Spatial and temporal analysis of rainfall and temperature trend of India   总被引：3，自引：1，他引：2  

Arun Mondal  Deepak Khare  Sananda Kundu 《Theoretical and Applied Climatology》2015,122(1-2):143-158

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Prebiotic organic synthesis in early Earth and Mars atmospheres: Laboratory experiments with quantitative determination of products formed in a cold plasma flow reactor     

Michael N. Heinrich  Bishun N. Khare 《Icarus》2007,191(2):765-778

The goal of this study was to explore prebiotic chemistry in a range of plausible early Earth and Mars atmospheres. To achieve this laboratory continuous flow plasma irradiation experiments were performed on N₂/H₂/CO/CO₂ gas mixtures chosen to represent mildly reducing early Earth and Mars atmospheres derived from a secondary volcanic outgassing of volatiles in chemical equilibrium with magmas near present day oxidation state. Under mildly reducing conditions (91.79% N₂, 5.89% H₂, 2.21% CO, and 0.11% CO₂), simple nitriles are produced in the gas phase with yield (G in molecules per 100 eV), for the key prebiotic marker molecule HCN at G∼1×¹⁰⁻³ (0.1 nmol J⁻¹). In this atmosphere localized HCN concentrations possibly could approach the 10⁻² M needed for HCN oligomerization. Yields under mildly oxidizing conditions (45.5% N₂, 0.1% H₂, 27.2% CO, 27.2% CO₂) are significantly less as expected, with HCN at G∼3×¹⁰⁻⁵ (). Yields in a Triton atmosphere which can be plausibly extrapolated to represent what might be produced in trace CH₄ conditions (99.9% N₂, 0.1% CH₄) are significant with HCN at G∼1×¹⁰⁻² (1 nmol J⁻¹) and tholins produced. Recently higher methane abundance atmospheres have been examined for their greenhouse warming potential, and higher abundance hydrogen atmospheres have been proposed based on a low early Earth exosphere temperature. A reducing (64.04% N₂, 28.8% H₂, 3.60% CO₂, and 3.56% CH₄), representing a high CH₄ and H₂ abundance early Earth atmosphere had HCN yields of G∼5×¹⁰⁻³ (0.5 nmol J⁻¹). Tholins generated in high methane hydrogen gas mixtures is much less than in a similar mixture without hydrogen. The same mixture with the oxidizing component CO₂ removed (66.43% N₂, 29.88% H₂, 0% CO₂, and 3.69% CH₄) had HCN yields of G∼1×¹⁰⁻³ (0.1 nmol J⁻¹) but more significant tholin yields.  相似文献   

Do damped and sub-damped Lyman-alpha absorbers arise in galaxies of different masses?     

Varsha P. Kulkarni  Pushpa Khare  Debopam Som  Joseph Meiring  Donald G. York  Celine Péroux  James T. Lauroesch 《New Astronomy》2010,15(8):735-743

We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra differ intrinsically in metallicity, and whether they could arise in galaxies of different masses. Using the recent measurements of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm that sub-DLAs have higher mean metallicities than DLAs, especially at z ? 2. We find that the intercept of the metallicity-redshift relation derived from Zn and S is higher than that derived from Fe by 0.5–0.6 dex. We also show that, while there is a correlation between the metallicity and the rest equivalent width of Mg II λ2796 or Fe II λ2599 for DLAs, no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II selection criteria employed in the discovery of both types of systems at lower redshifts, the difference between metallicities of DLAs and sub-DLAs appears to be real and not an artefact of selection. This conclusion is supported by our simulations of Mg II λ2796 and Fe II λ2599 lines for a wide range of physical conditions. On examining the velocity spreads of the absorbers, we find that sub-DLAs show somewhat higher mean and median velocity spreads (Δv), and an excess of systems with Δv > 150 km s^?1, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and thick disk stars, possibly suggesting different stellar populations. The absorber data appear to be consistent with galaxy down-sizing. The data are also consistent with the relative number densities of low-mass and high-mass galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on average than DLAs.  相似文献   

Electrochemical interaction of Shewanella oneidensis MR-1 and its outer membrane cytochromes OmcA and MtrC with hematite electrodes     

