JOURNAL OF RESEARCH ON MANY BODY SYSTEMS
Year:2017 | Volume:7 | Issue:13 |Papers Count:20

In this study, we modified the two-scale method proposed by Ebrahimi and Koochi to simulate electron diffusion in a disordered nano-structured semiconductor and study the effect of recombination process in localized traps, on electron transport. In the first scale, we estimate the mean electron residence time for nano particles with an arbitrary coordination number. In the second scale, we estimate the electron lifetime when it travels through a disordered percolating cluster of nano particles. The electron residence time on each particle was evaluated in the first scale. Some of the nano particles have recombination centers. We find that while employing the two-scale method decreases the computational time drastically, it produces the correct dependence of diffusion coefficients on the material’ s porosity.

This research discussed the simulation of the oblique column layers of cadmium telluride and zinc sulfide with different growth angles on glass substrate. The obtained results from the simulation were compared with the experimental results. For the simulation of the growth process, the NASCAM simulation code, that works based on monte carlo, was used. First, using SRIM software and SIMTRA software's, the energy and the particles angle, moving to the substrate, and the movement time are calculated. This file is then used as the input of NASCAM software for calculation of the layer structures. Finally, to show the column, the output data of the NASCAM software was fed into JMOL and PROSTAT software's. The results of the simulation, compared with the experimental results, showed conformity in terms of angle and structure.

In this study, we examined the entanglement and decoherence properties of an open quantum system consisting of a three-mode asymmetric harmonic oscillator. The basset-hound state was initially chosen and Markovian approximation was assumed. Using PPT criterion and purity, we investigated the effect of the parameters of the system, the initial state and the environment on the evolution of the entanglement and decoherence. It was observed that the latter properties are dependent on the environmental parameters (temperature and dissipation coefficient), the initial state parameter (squeezing parameter) and the system parameter (asymmetric parameter). We observed that entanglement and purity are both decreasing functions of temperature, dissipation coefficient and the asymmetric parameter. On the other hand, purity is a decreasing function of the squeezing parameter, while the entanglement is an increasing function of the latter.

In this study, the crystalline structure and magnetic properties of Pr2-yLayFe17-xGax polycrystalline compound are investigated by means of powder X-ray diffraction, vibrating Sample Magnetometer (VSM) and Superconducting Quantum Interference Device (SQUID) magnetometer. The ternary intermetallic compounds Pr2-yLayFe17-xGax have been synthesized and the results show that the single phase sample with the expected rhombohedral structure is formed. Upon La and Ga substitution, the lattice parameters are increased and due to the change of the anisotropy and exchange effects, the Curie temperature, magnetisation behavior and saturation magnetization is changed. The Curie temperature is decreased due to the increasing of unit cell by La substation whereas; the Ga substation for Fe in the samples causes the increases of Curie temperature. The La and Ga substation leads to the decrease of saturation magnetisation as a result of reduction of the average Fe– Fe hybridization and the increase of the content of the nonmagnetic element.

Geomagnetic storms disrupt space navigation systems such as satellite with rapid and large changes in particle flux. To study the effects of cosmic rays and calculate the rate of faults and errors and provide a suitable shield against them, we need to know the energetic particles flux. In the present work, we have obtained protons flux and energy range by simulating in different solar cycles and in 4 major solar flare events. In the first step of the proton flux simulation, we have used OMEREH. software; We have then compared the obtained data from the simulation with the experimental data from AMS collaboration and they were in a good agreement with each other. In the next step, first we have determined satellite’ s coordinates and properties using OMEREH; then we have calculated the flux of energetic protons that collide to a typical satellite in Leo orbit at the time of flares occurrence. The number of solar events increases in solar maximum. Therefore, these analyses should be done carefully and the design should be more significant in long-term space missions.

In this paper, we aim to investigate the electric conductivity of an out of equilibrium system of QCD at low temperatures. One way to study such systems is to apply a time dependent electric field and examine the out of equilibrium behavior of the system. The electric field produces pairs of quarks and antiquarks from the field theory vacuum leading to an electric current. By using the relation between the applied electric field and its relevant current, the electric conductivity of the field theory can be obtained. We use a non-critical holographic model of QCD to study the time dependent out of equilibrium solution of the system non-perturbatively and examine the effects of parameters such as electric field magnitude and frequency as well as the charge density on electric conductivity. Finally, we compare our results with those from other holographic models.

Reduced graphene oxide-ZnO (72/0، 36/0، 18/0= GO/Zn(Ac)) was synthesized using GO and Zn(Ac) by a chemical bath root. The optical properties were performed by FTIR and DRS spectroscopies and the structural properties by XRD, SEM and EDS observations. The DRS spectra of rGO-ZnO show an absorption edge at about 389 nm. The vibration modes related to ZnO bonds and also reduction of GO were observed by FTIR spectra. The XRD, EDS and SEM results showed that ZnO was formed in a hexagonal structure on the rGO surfaces. The toxicity of the prepared samples was studied on (N2A) cellulose. It was shown that GO and rGO-ZnO with 0. 18 and 0. 36 GO/Zn(Ac) ratio have similar toxicity behaviors in higher concentration compared to the 0. 72 which shows toxicity in lower concentrations.

