We study relativistic solutions of anisotropic compact stars with Finch-Skea (FS) metric in f (T) gravity framework. The modified FS geometry is considered to obtain the equation of state (EoS) for different known stellar objects with given mass and radius. The modified Chaplygin gas (MCG) EoS is also considered to obtain stellar objects as the EoS inside the star is not yet known. The results obtained here is important in the two cases to understand properties of known stars, which are however not known observationally. The physical features of known stars are analyzed here and found that compact star formation may be possible with repulsive core. In the case of MCG in f (T) gravity compact stars may be obtained with anisotropic fluid (p t > p r), with maximum anisotropy at the center of the star, which however is not found when MCG is absent.
Gravastars have been considered as a feasible alternative to black holes in the past couple of decades.
Stable models of gravastar have been studied in many of the alternative gravity theories besides standard General
Relativity (GR). The Rastall theory of gravity is a popular alternative to GR, specially in the cosmological and
astrophysical context. Here, we propose a stellar model under the Rastall gravity following Mazur-Mottola's [1,2]
conjecture. The gravastar consists of three regions, viz., (I) Interior region, (II) Intermediate shell region,
and (III) Exterior region. The pressure within the interior core region is assumed with a constant negative
matter-energy density which provides a repulsive force over the entire thin shell region. The shell is assumed to
be made up of fluid of ultrarelativistic plasma which follows the Zel'dovich's conjecture of stiff fluid [3,4].
It is also assumed that the pressure is proportional to the matter-energy density according to Zel'dovich's conjecture,
which cancel the repulsive force exerted by the interior region. The exterior region is completely vacuum which is
described by the Schwarzschild-de Sitter solution. Under all these specifications we obtain a set of exact and
singularity-free solutions of the gravastar model presenting several physically valid features within the framework
of Rastall gravity. The physical properties of the shell region namely, the energy density, proper length, total
energy and entropy are explored. The stability of the gravastar model is investigated using the surface redshift
against the shell thickness and maximizing the entropy of the shell within the framework of Rastall gravity.
We study evolution of primordial black holes (PBH) in the f(Q) modified gravity for matter accretion from the cosmic fluid surrounding the PBH. For matter described by non-linear equation of state $$p=f(\rho )$$
p
=
f
(
ρ
)
, the accretion of matter in PBH is probed. Two different branches of non-linear EoS is considered here namely, (i) modified Chaplygin gas (MCG) and (ii) viscous fluid in addition to barotropic fluid. We also probe the EoS needed for the emergent universe which admits different compositions of the cosmic fluid surrounding the black hole to probe the evolution and then compared the evolutionary features for the other polynomial form of the EoS. In f(Q) modified gravity, primordial black holes are found to gain mass in the early epoch which finally attains a saturated mass. The picture is different from that of GR as well as $$f(\mathcal {T})$$
f
(
T
)
gravity. We have also compared the PBH evolution in f(Q)-gravity with or without the MCG.
Soaking characteristics of white rice grain in water are studied at 25, 40, 60, 70 and 80°C. The kinetics of mass transfer are modeled using a linear driving force (LDF) approximation with constant diffusivity, which is capable of predicting the moisture ratio profile with time. This approximation is a relatively new approach in food engineering applications for systems in which the rate of mass transfer is controlled by intra-particle diffusion and nonlinear adsorption through porous adsorbent. The mass transfer is also modeled through Fick's law for unsteady-state diffusion using finite difference (FD) method, and compared with the LDF model. In general, the moisture uptake curves calculated with this new approximation compare favorably with the finite difference solution obtained in spherical coordinates, producing results of similar accuracy. Both the methods give a good agreement with the experimental data. The values of the effective diffusion coefficients are between 7.33×10 -11 m 2 /s and 1.43×10 -10 m 2 /s for a temperature of 25 and 80°C respectively. Although gelatinization of starch is observed at a higher temperature which influences the increase in moisture content, the moisture uptake curves calculated with this new approximation compare favorably with the numerical solution of the non-linear diffusion equation. As such, it can be safely used to predict the unsteady-state moisture absorption kinetics of a rice grain, for the temperature range investigated.
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