مجله پژوهش فیزیک ایران
سال بیست و دوم شماره 2 (تابستان 1401)

SmFeAsO0.7F0.3 polycrystalline bulk iron-based compound were prepared by one-step solid state reaction method at low sinter temperature. The aim was: to find the optimum preparing method for the compound and then to study its structural properties. The X-ray diffraction spectrum of the samples was analyzed using MAUD software. XRD measurements were used to characterize the crystal structure, phase purity, lattice parameters, ‎unit cell volume and bonding angles and intervals of the samples. The results were compared with JCPDS reference pattern and the reports in the literatures, to ensure the accuracy of the synthesis. The XRD analyses revealed an increase in the phase purity above 80%, by lowering the sinter temperature down to 900 ºC. Also, the samples have a tetragonal crystal structure with P4/nmm symmetry, at room temperature. The SEM images show the samples are almost homogeneous with some porosity. The porosity decrease and the grain size grow by decreasing the sinter temperature. These results show the preparation of good quality samples at low temperature of 900 ºC compared to 1200 ºC which usually is used for preparation of this family of compound.

In this work, we present the thermoelectric properties of a novel two-dimensional (2D) B2CO monolayer obtained using first principles calculations. We investigated the electronic band structure and density of states based on density functional theory and using the QUANTUM ESPRESSO computational package. Thermoelectric properties were calculated using the semiclassical Boltzmann transport equation in relaxation time approximation and within Boltztrap computational package. These electrical transport properties include the electrical conductivity coefficients (sigma), thermal conductivity (κe), the Seebeck coefficient (S) and dimensionless figure of merit (ZT), which are suitable for designing thermoelectric devices. According to our results, two-dimensional (2D) B2CO monolayer indicates an indirect band gap semiconductor with value of 1.68 eV. The numerical results show almost isotropic transport properties for the 2D B2CO monolayer. In particular, the thermoelectric study shows a good thermoelectric performance of the 2D B2CO monolayer with high figure of merit, so that, the nanostructure of B2CO is an n-type semiconductor and Seebeck coefficient and figure of merit at room temperature were obtained as -2595 µV/K and 1, respectively.

On an atomistic scale, free energy calculations are important for our understanding of biological processes, which provides an insight to grasp the various mechanisms. Over the years, many computational methods have been developed to calculate free energy differences such as geometrical (e.g. umbrella sampling) and alchemical methods. In this work, we present alchemical-free energy methods, thermodynamic integration (TI) and free energy perturbation (FEP), to investigate polarization effect of paclitaxel drug. Then, we have compared our simulation studies using TI, FEP, and Hamiltonian replica exchange FEP from the perspective of computational cost and accuracy.

Recently, we generated the evolution equations of the parton distribution functions (PDF) usually used in the hadrons phenomenology using the stochastic modeling of the non-equilibrium statistical mechanics in the momentum space. The evolution equations obtained from stochastic modeling are the same as the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equations, but are obtained by a more simplistic mathematical procedure based on the non-equilibrium statistical mechanics and the theory of Markov processes. In this paper, we analytically solve the parton evolution equation for the non-singlet quark distribution function in the small-x (the longitudinal momentum fraction) region through the Kramers-Moyal expansion of the master equation. Finally, we compare the cutoff dependent non-singlet quark distribution function obtained from the analytical solution by considering the strong ordering and the angular ordering constraints with the ordinary non-singlet quark distribution function produced by the MMHT2014 group. In general, we show that our results at the small x and moderate Q2 (the energy scale) are in good agreement with the results of the MMHT2014 group.

