scholarly journals Spherically symmetric anisotropic charged solution under complete geometric deformation approach

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
S. K. Maurya ◽  
Asma Mohammed Al Aamri ◽  
Athari Khalifa Al Aamri ◽  
Riju Nag
Keyword(s):  
Systematic Approach ◽  
Compact Objects ◽  
System Of Equations ◽  
Field Equations ◽  
Stellar Objects ◽  
Spacetime Geometry ◽  
Geometric Deformation ◽  
Physical Validity ◽  
The Stability ◽  
The Impact

AbstractWe present a new systematic approach to find the exact gravitationally decoupled anisotropic spherical solution in the presence of electric charge by using the complete geometric deformation (CGD) methodology. To do this, we apply the transformations over both gravitational potentials by introducing two unknown deformation functions. This new systematic approach allows us to obtain the exact solution of the field equations without imposing any particular ansatz for the deformation functions. Specifically, a well-known mimic approach and equation of state (EOS) have been applied together for solving the system of equations, which determine the radial and temporal deformation functions, respectively. The matching conditions at the boundary of the stellar objects with the exterior Reissner–Nordström metric are discussed in detail. In order to see the physical validity of the solution, we used well-behaved interior seed spacetime geometry and solved the system of equations using the above approaches. Next, we presented several physical properties of the solution through their graphical representations. The stability and dynamical equilibrium of the solution have been also discussed. Finally, we predicted the radii and mass-radius ratio for several compact objects for different decoupling parameters together with the impact of the decoupling parameters on the thermodynamical observables.

scholarly journals Compact stars in f(ℛ,𝒢,𝒯 ) gravity

2021 ◽  
Vol 36 (24) ◽  
pp. 2150165
Author(s):  
M. Ilyas
Keyword(s):  
Test Particle ◽  
Gravitational Theory ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Compact Objects ◽  
Compact Stars ◽  
Energy Conditions ◽  
Field Equations ◽  
Physical Features ◽  
The Impact

This work is to introduce a new kind of modified gravitational theory, named as [Formula: see text] (also [Formula: see text]) gravity, where [Formula: see text] is the Ricci scalar, [Formula: see text] is Gauss–Bonnet invariant and [Formula: see text] is the trace of the energy–momentum tensor. With the help of different models in this gravity, we investigate some physical features of different relativistic compact stars. For this purpose, we develop the effectively modified field equations, conservation equation, and the equation of motion for test particle. Then, we check the impact of additional force (massive test particle followed by a nongeodesic line of geometry) on compact objects. Furthermore, we took three notable stars named as [Formula: see text], [Formula: see text] and [Formula: see text]. The physical behavior of the energy density, anisotropic pressures, different energy conditions, stability, anisotropy, and the equilibrium scenario of these strange compact stars are analyzed through various plots. Finally, we conclude that the energy conditions hold, and the core of these stars is so dense.

scholarly journals Stability and improved physical characteristics of relativistic compact objects arising from the quadratic term in $$p_r = \alpha \rho ^2 + \beta \rho - \gamma $$

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
S. Thirukkanesh ◽  
Robert S. Bogadi ◽  
Megandhren Govender ◽  
Sibusiso Moyo
Keyword(s):  
Equation Of State ◽  
Gravitational Potential ◽  
Equations Of State ◽  
Quadratic Equation ◽  
Physical Characteristics ◽  
Compact Objects ◽  
Quadratic Term ◽  
Stellar Objects ◽  
Quadratic Equation Of State ◽  
The Stability

AbstractWe investigate the stability and enhancement of the physical characteristics of compact, relativistic objects which follow a quadratic equation of state. To achieve this, we make use of the Vaidya–Tikekar metric potential. This gravitational potential has been shown to be suitable for describing superdense stellar objects. Pressure anisotropy is also a key feature of our model and is shown to play an important role in maintaining stability. Our results show that the combination of the Vaidya–Tikekar gravitational potential used together with the quadratic equation of state provide models which are favourable. In comparison with other equations of state, we have shown that the quadratic equation of state mimics the colour-flavour-locked equation of state more closely than the linear equation of state.