Leisa A. Meitl  Carrick M. Eggleston  Patricia J.S. Colberg  Nidhi Khare  Catherine L. Reardon  Liang Shi 《Geochimica et cosmochimica acta》2009,73(18):5292-5307

Bacterial metal reduction is an important biogeochemical process in anaerobic environments. An understanding of electron transfer pathways from dissimilatory metal-reducing bacteria (DMRB) to solid phase metal (hydr)oxides is important for understanding metal redox cycling in soils and sediments, for utilizing DMRB in bioremedation, and for developing technologies such as microbial fuel cells. Here we hypothesize that the outer membrane cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 are the only terminal reductases capable of direct electron transfer to a hematite working electrode. Cyclic voltammetry (CV) was used to study electron transfer between hematite electrodes and protein films, S. oneidensis MR-1 wild-type cell suspensions, and cytochrome deletion mutants. After controlling for hematite electrode dissolution at negative potential, the midpoint potentials of adsorbed OmcA and MtrC were measured (−201 mV and −163 mV vs. Ag/AgCl, respectively). Cell suspensions of wild-type MR-1, deletion mutants deficient in OmcA (ΔomcA), MtrC (ΔmtrC), and both OmcA and MtrC (ΔmtrC–ΔomcA) were also studied; voltammograms for ΔmtrC–ΔomcA were indistinguishable from the control. When the control was subtracted from the single deletion mutant voltammograms, redox peaks were consistent with the present cytochrome (i.e., ΔomcA consistent with MtrC and ΔmtrC consistent with OmcA). The results indicate that OmcA and MtrC are capable of direct electron exchange with hematite electrodes, consistent with a role as terminal reductases in the S. oneidensis MR-1 anaerobic respiratory pathway involving ferric minerals. There was no evidence for other terminal reductases operating under the conditions investigated. A Marcus-based approach to electron transfer kinetics indicated that the rate constant for electron transfer k_et varies from 0.025 s⁻¹ in the absence of a barrier to 63.5 s⁻¹ with a 0.2 eV barrier.  相似文献   

Textural characteristics,distribution pattern and provenance of heavy minerals in glacial sediments of Schirmacher Oasis,east Antarctica     

Ashok K. Srivastava  Pravin S. Ingle  Neloy Khare 《Journal of the Geological Society of India》2010,75(2):393-402

Heavy minerals of twenty sediment samples, belonging to polar ice sheet, lake, mainland area and shelf region of Schirmacher Oasis, east Antarctica, have been studied for their textural characteristics, abundance and provenance determination. The heavy crop is represented by zircon, tourmaline, rutile, garnet, hypersthene, hornblende, chlorite, enstatite, lawsonite, kyanite, sillimanite, zoisite, andalusite, spinel, topaz and opaques. The assemblage, in general, is dominated by hornblende-hypersthene-garnet assemblage, followed by kyanite-sillimanite-andalusite and zircontourmaline-rutile. The high concentration of specific minerals of metamorphic origin reveals high-grade metamorphic terrain as the primary source. The ZTR ratio is low showing low mineralogical maturity. An attempt has also been made to compare the trends of heavy minerals of various sub glacial regions with those of the average values of entire area.  相似文献   

Narrow associated quasi-stellar object absorbers: clustering, outflows and the line-of-sight proximity effect     

Vivienne Wild  Guinevere Kauffmann  Simon White  Donald York  Matthew Lehnert  Timothy Heckman  Patrick B. Hall  Pushpa Khare  Britt Lundgren  Donald P. Schneider  Daniel Vanden Berk 《Monthly notices of the Royal Astronomical Society》2008,388(1):227-241

