نشریه پژوهش سیستم های بس ذره ای
سال دهم شماره 3 (پیاپی 26، پاییز 1399)

In the vicinity of the sun, studying of motions, velocities and features of local stars is a suitable way to cognition of dynamical features of galaxy stars, the source of galaxy disc and also the steps of star evolution. Using the results of big observatories and valid catalogs, many different researches has been done at this field. At present work, using the Hipparcos satellite data, a sample of stars in vicinity of the sun are studied and three parts of velocities of 493 stars which are located in 15 parsec from the sun such as transition velocity, radial velocity and their parallax are obtained. Also, local stars properties such as mass, their distribution in the galaxy, radius, temperature, galactic position and their relation with galactic velocities are investigated and finally the evolution of stars is predicted in the galaxy.

This study aims to investigate changes in radon concentrations in residuals areas, using a sample closed room with the surface area of 12 m2. In the room, radon gas emitted from the floor and walls surfaces with different emission rates, and gaps under the door and around the window were the natural ventilation routes. Radon concentrations were measured in different points of the room in different circumstances and times using an accurate radon detector and then compared with the simulation results from Computational Fluid Dynamics (CFD) technique under corresponding conditions and times. The analytical data were used to validate the results of these two techniques. The results indicate that the radon concentration decreases from a relatively uniform distribution of about 81 Bq/m3 to a relative non-uniform distribution in the range from 12 Bq/m3 to 44 Bq/m3 after a very slow natural ventilation. The simulation results demonstrate an appropriate agreement with the experimental data that indicate the accuracy of performed modeling.

Charge carriers in transition metal dichalcogenides have the charge, spin and valley degrees of freedom. In this paper, we investigate the electron transport properties through the WSe2 junctions sandwiched between normal silicene sheets in the presence of Zeeman spin ( Ms ), valley ( Mv ) exchange fields and an electric potential U. We have evaluated the spin and valley polarization and conduction using the Landauer-buttiker scattering formula. Our findings show that the conductivity of normal monolayer silicene with intrinsic band gap in the presence of tungsten-diselneed barrier can be controlled by adjusting the Zeeman spin and valley fields. Spin and valley polarization is reported to be about 80%. Another result is that the valley switching can occur with adjusting the intensity of the spin and valley fields. We also show that increasing the length of the middle region, on account of the Klein tunneling phenomenon, cannot prevent passage of charge carriers and we have an oscillating current even for large length of the barrier region.

In this work, using the tight-binding approximation and kinetic coefficient matrix, the electrical and thermoelectric properties of four different configurations of single/bilayer graphene junctions with armchair and zigzag edges are studied. These electrical transport properties include the electrical conductivity coefficients (G), thermal conductivity (κ_e), thermoelectric power (S) and figure of merit (ZTe), which are suitable for designing thermoelectronic devices. The numerical results show that the system can exhibit a metallic or semiconductive behavior with a special edge under different geometric conditions. This makes it possible to exhibit that the thermoelectric power and thermoelectric performance of a relatively large size under particular conditions. Also, the role of carriers (electron or hole) is clearly demonstrated in terms of electrical and thermoelectric properties. The results may be useful in designing nanoelectronic devices based on two-dimensional layers.

In the present work we study the process of gravitational collapse of a homogeneous dust in the framework of generalized Rastall gravity. In this theory, the Rastall coupling parameter is a variable and since this parameter represents the measure of mutual interaction between matter and geometry it is expected that such an interaction affects the collapse dynamics and its end product. Motivated by this idea, we search for non-singular solutions for the interior spacetime of the collapsing dust fluid. We observe that this scenario is feasible for a suitable choice of the functionality of the coupling parameter such that the singularity present in homogeneous dust collapse is replaced by a non-singular bounce where the energy density and spacetime curvature are finite. We also observe that such a variable coupling affects the dynamics of apparent horizon so that, in comparison to the singular case where the apparent horizon covers the spacetime singularity, the apparent horizon can be delayed or failed to form providing thus the possibility of detecting the bouncing object by external observers.

