Iranian Journal of Physics Research
Year:2018 | Volume:18 | Issue:1 |Papers Count:20

In this paper, we consider a massive charged scalar field coupled to a uniform background electric field in a 3 dimensional de Sitter spacetime. We also consider the constant value of the dimensionless coupling of the scalar field to the scalar curvature of a 3 dimensional de Sitter spacetime equal to 1/8. We compute the expectation value of the trace of the energy-momentum tensor in the in-vacuum state, showing that by using te adiabatic subtraction regularization method, the linear ultraviolet divergence is removed and a finite expression is obtained. We investigate the behavior of the regularized trace with different intensities of the scalar field mass and electric fields. We show that the trace as a function of the electric field has a discontinuity where it changes the sign. In the case of a scalar field conformally coupled to the de Sitter spacetime, we show that the trace vanishes and there is no trace anomaly. We discuss the gravitational backreaction effect of the created Schwinger pairs.

Ground state Positronium (Ps) formation and the 2s state of hydrogen atom by positron impact in the intermediate and high energy range have been studied within the framework of Eikonal direct approximation. The eikonal chargeexchange scattering amplitude and the differential and total cross sections have been computed by reducing the sixdimensional integrals to one-dimensional ones; the results have been compared with some existing theoretical results and the experimental findings.

Using the Dirichlet-Neumann mapping method, we were able to calculate the photonic band structure of the annular metal photonic crystals. The surveyed grid is square and scattering centers (bars) are in the form of air rings located on the metal surface, as well as metal rings located in the air. The photonic band structure is calculated for both polarizations E and H for electromagnetic waves. The results indicate that there are frequency bands (photon strips) plus flat bands at low light speeds. The effect of the size of the air and metal rings on photonic tape structures has been theoretically investigated.

According to the perturbation order, the equations related to the motion of low-energy string effective action are, in fact, a type of generalization of Einstein equations. Thus, by usingthe conformal transformation of the metric tensor, the lowenergy string effective action into f (T) gravity is shown, with a relationship between the dilaton field and the torsion scalar. Considering a homogeneous and isotropic universe for the canonical Lagrangian of f (T) gravity, we show that this lagrangian is kept invariant under the transformations of the metric tensor and abelian duality (scale factor duality). Finally, by the use of the dualized Lagrangian and also, the invariance of torsion scalar T under the transformation of the scale factor duality a(t) 1/ a(t), the precise form of the f (T) function is obtained.

In this paper, we use the holographic renormalization method to calculate the two-point correlation functions of the CFT stress tensor. In the gravity side, we write the asymptotically AdS spacetimes in the BMS gauge and apply the standard holographic renormalization method for these space-times. The significance of using multi-point functions in this gauge is that its flat-space limit is well-defined. We discuss this point in the last section of the paper.

In this study, the particle vibration coupling for nuclei around 208Pb addressed. Hamiltonian matrix was constructed on the basis of particle vibration eigenvectors; then, after matrix Diagonalization, fitting with the experimental states was done. Therefore, a set of pure single particle states were obtained which were also called modified experimental levels. The results showed that the neutron and proton energy gap wasconsiderably increased to 0. 81 MeV and 0. 39 MeV in the modified spectrum, respectively. The shell model parameters of phenomenological Woods-Saxon (WS) potential was then adjusted to reproduce these modified experimental states. The results showed that the WS potential could predict the experimental states more precisely with the help of new parameters.

First, the structure function of the many fermion systems is written in terms of the fluctuation of the target density and the value of this function is calculated at very small momentum transfer. It is shown that the value of the structure function at very small momentum transfer can be calculated from two different ways; one is the mathematical straight way and the other one is the sum rules of the quantum fluids not equal; this is a paradox for the many-fermion systems. Finally, to resolve this paradox, we correct the response function or the structure function of the many fermion systems and offer a new defination for these functions.

In this paper, the effect of titanium dioxide nanoparticles on the response of the freely suspended nano-fluid was investigated in an external electric field. Applying the external electric field to liquid film carrying electric current caused the layer rotation. It was due to the surface charge response of the layer to the electric field. The effect of surface charge on titanium dioxide nano-fluid rotation at various concentrations was studied. The results showed that the presence of nanoparticles in the fluid doubled the rotation velocity. Also, the effect of ultraviolet radiation on the rotation velocity of the fluid was examined, showing that there was no significant impact on rotation velocity. Finally, the needed time to reach the maximum rotation velocity of the nano-fluids layers was measured.

