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Jahrom, Iran

Ghanaatian M.,Payame Noor University | Bazrafshan A.,Jahrom University
International Journal of Modern Physics D

In this paper, we present the static charged solutions of quartic quasi-topological gravity in the presence of a nonlinear electromagnetic field. Two branches of these solutions present black holes with one or two horizons or a naked singularity depending on the charge and mass of the black hole. The entropy of the charged black holes of fourth-order quasi-topological gravity through the use of Wald formula is computed and the mass, temperature and the charge of these black holes are found as well. We show that black holes with spherical, flat and hyperbolical horizon in quasi-topological gravity are stable for any allowed quasi-topological parameters. We also investigate the stability of nonlinear charged black holes. © 2013 World Scientific Publishing Company. Source

Ghanaatian M.,Payame Noor University | Bazrafshan A.,Jahrom University | Brenna W.G.,University of Waterloo
Physical Review D - Particles, Fields, Gravitation and Cosmology

In this paper we elucidate some of the effects of the quartic quasitopological term for Lifshitz-symmetric black holes. The field equations of this theory are difficult to solve exactly; here we use numerical solutions both to verify previous exact solutions for quartic quasitopological anti-de Sitter black holes as well as to examine new quasitopological Lifshitz-symmetric black hole solutions, in order to determine the effect of the quartic coupling parameter on the black hole's thermodynamic behavior. We find that the quartic parameter controls solutions very similarly to the cubic parameter, allowing for the construction of a theory with another free parameter which may find meaning in the phase transition behavior of a gauge/gravity context. © 2014 American Physical Society. Source

Naseri M.G.,University of Malayer | Halimah M.K.,University Putra Malaysia | Dehzangi A.,National University of Malaysia | Kamalianfar A.,Jahrom University | And 2 more authors.
Journal of Physics and Chemistry of Solids

Abstract This study reports the simple synthesis of MFe2O 4 (where M=Zn, Mn and Co) nanostructures by a thermal treatment method, followed by calcination at various temperatures from 723 to 873 K. Poly(vinyl pyrrolidon) (PVP) was used as a capping agent to stabilize the particles and prevent them from agglomeration. The pyrolytic behaviors of the polymeric precursor were analyzed by use of simultaneous thermo-gravimetry analyses (TGA) and derivative thermo-gravimetry (DTG) analyses. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of metal oxide bands for all the calcined samples. Magnetic properties were demonstrated by a vibrating sample magnetometer (VSM), which displayed that the calcined samples exhibited different types of magnetic behavior. The present study also substantiated that magnetic properties of ferrite nanoparticles prepared by the thermal treatment method, from viewing microstructures of them, can be explained as the results of the two important factors: cation distribution and impurity phase of α-Fe2O3. These two factors are subcategory of the preparation method which is related to macrostructure of ferrite. Electron paramagnetic resonance (EPR) spectroscopy showed the existence of unpaired electrons ZnFe2O4 and MnFe2O4 nanoparticles while it did not exhibit resonance signal for CoFe 2O4 nanoparticles. © 2013 Elsevier Ltd. All rights reserved. Source

Bahadoran M.,University of Technology Malaysia | Afroozeh A.,University of Technology Malaysia | Afroozeh A.,Jahrom University | Ali J.,University of Technology Malaysia | Yupapin P.P.,King Mongkuts University of Technology Thonburi
Optical Engineering

We propose a novel design of optical buffer to generate slow light based on delay time. In the framework of the nonlinear waveguide, we investigate propagation of solitons through microring resonators. Dynamical control over slow-light solitons is realized via controlling fields generated by bright soliton and Gaussian pulse. The nonlinear dependence of the velocity of the signal on the controlling field is analytically described. The buffering effect is achieved by slowing the optical signal using an external control light source to vary the dispersion characteristic of the medium via microring resonators. A graphical approach with a signal flow graph method is used to derive the optical transfer functions in z-domain of filters. The characteristics of the optical buffer devices including the transmittance and time delay of the through and drop port are simulated. Simulated results show the criteria of achieving slow light in semiconductor microring resonators. Finally, output signal shows the delay time rate by propagation through the semiconductor microring resonators. © 2012 Society of Photo-Optical Instrumentation Engineers. Source

Dehghani M.H.,Shiraz University | Dehghani M.H.,Research Institute for Astrophysics and Astronomy of Maragha RIAAM | Bazrafshan A.,Shiraz University | Bazrafshan A.,Jahrom University | And 4 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology

We construct quartic quasitopological gravity, a theory of gravity containing terms quartic in the curvature that yields second-order differential equations in the spherically symmetric case. Up to a term proportional to the quartic term in Lovelock gravity we find a unique solution for this quartic case, valid in any dimensionality larger than 4 except 8. This case is the highest degree of curvature coupling for which explicit black hole solutions can be constructed, and we obtain and analyze the various black hole solutions that emerge from the field equations in (n+1) dimensions. We discuss the thermodynamics of these black holes and compute their entropy as a function of the horizon radius. We then make some general remarks about K-th order quasitopological gravity, and point out that the basic structure of the solutions will be the same in any dimensionality for general K apart from particular cases. © 2012 American Physical Society. Source

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