Iranian Journal of Physics Research
Year:2003 | Volume:3 | Issue:3|Papers Count:9

Yrast states in mirror nuclei 55CO and 55Ni have been populated with a radioactive ion beam using the Isotope Separator On-Line method. A shielded array of 7 Compton suppressed germanium detectors recorded reaction gamma-rays. For channel selection, an array of 128 independent silicon detectors was used to differentiate exit channels with different number of proton and alpha particles emitted. From gamma-gamma and gamma-particle coincidences, three lines in 55CO and one line in 55Ni was obtained for the first time.

The electronic structure, density of state (DOS) and electronic density of state in paraelectric cubic crystal BaTiO3 are studied using full potential-linearized augmented plane wave (FP-LAPW) method in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA) by the WIEN2K package. The results show a direct band gap of 1.8 eV at the r point in the Brillouin zone. The calculated band structure and density of state of BaTiO3 are in good agreement with theoretical and experimental results.

In this paper, the analytical solutions of Brans-Dicke (B-D) equations with cosmological constant are presented, in which the equation of state of the universe is p=mΛ0ρ, under the assumption ΦRn=C between the B-D field and the scale factor of the universe. The flat (k=0) Robertson - Walker metric has been considered for the metric of the universe. These solutions are rich in the sense that they include dust B-D theory with cosmological constant, Nariai Λ=0 solutions, vacuum solutions of Ohanien - Tupper and inflationary Λ=0 solutions.

In this research parameterization of the precipitation process in Ogura & Takahashi (0- T) thunderstorm model was improved in microphysical processes, specially in the autoconversion process to form raindrops, in the glaciation process and in the terminal velocities of rain and hail. The rainfall intensity became much heavier with Kessler's parameterization, the second peak of the rainfall intensity disappeared with Bigg's freezing probability, and the rainfall intensity became much heavier and sharper with Lin et al's terminal velocities of rain and hail than in the O-T original model. Finally, the derived rainfall pattern based on the improved model has much similarities to the observation data.This paper expresses the basic research for studying the physical treatment in clouds. The modified 0- T model has different applications in analyzing radar observation data, estimate the potential of soil erosion, parameterization of shower in mesoscale numerical weather prediction and etc.

In magnetic recording media, the remnant magnetization loop, Mr (H) has some parameters, which explain the properties of the medium in view of the storage density and signal-to-noise ratio. It is necessary to find the mechanism of Mr variations from the statistical characteristics of the system. We have prepared samples of single-domain acicular iron particles with 0.3 µm length, and the oriented textures of particles formed. The easy axis distribution of particles in the samples was determined using the results of magnetic measurements. The effect of the distribution width on Mrand coercively (Hc) have been studied. The deviation of results from the Stoner-Wohlforth model for Hc indicates a correlation in the medium due to the dipole-dipole interaction. We also present a technique for determining the switching field distribution in medium, which has been used for various samples. A narrow distribution leads to narrow transition regions in the recording media, and an increase of signal. A high switching field at the maximum of distribution indicates the ability of high recording density.

The wind drift motion of the water which is produced by the stress of the wind exerted, upon the surface of the ocean is described by Ekman's theory (1905). Using the mean monthly values for the wind stress and SST, seasonal Ekman transport for the Persian Gulf was computed and contoured. The geostrophic winds have combined with the SST to estimate the effect of cooling due to Ekman transport of colder northern waters and inflow from the Oman Sea. The monthly SST mainly obtained from the 1°xl°grided data of Levitus atlas and Hormuz Cruis Experiment for 1997. Analyses show a NW to SE Ekman transport due to wind stress and significant interannual variability of SST on sea surface in the Persian Gulf. The seasonal variation of SST shows a continental pattern due to severe interaction between the land and sea. But these variations somehow moderates because of Ekman transport in Persian Gulf.

The electronic and structural properties of CaS are calculated using full potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation energy. For both structures, NaCl structure (BI) and CsCl structure (B2), the obtained values for lattice parameters, Bulk modulus and its pressure derivative and transition pressure are in reasonable agreement with the experimental values. For electronic properties, the obtained value for band gap is smaller than the experimental value as well as other calculated results based on density functional theory. Engel and Vosko calculated an exchange potential for some atoms within the so-called optimize-potential model and then used the virial relation and constructed a new exchange-correlation functional (EV-GGA). We used that functional and obtained reasonable results for band gap. Finally we investigated the possibility for a third phase (Zinc Blend structure) for this crystal.

A second-order approximation to the Faddeev-Watson-Lovelace treatment of the rearrangement channel is used in a three-body scattering cross sections. In this formalism, the Three-body wave function is expressed by three coupled integral equations, the Faddeev equations, which contain the two-body (off-shell) transition amplitudes, and proved the uniqueness of their solutions. This amplitude corresponds to the summing of infinite numbers of terms involving the electron-projectile and electron-target nuclear potentials in a Born expansion of the transition operator. It thus represents a considerable improvement over a treatment involving only the second-order Born approximation. Application of this method is tedious because of a difficulty arising from the complicated nature of the two-body off shell Coulomb T-matrix, which is the basic dynamical ingredient in the formalism. The difficulty arises from the fact that the Coulomb T-matrix does not have a well-defined on-shell limit.Expressions are derived for projectile scattering angles in the extreme forward directions and for angles centered about the local maximum of the differential cross section [at (me/Mp)Sin60°, where me is the electron mass and Mp is the projectile mass] known as the Thomas peak. A mixture of analytical and numerical methods have been used to calculate the transition amplitudes for state to state [H++H(nlm)®H(N'L'M')+H+] reaction and therefore the corresponding cross sections.Many numerical and analytical calculations are available within a near-the-shell limit for 1s-1s transition of electron-capture process in proton hydrogen collision, but no calculation was performed for the state (nlm) to state (n'l'm'). We have compared the calculated differential cross sections for electron capture of different states and also with the available measured cross sections in the literature.

The basic requirements of the CdS thin films on their applications are high optical transparency, low electrical resistivity, and better crystalinity (e. g. high orientation). Firstly, we prepared CdS films by thermal evaporation techniques on glass substrate and then studied their photoconductivity from room temperature to 200°C. Secondly, we prepared CdS films with impurities of Cu, Ag, Au and AI. In doped films with Cu, Ag and Au, we found CdS peak shifts towards lower energies. Our aim was to use a new and initiative method' for temperature and impurities effects on CdS photoconductors.