18 research outputs found
Light Deflection by Rotating Regular Black Holes with a Cosmological Constant
Using the Gauss-Bonnet theorem, we compute and examine the deflection angle
of light rays by rotating regular black holes with a cosmological constant. By
the help of optical geometries, we first deal with the Hayward black holes with
cosmological contributions. Then, we reconsider the study of the Bardeen
solutions. We inspect the cosmological constant effect on the deflection angle
of light rays. Concretely, we find extra cosmological correction terms
generalizing certain obtained findings. Using graphical analysis, we provide a
comparative discussion with respect to the Kerr solutions. The results confirm
that the non-linear electrodynamic charges affect the space-time geometry by
decreasing the deflection angle of light rays by such cosmological black holes.Comment: latex, 16 pages, 4 figures. Accepted for publication in Chin. J. Phys
202
Deflection angle and Shadows by Black Holes in Starobinsky-Bel-Robinson Gravity from M-theory
Motivated by M-theory compactifications, we investigate optical properties of
black holes in the Starobinsky-Bel-Robinsion gravity. Precisely, we study the
shadows and the deflection angle of light rays by non-rotating and rotating
black holes in such a novel gravity. We start by discussing the shadows of the
Schwarzschild-type solutions. As expected, we obtain perfect circular shadows
where the size decreases with a stringy gravity parameter denoted by .
We show that this parameter is constrained by the shadow existence. Combining
the Newman-Janis algorithm and the Hamilton-Jacobi mechanism, we examine the
shadow behaviors of the rotating solutions in terms of one-dimensional real
curves. Essentially, we find various sizes and shapes depending on the rotating
parameter and the stringy gravity parameter and , respectively. To
inspect the shadow geometric deformations, we investigate the astronomical
observables and the energy emission rate. As envisaged, we reveal that and
have an impact on such shadow behaviors. For specific values of , we
remark that the obtained shadow shapes share certain similarities with the ones
of the Kerr black holes in plasma backgrounds. Using the Event Horizon
Telescope observational data, we provide predictions for the stringy gravity
parameter which could play a relevant role in M-theory
compactifications. We finish this work by a discussion on the behaviors of the
light rays near to such four dimensional black holes by computing the
deflection angle in terms of a required moduli space.Comment: Latex, 27 pages, 10 figures. Authors in alphabetical orde
Light Behaviors around Black Holes in M-theory
We study the deflection angle and the trajectory of the light rays around
black holes in M-theory scenarios. Using the Gauss-Bonnet theorem, we first
compute and examine the deflection angle of the light rays near four and
seven-dimensional AdS black holes obtained from the M-theory compactifications
on the real spheres on and , respectively. We discuss the effect of
the M-theory brane number and the rotating parameter on such an optical
quantity. We then investigate the trajectories of the light rays using the
equation of motion associated with and branes.Comment: Latex, 22 pages, 8 figure
Synthesis and Characterizations of Bare CdS Nanocrystals Using Chemical Precipitation Method for Photoluminescence Application
Bare cadmium sulfide (CdS) nanocrystals were successfully synthesized by the thermolysis of a single-source organometallic precursor, cadmium chloride hemipentahydrate (CdCl2⋅2.5H2O) with thiourea in ethanol. The microstructure of the CdS samples was characterized using XRD, TEM, and Raman spectroscopy. The XRD's results showed that there was a transformation from cubic to hexagonal crystalline phase when higher mass of CdCl2⋅2.5H2O was used. Further experimental with different Cd2+ source showed ion Cl− originated from CdCl2⋅2.5H2O attributed to this crystalline phase transformation. The UV-Visible analysis indicated that quantum confinement effect took place when compared to the bulk CdS. However, the photoluminescence experiments revealed that the red-light emission was observed in all samples. This finding could be ascribed to deep trap defects that were due to sulfur vacancies as suggested by XPS and also the fact that the bare CdS nanoparticles are in contact with each other as shown in the TEM images
Growth and characterisation of carbon nanostructures obtained by MPACVD system using CH4/CO2 gas mixture
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