scholarly journals Accretion disks around a mass with quadrupole QUADRUPOLE

2021 ◽  
Vol 79 (1) ◽  
pp. 352-358
Author(s):  
S. Toktarbay ◽  
◽  
A.Zh. Abylaeva ◽  
G.N. Khudaibergenova ◽  
B.S. Nasyrova ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Test Particle ◽  
Compact Objects ◽  
Geodesic Line ◽  
Field Equations ◽  
Schwarzschild Solution ◽  
Test Particles ◽  
Line Equation ◽  
The Stability

In this work, we consider the exterior static axisymmetric gravitational of compact objects. We investigate the properties of the q-metric which is the simplest generalization of the Schwarzschild solution that contains a quadrupole parameter. The geodesic line equation is derived from the field equations and the orbits of the test particle are investigated. We consider the stability properties of test particles moving along circular orbits around a mass with quadrupole. We show that the quadrupole modifies drastically the properties of an accretion disk made of such test particles.

scholarly journals Charged compact star in f(R, T) gravity in Tolman–Kuchowicz spacetime

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Pramit Rej ◽  
Piyali Bhar ◽  
Megan Govender
Keyword(s):  
Modified Gravity ◽  
Line Element ◽  
Compact Star ◽  
Stellar System ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Field Equations ◽  
Compactness Factor ◽  
Physical Validity ◽  
The Stability

AbstractIn this current study, our main focus is on modeling the specific charged compact star SAX J 1808.4-3658 (M = 0.88 $$M_{\odot }$$ M ⊙ ,  R = 8.9 km) within the framework of $$f(R,\,T)$$ f ( R , T ) modified gravity theory using the metric potentials proposed by Tolman–Kuchowicz (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) and the interior spacetime is matched to the exterior Reissner–Nordström line element at the surface of the star. Tolman–Kuchowicz metric potentials provide a singularity-free solution which satisfies the stability criteria. Here we have used the simplified phenomenological MIT bag model equation of state (EoS) to solve the Einstein–Maxwell field equations where the density profile ($$\rho $$ ρ ) is related to the radial pressure ($$p_{\mathrm{r}}$$ p r ) as $$p_{\mathrm{r}}(r) = (\rho - 4B_{\mathrm{g}})/3$$ p r ( r ) = ( ρ - 4 B g ) / 3 . Furthermore, to derive the values of the unknown constants $$a,\, b,\, B,\, C$$ a , b , B , C and the bag constant $$B_{\mathrm{g}}$$ B g , we match our interior spacetime to the exterior Reissner–Nordström line element at the surface of stellar system. In addition, to check the physical validity and stability of our suggested model we evaluate some important properties, such as effective energy density, effective pressures, radial and transverse sound velocities, relativistic adiabatic index, all energy conditions, compactness factor and surface redshift. It is depicted from our current study that all our derived results lie within the physically accepted regime which shows the viability of our present model in the context of $$f(R,\,T)$$ f ( R , T ) modified gravity.

Anisotropic solution for compact objects in f(𝒢,𝒯) gravity

2020 ◽  
Vol 35 (22) ◽  
pp. 2050121
Author(s):  
M. Sharif ◽  
Aroob Naeem
Keyword(s):  
Compact Star ◽  
Compact Objects ◽  
Anisotropic Solution ◽  
Stellar Objects ◽  
Energy Bounds ◽  
Compactness Factor ◽  
Celestial Bodies ◽  
Specific Formula ◽  
The Stability ◽  
Spherically Symmetric Metric

