Cornell potential is known to represent the quark-antiquark confinement interaction. In addition to the Cornell potential, there have been other interactions in the literature that demonstrate ...confining structure in the quark-antiquark system. Guendelman has proposed a nonlinear electrodynamics (NED) model which results in electric potential in the form of Cornell interaction. In this study, we propose two NED models whose electric potential is in the form of two other confining potentials. We also study the coupling of gravity to one of these models which are in the form of a correction to linear Maxwell's theory. We find spacetime which can be a black hole or a naked singular particle. In the zeroth approximation, we examine the circular speed of a distant test particle orbiting the central black hole. The Newtonian potential due to the spacetime at the location of the distant particle possesses an additional term proportional to the NED parameter. Due to the presence of such a term, the speed-radius curve gets improved from the pure Reissner-Nordstrom. It is a kind of weaker confinement acting on distant parts of a galaxy due to a supermassive central black hole.
In this study, we explicitly prove that the null circular orbit outside the spherically symmetric asymptotically flat hairy black hole is not stable. Although, if there is more than one external ...light ring at least one of them is stable. The existence of such geodesics has been proved in the recent work of Hod as well as Peng whereas its stability was left uncommented.
In this research, we prove analytically that a generic spherically symmetric thin-shell wormhole (TSW) with its throat located at the innermost photonsphere of the bulk asymptotically flat black hole ...and supported by a generic surface barotropic perfect fluid is unstable against a radial linear perturbation. This is the generalization of the instability of the Schwarzschild TSW (STSW) with the throat’s radius located at
a
0
=
3
M
that was revealed by Poisson and Visser in their seminal work (Poisson and Visser in Phys Rev D 52, 7318, 1995). where they studied the mechanical stability of STSW. Our proof provides a link between the instability of the null circular geodesics on the innermost photonsphere of a generic static spherically symmetric asymptotically black hole and the TSW constructed in the same bulk with
a
0
=
r
c
where
a
0
and
r
c
are the radius of the TSW and the innermost photonsphere, respectively. For asymptotically flat spherically symmetric black holes possessing more than one photonspheres, the number of the photonspheres is odd and at least one photonsphere is stable which implies the corresponding TSW with its throat identical with the stable photonsphere is also stable.
In this study, we present an exact dirty/hairy black hole solution in the context of gravity coupled minimally to a nonlinear electrodynamic (NED) and a Dilaton field. The NED model is known in the ...literature as the square-root (SR) model i.e.,
L
∼
-
F
.
The black hole solution which is supported by a uniform radial electric field and a singular Dilaton scalar field is non-asymptotically flat and singular with the singularity located at its center. An appropriate transformation results in an interesting line element
d
s
2
=
-
1
-
2
M
ρ
η
2
ρ
2
η
2
-
1
d
τ
2
+
1
-
2
M
ρ
η
2
-
1
d
ρ
2
+
ϰ
2
ρ
2
d
Ω
2
with two parameters – namely the mass
M
and the Dilaton parameter
η
2
>
1
(
ϰ
2
=
1
η
2
) – which may be simply considered as the dirty Schwarzschild black hole. This is because with
η
2
→
1
the spacetime reduces to the Schwarzschild black hole. We show that although the causal structure of the above spacetime is similar to the Schwarzschild black hole, it is thermally stable for
η
2
>
2
. Furthermore, the tidal force of this black hole behaves the same as a Schwarzschild black hole, however, its magnitude depends on
η
2
such that its minimum is not corresponding to
η
2
=
1
(Schwarzschild limit).
We introduce a two-parameter static, nonspherically-symmetric black hole solution in the Einstein theory of gravity coupled with a massless scalar field. The scalar field depends only on the polar ...coordinate
θ
in the spherical coordinates representation. The scalar invariant of the spacetime, namely, the Kretschmann scalar reveals that the black hole is singular on its axis of symmetry for all nonzero values of the scalar charge. It also manifests two surfaces of singularity for a certain interval of the value of the scalar charge. These singularities are hidden behind the event horizon’s surface except the singularity on the axis which is naked. The energy-momentum of the scalar field satisfies all energy conditions. A simple investigation reveals that the circular orbits of massive and massless particles in the equatorial plane are identical to those near a Schwarzschild black hole.
