مجله پژوهش فیزیک ایران
سال بیست و چهارم شماره 4 (زمستان 1403)

In the present study, we have demonstrated that the core location of cosmic ray air showers can be determined by utilizing a virtual dense array and comparing the intensity of experimental signals received by antennas within a cosmic ray radio array with those received by their corresponding antennas in a dense array. Specifically, this method is applied to the coordinates of the SURA radio array. Additionally, to reduce the simulation time the number of antennas in the dense array is optimized. Moreover, we investigate the influence of the primary energy and the zenith angle of the dense array on the accuracy of the method. We have shown that within a limited range, a dense array with a specified primary energy and zenith angle can effectively determine the core location of cosmic rays with various energies and zenith angles while maintaining acceptable accuracy of the method.

It is possible to extend the shelf life and reduce the waste of agricultural products due to removing bacteria, viruses, insects and pests by means of gamma irradiation with the absorbed dose amount determined by microbiology and food laboratories. For this purpose, the design and construction of a self-shielded gamma irradiation system for irradiation of grains and legumes with radioactive sources of cobalt-60 with activity of 50 kilocuries was performed. In this system, agricultural products are fed in bulk into the input funnel with a conveyor belt. The products move from the inlet funnel to the spiral due to gravitational force and after passing through it, they enter the cask (irradiation chamber) to be irradiated. The absorbed dose amount of agricultural products depends on the time duration that they stay in the irradiation cask, their density, and their type of products, etc. Irradiation time can be adjusted by changing the rotational speed of the screw conveyor considering the last amount of activity remained in the cask at the time of irradiation by means of a software product. The design and construction of type 1 radiation system is based on ANSI/HPSN43.7-2018 standard designed using Solidworks software and basic biological shielding standard ISIRI7751 modeled and calculated by MCNPX software. Other designs and constructions, including industrial and facility drawings, electrical drawings, structural analysis, welding and electrical and control systems were also carried out based on their respective standards. The built mechanical structure can withstand 140kN of loading. The unique design of the entrance chamber in a form of a step instead of a spiral reduces the volume of lead material required for shielding by 2 tons compared to a similar irradiation system made in Hungary. The output mass flow rate of irradiated products in this system is about 1 ton/hour for wheat with dose of 200 grays. The dose uniformity ratio of 2 was obtained, which is acceptable for industrial radiation works.

In this paper, an optical fiber temperature sensor is designed that uses isopropanol to increase temperature sensitivity and deep learning to characterize changes in the three-dimensional pattern of light propagation along the optical fiber and determine the ambient temperature. In other words, changing the ambient temperature changes the refractive index of isopropanol and causes a change in the appearance of the interference pattern of the guided modes inside the optical fiber, which identifies the pattern based on deep learning detects the changes in the appearance of light emission and estimates the ambient temperature optimally. In this regard, the mentioned optical fiber was simulated by Rsoft software for 106 different temperatures and their 3D propagation patterns were obtained. From the collection of simulated patterns, a complete database of propagated light for the temperature range of -73 to 82 degrees Celsius has been formed. The mentioned database is entered into the pattern recognition algorithm based on deep learning, and the pattern recognition system is taught how the appearance of light propagation changes in the fiber with temperature changes. The model used in this article is inspired by the AlexNet network and can obtain the ambient temperature with a minimum mean square error of 2.

Radiative cooling structures can reach a temperature below the ambient temperature by reducing the absorption of radiative energy from the surrounding environment, while maximizing the radiative energy emission. These structures have received extensive attention given their potential to reduce buildings’ electrical power consumption. To achieve this goal, a structure with specific electromagnetic properties regarding wave absorption and transmission should be designed. The proposed structure should simultaneously have 1) good reflectance across the Sun radiation spectrum, and 2) good emittance (absorptance) in the atmospheric window wavelength range. In this article, the SU-8 photoresist material was proposed to fulfill the emission condition, and to fulfill the reflection condition, the Bragg reflector was considered and analyzed.

The Future Circular Collider (FCC-ee), with its clean experimental environment, high energy, and luminosity, offers a unique opportunity for the precise study of the properties and interactions of top quarks. In this study, we have investigated the potential sensitivity of the FCC-ee to flavor-changing neutral current (FCNC) processes involving top quarks using an effective Lagrangian approach. To this end, the production of top quarks in electron-positron collisions at center-of-mass energies of 240 GeV and 365 GeV has been simulated, considering the full hadronic decay of the W boson resulting from the top quark decay. The results of the analyses show that by combining these center-of-mass energies and considering integrated luminosities of 5 ab⁻¹ and 1.5 ab⁻¹, an FCNC sensitivity on the order of 10⁻⁵ can be achieved. These findings highlight the significant potential of the FCC-ee for discovering and precisely studying FCNC processes, which could contribute to a better understanding of physics beyond the Standard Model.