Considering the position-dependent effective mass in the study of quantum mechanical systems, a wide range of solvable potentials has been obtained. These potentials are obtained by applying canonical transformations to the Schrödinger equation. In this method, the internal functions introduced by Levai for solvable potentials with constant mass have been used, and the eigenfunctions and eigenvalues have been fully obtained. The eigenfunction of these solvable potentials can be obtained based on specific known functions (Jacobian, generalized Laguerre, and Hermit polynomials). Some of these potentials are Scarf-II, Pöschl-Teller, Rosen-Mörse-II and Eckart, whose applications have been described in physical systems. Finally, all the results are placed in a table and the figures of the desired functions is drawn for specific values

In the present study, the potassium chloride-assisted solution combustion method was used to synthesize cobalt ferrite nanoparticles. Potassium chloride salt was used as a specific surface enhancer and nitric acid was used as an auxiliary oxidizer and pH regulator. The simultaneous effect of the initial pH of the solution and the amount of added potassium chloride salt on the specific surface area, structural, microstructural and magnetic properties of synthetic powders were studied. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR), Vibrating Sample Magnetometer (VSM) at room temperature and Brunnauer–Emmet–Teller (BET) method were used for those purposes. The results showed that the initial pH and the amount of potassium chloride salt had an interaction effect on the specific surface area of cobalt ferrite powders. Under optimal conditions, cobalt ferrite powders with high specific surface area of 87.77 m2g-1 were successfully synthesized. Synthetic powders had mesoporous microstructure and hard magnetic behavior.

Machine learning, as one of the most powerful tools, has provided an unprecedented perspective on the study of classifying different phases and phase transitions between them in condensed matter physics. Here, we employed unsupervised machine learning algorithms to investigate magnetic ground states for systems of spontaneous symmetry breaking below the Curie temperature. In this study, we investigate the classical phase diagram of the Heisenberg model on square and honeycomb lattices using the deep machine learning algorithm. In the classical treatment, our findings show a good agreement with the classical phase of the Heisenberg model obtained by means of other conventional methods.

BiVO4 thin films with thickness of ~ 1.3 μm were deposited on ITO substrate via pulsed-spray pyrolysis deposition. X-ray diffraction pattern revealed that BiVO4 layers have been crystallized in tetragonal scheelite phase with average crystallite size of ~ 16 nm. According to UV-visible absorption spectra, a band gap energy of ~2.47 eV was determined for the synthesized layers. Scanning electron microscopy observations indicated that a porous BiVO4 structure with average pore diameter of ~ 162 nm and worm-like fine particle diameter of ~ 208 nm has been synthesized. Oxygen vacancies have been induced into the layers via an electrochemical reduction treatment (ET). This employed process increased the surface-related capacitance by about 6 times. A double charge transport resistance and half capacitance for Helmholtz layer was determined after ET, indicating electron transfer from space charge layer to Helmholtz layer upon ET. Using electrochemical impedance spectroscopy, it was found that effective charge carrier life time inside the BiVO4 thin films increased to ~25 ms which is 2-fold longer than the time before electrochemical reduction treatment.

In this paper, two structures of surface plasmon resonance fiber optic biosensors with the addition of a thin layer of titanium dioxide and barium titanate are introduced and studied comparatively. The sensitivity of these biosensors has been calculated using the transfer matrix method. Adding a thin layer of barium titanate and titanium dioxide after the gold layer, both make increase the sensitivity of the biosensor due to the transfer of free charge between the gold and the dielectric. The obtained results of the comparative study show that the titanium dioxide layer can be a suitable alternative to barium titanate for further increase of the sensitivity of the fiber optic surface plasmon resonance biosensor.

Filamentation instability is an electromagnetic wave that grows normal to the proton-driven direction in fast ignition scenario that can reduce beam quality or dissipate it due to pinching force before this beam reaches the dense core. On the other hand, producing an isotropic pre-compressed fuel is almost impossible in this process. Therefore, Weibel instability may cumulate with filamentation instability. Consequently, the instability growth rate can increase or decrease. In this study, first, the growth rate of this instability is obtained due to variations of beam density and energy in the cold model. Then the dispersion equation of this system is derived with saddle-point approximation of Maxwell-Jüttner distribution and Vlasov equation. Numerical results show that if the parallel temperature (T∥) is selected more than the perpendicular temperature (T⊥) of the background (positive anisotropy), the cumulative effect can increase the instability growth rate compared to isotropic fuel. In addition, instability decreases in negative anisotropy. For instance, if medium temperature anisotropy is selected 50%, the growth rate increases 2.59 times relative to the isotropic state for a proton beam with a density ratio of 0.1. Also, the growth rate can be reduced by half in -50% anisotropy for this medium. Furthermore, fluctuations in the growth rate due to temperature anisotropy are severe for dilute beams. However, this instability may quench for density ratios less than 0.1

