مجله پژوهش فیزیک ایران
سال بیست و یکم شماره 3 (پاییز 1400)

Two dark energy models $Lambda sim (frac{dot{a}}{a})^{2}$ and $Lambda sim frac{ddot{a}}{a}$ are studied by taking into account the gravitational constant G is a time-dependent parameter in the framework of Chern-Simons modified gravity. It is found that the gravitational constant shown the increasing behavior proportional to those of the time parameter for each model. These models are compared with observational results by regulating the values of the parameters. Our investigations indicated that the model $Lambda sim (frac{dot{a}}{a})^{2}$ is generally attractive in nature while the other model $Lambda sim frac{ddot{a}}{a}$ coincides to repulsive situation and consequently match with the current scenario of the accelerating universe. We calculated the variation of G(t) which showed that it changes rapidly when the value of $omega$ is taken between the limit $-1.33 <omega< -0.79 $. It is viewed that due to the composite influence of time-variable $Lambda$ and G(t), the universe expanded with acceleration. Further, it is estimated that  the range for variation of G(t) with  proper tuning of parameters $alpha$ and $beta$ is given as $-(1.89pm 0.10)times 10^{-11}yr^{-1}<frac{dot{G}}{G}<0$ which match with Ia type supernova.

This work aims to use an important method Galitskii-Migdal-Feynman (GMF) for ‎diatomic molecules 132Xe2, to calculate the effective phase shifts which are then used to ‎compute the effective total and viscosity cross sections at low density and temperature . ‎this study has shown that it’s crucial to include partial waves up to ‎ ‎; for ‎ ‎, the ‎effect of the potential becomes negligible .‎‎ Comparing with partial waves cross sections we deduce that the cross section is ‎dominated by S-wave scattering for low energy (wave number k < 0.1 Å-1), otherwise D ‎and G partial waves dominate . The highest peak rises from the partial effective D and G-‎wave resonance, where the system sustains a quasi-bound state trapped by the centrifugal barrier. The average cross section is also determined. ‎

For an external radiotherapy procedure, the tissue phantom ratio (TPR20,10) is used as a quality index. This work presents an estimate of TPR20,10 using two cylindrical ionization chambers (NE2571 Farmer and PTW30013) in three high-energy photon modes (6, 10 and 15 MV) using both the Monte Carlo (MCNP) process and the experimental setup. The MCNP (version MCNP5) was used for the simulation of photon beams delivered by Varian-2300CD for the determination of TPR20,10 according to technical report series (TRS) 398. Again applying the same protocol TPR20,10 values were measured experimentally with NE2571 Farmer and PTW30013 chambers for the same medical linear accelerator (LINAC). The differences of TPR20, 10 between MCNP and experimental values were found for NE2571 Farmer chamber within 4.17 percent, 2.9 percent and 2.5 percent and similarly, these were within 3.89 percent, 2.71 percent and 1.98 percent at 6, 10 and 15 MV respectively for PTW30013. The TPR20,10 values simulated by our calculated MCNP demonstrated strong agreement with our experimental results.

Calculations of the α-decay half-lives ofPt isotopes have been carried outusing the modified Gamow-like model (MGLM) and deformed Woods-Saxon potentialmodel. In order to see the effect of using deformed nuclear potential on the α-decay half-lives of the Platinum isotopes, the spherical Woods-Saxon potential has also beenemployed in the computation. When compared with experimental data, all the modelsgive very good descriptions of the experimental half-lives. The comparison also suggeststhat the calculated half-lives considering deformation give better agreement with theexperimental data than the results using spherical configuration. New parameter valueswere obtained for the MGLM model (termed MGLM2). The MGLM2 model gives betterdescriptions of the half-lives than the MGLM1 model.

High energy cosmic rays hitting the earth atmosphere induce extensive air showers propagating downward with a high gamma factor. Determining the core location of such air shower is a necessary step to measure other important characteristics of a cosmic ray such as the lateral distribution function. In this study and based on computer simulations and radio signal analyses we investigate the relation between normalized radio signal phase angle emitted from particles in an air shower to the position of a shower core. We perform a series of simulations based on CORSIKA and COREAS code for cosmic rays with different types of primary particles with an energy range from 0.1 to 1 EeV. The results show a direct relationship between the average slope of normalized radio signal phase angle as a function of frequency to the absolute distance from extensive air shower core location. We have calculated the normalized radio signal phase angle to have the absolute minimum value at close distances to a shower core location. We discuss a possible approach to estimate core location with different types of virtual radio arrays.