In this paper, we consider a new solution to discuss the physical aspects of anisotropic compact celestial bodies in the background of [Formula: see text] theory. We take static spherically symmetric metric to describe the internal region of the stellar objects and apply the embedding class-I method to get the metric solution corresponding to a specific [Formula: see text] model. By matching the interior and exterior geometries at the boundary, we find the values of unknown constants. We check the stability and viability of the resulting solution through various parameters that include energy bounds, causality condition, Herrera’s condition, role of adiabatic index, redshift and compactness factor. The graphical interpretation is done for some particular compact star candidates, i.e. LMC X-4, Cen X-3, 4U 1820-30 and Vela X-1. We conclude that our model provides physically acceptable structure of the considered compact objects and is also stable.

Anisotropic solution for compact star in 5D Einstein–Gauss–Bonnet gravity

2021 ◽  
Vol 36 (32) ◽  
Author(s):  
S. K. Maurya ◽  
Anirudh Pradhan ◽  
Ayan Banerjee ◽  
Francisco Tello-Ortiz ◽  
M. K. Jasim
Keyword(s):  
Compact Star ◽  
Compact Objects ◽  
Compact Stars ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Bonnet Gravity ◽  
Spacetime Geometry ◽  
Equilibrium Configurations

In astronomy, the study of compact stellar remnants — white dwarfs, neutron stars, black holes — has attracted much attention for addressing fundamental principles of physics under extreme conditions in the core of compact objects. In a recent argument, Maurya et al. [Eur. Phys. J. C 77, 45 (2017)] have proposed an exact solution depending on a specific spacetime geometry. Here, we construct equilibrium configurations of compact stars for the same spacetime that make it interesting for modeling high density physical astronomical objects. All calculations are carried out within the framework of the five-dimensional Einstein–Gauss–Bonnet gravity. Our main interest is to explore the dependence of the physical properties of these compact stars depending on the Gauss–Bonnet coupling constant. The interior solutions have been matched to an exterior Boulware–Deser solution for [Formula: see text] spacetime. Our finding ensures that all energy conditions hold, and the speed of sound remains causal, everywhere inside the star. Moreover, we study the dynamical stability of stellar structure by taking into account the modified field equations using the theory of adiabatic radial oscillations developed by Chandrasekhar. Based on the observational data for radii and masses coming from different astronomical sources, we show that our model is compatible and physically relevant.

scholarly journals Anisotropic compact stars in f(R) gravity

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
G. G. L. Nashed ◽  
S. Capozziello
Keyword(s):  
Radial Component ◽  
Compact Objects ◽  
Compact Stars ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Interior Solution ◽  
Star Model ◽  
Differential Relation ◽  
Stellar Objects ◽  
The Stability

AbstractWe derive a new interior solution for stellar compact objects in $$f\mathcal {(R)}$$ f ( R ) gravity assuming a differential relation to constrain the Ricci curvature scalar. To this aim, we consider specific forms for the radial component of the metric and the first derivative of $$f\mathcal {(R)}$$ f ( R ) . After, the time component of the metric potential and the form of $$f({\mathcal {R}})$$ f ( R ) function are derived. From these results, it is possible to obtain the radial and tangential components of pressure and the density. The resulting interior solution represents a physically motivated anisotropic neutron star model. It is possible to match it with a boundary exterior solution. From this matching, the components of metric potentials can be rewritten in terms of a compactness parameter C which has to be $$C=2GM/Rc^2<<0.5$$ C = 2 G M / R c 2 < < 0.5 for physical consistency. Other physical conditions for real stellar objects are taken into account according to the solution. We show that the model accurately bypasses conditions like the finiteness of radial and tangential pressures, and energy density at the center of the star, the positivity of these components through the stellar structure, and the negativity of the gradients. These conditions are satisfied if the energy-conditions hold. Moreover, we study the stability of the model by showing that Tolman–Oppenheimer–Volkoff equation is at hydrostatic equilibrium. The solution is matched with observational data of millisecond pulsars with a withe dwarf companion and pulsars presenting thermonuclear bursts.