We study the interaction of a microwave cavity with a magnetic sphere. We show that achieving the strong coupling regime in this hybrid system is feasible. The simulation results demonstrate that the coupling rate is proportional to the square root of the volume of the magnet and also is mode dependent and decreases with increasing the mode index. Since the dielectric constant of the magnetic sphere differs from that of the medium, it can act as a spherical cavity, and coupling between its eigenmodes and the electric field of the microwave cavity also occurs. The reflection spectrum includes more than one anti-crossing for relatively larger magnetic spheres

The purpose of this study is to reduce the temperature of the attic of the building of department of physics in university of Tehran. To achieve this goal, eighteen natural ventilators with the area of 0.25 m2 each were installed on the roof. The natural ventilators alone did not decrease the temperature significantly. To help natural ventilation, a laminar flow of air from the floors to the attic was provided. This led to a temperature decrease around 1.5 to 2o C. In addition, a powered ventilation was resulted 3 to 8o C temperature decrease. Since the volume (4533 m3) and area (1416 m2) of the attic are too large, further tests were conducted on two small models (47×33×51 cm3) of the attic, build from the same material as the main attic. The models were used to investigate the effect of covering the roof with aluminum foil and painting the roof with a withe color as a reflector, and installation of polystyrene panels under the roof as an insulator. Covering with aluminum foil, painting in withe, and installation of polystyrene resulted in 3-5, 2-3.5, and 1-2 degrees decrease in temperature, respectively. Reason of these changes was explained by reflection spectrum of UV-Vis-NIR spectrophotometry. Finally, the attic was simulated by the COMSOL Multiphysics software. It showed that a temperature reduction of 10 degrees could be accomplished by installation of six fans as inlet in the gables, three in each gable. Each fan has to generate 4 m/sec air flow velocity.

Quantum sensors have a significant advantage over their classic counterparts, and hence their practical application is of particular importance. However, in many practical scenarios, it is not possible to measure or estimate at close distances and endangers the security of the process. In this paper, with the help and inspiration of the quantum teleportation process, we propose the design of a sensor remotely estimating the parameter encoded into the quantum state of a quantum system. We show how the control over classical and quantum noises, affecting the sensor, can enhance the estimation. Moreover, the practical implementation of this project is discussed in detail.

In this study, the statistical correlation of the electric quadrupole transition probabilities in the spherical nuclei is investigated. To this aim, the spherical even-even nuclei in the 100 < A < 126 mass region are selected and the electric quadrupole transition rates of different levels in the ground band are determined by the interacting boson model in the U(5) dynamical limit. A non-parametric kernel density estimation method is used in the framework of nearest neighbor spacing distribution of random matrix theory to consider the statistical correlation of these quadrupole transition rates. Also, the Kullback-Leibler divergence is used to describe the regular or chaotic behavior of the considered sequences. The results show the correlation of the electric quadrupole transition probabilities between different levels of the ground band. Also, the correlation increased for such transitions that the angular momentum of the initial state of quadrupole transitions increased.

The spatially resolved stellar mass maps of high-redshift (z<2) galaxies are used to separate merging and non-merging galaxies. For this purpose, we used the combination of non-parametric indices such as asymmetry (A), Gini and M20 coefficients. Classification based on the stellar mass maps reduces the effect of large star-forming clumps and hence increases the robustness of the sample selection method. We compared the relative fraction of merging systems with log(M) > 10.5 solar mass, with respect to the star-forming galaxies above and below the star-forming main sequence (SFMS) at different redshift ranges. We found that the fraction of mergers above and below the SFMS at each redshift is comparable. The results show that mergers have small effects on the star-formation rates and the distribution of the merging galaxies about the SFMS.