In the present research, we aim to study the synthesis of some isotopes of Flerovium 287 114Fl, 288 114Fl, 289 114Fl and 290 114Fl in the island of stability produced in the nuclear fusion of Ca ions with 239Pu, 240Pu, 241Pu, and 242Pu nuclei and to investigate the effect of different directions of target nuclei on the parameters of the fusion barriers We show that the contact angles of target nuclei influence the parameters of the fussion barriers of 48Ca ions with Pu different isotopes; and also we obtain the parameters of the fusion barriers for the synthesis of 287Fl, 288Fl, 289Fl and 290Fl nuclei and compare them with each other. . Also, we show that the minimum necessary energies for the synthesis of287Fl, 288Fl, 289Fl and 290Fl nuclei are 184. 16 MeV, 183. 95 MeV, 183. 75 MeV and 183. 56 MeV, respectively. Finally, in the framework of the statistical model, we attempt to estimate the evaporation residue cross section for 286Fl, 287Fl nuclei after the emission of three and four neutrons from 290Fl nuclei, showing that in the statistical model framework the results of calculations are in agreement with the experimental data.

baryonic matter distribution in the large-scale structures is one of the main questions in cosmology. This distribution can provide valuable information regarding the processes of galaxy formation and evolution. On the other hand, the missing baryon problem is still under debate. One of the most important cosmological structures for studying the rate and the distribution of the baryons is galaxy clusters. In this work, it is proposed that the kinetic Sunyaev-Zel'dovich effect in galaxy clusters, which has a supernova type Ia (SNe Ia) in their brightest central galaxy, can be used to obtain the optical depth profile of the galaxy cluster. To obtain this profile, the bulk velocity is calculated by SNe Ia. We show that for galaxy clusters in the redshift range of z  0. 15, we can find the optical depth with 100 kpc resolution, which is the same as 1 arc minute resolution in cosmic microwave background observations.

In this work, we study the anisotropic inflationary models. In these models, an abelian gauge field non-minimally coupled to the inflaton field plays a role in the inflation dynamicIn a gauge field, the backgroundanswer is anisotropic, in the form of metric Bianchi. In order for the model to be consistent with the observations, the level of anisotropy should be small. The anisotropy power spectrum is obtained by calculating cosmological perturbation using  N formalism. We show that the criticism levelled in [4] does not apply and we can repeat the calculations in the nonabsorbence by calculating the anisotropy spectrum. Using the constraint on the quadrupole anisotopy, we show that the contribution of the gauge field to total energy density should be very small

Optimum distance is defined as a distance from the air-shower core in which the density of a number of particles calculated by the lateral distribution function at that distance has the least uncertainty. Furthermore, with a good approximation, this distance is independent of the characteristics of primitive ray and it only depends on the geometric shape of array. In this paper, by simulating 1000 vertical EAS of protons with the energy 300 TeV, using the CORSIKA Monte Carlo code and trigger condition, the calculated distance for the array triggering ALBORZ-1 was found to be equal to 9± 1 m. Also, it was found that this distance as well as the density of the number of calculated particles was independent of the lateral distribution function used in the calculations.

In this paper, the crystal field parameters (CFPs) have been calculated in the framework of the density functional theory using a novel theoretical approach proposed by Pavel Nová k et al. and extracting the WANNIER functions from the Bloch eigenstates for the CeCl3 compound. Then, the calculated CFPs have been used in an effective atomic-like Hamiltonian, including the crystal field, 4f-4f correlation and spin-orbit coupling, and the splitted energy levels of Ce3+ ion by crystal field have been derived by diagonalization of the Hamiltonian. A hybridization parameter, , has been used to improve the results. The results are found to be in agreement with the experimental data.

In the Fourier domain optical coherence tomography, a picture of the optical thickness (multiplication of the refractive index n in physical thickness d) is obtained; e. g. for the retinal layers, it is used to diagnose many diseases throughout the hospitals in the country. In this work, we introduce a method for a discrete and simultaneous measurement of the refractive index and the physical thickness of multiple layers using Fourier domain optical coherence tomography, without additional information regarding the structure of the sample under investigation. In this method, the only input data are the spectrum of the FD-OCT system and the optical thickness of the sample layers (OPLs), asobtained from Fourier transform of interference spectrum. The results of simulation indicate that the accuracy of the extracted parameters depends on the difference in the refractive index of sample interfaces, because the more the difference in the refractive index, the more the optical reflection index. Furthermore, we show that the accuracy of the extracted parameters is influenced by the accuracy of measuring OPLs. So, we introduce a method to optimize the accuracy of parameters in spite of uncertainty in measuring OPLs. Simulation results show that for transparent biological samples merged into the aqueous media, if sample layers have a refractive index less than 1. 55, these parameters can be extracted with an error less than 0. 001.

