Nonlinear propagation of Alfvén waves in cometary plasmas

Large-amplitude Alfvén waves propagating along the guide magnetic field in a three-component plasma are shown to be spatially localized due to their nonlinear interaction with nonresonant electrostatic density fluctuations. A new class of subsonic Alfvén soliton solutions are found to exist in the three-component plasma. The Alfvén solitons can be relevant in explaining the properties of hydromagnetic turbulence near the comets.     

A new low-frequency electrostatic mode in a nonuniform electron-positron plasma

The existence of a novel low-frequency electrostatic mode, which is due to the gravitational acceleration in a nonuniform electron-positron plasma, is pointed out. At large amplitudes, the unstable modes self-organize to form dipolar vortices.     

Urban land use mapping: A case study of ahmedabad city and its environs

Proper urban planning and effective implementation requires reliable urban land use statistics. In this context, satellite remote sensing data has been studied using both visual and digital techniques. A portable eight-band radiometer has been used to collect spectral signatures of surface features present in Ahmedabad city and its environs. Using these signatures a suitable approach employing visual and digital techniques has been developed for urban land use/sprawl mapping. Urban land-use maps of Ahmedabad city and its environs were prepared on 1:25,000 scale and for Ahmedabad Urban Development Authority Area on 1:50,000 scale using this methodology. It has been found that edge-enhancement techniques are useful to enhance the contrast among different urban land uses. Classification techniques such as MXL and Bayes classifiers are not successful in discriminating urban land uses. Tonal characteristics alongwith other elements of interpretation are required to classify urban land uses such as residential, industrial etc. Spatial distribution of various urban and uses and the space devoted to each urban land use has been brought out.     

Barotropic-Baroclinic instability of mean zonal wind during summer monsoon

Barotropic-Baroclinic instability of horizontally and vertically shearing mean monsoon flow during July is investigated numerically by using a 10-layer quasi-geostrophic model. The most unstable mode has a wavelength of about 3000 km and westward phase speed of about 15 m sec^–1. The most dominant energy conversion is from zonal kinetic energy to eddy kinetic energy. The structure of the most unstable mode is such that the maximum amplitude is concentrated at about 150 mb and the amplitude at the lowest layers is negligibly small. Barotropic instability of the zonal flow at 150 mb seems to be the primary excitation mechanism for the most unstable mode which is also similar to the observed westward propagating waves in the upper troposphere during the monsoon season. The results further suggest that Barotropic-Baroclinic instability of the mean monsoon flow cannot explain the occurrence of monsoon depressions which have their maximum amplitude at the lower levels and are rarely detected at 200 mb.     

A note on palaeozoic bryozoa from the nayar phyllite formation,pauri garhwal,U.P.

This note records the discovery of bryozoan fossils collected from Nayar Phyllite Formation exposed around Satpuli, from a locality SSW of Ira (29° 53′32″: 78° 46′52″) in Pauri Garhwal district, U.P. On the basis of preliminary studies the fossil assemblage has been assigned to the families Phylloporinidae and Fenestellidae. The assemblage tentatively indicates Ordovician — early Silurian age for the formation.     

Acute and Chronic Toxic Effects of Cadmium on some Haematological,Biochemical, and Enzymological Parameters in the Fresh Water Teleost Fish Channa punctatus Akute und chronisch toxische Wirkungen von Cadmium auf einige hämatologische,biochemische und enzymologische Parameter im Süßwasserfisch Channa punctatus

The haematological, biochemical, and enzymological alterations produced on exposure of Channa punctatus to LC₅₀ (11.2 mg/L) for 96 h and to a sublethal concentration (1.12 mg/L) of cadmium (Cd²⁺) for 15, 30, 60, and 120 days have been studied. The fish were hypoglycemic and hypolactemic. The pyruvate content of blood and liver decreased in acute and all stages of chronic exposure except for 30 days where significant increase was recorded. Depletion was noted in the total protein and glycogen content of liver and muscle, and the level of lactate in liver in the two types of exposure. The levels of muscle lactate and pyruvate increased in both exposures. The activities of hexokinase, glucose-6-phosphatase, and lactate dehydrogenase decreased in liver after 96 h and all stages of chronic exposure except 30 days. The activities of hexokinase and lactate dehydrogenase in muscle and glutamate-oxalacetate transaminase and glutamate-pyruvate transaminase in serum, liver, and muscles increased in all exposures. The activities of succinate and malate dehydrogenases in liver and muscles decreased after acute and all stages of chronic exposure. The above results suggest that glycolysis and gluconeogenesis were impaired in liver but glycolysis prevailed in muscle. Aerobic oxidation is adversely affected in metal exposed fish, while proteolysis was increased.     

Toxicity of the Herbicide 2.4-D-Na to Two Species of Freshwater Prawn of the Genus Macrobrachium

In batch experiments with exposure for 24 to 96 h Macrobrachium naso and M. dayanum were exposed to solutions of the sodium salt of 2,4-dichlorophenoxy acetic acid. The LC_50,96h are 2.397 g/l for Macrobrachium naso and 2.275 g/l for M. dayanum. No mortality was observed in solutions of 2.1 and 1.85 g/l. The differences in toxicity are not dependent on the size of the organisms, but they are species-specific.     

Aldrin Induced Changes in the Activities of Three Phosphatases of Macrobrachium lamarrei (H. Milne EDWARDS)

Macrobrachium lamarrei is exposed to 0.008, 0.017 and 0.021 mg/1 aldrin (0.4, 0.8 and 1.0 of the LC_50,96h) for 24… 96 h and after exposure the activities of the acid, alkaline and glucose-6-phosphatases are determined. With concentration and time of exposure the acid phosphatase shows an increasing activity up to 170 % compared with the control, which is interpreted as a part of prenecrotic changes in the cells. With concentration and time of exposure the alkaline phosphatase shows a decreasing activity down to 20 % of the control, which is indicative of considerable disturbances of the total metabolism. The glucose-6-phosphatase shows an increasing activity with the aldrin concentration up to 150 % during 72 h; then the activity drops to 60… 80 %. The initial rise in the glucose concentration of blood caused by that is the clear consequence of a stress reaction and the change of metabolism resulting from it.