Iranian Journal of Physics Research
Year:2012 | Volume:12 | Issue:3|Papers Count:16

According to the Titus-Bode law, orbits of planets in the solar system obey a geometric progression. Many investigations have been launched to improve this law. In this paper, we apply square and exponential models to planets of solar system, moons of planets, and some extra solar systems, and compare them with each other.

In this research, a low temperature in-field 57Fe Mossbauer spectroscopy is used for investigation of anomalous magnetic properties of MnZn nanoferrite. Based on Mossbauer spectroscopy results, the reduced saturation magnetization of MnZn nanoferrite in respect to that of bulk sample is due to nonequilibrium cation distribution and spin disorder. The enhanced Curie temperature of MnZn nanoferrite in respect to that of bulk sample can be attributed to the strengthening of the (A)-O-[B] superexchange interactions due to an increase of the magnetic ion concentration in the (A) site.

In this work,copper/palladium (Cu/Pd) multilayer nanowires were successfully prepared by electrode position method using polycarbonate template. The fabrication of Pd/Cu multilayer nanowires was controlled by analyzing the current–time transient during electrode position using potentiostat. The morphological properties of the nanowires were studied by scanning electron microscopy (SEM) and result showed that almost each nanowire had the same length of » 4 mm and the diameter of 90 nm .X-ray diffraction pattern showed that Pd and Cu grow in their face-centered-cubic (fcc) lattice structures. The chemical composition was determined by examination of the energy dispersive X-ray (EDX) spectra.

The flux-pinning mechanism and activation energy of 10 wt % malic acid-doped MgB2 were investigated by measuring of the critical current density and resistivity as a function of magnetic field and temperature. A crossover field, Bsb, was observed from the single vortex to the small vortex bundle pinning regime. For the sintered sample, the temperature dependence of Bsb(T) at low temperature is in good agreement with the dl pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation. The activation energy was decreased by increasing the magnetic field and increased by increasing sintering temperature.

Deviation angles of secondary electrons and muons in simulated extensive air showers were studied. The angles have wide distribution, whose width depends on energy cuts imposed on shower particles. In this work, variation of deviation angles with the energy of secondary particles, shower energy, primary direction, and core distance was investigated. The results put limitations on application of hodoscopic devices in cosmic ray and gamma ray observations.

Effects of quantum size and potential shape on the spectra of an electron and a hydrogenic-donor at the center of a permeable spherical cavity have been calculated, using linear variational method. B-splines have been used as basis functions. By extensive convergence tests and comparing with other results given in the literature, the validity and efficiency of the method were confirmed.

Nonlinear Dust lattice modes are studied in a hexagonal two-dimensional dusty plasma lattice, in presence of charge gradient of dust particles. In this lattice, such gradients affect nonlinear behavior of dust lattice waves. The amplitude modulation of off-plane transverse dust lattice wave packets is investigated considering the anisotropy of interactions, caused by the height-dependent charge variations. A nonlinear Schrodinger equation described time evolution of modulated off-plane transverse dust lattice wave packet. Calculations show that the charge gradient changes the stability condition of the solution of the nonlinear Schrodinger equation.

In this study, relativistic Vlasov simulation of plasma for expansion of collisionless plasma for into vacuum is presented. The model is based on 1+1 dimensional phase space and electrostatic approximation. For this purpose, the electron dynamics is studied by the relativistic Vlasov equation. Regardless of the ions temperature, fluid equations are used for their dynamics. The initial electrons distribution function is the relativistic Maxwellian. The results show that due to the electrons relativistic temperature, the process of the plasma expansion takes place faster, the resulting electric field is stronger and the ions are accelerated to higher velocities, in comparison to the non-relativistic case.

In this study, we prepared the binary-binary TCO compounds of SnO2-ZnO by the spray pyrolysis technique. We also investigated the role of MgF2/SiO2 antireflection coatings in reducing optical reflectance in the visible region of TCO. Before preparation, we simulated the optical transmition of the films for optimizing the layer thicknesses. The results of this study showed increasing of optical transmittance in the visible region of TCO by adding antireflection coating layers.

