مجله پژوهش فیزیک ایران
سال دوازدهم شماره 2 (تابستان 1391)

In the wave scattering from rough surfaces investigated by using the surface morphology and the vertical AFM, in general the correct and complete results cannot be obtained. If the roughness with respect to the wavelength is more than a critical limit, the theoretical calculation is not the same as the experimental data, and this inequality cannot be corrected without considering the shadowing effect. In this paper, instead of direct considering of the shadowing effect on scattering equations, we investigated its effect on the surface characteristics. If the shadowing exists, some parts of the surface cannot be seen depending on the incident angle and the wavelength. In this study, the effects of the shadowing on the surface characteristics of a self-affine experimental sample were investigated under the Born approximation.

In this work، on the basis of density functional theory and the generalized gradient approximation (GGA) we optimized the electronic structure of the unsaturated and hydrogen saturated ZnO nanowires with [0001] orientation. Studying the effects of a uniaxial strain on the nanowires، we calculated the Young’s modulus and the effective piezoelectric coefficient of the nanowires. Furthermore، the effect of this uniaxial strain on the imaginary part of dielectric function of the nanowires was investigated.

In this study، we investigated the spin dependent electronic transport of a fishbone-like nanostructure including two magnetic atoms at its ends. The electronic conductance of this nanostructure for three different orientations of atomic magnetic moments was numerically studied when the structure was sandwiched between two nonmagnetic leads. By using Green’s function technique at the tight-binding model، we calculated the spin dependent electronic transmission coefficient. The calculated results revealed that the conductance depends on the incident electron energy as well as the magnitude and orientation of atomic magnetic moments in the nanostructure.

In this article، a causal model on the basis of trajectory is introduced for description of quantum systems. This theory is structurally very similar to Bohme mechanics، and like Bohme theory reproduces all statistical consequences of standard quantum mechanics. Particle trajectories in this model are different from anticipated ones by Bohme model. Quantum potential (force) form، which is given، is different from Bohme theory. Actually، this model will convert to Bohme theory by annihilating the free parameter (μ). Theoretical properties of this model are investigated in the same way as Galilean invariance. Also، a precise comparison between this theory and Bohme mechanics is made، and some suggestions are presented (through transit time distribution) for experimental distinction between these two models. Finally، extension of this theory is investigated

Nearly simultaneous multiband monitoring of blazars is very limited and most studies reported in literature are conflicting، too. Although optical variability on intra-night timescales is now a well established phenomenon for blazars، its relationship to long-term variability remains unclear. Possible clues could come from monitoring the optical spectrum for correlation with brightness. The presence or absence of bluer color in blazar color index، when its luminosity is increased on intra-night and inter-night timescales، can provide interesting clues to the origin of blazar variability from hourly to much longer timescales. Luminosity of blazars varies at all wavelengths over a variety of timescales. Various models have been proposed to explain blazar variability. However، the mechanism responsible for variability is not conclusively understood. One factor which can discriminate the various variability models is that of color (spectral index) variations of blazars. This factor may help to better understand the mechanism of blazar variability. Therefore، it was initially proposed، by the second author of this paper to the OHP observatory، to carry out quasi-simultaneous multiband monitoring of one of the brightest blazer، Mrk180. Fortunately، it was accepted by the scientific team of the observatory and the 1. 20m telescope time was allocated to the project from 23 to 28 April 2009. Because of the weather conditions، we could only monitor this blazar for three nights. Raw data processing and data reduction were performed using the standard system of Europe Southerner Observatory، ESO-MIDAS. We considered two reference stars and measured the magnitudes of the reference stars and the blazar Mrk 180 and then plotted the light curves and the color index diagrams. The light curves showed the optical variations of the blazar. The maximum amplitude value of its variations was 0. 185 mag for the V filter. Investigating the blazar color index shows its variations on intra-night and inter-night timescales.

Coupled-channels Faddeev-Yacubovsky as well as AGS calculations of three-body, J π =0¯ K(NN)I=1(I=1/2) quasibound state in the KNN- πΣ N system were performed in momentum space and the dependence of the three-body energy on the two-body KN- πΣ interaction was investigated.

In this paper، we considered cosmological constant as a variable and studied properties and the thermodynamics stability of BTZ black hole from a geometric perspective. Also، we examined the correspondence between thermodynamic curvature singularities and phase transitionpoints with different thermodynamic metrics. We found that theQuevedo metric cannot predict the phase transition points in two ensembles. This result is also valid for the kerr-de sitter spacetime.

The phase space which is related to the motion of massive particle on 1+3- De sitter space is a 3-dimensional complex sphere. Our main aim in this study is discribing this movement in the frame quantum mechanics. Transfering from classical mechanic to quantum mechanics is possible by means of coherent states. Thus, after determination of this state, we quantize some of the classical observables.

In this research, the effect of the uniform electric field on the ground-state of a centered hydrogenic donor impurity in a GaAs/AlAs spherical quantum dot was studied using infinite potential model. In presence of strong electric field, due to the stark effect (perturbing electric field), the ground state energy would increase linearly. In presence of weak electric fields, the normalized binding energy was calculated by using perturbation method with effective mass approximation. This energy was investigated with respect to electric field strength. Studies show the proper choice of radius of quantum dot and electric field will clearly influence the normalized binding energy. The resulting influence may be used to calculate the small changes in quantum dot radius and thus detect different electric field strengths.

In this study، we investigated the electronic conductance of two typical single-wall nanotubes with square lattice by using Green’s function method in tight-binding approximation. Then the effect of various factors such as presence of symmetrical bond defects، the distance between two defects and the nanotube hopping energies was studied on the system electronic conductance. The square and rhombic nanotubes showed metallic and insulator/semiconductor behaviors، respectively.

In this paper، a system with spin S=3/2 with general isotropic nearest neighbor exchange within a mean field approximation possess is discnssed. We derive equations describing non-Heisenberg isotropic model using coherent states of SU (4) group in real parameters and then obtain dispersion equations of spin wave of dipole and quadrupole branches for a small linear excitation from the ground state.

This paper describes the synthesis of Pb (Zr0. 95Ti0. 05) O3 powder by sol gel and solid state methods. PZT powders were fabricated by solid-state reaction process using metal oxides and in sol gel method salts and organic compounds were employed. The powders were calcined at 700 and 950 oC in sol gel and solid state methods، respectively. The synthesized powders were analyzed by FTIR and XRD. The average crystal grain size of PZT powders determined by X-ray diffraction method using the Scherrer equation، and in sol gel and solid state methods measured 42 and 330 nm، respectively. The optical constants of powders were evaluated and compaed using FTIR transmittance spectroscopy and Kramers-Kronig analysis.