Fast Transients with the Square Kilometre Array and its Pathfinders: An Indian Perspective

In the rapidly developing field of study of the transient sky, fast radio transients are perhaps the most exciting objects of scrutiny at present. The SKA, with its wide field-of-view and significant improvement in sensitivity over existing facilities, is expected to detect a plethora of fast transients which, in addition to help resolve the mysteries surrounding their nature and origin, will also lead to other interesting applications in astrophysics. We explore some of these possibilities here, and also emphasize the current status and future plans of the Indian community working in this area, in the context of ongoing work and extension of this to the SKA.     

Application of Hidden Markov Model for avalanche danger simulations for road sectors in North-West Himalaya

Seismic hazard assessment is the key tool for rational planning, safety and design of infrastructures in seismically vulnerable regions. Gujarat is the only state in peninsular India with the maximum seismic hazard of large shallow earthquakes originating from intra-plate seismicity. Probabilistic seismic hazard assessment (PSHA) of Gujarat is carried out in this paper. Three seismogenic sources, namely Kutch, Saurashtra and Mainland Gujarat, are considered, and seismicity parameters are estimated separately for each region taking into account the completeness of the available earthquake data. Peak ground acceleration (PGA) of the horizontal component and spectral acceleration at specific periods are considered as the intensity measures. Ground motion predictive equation chosen was reported to be based on simulated ground motions and verified against the strong motion records in the study region. Results are reported for the 17 major cities at the bedrock and also for the soil sites. Apart from hazard curves, 2475 and 475 years of return periods are considered for the PGA and uniform hazard spectra (UHS). The results are compared with the present recommendations of Indian Standards. Key observations include (1) Indian Standards underpredict PGA in the entire Gujarat when the soil sites are considered and in a few cities even at the bedrock; (2) amplification of PGA (or short period hazard) on account of soil sites should be included in the Indian Standard, which is currently absent; (3) shape of the UHS indicates that a separate amplification is required at the hyperbolic portion; and (4) ratio of 2475–475 years of PGA, which is considered 2.0 in Indian Standard, should be reduced to 1.5. Time-dependent recurrence model is also included in this paper and compared with conventional PSHA. General observations include that (1) hazard may increase significantly on account of time dependency; (2) this also influences the disaggregation and in turn the selection of ground motions; and (3) time since last earthquake significantly influences the extent of the effect of time dependency.     

Hydro-chemical analysis and ionic flux of meltwater runoff from Khangri Glacier,West Kameng,Arunachal Himalaya,India

The detailed hydro-chemical study of meltwater draining from Khangri glacier Arunachal Pradesh has been carried out to evaluate the major ion chemistry and weathering processes in the drainage basin. The investigative results shows that the meltwater is almost neutral to slightly acidic in nature with Mg–HCO₃-dominated hydro-chemical facies. In glacial meltwater, Ca^+?2 is the most dominated cation followed by Mg⁺², Na⁺, and K⁺, while HCO₃^? is the most dominant anion followed by SO₄^2?, NO₃^?, and Cl^?. The dominant cations such as Ca⁺² and Mg⁺² show a good relation with the minerals abundance of the rocks. Calcite (CaCO₃) and biotite [K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂] are the most abundant minerals in the deformed carbonate-rich metasedimentary rocks near to the snout with some K feldspar (KAlSi₃O₈) and quartz (SiO₂). This suggests Ca⁺² have definitely entered into the water due to the dissolution of calcite and Ca feldspar (CaAl₂Si₂O₈), while one of the source of Mg⁺² is biotite. Na feldspar (NaAlSi₃O₈) has contributed towards the availability of sodium ion, while potassium ion is derived from the chemical weathering of K feldspar and biotite. The chemical weathering is the foremost mechanism controlling the hydro-chemistry of the Khangri glacier because of the least anthropogenic interferences. The mineralogy of surrounding rocks is studied to understand better, the rock–water interaction processes, and their contribution towards ionic concentration of meltwater. The meltwater discharge and individual ion flux of the catchment area have also been calculated, to determine the ionic denudation rate for the ablation season. The high elemental ratio of (Ca?+?Mg)/(Na?+?K) (7.91?±?0.39 mg/l) and low elemental ratio of (Na?+?K)/total cations (0.11?±?0.004) indicate that the chemical composition of meltwater is mainly controlled by carbonate weathering and moderately by silicate weathering. The scatter plot result between (Ca?+?Mg) and total cations confirms that carbonate weathering is a major source of dissolved ions in Khangri glacier meltwater. In addition, the statistical analysis was also used to determine the correlation between physical parameters of glacier meltwater which controlled the solute dynamics.     

