Dynamics of shearing viscous fluids in f(R,T) gravity

2017 ◽  
Vol 27 (01) ◽  
pp. 1750181 ◽  
Author(s):  
Hina Azmat ◽  
M. Zubair ◽  
Ifra Noureen
Keyword(s):  
Cylindrical Symmetry ◽  
Dynamical Analysis ◽  
Index Formula ◽  
Anisotropic Fluid ◽  
Perturbation Approach ◽  
Field Equations ◽  
Dynamical Equations ◽  
Cylindrical System ◽  
Pressure Anisotropy ◽  
The Stability

In this paper, we have analyzed the dynamical stability of shearing viscous anisotropic fluid with cylindrical symmetry in [Formula: see text] theory. We have chosen two viable [Formula: see text] models for dynamical analysis, and explored their nature and role for stable stellar configuration. Modified field equations and corresponding dynamical equations have been constructed, perturbation approach is adopted to deal with complexity of these equations. With the help of perturbed dynamical equations, the evolution equation has been established to analyze the role of shear viscosity and pressure anisotropy on dynamics of cylindrical system. The adiabatic index [Formula: see text] is used to investigate the instabilities appearing in Newtonian (N) and post-Newtonian (pN) approximations. Some conditions are found for material variables that are required to meet the stability criterion. We compare the outcomes of our analysis with the results of various models available in literature to reach at more comprehensive conclusion.

Dynamical analysis for cylindrical geometry in non-minimally coupled f(R,T) gravity

2021 ◽  
Author(s):  
M. Z. Bhatti ◽  
Z. Yousaf ◽  
M. Yousaf
Keyword(s):  
Perturbation Technique ◽  
Dynamical Behavior ◽  
Momentum Tensor ◽  
Dynamical Analysis ◽  
Dynamical Equations ◽  
Physical Constraints ◽  
Cylindrical System ◽  
Modified Gravity Theory ◽  
The Stability ◽  
Tensor Formula

This paper aims to investigate the stability constraints under the influence of particular modified gravity theory [Formula: see text], i.e. [Formula: see text] gravity in which the Lagrangian is a varying function of [Formula: see text] and trace of energy momentum tensor ([Formula: see text]). We examine stable behavior for compact cylindrical star having anisotropic symmetric configuration. We establish dynamical equations as well as equations of continuity in the background of this particular non-minimal coupled [Formula: see text]. We utilize perturbation technique which will be applied on geometrical as well as material physical quantities to constitute collapse equation. We continue this significant investigation to understand the dynamical behavior of considered cylindrical system under non-minimal coupled [Formula: see text] functional, i.e. [Formula: see text]. This gravitational function gives compatible findings only for [Formula: see text], also [Formula: see text] and [Formula: see text] considered in this astrophysical model as coupling entity. This model contains [Formula: see text] which is constant entity, having the values of order of the effective Ricci scalar [Formula: see text]. Furthermore, we impose some physical constraints to determine and maintain the stability criteria by establishing the expression of adiabatic index, i.e. [Formula: see text] for cylindrical anisotropic configuration, in Newtonian [Formula: see text] and post-Newtonian ([Formula: see text]) eras.

Impact of f(R,T) gravity in evolution of charged viscous fluids

2021 ◽  
Vol 30 (04) ◽  
pp. 2150027
Author(s):  
I. Noureen ◽  
Usman-ul-Haq ◽  
S. A. Mardan
Keyword(s):  
Stability Analysis ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Viscous Fluids ◽  
Fluid Distribution ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stability Of Stars ◽  
The Stability

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of [Formula: see text] gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

Study of tilted cylindrical quark star

2020 ◽  
Vol 35 (14) ◽  
pp. 2050110
Author(s):  
M. Sharif ◽  
Sumaira Nazir
Keyword(s):  
Numerical Solution ◽  
Energy Conditions ◽  
Fluid Distribution ◽  
Quark Star ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stellar Matter ◽  
Mit Bag Model ◽  
Pressure Anisotropy ◽  
Physical Features

In this paper, we study perfect, anisotropic and anisotropic dissipative cylindrical quark star for the tilted observer. To this end, the field equations and dynamical equations are formulated and assume MIT bag model to find a numerical solution of the field equations. The behavior of resulting model is investigated by plotting density, pressure, anisotropy and energy conditions. We check viability of the solutions through physical features related to stellar matter configuration. Finally, we discuss stability for all the cases of fluid distribution.

