نشریه پژوهش سیستم های بس ذره ای
سال نهم شماره 2 (پیاپی 21، تابستان 1398)

In this article, using the coupled-channel procedure, invariant mass spectra of in-flight kaon interaction on the deuteron target is investigated. In the calculation of interaction cross section, two processes as one- and two-interaction process are considered. The one-interaction process dominate at low values momenta of the incident kaon whereas the two-interaction contribution is not negligible at high values and both processes should be considered in the total cross section amplitude. By using analysis and considering of population, the sub-threshold theoretical invariant mass spectra are fitted to Braun’s data that the mass and width of are respectively extracted and . Although the present result, is fairly good agreement with the results of the chiral models, but does not consistent with the current value of the Particle Data Group.

In this paper, the contribution of Sr and Hf atoms in piezoelectric properties of tetragonal SrHfO3 with P4mm space group, were investigated by using first principle calculations based on density functional perturbation theory. Lattice constants, Born effective charges, piezoelectric constant and Sr and Hf contributions in total polarization and piezoelectric coefficient were calculated. Our results show that tetragonal SrHfO3 has piezoelectric property and its polarization and piezoelectricity mainly come from Hf atoms. The effect of lattice constant changes on polarization and piezoelectric constant were also studied. It was found that polarization and piezoelectric constant enhance by increasing lattice parameter and at c=4.5 Å, Sr atom contributes 50% of the total piezoelectric constant. This behavior assigns to significant covalent bonding between Sr and surrounding O atoms.

Abstract In this article regarding the charged impurities as scattering centers, we investigate their effects on the conductivity in the two dimensional graphite. First by considering the importance of the influence of screening on the impurities and static polarization, by the use of effective mass approximation and k.p equation, the conductivity versus sheet carrier concentration for different temperatures is calculated and plotted. We have shown that the conductivity at low temperatures behaves like a metal, while at high temperatures shows insulating behavior. Also the charged carrier transport and the effect of different charged impurity distributions for the two impurity distribution cases of uniform random and cluster is calculated and studied. The obtained results are in agreement to recent experimental and theoretical data.

In this paper we review several kinds of Chaplygin gas as a model of dark energy and introduce developed Chaplygin gas which is unification of all previous models. Dark energy considered as fluid of many body system with specific equation of state. We show, as a main goal of this paper that developed Chaplygin gas equation of state can be obtained from string theory like ordinary Chaplygin gas equation of state. We write string Hamiltonian and obtain equation of motion. Then compare it with Euler equation in fluid mechanics which yields to a differential equation. Solving this differential equation give us developed Chaplygin gas equation of state.

In this study, the electronic and transport properties of pentacene and perfluropentacene are investigated using first principle calculations based on density functional theory and non-equilibrium Green’s function. The results show that the HOMO-LUMO gap of perfluropentace is about 0.2 eV smaller than that of pentacene which is comparable with the reported value of 0.2 eV. For both molecules, the most contribution in DOS around Fermi energy is related to 2p orbitals of carbon. Electron transport calculations are investigated for both molecules of pentacene and perfluropentacene in Au(111)/molecule/Au(111) junction. Transmission coefficients and I-V curves up to 2V have been calculated and compared for both molecules. The transmission coefficients are composed from resonant peaks which are mostly originated from HOMO and LUMO peaks of the molecules. The calculated current in Au/pentacene/Au junction is more than the current in Au/perfluropentacene/Au junction except a small interval around 1V, in a way that the difference between the currents get the maximum value of 5μA at 2V.

In this work, the electronic properties of the cubic Gadolinium oxide were investigated using the full-potential linearized augmented plane wave method in the density functional theory (DFT) framework. The calculations are performed within the generalized gradient approximation (GGA), adding an empirical Hubbard U potential. The behavior of the Electric Field Gradient was analyzed and compared with experimental data’s. Moreover, the total and partial densities of states of cubic Gd2O3 are presented and the contribution of different orbitals was analyzed from the total and the partial density of states curves. The calculations are in good agreement with the theoretical and experimental values.

Stanene, a two-dimensional nanostructure of Sn atoms, has a honeycomb structure. The strong intrinsic spin-orbit interaction of stanene causes an energy gap 0.07 eV in its band structure. In this research, the electronic properties of the stanene nanoribbons with the zigzag edges are investigated by the tight binding model and the Green’s function method and in the presence of electric and magnetic fields. In the presence of a vertical electric field, we observe metal-semimetal and semimetal-semiconductor phase transitions in the system. In the presence of a transverse electric field and or magnetic field, we will have spin band splitting. Our results show that by tuning the magnitude and direction of the electric and magnetic fields, we can control the electrical, spin and optical properties of the system.