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3), we investigate how narrow (<700 km s⁻¹) C  iv and Mg  ii quasar absorption-line systems are distributed around quasars. The C  iv absorbers lie in the redshift range 1.6 < z < 4 and the Mg  ii absorbers in the range 0.4 < z < 2.2. By correlating absorbers with quasars on different but neighbouring lines of sight, we measure the clustering of absorbers around quasars on comoving scales between 4 and 30 Mpc. The observed comoving correlation lengths are   r _o∼ 5 h ⁻¹Mpc  , similar to those observed for bright galaxies at these redshifts. Comparing correlations between absorbers and the quasars, in whose spectra they are identified, then implies: (i) that quasars destroy absorbers to comoving distances of ∼300 kpc (C  iv ) and ∼800 kpc (Mg  ii ) along their lines of sight; (ii) that ≳40 per cent of C  iv absorbers within 3000 km s⁻¹ of the quasi-stellar object are not a result of large-scale clustering but rather are directly associated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow velocities of the order of 12 000 km s⁻¹; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars and (v) that a small high-velocity outflow component is also observed in the Mg  ii population. We also find an indication that absorption systems within 3000 km s⁻¹ are more abundant for radio-loud quasars than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive haloes, or that their radio activity generates an additional low-velocity outflow, or both.  相似文献   

Morphometric and rheological study of lunar domes of Marius Hills volcanic complex region using Chandrayaan-1 and recent datasets     

A S Arya  R P Rajasekhar  Koyel Sur  B Gopala Krishna  K Suresh  T P Srinivasan  K V Iyer  P Chauhan  Ajai  A S Kiran Kumar  A D Pandey  A Khare  P K Verma 《Journal of Earth System Science》2018,127(5):70

Marius Hills volcanic complex is one of the most important regions on the lunar surface having an abundant number of volcanic features like domes and cones. Systematic mapping of 106 domes/cones in the Marius Hills region was carried out in this study using high-resolution orthoimage and digital elevation models of Chandrayaan-1 and Kaguya missions. Various morphometric parameters like diameter, height, volume, flank slope, circularity index and form factor are derived for all the mapped domes. The rheological parameters, such as viscosity and eruption rate are estimated for isolated domes and cones superimposed over low domes. The morphometric and rheological properties of these domes are comparable to those located in the area near to Hortensius crater and other mare regions. Surface ages derived for a selected region in NW portion of the Marius Hills volcanic complex using crater size-frequency distribution technique yields ages of 2.98 and 1.91 Ga. It suggests that the domes in this region formed at about 2.98 Ga ago, and then, the younger mare basalts likely embayed this region about 1.98 Ga ago. Stratigraphic sequence of rilles, wrinkle ridge and domes shows that wrinkle ridges are the oldest, while the rilles are younger than the domes.  相似文献   

Neutrino degeneracy and the primordial abundance of helium and deuterium     

Pushpa Khare  B. B. Deo 《Journal of Astrophysics and Astronomy》1983,4(4):301-306

Recent observations indicate that the primordial abundance of⁴He could be smaller than 0.24. It may then be necessary to invoke neutrino degeneracy in the early universe to explain the primordial abundances of helium and deuterium. It is shown here that the necessary degeneracy, though small, gives rise to a large asymmetry between the present number densities of neutrinos and antineutrinos. The effect of degeneracy on the upper limit to the neutrino masses is also considered.  相似文献   

Formate and acetate levels compared in monsoon and winter rainwater at Dayalbagh, Agra (India)     

Nandini Kumar  U. C. Kulshrestha  A. Saxena  P. Khare  K. M. Kumari  S. S. Srivastava 《Journal of Atmospheric Chemistry》1996,23(1):81-87

A total of 59 rainwater samples were collected during the winter and monsoon (1991–92) at Dayalbagh, Agra. This site is relatively free from the influence of anthropogenic emissions and the volume-weighted average concentrations (VWA) of formate in the winter and monsoon were 22.5±6, 16.1±3 while acetate VWAs were 17.1±5 and 13.8±3 mol l^-1, respectively. Although the VWAs varied between seasons, it was not statistically different. Total deposition (in mmol m^-2) varied between season (winter formate, 1.4; acetate, 1.1; monsoon formate, 7.4; acetate, 6.4). A difference in VWA values may have occurred as a result of the dilution factor; the total rain depth from collected samples in the monsoon was 46 cm while that in winter was 6.3 cm. Sources at this site may be anthropogenic and natural; scavenging from the vapour phase, washout of soil particles and emissions from vegetative sources are probably important sources for formate and acetate.  相似文献   

Can benthic foraminiferal morpho-groups be used as indicators of paleomonsoonal precipitation?     

Rajiv Nigam  Neloy Khare  D.V. Borole 《Estuarine, Coastal and Shelf Science》1992,34(6)

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