Iranian Journal of Physics Research
Year:2005 | Volume:4 | Issue:3|Papers Count:15

Using a tight-binding model and transfer-matrix technique, as well as Lanczos algorithm, we numerically investigate the nature of the electronic states and electron transmission in site, bond and mixing Fibonacci model chains. We rely on the Landauer formalism as the basis for studying the conduction properties of these systems. Calculating the Lyapunov exponent, we also study the localization properties of electronic eigenstates in the Fibonacci chains.. The focus is on the significance of the relationship between the transmission spectra and the nature of the electronic states. Our results show that, in contrast to Anderson's localization theorem, in the Fibonacci chains the electronic states are non-localized and the transparent states occurr near the Fermi level.

Band offsets at semiconductor heterojunctions have been shown to be critically dependent on a number of factors. By applying the ab-initio pseudopotential method to the strained InGaAs/GaAs superlattice, we have been able to determine the dependence of the offsets on the strain in the system and on the indium composition. In addition, we have shown that it is possible to control the interface band discontinuities by the introduction of an interlayer of Ge at the interface.

It is ten years since the Iranian Journal of Physics Research has been in publication. For the Occasion of the 10th anniversary of its publication, we have planned several changes and modifications. These includes increasing the annual issues to four and omission of 'Introduction of Previously-Published Papers in International Journals' section. In this article some statistical information of the published articles is given together with the index of the journal's referees. As weenter the second decade of our publication, we face several questions. In this article we share these questions with our readers in the hope of finding the best possible solutions, so that we would be able to publish a better journal in future.

Patterns formed by the flow of an inhomogeneous fluid (suspension) over a smooth inclined surface were studied. It was observed that fractal patterns formed. There exists a threshold angle for the inclination above which, global fractal patterns are formed. This angle depends on the particle size of the suspension. We observed that there are two fractal dimensions for these patterns, depending on the area from which the pattern is extracted. If the pattern is taken from the top which only consists of the beginning stages of the pattern forming, one finds two fractal dimensions i.e. 1.35-1.45 and 1.6-1.7, in which the first one is dominant. And if the entire pattern is taken, then fractal dimension 1.6-1.7 is observed. The first fractal dimension belongs to the class of flow of water over an inhomogeneous surface, and the second one corresponds to the river network. This may imply that both universality classes are present. However, disorder is present in the fluid and is transferred to the surface. We have also determined the fractal dimension of the patterns formed below the threshold angle. We find it to be between 1.57 to 1.7.

Optogalavanic technique has been used widely in laser spectroscopy. In this paper we have presented the results of an experimental three- step photo- excitation of Gd atom, using optogalvanic technique. Three tunable dye laser pulses were applied to excite the Gd atom in a three-step photo - excitation process. The optogalvanic signal was used to monitor the laser wavelength and 'efficiency of the excitation process, The results show that the optogalvanic signal is very sensitive to the first photo- excitation step in comparison with those of the second and the third step.

Optical spatial screening solitons in photorefractive crystals in a one-dimensional case based on Kukhtarev model is studied. The new numerical scheme according to the Crank-Nicholson method accompanied by the central difference method is introduced to find the bright soliton solution. Simulation of the propagation is performed to show the dynamical evolution of solitons and check their stability. Numerical investigation of the interaction between incoherent screening photorefractive solitons is also performed. The influence of intensity and initial separation of the mutually incoherent self-trapped beams are discussed in detail.

The density functional theory analogue of Percus Yevick (PY) and Hyper-Netted chain (HNC) has been used to write the grand potential of a liquid with cylindrical and ellipsoidal molecules. The integral equations for the density can be obtainedby minimizing the grand potential with respect to the density. Some kinds of liquid crystals, can have the cylindricalor ellipsoidal rigid molecules. In this study we have calculated the density profile of this kind of liquids confinedbetween hard walls and we compared the results. As it is seen from the graphs of the density profiles the molecules can be arranged as layers with respect to the walls.

Our aim in this paper is to find the observable effects of the generalized commutators. For this purpose we investigate two problems in quantum mechanics with minimal length procedure. Firstly, we study hydrogen atom energy levels via minimal length uncertainty relation algebra. From comparing our results, with experimental data we estimate an upper limit for minimal length. Secondly, we investigate statistical mechanics and density of states in phase space via minimal length uncertainty relation and find a correction for white dwarf mass limit. Finally, we study classical implication of minimal momentum uncertainty relations. With this procedure we have corrected the Keplerian third law and some results have been obtained.

Methane conversion to higher hydrocarbons by pulsed glow discharge at the atmospheric pressure was investigated. The energy efficiency up to 10 % was obtained which is higher than any value ever published for nonequilibrium plasma conversion of pure methame. This method has a potential for development and it is expected that the energy efficiency will be improved further if the plasma parameters are optimized.

A detailed analysis of electron trajectories in a realizable helical wiggler free electron laser with ion channel guiding. using electron (single particle dynamics) is presented. Conditions for stability of electron orbit have been investigated, calculations are made to illustrate. Conclusion shows that there are differences stable (unstable) condition(s) electron trajectories between ideal helical wiggler (2D) and realizable helical wiggler (3D).

A plasma focus facility is a magnetically confinement fusion device, characterized by a relatively simple structure. Nowadays, it is a well-known fact that the theory of shock waves stands for temperature increment in plasma of a PF device. On the other hand, we also know that computer simulations can make experimental works easier and more cost effective. So based on the MHD theory, shock wave propagation in plasma of the PF devices, have been simulated. The simulated results were cross compared experimentally. We observed that in both cases, the order of results (shock wave velocity)was the same.

(YGdSm) 123 sample with nominal composition (Y0.33 Gd0.33 Sm0.33) Ba2Cu3OX, also YGdEu1 and YGdEu2 samples with nominal composition (Y0.33 Gd0.33 EU0.33) Ba2Cu3OX were prepared at different oxygenation conditions. All the samples were analysed by ac susceptibility, resistivity, critical current density (Jc), SEM, XRD and EDX. The critical current density measurements show that the Jc increases in (YGdSm) 123 and YGdEu1 samples comparing to (Y123) sample, so that the value of Jc in YGdEu1 is almost 2 times greater than (Y123) sample. May be the presence of Eu and Sm ions on the BaO planes act as the impurity and lead to local pinning and so increases the critical current density.