Iranian Journal of Physics Research
Year:2013 | Volume:12 | Issue:4|Papers Count:15

In this paper, stimulated Raman scattering (SRS) and electron heating in laser plasma propagating along the plasma fusion is investigated by particle-in cell simulation. Applying an external magnetic field to plasma, production of whistler waves and electron heating associated with whistler waves in the direction perpendicular to external magnetic field was observed in this simulation. The plasma waves with low phase velocities, generated in backward-SRS and dominateing initially in time and space, accelerated the backward electrons by trapping them. Then these electrons promoted to higher energies by the forward-SRS plasma waves with high phase velocities. This two-stage electron acceleration is more efficient due to the coexistence of these two instabilities.

The recent investigations show that the size and mass number of the target nucleus in the heavy-ion fission reactions are very important for the angular distribution of fission fragments. In this work, we consider the behavior of fission fragment angular anisotropies within the standard saddle-point statistical model for the 168O, 188O, 199F, 2412Mg, 2814Si, 3216 S+20882Pb fission reaction systems. As a result, a relation is found between the average contribution of non-compound nucleus fission and the mass number of projectile for these systems. It is also obtained that the onset of this contribution is significant for the projectile with the mass number greater than 20, as well as this quantity is an increasing function of the mass number of projectile. Finally, the comparison condition between a, and aBG is modified for these reaction systems.

Because the key issue in quantum information and quantum computing is entanglement, the investigation of the effects of environment, as a source of quantum dissipation, and interaction between environment and system on entanglement and quantum phase transition is important. In this paper, we consider two-qubit system in the anisotropic Heisenberg XXZ model with the Dzyaloshinskii-moriya interaction, and accompanied quantum dissipation. Using Lindblad dynamics, the coupling effect and also temperature effect on concurrence, as a measure of entanglement of system, is obtained. The role of DM interaction parameters in the evolution of entanglement is investigated. Furthermore, using derivative of concurrence, the effects of dissipation and DM interaction parameter on quantum phase transition are obtained. It should be noted that spin-orbit interaction or DM parameter intensively influence the process of impressments of dissipation on entanglement measure and quantum phase transition. The current research is very important in the topics of nanometric systems.

In this article, non-linear Landau damping and generation of BGK mode in non-magnetized plasma are studied by using particle simulation. As plasma environment consists of electrons and ions, it is simulated by particle method and it is supposed that ions are considered as a motionless background. On the other hand, electron’s dynamic is obtained from solving Newton’s equation and the electrons are supposed as particles. In the non-linear region, trapping of particles in potential well is investigated. These trapped particles account for stopping linear landau damping and entering to the non-linear region, and as a result of this process, the amplitude of electrostatic wave oscillates around an approximately constant magnitude. The effect of collision between particles has been studied with the help of a simple model for the collision term in the simulation code and the result of the simulation code with the theoretical result is compatible. For this purpose, it is expected that the exponential damping of electrostatic waves is due to the collision, and the ratio of this damping is in proportion with collision frequency.

‎The possibility of symmetrical s-wave superconductivity in the honeycomb lattice is studied within a strongly correlated regime, using the Hubbard model. The superconducting order parameter is defined by introducing the Green function, which is obtained by calculating the density of the electrons. In this study showed that the superconducting order parameter appears in doping interval between 0 and 0.5, and x=0.25 is the optimum doping for the s-wave superconductivity in honeycomb lattice.

In this paper, ZnO thin film was prepared by sol-gel process on glass substrates. The deposited films were dried at 100 and 240oC and then annealed at 300, 400 and 500oC. The two-probe measurement showed that resistance of as-prepared films is very high. The KrF excimer (l=248 nm) laser irradiation with 1000 pulses, frequency of 1 Hz and 90 mJ/cm2 energy on surface of film resulted in the reduction of the films electrical resistance. X-ray diffraction (XRD) patterns confirmed the improved hexagonal wurtzite structure of film, and AFM and FE-SEM analyses showed regular and spherical grain was formed on the surface. The particle size was increased from ~10 to ~30 nm after leaser irradiation. Generally, it was showed that electrical, structural and morphological properties of films improve considerably by laser irradiation.

In this paper, the invariant mass spectra of Ù(1405)®(Sp)0 in high energy proton-proton collisions in center of mass frame have been theoretically investigated. In pp collision the Ù(1405) formation possibility has been taken into account and its decay rate to (Sp)0 channels, has been calculated with T-matrix elements and Green’s function method. Finally, the results have been compared with the ANKE data for the first time, and using X2 method the confidence level diagrams have been obtained. The X2 fitting shows a good agreement between experimental data and the ones obtained in current paper.

