JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2013 | Volume:7 | Issue:7|Papers Count:8

Nanocrystalline Pb1–3x/2GdxTiO3 (where x = 0.01) abbreviated as PGT has been synthesized by high energy ball milling at room temperature. X-ray analysis shows that single-phase tetragonal structure of nanocrystalline PGT was formed after 15-h milling. The average crystallite size was found to be 17 nm. The frequency-dependent AC conductivity of the PGT ceramic was studied in the range 100°C to 525°C. Complex impedance analysis suggested the dielectric relaxation to be of non-Debye type. The activation energy was found to be 1.04 ev. The mechanism of charge transport in nanocrystalline PGT was successfully explained by correlated hopping model.

We hereby introduce a research about a grand canonical ensemble for the extended two-site Hubbard model, that is, we consider the intersite interaction term in addition to those of the simple Hubbard model. To calculate the thermodynamical parameters, we utilize the nonextensive statistical mechan- ics; specifically, we perform the simulations of magnetic internal energy, specific heat, susceptibility, and thermal mean value of the particle number operator. We found out that the addition of the inter- site interaction term provokes a shifting in all the simulated curves. Furthermore, for some values of the on-site Coulombian potential, we realize that, near absolute zero, the consideration of a chemical potential varying with temperature causes a nonzero entropy.

It has been shown that the overdense plasma in the resonance conditions can be totally transparent to the incident electromagnetic waves, due to the excitation of the surface modes or plasmons. This scenario requires excitation of a single surface mode which is provided by placing a dielectric layer in front of the incident wave. Here, it is shown that this procedure would be complete and more efficient by arranging the conditions to excite coupled surface modes, namely by placing two dielectrics on both sides of the plasma layer. The results show that in this case, the overdense plasma slab could poses high transmittance in spite of the presence of the dissipative effects. In addition, in this case, the resonance conditions can be achieved more easily and efficiently, and can be used for wider range of the overdense plasma widths.

The ultrasonic velocity, density, and viscosity have been measured for ternary mixtures of nitrobenzene, N,N-dimethylformamide, and cyclohexane at temperature T = 318 K at different frequencies such as 2, 4, 6, and 8 MHz. The experimental data have been used to calculate the acoustical and thermodynamical parameters like adiabatic compressibility, free length, free volume, internal pressure, acoustic impedance, Gibbs free energy, and their excess values. In particular, it is seen that the response of these parameters to frequency is less prominent in comparison to that of the ternary mixtures containing N,N-dimethylformamide, cyclohexane, and chlorobenzene.

In the framework of fractional action cosmology, we have reconstructed the scalar potentials and scalar fields, namely, quintessence, phantom, tachyon, k-essence, Dirac-Born-Infeld-essence, hessence, dila- ton field, and Yang-Mills field. To get more physical picture of the variation of the scalar field and potential with time, we express a scale factor in emergent, logamediate, and intermediate scenarios, under which the universe expands differently.

In this work, we discussed the ‘modified holographic Ricci dark energy’ cosmological model based on El-Nabulsi fractional action cosmology. corresponding related cosmological parameters have been reconstructed. It has been observed that the equation of state parameter behaves like quintessence. Finally, through a test by the squared speed of sound, the proposed reconstruction model is found to be classically unstable.

In this work, we developed the rescaled range method and its formalism to investigate the surface morphology dynamics of indium tin oxide (ITO) thin films. The dynamic scaling behavior of grown ITO thin films, which were prepared by electron beam deposition method on float glass substrates at room temperature, was studied through atomic force microscopy (AFM). AFM data indicated that the average surface roughness values of the films decreased as the film thickness increased from 100 to 250 nm. Based on fractal concept and statistical physics techniques, the irregularities of the ITO films were analyzed. The roughness exponent H and the growth exponent b for ITO films were determined to be 0.71±0.01 and 0.11±0.01, respectively. The fractal analysis reveals that the value of the fractal dimension Df (Df=3-H) falls within the range 2.29 to 2.24 depending upon the films thickness. These results show that the growth process of the films can be described by the combination of Edwards-Wilkinson and Mullins diffusion models.

The a-Fe2O3 nanoparticles have been synthesized using some surfactants in micro-emulsion method. Magnetization, M (H), of samples was measured at room temperature. Magnetic hysteresis loops were observed in all samples. A new magnetization function (H-A model) was offered to explain the field dependence of the magnetization behavior of a-Fe2O3. In this work, the magnetization curve of all samples was analyzed based on MBrillouin, MBrillouin-Akulov, and MBrillouin-(H-A) model. The experimental data have fitted with the MBrillouin-(H-A) model, and the best fitting parameters were analyzed.