نشریه پژوهش سیستم های بس ذره ای
سال دوازدهم شماره 2 (پیاپی 33، تابستان 1401)

The interaction of the electron-neutrino beam with the plasma in the universe is an important and appropriate process to obtain the amount of magnetic field in the plasma. In this study, the azimuthal magnetic field generated by electron-neutrino with orbital angular momentum is presented. Laguerre Gaussian neutrino transferring through a dense plasma could  produce a magnetic field. The origin of the magnetic field that existed at the beginning of the universe is unknown. This method is one of the candidates for magnetic field generation in the early universe. Using this interaction for supernova explosion produced good results. The azimuthal magnetic field is calculated up to 107 Gauss by this model.

In this study, using density functional theory and Boltzmann equation, the thermoelectric properties of perfect and porous phosphorene nanosheets are calculated and compared at different temperatures including 100, 200 and 300 K. The results show that the maximum seebeck coefficient at 300 ° K for porous nanosheet is about twice the corresponding amount of the perfect one. A good thermoelectric material should have a high electrical conductivity as well as a low thermal conductivity. Although the electrical conductivity of the perfect sample is higher than that of the porous one at all studied temperatures, the electronic contribution of the thermal conductivity related to porous phosphorene is less than the thermal conductivity of the perfect one. At all studied temperatures, the maximum figure of merit (ZT) in porous phoephorene, is higher than the ZT in the perfect nanosheet. The results of this study indicate that two-dimensional porous phosphorene is a promising material for thermoelectric applications and even demonstrates a better performance than the perfect 2D-phosphoren.

In this paper, using the non-equilibrium molecular dynamics (NEMD) simulation approach, and the effective medium approximation (EMA) method, we investigate the effect of graphene nanoscale filler, as an enhancer, on the effective thermal conductivity of polyethylene-based nanocomposites. Our results suggest that the thermal conductivity of polyethylene at room temperature was estimated to be nearly 0.21 W/m.K, through using the reactive bond order (AIREBO) interatomic potential. This study shows that by increasing the volume fraction of graphene nanofillers, the effective thermal conductivity of the nanocomposite increases. We also observed that by increasing the volume fraction of graphene from 1% to 3%, the normalized thermal conductivity of nanocomposite increases to nearly 55%..

This study investigates the effects of intense magnetic field on Equation of State (EOS) and bulk properties of neutron stars (NS). We have used a variational many-body approach to obtain the EOS of core of NS and various models are considered as basic EOS of crust of neutron stars. In this study, we focused on Landau levels of electrons. It is shown that by increasing the magnetic field, the pressure of NS is increased. Finally, the mass-radius relation of a neutron star is extracted by solving the hydrostatic equilibrium equations. It is shown that the magnetic field does not have a considerable effect on maximum mass which is obtained 2.3Mʘ by employing EOS in this study. Instead, by increasing the magnetic field inside the NS, the radius of star increases depending on the crust EOS.

In this paper, the structural, thermodynamic properties and phonon dispersion of thorium carbide are investigated through the density functional theory and the density-functional perturbation theory by using ab initio calculations within the framework of the plane-wave method. Ultrasoft pseudopotentials with GGA-PBE functional are utilized for the exchange and correlation potential. Thermodynamic properties of ThC are studied for the first time under the quasi-harmonic Debye-Gruneisen model as was implemented in the GIBBS2 code. Structural properties including lattice constant (a0), bulk modulus (B0) and the first derivative of the bulk modulus (B0') are calculated by fitting the third-order Birch-Murnaghan equation of state and compared to other theoretical and experimental works that revealed a good agreement. The phonon band structure is calculated from the density-functional perturbation theory for the lattice constant and investigated experimentally and the obtained phonon gap was about 185 cm-1. It was observed that the Debye temperature decreases with increasing the temperature at a constant pressure while it increases with increasing the pressure for all temperatures. The Vibrational Helmholtz free energy, the Gibbs free energy, the adiabatic bulk modulus, and the isothermal bulk modulus decreased with increasing the temperature at a given pressure.

We investigate Q^2 evolution of gluon distribution function in small-x region. In general, the evolution of parton distribution functions of hadrons is given by linear DGLAP evolution equations. In small-x region the gluon density increases. So in order to consider the effect of gluon recombination in this region, some corrections as nonlinear terms are added to DGLAP equations. This modified equation is known as GLR-MQ evolution equation. In this work, the GLR-MQ equation for gluon distribution of proton is solved and the obtained results compared with those of DGLAP evolution equation. We also calculate the first and second order Mellin moments of this distribution. The obtained results show important effect of nonlinear corrections on the evolution of gluon distribution function.