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61.
In this work, we have assumed the generalized Vaidya solution in Lovelock theory of gravity in (n+2)-dimensions. It has been shown that Gauss-Bonnet gravity, dimensionally continued Lovelock gravity and pure Lovelock gravity
can be constructed by suitable choice of parameters. We have investigated the occurrence of singularities formed by the gravitational
collapse in above three particular forms of Lovelock theory of gravity. The dependence of the nature of singularity on the
existence of radial null geodesic for Vaidya space-time has been specially considered. In all the three models, we have shown
that the nature of singularities (naked singularity or black hole) completely depend on the parameters. Choices of various
parameters are shown in tabular form. In Gauss-Bonnet gravity theory, it can be concluded that the possibility of naked singularity
increases with increase in dimensions. In dimensionally continued Lovelock gravity, the naked singularity is possible for
odd dimensions for several values of parameters. In pure Lovelock gravity, only black hole forms due to the gravitational
collapse for any values of parameters. It has been shown that when accretion is taking place on a collapsing object, it is
highly unlikely to get a black hole. Finally on considering the phantom era in the expanding universe it is observed that
there is no possibility of formation of a black hole if we are in the Gauss-Bonnet gravity considering the accreting procedure
upon a collapsing object. 相似文献
62.
Nairwita Mazumder Ritabrata Biswas Subenoy Chakraborty 《Astrophysics and Space Science》2011,334(1):183-186
Recent observational evidences demand that the universe is going through an accelerating phase and hence in the frame work
of Einstein gravity the matter should be exotic in nature. In the present work, we study the evolution of the apparent and
event horizons across phantom barrier (a cosmological constant) and examine the validity of the generalized second law of
thermodynamics (GSLT) for the universe bounded by the horizons. 相似文献
63.
The pivotal point of the paper is to discuss the behavior of temperature, pressure, energy density as a function of volume along with determination of caloric EoS from following two model: w(z)=w 0+w 1ln(1+z) & . The time scale of instability for this two models is discussed. In the paper we then generalize our result and arrive at general expression for energy density irrespective of the model. The thermodynamical stability for both of the model and the general case is discussed from this viewpoint. We also arrive at a condition on the limiting behavior of thermodynamic parameter to validate the third law of thermodynamics and interpret the general mathematical expression of integration constant U 0 (what we get while integrating energy conservation equation) physically relating it to number of micro states. The constraint on the allowed values of the parameters of the models is discussed which ascertains stability of universe. The validity of thermodynamical laws within apparent and event horizon is discussed. 相似文献
64.
Ghodrat Ebadi Aida Mojaver Daniela Milovic Stephen Johnson Anjan Biswas 《Astrophysics and Space Science》2012,341(2):507-513
In this paper, we present G′/G-expansion method, exp-function method, modified F-expansion method as well as the traveling wave hypothesis for finding the exact traveling wave solutions of the quantum Zakharov-Kuznetsov equation which arises in quantum magneto-plasmas. By these methods, rich families of exact solutions have been obtained, including soliton solutions. This work continues to reinforce the idea that the proposed methods, with the help of symbolic computation, provide a powerful mathematical tool for solving nonlinear partial differential equations. 相似文献
65.
Naresh Kumar Ram Niwas M. L. Khichar R. K. Saini Barun Biswas 《Journal of the Indian Society of Remote Sensing》2013,41(2):309-317
Present study was designed to determine the effect of various growing environments on sucking pest population dynamics in cotton and to work out their relation with spectral indices. Crop spectral reflectance in four IRS bands was measured with ground truth radiometer during 1000–1200 h in all the treatment combinations. Incidence of sucking pest in cotton was found out to be highly influenced by growing environments. The leafhopper and whitefly population was highest in 15 May sown cotton crop and was lowest in 15 April sown crop. Cultivar HS-6 was highly affected by both the sucking pest than the other cultivar H-1226. The spectral indices (SR, NDVI and TVI) were highest in 15 April sown crop at all the phenophases and were lowest in 15 May sown crop. The cultivar H-1226 showed higher values of spectral indices as compared to HS-6. The relationship of pests’ population with various spectral indices was established. Multiple regression models based on spectral indices can be used for prediction of sucking pest population more than 69 and 74 % accuracy in leafhopper and whitefly, respectively in cotton crop. 相似文献
66.
