Iranian Journal of Physics Research
Year:2005 | Volume:5 | Issue:2|Papers Count:11

A constant volume, atmospheric pressure Zr/Ba/Na fluoride glass has been simulated by molecular dynamics with the limitations of the Born - Mayer - Huggins potentials, used previously and resulting in high simulation pressures, having been overcome. The simulated structure of this glass as well as its activation energy for diffusion is in very good agreement with those experimentally observed. To highlight the changes brought on by the decrease in pressure, the simulation at atmospheric pressure has been compared with one at high pressure. The results show that structural energy (total and potential), specific heat and pressure derivative changes occur with the reduction in pressure. In addition, a greater structural relaxation rate and a glass with a lower configurational variation were also observed. The glass transition has also been studied and it was found, on moving from glass to liquid temperatures, to be caused by the breaking of structural and geometric constraints. As expected, a sharp increase in the MSD was observed after the glass transition.

Using the forced oscillator method (FOM) and the transfer - matrix technique, we numerically investigate the nature of the phonon state and the wave propagation, in the presence of an external force, in the chains composed of Fibonacci lattices of type site, bond and mixing models, as the quasiperiodic systems. Calculating the Lyapunov exponent and the participation ratio, we also study the localization properties of phonon eigenstates in these chains. The focus is on the significant relationship between the transmission spectraand the nature of the phonon states. Our results show that in the presence of the Fibonacci lattices, at low and medium frequencies the spectra of the quasiperiodic systems are not much different from those of the periodic ones and the corresponding phonon eigenstates are extended. However, the numerical results of the calculations of the transmission coefficient Γ (w), the inverse Lyapunov exponentr (w)-1 and the participation ratio PR (w) show that at high frequencies, in contrast with similar ones in disordered systems, the phonon eigenstates are delocalized.

We present a mathematical method to describe motion of a system based on 3 identical body forces. The 3-body forces are more easily introduced and treated within the hyperspherical harmonics. We have obtained an exact solution of the radial Schrödinger equation for a 3- body system in three dimensions. The interact potential V is assumed to depend on the hyperradius X only where x is a function of the Jacobi relative coordinates p and λ which are functions of the three identical particles, relative positions →r12 , →r23 and →r31 .This method has been extensively used in nuclear and molecular physics. This work is interesting to those who are studying hadronic and bosonics physics and problems consisting three -body systems.

A local interaction in noncommutative space modifies to a non-local one. For an assembly of particles interacting through the contact potential, formalism of the quantum field theory makes it possible to take into account the effect of modification of the potential on the energy of the system. In this paper we calculate the energy shift of an assembly of non-relativistic fermions, interacting through the contact potential in the presence of the two-dimensional noncommutativity.

We consider Bethe-Salpeter (BS) equation for the bound state of two point particles in the non-commutative space-time. We subsequently explore the BS equation for spin0-spin0, spin1/2 - spin1/2 and spin0 - spin1/2 bound states. 222 we show that the lowest order spin independent correction to energy spectrum in each case is of the order өα4 while the spin dependent one in NC space, is started at the order θα6.  

In this paper a simple model calculation of spin wave is given for the ferromagtic layer in ultra thin ferromagnetic/antiferromagnetic bilayer. In this model the magnetic layer is assumed as an isolated layer but the effect of antiferromagnetic layer on ferromagnetic layer and unidirectional anisotropy, is given in the effective field applied on each spin. The thin layer is assumed as two-dimensional plate. In this model the exchange coupling and dipoles interactions are assumed in the ferromagnetic layer. The spin wave frequencies are calculated for long spin waves. The observed data is fitted into this theory. In the light of this theory, important information can be obtained about the existing fields in the ferromagnetic/antiferromagnetic bilayer. These studies are very important because the ferromagnetic/antiferromagnetic bilayer is used in sensors and spin valves that are used in reading data from the hard disk of computer.

 In this paper the cycle of muon catalyzed fusion processes has been simulated using Monte-Carlo methods. This simulation starts when muon enters the D/T mixture and follows the actual trajectories of the muonic atoms among the proceeding collisions, by using their cross sections. For this purpose a computer code has been written by Fortran language. The time dependence of the processes is taking into account and the time spectrum of the events in the µCF cycle has been obtained. The time spectrum of neutrons created in fusion and energy spectrum of muonic atoms have been calculated. One can obtain more detailed information such as fusion yield per muon (x), cycling rate (λc) and total sticking coefficient W, for various hydrogen isotopic concentrations, by expending the Monte-Carlo simulation. Results have been compared with some experimental data and the other calculation methods.

In various statistical mechanical models, introduction of a metric into space of parameters gives a new perspective to the phase structure. In this paper, the scalar curvature R of this metric for a one dimensional four-state complex spin model is calculated. It is shown that this parameter has a similar behavior to the Ising and Potts models.  

In this research, thin films of Zr/ZrO2 composites were deposited by reactive magnetron sputtering technique on Si and fused Silica substrates, and their structures were investigated by XRD method. During the deposition of the cermets layers, a Zr metallic target was sputtered in a gas mixture of Ar and O2. By controlling of O2 flow rate, the different metal volume fractions in the cermet layers were achieved. The optical response of the samples was studied using spectroscopy methods. Also the effect of vacuum annealing on the structures and the optical properties were studied. XRD results indicated that the prepared samples were amorphous and vacuum annealing induced crystallization in the cermet films. This research also showed that without doping, the tetragonal phase of zirconia can be stabilized at a temperature lower than the normal transition temperature. This is "grain size stabilization" and relates to the small size of the crystallites. In order to study the electron diffraction in the selected area patterns (SAD), the samples were analyzed by a high-resolution transmission microscope. The SAD results showed that all of the as prepared samples were amorphous showing evidence of very small Zr crystallites immersed in dielectric medium.The SAD results are in close agreement with those obtained by XRD analysis.

Electronic properties of CaTiO3 crystal in paraelectric and ferroelectric phases have been studied by first principles, using Hohenberg-Kohn-Sham density functional theory (DFT). In paraelectric phase the results show an indirect band gap of about 2eV at Γ-R direction in the Brilluoin zone and a strong hybridization between Ti-3d and O-2P orbital. In ferroelectric phase a direct band gap of about 1eV is seen at Γ point. Up to our knowledge no data has been reported on the ferroelectric phase so far, therefore our results might be useful for the future works.