Exsolution textures in orthopyroxene in aluminous granulites as indicators of UHT metamorphism: New evidence from the Eastern Ghats Belt, India

Highly aluminous orthopyroxene, coexisting with sapphirine, cordierite, sillimanite, quartz and garnet in various combinations, constitute granoblastic mosaic peak metamorphic assemblages in aluminous granulites from three localities in the Eastern Ghats Belt, India. Orthopyroxene contains four types of intergrowths: (a) involving sapphirine with or without cordierite, (b) involving spinel, but without sapphirine, (c) involving cordierite, but without sapphirine and spinel, and (d) involving garnet, without sapphirine, spinel or cordierite. On the basis of textural and compositional data, origin of the intergrowths is ascribed to breakdown of Mg-Tschermak component, locally also involving Fe- and Ti-Tschermak. An attempt is made to compute the “pre-breakdown” compositions of orthopyroxene by image analysis, which shows maximum Al₂O₃ content of 13.4 wt.% in the pristine orthopyroxene. Geothermometry, phase equilibria consideration and application of existing experimental data on alumina solubility in orthopyroxene coexisting with sapphirine and quartz, collectively indicate extreme thermal conditions of metamorphism (> 1000 °C) for the studied assemblages. This re-affirms the notion that Al₂O₃ solubility in orthopyroxene is the most powerful indicator of UHT metamorphism (Harley, S.L., 2004. Extending our understanding of ultrahigh temperature crustal metamorphism. J. Mineral. Petrol. Sci. 99, 140–158). The intergrowths are considered to have formed due to cooling from the thermal peak spanning a temperature range of approximately 150 °C. Appearance of diverse types of intergrowths is probably related to subtle differences in bulk composition, particularly Fe:Mg ratios.     

The AGN and gas disc in the low surface brightness galaxy PGC 045080

We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disc and massive H  i gas content. Radio continuum observations of the galaxy were carried out at 320, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disc at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with active galactic nucleus (AGN) activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the Hα flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centres can host significant AGN activity. We also mapped the H  i gas disc and velocity field in PGC 045080. The H  i disc extends well beyond the optical disc and appears warped. In the H  i intensity maps, the disc appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disc but is fairly uniform in the other half. We derived the H  i rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ∼190 km s⁻¹.     

Rapidly rotating stellar models with radiation pressure

A modified perturbation technique, developed earlier by the authors, has been used to study the effect of rapid uniform and differential rotation on the equilibrium structure of early type stars. The models are in convective equilibrium with significant radiation pressure. The effect of both uniform and differential rotation on various structural parameters like mass, radius, central condensation etc., are calculated for different values ofy _c (the ratio of central radiation pressure to central gas pressure).     

Radial and nonradial oscillations of partially-degenerate stellar masses

The radial and nonradial modes of oscillation of partially degenerate stellar masses have been studied. It is found that the radial mode shows a decrease with increased central condensation and the configuration tends, therefore, towards a marginally stable point with increased degeneracy. The nonradial modes forl=2 and 3 also shows a similar trend. However, the decrease is slower than the corresponding radial mode.     

Exact solution of the problem of diffuse reflection and transmission in Rayleigh scattering by use of the Laplace transform and the theory of linear singular operators

We have considered six scalar equations which are obtained from the vector transport equation for radiative transfer to the problem of diffuse reflection and transmission in finite plane-parallel Rayleigh scattering atmosphere. By use of the Laplace transform and the theory of linear singular operators these equations have been solved exactly to get the angular distribution of the intensity diffusely reflected from the surface and diffusely transmitted below the surface.     

Inhomogeneous perfect fluid cosmologies in (4+1) dimensions

Exact solutions are obtained in (4+1) dimensions for plane symmetric and cylindrically symmetric inhomogeneous spacetimes. In the former case the three space depends on time only while the metric corresponding to the extra dimension is dependent on space as well as time coordinates. The cylindrically symmetric nonstatic solutions for the perfect fluid have no singularity near the axis, but show big bang type of singularity in the finite past. One of the classes of such solutions satisfies the barotropic equation of state of the form =p. Static solutions with cylindrically symmetric solutions are also obtained in 5 dimensions.     

The effect of solar parameters on seasonal variation of 5893 Å line intensity at Calcutta

The purpose of this paper is to present the correlation of seasonal variation of 5893 Å line intensity with relative sunspot numbers, solar flare numbers and the variable component of 10.7 cm solar flux. A study has been made and the following important results have been obtained.

1. The intensity of 5893 Å line at Calcutta shows periodic variation with different solar parameters during descending part of secondary peak of 21st solar cycle (1984–1985).
2. 5893 Å line intensity of Mt. Abu also shows periodic variation with solar parameters during the period 1965–1968 when there was a peak phase of 20th solar cycle.
3. A possible explanation for such type of variation is also presented.

     

Inventory of degraded lands of Palamau district, Bihar — A remote sensing approach

In this study, an attempt has keen made for the identification, categorisation and mapping of degraded lands in Palamau district of Bihar using remotely sensed data (IRS-1A, raise colour composite, on 1:50,000 scale), It was observed that water erosion is the main cause of land degradation affecting 6.27 per cent area of the district, of which 5.22 per cent is subjected to severe to very severe erosion and remaining 1.05 per cent is moderately to severely gulleid land Degradation due to rock quarries, mine spoils and dumps accounted for only 0.01 per cent of the district area. Degraded lands were mostly confined to agricultural areas (4.76%) follwed by forest lands (1.10%) and opert-scrub/pastures (0.42%), respectively, Subdivision-wise categorisation of degraded lands was also attempted for efficient location-speeific reclamation planning and easy monitoring.     

Observed variations of σθ and σΦ in the nocturnal drainage flow in a deep valley

The variations of and in the drainage flow in the Brush Creek valley of western Colorado are investigated using data from Doppler acoustic sodars and instrumented towers. The data were obtained on two experimental nights during the 1984 ASCOT field study. There is good agreement between the variations derived from low-level observations of the sodars and those derived from the towers located throughout the valley. The observed hourly average and in the nocturnal drainage flow are about 20 ° to 25 ° and 5 °, respectively; these values are much larger than those generally observed over flat terrain during nighttime stable conditions. After sunrise (about 0600 MST), as the valley warms and the flow direction changes to up-valley, these parameters increase sharply to their peak values at about 0800 MST and then decrease to their normal daytime values after about two hours.In the drainage flow, the hourly average varies inversely with wind speed according to the relation u 0.7ms^-1. The vertical standard deviation is much less enhanced by complex terrain than the horizontal standard deviation. The observed values are predicted fairly well by the local similarity theory.Oak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 andOak Ridge Associated Universities (ORAU) Summer Research Participant at ATDD in 1987 and