Chhotanagpur granite gneiss in relation to the schistose rocks around Murhu,Ranchi district,Bihar: a structural approach

Structural analysis of the Chhotanagpur gneiss and the adjoining schistose rocks of the Singhbhum Group indicates perfect conformity in their structures on macroscopic, mesoscopic and microscopic scales. This precludes the possibility of the gneissic rocks having intruded into the deformed and metamorphozed schistose rocks. The observed features can be best explained by considering the gneissic rocks as the basement and the schistose rocks as the cover, both deformed and metamorphozed together. However, this does not exclude the possibility of the gneissic rocks being reactivated and intruding elsewhere.     

Thermonuclear X-ray burst of MXB 1658-298 with <Emphasis Type="Italic">NuSTAR</Emphasis>

MXB 1658-298 is a transient Low-Mass X-ray Binary (LMXB), which shows eclipses, dips and bursts in its light curve. This source has undergone three active periods separated by long quiescent phases. The latest phase of enhanced X-ray emission was observed during 2015–2016. We have analysed broadband data from Swift/XRT and NuSTAR observations carried out in 2015. During NuSTAR observation, one thermonuclear X-ray burst took place. The X-ray emission during the burst was brighter by a factor of \(\sim 200\), compared to the pre-burst emission. This work focuses on the spectral analysis of MXB 1658-298 during the persistent and the burst phases using NuSTAR observation of 2015. We have also determined the temperature and radius evolution during the burst using the time-resolved spectroscopy. The burst phase shows mild Photospheric Radius Expansion (PRE).     

Mountain erosion and mitigation: global state of art

Mountain erosion mapping is one of the important aspects for monitoring environmental degradation. Global climate change coupled with human activities is eroding the mountain regions of the world at an alarming rate. The various types of erosion can be classified as water erosion, aeolian erosion, glaciered erosion, gravity erosion and man-made erosion. Tectonic activity also plays a major role towards mountain erosion. Soil erosion along with debris flow and rock falling not only causes loss of human life and property, but also affects the climatic condition of the mountain regions. Mountain erosion mitigation and protection methods include wire mesh fencing with inclusion of brush layers and brush mats on fascines, constructing check dams and slope benches and application of bioengineering works such as plantation and vegetation growth. This study consists of the global scenario with some of the state-of-the-art methods for mitigation and mappings of mountain erosion. The erosion in mountainous regions can be controlled with the help of suitable vegetation and plant growth, with installation of special bioengineered materials. However, public awareness is also considered as an important factor. Moreover, it is found that mapping the rate of erosion greatly helps to make proper action plan against the erosion process.     

On thermonuclear convection: I shellular instability

Abstract

As the sun evolves, a sharp compositional peak of He ³ builds up in the core. Nuclear reactions involving He ³ are very temperature sensitive, as a result, this He ³ layer is susceptible to thermal instability. The small horizontal wavenumber g-modes have large time scales, comparable to the thermal time scale. Using a two-layer model, we find that such “shellular modes” are the most unstable. As a result of nuclear heating, these modes may be excited in the solar core in a shallow layer confined to the He ³ zone. A possible effect of such shellular convection on the solar neutrino problem is discussed. In this paper we discuss the linear theory; the nonlinear effects will be treated in a subsequent paper.     

Evaluation of horizontal stiffness of fibre‐reinforced elastomeric isolators

Unbonded fibre‐reinforced elastomeric isolator (U‐FREI) is relatively new seismic base isolator in which fibre layers are used as reinforcement to replace steel shims as are normally used in conventional isolators. Further, the top and bottom end steel connector plates of conventional isolators are also removed. In general, the horizontal response of U‐FREI is nonlinear because of reduction in contact area due to rollover deformation and reduction in shear modulus of isolator under large deformation. Thus, evaluation of horizontal stiffness of U‐FREI is a challenging problem. Most previous studies were focused on the investigation of horizontal response of scaled models of U‐FREIs with low shape factors. A few analytical approaches were suggested for predicting the horizontal response of U‐FREI; but their results were not in good agreement with experimental observations. In the present study, the horizontal responses of prototype U‐FREIs are evaluated under a constant vertical pressure and cyclic loading using both experiments and finite element analysis. Prototype U‐FREIs with different shear moduli and with different shape factors are considered. Finite element simulations of corresponding bonded FREIs are also performed under the same loadings as in U‐FREIs. A rational analytical approach including the influence of rollover deformation and simultaneous reduction in shear modulus is proposed as a basic analytical tool for predicting the horizontal stiffness of FREIs (both bonded and unbonded). It is in reasonably good agreement with the results obtained from experiments and numerical analysis. Copyright © 2017 John Wiley & Sons, Ltd.     

Orbital evolution measurement of the accreting millisecond X-ray pulsar SAX J1808.4-3658

We present results from a pulse timing analysis of the accretion-powered millisecond X-ray pulsar SAX J1808.4-3658 using X-ray data obtained during four outbursts of this source. Extensive observations were made with the proportional counter array of the Rossi X-ray Timing Explorer (RXTE) during the four outbursts that occurred in 1998, 2000, 2002 and 2005. Instead of measuring the arrival times of individual pulses or the pulse arrival time delay measurement that is commonly used to determine the orbital parameters of binary pulsars, we have determined the orbital ephemeris during each observation by optimizing the pulse detection against a range of trial ephemeris values. The source exhibits a significant pulse shape variability during the outbursts. The technique used by us does not depend on the pulse profile evolution, and is therefore, different from the standard pulse timing analysis. Using 27 measurements of orbital ephemerides during the four outbursts spread over more than 7 years and more than 31,000 binary orbits, we have derived an accurate value of the orbital period of 7249.156862(5) s (MJD = 50915) and detected an orbital period derivative of (3.14 ± 0.21) × 10⁻¹² s s⁻¹. We have included a table of the 27 mid-eclipse time measurements of this source that will be valuable for further studies of the orbital evolution of the source, especially with ASTROSAT. We point out that the measured rate of orbital period evolution is considerably faster than the most commonly discussed mechanisms of orbital period evolution like mass transfer, mass loss from the companion star and gravitational wave radiation. The present time scale of orbital period change, 73 Myr is therefore likely to be a transient high value of period evolution and similar measurements during subsequent outbursts of SAX J1808.4-3658 will help us to resolve this.     