Nanoflares are the small impulsive sudden energy releases, due to the explosion of solar background. Thus, determination of their energies and distributions is important. Recent observations and simulation models have shown that the frequency of their energies follows power-law. According to Parker hypothesis, if these exponents are greater than critical value 2, the contributions of nanoflares to the heating of solar corona is more significan. Here, the extreme ultra-violet (EUV) emission radiances of corona observed by STEREO/EUVI taken on 11 and 12 Jun 2007 are analyzed. To simulate the EUV irradiance, a simple nanoflare model with three key parameters (the flare rate, the flare duration time, and the exponent of the power- law) is applied. Based on genetic algorithm, the lengths of data points are reduced. The resultant light curves are fed to the Support Vector Machine (SVM) classifier. The produced light curves of quiet and active regions of the solar corona are classified and the set of power- law exponent, the flare duration time and the flare rate parameters are obtained. The flare duration time is estimated about 80 minutes. The power-low exponents range about 2.5-2.7.

Calculation of Hall coefficient in semiclassical approach requires the first and the second derivatives of the energy bands at the Fermi level. We use the Maximally Localized Wannier Function technique to determine the required band derivatives and calculate the ordinary Hall conductivity and ordinary Hall coefficient in Al, Cu, Pd, Li, Au, Ag and Pb cubic metals.

The number of neutrons emitted by compound nucleus before reaching the saddle-point (vpre) is calculated for 168O+20882Pb, 126C+23692U, 115B+23793Np and 188O+19779Au, heavy-ion induced fission reaction systems. The behavior of angular anisotropies of fission fragments is normal for 168O+20882Pb and 188O+19779Au reaction systems, since the targets have spherical shapes. For these systems, the agreement between the angular anisotropies experimental data, as well as the predictions of standard saddle-point statistical model is high. And as the mass asymmetry, parameters is greater than the Businaro-Gallone asymmetry parameters a BG for the other two systems, the behavior of angular anisotropies of fission fragments is expected to be normal. Overall, an anomalous behavior in the angular anisotropies for these systems and the contributions of non-compound nucleus events are observed.

In this paper, the method of identifying of the similar solar flux tubes from image sequence EUVI/STEREO is presented. Using the oriented coronal curved loop tracing, the loops of an image are labeled. Based on local maxima intensities, the width of loops is determined. The Zernike moments of each loop are calculated and fed to probabilistic network classifier. Also, 588 loops from STEREO are studied.

Carbon nanofibers (CNFs) decorated with Cu2O particles were grown on a Ni catalyst layer deposited on a Cu substrate by thermal. chemical vapor deposition from liquid petroleum gas. Ni catalyst nanoparticles with different sizes were produced in an electroplating system at 35oC. These nanoparticles provide the nucleation sites for CNF growth, removing the need for a buffer layer. High temperature surface segregation of the Cu substrate into the Ni catalyst layer and its exposition to O2 at atmospheric environment, during the CNFs growth, lead to the production of CNFs decorated with Cu2O particles. The surface morphology of the Ni catalyst films and grown CNFs over it was studied by scanning electron microscopy. Transmission electron microscopy and Raman spectroscopy revealed the formation of CNFs. The selected area electron diffraction pattern and electron diffraction studies show that these CNFs were decorated with Cu2O nanoparticles.

In this study, indium-tin-oxide thin films in different thickness ranges were prepared by electron beam evaporation method on the glass substrate at room temperature. The thicknesses of films were 100, 150 and 250 nm. Using fractal analysis, morphological characteristics of surface films thickness in amorphous state were investigated. The results showed that by increasing thickness, surface roughness (RMS) and lateral correlation length (x) were decreased. Also, the roughness exponent a and growth exponent b were determined to be 0.72±0.01 and 0.11, respectively. Based on these results, we understand that the growth films can be described by the combination of the Edwards-Wilkinson equation and Mullins diffusion equation.

Polycrystalline samples of Nd1-xPrxBa2Cu3O7-d with 0£x£0.30 were made by standard solid state methods. The transport and superconducting properties were studied by the resistivity and the thermoelectric power measurements as a function of temperature and doping concentration. The resistance and the thermoelectric power were increased by increasing doping concentration. The pseudogap temperature was measured from downturn deviation in a linear dependence of resistance as a function of temperature. The resitivity, the thermoelectric power, the critical temperature, and the pseudogap temperature results suggested that the hole concentration in CuO2 planes was decreased by increasing Pr doping concentration. The resistivity and the thermoelectric power results were analyzed by the bipolaron and the phenomenological narrow band model, respectively. A good agreement between models and data was obtained. On the basis of these models, it was inferred that the localization tendency is one of the main reasons for decreasing the hole concentration in the CuO2 plane, which results in the strong depression of the superconductivity.