In this paper, we study the cosmic evolution of the holographic dark energy (HDE) model with the Hubble radius as the IR cut-off in the Rastall theory and study its dynamical behavior by two different approaches. In the first approach, we consider the vacuum energy as a candidate for dark energy, HDE, by using Cohen formulation. In the second approach we assume DE as a combination of the Rastall term and vacuum energy. We calculate the cosmological parameters, such as: equation of state, deceleration and the dimensionless density parameters of the models in both non-interacting and interacting cases for both approaches. Our studies show that, in the first approach HDE model in Rastall gravity can explain the current accelerated Universe even without interaction between two dark sectors. But the dimensionless density parameter model becomes a constant. Therefore we introduce the second approach that its dimensionless density parameter is dynamic and its evolution behavior is in agreement with the recent observational data. We have also find that in this model the Universe has a transition from the decelerated phase to accelerated phase at the redshift which is in the agreement with the cosmological observation. Also, we investigate the classical stability of

Nonlinear propagation and energy of dust ion acoustic waves in magnetized dusty plasma with Fermi-Dirac distributed inertia less electrons and positrons, cold classical ions and negative dust grains which are affected by dust charge variations, are studied using the quantum hydrodynamic theory. The Zakharov-Kuznetsov (ZK) equation is derived by employing the reductive perturbation technique which governs the dynamics of small-amplitude solitary waves in magnetized dusty plasma. The properties of the energy and solitary wave structures are analyzed numerically with the system parameters .To show these we study the behavior of dust ion acoustic wave as well as its energy for several values of the electron cyclotron to electron plasma frequency ratio ( ), dust concentration (d), non dimensional quantum parameter (H) and the direction cosine of the wave propagation vector with the Cartesian coordinates (l), keeping the other plasma parameters fixed. The results of the present research can be useful for future investigations of astrophysical dusty plasma.

Studying scalar field around black holes in the context of the no-hair theorem is an important and interesting subject. We investigate no scalar hair theorem for an asymptotically flat horizon-less neutral compact reflecting star. A reflecting star is an object with a reflecting boundary (instead of the absorbing event horizon) on which the scalar field or its derivative are zero . We consider a non-minimal kinetic coupling model such that in the kinetic part, the scalar field is non-minimally coupled to the Einstein tensor. We show that in contrast to the black hole cases, there is no non-trivial hair in this problem.

In this paper, after addressing various future singularities, predicted for Cosmos, an introductory note on Rastall theory is provided. Thereinafter, considering a flat Universe, the Friedmann equations of Rastall theory are derived, and the possibility of obtaining various singularities are studied in two cases. In the first case, the cosmic fluid is an isotropic and homogenous fluid while the ratio of its pressure and density is constant. In the second case, the mentioned ratio is not always constant and Universe evolves with a specified rate. The study claims that whereas it is not predicted any future singularity for the first model of cosmos, some types of future singularities may be inevitable in the second one.

Multipactor(MP) is an unwanted phenomenon which is occurred in the radio frequency vacuum devices. Research to find a convenient method to lower the MP threshold or move it away from the operational range is an important key in the design of microwave components. In this regard, the accuracy of predicting the MP threshold is essential. In the simulation of MP, the secondary electron yield model is typically built in the commercial code; CST code. The accuracy of the results of MP simulation is mainly determined by the variation of secondary electron yield model. Therefore, in this paper, we calculate the effect of the variation of the secondary electron yield on the results of the MP simulation. For this purpose, the generalized polynomial chaos method is employed using Python programming. This method is based on an orthogonal polynomial expansion. Here, MP in the rectangular waveguide, Cornell Electron Storage Ring input coupler, is studied.

In this study, using the passive spectroscopic method, a two-channel visible light channel Ava-Spec-ULS3648TEC-2-RS-USB2, high-emission spectral line set, to detect the presence of carbon, nitrogen, Oxygen, iron, chromium and tungsten have been identified in the IR-T1 tokamak plasma. Spectroscopic operations were performed during the period of electrical discharge inside the tokamak plasma. After performing the fitting and normalization, the effective width (FWHM) is calculated for each spectral line. Using Doppler broadening profiles and instrument, the hydrogen temperature is obtained at 4.4 eV, which is comparable to the results of COMPASS and ISTTOK tokamak. By calculating the Doppler broadening profiles and instrument, and using the information from the spectral lines, the ionic impurity temperature at the edge of the IR-T1 tokamak plasma is estimated at about 2.3 eV and at the core at about 40eV. Then, the effect of variation of biasing voltage on the FWHM of hydrogen (Hβ) - Stark broadening - and the effect of variation of magnetic field on the FWHM of iron ion (Fe I) - Zeeman broadband- are investigated. The results show the dependence of the radiation intensity and the temperature of the hydrogen on the biasing voltage.

In this paper, we study a family of dynamical wormhole solutions in an inhomogeneous spherically symmetric space time by considering a specific radial dependent redshift function . Using a generalized Friedmann-Robertson-Walker spacetime, we derive analytical evolving wormhole geometries by assuming a particular equation of state for energy density and pressure profiles. We calculate these classes of solutions for zero separation constant and their scale factor. The rate of expansion of these evolving wormholes is determined only by the standard Friedmann equation in cosmology . We introduce exact asymptotically flat solutions that respect energy conditions at throat. Finally, we investigate the weak energy condition for these solutions with detail