In this study, we report the synthesis and characterization of YBa2Cu3O7-δ (YBCO) high temperature superconductor prepared by solid state method and doped with Nb in different weight percentages, 0, 0.01, 0.02 and 0.05 wt%. The x-ray diffraction (XRD) analysis confirms the formation of orthorhombic phase of superconductivity for all the prepared samples. We evaluated the effects of Nb doping on the normal state resistivity (ρ), superconducting transition temperature (Tc), scanning electron microscope (SEM. The critical current densities, JC as a function of temperature have been calculated using the critical state model from the hysteresis loops up to 1T at temperature range of 10K to 60K. Magnetic flux pinning, FP of samples was calculated by using Lorentz force. XRD analysis show a shorter c axis parameter and higher orthoromthcity than the pure Y-123 and other Nb doped samples. It was also found from critical current density and magnetic flux pinning force measurement the 0.01 wt% Nb substation for Y on YBCO superconductors improve the critical current density and flux pinning force.

We have investigated the effect of Niobium and Nano CuO (40 nm) dopingY1-xNbxBa2Cu3O7-∂ compounds with 0.00 ≤ x ≤ 0.05 wt. %, prepared by the conventional solid-state method by means of XRD, SEM, R(T) and magnetic loops (M-H) measurements. The critical current densities, Jc as a function of temperature have been calculated using the critical state model from the hysteresis loops up to 1 kG at the temperature range of 10-60 K. Magnetic flux pinning, Fp of samples was calculated by using Lorentz force. The temperature dependence of the electrical resistivity measurement curves indicated that the sample with x=0.01 wt.% has a high transition temperature, Tc. XRD analysis shows a shorter c axis lattice parameter and higher orthoromthcity than the pure Y-123 and other Nb-doped samples. It was also found from Jc and Fp measurement, that the 0.01 wt.% Nb substation for the Y on YBCO superconductor improves the Jc and Fp.

Solar acoustic oscillations are actually the same 5 minute oscillations that appear in the photosphere. These oscillations appear to be unable to penetrate into the solar corona due to the acoustic cut off of stratified atmosphere and the sharp temperature gradient in the transition region. The 5 minute acoustic oscillations may resonantly convert into Alfven waves in the region of the solar atmosphere. By perturbing the equilibrium state of the magnetised plasma, we showed that the acoustic and Alfven waves can interact through the nonlinear terms of the ideal MHD equations. We found that Alfven waves with twice the period of acoustic waves may propagate to upper layers when the speeds of sound and Alfven waves are equal, . This condition is obtained when, .

ZnS film has been deposited on PbS buffer layer using thermal evaporation, the ZnS film has nanostructure (nanowires) due to effect of PbS which play role of catalyst. This growth for non doped films have dense structure (for PbS and ZnS films). SEM morphology of ZnS/PbS, ZnS and PbS have been studied in details (surface and cross section). Atomic force microscopy (AFM) used to characterized the thins films (ZnS and PbS). X-ray photoelectron spectroscopy (XPS) and EDX techniques have utilized to know the chemical and stoichiometry of deposited films. The crystallographic properties have been studied using XRD patterns, it found that the results in Raman and XRD characterization have a good agreement. UV-Vis spectroscopy is used to acquire an idea about optical properties of thin films deposited on glass substrate. The deposited ZnS nanowires and thin film have hexagonal phase, which indicate to the buffer layer, which does not affects the structural but changes the growth mechanism. High Resolution Transmission Electron Microscope (HRTEM) images have confirmed the formation of ZnS nanowires.

A new type of symmetry in the large deviation function of a time-integrated current is introduced. This current is different from the fluctuating entropy production for which the large deviation function is symmetric in the content of the fluctuation theorem. The origin of this symmetry, similar to that of the Gallavotti-Cohen-Evans-Morriss symmetry, is related to time-reversal. The symmetry is more unveiled when one performs an appropriate grouping of stochastic trajectories in the space of microscopic configurations. It turns out that the characteristic polynomial of the modified generator of this current is not symmetric; however, its minimum eigenvalue is symmetric.

Zinc chalcogenide quantum dots (QDs) doped with paramagnetic transition metal ions (particularly ZnS:Mn QDs) are new attractive but rarely examined semiconductor nanocrystals that have excellent optical properties and enhanced thermal and environmental stability compared to Cd-based QDs. In this paper, we demonstrate a dye-based random laser (RL) with nonresonant feedback using ZnS:Mn QDs as the scattering medium that are dispersed in a Rhodamine B (RhB) dye solution. The nonlinear variation of the emission spectrum as a function of the excitation energy implies a random lasing threshold. Moreover, we observe a blue-shift of the emission wavelength by 10.3 nm and a 5.3 times decrease in the RL threshold by increasing the scatterer concentration. We also provide a theoretical discussion based on the diffusion theory for explaining the observed experimental results.