In this paper, the structural, electrical, and optical properties of copper-doped amorphous carbon films were investigated and the relation of these properties with a plasma-produced chemical active species in simultaneous direct current and radiofrequency magnetron sputtering was studied. The effect of changing the power of a direct current power supply at constant power of radio frequency on the film properties was investigated. Raman spectroscopy of the films indicated that the G peak position and ID / IG ratio increased, which indicates a decrease in the SP3 bonding in the film structure. Optical emission spectroscopy (OES) was also performed to investigate the dominant chemical active species produced in the plasma environment and showed that Cu active species decreased with increasing power. Also, the results showed that by increasing the power of direct current to the graphite target from 60 to 120 W as well as keeping the radio frequency power constant at 10 W which connected to copper target, the optical absorption coefficient of the films increased. Also, the optical band gap grew from 0.92 ev to 1.5 ev. The refractive index of the deposited films analyzed by ellipsometry showed a decreasing trend from 1.85 to 1.24 with increasing power.

In this article, the use of annular fuel instead of solid fuel is investigated in the core of the Bushehr reactor. In annular geometry, the fuel has two internal and external channels and two surfaces for temperature exchange. The current solid fuel used in the Bushehr reactor and five types of annular geometries were simulated in the MCNPX.2.6.0 nuclear code. After validating the simulation, some neutronic parameters have been calculated by the code. By analyzing the results, the optimal annular geometry has been introduced and suggested. After the neutronic analysis, the chosen annular geometry has been analyzed from the thermohydraulic point of view in the COBRA code and FLUENT software. According to the obtained results, the use of annular fuel, the burnup increases by about 4.01 GWd/MTU. Also annular fuel usage decreases the maximum temperature of the fuel center by about 300 K. It also increases the safety margin of MDNBR from 1.7 in solid fuel, to 2.5 in the outer cladding, and to 3.7 in the inner cladding of annular fuel.

The dynamics of a heterostructure composed of antiferromagnetic and ferromagnetic layers, separated by a metalic layer, has been investigated. By adjusting the applied magnetic field so that the frequency of one of the antiferromagnetic modes lies in the frequency range of the ferromagnetic layer, coherent coupling can be achieved due to interlayer exchange interaction. Moreover, the magnetization dynamics within the magnetic layers induce spin pumping into the metal, generating a spin accumulation in the metallic layer. The spin accumulation generates a spin transfer current from the metal to the magnetic layers, which can result in dissipative coupling between the dynamics of the antiferromagnetic and ferromagnetic layers. This coupling manifests as level attraction in the system's eigenmodes. The indirect coupling between the dynamics of the magnetic layers can be either coherent or dissipative, depending on the thickness of the metallic layer; for thin metallic layers, where interlayer exchange interaction is dominate, coherent coupling emerges, whereas in thick layers, where exchange interaction is negligible, dissipative coupling prevails.

A hybrid system consisting of a magnet and a microwave cavity has been investigated. The strong coupling between the magnet and the microwave cavity, where the coupling strength significantly exceeds the losses of both subsystems, creates an extrinsic dissipation channel for the magnet that depends on the temperature, intrinsic damping, and excitation energy of the cavity. The results indicate that, in the resonant case, the excitation of the microwave cavity leads to anti-damping for the magnet via this dissipation channel.

The Schwarzschild solution was obtained in 1916 as the first solution to Einstein’s field equations based on spherical symmetry, which was considered a new idea in the use of symmetry at the time. In this study, it is tried to reformulate the solutions of Einstein’s field equations with spherical symmetry in both the presence and absence of the cosmological constant based on the invariants (or first integrals) of the symmetry groups. The method used in this article is a combination of four well-known symmetries: Lie point symmetry, λ-symmetry, Darboux polynomials, and the extended Prelle-Singer method. In this method, to resolve the Schwarzschild problem, a combination of the mentioned symmetries is used in such a way that the independent invariants are obtained in a systematic and algorithmic way. Based on this, a symmetry theory is provided for us. With the help of this theory, one can use symmetries in the best possible way, far from any confusion, and achieve the desired solutions with a specific solution, which is to find independent invariants.

