Iranian Journal of Physics Research
Year:2011 | Volume:10 | Issue:4|Papers Count:22

In this paper some characteristics of age parameter (s) are studied on the basis of showers from Yakutsk array data having energy ranging from 1018 eV to 1019 eV.

This paper studies improved factorization method, in the heavy quark limit, for B ®K p decays. Paying attention to strong interaction scale AQCD, and calculating all parameters depending on that in the particular scale (the same as µ ) show that we can obtain better and comparable results for branching ratios such as BR(B0®K0p0)=8.5+0.7-0.5×10-6 and BR(B®pk0)=2.26+0.17-0.15×10-5, and for CP-asymmetry such as, ACP(B®Kp0)=0.045 and ACP(B ®Kp0)=0.0085, which are very close to experimental values. In this framework, we fix AQCD=225Mev, and also calculate parameters such as Wilson coefficients,   aS, C8g and in this scale.

In this paper, we study particle aspects of the  j6 kinks in an external potential. The external potential is implemented by breaking the translational invariance of the system. The dynamics of the kink is calculated for the simple harmonic oscillator (SHO) and barrier potentials. The periodic motion of the kink in the SHO case is compared to the corresponding ordinary (classical) motion. It is found that for small amplitude oscillations, considerable deviation from the conventional SHO motion happens. As for the barrier potential, it is found that tunneling happens if barriers are thin enough. The tunneling time is calculated as a function of the barrier width.

In this work, the gravitational collapse of a spherically symmetric null shell with the flat interior and a charged Vaidya exterior spacetimes is studied. There is no gravitational impulsive wave present on the null hypersurface which is shear-free and contracting. It follows that there is a critical radius at which the shell bounces and starts expanding.

Muon-electron ratio and median zenith angle of Extensive Air Shower (EAS) is calculated for the energy range of 1019 to bigger than 1020 eV. The results are compared with the simulation work of Capdevielle et al. The results show a good correspondence with proton primary composition up to energy level of 7×1019 eV. In higher energies above GZK cut off, a considerable increase is calculated in cosmic primary photons. In addition, event frequency distribution above energy 7×1019 eV shows increasing concentration towards super galactic plane.

  Amorphous GeOx/SiO2 multilayers (1<X2 and SiO2 powders onto the Si substrates maintained at 100°C. Structural study by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared-absorption (FTIR) spectrometry, and transmission electron microscopy (TEM) was carried out. These techniques allowed us to follow the structural evolution, and phase decomposition due to annealing in the GeOx thin films and the multilayers annealed up to 900°C, and appearance of amorphous and crystallized germanium aggregates. For Ta≥400°C, the photoluminescence band around 1eV attributed to confinement effect in amorphous germanium aggregates was observed. Comparison of the luminescence in multilayer and GeOx thin film showed that in multilayer, although the control of the nanocrystals size isn't complete, the SiO2 barriers tend to enhance the intensity and reduce FWHM of the luminescence bands. This means that the confinement effect in the germanium aggregates in GeOx matrix is enhanced in multilayer system.

Thin layers of ZnS in two different temperature conditions of 25 or 20000C and also with different thicknesses from 100nm to 600nm were prepared by physical vapor deposition. Absorption and also transmission spectra of the films were obtained to determine absorption coefficient, extinction constant and optical band gap of the films. It was found that by decreasing the substrate temperature or decreasing the film's thickness, optical band gap of ZnS films were increased or decreased, respectively. These phenomena can be attributed to the quantum size effect.

In this paper, selection of proper method for titanium coating on copper substrate is studied to construct nuclear targets for neutron production in particle accelerators. In order to construct such targets, it is necessary to deposit, through the coating methods, the proper coating of titanium on copper. Among different coating methods, ion plating and sputtering, due to the high coating yield and stability of titanium layers, has been selected. To compare different amounts of hydrogen absorption, two series of targets, different in the coating methods, were exposed to the similar conditions under 40 bar hydrogen gas. Comparison of elastic recoil particles (ERD) results of two series of the targets showed that hydrogen atoms permeated in deeper layer of targets, which were deposited by ion plating, than the targets deposited by sputtering. Hence, it was concluded that the ion plating method is more suitable to make nuclear targets.

In this work, gamma exposure buildup factors (E.B.F.) for plane sources and two-layer shields of water and lead were calculated. Also, coherent scattering effect usually left unattended in this type of geometry and application was considered. First, gamma EBFs were calculated by using MCNP, without considering coherent scattering effect for a normal and anisotropic plane source and double stratified layers of water-lead and lead-water. Then, the above-mentioned factors were calculated by considering coherent scattering effect, and influence of coherent scattering and also fluorescence radiations on E.B.F. was studied. Due to coherent scattering, EBFs were increased in both layers, especially for sources with low energies and layers with more mean free paths. Regarding the high accuracy of statistical calculation and the applied cross sections, more complete results in comparison with previous works for the mentioned geometry were obtained.