Investigation of ion acoustic solitons in three component plasma including positive and negative ions and Maxwellian electrons shows that negative to positive relative ion density plays a critical role so that by changing v over the range of 0<v<1 compressive or rarefactive solitons will propagate. In this paper, it is shown that due to the superthermal electrons, there are three domains for v so that in the first one only compressive solitons are allowed, in the second one compressive and rarefactive solitons coexist together and in the third one only rarefactive solitons are observed. The results from sagdeev potential in weak nonlinear region are in good agreement with analytic results obtained from KdV equation.

A new concept for inertial confinement fusion called fast-shock ignition (FSI) is introduced as a credible scheme in order to obtain high target gain. In the proposed model, the separation of fuel ignition into two successive steps, under the suitable conditions, reduces required ignitor energy for the fuel ignition. The main procedure in FSI concept is compressing the fuel up to stagnation. Then, two high intensity short pulse laser spikes with energy and power lower than those required for shock ignition (SI) and fast ignition (FI) with a proper delay time are launched at the fuel which increases the central hot-spot temperature and completes the ignition of the precompressed fuel. The introduced semi-analytical model indicates that with fast-shock ignition, the total required energy for compressing and igniting the fuel can be slightly reduced in comparison to pure shock ignition. Furthermore, for fuel mass greater than, the target energy gain increases up to 15 percent and the contribution of fast ignitor under the proper conditions could be decreased about 20 percent compared with pure fast ignition. The FSI scheme is beneficial from technological considerations for the construction of short pulse high power laser drivers. The general advantages of fast-shock ignition over pure shock ignition in terms of figure of merit can be more than 1.3.

In this study, the pure manganese ferrite nanoparticles and those dispersed in silica were prepared by the sol-gel method. The average size of particles, which is estimated from Scherrer formula, is about 6 nm for pure sample and 5 nm for silica dispersed sample. The particles size values are in agreement with the TEM results. Results of magnetization measurements showed that these samples have zero coercivity and are super paramagnet at room temperature. Using the results of ac magnetic susceptibility measurements and analysis by different models, super paramagnetic behavior of magnetic nanoparticles was studied. The behavior of pure sample is interacting super paramagnet and in the silica dispersed sample, the interaction between nanoparticles decreases and the behavior of this sample is non-interacting super paramagnet. It seems that by dispersing the nanoparticles in silica, the distance of particles increases and interaction between ferrite nanoparticles decreases.

In this paper, the importance of the buncher in linear electron accelerators is discussed and two types of bunchers, velocity-modulation and disk-loaded, are introduced. Higher bunching factor, larger initial phase range, and smaller final phase range are favorable in the disk-loaded buncher. Our investigations showed that the aforementioned situations can be met by appropriate changes in the field strength and the phase velocity. In this study, factors affecting the bunching of electrons have been surveyed using the equations of electron motion. The dynamics of the electron movement through the buncher has been simulated. The results of simulation and calculations revealed that: (1) in order to deliver the maximum energy to the electrons, phase velocity should vary so that a phase of – 90 degrees is achieved by the electrons after the bunching, (2) reducing the initial field strength also increases the initial phase range. If the field strength is large from the beginning, the phase velocity variations will be large and rapidly reach a value of 1. In this case, the initial phase range will become small, (3) the electron gun voltage changes the initial phase; the larger the value of the gun voltage, the wider the initial phase range, and vice versa. The result of this study is going to be applied for design and fabrication of the first Iranian linear accelerator that is under construction.

Using the quantum game formalism in 3-player system, we calculate the Nash equilibrium in quantum Prisoners’ Dilemma by increasing parameters of unitary operator. Since, the entanglement plays an important role in quantum states of particles quantum game, actually its effect on the obtained results of Nash equilibrium is investigated. It is shown that increasing the parameters enhances the game payoff function.

In this paper, the Schrodinger equation for a quantum wire is solved using a finite difference approach. A new aspect in this work is plotting wave function on cross section of rectangular cross-sectional wire in two dimensions, periodically. It is found that the correct eigen energies occur when wave functions have a complete symmetry. If the value of eigen energy has a small increase or decrease in neighborhood of the correct energy the symmetry will be destroyed and aperturbation value at the first of wave function will be observed. In addition, the demand on computer memory varies linearly with the size of the system under investigation.