•The effects of building orientation, heat treatment, and surface finish on the fatigue strength of SLM steels.•The effects of manufacturing parameters on the fatigue strength of SLM steels.•Defects ...and crack-microstructure interactions in SLM steels based on their manufacturing parameters.•Knowledge gaps in the field of fatigue characteristics of SLM steels and necessity of further study in this regards.
Additive manufacturing is extending its influence on various modern industries, including automobile, aerospace, aviation, and maritime. This is specifically true for selective laser melting since it is capable of manufacturing dense parts from metal and alloy powders. Thus, the performance of materials processed by selective laser melting has become the focus of many studies recently. However, their fatigue endurance is yet to be understood comprehensively, and few studies have been carried out on this topic thus far. The lack of understanding is often attributed to the considerable number of manufacturing parameters, which also hinders employing selective laser melting for typical industrial applications. Among the various materials processed by selective laser melting, steel is one of the most attractive ones to manufacturers due to its broad range of properties and applications. This paper aims to describe the studies carried out on the fatigue properties of diverse types of steel manufactured by selective laser melting. It also reviews the parameters which are recognized to be effective on the fatigue behaviour of these steels. These parameters include building orientation, heat treatment, surface quality, energy density, and service condition of the final product. Recent studies on selective laser melting along with the variety of its influential parameters on the fatigue strength highlight a knowledge gap towards reaching a comprehensive understanding of the fatigue behaviour of steels manufactured by this process. Based on this fact, some of these gaps are discussed as the potential topics for the future studies in the field of additive manufacturing at the end of this review.
Null energy condition (NEC) is revisited in the context of thin-shell wormholes (TSW). In a generic spherically symmetric configuration we introduce the condition upon which NEC is satisfied. Also, ...we present a general condition which specifies the stability of the generic spherically symmetric TSW against a radial linear perturbation. Furthermore, we introduce a specific bulk metric in the framework of gravity coupled minimally with nonlinear electrodynamics such that the corresponding TSW satisfies NEC, unconditionally. We study the mechanical stability of this TSW and show that, with a variable equation of state of the fluid present at the throat, this TSW remains stable irrespective of the value of the speed of sound.
The nonlinear Maxwell Lagrangian preserving both conformal and SO(2) duality-rotation invariance has been introduced very recently. Here, in the context of Einstein’s theory of gravity minimally ...coupled with this nonlinear electrodynamics, we obtain a black hole solution which is the Reissner–Nordström black hole with one additional parameter that is coming from the nonlinear theory. We employ the causality and unitarity principles to identify an upper bound for this free parameter. The effects of this parameter on the physical properties of the black hole solution are investigated.
Hardware components are an integral part of Hardware Define Radio (HDR) for seamless operations and optimal performance. On the other hand, Software Define Radio (SDR) is a program that does not rely ...on any hardware components for its performance. Both of the latter radio programmers utilize modulation functions to make their core components from signal processing viewpoint. The following paper concentrates on SDR based modulation and their performance under different modulations. The bit error rate (BER) of modulations such as PSK, QAM, and PSAM were used as indicators to test channel quality estimation in planar Rayleigh fading. Though it is not commonly used for channel fading, the method of the adder determines the regionally segmented channel fading. Thus, the estimation error of the channel change substantially reduces the performance of the signal, hence, proving to be an effective option. Moreover, this paper also elaborates that BER is calculated as a function of the sample size (signal length) with an average of 20 decibels. Consequently, the size of the results for different modulation schemes has been explored. The analytical results through derivations have been verified through computer simulation. The results focused on parameters of amplitude estimation error for 1dB reduction in the average signal-to-noise ratio, while the combined amplitude deviation estimation error results are obtained for a 3.5 dB reduction.
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