Effect of silica concentration on the diopsidic pyroxenes in the system diopside-CaTiAl2O6SiO2

The effect of silica concentration on the solubility of Al and Ti in diopsidic pyroxenes has been investigated at one atmosphere in the system diopside-CaTiAl₂O₆-SiO₂ at temperatures between 1150–1420° C. The composition of pyroxene in the system diopside-CaTiAl₂O₆-SiO₂ is influenced by the total SiO₂ content. Near the join diopside-CaTiAl₂O₆, the pyroxene forms a solid solution with the CaTiAl₂O₆ molecule, and co-exists with perovskite for compositions greater than 11 weight percent CaTiAl₂O₆. Anorthite is an accompanying phase. With increasing total SiO₂ content a series of mineralogical changes involving Ti-bearing phases occur. Sphene solid solution co-exists with diopside solid solution, anorthite, and perovskite in a small compositional range near the diopside-CaTiAl₂O₆ join. Additional total SiO₂ results in the elimination of perovskite and a decrease of solid solution in the pyroxenes. With further increase in SiO₂ content, tridymite appears and the pyroxene is approximately pure diopside. Rutile joins diopside, anorthite, sphene solid solution and tridymite over a broad compositional range in the Ti, Si-rich part of the system. These results demonstrate that increased silica concentration decreases the solubility of Al and Ti in diopsidic pyroxenes and controls the stability of co-existing Ti-bearing phases.     

Random Forest-Based Prospectivity Modelling of Greenfield Terrains Using Sparse Deposit Data: An Example from the Tanami Region,Western Australia

Data-driven prospectivity modelling of greenfields terrains is challenging because very few deposits are available and the training data are overwhelmingly dominated by non-deposit samples. This could lead to biased estimates of model parameters. In the present study involving Random Forest (RF)-based gold prospectivity modelling of the Tanami region, a greenfields terrain in Western Australia, we apply the Synthetic Minority Over-sampling Technique to modify the initial dataset and bring the deposit-to-non-deposit ratio closer to 50:50. An optimal threshold range is determined objectively using statistical measures such as the data sensitivity, specificity, kappa and per cent correctly classified. The RF regression modelling with the modified dataset of close to 50:50 sample ratio of deposit to non-deposit delineates 4.67% of the study area as high prospectivity areas as compared to only 1.06% by the original dataset, implying that the original “sparse” dataset underestimates prospectivity.     

Rapid optical variability in radio-quiet QSOs

We report results of the observations at the Vainu Bappu Observatory and the Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar objects (RQQSOs) during 1996–99. This is a part of our ongoing programme to search for intranight optical variability in RQQSOs. Additional evidence for very rapid variability in three of the five optically bright and very luminous RQQSOs we had observed earlier, 1049−006, 1444+408 and 1630+377, was found. Of the three newly observed RQQSOs, the data for 0043+039 are too noisy to allow conclusions about variability to be drawn, but 0748+294 and 0824+098 show strong hints of microvariability. We also present a summary of the results from our entire programme to date, which includes observations of 16 radio-quiet QSOs and one radio-weak QSO, and compare the general properties of rapid variability in radio-quiet versus radio-loud AGN as determined from our work and that of several other groups. Observations of this kind are likely to play a key role in understanding the relative contributions of accretion discs and relativistic plasma jets to rapid optical fluctuations of AGN.     

Geo-spatial approach for phytodiversity characterization in Panna National Park (part), M.P. (India)

Panna National Park is situated in the north-central part of Madhya Pradesh, India. Landscape parameters like fragmentation, porosity, patchiness and jaxtaposition have been analysed for disturbance gradient characterization. Disturbance on biodiversity due to human activities has been studied both qualitatively and quantitatively. The species richness is highest in northern mixed dry deciduous forest followed by dry deciduous open scrub and southern tropical dry deciduous teak forest. Species richness of the open thorny dry deciduous forest with grasses is found to be the lowest. Disturbance analysis indicates that 22.02% of the southern slightly moist teak forests are highly disturbed whereas Anogeissus forest and Riverine forest have 17.04% and 12.41% of the area under high disturbance, respectively. A total of 88 field sample plots were laid to enumerate trees, shrubs, herbs, climbers, etc. Biological richness parameters such as Shannon-Wiener biodiversity index, biodiversity value, ecosystem uniqueness were derived from field data. High biological richness is found in northern mixed dry deciduous forest and mixed dry deciduous forest with bamboo. More than 99% of such areas are falling under medium to high biological richness. Nearly 55% of the gentle and flat to gentle, slope categories were found to have low biological richness. Phytosociological analysis of sampled field data indicated that the number of trees per unit area is the lowest in the Savannah. In inaccessible areas, the species richness and number of trees per unit area is very high. Main forces causing disturbance are search for diamonds, dams on river Ken, settlements in and around the park, grazing and resource utilization by villagers for fodder, animal grazing, fuel-wood, timber, etc.     