Exact wormholes solutions without exotic matter in f(R,T) gravity

2019 ◽  
Vol 16 (03) ◽  
pp. 1950046 ◽  
Author(s):  
M. Zubair ◽  
Rabia Saleem ◽  
Yasir Ahmad ◽  
G. Abbas
Keyword(s):  
Momentum Tensor ◽  
Exotic Matter ◽  
Gravity Models ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Energy Tensor ◽  
Field Equations ◽  
Stress Energy ◽  
Symmetric Geometry ◽  
The Stability

This paper is aimed to evaluate the existence of wormholes in viable [Formula: see text] gravity models (where [Formula: see text] is the scalar curvature and [Formula: see text] is the trace of stress–energy tensor of matter). The exact solutions for energy–momentum tensor components depending on different shapes and redshift functions are calculated without some additional constraints. To investigate this, we consider static spherically symmetric geometry with matter contents as anisotropic fluid and formulate the Einstein field equations for three different [Formula: see text] models. For each model, we derive expression for weak and null energy conditions and graphically analyzed its violation near the throat. It is really interesting that wormhole solutions do not require the presence of exotic matter — like that in general relativity. Finally, the stability of the solutions for each model is presented using equilibrium condition.

Gaussian distributed wormholes exhibiting conformal motion in f(T) gravity

2019 ◽  
Vol 16 (09) ◽  
pp. 1950143 ◽  
Author(s):  
G. Mustafa ◽  
Saira Waheed ◽  
M. Zubair ◽  
T. Xia
Keyword(s):  
String Theory ◽  
Energy Density ◽  
Analytic Solution ◽  
Numerical Approach ◽  
Anisotropic Fluid ◽  
Matter Distribution ◽  
Field Equations ◽  
Conformal Motion ◽  
Free Parameters ◽  
The Stability

This paper investigates the possibility of static spherical symmetric wormholes existence exhibiting conformal motion in a generalized teleparallel formulation, namely [Formula: see text] gravity. For this purpose, we assume the matter distribution as anisotropic fluid with energy density of Gaussian distribution, a well-known non-commutative aspect of string theory. By using non-diagonal tetrad components in the torsional formulation, we consider three interesting viable models of [Formula: see text]. In each case, due to the complexity of the resulting field equations, it is seen that the analytic solution is difficult to find. Thus the feasible and realistic wormholes are acquired using numerical approach by fixing the involved free parameters suitably. Furthermore, we investigate the stability of these wormhole solutions graphically and it is shown that the obtained wormhole solutions are physically stable in all cases.

Complexity factor for charged dissipative dynamical system

2020 ◽  
Vol 35 (28) ◽  
pp. 2050231
Author(s):  
M. Sharif ◽  
Saher Tariq
Keyword(s):  
Dynamical System ◽  
Electromagnetic Field ◽  
Maxwell Field ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Spherical System ◽  
Structure Scalars ◽  
Dissipative Dynamical System ◽  
The Stability ◽  
Dissipative Fluids

In this paper, we examine the complexity factor for a dynamical spherical system with dissipative charged anisotropic fluid. We evaluate the Einstein-Maxwell field equations and structure scalars using Bel’s approach which help to discuss the structure as well as evolution of a self-gravitating system. We measure the complexity factor for the pattern of evolution through the homologous condition and homogeneous expansion. We also analyze the stability of vanishing complexity condition for dissipative and non-dissipative fluids. It is found that the complexity as well as stability of the spherical system increases and decreases, respectively, under the effects of electromagnetic field.

scholarly journals Evolution of inhomogeneous LTB geometry with tilted congruence and modified gravity

2017 ◽  
Vol 95 (12) ◽  
pp. 1246-1252 ◽  
Author(s):  
Z. Yousaf ◽  
M. Zaeem-ul-Haq Bhatti ◽  
Aamna Rafaqat
Keyword(s):  
Transport Equation ◽  
Modified Gravity ◽  
Stability Region ◽  
Moving Frames ◽  
Field Equations ◽  
Dynamical Equations ◽  
Inhomogeneous Universe ◽  
The Stability ◽  
The Relationship ◽  
The Universe

