Gravitational instability for some astrophysical systems

The gravitational instability of an infinite homogeneous self-gravitating mixture through porous medium in the presence of a variable horizontal magnetic field varying in vertical directions has been considered to include, separately, the effects due to suspended particles and collisions between ionized and neutral components. The dispersion relations in both cases have been obtained. It has been found that Jeans's criterion of instability holds good even if the effects due to suspended particles, collisions, porosity, and variable magnetic field are considered.     

Terrestrial vegetation dynamics and global climate controls

Monthly data from the moderate resolution imaging spectroradiometer (MODIS) and its predecessor satellite sensors was used to reconstruct vegetation dynamics in response to climate patterns over the period 1983–2005. Results suggest that plant growth over extensive land areas of southern Africa and Central Asia were the most closely coupled of any major land area to El Niño–southern oscillation (ENSO) effects on regional climate. Others land areas strongly tied to recent ENSO climate effects were in northern Canada, Alaska, western US, northern Mexico, northern Argentina, and Australia. Localized variations in precipitation were the most common controllers of monthly values for the fraction absorbed of photosynthetically active radiation (FPAR) over these regions. In addition to the areas cited above, seasonal FPAR values from MODIS were closely coupled to rainfall patterns in grassland and cropland areas of the northern and central US. Historical associations between global vegetation FPAR and atmospheric carbon dioxide (CO₂) anomalies suggest that the terrestrial biosphere can contribute major fluxes of CO₂ during major drought events, such as those triggered by 1997–1998 El Niño event.     

Geniculate coralline algae from the Neogene-Quaternary sediments in and around Porbandar,southwest coast of India

The present paper documents nine geniculate coralline algal species, namely Arthrocardia cretacica, Calliarthron antiquum, Corallina hayasaki, C. marshallensis, C. prisca, C. typica, Jania mengaudi, J. sripadaraoi and J. vetus from Neogene-Quaternary sediments of Porbandar area, Saurahtra, Gujarat. Out of nine species, six species namely Arthrocardia cretacica, Calliarthron antiquum, Corallina hayasaki, C. marshallensis, C. prisca and C. typica occur in the Dwarka Formation (lower-middle Miocene), one species Jania sripadaraoi occurs in the Adatiana Member of the Miliolite Formation (early middle-late Pleistocene) and two species namely, Jania mengaudi and J. vetus occur in the Porbandar Calcarenite Member of the Chaya Formation (late Pleistocene-late Holocene). These species indicate that the Dwarka Formation and the Adatiana Member of the Miliolite Formation were deposited in tropical marine environment with moderate to low energy conditions at depths ranging from intertidal to 60 m, and that the Porbandar Calcarenite Member of the Chaya Formation was deposited in a tropical marine environment under moderate to low energy conditions at depths ranging from 40 m to 60 m.     

A note on rare structure of fossil coralline algae from the southwest coast of India

The coralline algae (Rhodophyta) are well preserved in the sediments of the Dwarka Formation in and around Porbandar area, southwest coast of India. There are few records of the preservation of genicula in the fossil coralline algae. Three algal fragments with genicula are noted and recorded from the area.     

The structure of the equatorial mesosphere at Thumba

The structure of the equatorial mesosphere is being investigated at Thumba by rocket borne ultraviolet absorption photometry as well as by the meteorological M-100 rocket launching programme. Whereas the meteorological M-100 rocket luanching programme has been regular, the UV absorption studies have been few in number and sporadic in nature. In this paper an attempt is made to consolidate the results so far obtained from both these investigations.     

Some geoelectrical investigations for potential groundwater zones in part of Azamgarh area of U.P.

Summary The results of some electrical sounding measurements have been used for defining potential groundwater zones in part of Azamgarh district of Uttar Pradesh, India. The area covered is a part of gangetic alluvial tract. Aquifers consist of lenticular sand masses distributed within the alluvium. The ideal geoelectrical conditions, generally desired for the interpretation of resistivity curves, lack in the area. Among the number of layers encountered in lithologs, only a few are delineated by quantitative interpretation of the sounding data. A study of the total transverse resistance and longitudinal conductance for a particular depth of the alluvial column has helped in defining potential groundwater zones.