Reactivity worth of control rods as a main parameter in different nuclear reactor fields such as safety, design, and operation that could be calculated or measured with different experimental and theoretical methods. Reliable answers in calculations necessitate taking into account different characteristics such as geometries, materials, temperatures, spatial nodes, libraries, and energy groups. Reactivity worth of different core states of a Material Testing Reactor (MTR) is calculated using MCNPX 2.6.0 code and MTR_PC package as Monte Carlo and deterministic approaches respectively. It is seen that the MTR_PC and MCNPX results has considerable differences up to 51%. Therefore, an exhaustive study is done concentrating on different involved parameters. Precise modification of inputs, applying one common library in the two approaches, correcting spatial nodes, and employing more energy groups in the deterministic approach are performed. It is determined that the effect of the spatial nodes is much more important than the other parameters in the deterministic method. Finally, results of two approaches are found to be satisfactory as discrepancy is less than 11%.

The absorption performance and evolution of the organic dye disperse blue 1 (DB1) in dioxane at different concentrations was investigated. The nonlinear absorption coefficient has been measured through the open aperture Z-scan technique, whose values increased exponentially from 0.997×10-3 to 11.7×10-3 cm/W as the dye concentration increased from 3.7×10-5 to 74.6×10-5 M. Also, DB1 optical power limiting characteristics appeared at high laser light intensities, whereby very dilute solution of the order of ~10-4 M was sufficient to limit the transmitted ‎power of the incident laser light by ~90%.

Nuclear Reaction Analysis (NRA) is employed to perform depth profiling of the light elements (carbon, nitrogen, oxygen …) in the heavy element substrates. To conduct the analysis, the availability and reliability of the respective differential cross-sections are among crucial factors to achieve the reliable results. In this work, we made a theoretical attempt to calculate the angular distribution of the transfer reaction (stripping reaction) 16O(d,p0)17O reaction at 1.3 and 1.6 MeV energies in the lab frame, which are usable in NRA. Moreover, the optical potential parameters, which are obtained through the work, can be utilized by the global optical potentials.

On one hand a two-level atom is utilized as a qubit in quantum information technology and on the other hand the light in quantum optics is usually in the squeezed state. These reasons motivated us to explore the dynamic of a two-level atom which is driven by a field in the squeezed state. To this goal, the atom operators and the Heisenberg-Langevin equation have been employed. The master equation which reveals the dynamic of the atom has been derived using some features of the squeezed state and doing some algebra. Finally, the dynamic of the two-level atom which is driven by squeezed state field has been simulated by the derived master equation. Also, the effect of atom parameters on the dynamic has been investigated.

Short and intense laser pulses in laser-plasma interaction stimulate various local structures like solitary waves in the plasma. Relative salitons should be given special attention because the amplitude of the electromagnetic field is intense enough to set plasma electrons in relativistic motions. In the interaction of intense laser with plasma, collisions can play an important role in the physical phenomena. In this paper, the effect of the collision on the emission of solitons is investigated by considering the interaction of an intense laser with plasma. Then, the NLS equation is numerically solved and the different results are compared with each other. Also, the stability conditions of individual waves and the effect of the collision on these waves are investigated.

In this research, we investigate the electron transport in fullerene and fullerane nanocages. We study the electron transport of these systems based on the tight-binding model with the approximation of the nearest neighbors and the formulation of the Green’s function. In this research, we consider the type of electrodes attached to molecules as cumulene carbon chains, and investigate the effect of the position of the electrodes on the electron conductance of the mentioned nanocages. We obtain the structural properties of the molecules with the help of density functional theory, and the use of the B3LYP hybrid function. We study the electrical conductance of these systems by forming molecular bridges between two cumulene electrodes. To do this, we first obtain the stable states of the connection of the electrodes to the desired systems using the density functional theory. Our results show that by changing the position of the connection of the electrodes to the fullerene cage, the electrical properties of these systems can be controlled to observe the phase transition between semiconducting and metal behavior. Also, due to the localization phenomenon, fulleranes are always insulator.

Consider an open quantum system S , interacting with its environment E. Whether the reduced dynamics of the system can be given by a linear map, or not, is an important subject, in the theory of open quantum systems. Dominy, Shabani and Lidar have proposed a general framework for linear Hermitian reduced dynamics. They have considered the case that both the system and the environment are finite dimensional. Their framework can be generalized to include the case that the environment is infinite dimensional too. In this paper, after demonstrating this generalization, we discuss the role of the convexity of the set, of possible initial states of the system-environment, in their framework. Next, we give a proof for the existence of the operator sum representation, for arbitrary linear Hermitian map. This proof enables us to prove the Choi-Jamiołkowski and the Jamiołkowski isomorphisms, straightforwardly.

