JOURNAL OF RESEARCH ON MANY BODY SYSTEMS
Year:2018 | Volume:8 | Issue:16 |Papers Count:15

2-dimensional layers of transition metal dichalcogenids (TMDCs) with direct band gap in the visible and infrared range have shown open horizon in photonics and optoelectronics. Among TMDC family, MoSe2, WSe2, MoS2 and WS2 monolayers have shown special optical properties. In this paper, the permittivity constant of aforementioned monolayers are calculated based on Lorentz, Lorentz- Gauss and Lorentz –Drude-Gauss models with quite acceptable consistency to their experimental values. Optical absorption response of these photovoltaic monolayers is similar to imaginary component of their permittivity. In addition, based on investigation of optical absorption in presence of substrates, it is found that the absorption decreases which is more pronounced while refractive index of substrates increases. Such thin layers with absorption efficiency above 10% with thickness below 1 nm are suitable candidates for solar cell and photovoltaic applications.

Two dimensional Molybdenum disulfide, MoS2, crystal has attracted intense attention for its application in the THz optoelectronics and can be used for transparent electrode in the nanoscale research area. In this paper, we design structures including MoS2 monolayer on different substrates and different layer positions in one-dimensional photonic crystals (1DPCs) toward decreasing the optical absorption and increasing the optical transmission. The THz refractive index of MoS2 taken from Drude model is calculated. Transmission and absorption spectra in the THz range for either of TE or TM modes is calculated based on the transfer matrix method (TMM). In continue we show that the absorption spectrum can be tuned by changing different materials and incident angles for either of TE or TM modes. We finally in our best design achieved absorption smaller than MoS2 monolayer and nearly 100% transmission. Such results are useful for application in nano-bulding blocks including transparent electrode in future photonics and electronics devices.

In this article, the electronic and optical properties of graphene with BC3 substrate are investigated. The calculations are performed on the basis of full potential linearized augmented plane waves in the framework of density functional theory. The total energy calculations of AA and AB configurations show that the AB stacking configuration is more stable than AA stacking configuration. The monolayer graphene has zero band gap while graphene with BC3 substrate has a small band gap of 0.15 eV at K point. The intrinsic properties of graphene such as linear dispersion of electronic bands near the K point and high carrier mobility are retained in the graphene with BC3 substrate. The dielectric function of graphene with BC3 substrate can be considered as the superposition of dielectric function of graphene and BC3 monolayer where the interaction between graphene and monolayer BC3 leads to the shift of peak positions. These results can be used in designing new opto-electronic devices such as field effect transistors.

One of the non-destructive methods in evaluating the characteristics of irradiated fuels in any reactor is the gamma radiation spectroscopy. A qualitative and quantitative analysis of the spectrum of an irradiated fuel and the estimation of some fissile products as a fuel burnup and the power peaking factor monitors in a fuel assembly is necessary. On the other hand, some experimental constraints, including the resolution of the detector energy, prevent the detection of some fission products and hide certain information in the spectrum. Therefore, in this study, the content of fissile fragments of Tehran Research Reactor fuel at different cooling times (3, 30, 120, 360 and 720 days) was evaluated with the ORIGEN2.1 computational code and the spectrum of fission products by Monte Carlo code MCNPX2.7 have been simulated. Then fission products that can be considered as a good monitors of fuel burnup have been analyzed.

Based on the Monte Carlo simulation and the RKKY model, magnetic properties of mixed spin (3.2,1,1.2) ferrimagnetic ternary alloys of the type ABxC1-x are investigated. To do this, the influence of exchange energy and single ion-anisotropy on the magnetic hysteresis loop and magnetic susceptibility of ternary alloys with amorphous structures are examined. Our simulations reveal that the changes in exchange energy and single ion-anisotropy have a great influence on the magnetic hysteresis loop. It is seen that for some values of these parameters the stepwise curves and the triple hysteresis loop are appeared. Furthermore, the influence of concentration on the behaviour of thermal magnetization is studied. Our results indicate that for some values of concentration, the compensation temperature becomes less than the phase temperature.

In this paper we give an introduction to the ideas of quantum thermodynamics, using only basic concepts from quantum and statistical mechanics. Then, we discuss the framework of non-equilibrium processes in quantum systems and introduce how to calculate quantities such as work and irreversible entropy in these processes. We then apply these results to the problem of atom-cavity system while their interaction describe by Jaynes-Cummings model with both weak and strong atom-cavity coupling. Here, we introduce the concept of quantum thermodynamics of close quantum system and so by considering a good cavity, coupling of cavity modes with its reservoir has been omitted.

The radial profile of potential structure and neutron production rate in spherical inertial electrostatic confinement fusion devices (IECF) using deuterium fuel is investigated. With the introduction of ion and electron distribution functions and numerical solution of Poisson's equation, the potential is determined. Using energy distribution function, calculated fusion reaction rate. The dependence of the potential structure and rate of neutron production on some important parameters as the spreads in the energy and angular momentum, the number of secondary electrons generated from the cathode surface, input power and working pressure is evaluated And is shown with control some of the parameters and variables, can increase the rate of neutron production.