Petrology and Sr-Nd isotope systematics of the Ahobil kimberlite (Pipe-16) from the Wajrakarur field,Eastern Dharwar craton,southern India

Detailed mineralogical, bulk-rock geochemical and Sr-Nd isotopic data for the recently discovered Ahobil kimberlite(Pipe-16) from the Wajrakarur kimberlite field(WKF), Eastern Dharwar craton(EDC),southern India, are presented. Two generations of compositionally distinct olivine, Ti-poor phlogopite showing orangeitic evolutionary trends, spinel displaying magmatic trend-1, abundant perovskite, Tirich hydrogarnet, calcite and serpentine are the various mineral constituents. On the basis of(i) liquidus mineral composition,(ii) bulk-rock chemistry, and(iii) Sr-Nd isotopic composition, we show that Ahobil kimberlite shares several characteristic features of archetypal kimberlites than orangeites and lamproites. Geochemical modelling indicate Ahobil kimberlite magma derivation from small-degree melting of a carbonated peridotite source having higher Gd/Yb and lower La/Sm in contrast to those of orangeites from the Eastern Dharwar and Bastar cratons of Indian shield. The T_Dm Nd model age(～2.0 Ga) of the Ahobil kimberlite is(i) significantly older than those(1.5～1.3 Ga) reported for Wajrakarur and Narayanpet kimberlites of EDC,(ii) indistinguishable from those of the Mesoproterozoic EDC lamproites,and(iii) strikingly coincides with the timing of the amalgamation of the Columbia supercontinent. High bulk-rock Fe-Ti contents and wide variation in oxygen fugacity fO_2, as inferred from perovskite oxybarometry, suggest non-prospective nature of the Ahobil kimberlite for diamond.     

Dynamic response analysis of tube array in partially filled calandria

An efficient procedure is presented for dynamic response analysis of horizontal tube array in partially filled calandria including hydrodynamic interaction effects. The procedure is general enough to consider the transfer of energy between the fluid-coupled tubes, and effects of moderator sloshing on the magnitude and the distribution of hydrodynamic forces. It has been demonstrated that the conventional added mass approach fails to represent behaviour of the tube array correctly, and it is therefore necessary to consider the flexibility of all the tubes along two directions simultaneously. The procedure presented can simulate the added damping effects due to hydrodynamic interaction. The possible use of a tuned damper tube is suggested for controlling sloshing effects for tube array in a calandria where tube frequencies and sloshing frequencies are closely spaced. The presence of surface damping in the tuned tube further brings down the response, and the suggested procedure can be effectively used to control unwarranted sloshing effects. Copyright © 1999 John Wiley & Sons, Ltd.     

In silico analysis of chromium-reducing OXR genes derived from tannery effluent-contaminated soil metagenome

Tannery effluent waste comprises various potentially toxic metals, including chromium (Cr) with varying acute or chronic toxicity. Cr(VI) is known to be a category-A carcinogen. Reduction of toxic Cr(VI) to Cr(III), which has lesser bioavailability, is one of the mechanisms used by many microbes to withstand Cr(VI) toxicity in the contaminated effluents. Oxidoreductase (OXRs) reduces toxic Cr(VI) to Cr(III); hence a thorough understanding of the OXRs is important for developing a suitable strategy to minimize Cr(VI) toxicity. Therefore, the OXR-encoding genes were sequenced using metagenomic DNA shotgun sequencing from the tannery effluent-contaminated soil. Six OXR-encoding genes were expressed in Escherichia coli, and OXR activity was confirmed by in situ quantitative assays. The six proteins were subjected to phylogenetic and evolutionary analysis. Further, detailed structural analysis of the two OXRs, namely, OXR3 and OXR8 with lowest and highest activity respectively, were investigated in silico for structural characteristics. The results revealed that both the proteins were soluble FMN-linked oxidoreductases. Eight conserved active site residues (Pro24, Thr26, Ala59, Tyr139, His178, Tyr180, His219, Tyr221, Arg269, and Lys360) in the enzyme OXR3 were predicted. Similarly, nine conserved active site residues (Pro20, Thr22, Ala55, Glu97, His191, Tyr193, Arg241, Cys334, and Arg335) were predicted in OXR8. The tertiary structure of OXR8 was an aldolase TIM barrel structure, like Thermus scotoductus chromate reductase. Docking with FMN revealed the involvement of all the nine predicted active site residues in FMN binding with Pro20, Thr22, and Cys334 as the most important ones.     

Drought hotspot analysis and risk assessment using probabilistic drought monitoring and severity–duration–frequency analysis

Drought hotspot identification requires continuous drought monitoring and spatial risk assessment. The present study analysed drought events in the agriculture‐dominated mid‐Mahanadi River Basin in Odisha, India, using crop water stress as a drought indicator. This drought index incorporated different factors that affect crop water deficit such as the cropping pattern, soil characteristics, and surface soil moisture. The drought monitoring framework utilized a relevance vector machine model‐based classification that provided the uncertainty associated with drought categorization. Using the proposed framework, drought hotspots are identified in the study region and compared with indices based on precipitation and soil moisture. Further, a bivariate copula is employed to model the agricultural drought characteristics and develop the drought severity–duration–frequency (S–D–F) relationships. The drought hotspot maps and S–D–F curves are developed for different locations in the region. These provided useful information on the site‐specific drought patterns and the characteristics of the devastating droughts of 2002 and 2012, characterized by an average drought duration of 7 months at several locations. The site‐specific risk of short‐ and long‐term agricultural droughts are then investigated using the conditional copula. The results suggest that the conditional return periods and the S–D–F curves are valuable tools to assess the spatial variability of drought risk in the region.     

Intra-day variability of three Seyfert galaxies measured with XMM-Newton

We present and analyze the variability of three Seyfert galaxies on intra-day timescales. We have analyzed in a uniform manner the 38 longest( 30 ks) observations made for NGC 4051, MCG-06–30–15 and NGC 4151 by XMM-Newton between 2000 and 2015. The nuclei were quite active during essentially all of these observations and the overall X-ray fluxes(0.3–10 keV) varied by an order of magnitude. Most of the observations do appear to show characteristic timescales, estimated through their auto-correlation functions, ranging between ~2.9 ks and ~45.3 ks. The hard(2–10 keV) and soft(0.3–2.0 keV) bands are very well correlated but consideration of their hardness ratios shows that the sources typically soften during flares. We also provide new estimates of the central black hole masses for these three AGNs that support the hypothesis that Narrow Line Seyfert 1 galaxies have relatively small central black holes.