Sejuti Naha Biswas Nallamuthu Godhantaraman Ranjit K. Sarangi Bhaskar D. Bhattacharya Santosh K. Sarkar Kamala K. Satpathy 《洁净——土壤、空气、水》2013,41(4):333-339
An intense monospecies bloom of the centric diatom Hemidiscus hardmannianus (Greville) Mann. (Bacillariophyceae) occurred in the coastal waters of Sundarban mangrove wetland, India on 22 July, 2010. The species was abruptly flourished (mean density 8.86 × 106 cells/L) resulting intense green coloration of water. The greatest impoverishment of diversity and density of phytoplankton, micro‐ and mesozooplankton community was observed during the bloom. The phytoplankton community showed an extreme reduction in diversity (12 species to one) and sharp decrease in standing stock (12.84 × 103 to 8.86 × 106 cells/L) during this period. The late bloom condition coincided with sudden and huge arrival of a clupoid fish Hilsa ilisha which forms the most potential fisheries in Sundarban deltaic region. An attempt has been made to correlate the satellite remote sensing‐derived information to the bloom conditions. The MODIS‐Aqua derived chlorophyll and TMI satellite derived sea surface temperature and wind speed maps have been interpreted. 相似文献
67.
We examine the influence of attenuation and site on the spectra of microearthquakes having origin within the Shillong region. The ratios of spectral amplitudes at lower and higher frequencies are measured for three different stations at varying epicentral distances to estimate Q value for both P- and S-wave in near and sub-surface layer. The average estimates of Q P and Q S are found to be 178 and 195. The ratio of Q S to Q P emerges to be greater than unity in major parts of the Shillong area, suggesting dominance of dry crust prevailing in Shillong region. The variation in corner frequencies for these spectra is inferred to be characteristics of the site. Besides, the disparity in spectral content with reference to hard rock site yields the inference that the incoming seismic signals get amplified considerably while traversing from southern part to northeastern part of Shillong, best outlined at 2 to 5 Hz, which is well corroborated by the existing lithology. 相似文献
68.
69.
Gautam Sen Michael Bizimis Reshmi Das Dalim K. Paul Arijit Ray Sanjib Biswas 《Earth and Planetary Science Letters》2009,277(1-2):101-111
Kutch (northwest India) experienced lithospheric thinning due to rifting and tholeiitic and alkalic volcanism related to the Deccan Traps K/T boundary event. Alkalic lavas, containing mantle xenoliths, form plug-like bodies that are aligned along broadly east–west rift faults. The mantle xenoliths are dominantly spinel wehrlite with fewer spinel lherzolite. Wehrlites are inferred to have formed by reaction between transient carbonatite melts and lherzolite forming the lithosphere. The alkalic lavas are primitive (Mg# = 64–72) relative to the tholeiites (Mg# = 38–54), and are enriched in incompatible trace elements. Isotope and trace element compositions of the tholeiites are similar to what are believed to be the crustally contaminated Deccan tholeiites from elsewhere in India. In terms of Hf, Nd, Sr, and Pb isotope ratios, all except two alkalic basalts plot in a tight cluster that largely overlap the Indian Ridge basalts and only slightly overlap the field of Reunion lavas. This suggests that the alkalic magmas came largely from the asthenosphere mixed with Reunion-like source that welled up beneath the rifted lithosphere. The two alkalic outliers have an affinity toward Group I kimberlites and may have come from an old enriched (metasomatized) asthenosphere. We present a new model for the metasomatism and rifting of the Kutch lithosphere, and magma generation from a CO2-rich lherzolite mantle. In this model the earliest melts are carbonatite, which locally metasomatized the lithosphere. Further partial melting of CO2-rich lherzolite at about 2–2.5 GPa from a mixed source of asthenosphere and Reunion-like plume material produced the alkalic melts. Such melts ascended along deep lithospheric rift faults, while devolatilizing and exploding their way up through the lithosphere. Tholeiites may have been generated from the main plume head further south of Kutch. 相似文献
70.