LRS Bianchi type-II massive string cosmological model in General Relativity     

Anirudh Pradhan  Parashuram Ram  Rekha Singh 《Astrophysics and Space Science》2011,331(1):275-279

The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological model representing massive string. The energy-momentum tensor for such string as formulated by Letelier (Phys. Rev. D 28:2414, 1983) is used to construct massive string cosmological model for which we assume that the expansion (θ) in the model is proportional to the shear (σ). This condition leads to A=B ^m , where A and B are the metric coefficients and m is proportionality constant. For suitable choice of constant m, it is observed that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string at the late time. Our model is in accelerating phase which is consistent to the recent observations of type Is supernovae. Some physical and geometric behavior of the model is also discussed.  相似文献   

An interacting and non-interacting two-fluid scenario for dark energy in FRW universe with constant deceleration parameter     

Anirudh Pradhan  Hassan Amirhashchi  Bijan Saha 《Astrophysics and Space Science》2011,333(1):343-350

In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic FRW universe filled with barotropic fluid and dark energy. The scale factor is considered as a power law function of time which yields a constant deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. The cosmic jerk parameter in our derived models is consistent with the recent data of astrophysical observations. It is concluded that in non-interacting case, all the three open, close and flat universes cross the phantom region whereas in interacting case only open and flat universes cross the phantom region. We find that during the evolution of the universe, the equation of state (EoS) for dark energy ω _D changes from ω _D >−1 to ω _D <−1, which is consistent with recent observations.  相似文献   

Anisotropic Bianchi type-I models in string cosmology     

Anirudh Pradhan  D. S. Chouhan 《Astrophysics and Space Science》2011,331(2):697-704

The present study deals with a spatially homogeneous and anisotropic Bianchi-I cosmological models representing massive strings. The energy-momentum tensor, as formulated by Letelier (1983), has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor. The Einstein’s field equations have been solved by applying a variation law for generalized Hubble’s parameter in Bianchi-I space-time. We have analysed a comparative study of accelerating and decelerating models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times, which is in agreement with current astronomical observations.  相似文献   

Dark energy models with anisotropic fluid in Bianchi Type-VI 0 space-time with time dependent deceleration parameter     

Anirudh Pradhan  Rekha Jaiswal  Kanti Jotania  Rajeev Kumar Khare 《Astrophysics and Space Science》2012,337(1):401-413

We present two dark energy (DE) models with an anisotropic fluid in Bianchi type-VI ₀ space-time by considering time dependent deceleration parameter (DP). The equation of state (EoS) for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations. Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the EoS parameter for DE changes from ω>−1 to ω=−1 in first model whereas from ω>−1 to ω<−1 in second model which is consistent with recent observations. The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent type Ia supernovae observations. The cosmic jerk parameter in our derived models is also found to be in good agreement with the recent data of astrophysical observations. The physical and geometric aspects of both the models are also discussed in detail.  相似文献   

Bulk viscous LRS Bianchi-I Universe with variable G and decaying Λ     

Anil Kumar Yadav  Anirudh Pradhan  Ajay Kumar Singh 《Astrophysics and Space Science》2012,337(1):379-385

The present study deals with spatially homogeneous and totally anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with variable G and Λ in presence of imperfect fluid. To get the deterministic model of Universe, we assume that the expansion (θ) in the model is proportional to shear (σ). This condition leads to A=ℓB ⁿ , where A, B are metric potential. The cosmological constant Λ is found to be decreasing function of time and it approaches a small positive value at late time which is supported by recent Supernovae Ia (SN Ia) observations. Also it is evident that the distance modulus curve of derived model matches with observations perfectly.  相似文献   

Two-fluid scenario for dark energy models in an FRW universe-revisited     

Bijan Saha  Hassan Amirhashchi  Anirudh Pradhan 《Astrophysics and Space Science》2012,342(1):257-267

