Search

In the context of modified gravity, we study the appearance of anisotropic compact stellar objects. The space–time geometry is characterized by the metric potentials, and to solve the field equations, we consider their specific form known as the Tolman–Kuchowicz space–time. The obtained solutions are free of singularities and satisfy all requirements for stellar objects. We consider the observational data for models of the stars Cen X-3, EXO 1785-248, and LMC X-4, and taking these data into account, we obtain the values of the physical parameters from the matching conditions for the interior Tolman–Kuchowicz space–time and the exterior Schwarzschild metric. In addition, we discuss some physical attributes of anisotropic compact stellar structures to verify the physical validity and stability of the proposed model. We perform a three-dimensional graphical analysis that allows obtaining a representation of the physical behavior of these compact objects. We note that all three compact objects correspond to physically accepted models. [ABSTRACT FROM AUTHOR]

We study compact stars for f() gravity model using modified Tolman–Oppenheimer–Volkoff equation. Firstly, the hydrostatic equilibrium equations have been developed in the context of f() gravity. Secondly, the profiles of energy density, pressure and mass of stars are investigated through two different equations of state models, p = ωρ5/3 and p = a(ρ – 4b), ρ being the energy density, ω, a and b are the specific constants. For f() = α model with α being an arbitrary constant, the physical attributes of the compact objects have been discussed for the different values of model parameter α. It is concluded that in the framework of f() gravity, neutron and strange stars follow physically accepted patterns and the results agree with those already available in literature. [ABSTRACT FROM AUTHOR]

The total lead content in the soil itself is insufficient as a measure to indicate the actual environmental risks related to the presence of lead in the soil. Understanding the mobility of lead and its chemical speciation in soil solution is of great importance for accurately assessing environmental risks posed by lead. Therefore, a laboratory study was carried out to evaluate the effect of inorganic amendments (gypsum, rock phosphate and di-ammonium phosphate) on lead mobility and chemical speciation under different moisture regimes (flooding regime and 75 % field capacity) in normal and salt-affected lead-contaminated soils. After 2, 7, 15, 30, 100 and 110 days of incubation, pore water samples were collected by using Rhizon soil moisture samplers. In order to estimate the chemical speciation of lead in pore water, Visual MINTEQ 3.0 modeling approach was used. The results showed that presence of free Pb, PbCl, Pb(SO), and PbHPO was significantly ( P ≤ 0.05) affected by the soil moisture regime, incubation time and applied amendments in lead-contaminated soils. The Visual MINTEQ 3.0 predicted free Pb species concentration was found higher in lead-contaminated soils, while PbCl was more pronounced in salt-affected soils. Gypsum increased the occurrence of Pb(SO), while di-ammonium phosphate and rock phosphate enhanced the PbHPO species formation and decreased free Pb species in pore water. Thus, gypsum is the most effective in reducing lead and free Pb species concentrations in the pore water under different soil moisture regimes and incubation times in normal and salt-affected lead-contaminated soils. [ABSTRACT FROM AUTHOR]