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41.
By considering the Robertson-Walker line element exact cosmological solutions have been obtained by taking spin-half-generated particles as matter sources in the Jordan-Brans-Dicke theory. There exist exact solutions for which the gravitational constant decreases linearly with time and the mass of the Universe increases proportionally to the square of its age while the density decreases with time. The results have been studied corresponding to the three values of curvature index. It has been shown that the expansion law is determined by the particles created by the expansion itself. 相似文献
42.
43.
Kasturi Chakraborty P. K. Mukhopadhyay Praveer Pankaj 《Journal of the Geological Society of India》2016,87(6):631-660
The western part of Cuddapah basin has been considered as a foreland to the fold-thrust belt represented by eastern Nallamalais and Nellore schist belt. The igneous activities, in the form of lava flows and sills, in western Cuddapahs have been a subject of controversy since tectonogenetic models ranging from a mantle plume to lithospheric extension have been suggested. The present work covers a detailed study of the mafic sills and lava flows of Vempalle and Tadpatri formations in western Cuddapahs, which earlier workers have also noted. A detailed field and laboratory work in this study brings out, for the first time, five distinct petrographic and geochemical varieties of sills. Geochemical studies also suggest that the different sill types have originated from varying degrees of partial melting of a metasomatized subcrustal lithospheric mantle, the metasomatism of source being attributed to older Archaean convergent settings/greenstone belts that the basin unconformably overlies. The possible contribution of any small plume is only heating and doming of overlying mantle that induced incipient crustal rifting. Our geochemical studies on the lava flows of Vempalle Formation also suggest that the magma was derived from small degree of partial melting of spinel-garnet peridotite mantle in a rift setting. 相似文献
44.
M. Geetha Devi Z. S. Shinoon Al-Hashmi G. Chandra Sekhar 《International Journal of Environmental Science and Technology》2012,9(4):713-718
In this study, a naturally available crab shell chitosan of low molecular weight (20?kDa) has been used as adsorbent to evaluate the pollution load in vegetable oil mill effluent. A series of batch experiment was conducted by varying chitosan dosage (100?C400?mg), pH (2?C9), stirring time (15?C90)?min and agitation speed (25?C150?rpm) to study their effects on adsorption and flocculation processes. The parameters considered for adsorption study are chemical oxygen demand, total suspended solids, electrical conductivity and turbidity. The maximum reduction in chemical oxygen demand, total suspended solids, electrical conductivity and turbidity is 74, 70, 56 and 92?% , respectively. The observed experimental result showed that crab shell chitosan could able to reduce significantly the chemical oxygen demand, turbidity, electrical conductivity and suspended matter. The optimum conditions were estimated as 400?mg/l chitosan, pH 4 and 45?min of mixing time with mixing speed of 50?rpm. Chitosan showed very good pollution removal efficiency and can be used for the effective treatment of vegetable oil mill effluent. 相似文献
45.
Friedmann Robertson Walker cosmological models with bulk viscosity are constructed in the scale covariant theory of gravitation.
A new class of solutions for the field equations of the model is found by applying variable deceleration parameter. Some physical
models of these solutions are briefly discussed in this paper. 相似文献
46.
Chanthran Shyama Sundari Devi Lim Phaik Eem Poong Sze-Wan Du Jianguo Loh Kar-Hoe 《中国海洋湖沼学报》2021,39(1):372-381
Journal of Oceanology and Limnology - Length-weight relationship provides basic information of a fish’s condition while the morphometric data of otolith has been traditionally used to... 相似文献
47.
M. K. Bera Kasturi Bhattacharya A. Sarkar A. Samanta Kishor Kumar Ashok Sahni 《Journal of the Geological Society of India》2010,76(3):275-282
Oxygen isotope composition (δ18O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of
past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number
of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available
methods, the chemical procedure for extraction of very small amount (<1000 μg) PO4
−3 from bioapatite and on-line mass spectrometric measurement of its δ18O composition by high temperature (∼1450°C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with
interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ18O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the
Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats.
The freshwater δ18O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is
not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene
time. 相似文献
48.
The peridotites of the Manipur Ophiolite Complex (MOC) have been examined based on mineral chemistry, major elements and PGE
contents. They represent high-magnesian cumulates with Mg# > 0.90 (Mg/Mg+Fe) in olivine and Cr# > 0.12 (Cr/Cr+Al) in spinel.
High Mg* contents of the olivine show that these rocks are most likely derived from partial melting of the residual upper
mantle. The peridotites contain higher concentration of Palladium Group PGE (PPGE) (Rh=4.4−6.6ppb; Pd=336−458ppb and Pt=14.6−36.4ppb)
than the Iridium Group PGE (IPGE) (Os=2.4−5.8ppb; Ir=3.2−4.16ppb and Ru=5.2−7ppb). These are characterized by overall enrichment
of PGE concentration (σPGE=365.8 − 516.6 ppb) and high ratio of (Pt+Pd)/(Os+Ir+Ru). This suggests that the rocks are formed
by partial melting and crystal fractionation of olivine-rich (picritic) magma. 相似文献
49.
Modeling forest fire risk in the northeast of Iran using remote sensing and GIS techniques 总被引:3,自引:1,他引:2
Fire in forested areas can be regarded as an environmental disaster which is triggered by either natural forces or anthropogenic activities. Fires are one of the major hazards in forested and grassland areas in the north of Iran. Control of fire is difficult, but it is feasible to map fire risk by geospatial technologies and thereby minimize the frequency of fire occurrences and damages caused by fire. The fire risk models provide a suitable concept to understand characterization of fire risk. Some models are map based, and they combine effectively different forest fire–causing variables with remote sensing data in a GIS environment for identifying and mapping forest fire risk. In this study, Structural Fire Index, Fire Risk Index, and a new index called Hybrid Fire Index were used to delineate fire risk in northeastern Iran that is subjected to frequent forest fire. Vegetation moisture, slope, aspect, elevation, distance from roads, and vicinity to settlements were used as the factors influencing accidental fire starts. These indices were set up by assigning subjective weight values to the classes of the layers based on their sensitivity ratio to fire. Hot spots data derived from MODIS satellite sensor were used to validate the indices. Assessment of the indices with receiver operating characteristic (ROC) curves shows that 76.7 % accuracy of the HFI outperformed the other two indices. According to the Hybrid Fire Index, 57.5 % of the study area is located under high-risk zone, 33 % in medium-risk zone, and the remaining 9.5 % area is located in low-risk zone. 相似文献
50.
Venugopal Chandu E. Savithri Devi R. Jayapal George Samuel S. Antony G. Renuka 《Astrophysics and Space Science》2012,339(1):157-164
Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary
environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study
the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons.
Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular
direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian
distributions with different temperatures. We find that for frequencies w* < wcH +\omega^{*} < \omega_{c\mathrm{H}^{ +}} (ω
∗ and wcH +\omega_{c\mathrm{H}^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively
charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion
mass. 相似文献