The cosmic censorship conjecture proposed by Penrose states that the singularity of a black hole is covered by the event horizon and is not naked. The first examples of violation of this conjecture are from the models of the spherical collapse of the perfect fluid black hole in the dust state. In this article, we examine an important class of LTB spherical dust collapse models in which there is a naked singularity. We will first show that the singularity of a black hole will be spacelike. We then show that the event horizon will be outside the singularity. We will also show that if the energy condition is met, the famous category of these models will not have a naked singularity. We will conclude that the strong cosmic censorship conjecture will be held

In this paper the heating effects was investigated with SAMI2 model. An external Gaussian heating source was considered in electron temperature equation that models the radio frequency heating. The effects of the heating were investigated as a function of the heating period, intensity of the heating source, height of the heating center and different latitude of the heating in Iran coordinates.  Results of the simulations show that height of the heating and intensity of the source have main role in the distribution function of the electron density and temperature. This distribution in heating zone and conjugate point was shown. In early time of heating, by increasing the height, the electron temperature was increased dramatically. At low intensity of the heating source, the electron temperature wasn’t increased. However, the electron temperature was increased in heating zone after 30 minutes. Also, the heating distributes the electron density counter which represents the reduction of the electron density and the formation of the duct in heating zone and the growth of the electron density at conjugate point. The results show that at low latitude, electron temperature at heating zone and conjugate point was increased more.

In this work, we study the standard model of cosmology in the context of cosmographic approach. We want to determine whether the cosmographic tension of the standard model that is reported in recent studies, depends on the statistical errors of the observational data or not. To do this, we produce three catalogues of mock data for the distance modulus of type Ia supernovae using a canonical value for matter density in the framework of standard model. In the first catalogue, the errors of mock data have been chosen equal to the errors of real data in Pantheon catalogue. In the second and third catalogues, the errors of mock data have been chosen equal to half and twice the real errors in Pantheon sample, respectively. In the next step, using the generated mock data, we minimize the least square function in the context of Markov Chain Monte Carlo method and put constraints on the cosmographic parameters in both model independent cosmographic approach and standard model. Our results show that decreasing the error of mock data can remove the cosmographic tension of the standard model. Also, the larger errors increase the deviation of standard model from cosmographic method. Hence, the cosmographic tension of the standard model which is recently reported by the Hubble diagrams of quasars and Gamma-Ray-Burst can be essentially due to large error bars of these observational data and so not a physical tension.

In this paper, we have studied the dynamical phase diagram of the Su-Schrieffer-Heeger model using the notion of dynamical quantum phase transition in the ramped quench case. We have shown that, when the quench crosses both the critical points of the model, the phase diagram of the model includes two regions with dynamical quantum phase transition and no dynamical quantum phase transition. We have shown that if the sweep velocity is smaller than the critical value, the system shows dynamical quantum phase transition. If the quench crosses the single critical point, the system always shows the dynamical quantum phase transition

In this research, atom-cavity entanglement in closed Jaynes – Cumming model has been used with the assumption of large detuning between atom and cavity, to simulate the state transfer from atom to cavity radiation. A two-level atom which is prepared in a half-half superposition between the ground and excited states, has been exposed to initially coherent radiation field which is far from resonance with the atom. Mixture of each subsystem, linear entropy, entanglement, Von Neumann entropy and Schmidt decomposition of composite system as a function of time, has been determined analytically, for the first time. Assuming large frequency differences between atom and radiation, the simulation is shown no energy is transferred between atom and radiation due to large detuning, even though atom-radiation entanglement took place. Also, it has been shown that a particular measurement on the atom in this composite entangled system, can project the composite system into a separable (non-entangled) state so that the radiation state is changed into a superposition of the coherent state which is called the cat state. The conditions required to transfer radiation into odd and even cat states have been particularly investigated.

Control of quantum dynamics with high fidelity in the presence of noise is one of the requirements of quantum technologies. Here we develop a variational control approach for open quantum systems which is completely based on dynamics (process matrix) and is independent of initial conditions. We obtain a set of equations for optimal control of an open quantum system. We solve these equations iteratively for the particular case of simulating a dynamics in a preset time.

