Charged gravastars in modified Gauss–Bonnet gravity

This work probes the influence of charge field on the unique stellar structure, regarded as gravastar, under the corrections of [Formula: see text] theory, i.e. [Formula: see text] theory, where [Formula: see text] is named as Gauss–Bonnet invariant. The gravastar has also been recognized as an alternate candidate of black hole structure and is illustrated by three distinct regions termed as (1) the exterior (2) the intermediate thin shell (3) the interior domain. We discussed the mathematical solutions for each of three regions separately with the assistance of different equation-of-states (EoS). The exterior charged vacuum domain is expressed by the Reissner–Nordström solution. The central region is illustrated by the EoS, i.e. a positive pressure of ultra-relativistic matter is equal to the energy density. Whereas, the interior domain reflects that the negative pressure is equal to energy density and manifests a non-attractive force over the central spherical shell. We deduce that in the context of [Formula: see text] theory, the nonsingular charged model with distinct physical features, such as energy, length, entropy, is physically viable and consistent.

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The Proton and Neutron as Distortional Structures in the Geometric Manifold

10.21203/rs.3.rs-949816/v1 ◽

2021 ◽

Author(s):

Dale. R. Koehler

Keyword(s):

Energy Density ◽

Negative Pressure ◽

Positive Charge ◽

Core Region ◽

Positive Pressure ◽

Potential Well ◽

Space Model ◽

The Core ◽

Density Behavior ◽

Distorted Geometry

Abstract It is shown in the present work that the distorted-space model of matter as extended to mimics of the proton and neutron can be described as muonic-based structures. These distorted-geometry structures exhibit non-Newtonian features wherein the hole or core-region fields of the structure (negative pressure core for a positive-charge positive-pressure large-r structure) do not behave functionally in a r−4 manner and terminate at zero at the radial origin (no singularity). Of particular interest is that of r−6 energy-density behavior at structural radial distances near the core of the distortion, a region also displaying potential-well behavior.

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The thermal-like equilibrium universe in f(R) gravity

Modern Physics Letters A ◽

10.1142/s0217732316501984 ◽

2016 ◽

Vol 31 (36) ◽

pp. 1650198

Author(s):

Yi-Huan Wei ◽

Jia-Xin Zhao ◽

Xiao Cui

Keyword(s):

Energy Density ◽

Apparent Horizon ◽

Late Time ◽

Time Form ◽

Relativistic Matter

Some problems of the thermal-like equilibrium (TLE) universe in f(R) gravity are studied. Given the energy density of the TLE universe, the late-time form of f(R) is obtained. For the TLE universe driven by the non-relativistic matter, the energy of the apparent horizon (AH) and the ratio between it and the energy inside the AH are calculated.

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High performance asymmetric supercapacitors with ultrahigh energy density based on hierarchical carbon nanotubes@NiO core–shell nanosheets and defect-introduced graphene sheets with hole structure

RSC Advances ◽

10.1039/c6ra27369f ◽

2017 ◽

Vol 7 (13) ◽

pp. 7843-7856 ◽

Cited By ~ 39

Author(s):

Zenghui Qiu ◽

Dawei He ◽

Yongsheng Wang ◽

Xuan Zhao ◽

Wen Zhao ◽

...

Keyword(s):

Carbon Nanotubes ◽

Energy Density ◽

High Performance ◽

Cost Effective ◽

Graphene Sheets ◽

Core Shell ◽

Ultrahigh Energy ◽

Asymmetric Supercapacitors ◽

Hierarchical Carbon ◽

Hole Structure

In this work, we report a fast and cost-effective cobalt catalyzed gasification strategy to obtain defect-introduced graphene sheets (DGNs) with hole structure.

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On the electrostatic energy of two point charges

Revista Brasileira de Ensino de Física ◽

10.1590/s1806-11172014000300001 ◽

2014 ◽

Vol 36 (3) ◽

Author(s):

A.C. Tort

Keyword(s):

Fixed Point ◽

Energy Density ◽

Electrostatic Field ◽

Electrostatic Energy ◽

Field Energy ◽

Field Energy Density ◽

Physical Features

The electrostatic field energy due to two fixed point-like charges shows some peculiar features concerning the distribution in space of the field energy density of the system. Here we discuss the evaluation of the field energy and the mathematical details that lead to those peculiar and non-intuitive physical features.