In this paper, we study the numerical analysis of fold-pitchfork bifurcation with Z2 symmetry. For this purpose, explicit formulas for the critical coefficients of this bifurcation are obtained and non-degeneracy conditions of this bifurcation are determined. Then, local bifurcations, bifurcation curves and phase portraits are computed by MatCont toolbox. We will emphasize an example serving as a model of pipe flow.

In this study, based on Density Functional Theory (DFT), the effect of solution on the g-tensor, the hyperfine coupling constant of atoms and finally, the EPR spectrum of alanine free radicals induced by ionizing radiation such as electron and gamma was investigated by applying implicit models such as COSMOand explicit models such as introduction of hydrogen bonds to the cluster structures. The results indicated that there was a good consistency between the g-tensor and hyperfine coupling constant of atoms and the experimental data in the solution; also, there was also qualitative consistency in the crystal by the introduction of the hydrogen bond of the water molecule to the cluster models. The use of different clusters in the formation of hydrogen bonds of water molecule with radicals showed that in the first shell, four, seven and six water molecules were required for R1, R2 and R3 radicals, respectively. Finally, the effect of solution on the EPR spectrum was predicted without changing the radical nature.

In this paper, we have simulated the physical properties of BaMnxMo1-xO3 (x=0, 0. 5, 1) perovskite compound by the density functional theory and Hubbard model, using the Espersso code. To calculate the exchange-correlation potential in the Kohn Sham equations, the generalized gradient approximation (GGA) has been used. Also, because the calculated results indicate that U parameter plays a vital role in determining the electronic characterization in our compound, we have repeated our calculations using the LDA+U instead of the GGA approximation. In both GGA and LDA+U approximations, we have studied the ferromagnetic state of the cubic phase of BaMnxMo1-xO3 (x=0, 0. 5, 1) compound. Then, we have investigated the behaviour of the Lattice Parameter, Cohesive Energy, Total Magnetization and Bulk Module of the corresponding compound for the different values of x. After that, by fitting our results using the second order polynomial function, we have studied the reasons for the deviation from Vegard’ s law for each parameter.

In this paper, in order to achieve a suitable spectrometer for detecting nuclear radiations at room temperature, the effect of adding the element Hg to the binary compound semiconductor ZnTe was studied completely. For this purpose, the electronic structure and transport properties of semiconductors in the ternary compound ZnxHg(1 x)Te (ZHT) were simulated using ABINIT as a computational code based on density functional theory; d the range x  0. 8 was appropriate. In addition, by using the MCNP software, the response function of this ternary compound, in comparison with the current room temperature CdTe spectrometer, was presented. This simulation as well as the comparison showed that the above compound for the spectrometer of nuclear radiations could be suitable at room temperature.

In this paper we study a dark energy model in which tachyon scalar field non-minimally coupled with kinetic energy and Gauss-Bonnet invariant. Energy density   , pressure p and scalar field equation of motion have been calculated and then equation of state parameter has been extracted. We have investigated the conditions required for    1 crossing in such a model. It is shown that phantom divide crossing can be realized in our model.

Electromagnetically induced transparency (EIT) is an optical phenomenon characterized by the elimination of the effect of a medium on a propagating beam of electromagnetic radiation in a specific frequency band. In this study, EIT was investigated at a proposed metamaterial with millimeter dimensions and in the GHz frequency area. The computation results indicated that EIT with the high transmission rate and the high Q factor occurred in certain frequencies by breaking the symmetry in this structure. The sensitivity studies showed that the use of silver in the structure increased the quality factor so significantly that this quantity reached to 338 for gold and copper, while it was 677 for silver. In addition, By reducing the temperature, the transmission rate in the structure was increased, reaching the acceptable degree of 98%. This structure could be, therefore, an appropriate option for slow light usages, and it could be utilized for light amplification in microwave structures.