In this paper, we consider the analysis of the one-loop effective action for the gluons coupled to the quarks in (1+2)-dimensional spacetime. By integrating out the quark fields, we compute the one-loop Feynman graphs of the one, two, three and four-point functions for the gluon. It is explicitly shown that the resulting effective action leads to the non-Abelian Chern-Simons and pure Yang-Mills action at the low-energy limit.

Interest in slot scanning imaging system has been increased recently because of its advantages such as high image resolution, reduction in patient dose and reduction in image distortion. The purpose of this study is to simulate a slot scanning imaging system using GATE multi-purpose Monte Carlo code and design an object phantom to evaluate image quality. The energy spectrum of X-ray in the radiological diagnostic range was simulated by GATE Monte Carlo code. An object phantom consisting of stripes with different thicknesses of copper was then designed to determine CNR and line pairs per millimeter to determine spatial resolution.The results showed that the simulated energy spectrum were in accordance with experiment. The evaluated parameters of image quality obtained from the simulations were compared with X-ray images using standard image quality criteria to determine the capabilities of the slot scanning imaging method. The spatial resolution of the simulated images was obtained to be 1.6 lp / mm for the slot scanning method, which is in the range of clinical radiology images. Therefore, this simulated model can be used to investigate and optimize other influential parameters such as filtration effect and collimator slit width effect, object distance to the detector ... in slot scanning imaging system.

AbstractThe violation of Bell’s inequality in quantum mechanics implies that there exist nonlocality and entanglement. When the density matrix of a composite system cannot be written as a convex combination of the product of the density matrices of its subsystems, we say there exists entanglement. For pure states, the existence of entanglement always leads to the violation of Bell’s inequality. However, in the case of the mixed states, there may be entanglement, but Bell's inequality is not violated and in other words, the nonlocality is not manifested. In addition to Bell's inequality, quantum teleportation is also a manifestation of nonlocality. Quantum teleportation using entangled states is more successful than quantum teleportation with separable states. Therefore, the corresponding fidelity of teleported state with the initial state (in short, the fidelity) of the former is always greater than the fidelity of the latter. In this paper, for Werner's state, we will show that in a range of the related parameter, while the CHSH inequality is violated, the fidelity, which indicates the amount of success of quantum teleportation, is lower than the upper bound of the corresponding fidelity for states that can be simulated with a local hidden variable theory. Meanwhile, we will see that for Gisin's state with hidden nonlocality, filtering, which leads to the appearance of nonlocality and more specifically leads to the violation of the CHSH inequality, also increases the fidelity.

In this paper, we introduce a percolation model consisting of random walk movements on a lattice. Random walk not only has local movements, but also has non-local movements on the lattice. We obtain the percolation transitions and critical exponents for this model. Our findings show that the percolation threshold decreases with increasing non-local movements. Also, we find the universal scaling functions for the size of the largest gap and biggest cluster by the extreme value theory.

Interaction between two diseases can be as competition and cooperation. In this work, we study these interactions for two diseases that spread simultaneously on a multiplex network. We assume that each disease spreads in one layer of the network with a different structure than the other layer. We consider an asymmetric case in which one disease propagates according to the SIR dynamics, and another one follows the dynamics of the SIS model. By using the heterogeneous mean-field theory, we find the epidemic threshold of each disease in the case of cooperation and competition. We also obtain the phase diagram of the model that contains information about the prevalence of diseases.

In this paper, using molecular dynamics simulation, the wettability dependence of a graphite surface consisting of two layers of graphene on temperature is studied for three water models. For each given temperature, the wettability of the graphite surface is determined by estimating the contact angle of the macroscopic droplet using extrapolation method in terms of inverse radius for water nanodroplets. Although the used models show little wettability at room temperature, the result of our simulations suggests a wetting transition event for all three models studied at temperatures lower than their critical temperature. The observed trend for the dependence of the contact angle on temperature and the approximate value of the transition temperature is comparable to the experimental results recently reported for graphite. Fitting the curves to a proposed model shows that the wetting transition event is first order for all three models.

Bismuth based high Tc superconductors are among the materials that have been extensively appreciated in terms of their application. Since this type of superconductors are very sensitive with respect to synthesis process, here, we consider effect of synthesis process on the electrical, magnetic and superconducting properties of Pb-BSCCO compound. The samples were prepared by both solid state and sol-gel reaction. In both of the preparation routes, two different methods of Cold Press (CP) and Spark Plasma Sintering (SPS) were used to compress the samples after, the completion of their calcination and grinding. In the next step, the samples put through the thermal process of sintering with different temperatures with respect to their preparation method. The results of the measurements indicate better superconducting properties in sol-gel method compare to the solid-state method. Also, it indicates better superconducting properties in Cold Press samples with respect to the samples prepared by SPS method. To compare the sintering temperature indicates that 825 and 830 oC are suitable temperature for sol-gel and solid-state samples, respectively, in Cold Press process.