مجله ایرانی علوم و تکنولوژی-ب
سال:1375 | دوره: | شماره: |تعداد مقالات:6

The connectivity constant mu of Hamiltonian walk on Sierpinski gasket with an arbitrary decimation number b has been given in terms of the number of possible walks in fractals of order M = 2.

The Bethe-Salpeter equation is solved in the ladder approximation and in the heavy quark limit to find appropriate heavy meson wave functions. The current-induced transition matrix elements are evaluated for B--> D and D--> K semileptonic weak decay in the Bethe-Salpeter formula to give q(2)-dependence of the form factors. The results are consistent with the monopole form factor of the Korner-Schuler model, f(0)/(1-q(2)/q(c)(2)).

The conceptual design of the pellet suspension reactor, PSR, which is absolutely passively safe against LOCA and LOFA accidents, is discussed elsewhere. The dynamics of a continuously fuelled pellet suspension reactor based on an isothermal and non-linear description of neutron-nuclide interactions, an considered herein. Also, the stability studies have already taken place for this on-line fuelled system and for this purpose analysis is done by application of the Hurwitz criteria. We find that, in general and for a plausible range of operational refueling conditions, such systems are absolutely stable.

The structural and electronic properties of NaCl in Rocksalt and CsCl phases are investigated under high pressure using total energy minimization techniques. The Kohn-Sham equations are solved within the local density approximation using the pseudopotential method with a plane wave basis set. The calculated structural properties such as lattice parameter, bulk modulus and its pressure derivative are in reasonable agreement with the experiment. At zero pressure the Rocksalt phase is found to be lower in energy than a hypothetical CsCl structure. However, we predict a phase transition into CsCl structure at high pressures. The electronic band structure at normal and high pressures is also calculated. It is found that metallization occurs for Rocksalt and CsCl structures at ultrahigh pressures.

The magnetic rotation of an electric are was selected to distribute electrical energy over plasma gas to produce a plasma of nearly uniform temperature. By injection of chromite ore into the hot plasma gases, its conversion to ferro-chrome was investigated. The swirl which is produced by magnetic rotation of the are will change the usual gas velocity profiles in plasma gases, which in turn will change the particle trajectories and residence time in plasma, resulting its conversion to ferro-chrome. A model was developed to predict particle trajectories and temperature in magnetically rotated plasma. The effect of plasma variables such as power input, gas flow rate and are rotation on the conversion of chromite to ferro-chrome was investigated. It was noticed that some of the melted particles showed nearly complete oxygen removal while the others showed no significant reduction.

A new method was developed to fabricate in-situ YBa2Cu3O7-delta-Ag thin films on MgO (100) substrate using combined DC magnetron spattering and Ag evaporation techniques. The films with multilayer structure YBCO/YBCO-Ag/YBCO/MgO (100) were deposited in a temperature range of 650-710 degrees C. Several analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) and T-c measurement, have been applied to characterize the deposited films. XRD analysis indicates that films exhibit a preferred orientation along the c-axis normal to the substrate surface. The c-lattice parameter remained almost unchanged with Ag addition. The transition temperatures (T-c) gradually decreased with increasing Ag concentration from 90 K (0 at.% Ag) to 72 K (22.3 at.% Ag) for the deposited films.