In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy by revisiting the recent results (Amirhashchi et al. in Chin. Phys. Lett. 28:039801, 2011a). To prevail the deterministic solution we select the scale factor which generates a time-dependent deceleration parameter (DP), representing a model which generates a transition of the universe from the early decelerating phase to the recent accelerating phase. We consider the two cases of an interacting and non-interacting two-fluid (barotropic and dark energy) scenario and obtained general results. The cosmic jerk parameter in our derived model is also found to be in good agreement with the recent data of astrophysical observations under the suitable condition. The physical aspects of the models and the stability of the corresponding solutions are also discussed.  相似文献   

Manifestation of Remote Sensing Data in Modeling Urban Sprawl Using the SLEUTH Model and Brute Force Calibration: A Case Study of Sana’a City, Yemen     

Mohamed Al-shalabi  Biswajeet Pradhan  Lawal Billa  Shattri Mansor  Omar F. Althuwaynee 《Journal of the Indian Society of Remote Sensing》2013,41(2):405-416

Sana’a the metropolitan capital of Yemen, has experienced rapid spatial growth and uncontrolled development for decades. In the absence of a means to forecast and predict urban growth trends, planning and urban policy decisions have been found wanting. In this study the SLEUTH (Slope, landuse, exclusion, urban extent, transportation and hillshade) model which has been widely and successfully applied in developed countries, has been applied to predict the spatial urban sprawl pattern from 2004–2020 in Sana’a. This was to provide the necessary forecast for better planning and decision making. The model performed well as per the calibration coefficient values. The results showed that there will a 29 % increase in spatial urban sprawl growth during the modeling period. Growth of the sprawl will be mainly at the edges of the urban boundary, there will also be a wide area of scattered urban clusters. Factors that will have major influence on spatial expansion of the city will be diffusion, natural and internal growth, slope (that will hinder spread) and transportation (along which most of the urban sprawl will occur). The study also provides an insight into how the SLEUTH model performs in a poorly planned urban environment as compared to the planned and controlled environment where it has been applied.  相似文献   

Comparative assessment of water surface level using different discharge prediction models     

Mokhtar  Ernieza Suhana  Pradhan  Biswajeet  Ghazali  Abd Halim  Shafri  Helmi Zulhaidi Mohd 《Natural Hazards》2017,87(2):1125-1146

Natural Hazards - Discharge is traditionally measured at gauge stations located at discrete positions along the river course. When the volume of water discharge is higher than the river bank,...  相似文献   

A new generalized soil thermal conductivity model for sand–kaolin clay mixtures using thermo-time domain reflectometry probe test     

Nan Zhang  Xinbao Yu  Asheesh Pradhan  Anand J. Puppala 《Acta Geotechnica》2017,12(4):739-752

As the demand of exploitation and utilization of geothermal energy increases, more geothermal-related earth structures occur recently. The design of the structures depends upon an accurate prediction of soil thermal conductivity. The existing soil thermal conductivity models were mostly developed by empirical fits to datasets of soil thermal conductivity measurements. Due to the gaps in measured thermal conductivities between any two tested natural soils, the models may not provide accurate prediction for other soils, and the predicted thermal conductivity might not be continuous over the entire range of soil type. In this research, a generalized soil thermal conductivity model was proposed based on a series of laboratory experiments on sand, kaolin clay and sand–kaolin clay mixtures using a newly designed thermo-time domain reflectometry probe. The model was then validated with respect to k _dry–n (thermal conductivity of dry soils and porosity) and k _r–S _r (normalized thermal conductivity and degree of saturation) relationships by comparing with previous experimental studies. The predicted thermal conductivities were found to be in a good agreement with the experimental data collected from both this study and the other literatures with at least 85% confidence interval. It is concluded that the proposed model accounts for the effects of both environmental factors (i.e., moisture content and dry density) and compositional factors (i.e., quartz content and soil type) on soil thermal conductivity, and it has a great potential in predicting soil thermal conductivity more accurately for geothermal applications.  相似文献   

Flood susceptibility analysis and its verification using a novel ensemble support vector machine and frequency ratio method   总被引：3，自引：2，他引：1  

Mahyat Shafapour Tehrany  Biswajeet Pradhan  Mustafa Neamah Jebur 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(4):1149-1165

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