60 research outputs found
Details on the Positronium Hyperfine Splitting due to Single Photon Annihilation
A detailed presentation is given of the analytic calculation of the
single-photon annihilation contributions to the positronium ground state
hyperfine splitting to order in the framework of non-relativistic
effective theories. The current status of the theoretical description of the
positronium ground state hyperfine splitting is reviewed.Comment: 27 pages, latex, 5 postscript figures; typos correcte
A study on the dependence of structure of multi-walled carbon nanotubes on acid treatment
In the current research, the role of both concentrated nitric acid and ultrasound waves on oxidation of multi-walled carbon nanotubes (MWNTs) was studied. The functionalized MWCNTs were characterized by transmission electron microscopy (TEM), thermogravimetric analyzer, and Fourier transform infrared spectroscopy (FTIR) techniques. It was found that desirable modifications to MWNTs occurred after acid treatment. Carboxylic acid groups were appeared on the side surfaces of MWNTs. FTIR presented the formation of oxygen-containing groups such as C=O and COOH after modification by concentrated nitric acid. The TEM images showed that the aspect ratio of opened MWCNTs was controlled by both ultrasonic waves and acid treatment time. It was also found that the exposure of about 4 h in nitric acid led to the highest removal of the impurities with the least destructive effect
Thermodynamics and reentrant phase transition for logarithmic nonlinear charged black holes in massive gravity
We investigate a new class of -dimensional topological black hole
solutions in the context of massive gravity and in the presence of logarithmic
nonlinear electrodynamics. Exploring higher dimensional solutions in massive
gravity coupled to nonlinear electrodynamics is motivated by holographic
hypothesis as well as string theory. We first construct exact solutions of the
field equations and then explore the behavior of the metric functions for
different values of the model parameters. We observe that our black holes admit
the multi-horizons caused by a quantum effect called anti-evaporation. Next, by
calculating the conserved and thermodynamic quantities, we obtain a generalized
Smarr formula. We find that the first law of black holes thermodynamics is
satisfied on the black hole horizon. We study thermal stability of the obtained
solutions in both canonical and grand canonical ensembles. We reveal that
depending on the model parameters, our solutions exhibit a rich variety of
phase structures. Finally, we explore, for the first time without extending
thermodynamics phase space, the critical behavior and reentrant phase
transition for black hole solutions in massive gravity theory. We realize that
there is a zeroth order phase transition for a specified range of charge value
and the system experiences a large/small/large reentrant phase transition due
to the presence of nonlinear electrodynamics.Comment: 14 pages (one column), 12 captioned figure
Is the compact binary coalescence, GW190425, a strange quark star?
In this study, the effects of different QCD models in the structure of
strange quark star (SQS) are investigated. In these models, the running
coupling constant has a finite value in the infrared region of energy. By
imposing some constraints on the strange quark matter (SQM) and by exploiting
the analytic and background perturbation theories, the equations of states for
the SQM are obtained. Then, the properties of SQSs in general relativity are
evaluated. By using component masses of GW190425 as well as some conversion
relations between the baryonic mass and the gravitational mass, the remnant
mass of GW190425 is obtained. Our results for the maximum gravitational mass of
SQS are then compared with the remnant mass of GW190425. The results indicate
that the obtained maximum gravitational masses are comparable to the remnant
mass of GW190425. Therefore, it is proposed that the remnant mass of GW190425
might be a SQS.Comment: 8 pages, 5 figures, 4 tables. Added two section
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