Sharif Digital Repository

The magnetoresistance measurement of single phase polycrystalline Tm(Ba2-xPrx)Cu3O7+δ samples have been analyzed by the Ambegaokar and Halperine (AH) phase slip model. The magnetic field dependence of pinning energy power factors increase with the increase of Pr doping. The derived critical current density from the AH theory decreases with increasing magnetic field and Pr-doping for all superconducting samples. It shows that the Pr-doping plays the role of weak link. We have also investigated the normal state resistivity with the hopping model. We have found a CG-VRH cross-over with the increase of Pr content near metal insulator transition. The deacrease of the localization length of the... 

Single-phase polycrystalline NdBa2-xPrxCu 3O7+δ (0 ≤ x ≤ 0.5) have been prepared by the standard solid-state reaction. The results of X-ray diffraction measurements confirm the formation of 123 single phase. A superconductor-insulator transition at XcSIT = 0.3 has been observed for the samples. The magnetoresistance of the samples have been investigated within the thermally activated flux creep model. The pinning energy decreases with the magnetic field application and Pr-doping. A scaling relation as power law dependence of pinning energy to the magnetic field has been obtained. The derived pinning energy shows that the Pr-doping plays the role of weak link. The normal state resistivity... 

An analytical procedure for supersonic flutter analysis of two-dimensional panels was developed using unsteady potential flow aerodynamic theory. The local spatial influence was considered as an integral over the plate area. The U-g method was used for flutter prediction. Results indicate a stabilizing effect of the unsteady potential flow aerodynamics theory compared to the quasi-steady first-order piston theory  

The production of reducing gas is usually a bottleneck to capacity increase in direct reduction plants. Modelling and simulation of reducing gas production result in better design and operation of these plants. In the present work, a mathematical model is discussed that relates to a Midrex reformer, which is different from conventional steam reformers in some respects. Both process side and furnace side have been included in an integrated model. Simulation results have been tested against available data from an actual plant. The model predictions have been found to be reasonably accurate. The effects of three process variables, feed gas temperature, feed gas pressure and excess air, on... 

Rhenium distribution between Tri-n-butyl phosphate (TBP) dissolved in kerosene and sulfuric aqueous media is investigated under different temperatures, acidities, and TBP concentrations. Results show an exothermic extraction reaction with a distribution factor that decreases with the increase of the temperature and increases with the increase of the acidity and the TBP concentration. The stoichiometry of the reaction indicates neutralization of 1 mole of H+ with 1 mole of ReO4- and solvating of a neutral molecule with four molecules of TBP. The structure of the complexes formed is, therefore, 4TBP · HReO4. The apparent Gibbs free energy of the formation of 4TBP · HReO4 from TBP, ReO4-, and...