In this study, mesoporous ZnFe2O4 was synthesized via a simple and green hydrothermal method in presence of SDS as surfactant and analyzed by XRD, FT-IR, SEM, VSM, DRS and BET techniques. The SEM images showed that prepared particles had sizes about 50-150 nm. The obtained result from BET analysis show that mean of diameter of hollows were about 8.45 nm. The area and volume of hollows were 161.87 m2/g and 0.34 cm3/g, respectively. The VSM curve of mesoporous ZnFe2O4 showed the magnetic property of it. The adsorption ability of this magnetic mesoporous was studied for removal of methylene blue from aqua media.

Fission fragment angular distribution (FFAD) data are important to get new insights into the fission process. In this study, the frame work of statistical modeling is used to analyze FFAD from neutron induced fission of 234U.The results have been compared with recent experimental data of 234U(n, f) reaction measured at the n_TOF facility in CERN. Accurate analysis was performed in order to deduce the variance K02 of the K- distribution of levels in the transition nucleus at neutron energies from threshold up to 50 MeV. We show the method in which the quantitative values of K02 is obtained. We have also studied the periodic structure of anisotropy related to the set of (n,xn) reaction in comparison with related cross section performed with TALYS1.8 code. The comparison of the variance with the cross section clearly illustrates the strong correlation between the value of the variance and the opening of a fission chance. We show that whenever the probability of reaction in a new channel and cross section increases, K02 decreases; so the minimum of K02 can show the maximum probability of (n,f)xn reaction. The results are in a good agreement with similar calculations in232Th(n,f) and 238U(n,f) reactions.

In this study, the ground states of five non-stable isotopes (Ne) were analyzed using single neutron-knockout reaction data. Initially, using the Glauber optical model, single particle cross sections are calculated in two steps. Then spectroscopy factor of each single particle state was extracted by shell model code OXBASH . The combination of these two quantities were compared with the experimental data. The abundance percent of ground states of residual nucleus(fragment) A-1 is more than its excited states( more than 60%). The contribution of break up is more than elastic scattering. The even isotopes show more agreement than odd ones . With attention to low variance of single particle cross sections to energy ( to %) , the more contribution of disagreement may be assigned to the uncertain of nuclear density

The electronic properties of MAPbX3(MA= CH3NH3+) units employing the experimental cell parameters (6.33,5.95 and5.66 Å for X = I,Br and Cl, respectively),FAPbX3(FA=( CH-(NH2)2+) units employing the experimental cell parameters (6.36 , 5.99 and5.60 Å for X = I ,Br and Cl, respectively) perovskite in the cubic phase are systematically studied using the first-principles calculations. We correlate our experimental results with first-principles theory and provide an insight into important parameters like; lattice constants, electronic structure , static and high-frequency dielectric constants, Reflection coefficient, Absorption coefficient , Optical conductivity , Refractive index,in these perovskite .Our calculations are performed using the Quantum-Espresso pakage in the framework of density functional theory (DFT). The projector augmented-wave (PAW) pseudopotentials are used within energy cutoff of 408 Ev for the plane-wave basis functions.For the exchange-correlationfunctional, the generalized gradient approximation(GGA) of Perdew-Burke-Ernzerhof(PBE) is used to relax the structural parameters. We substituted I- to Br- to Cl- in order to tune the bandgap from 1.6 eV to 2.4 ev to 3.2 eV of these materials. Electronic structure calculations reveal that electronic properties are mainly governed by Pb 6p and halide p orbitals. spin-orbit coupling (SOC) is included in all the calculations. All calculations reported in agreement with experimental data.

At the present work the ab-initio calculations based on pseudo-potential plane wave method was performed to fully relativistic study the structural, electronic and phononic properties of GaBi compound in the CsCl and NaCl(RS) phases. This compound has the stable Zinc-Blende phase that in this phase is semi-metal while in the under pressures in the other word in CsCl and NaCl phases has a metallic behavior. It is determined from the entropy graph in terms of Pressure that the Spin-Orbit interaction affects the order of the transition phase of this composition. By analyzing the phonon dispersion curves can be found that GaBi compound in this phases is unstable.

In this paper, the 180-188Hg isotopic chain is studied in the transitional region between the prolate and oblate shapes. To this aim, we have used a two parametric transitional Hamiltonian in the interacting boson model. With using Catastrophe theory in combination with coherent state formalism, we have determined the energy surfaces in this transitional region. The results of this study for energy levels and quadrupole transition probabilities are in the satisfactory agreement with experimental counterparts. Also the results for the control parameter of transitional Hamiltonian and the variation of energy surfaces propose a first order phase transition in this isotopic chain and suggest 188Hg nucleus as the best candidate for the O(6) dynamical symmetry limit or Z(5) critical point symmetry.

One of the concepts of nanoscale is the movement of the magnetic domain wall and is used in various areas, for example storage of data in memory. Magnetic fields begin to move due to external factors, such as external magnetic fields or current, and at the start of motion, the motion of the magnetic domain wall acts as a power function to external factors, that called the creep exponent. In this paper, we have tried to simulate domain wall movement with the use of the explosive percolation or sudden bridging as new model in percolation, and the ability to creep exponent the movement of the magnetic wall during the simulation is obtained. The magnitudes of this exponent are reported according to empirical experiments and various simulations of different numbers, which we obtained in this model 2.2.