In this paper, we apply the Newtonian limit to the general relativistic magnetohydrodynamic (GRMHD) equations that govern the motion of magnetoplasma accreting onto a static black hole. We study the time evolution of a non-viscous, magnetized, thick accretion disk in the presence of the central black hole's dipolar magnetic field. With the presence of finite electrical conductivity in the fluid, the magnetic stress effectively replaces the viscous shear stress in the standard disk model and is responsible for the transfer of angular momentum. All physical quantities of the system are functions of three variables: t, r, and θ. We determine the time dependence of the system's physical functions using the self-similar method. With suitable physical assumptions, we derive the spatial dependence of the functions as accurately as possible through analytical solutions, and, when necessary, through numerical methods. Self-similar solutions indicate that over time, the accretion and rotation of the fluid slow down, the disk becomes less dense, cooler, and less pressurized, and the electrical conductivity of the fluid also decreases. As the electrical conductivity of the fluid increases, the accretion and rotation of the fluid slow down, and the disk becomes denser and cooler, but the mass accretion rate increases. The azimuthal electric current density generated by the motion of the magnetofluid determines the magnetic field structure within the disk and results in a polar component for the disk's magnetic field. Due to the finite electrical conductivity of the fluid, at the boundary surface of the disk, the constant magnetic field lines of the disk connect to the dipolar magnetic field lines of the central black hole. Over time, this configuration remains stable because the time dependence of the magnetic field components of the disk is similar.

X-ray detectors, which generally enjoy very good detection efficiency and spatial resolution, have many applications including in radiography and basic research. Many of the existing radiographic methods are extremely inefficient and time-consuming, making them improper for real-time applications. A solution to avoid such a problem has been to develop structured scintillation films such as CsI, which have high density and fast response, and at the same time, have the possibility of being grown as compact micrometer structures – suggesting a way to attain better image qualities. Employing the Geant4 Monte Carlo toolkit, we have used a simple geometry to serve as a radiography system, which includes a polymer layer as a camera, a structured layer of micro-columnar scintillators as x-ray converters, and an aluminum layer as a light reflector. Hence, for pencil-beam x-rays we investigated the dependence of blurring on the production depth of the resulting optical photons.

Graphene, the mother of 2D materials, has become a unique material for use in a wide range of applications due to its extraordinary properties such as electric conductivity, thermal conductivity, high charge carrier density, high charge mobility, and good optical and chemical properties. In this research, Cr electric contacts were produced by photolithography on the desired substrate, and monolayer graphene was transferred on top. Samples were functionalized at 15s and 30s in 20-50 W SF6 plasma. Optical, electron, and atomic force microscopic techniques along with Raman spectroscopy and energy dispersive X-ray analysis were used to examine the quality, continuity, elemental and structural properties of the samples. Current voltage before and after graphene functionalization demonstrated that at a specific plasma time, plasma power between 20-50 W is not a critical parameter rather, plasma time is the critical parameter in current modification. 15s SF6 plasma reduces the current passing through monolayer graphene due to its high electron affinity and further increases the plasma time to 30s, diminishes monolayer graphene conductivity, and turns into an insulating 2D material with atomic thickness. Raman spectroscopy of fluorinated monolayer graphene demonstrated that an increase in time and plasma power, decays crystal structure and increases impurities and defects in the lattice. These were qualitatively extracted from the Raman spectra and discussed. Finally, fluorine was sandwiched between two conductive and nonconductive layers and restored electrical current. Applying back-gate voltage had an insignificant impact on the current modification of graphene.

Bacteria can move for various reasons, including in response to chemical stimuli in the environment. In this article, we model the movement patterns of a typical bacteria in the form of a discrete-time Markov chain in one dimension (one-dimensional running and tumble model). Then with the help of the large deviation theory, the behavior of the probability density function of current (displacement per unit time), as a dynamical variable that is defined on the moving path, is studied. We will show that it is possible to observe a dynamical phase transition in the system.