Mathematical Evaluation of the Impact of Awareness on Epidemic Model using Weighted Network

2019 ◽  
Vol 1 ◽  
pp. 214-223
Author(s):  
G O Agaba
Keyword(s):  
Infectious Disease ◽  
Mathematical Model ◽  
Human Population ◽  
System Analysis ◽  
Biological Systems ◽  
System Of Equations ◽  
Weighted Network ◽  
The Stability ◽  
Mathematical Evaluation ◽  
The Impact

The applications of graph theory in the area of networking are of great significance in system analysis of different varieties, including biological systems. In biological systems, the use of networks finds importance in the study of epidemic and its control. A practical example include the evaluation of the spread of disease within human population and the impact of awareness circulating admist the same population as a result of the infection. Agaba et al. in 2017 proposed a mathematical model that analysed the impact of awareness on the spread of infectious diseases. This was done using the stability analyses of the various steady states of the system of equations and also through the evaluation of some numerical simulations. This paper, with the aid of the system of equations developed by Agaba et al., 2017b, studies the impact of awareness spreading simultaneously with an infectious disease within human population using weighted network.

Dietary Vitamin and Stability of Oral Anticoagulation: Proposal of a Diet with Constant Vitamin K1 Content

1997 ◽  
Vol 77 (03) ◽  
pp. 504-509 ◽  
Author(s):  
Sarah L Booth ◽  
Jacqueline M Charnley ◽  
James A Sadowski ◽  
Edward Saltzman ◽  
Edwin G Bovill ◽  
...  
Keyword(s):  
Dietary Intake ◽  
Vitamin K ◽  
High Performance ◽  
Case Reports ◽  
Food Composition ◽  
Dietary Guidelines ◽  
Dietary Vitamin ◽  
Vitamin K1 ◽  
The Stability ◽  
The Impact

SummaryCase reports cited in Medline or Biological Abstracts (1966-1996) were reviewed to evaluate the impact of vitamin K1 dietary intake on the stability of anticoagulant control in patients using coumarin derivatives. Reported nutrient-drug interactions cannot always be explained by the vitamin K1 content of the food items. However, metabolic data indicate that a consistent dietary intake of vitamin K is important to attain a daily equilibrium in vitamin K status. We report a diet that provides a stable intake of vitamin K1, equivalent to the current U.S. Recommended Dietary Allowance, using food composition data derived from high-performance liquid chromatography. Inconsistencies in the published literature indicate that prospective clinical studies should be undertaken to clarify the putative dietary vitamin K1-coumarin interaction. The dietary guidelines reported here may be used in such studies.

IMPACT OF GOVERNMENT DEBT ON FINANCIAL SECURITY OF UKRAINE

2017 ◽  
Author(s):  
Olena Pikaliuk ◽  
◽  
Dmitry Kovalenko ◽  
Keyword(s):  
Economic Development ◽  
Public Debt ◽  
Positive Impact ◽  
The State ◽  
Financial Security ◽  
State Budget ◽  
The Public ◽  
Debt Security ◽  
The Stability ◽  
The Impact

One of the main criteria for economic development is the size of the public debt and its dynamics. The article considers the impact of public debt on the financial security of Ukraine. The views of scientists on the essence of public debt and financial security of the state are substantiated. An analysis of the dynamics and structure of public debt of Ukraine for 2014-2019. It is proved that one of the main criteria for economic development is the size of public debt and its dynamics. State budget deficit, attracting and using loans to cover it have led to the formation and significant growth of public debt in Ukraine. The volume of public debt indicates an increase in the debt security of the state, which is a component of financial security. Therefore, the issue of the impact of public debt on the financial security of Ukraine is becoming increasingly relevant. The constant growth and large amounts of debt make it necessary to study it, which will have a positive impact on economic processes that will ensure the stability of the financial system and enhance its security.

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