In this paper, we have studied some nonlinear Schrodinger equations appeared inmany body systems such as a nanowire with a soft polar layer, a quantum well in the presence of the electron-electron interactions, Grass-Pitaevskii equation for Bose-Einstein condensate in the presence on the two and three body interactions. Calculation of the ground state energy of these systems by analytical methods is very difficult. Solution of these equations through numerical methods like self-consistent one also needs complicated computer programming. In this paper, Ground state energy have been obtained by means of the Euler-Lagrange Variational method as well as simple and appropriate trial wave-functions.Comparison of the result we have obtained with the Varational technique and the available methods in the literatures shows the high accuracy of this method.

In this paper, we have investigated the transport properties of the Dirac fermions on a topological insulator surface in the presence of external electric and magnetic fields. For this reason, firstly we obtain the eigen energies (or eigenvalues) by using the Dirac Hamiltonian of the system for transmitted electrons via the surface and the Lorentz transformations. The conductance of the system is calculated by Landauer equation. Also, the effects of electric and magnetic fields are investigated on the conductance and Fano factor effect. The application of the present results may be useful in designing devices based on molecular electronics in nanoscale.

In cavity opto-mechanical cooling, driving laser optical field, exerts extra decay to the mechanical mode of cavity, and cause a return to the ground state. In this study, quantum cooling of an opto-mechanical cavity in contact with a thermal bath, has been simulated by using Quantum Toolbox in Python “QuTiP”. Simulation results show that, the cavity cooling process, takes more time with increasing the decay rate of optical modes and go faster with increasing the decay rate of mechanical modes. Also this process takes less time with the increasing coupling constant of optical and mechanical modes. By adding a qubit to the system, simulation shows that the cooling process could happen faster in compare to the previous.

Taking advantage of chemical potential (mc) one layer and multi layers graphene nano ribbons, we designed and analyzed performance of plasmonic switches at mid-IR wavelengths. By slight varying the chemical potential of graphene, significant resonance shifts (Dl) and modulation depth (MD) achieved. Finite element method numerical simulation show that plasmonic switch made of hexagonal boron nitride (hBN)/Graphene suffering relatively large MD and wavelength shifts with N=6, and varying mc from 0.3eV- 0.4eV, 14 dB and 2.8 µm, respectively. The proposed structure could be useful for research in compact and largely tunable mid-infrared photonic devices to realize on-chip CMOS optoelectronic systems.

In this work, the propagation of the electrostatic drift waves is studied in a non-uniform quantum plasma medium. The analytical expression for dispersion relation of the waves is derived by taking into account the resistivity and quantum aspects of the medium. It has been shown that the quantum effects, alter the dispersion relation of the drift modes. The result is the appearance of modified electron diamagnetic drift waves as well as ion acoustic waves. Furthermore, the velocities of these waves are greater than their classical case. The graphical analysis also revealed that the quantum corrections cause electron branch of the drift waves to become propagative. In the presence of resistivity, the electron drift wave is always unstable, whereas the ion branch of the drift wave becomes damped. On the other hand, in the absence of quantum aspects and given zero resistivity, the two generated ion acoustic and electron drift waves are completely stable.

In this work, the behavior of electromagnetic ion waves in a warm plasma considering the quantum forces related to the electron spin and the quantum diffraction effects of all plasma particles is investigated. The results show that the quantum correction associated with the quantum potential of ions and electrons has a significant effect on the dispersion of waves and introduces non-linear terms in the dispersion relation. We also find that the spin of electrons contributes to the linear part of the dispersion relation via modification of the Alfven velocity. Moreover, the spin effect of electron decreases the contribution of quantum potential on the dispersion of wave modes. Finally, some special cases in classical and quantum regimes are discussed.

Complex structure of human language enables us to exchange very complicated information. This communication system obeys some common nonlinear statistical regularities. We investigate four important statistical features of Persian language. We perform our calculations for adopted works of six famous Persian litterateurs. Zipf’s law and Heaps’ law, which imply well-known power-law behaviors, are established in this language, showing a qualitative inverse relation with each other. Furthermore, the informational content associated with the words ordering, is measured by using an entropic metric. This metric can be applied in words relevancy ranking process. We also calculate fractal dimension of words in the text by using box counting method. The fractal dimension of each word, that is a positive value less than or equal to one, exhibits its spatial distribution in the text. Generally, we can claim that the Persian language follows the mentioned statistical laws, like the other languages studied in previous works.

The recent data from observational Planck data about inflation indicate that our universe was nearly de Sitter space-time in the early times which results in an approximate scale-invariant spectrum. These observational data from scalar spectral index and curved space-time symmetry condition stimulate us to use quasi-de Sitter modes during inflation. To obtain the alternative modes, for first time, we consider the asymptotic expansion of the Hankel functions up to the higher order of 1⁄kτ . In this paper, we review the results due to selection of the generalized form of the asymptotic de Sitter inflationary modes, such as higher order corrections of power spectrum and particle creation, trans-Planckian corrections, equation of state, and non-minimal coupling inflation. These results are general and in flat and de Sitter limit confirm the conventional results. Finally, to reconstruction of the modes we fit the power spectrum of temperature anisotropies for model with ΛCDM model and Planck data.