Benthic Superheroes: Living Foraminifera from Three Bays in the Mission-Aransas National Estuarine Research Reserve,USA

Studies of living foraminiferal assemblages provide much information about their roles in present environments and a perspective on interpreting the past. Along modern coasts, benthic Foraminifera act as ecological indicators in their responses to different natural and anthropogenic conditions, such as food availability, oxygen concentrations, salinity, and trace metal concentrations. A detailed survey of foraminiferal populations was undertaken in the Mission-Aransas National Estuarine Research Reserve, Texas, close to the time of its establishment in 2006. The purpose was to gauge the overall status of populations and provide baseline data for future comparison. The arid south Texas Gulf Coast is a variable and often harsh environment where biota are subject to multiple anthropogenic stressors. Despite these rigors, living Foraminifera were prolific in the Reserve. This paper discusses the results from Mesquite (July 2008), Copano (May 2006), and Mission Bays (June 2006). Populations were robust in each bay, with Ammonia parkinsoniana, Ammotium salsum, and Elphidium excavatum being most abundant. Highest numbers corresponded mainly to areas of greater circulation. In Mission Bay, elemental analysis of shells, prompted by the presence of sulfur grains in sediments and by yellow tests, detected elevated levels of barium, strontium, and iron. Most sediment samples were black and sulfidic, and ubiquitous framboidal pyrite in sediment and shells suggests that forams were frequently subject to low-oxygen conditions. Abundant living numbers, tolerance of low-oxygen conditions, and the ability to cycle trace metals emphasize the resilience of Foraminifera in taxing environments and their integral position as lower trophic level members.     

A decadal historical satellite data analysis for flood hazard evaluation: A case study of Bihar (North India)

Flood is one of the major recurrent natural disasters faced by the state of Bihar in north India. In the present study the authors assess the severity of flood hazard in Bihar, using 128 decadal historical satellite datasets acquired during different flood magnitudes during 1998 to 2010. The satellite‐based observations have been analysed in conjunction with the hydrological data, for assessing the frequency of inundation, severity of flood hazard and cropped land under flood hazard. This study assesses the spatial distribution of flooding and creation of systematic flood hazard database, which can be analysed from a spatial dimension in GIS. It is observed that about 24.56 lakh ha of the state's area and about 15.85 lakh ha of the cropped area are vulnerable to flood hazard. North Bihar is more vulnerable to flooding; 8 of the 10 areas identified as worst flood‐affected districts lie in this region.     

Assessment of groundwater quality with special reference to arsenic in Nawalparasi district,Nepal using multivariate statistical techniques

Groundwater is a precious resource for humankind not only in Nepal but also across the globe due to its diverse functions. A total of 48 groundwater samples were collected from three villages of Nawalparasi district, Nepal, during pre-monsoon and monsoon to estimate the overall groundwater quality and to identify the sources of contamination with emphasis on arsenic (As). The average concentrations of all tested groundwater quality parameters (temp., pH, EC, ORP, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^?, F^?,SO₄ ^2?, PO₄ ^3?, HCO₃ ^?, NO₃ ^?, Cu, Ni, Mn, Cd, Pb, Fe, Zn, Cr, and As) were well within permissible limits of WHO for drinking water, except for Ni, Cd, Pb, Cr, and As. Concentration of As ranged from 60 to 3,100 μg L^?1 and 155 to 1,338 μg L^?1 in pre-monsoon and monsoon, respectively. The Piper diagram of the groundwater chemistry showed groundwater of Nawalparasi belongs to Ca–Mg–HCO₃ and Mg–HCO₃ water type with HCO₃ ^? as dominant ions. As content in the study area was negatively correlated with Fe in pre-monsoon, while it was positively correlated in monsoon. Furthermore, As was negatively correlated with oxidation reduction potential suggesting reducing condition of groundwater. Principal component analysis revealed seven major factors that explained 81.996 and 83.763 % of total variance in water quality in pre-monsoon and monsoon, respectively. The variance of water quality was related mainly with the degree of water–rock interaction, mineralization, and anthropogenic inputs.