This paper studies the theory of thermal properties of graphene nanowiggles, with Zigzag edge and Armchair in different size and geometry. In order to calculate the phonon dispersion spectrum, specific heat and thermal conductivity properties, we use the four-nearest-neighbor force-constant model and Landauer theory calculations. The results show that the thermal properties studied differ significantly compared to complete nanoribbons, especially at low frequencies. In detail, in acoustic modes, the thermal conductivity and the transmission coefficient of the phonon reduce sensitively due to the special structures of the edge in compared to the perfect nanoribbons which causes the dispersion of the phonon from the edges. There are also significant changes in the of thermal capacity, and calculating the out-of-plane and in-plane phonon modes also shows that the in-plane phonon modes play a greater role in the thermal conductivity. These results can be useful in improvement and designing electronic and thermoelectric nanodevices.

In this work, we theoretically investigate the spin dependent conductance and polarization in a Hexagonal graphene ring (HGR) with zigzag edges connected to three semi-infinite leads in the presence of a perpendicular magnetic flux and Rashba spin-orbit interaction (RSOI). Results are obtained using the tight-binding model within the non-equilibrium Green’s function formalism and suggest that in the absence of magnetic flux, for appropriate values of Rashba strength and energy of the incoming electrons; high spin-polarized conductances with opposite direction can be obtained for right up and right down leads, respectively. In this case, the system can act as a spin spliting device. In addition, it is found that by applying a magnetic flux to the central region of the HGR, it is possible to determine the magnitude and direction of polarization in output leads due to the time reversal breaking so, the system can be consider as a good candidate for the spintronic applications.

Reducing the dimensions of nano-switches is very important in terms of integration, but for some reasons, including empirical obstacles or theoretical complexity, nano-switches with small lengths have not been studied yet. In this study, the performance of graphene nano-switches with lengths of less than 30nm and very low plate spacing (about nm2) is simulated using a combination of molecular dynamics and method of moments. The obtained results are compared with some of the available theoretical models. The results show that by decreasing the length of the nano-ribbons or increasing distance between plates, the pull-in voltage of the nano-switches is increased. The results also show that in long nano-ribbons, there is a good agreement with theoretical results, but in the short ones, the existing theoretical relations are not sufficiently precise and cannot predict the pull-in voltage accurately. Furthermore the results show that the switching times of the simulated nano-switches are considerable less than conventional nano-switches.

Pure and Mn-doped ZnO nano films were prepared onto glass substrates using the sol - gel method, and optical properties of pure and ZnO:Mn were investigated with regard to different thickness, different annealing temperature and effects of layers. According to our results, increasing the thickness and annealing temperature decrease the measured transmittance spectrum. XRD spectrum shows the crystal structures are formed at high annealing temperature. The band gap energy of nano-films decreases with increasing the annealing temperature (3.45 eV-3.84 eV) and thickness of the nano films (3.38 eV-3.41 eV). This increase is due to improvement of the crystal quality owing to the increase of annealing and thickness of the nano films. Influence of four different solvents that used in the samples, also was investigated. The results of calculating band gap show that the prepared sample by methanol has the highest energy gap and the smallest grain size. This solvent has also the highest transmittance. Samples prepared by ethanol and 1-butanol have the most penetration depth. Gas sensing performance of ZnO depends on the grain size, so using methanol on ZnO can be used in the gas sensor devices for more precise result.

The GaAs nano-layer has received much attention due to its wide application. Due to the importance of the GaAs nano-layer, in this paper, using two Mn and Fe impurities, the probabily of the metallic to semiconductor phase transition and vice versa, as well as the displacements of the optical coefficients peaks of this nano-layer are investigated. For this purpose, the structural, electronic and magnetic properties of pure GaAs nano-layer and this nano-layer with Mn (GaAs+Mn) and Fe (GaAs+Fe) impurities located at the nanolayer surface are investigated using the density functional theory. The electron density of states, linear coefficients of electronic specific heat, band structures and the total and local magnetic moment at impurity atomic position of these nano-layers are calculated and compared. The real and imaginary parts of dielectric function, static dielectric functional, uniaxial anisotropy, reflectivity, absorption, electron energy loss function and optical conductivity of pure GaAs , GaAs+Mn and GaAs+Fe nano-layers for electric field parallel and perpendicular to nano-layer surface within GGA and GGA_EV approaches are investigated and compared.

We study the electromagnetic response of Otto configuration including graphene layer in THz frequencies (.5-10 meV). Due to the excitation of SPPs a minimum in the intensity of the reflected beam appears at the angle of total internal reflection. The position of the minimum depends on the physical parameters of the structure. We study its position changing the angle and frequency of incident beam. Effects of the physical parameters such as the thickness of the air gap, dielectric constant of the substrate and conductive tunability of graphene are investigated. Our results can be important in designing the SPR based devices.