Geochemical studies on Kashmir loess profiles     

G. S. Lodha  K. J. S. Sawhney  H. Razdan  D. P. Agrawal  N. Juyal 《Journal of Earth System Science》1987,96(2):135-145

Major and trace element concentrations of a few representative loess profiles in Kashmir valley are studied using EDXRF spectroscopy. Principal component analysis for pattern recognition has been employed to study association between elemental concentration variations in various horizons. The present study reveals that elements related to clay illuviation (K, Rb, Fe, Ti, Mn) and plant activity (Cu, Zn) are generally higher in B horizon of the palaeosols whereas Ca and Sr have a high concentration in the loess layers. Such an elemental concentration variation provides us with an objective index for identification and confirmation of palaeosols. There is further a close association in the movement of (i) K, Rb, (ii) Fe, Ti, Mn, (iii) Cu, Zn and (iv) Ca, Sr. These clusters of elements are also present in modern soils, suggesting that the soil characteristics in palaeosols have been preserved. Concentration of iron and titanium is also observed to be higher in loess profiles on Pir Panjal mountain flank which is dominated by basic rocks, compared to profiles on Himalayan flank, suggesting that the loess in Kashmir might have been derived from the nearby rocks in a localized way.  相似文献   

Determination of thermodynamic properties of (Fe,Mg)-pyroxenes at 1000 K by the emf method     

K.C. Sharma  R.D. Agrawal  M.L. Kapoor 《Earth and Planetary Science Letters》1987,85(1-3)

Emf measurements were made on the cell Pt|Fe,(Fe,Mg)_xSi₂O₆,SiO₂|(ZrO₂)_0.85(CaO)_0.15|Fe,FeO|Pt at 1000 K. Using the present data, the standard free energy of formation of ferrosilite (compound FeSiO₃), from the component oxides FeO and SiO₂, is calculated to be −6.35 ± 0.80 kJ/mol. The activity-composition relation for pyroxene solid solution shows that it has a positive deviation from ideality at 1000 K. The present results are compared with the results of other workers.ΔG_mix andΔG^ex are calculated and plotted againstN_FeSiO3.  相似文献   

Heat and mass transfer of an oscillatory flow with Hall current     

H. L. Agrawal  P. C. Ram  V. Singh 《Astrophysics and Space Science》1983,90(2):445-454

In the first part of these notes new expressions—simpler than any previously obtained—are presented in integral form for the derivatives of the α _n ⁰ -functions (required for an interpretation of the observed light changes of eclipsing variables) with respect to the fractional radiir _{1, 2} and projected separation δ of their centres in terms of the modified Bessel functionsK _{0, 1} (x) of the second kind; and utilized for establishing new asymptotic formulae for the computation of ‘boundary integrals’ of the formJ _?1 ⁰ ,n(μ). In the second part of this paper, by a resort to bi-polar coordinates, we shall establish a new type of expansions for the α _n ⁰ -functions valid for any type of eclipses, and converging faster than the expansions of the cross-correlation integral of the form (1) for α _n ⁰ that have so far been established.  相似文献   

Journey through the birth,growth and maturity of X-ray astronomy     

Prahlad Chandra Agrawal 《天文和天体物理学研究(英文版)》2019,(10)

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Energy spectrum and time variations of hard X-rays from Cyg X-1     

P. C. Agrawal  G. S. Gokhale  V. S. Iyengar  P. K. Kunte  R. K. Manchanda  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):408-424

Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E ^{–(1.92±0.10)} photons cm^–2s^–1 keV^–1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E ^{–(1.89±0.22)} photons cm^–2s^–1 keV^–1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of E ^–2, while below 20 keV the spectrum varies fromE ^–1.7 toE ^–5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.  相似文献   

Time variations of hard X-rays from Sco X-1     

M. Matsuoka  M. Fujii  S. Miyamoto  J. Nishimura  M. Oda  Y. Ogawara  S. Hayakawa  I. Kasahara  F. Makino  Y. Tanaka  P. C. Agrawal  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):472-490

Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation.  相似文献   

Reduction of structural Fe(III) in nontronite by methanogen Methanosarcina barkeri     

Deng Liu  Michael E. Bishop  Abinash Agrawal  Dennis D. Eberl 《Geochimica et cosmochimica acta》2011,75(4):1057-60

Clay minerals and methanogens are ubiquitous and co-exist in anoxic environments, yet it is unclear whether methanogens are able to reduce structural Fe(III) in clay minerals. In this study, the ability of methanogen Methanosarcina barkeri to reduce structural Fe(III) in iron-rich smectite (nontronite NAu-2) and the relationship between iron reduction and methanogenesis were investigated. Bioreduction experiments were conducted in growth medium using three types of substrate: H₂/CO₂, methanol, and acetate. Time course methane production and hydrogen consumption were measured by gas chromatography. M. barkeri was able to reduce structural Fe(III) in NAu-2 with H₂/CO₂ and methanol as substrate, but not with acetate. The extent of bioreduction, as measured by the 1,10-phenanthroline method, was 7-13% with H₂/CO₂ as substrate, depending on nontronite concentration (5-10 g/L). The extent was higher when methanol was used as a substrate, reaching 25-33%. Methanogenesis was inhibited by Fe(III) reduction in the H₂/CO₂ culture, but enhanced when methanol was used. High charge smectite and biogenic silica formed as a result of bioreduction. Our results suggest that methanogens may play an important role in biogeochemical cycling of iron in clay minerals and may have important implications for the global methane budget.  相似文献   

X-rays from supernovae remants 3C 400.2 (≡ G53.7-2.2) and MSH 15-56     

P. C. Agrawal  G. R. Riegler  K. P. Singh 《Astrophysics and Space Science》1983,89(2):279-283

Detection of two new soft X-ray sources and their identification with the supernova remnants (RNRs) 3C400.2 and MSH 15-56, is reported. From the observed X-ray flux in the 0.7–2.0 keV energy range, the X-ray luminosity of 3C400.2 is derived to be in the range of (2.7–5.3)×10³⁵ ergs s^?1 and that of MSH 15-56 in the range of (0.9–1.6)×10³⁵ ergs s^?1. If we use the standard adiabatic shockwave model for the SNR's, an age of ～(1.4–3.2)×10⁴ yr is derived for 3C400.2 whereas MSH 15-56 is found to be younger of an age of (5–10)×10³ yr.  相似文献   

Heat and mass transfer in rotating fluid with Hall current,I     

H. L. Agrawal  P. C. Ram  V. Singh 《Astrophysics and Space Science》1983,96(2):245-254

Hall effects on the hydromagnetic free convection resulting from the combined effects of thermal and mass diffusion of an electrically conducting liquid past an infinite vertical porous plate in a rotating system have been analysed. The expressions for the mean velocity, mean temperature in the boundary layer and the mean skin friction, the mean rate of heat transfer on the plate are derived. The effects of magnetic parameterM, Hall parameterm, Schmidt number Sc, and Ekman numberE on the flow field, are discussed with the help of graphs and tables.  相似文献   

Data modelling for crude oil migration studies using ranking method: a rapid geo-tracer technique for geochemists     

Oluwabamise L. Faboya  Oluwadayo O. Sonibare  Olusola T. Faboya  Utkarsh Agrawal  Zewen Liao  O. Ekundayo 《中国地球化学学报》2018,37(6):901-910

The direction of oil charges within a field in the Niger Delta, Nigeria was determined by the sum of differences ranking method of carbazole concentrations after ascertaining other possible geological constraints on their compositional variations. The principle is that the smaller the sum, the closer the well to the source kitchen. The approach makes use of carbazoles’ interaction with the matrix, which leads to a reduction in their concentration with increasing distance from the source kitchen, allowing prediction of the charging direction. A wide range of compositional variations was observed for C₁ (806.72–2152.90 μg/g) and C₂ (767–2469.72 μg/g) carbazoles within the field. Based on these results, we inferred a filling pathway orientation from west to east. This suggests that the source kitchen—the most promising region for oil exploration—is located in the western part of the oil field.  相似文献