, which can be a great proxy for future development of field or mine planning.     

Halo ejection in distant radio galaxies: jet feedback in massive galaxy formation

We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s⁻¹ and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km s⁻¹. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of ∼60 kpc along the radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most of their interstellar medium before evolving to become “red and dead” Elliptical galaxies.     

Smoothed particle hydrodynamic simulations of viscous accretion discs around black holes

Viscous Keplerian discs become sub-Keplerian close to a black hole since they pass through sonic points before entering into it. We study the time evolution of polytropic viscous accretion discs (both in one- and two-dimensional flows) using smoothed particle hydrodynamics. We discover that for a large region of the parameter space spanned by energy, angular momentum and polytropic index, when the flow viscosity parameter is less than a critical value, standing shock waves are formed. If the viscosity is very high then the shock wave disappears. In the intermediate viscosity, the disc oscillates very significantly in the viscous time-scale. Our simulations indicate that these centrifugally supported high density regions close to a black hole play an active role in the flow dynamics, and consequently, the radiation dynamics.     

Strange pulsar hypothesis

It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than ∼10⁸ G. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which cannot be lowered by the system spontaneously.     

A proposed method for measurement of cosmic-ray mass composition based on geomagnetic spectroscopy

The effect of the geomagnetic Lorentz force on the muon component of extensive air shower (EAS) has been studied in a Monte Carlo generated simulated data sample. This geomagnetic field affects the paths of muons in an EAS, causing a local contrast or polar asymmetry in the abundance of positive and negative muons about the shower axis. The asymmetry can be approximately expressed as a function of transverse separation between the positive and negative muons barycentric positions in the EAS through opposite quadrants across the shower core in the shower front plane. In the present study, it is found that the transverse muon barycenter separation and its maximum value obtained from the polar variation of the parameter are higher for iron primaries than protons for highly inclined showers. Hence, in principle, these parameters can be exploited to the measurement of primary cosmic-ray mass composition. Possibility of practical realization of the proposed method in a real experiment is briefly discussed.