The goal of this paper is to shed some light on the significance of congruence of observers, which seems to affect the dynamics of the universe under Palatini f(R) formalism. Starting by setting up the formalism needed, we have explored the field equations using Lemaitre–Tolman–Bondi geometry as an interior metric. We have formulated the relationship between the matter variables as seen by the observers in both co-moving and non-co-moving frames. The dynamical equations are evaluated to study the dynamics of inhomogeneous universe by exploring conservation equations along with the Ellis equations. We have also explored a collapsing factor describing the bouncing phenomena via transport equation and conclude the stability region.

Instability analysis of expansion-free sphere in f(𝒢) gravity

2017 ◽  
Vol 26 (09) ◽  
pp. 1750104
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Dynamical Instability ◽  
Anisotropic Fluid ◽  
Free Fluid ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
First Order ◽  
Text Model ◽  
Metric Functions ◽  
Anisotropic Pressures

The aim of this paper is to study the dynamical instability of expansion-free spherically symmetric anisotropic fluid in the framework of [Formula: see text] gravity. We apply perturbation scheme of the first-order to the metric functions as well as matter variables and construct modified field equations for both static and perturbed configurations using power-law [Formula: see text] model. To discuss the instability dynamics, we use the contracted Bianchi identities to formulate the dynamical equations in both Newtonian and post-Newtonian regimes. It is found that the range of instability is independent of adiabatic index for expansion-free fluid but depends on anisotropic pressures, energy density and Gauss–Bonnet (GB) terms.

Stable wormholes solutions in the background of Rastall theory

2019 ◽  
Vol 35 (07) ◽  
pp. 2050035 ◽  
Author(s):  
G. Mustafa ◽  
M. R. Shahzad ◽  
G. Abbas ◽  
T. Xia
Keyword(s):  
Shape Function ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Major Purpose ◽  
Energy Bounds ◽  
Current Scenario ◽  
The Stability ◽  
And Behavior ◽  
Modified Theory

In this study, we explore the spherically symmetric static wormhole solutions in the Rastall modified theory of gravity. For this, we consider the anisotropic fluid distribution to construct the field equations for Rastall background. Further, we calculate the matter density function and pressure components for anisotropic fluid from the field equations. Furthermore, we employ the traceless fluid by using a particular equation of state (EoS) to analyze the necessary properties of shape function for wormholes and behavior of energy bounds. However, the major purpose of this study is to acquire the wormhole solutions for traceless fluid in the Rastall background. Moreover, we examine the stability of different forces acting on the system. At the end, it is concluded that our solutions under this current scenario are physically acceptable.

scholarly journals Performance Analysis of a Peak-Current Mode Control with Compensation Ramp for a Boost-Flyback Power Converter

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Juan-Guillermo Muñoz ◽  
Guillermo Gallo ◽  
Gustavo Osorio ◽  
Fabiola Angulo
Keyword(s):  
Closed Loop ◽  
Power Converters ◽  
Monodromy Matrix ◽  
Current Mode ◽  
Power Converter ◽  
Dynamical Analysis ◽  
Dynamical Equations ◽  
Peak Current ◽  
Operation Conditions ◽  
The Stability

High voltage gain power converters are very important in photovoltaic applications mainly due to the low output voltage of photovoltaic arrays. This kind of power converters includes three or more semiconductor devices and four or more energy storage elements, making the dynamical analysis of the controlled system more difficult. In this paper, the boost-flyback power converter is controlled by peak-current mode with compensation ramp. The closed-loop analysis is performed to guarantee operation conditions such that a period-1 orbit is attained. The converter is considered as a piecewise linear system, and the closed-loop stability is determined by using the monodromy matrix, obtained by the composition of the saltation matrixes with the solutions of the dynamical equations in the linear intervals. The largest eigenvalue of the monodromy matrix gives the stability of the period-1 orbit, and a deep analysis using bifurcation diagrams let us reach a conclusion about the loss of the stability, which is experimentally verified. To avoid overcompensation effects, the minimum value required by the compensation ramp is obtained, and the minimum and maximum values of the load resistance are found too. The system has a good transient response under disturbances in the load and in the input voltage.

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