Single and double equilibrium bond lengths of the fcc-C60 crystal were calculated in the absence and presence of the endohedral C atom as an impurity doped into each C60 cluster, i.e., fcc-C@C60, by means of fully-relaxed self-consistent calculations within the density functtional theory (DFT) employing the full potential-augmented plane waves plus local orbital (FP-APW+lo) method. The result shows that the single and double bond lengths were decreased for the doped case of fcc-C@C60 when compared with the pure fcc-C60. The reduction in the bond lengths by the carbon impurity doping is attributed to the bond alternation effect and reduction of the symmetry in the C60 molecule. The result shows that the impurity injection gives rise to change in the electron charge distribution and as a result to change in electronic properties

Studying confined quantum systems (CQS) is very important in nano technology. One of the basic CQS is a hydrogen atom confined in spherical cavity. In this article, eigenenergies and eigenfunctions of hydrogen atom in spherical cavity are calculated, using linear variational method. B-splines are used as basis functions, which can easily construct the trial wave functions with appropriate boundary conditions. The main characteristics of B-spline are its high localization and its flexibility. Besides, these functions have numerical stability and are able to spend high volume of calculation with good accuracy. The energy levels as function of cavity radius are analyzed. To check the validity and efficiency of the proposed method, extensive convergence test of eigenenergies in different cavity sizes has been carried out.

One dimensional quantum Ising model with nearest neighbor interaction in transverse magnetic field is one of the simplest spin models which undergo quantum phase transition. This model has been precisely solved using different methods. In this paper, we solve this model in uniform magnetic field -Jg sxn precisely using a new method called Continuous Unitary Transformations (CUT) or flow equations, and derive its expectation values <sxn>, <szn> and <sxnsxn+j>. Then, we apply this method on one dimensional quantum Ising model in staggered magnetic field (-1)nJgsxn. Results show that both models have the same critical properties as expected, and it was also found that spontaneous symmetry breaking cannot be derived from CUT.

In this paper, we study the robust technique of stimulated Raman adiabatic passage in an optical cavity considering decoherence effects of atomic spontaneous emission and cavity decay. Numerical solution of Liouville equation shows that the population transfer of the system is more sensitive to the cavity decay than the atomic spontaneous emission.

Influence of the partial substitution of Co for Fe on the structural, magnetic and magnetoelastic properties of Nd6Fe13Cu compounds are investigated. Analysis of X-ray diffraction patterns indicates that the multi-phase sample is formed for all samples. Upon Co substitution, the second phase Nd2Fe17, Nd2Fe17-yCoy with 0<y<1 and Nd2Fe17-zCoz with 1<z<2 is formed in the samples with x=0, 1, 2, respectively so that the lattice parameters are decreased and the Curie temperature is increased. Due to the ferromagnetic phase Nd2Fe17-yCoy in sample with x=1, the change of the anisotropy and increase of exchange effects are observed. The effects of long-range magnetic ordering processes on Néel temperature clearly appear in the temperature dependence of the spontaneous magnetostriction. Longitudinal (ll) and transverse (lt) magnetostrictions are measured to study the magnetoelastic behaviour of these compounds using a strain gauge method. In the low field region, magnetostrictive strains are small and then increase with increasing fields. Strong pining center of Nd atoms that creates large magnetocrystalline anisotropy prevents easy movement of domain walls. In the sample with x=0, the magnetostriction contribution from the rare earth sublattice (Nd) dominates at low temperature and the Fe sublattice contribution becomes increasingly important as temperature rises.

Solar radiation is an important climate parameter which can affect hydrological and meteorological processes. This parameter is a key element in development of solar energy application studies. The purpose of this study is the assessment of artificial intelligence techniques in prediction of solar radiation (Rs) using artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS). Minimum temperature, maximum temperature, average relative humidity, sunshine hours and daily solar radiation recorded in four synoptic stations (Esfahan, Urmieh, Shiraz and Kerman) were used during the period 1992-2006. The results showed that ANN and ANFIS intelligent models are powerful tools in prediction of global solar radiation for the selected stations. Prediction by ANN was found to be more accurate than ANFIS. Also, the accuracy of prediction in Kerman with higher sunny hours was better than other stations (R2>0.9). Additionally, using linear regression model, the most effective factors affecting Rs in each site was introduced. The results revealed that sunshine hour is the most important determining parameter affecting surface solar radiation. In contrast, in most sites minimum air temperature and mean relative humidity showed the least effect on surface global solar radiation.

Fast ignition is a new scheme for inertial confinement fusion (ICF). In this scheme, at first the interaction of ultraintense laser beam with the hohlraum wall surrounding a capsule containing deuterium-tritium (D-T) fuel causes implosion and compression of fuel to high density and then laser produced protons penetrate in the compressed fuel and deposit their energy in it as the ignition hot spot is created. In this paper, following the energy gain of spherical target and considering relationship of the burn fraction to burn duration, we have obtained the energy gain of conical targets characterized by the angle b, and found a hemispherical capsule (b=p/2) has a gain as high as 96% of that of the whole spherical capsule. The results obtained in this study are qualitatively consistent with Atzeni et al.'s studies of simulations.