Iranian Journal of Physics Research
Year:2008 | Volume:8 | Issue:1|Papers Count:9

We have grown TiO2 and AlN under ultra high vacuum and high pressure conditions and studied their structures with using AES and SEM techniques. The obtained results show that an amorphous film of TiO2 and AlN could be formed on silicon substrate. Furthermore, TiO2 and AlN are high– K dielectric materials and they can thus be replaced to ultra thin gate oxide film.

Barrabes-Israel null shell formalism is used to study the gravitational collapse of a thin cylindrical null shell in vacuum. In general the lightlike matter shell whose history coincides with a null hypersurface is characterized by a surface energy density. In addition, a gravitational impulsive wave is present on this null hypersurface whose generators admit both the shear and expansion. In the case of imposing the cylindrical flatness the surface energy-momentum tensor of the matter shell on the null hypersurface vanishes and the null hyper- surface is just the history of the gravitational wave.

Magnetically confined plasma can be heated with high power microwave sources. In spherical torus the electron plasma frequency exeeds the electron cyclotron frequency (EC) and, as a consequence, electromagnetic waves at fundamental and low harmonic EC cannot propagate within the plasma. In contrast, electron Bernstein waves (EBWs) readily propagate in spherical torus plasma and are absorbed strongly at the electron cyclotron resonances. In order to propagate EBWs beyond the upper hybrid resonance (UHR), that surrounds the plasma, the EBWs must convert via one of two processes to either ordinary (O-mode) or extraordinary (X-mode) electromagnetic waves. O-mode and X-mode electromagnetic waves lunched at the plasma edge can convert to the electron Bernstein waves (EBWs) which can propagate without and cut-off into the core of the plasma and damp on electrons. Since the electron Bernstein wave (EBW) has no cut-off limits, it is well suited to heat over-dense plasma by resonant absorption. An important problem is to calculate mode conversion coefficient that is very sensitive to density. Mode conversion coefficient depends on Budden parameter (h) and density scale length (Ln) in upper hybrid resonance (UHR). In Mega Ampere Spherical Tokamak (MAST), the optimized conversion efficiency approached 72.5% when Ln was 4.94 cm and the magnetic field was 0.475 Tesla in the core of the plasma.

In this paper a new method is introduced for studying time series of complex systems. This method is based on using the concept of entropy and Jensen-Shannon divergence. In this paper this method is applied to time series of billiard system and heart signals. By this method, we can diagnose the healthy and unhealthy heart and also chaotic billiards from non chaotic systems. The method can also be applied to other time series.

The most common reaction-diffusion model on a Cayley tree with the nearest neighbor interactions is introduced, and the shock measure on a Cayley tree with the nearest interactions is studied. This can be solved through the full-interval method; the evolution equation of the system can be solved exactly in a closed form. The stationary solutions of such models are discussed and the final configuration will be full of particles. Also, the dynamics solutions are investigated and the Hamiltonian spectrum will be discrete.

We have compared the structural, electrical, and magnetic properties of Ru(Gd1.5-xPrx)Ce0.5Sr2Cu2O10-d (Pr/Gd samples) with x = 0.0, 0.01, 0.03, 0.033, 0.035, 0.04, 0.05, 0.06, 0.1 and RuGd1.5(Ce0.5-xPrx)Sr2Cu2O10-d (Pr/Ce samples) with x = 0.0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 prepared by the standard solid-state reaction technique with RuGd1.5(GdxCe0.5-x) Sr2Cu2O10-d (Gd/Ce samples) with x= 0.0, 0.1, 0.2, 0.3. We obtained the XRD patterns for different samples with various x. The lattice parameters versus x for different substitutions have been obtained from the Rietveld analysis. To determine how the magnetic and superconducting properties of these layered cuprate systems can be affected by Pr substitution, the resistivity and magnetoresistivity, with Hext varying from 0.0 to 15 kOe, have been measured at various temperatures. Superconducting transition temperature Tc and magnetic transition Tirr have been obtained through resistivity and ac susceptibility measurements. The Tc suppression due to Gd/Ce, Pr/Gd and Pr/Ce substitutions show competition between pair breaking by magnetic impurity, hole doping due to different ionic valences, difference in ionic radii, and oxygen stoichiometry. Pr/Gd substitution suppresses superconductivity more rapidly than for Pr/Ce or Gd/Ce, showing that the effect of hole doping and pair breaking by magnetic impurity is stronger than the difference in ionic radii. In Pr/Gd substitution, the small difference between the ionic radii of Pr and Gd, and absorption of more oxygen due to higher valence of Pr with respect to Gd, decrease the mean Ru-Ru distance, and as a result, the magnetic exchange interaction becomes stronger with the increase of x. But, Pr/Ce and Gd/Ce substitutions have a reverse effect. The magnetic properties such as Hc, obtained through magnetization measurements versus applied magnetic field isoterm at 77K and room temperatures, become stronger with x in Pr/Gd and weaker with x in Pr/Ce and Gd/Ce substitutions.

Stochastic resonance (SR) is a phenomenon wherein the response of a nonlinear system to a weak periodic input signal is optimized by the presence of a particular level of noise. In this work we investigate the effect of Gaussian noise with the power law decaying temporal correlation, on the bistable systems as an example in which stochastic resonance occurs. We show that the correlation lowers the standard derivation of the noise at which SR takes place, but decreases the resonance amplitude.

In this paper the motion of electron in a miniband of a semiconductor superlattice (SSL) under the influence of external electric and magnetic fields is investigated. The electric field is applied in a direction perpendicular to the layers of the semiconductor superlattice, and the magnetic field is applied in different direction Numerical calculations show conditions led to the possibility of chaotic behaviors.

In this study, the design and construction of a pulse high repetition rate (HRR), transverse atmospheric pressure (TEA) CO2 laser with ultra violet preionization is presented. In this laser, normal pure, industrial gases and also a combination of spark and corona preionization are used. In semi-sealed off condition, we obtained 220 watts at 300 Hz, %7.7 efficiency, 735 mJ/pulse. The best records that we reached separately were 1.1 J/pulse, 320 Hz PRR, 11 MW peak power and 10.6% efficiency.