One of the common methods in the study of cosmic rays induced extensive air shower on the Earth's surface is using an array of scintillation detectors. Dimensions and distances between detectors are among the most important parameters that determine the energy range detectable by the array. Furthermore, the geometry of the array has an important role in determining of optimum distance Ropt, which is defined as the distance from the shower core, where uncertainty in lateral density of secondary particles is minimized. In the present work, dependence of Ropt on array geometry and characteristics of cosmic rays has been studied for the Alborz-1 array. It is shown that the value of ropt is independent on shower characteristics like energy, incident angle and primary mass. On the other hand, according to our results, the ropt value has explicit dependence on array geometry specially distances between detectors. Our investigation shows that the cluster layout is the best layout for the detectable energy range of ALBORZ-1 array (1015 eV). We have found Ropt= 9 ± 1m for the ALBORZ-1 array.

In this paper, we have studied the phase transition of nucleons, between a paired phase and a Fermi gas state, in 89Y and 208Pb nuclei. In order to conduct this study, the nuclear level density parameters of 89Y and 208Pb nuclei in the constant temperature model were extracted by the using of experimental data from Oslo group. The extracted results were used in the calculation of the cross sections of 208Pb (n, el), 208Pb(p, el), 89Y(n, el) and 89Y(p, el) nuclear reactions. According to the good agreement between the extracted results and corresponding experimental values for the cross sections, a constant temperature behavior, which can be interpreted as an evidence for the pairing phase transition, is confirmed for the nuclei. In addition, heat capacity of 89Y and 208Pb nuclei has been extracted from the experimental level densities and the effect of pairing phase transition of nucleons is studied within this thermodynamic quantity.

The Mullins– Herring equation is an important model in surface growth. This research aimed to explore quenched noise on this model using a new approach. The key point in this model is combination of the external force on the interface and quenched noise on one part with its strength adjusted with an external controllable parameter, g. It is shown that the dynamics of this model for some values of g have critical behaver. Also, our calculations show that, for g = 1 and 2 values there is no phase transition. The important feature of criticality is the existence of scaling exponents which in this study were computed numerically. As a result, for g = 3 the critical point was obtained (0. 6504). At this point, the total roughness exponent and local roughness exponent were obtained (1. 410 and 1. 011), respectively. The inequality of these two values, that is the total and local roughness exponents, is one of the most important effects of quenched noise in growth models which indicates the variation in structure of the produced surface.

Propagation of electrostatic waves in a quantum semiconductor plasma has been investigated by a quantum hydrodynamic model in the presence of an external magnetic field. The influence of quantum effects such as Fermi pressure, Bohm potential and exchange potential on the propagation properties of electrostatic waves has been investigated. We found that the quantum effects and external magnetic field significantly modify the electrostatic wave frequency.

In this paper, the effects of temperature on the refractive index layer of magnesium fluoride, MgF2, is investigated. The 2 MgF layers, using the electron gun, in temperatures of different 25, 100, 200, and o 300 C were deposited on the glass substrate ( BK7 ). In all samples, the deposition rate was R  5 6 Å /C. Transmission spectra of samples, using a spectrophotometer at wavelengths 400 1800 nm were determined. The sample produced at room temperature was annealed for 2 hours at o 300 C. Then, indexes of refraction of samples were calculated using three methods. The refractive indexes according to the methods were in a good agreement with one another. The results showed that by increasing the temperature from laboratory temperature to o 300 C, the refractive index of magnesium fluoride increased as a linear function from n =1. 32 to n =1. 39. Moreover, the index of refraction of the annealed sample increased conspicuously while the annealed sample showed some absorption.

In this article, the report of design, construction and optimization of an xenon flash-lamp pumped solid-state Nd: YAG laser in a ceramic cavity are presented. A laser rod of Nd: YAG with a 1. 1 wt% doping and a dimension of 80 mm×5 mm, as an active medium, and a xenon flash-lamp with a inner diameter of 7 mm, an arc length of 3 in, and a repetition frequency of 0. 2 Hz, as the pump source, were used. At first, the laser was optimized with Findlay-Clay method, in terms of the output coupler reflectivity. The gain and the loss for pump energy of 4. 9 J were achieved to be 0. 9 and 0. 005, respectively. Thus we calculated the optimum reflectivity as 32%. From a mirror with a reflectivity as 25% (which was the closest to our available reflectivity in laboratory) was used. A total electrical-to-optical efficiency of 3% was achieved at 1064 nm for 25% reflectivity for output coupler. For a 0. 2 Hz repetition rate and a pumping energy of 9 J, a beam spot size of 3. 98 and a quality factor of 17 were achieved. The results are valid for a cavity design with the mentioned parameters.

