مجله فیزیک کاربردی
سال نهم شماره 2 (پیاپی 17، تابستان 1398)

In physics and mathematics, research on the exact solutions of nonlinear differential equations is of great importance. Precise solutions play an important role in understanding the properties and quality of nonlinear phenomena. A wide range of exact solutions is nonlinear differential equations of soliton solutions. The study of solitons is very important because of their wide applications in various sciences such as fluid mechanics, plasma physics, astronomy, signal propagation in optical fibers and so on. In this study, we attempt to obtain the soliton solutions of the calogero-Bogojavolenski-Schiff equation by using the multiple exp-function method with Maple software. One-soliton, two-soliton, and three-soliton type solutions have been obtained by using the method. The results can be used as a benchmark for numerical solutions of the underlying equations and it can be analyzed in different branches of science and physics. Multiple exp-function method is very useful for solving multiple soliton solutions due to its simple calculations, and it is easy to be extended for solving other nonlinear developmental equations.

A compact model of synchrotron accelerator facility is proposed for the treatment of deep-seated tumors with proton therapy. The extracted beam from the existing C-30 cyclotron is first injected into the modelled synchrotron. The injected beam is specified with its longitudinal plane as well as its horizontal and vertical emittances. For this design to be compatible with the cyclotron C-30, the synchrotron should be kept compact and the number of magnet components must be low. The modeled synchrotron layout is designed using the computer codes MADX and AGILE in order to accelerate the injection proton ions from 30 MeV to a maximum extraction energy of 250 MeV with magnetic rigidity of 2.433 Tm. In this lattice arrangement with phase advance of about 90 degrees in two horizontal and vertical planes doublet cells are utilized. This ring consists of two long straight sections for RF and injection/extraction equipment, as well as four short straight sections. For chromaticity correction, two families of sextupoles are used. To prohibit emittance growth, a matching at injection in longitudinal plane was performed. The proton beam energy spread of 2% can be improved to 0.1% at injection by using the designed achromatic system. For the proton beam acceleration, a RF cavity with an approximate voltage of 160 V with a frequency in the range of 2.3 up to 14 MHz is used.

The excitonic wave-functions and dipole moments in a conic quantum dot with spherical base are numerically calculated. To perform the computations, a computer code, developed by the authors to solve Schrodinger equation based on the perturbation method of “configuration interaction”, is used. The results show that if the effective masses of electron and hole are equal, then exciton dipole moment of all excitonic eigen-states will be equal to zero. On the other hand, the exciton will have dipole moment when the masses of electron and hole are different. When the electron mass is larger than that of hole, the moment orientation is directed towards the cone apex and when the electron mass become smaller the direction is inverted. From this finding it is revealed that difference of electron and hole masses in quantum dots lacking inversion center (here a conic one) causes an intrinsic electrical polarization in the confined exciton.

The effect of nitrogen ion implantation on the zinc oxide semiconductor have been investigated. To this end, a thin layer of ZnO with thickness of 120 nm was bombarded with N+ ion with energy of 50 keV at a dose rate of 1014 (ion/cm2) with duration of 3 seconds. The effect of the N+ implantation on the crystalline structure was investigated by XRD and the surface morphology was investigated by the AFM and SEM. Also, the electrical conductivity and electrical resistance were measured by the point probe devices. Comparison of XRD diffraction patterns before and after ion implantation reveals that the crystalline structures show no specific changes, but only a very small shift to smaller angles. By comparison of AFM results before and after ion implantation, it is shown that the decrease in the roughness parameters doubled, which confirms the effectiveness of nitrogen ion implantation. The SEM images show that the uniformity of distribution of the particle sizes increases in nano scale after nitrogen implantation. In addition, it was found that the hardness of the zinc oxide structure was increased and the conductivity was decreased after nitrogen implanting.

In this paper a set of basis potential functions is introduced which could be used in expanding the MONDian potentials of razor-thin galactic disks. We modify Clutton-Brock basis potential functions in Milgrom’s formulation of Modified Newtonian Dynamics (MOND), for razor-thin galactic disks. Then, we use these new modified basis functions to expand modified potential functions of Kuzmin and exponential disks. We calculate expansion coefficients and Kouchi convergence to show that the MONDian potential functions expansions of these two sample disks, versus modified Clutton-Brock basis potential functions, with limited increase of expansion’s terms (up to 30 terms), converge to the exact values of their potentials. Therefore, Modified Clutton-Brock basis potential functions could be used as a set of basis functions for expansion of other MONDian potential functions of razor-thin galactic disks. These basis functions could also be applicable in simulations and codes which are used to study the dynamics of disk galaxies, especially in the methods like N-body simulations and particle mesh.

The prediction of fuel burnup of fuel assemblies in nuclear reactors is one of the most important issues in nuclear engineering and reactor physics. Currently, many researchers in different countries are working on improving fuel burnup in nuclear reactors and increasing their economic and safety indicators. The DRAGON4 code is a cell and fuel burnup calculation code which was developed at Montreal Polytechnic University of Canada. In this study, at first, the DRAGON4 code was verified for a fuel assembly of Bushehr nuclear power plant and then, the fuel burnup changes due to geometric changes in the mentioned fuel assembly have been investigated. Results of this simulation prove the validity of fuel rod pitch with consideration of safety and economy aspects in Bushehr nuclear power plant fuel assemblies.