Electron temperatures in W51 complex from high resolution,low frequency radio observations

W51 is a giant radio complex lying along the tangent to the Sagitarius arm at a distance of about 7 kpc from the Sun, with an extension of about 1° in the sky. It is divided into three components A, B, C where W51A and W51B consist of many compact HII regions while W51C is a supernova remnant. We have made continuum radio observations of these HII regions of the W51 complex at 240, 610, 1060 and 1400 MHz using GMRT with lower resolution (20″ × 15″) at the lowest frequency. The observed spectra of the prominent thermal subcomponents of W51 have been fitted to a free-free emission spectrum and their physical properties like electron temperatures and emission measures have been estimated. The electron temperatures from continuum spectra are found to be lower than the temperatures reported from radio recombination line (RRL) studies of these HII regions indicating the need for a filling factor even at this resolution. Also, the observed brightness at 240 MHz is found to be higher than expected from the best fits suggesting the need for a multicomponent model for the region.     

Arsenic mobility in fluvial environment of the Ganga Plain,northern India

In the northern part of the Indian sub-continent, the Gomati River (a tributary of the Ganga River) was selected to study the dynamics of Arsenic (As) mobilization in fluvial environment of the Ganga Plain. It is a 900-km-long, groundwater-fed, low-gradient, alluvial river characterized by monsoon-controlled peaked discharge. Thirty-six water samples were collected from the river and its tributaries at low discharge during winter and summer seasons and were analysed by ICP-MS. Dissolved As and Fe concentrations were found in the range of 1.29–9.62 and 47.84–431.92 μg/L, respectively. Arsenic concentration in the Gomati River water has been detected higher than in its tributaries water and characteristically increases in downstream, attributed to the downstream increasing of Fe₂O₃ content, sedimentary organic carbon and silt-clay content in the river sediments. Significant correlation of determination (r ² = 0.68) was also observed between As and Fe concentrations in the river water. Arsenic concentrations in the river water are likely to follow the seasonal temperature variation and reach the level of World Health Organization’s permissible limit (10 μg/L) for drinking water in summer season. The Gomati River longitudinally develops reducing conditions after the monsoon season that mobilize As into the river water. First, dissolved As enters into pore-water of the river bed sediments by the reductive dissolution of Fe-oxides/hydroxides due to microbial degradation of sedimentary organic matter. Thereafter, it moves upward as well as down slope into the river water column. Anthropogenically induced biogeochemical processes and tropical climatic condition have been considered the responsible factors that favour the release of As in the fluvial environment of the Ganga Plain. The present study can be considered as an environmental alarm for future as groundwater resources of the Ganga–Brahmaputra Delta are seriously affecting the human–environment relationship at present.     

Turbulent compressible convection with rotation–penetration below a convection zone

We examine the behaviour of penetrative turbulent compressible convection under the influence of rotation by means of three dimensional numerical simulations. We estimate the extent of penetration below a stellar-type rotating convection zone in an f-plane configuration. Several models have been computed with a stable-unstable-stable configuration by varying the rotation rate (Ω), the inclination of the rotation vector and the stability of the lower stable layer. The spatial and temporal average of kinetic energy flux (F_k) is computed for several turnover times after the fluid has thermally relaxed and is used to estimate the amount of penetration below the convectively unstable layer. Our numerical experiments show that with the increase in rotational velocity, the downward penetration decreases. A similar behaviour is observed when the stability of the lower stable layer is increased in a rotating configuration. Furthermore, the relative stability parameter S shows an S ^−1/4 dependence on the penetration distance implying the existence of a thermal adjustment region in the lower stable layer rather than a nearly adiabatic penetration region.     

Morpho‐sedimentary records at the Brahmaputra River exit,NE Himalaya: climate–tectonic interplay during the Late Pleistocene–Holocene

Morphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate–tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T₃, (2) a high‐angle fan (3) terrace T₂, (4) terrace T₁ and (5) a low‐angle fan. Geomorphic consideration suggests that the fan terrace T₃ and high‐angle fans are the oldest units and were coeval. The low‐angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T₃ formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high‐angle fan formed during 15–10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T₂ formed during 10–8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T₁ formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low‐angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault. Copyright © 2008 John Wiley & Sons, Ltd.     

