Weathering control over geomorphology of supermature Proterozoic Delhi quartzites of India

Quartz and quartzite are thought to be resistant as a mineral and a rock respectively; however, we have shown that the presence of small amounts of pyrite in the quartzites makes them vulnerable to weathering. We observe that weathering of Proterozoic quartzite in the semi‐arid conditions around Delhi proceeded from fractures towards the inside and produced weathering rinds. The chemical index of alteration (CIA), which is actually a measure of weathering of aluminosilicate minerals, increases from the core outwards, through the rinds. Although aluminosilicate minerals occur only as minor phases (<2 per cent), their weathering indicates a movement of the weathering front from the periphery towards the core. We have suggested a coupled mechanism in which the dissolution of pyrites by moving water produced a sulphate‐bearing acidic solution and ferrous iron, which reacted with aluminosilicate minerals and quartz, respectively. This initially makes the Delhi quartzite porous and subsequently friable. The total disintegration of grain to grain contacts imparted friability to this quartzite to produce silica sand. Subsequent physical erosion of loose sand, produced during rind development in the outermost zones, has given rise to features like tors, spheroids, gullies, cavities and small‐scale caves on these quartzites. Thus, the terrain has acquired ruggedness in semi‐arid conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

Model Tests and Field Experiments for Fragmentation Assessment During Ringhole Blasting in BG Panels

Experimental blasts were conducted in concrete blocks of known strengths to correlate field results in Blasting Gallery (BG) panels of GDK-10 Incline for improving fragmentation of coal to an optimum level so that blasted coal could easily be lifted totally by remote controlled LHDs and thereby mitigating the possibility of occurrence of spontaneous heating in BG districts before exhaustion of the panel. Various charge loading parameters and consequent breakage results were critically analyzed to arrive at a constructive conclusion, which could satisfactory improve the blast results.     

Local site effects in Latur, India: an empirical study based on the aftershocks of the Killari earthquake of September 29, 1993

The site amplification is estimated at five seismic stations of the Latur region using the horizontal to vertical spectral ratios of 33 aftershocks of the main Killari earthquake of September 29, 1993 (UTC). Spectral amplifications, ranging from a factor of 2–6 are found to vary with frequency at different places. Significant amplification is found at four sites within the Latur region, at Basavakalyan, Kasgi, Killari, and Mudgad Eakoji villages. Our results show a positive correlation between the site amplification and the damage pattern in area. The pattern and the nature of the site amplification estimated in the present study corroborates also with the analytical models and the borehole data indicating alternating layers of unconsolidated sediments and basaltic rocks.     

Influence of accretion-disk models on the structure of the Iron Κ<Subscript>α</Subscript> line

Broad iron Κ_α emission with a characteristic two-peaked profile is observed in most Seyfert galaxies in the X-ray. We have calculated the profiles of such lines emitted by an accretion disk in a Schwartzschild metric. The dependence of the temperature distribution in the disk on the line shape is demonstrated. All the calculations include general relativistic effects. The disk material is assumed to move in circular geodesics in the equatorial plane. The line profile is extremely complex, even in a traditional model for the radial temperature distribution, complicating interpretation of the observational data.     

Radio identification and continuum spectra of decameter-wavelength sources

The paper describes a method for the radio identification of decameter-wavelength sources based on their continuum spectra and analysis of their coordinates in relatively large error boxes surrounding a specified position on the sky. The distribution of continuum spectra and identifications in other wavelength ranges are analyzed for the resulting radio catalog. Using identifications with the FIRST and NVSS surveys, the statistics of the spectral index-size and spectral index-flux density distributions for steep-spectrum sources have been studied, and a catalog of ultrasteep-spectrum (α相似文献   

A coupled,dynamical and chemical model for the prestellar core L1544: Comparison of modeled and observed C<Superscript>18</Superscript>O,HCO<Superscript>+</Superscript>, and CS emission spectra

We consider radiative transfer in C¹⁸O, HCO⁺, and CS molecular lines in a spherically symmetrical, coupled, dynamical and chemical model of a prestellar core whose evolution is determined by ambipolar diffusion. Theoretical and observed line profiles are compared for the well-studied core L1544, which may be a collapsing protostellar cloud. We study the relationship between the line shapes and model parameters. The structure of the envelope and kinematic parameters of the cloud are the most important factors determining the shape of the lines. Varying the input model parameters for the radiative transfer—the kinetic temperature and microturbulent velocity—within the limits imposed by observations does not result in any substantial variations of the line profiles. The comparison between the model and observed spectra indicates that L1544 displays a flattened structure, and is viewed at an oblique angle. A two-dimensional model is needed to reproduce this structure.     

Laser microprobe for the study of noble gases and nitrogen in single grains: A case study of individual chondrules from the Dhajala meteorite

A laser microprobe capable of analysing nitrogen and noble gases in individual grains with masses less than a milligram is described. It can be used in both continuous wave (CW) mode, useful for stepwise heating of an individual grain, as well as in pulsed mode, useful for ablating material from a small selected area of a sample, for gas extraction. We could achieve low blanks (in ccSTP units) for 4He(4.8 x 10{-12}),²²Ne(1.0 x 10{-12}),³⁶Ar(1.0 x10 ^-13),⁸⁴Kr(2.9 x 10{-14}),¹³² Xe(2.6 x 10{-14}), and N (87 pg), using this system. Preliminary data for individual chondrules from the Dhajala meteorite show that noble gases and nitrogen from grains as small as 170 microgram can be analysed using the present laser microprobe setup. The amount of trapped neon in Dhajala chondrules is very small, and nitrogen in the chondrules is isotopically heavier as compared to the bulk meteorite.     

The chemical composition of stars in the globular clusters M 10, M 12, and M 71

The abundances of 19 chemical elements in the atmospheres of five stars belonging to three globular clusters have been determined by applying the model-atmospheremethod to 430.0–790.0 nm spectra obtained with the échelle spectrometer of the 6-m telescope of the Special Astrophysical Observatory. The abundances of silicon, calcium, iron-peak elements, copper, zinc, and neutron-capture elements follow the abundance patterns for halo stars. The abundance of sodium in M 10 giants provides evidence that different mixing mechanisms operate in halo and cluster stars or that light elements are enriched in different ways in the pre-stellar matter from which some globular clusters and halo stars were formed.     

The empirical Melchior laws and parametric excitation of the Chandler wobble

Models of the motion of the terrestrial reference frame with respect to an inertial frame can describe the motions of the Earth-Moon system, which are traditionally separated into precession, nutation, the polar motion, and rotation about the Earth’s axis. Existing theoretical models do not describe variations in the Earth-orientation parameters with the required accuracy, so that the current polar coordinates and duration of the day must be determined from observations. To improve theoretical models for the time dependence of the coordinates of the Earth’s pole, we examine the possible excitation of the Chandler wobble due to internal properties of the Earth-Moon system. A differential equation describing the parametric resonance in the Earth-Moon system is obtained for the first region of the parametric excitation. The solution of this equation analytically describes the finite amplitudes of the nonlinear conservative system. The theoretical results are compared with the empirical laws of Melchior deduced from observational data on the coordinates of the Earth’s pole.