In this paper, we have studied the spectral statistics of 101 even-even nuclei in the nearest neighbor spacing distribution framework. Sequences are prepared by using all the latest experimental data for 2+ levels of considered nuclei in the 40 ≥ A≥ 198 mass region. The maximum likelihood estimation technique has been used to extract the Berry-Robnik distribution’ s parameter which explores the regular or chaotic behavior of considered sequences. Sequences are classified as their mass, quadrupole deformation parameter, the energy ratio and the shell model configuration for the last protons and neutrons of all nuclei. Our results suggest a regular dynamics for these even mass nuclei. Also, the regularity is increased for light nuclei vis-a-vis heavier ones and also the deformed nuclei vis-a-vis spherical ones. Our results show a deviation of chaotic dynamics when the spins of proton levels are decreased or the spins of neutron levels are increased.

In this study, using a SU(1, 1) Lie algebra in the Hamiltonian of Interacting Boson Model (IBM-1), we have calculated the energy spectrum of chain Barium isotopes ( 124 130 Ba  ). We have obtained the constants of this spectrum by solving the Bethe equation using the Least Squares method with the Newton-Gauss and Genetic algorithms. Finally, we have compared the results of experimental spectra with theoretical spectra and undefined levels of these isotopes were calculated. The results showed that the genetic algorithm has a lower standard deviation compared with the Newton-Gauss algorithm, and also the results of experimental spectra are in good agreement with the theoretical spectra.

In this paper, the electronic and optical properties of Na2S in the orthorhombic structural phase have been investigated. Calculations were performed by using wien2k package which is based on density functional theory and FP-LAPW method. The results of band structure show that band gap is about 2. 405eV. The orbitals of S and N atoms have the most contribution in valance and conduction band, respectively. The optical properties such as the dielectric function, refractive index, extinction coefficient, absorption coefficient and Energy Loss function have been calculated. The maximum of imaginary part of the dielectric function occurs in 5. 5 eV and this point shows the maximum of absorption and extinctions. On the other hand, the maximum of the real part of dielectric function occurs in 5. 4 eV and this point shows the maximum of reflectance and energy refractive. The results are in good agreement with other available data.

By using the semi-classical Thomas-Fermi approximation in the framework of a phenomenological mean-field model, an explicit form of nucleonic chemical potential at different temperatures and densities is obtained. At finite temperatures, based on an extended statistical model, within Landau phenomenological theory, this explicit form is determined in terms of a new quantity known as extended effective mass which is a function of temperature, density and asymmetry parameter. By introducing the explicit form of nucleonic chemical potential, a new model for determination of the nuclear equation of state at different temperatures and densities with a behavior in agreement with the other elaborated theoretical models in this field is presented.

In this paper, the current-voltage characteristic of a 2π domain wall formed between two semiconducting magnetic nanowires of 𝑝-type material with very high spin polarization at a given temperature 𝑇 has been investigated. In this regard, the transmission and reflection probabilities of the carriers from the 2π wall have been obtained by solving the coupled Schrö dinger equations for the up and the down spin components of the wave function, and accordingly then the charge and spin current density has been calculated. In the study of spin-diode behavior of the domain wall, it has been shown that the threshold voltage of the diode increases with the domain wall width. Also, the nonlinear dependence of the spin polarization on the applied voltage has been determined for a spin transistor application.

In the present study, the excitation process has been reviewed by a semi classical formalism in charged particles impact with atomic hydrogen at the intermediate and high energy range. The multi channel Eikonal formalism has been implemented to calculate the scattering amplitudes. In this approach, as the first order Born approximation correction, the scattering amplitudes for ns and np excited states of atomic hydrogen have been calculated by proton impact analytically. The achieved differential and total cross section for n  2 state show a good agreement with available experimental and theoretical results at the intermediate and high energy range. By making use of formalism, the polarization coefficient of atomic hydrogen spectral lines can be calculated at the discussed energy range with good accuracy.

The sol-gel technique was used in the preparation of Cd doped Bi1. 64Pb0. 36Sr2Ca2-xCdxCu3O10 ceramic superconductors. In this study, the value of doping Cd varied from x = 0-0. 2 at different annealing times (32, 48, 56 and 64h) for preparing samples. To find the temperature of annealing, TGA analysis was done from dried gel. Analysis of XDR and SEM was carried out to study the morphology and microstructur of samples. The results of XRD indicated that the maximum values of the Bi-2223 phase percent were obtained for the sample doped with x = 0. 02 Cd. Likewise, the study of SEM images showed that this sample has a plate-like structure which increases the critical current density. The critical current density and the critical temperature of samples have been measured by the four-probe method. The results show that the sample which was doped with x = 0. 02 has maximum value of percentage of Bi – 2223 phase, critical current density and critical temperature.