Using two-dimensional particle-in-cell simulation of collisionless plasmoid instability, the waves generated during formation and growth of plasmoids are investigated. Magnetic reconnection is recognized as a fundamental phenomenon in the conversion of magnetic energy into heating energy and  particles acceleration in space and astrophysical plasmas. In this phenomenon stored magnetic energy abruptly released in form of violent plasma jets and non-thermal particles acceleration and relativistic particle acceleration. In large systems such as solar systems that the length of the  current layer is much greater than its thickness ,current sheets are affected by complex photospheric motion or external disturbances such as the eruption motion of magnetic structures. This violent plasma instability results in the breakup, fragmentation and formation of multiple current sheets. Therefore reconnection happens at several X points and magnetic islands or plasmids appear. Plasmoid chains are highly dynamic configurations and can fastly grow by coalescence bounce and repel smaller plasmoids. Understanding of the effects of charged particles on the earth's atmosphere depends on a better understanding of the plasmoid instability that we have addressed an aspect of it in this article. The acceleration of charged particles toward the earth's atmosphere is one of the most important consequences of magnetic reconnection and the formation of plasmids in the solar corona as well as in magnetopause and in the magnetotail. The study of electric field components, which are the most important factor of particle acceleration, is very important in recognizing these charged particles. Fourier analysis of electric field components shows different types of electromagnetic and electrostatic waves during the formation and growth of plasmoid instability in both states ωce> ωpe and ωce< ωpe. This analysis reveals that two electromagnetic right and left-hand polarized modes and whistler wave parallel to the initial magnetic field and also the extraordinary mode, ordinary mode and magnetosonic wave perpendicular to the current sheet are excited.

The aims of this work, is to investigate the adsorption of 5-Fluorouracil drug connected to the pristine, Titanium doped boron phosphide nanocage (B12P12) with adenine nucleobases by using density functional theory (DFT). For this means at the first step, we considered different configurations for adsorbing (5-FU) on the surface of nanocluster and adenine, and then all considered models are optimized at the WB97XD/Lanl2DZ level of theory by Gaussian (09) software. From optimized structures, geometrical parameters involve bond length and bond angle, thermodynamic, atom in molecule (AIM), reduced density gradient (RDG), Uv-visible spectrum, HOMO-LUMO orbitals, density of states (DOS), and quantum parameters are calculated and all results are analyzed. The calculated results reveal that in the Ti doped B12P12 nano cage, the gap energy and global hardness of system decrease significantly, and so the conductivity and reactivity of system increase from original state. This property is favorable for making sensitive sensor for this drug. The adsorption energy and enthalpy values for all studied models are negative, which indicate that the absorption process and their thermodynamic stability are favorable. The RDG and AIM results confirm that the adsorption of 5-FU drug connected to the nanocage with adenine is non-covalent type. The computational results demonstrate that the pristine and Ti–doped B12P12 can be used as a suitable candidate for fabricating detector and absorber for 5-FU drug.

In this paper, the statistical properties of 1- to 7- negative parity levels in the 170Tm nucleus are considered with emphasis on the nearest neighbor spacing distribution in the framework of random matrix theory. The latest available experimental data for different negative parity energy levels in the E≤  3000 keV region are used to classifiy in different sequences and are analysed. The Berry – Robnik distribution function and the least square extraction method have been used to determine the parameter of distribution function in considered sequences. The results 
show the adaptation of the statistical behavior of all considered negative parity levels with the Wigner distribution function and therefore, the statistical correlation of such levels. Also, the strong correlations are yield for the sequences prepared by levels with odd spin values while the 2- levels show a weak correlation and a Poisson-like behavior. The dependence of the statistical behavior of the negative parity levels to the energy was investigated which suggests the maximum correlation in the 1300  <E < 2100 keV energy region.

In this paper, electron acceleration by a radially polarized laser pulse in the presence of helical wiggler magnetic field and axial magnetic field has been studied. The governing equations on electron dynamics in the presence of these electric and magnetic fields were solved by the fourth order Runge-Kuta method. The effect of axial magnetic field and electron injection angle on energy gained by the electron was investigated. Numerical studies have shown that the final energy of an electron depends on the value of the magnetic field and the injection angle. It was seen that by applying a magnetic field of about 0.2 and the injection angle of about 11 degrees, the electron can gain final energy of about 3.8 GeV, which is 40 percent more than the case of zero degrees injection angle and the absence of external magnetic field.