Wavelength-dispersive x-ray fluorescence spectrometric determination of tantalum in columbite-tantalite using TaKα and an LiF 420 analysing crystal

The paper proposes a simple, accurate, precise, and rapid method for determining the high atomic number (Z) major-element, tantalum (Z = 73), in the rare mineral, columbite [(Fe,Mn) (Nb,Ta)₂O₆] — tantalite [(Fe,Mn) (Ta,Nb)₂O₆], by wavelength-dispersive x-ray fluorescence spectrometry (WDXRFS). The other major-element in columbite-tantalite is the lower atomic number niobium (Z = 41). The method uses the characteristic radiation, TaKα, and an LiF 420 analysing crystal, to overcome the problems associated with the serious x-ray spectral-line interference of the secondorder NbKα and NbKβ with the first-order TaLα1 and TaLβ1 respectively.     

Crustal shortening in convergent orogens: Insights from global positioning system (GPS) measurements in northeast India

Deformation in active mountain belts like the Himalaya is manifested over several spatial and temporal scales and collation of information across these scales is crucial to an integrated understanding of the overall deformation process in mountain belts. Computation and integration of geological shortening rates from retrodeformable balanced cross-sections and present-day convergent rates from deforming mountain belts is one way of integrating information across time-scales. The results from GPS measurements carried out in NE India indicate that about 15–20 mm/yr of convergence is being accommodated there. Balanced-cross sections from the NE Himalaya indicate about 350–500 km of shortening south of the South Tibet Detachment (STD). Geothermobarometry suggest that the rocks south of the STD deformed under peak metamorphic conditions at ∼ 22 Ma. This indicates a geological convergence rate of ∼ 16–22 mm/yr which appears to be fairly consistent with the GPS derived convergence rates. Approximately 1.5 to 3.5 mm/yr (∼ 10–20 %) of the total N-S of the present-day convergence in the NE Himalaya is accommodated in the Shillong Plateau. In addition, ∼ 8–9 mm/yr of E-W convergence is observed in the eastern and central parts of the Shillong Plateau relative to the Indo-Burman fold-thrust belt. Balanced cross-sections in the Indo-Burman wedge together with higher resolution GPS measurements are required in the future to build on the first-order results presented here.     

Palaeosol Control of Arsenic Pollution: The Bengal Basin in West Bengal,India

Groundwater in the Bengal Basin is badly polluted by arsenic (As) which adversely affects human health. To provide low‐As groundwater for As mitigation, it was sought across 235 km² of central West Bengal, in the western part of the basin. By drilling 76 boreholes and chemical analysis of 535 water wells, groundwater with <10 µg/L As in shallow aquifers was found under one‐third of a study area. The groundwater is in late Pleistocene palaeo‐interfluvial aquifers of weathered brown sand that are capped by a palaeosol of red clay. The aquifers form two N‐S trending lineaments that are bounded on the east by an As‐polluted deep palaeo‐channel aquifer and separated by a shallower palaeo‐channel aquifer. The depth to the top of the palaeo‐interfluvial aquifers is mostly between 35 and 38 m below ground level (mbgl). The palaeo‐interfluvial aquifers are overlain by shallow palaeo‐channel aquifers of gray sand in which groundwater is usually As‐polluted. The palaeosol now protects the palaeo‐interfluvial aquifers from downward migration of As‐polluted groundwater in overlying shallow palaeo‐channel aquifers. The depth to the palaeo‐interfluvial aquifers of 35 to 38 mbgl makes the cost of their exploitation affordable to most of the rural poor of West Bengal, who can install a well cheaply to depths up to 60 mbgl. The protection against pollution afforded by the palaeosol means that the palaeo‐interfluvial aquifers will provide a long‐term source of low‐As groundwater to mitigate As pollution of groundwater in the shallower, heavily used, palaeo‐channel aquifers. This option for mitigation is cheap to employ and instantly available.     

The subsurface megascopic characteristics of basalt and basement rocks from Koyna-Warna area of Maharashtra,India

Vertical deep boreholes of depth up to 1522.50m have been drilled in Koyna-Warna area of Maharashtra State within the Deccan Volcanic Province to study the most outstanding example of Reservoir Triggered Seismicity (RTS). The drilling of 9 bore-holes in the area has provided a window to earth scientists to peep into geological details available below Deccan Trap.The 932.50m thick pile of Deccan basalt, consisting of 30 flows at Rasati, near Koyna, which has been physically seen through cores, present a marvellous geological repository for observations. The megascopic characteristics of various flows and variation in composition have been presented in this paper. The microscopic and geochemical characteristics have been kept out of this communication, as the relevant studies are not completed to draw any conclusion. This study records the presence of granite wash (≈1m thick) over basement and below basalt representing Late Archaean to Cretaceous period hiatus. The basement rocks, presumably of Late Archaean age have been described mega-scopically. A fair picture of sub-surface pre-Deccan topography is shown with the help of borehole data, which confirm the nearly flat topography of pre-Deccan surface especially in this part of the area occupied by 30 flows of Deccan basalt. Correlation of 30 flows with the established stratigraphy has also been attempted for subsurface existence of Ambenali (Upper) and Poladpur Formations of Wai Subgroup in Koyna-Warna area.