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Non-Extensive Thermodynamics Effects in the Cosmology of f(T) Gravity

Symmetry ◽

10.3390/sym13010075 ◽

2021 ◽

Vol 13 (1) ◽

pp. 75

Author(s):

Asmaa G. Shalaby ◽

Vasilis K. Oikonomou ◽

Gamal G. L. Nashed

Keyword(s):

Dark Energy ◽

Equation Of State ◽

Energy Density ◽

Energy Equation ◽

State Parameter ◽

Gravitational Theory ◽

Density Parameter ◽

Dark Energy Density ◽

Equation Of State Parameter ◽

Relativistic Matter

Using f(T) gravitational theory, we construct modified cosmological models via the first law of thermodynamics by using the non-extensive thermodynamics framework, the effects of which are captured by the parameter δ. The resulting cosmological equations are modified compared to the standard Einstein-Hilbert ones, with the modifications coming from the f(T) gravitational theory and from the non-extensive parameter which quantifies the non-extensive thermodynamics effects quantified by the parameter δ, which when is set equal to unity, one recovers the field equations of f(T) gravity. We study in detail the cosmological evolution of the model in the presence of collisionless non-relativistic matter case, and we derive the exact forms of the dark energy density parameter and of the dark energy equation of state parameter, from which we impose constraints on the non-extensive thermodynamics parameter, δ, by using the Planck 2018 data on cosmological parameters. Accordingly, we repeat our calculations after including the relativistic matter along with the non-relativistic one, and we derive the new forms of the dark energy density parameter and of the dark energy equation of state parameter. Our study shows that the inclusion of non-extensive thermodynamic effects, quantified by the parameter δ, for a flat Friedmann-Robertson-Walker Universe, has measurable differences compared with the normal thermodynamics case. We confront our results with Type Ia supernovae observations for z≥0.4 and we obtain reasonably agreement with the observational data.

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Features of an analytical solution in Eddington inspired Born–Infeld (EiBI) gravity

Modern Physics Letters A ◽

10.1142/s0217732321500012 ◽

2021 ◽

pp. 2150001

Author(s):

Mithun Ghosh

Keyword(s):

Exact Solution ◽

Energy Density ◽

Analytical Solution ◽

Compact Star ◽

Paper Analysis ◽

Energy Conditions ◽

Spherically Symmetric ◽

Field Equations ◽

Equation Of States ◽

Future Implication

Recently, Harko et al. [Phys. Rev. D 88, 044032 (2013)] have derived an exact solution of the spherically symmetric field equations in EiBI gravity, describing a compact star with decreasing pressure but increasing energy density. We have explored some features of this solution by restricting the range of the parameter [Formula: see text] which satisfies four energy conditions for 10 equation of states (EOSs). Viability and deviations of these features in the light of updated observed properties of neutron stars (NS) have been explored completely. A comparison of those features with recent observations may uncover the future implication of this paper. Analysis of our results indicates that this solution may be used as an alternative EOS.

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VECTOR-FIELD MODEL WITH COMPENSATED COSMOLOGICAL CONSTANT AND RADIATION-DOMINATED FRW PHASE

International Journal of Modern Physics D ◽

10.1142/s0218271812500253 ◽

2012 ◽

Vol 21 (03) ◽

pp. 1250025 ◽

Cited By ~ 10

Author(s):

V. EMELYANOV ◽

F. R. KLINKHAMER

Keyword(s):

Vector Field ◽

Energy Density ◽

Cosmological Constant ◽

Planck Scale ◽

Vacuum Energy Density ◽

Dynamic Vacuum ◽

Type Interaction ◽

Friedmann Robertson Walker ◽

Matter Energy ◽

Relativistic Matter

A special model of a massless-vector-field is presented, which has an extra modified-gravity-type interaction term in the action. The cosmology of the model is studied with standard noninteracting relativistic matter added. It is found that this cosmology can have an early phase where the vector-field starts to compensate a (Planck-scale) cosmological constant and a late Friedmann–Robertson–Walker (FRW) phase where the relativistic-matter energy density dominates the dynamic vacuum energy density.

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A photoelectron microscope study of surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152021 ◽

1989 ◽

Vol 47 ◽

pp. 10-11

Author(s):

W. Engel ◽

M. Kordesch ◽

A. M. Bradshaw ◽

E. Zeitler

Keyword(s):

Electron Microscopy ◽

High Pressure ◽

Field Strength ◽

Uv Light ◽

Physical Property ◽

Photon Flux ◽

Mercury Lamp ◽

Object Surface ◽

The Sixties ◽

Physical Features

Photoelectron microscopy is as old as electron microscopy itself. Electrons liberated from the object surface by photons are utilized to form an image that is a map of the object's emissivity. This physical property is a function of many parameters, some depending on the physical features of the objects and others on the conditions of the instrument rendering the image.The electron-optical situation is tricky, since the lateral resolution increases with the electric field strength at the object's surface. This, in turn, leads to small distances between the electrodes, restricting the photon flux that should be high for the sake of resolution.The electron-optical development came to fruition in the sixties. Figure 1a shows a typical photoelectron image of a polycrystalline tantalum sample irradiated by the UV light of a high-pressure mercury lamp.

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