Motion of test particles in parabolic density distributions

A detailed study of the motion of test-particles [either having a nonzero rest-mass or zero rest-mass] has been carried out for Tolman's type VII solution with vanishing surface density, which is one of the few physically relevant exact solutions of Einstein's field equations for static and spherically symmetric mass distributions.The trapping angles, 0, at which the test-particles escape these configurations are calculated and the trajectories of test-particles are studied in detail. The types of trajectories found for this spacetime geometry are: (1) arc-like trajectories, (2) spiral-like trajectories ending into a circle of constant radius, (3) trajectories with a cusp at the minimum distance, (4) double-bounded trajectories, and (5) double-bounded trajectories with a cusp at the minimum distance. The test-particles following the trajectories of type (1) and type (3) escape the configuration while others are trapped within the structure. Besides the advancement of periastron of the orbits the retrogradation of periastrons are also observed.The stability of the structures is considered by using the variational method (Chandrasekhar, 1964a,b), and its is seen that the structures remain stable at least for a central redshift,z0, as large as 5.09.These studies may distinguish relativistic cluster from a Newtonian one and may find application to the local models of quasi-stellar objects (QSOs).     

Periodicities in natural remanent magnetization and palaeoclimatic records detected by walsh spectra

The time series consisting of nonsinusoidal Natural Remanent Magnetization (NRM) and palaeoclimatic variations for the past two million years have been spectrally examined by using a new Walsh transform technique. The results show statistically significant periodicities (at 95% confidence level) of approximately 92,000 years; 43,000 years and 21,000 years in the ensemble spectra of the NRM intensity (mineralogic) variations. These NRM periodicities are remarkably close to the well-known Milankovitch cycles. The ensemble spectra of palaeoclimatic records reveal only 41,000 years statistically significant (95%) periodicity corresponding to the obliquity cycle. The study suggests that NRM variations in deep sea sediments probably are more sensitive recorders of palaeoclimatic memory than the oxygen isotope variations.     

Avalanche hazard mitigation in east Karakoram mountains

Natural Hazards - Karakoram mountains range in north-western part of Himalayas is about 500 km in length and hosts some of the world’s highest peaks and longest glaciers. It is...     

Landsat data in preinvestment surveys—a case study of western Nepal area

In this paper an attempt has been made to estimate the growingstock showing high (51% and up), medium (25–50%) and low (below 25%) density areas and to prepare a broad landuse and forest cover type map by analysing black and white band 5 Satellite imagery (Landsat-1) on 1:1 m scale pertaining to Western Nepal area which comprises Karnali, Bheri, Babai and Rapti Catchments covering a geograghical area of about 50,000 sq km. The information regarding location, extent and area falling in forested and non-forested categories arrived at from Landsat maps provide basic information to planners at the time of formulation of inventory design before taking up preinvestment Surveys. In developing countries where vegetation stock maps are not readily available, forest resources map based on analysis of Landsat data can be prepared in less time and at a lower cost. Such maps may be immensely used by planners at regional or national level. The technique merits further investigation.     

Effect of anisotropy of the earth on the impedance measurements

Summary Electromagnetic field response of a homogeneous uniaxially anisotropic conducting medium has been investigated in the presence of a vertical electric dipole placed at a heighth above the conducting surface. Expressions for the horizontal components of electric and magnetic fields and hence that of vertical impedance of the field, as a function of the distance of the place of observation from the source, have been derived. Numerical computations have been done and curves are given to illustrate the influence of anisotropy on the amplitude values of the impedance on the surface of the conducting medium.N.G.R.I. Contribution number 71–279.     

High magnitude global seismicity and lateral velocity gradients

Summary A new significant correlation has been sought between high magnitude global seismicity and lateral surface wave velocity gradients. Rayleigh wave velocity divisioning of Eurasia, Africa, Pacific Ocean, Atlantic Ocean and Indian Ocean into regions of similar group velocity dispersion character of 30 sec period bySanto andSato [1]³) has been mainly used for calculating the gradients. It is quite striking to note that all earthquakes of magnitude 8.6 and above during 1897–1956 have occurred in regions having gradients of the order of 1.5·10^–3 sec^–1.Finally, some potential areas for high magnitude earthquake occurrences are predicted and the possible velocity gradients in regions, where division pattern is not yet investigated like South America and Australia, are also estimated.N.G.R.I. Contribution No. 70-170.     

Temporal Assessment of Growing Stock, Biomass and Carbon Stock of Indian Forests

The dynamics of terrestrial ecosystems depends on interactions between carbon, nutrient and hydrological cycles. Terrestrial ecosystems retain carbon in live biomass (aboveground and belowground), decomposing organic matter, and soil. Carbon is exchanged naturally between these systems and the atmosphere through photosynthesis, respiration, decomposition, and combustion. Human activities change carbon stock in these pools and exchanges between them and the atmosphere through land-use, land-use change, and forestry.In the present study we estimated the wood (stem) biomass, growing stock (GS) and carbon stock of Indian forests for 1984 and 1994. The forest area, wood biomass, GS, and carbon stock were 63.86 Mha, 4327.99 Mm³, 2398.19 Mt and 1085.06 Mt respectively in 1984 and with the reduction in forest area, 63.34 Mha, in 1994, wood biomass (2395.12 Mt) and carbon stock (1083.69 Mt) also reduced subsequently. The Conifers, of temperate region, stocked maximum carbon in their woods, 28.88 to 65.21 t C ha⁻¹, followed by Mangrove forests, 28.24 t C ha⁻¹, Dipterocarp forests, 28.00 t C ha⁻¹, and Shorea robusta forests, 24.07 t C ha⁻¹. Boswellia serrata, with 0.22 Mha forest area, stocked only 3.91 t C ha⁻¹. To have an idea of rate of carbon loss the negative changes (loss of forest area) in forest area occurred during 1984–1994 (10yrs) and 1991–1994 (4yrs) were also estimated. In India, land-use changes and fuelwood requirements are the main cause of negative change. Total 24.75 Mt C was lost during 1984–1994 and 21.35 Mt C during 1991–94 at a rate of 2.48 Mt C yr⁻¹ and 5.35 Mt C yr⁻¹ respectively. While in other parts of India negative change is due to multiple reasons like fuelwood, extraction of non-wood forest products (NWFPs), illicit felling etc., but in the northeastern region of the country shifting cultivation is the only reason for deforestation. Decrease in forest area due to shifting cultivation accounts for 23.0% of the total deforestation in India, with an annual loss of 0.93 Mt C yr⁻¹.     

Asthenospheric parameters of dipping plate regions by magnetotelluric investigations

The multifrequency resolving capability of the electromagnetic surface impedance parameter, employed in magnetotelluric investigations, has been examined for an upper mantle model incorporating (1) a deep-seated lithosphere-asthenosphere boundary and (2) preferred orientations of olivine crystals in the lithosphere, usually associated with the subducting plate boundary zones. Numerical results display the quantitative errors in the resolution of various anisotropic and dipping plate conditions. It is found that (1) conductivity anisotropy, particularly with higher dips, causes a significant dispersion in the impedance values and higher resolving power, and (2) variations in the geometrical/physical parameters are reflected predominantly in the phase component of the surface impedance. The study has relevance to the understanding of the electrical nature of materials, its relationship with physical properties and associated geothermal and seismic activities in the dipping plate regions.     

On the estimation of the vertical distribution of radiogenic heat production in the crust

Summary. A differential-difference equation governing the distribution of radiogenic heat in the crust has been obtained. The solution of this equation gives the exponential model of the heat production distribution with the logarithmic decrement as determined in Singh & Negi.