Propagation of surface waves on the surface of a non-homogeneous aeolotropic cylindrical shell

Summary The object of the present paper is to investigate the propagation of surface waves on a non-homogeneous aeolotropic cylindrical shell surrounded by vacuum. The elastic constantsc _ij (i, j=1,2...) and density of the material of the shell are assumed to be of the form and respectively, where _ij, ₀ are constants andk ₁,k ₂ are any integers.     

Asymmetric spreading across the Juan de Fuca and Gorda rises as obtained from a detailed magnetic survey

Marine magnetic data collected along 37 east-west lines off the Washington and Oregon coast between 42°N and 48°N westward to 144°W have been interpreted. Our interpretation shows that decrease in the offsets of the anomalies across the Surveyor fracture zone and the presence of undisturbed north-south lineations east of it are the result of continuous asymmetric spreading along the Surveyor fracture zone. The survey has delineated the extension of the Blanco fracture zone north-westward to about 133°W. Movement along the Blanco fracture zone was initiated about 15 million years ago. The undisturbed north-south trend of the magnetic anomalies between latitudes 42°N and 48°N and longitudes 133°W and 136°W is interpreted as the interval (22 to 15 my) during which the Juan de Fuca and Gorda rises were one continuous structure. West of 137° the Surveyor, Sedna and three minor fracture zones are mapped.     

Petrography and classification of the arenites of the Chari Series in the Jurassic rocks of Central Kutch,Gujarat (India)

The Chari arenites of the Jurassic rocks of Central Kutch form a real transition in the orthoquartzite—carbonate facies. The arenites pose a classificatory problem due to the presence of a good amount of reworked biogenic constituents. In order to get a correct picture, a new classification is proposed to classify these arenites in a meaningful manner, with quartz + rock fragments, felspar, and biogenic constituents as the three poles of the triangle.The petrographic characteristics of the arenites with a brief account of heavy-mineral and mechanical composition, is given. It is concluded that these arenites form a part of the orthoquartzite—carbonate facies.     

Semi-empirical method for calculation of maximum subsidence in coal mines

Summary Most empirical methods of subsidence prediction are based on the prior knowledge of the maximum possible subsidence, S_max, for a particular coalfield. The subsidence profile and other associated parameters along a desired line may be derived, in most cases, as a function of S _max. These methods are site specific and are not based upon the rational concepts of mechanics. Purely mechanistic methods, on the other hand, could not find wide application because of their limitations in representing the complex behaviour of a rockmass.Therefore a semi-empirical method of calculation of S _max or S, which is an improvement over the empirical method reported elsewhere (Bahuguna et al., 1991a), has been derived from combining the mechanistic and empirical approach. The effects of various parameters are studied by numerical modelling. These qualitative results are then used to influence the development of a more general semiempirical method. The method has been tested for 125 coal mine workings in India and 22 mines of the North Appalachian basin. The method is easily adaptable to other countries.     

Geomagnetic results from Sabhawala,Yangi-Bazar and Alma-Ata in relation to the asthenosphere beneath the Pamir-Himalaya

An attempt is made to study the properties of the Mohorovi?i? discontinuity and the asthenosphere beneath the Pamir-Himalaya from the geomagnetic results obtained at Sabhawala (Dehra Dun), Yangi-Bazar (Tashkent) and Alma-Ata observatories, situated on its southern and northern flanks, in a narrow longitude zone.Medium-sized induction arrows (Wiese vectors) for night-time “bay” events at all the three stations are found to point northward. The northward orientation at Sabhawala indicates a subsurface concentration of induced currents in a step structure at the Moho to the south of Sabhawala and higher electrical conductivity in the Aravalli-Cambay region, where high heat flow and gravity values have also been reported, supporting an elevated asthenosphere, as against the one beneath the western Himalaya. The arrows at Yangi-Bazar and Alma-Ata also show an east-west current channelling in another step structure at the Moho to the south of these stations and north of the Pamir and the Tien Shan mountains.The Sq variations of the H, D and Z components at the three stations, lying close to the northern Sq ionospherics current focus, reveal the characteristic features, without reflecting any unusual asthenospheric conditions in the region.It is concluded that the orogenesis of the Pamir-Himalaya mountain system in terms of plate tectonics or block uplift is different from that of the Cordilleran and Andean mountains in North and South America respectively, where subsurface conductive structures have been delineated from geomagnetic observations by earlier workers.