Dipolar interaction plays a significant role in describing various phenomena. Analyzing a many-body system with dipolar interaction is challenging due to the vector, anisotropic, and long-range characteristics of this interaction. In this paper, a tensor approach is used to study dipolar interaction, allowing the contribution of orientation and the location of dipoles to be separated. With this approach, it can be shown that in mean-field theory, a continuous magnetic phase transition occurs in an ordered two-dimensional array of magnetic nanoparticles under the influence of dipolar interaction. However, this phase transition becomes more complex when nanoparticles are embedded in elastic tissue. Such a system is crucial from a biological view. The tensor approach is also applicable for analyzing the elastic array of dipoles. The results show that the strain in the elastic tissue aligns with magnetic order in a way that further stabilizes the emergent magnetic order against thermal fluctuations. Although this stability does not reduce the system’s sensitivity to even the smallest external magnetic field at the critical point, and the system remains infinitely susceptible to an external magnetic field. This feature could be biologically important.

This paper studies the excitation of solitonic waves in a quantum plasma model within the weak relativistic regime. The model leads to a fourth-order nonlinear differential equation, which, due to its nonlinearity, introduces new and intriguing phenomena in the dynamics of the plasma environment. We successfully obtained stable and stationary solitonic solutions using the hyperbolic secant Sech-method without resorting to any simplifications. This approach, commonly known as the Tanh- method, is referred to as the sech- method here because the sech function is employed in deriving the solutions. The obtained stable and stationary solitonic waves are significant because they propagate with a constant size and shape in a highly dispersive plasma environment. These waves reveal bounded soliton waves for the vector potentials. Also, the density changes due to the influence of the thermal quantum effects are studied. It is observed that the group velocity of the solitonic solutions of the vector potential affects the density changes. The outcomes of this study and the dealing approach with this context help us better understand the dynamical phenomena of quantum plasmas.

This study explores the interaction of a colloidal particle with a wavy wall in a two-dimensional nematic liquid crystal. The particle is confined in a cell between two flat and wavy walls, all with homeotropic anchoring. The particle's interaction with the wall is determined by numerically minimizing the bulk Landau–de Gennes and surface energy using a finite element method. We discovered that within a range of each successive well and hill of a wavy wall, the particle can experience attractive and repulsive interactions, leading it to move along routes determined by energy gradients. The reorientation of the nematic field around the particle from the quadrupole configuration results in anisotropic particle-wall interactions near the wall. We considered the wavy wall with two different amplitudes to explore the impact of the magnitude of wells and hills on interactions. Our calculations demonstrate that increasing the amplitude can strengthen and expand the range of interactions.

One of the ways to absorb laser energy by plasma in thermonuclear fusion is called inverse bremsstrahlung absorption. In this process, energy is deposited through inverse bremsstrahlung radiation by plasma electrons. In the current work, inverse bremsstrahlung absorption in unmagnetized and inhomogeneous plasma is calculated. For this purpose, kinetic theory and Fokker-Planck equations are used and the Maxwellian distribution function is considered as the first isotropic distribution function. Then a numerical solution for solving the the laser electric field and the plasma dispersion function is proposed. After determining the inverse bremsstrahlung absorption, the effect of laser wavelength and plasma electron temperature on the absorption rate was studied. The results show that increasing the electron temperature and decreasing the laser wavelength increases the amount of absorption in unmagnetized and inhomogeneous plasma. Finally, The difference in inverse bremsstrahlung absorption in homogeneous and inhomogeneous plasmas was investigated.

We study several holographic entanglement measures in a specific Einstein-Maxwell-dilaton theory using gauge/gravity correspondence. In particular, we evaluate the holographic entanglement entropy, mutual information, and entanglement wedge cross-section in geometries that are dual to the boundary vacuum state. Our results reveal some generic properties of boundary information measures dual to the entanglement wedge cross-section, e.g., the entanglement of purification. We show that the critical separation for the transition of mutual information increases as we increase the non-locality parameter, hence the total correlation between the subsystems increases.

The exclusive decays of the Higgs boson into  and  mesons are being studied using the fragmentation approach. One of the dominant modes of the Higgs boson decay in the Standard Model is its decay into  pairs, which then directly decay into   and  mesons. In this article, the branching ratio and decay widths of the SM Higgs boson to the  and  mesons have been calculated by directly fragmenting the anti-quark  within the framework of perturbative Quantum Chromodynamics (pQCD) at leading order (LO). The results of these calculations are in very good agreement with those obtained by other authors.

In this article, we want to describe the phenomenon of one-dimensional blackbody radiation by using the theory of quantum electrodynamics and the theory of open quantum systems in Heisenberg's picture. For this purpose, we consider a Fabry-Perot cavity, which is in thermal equilibrium with its environment at a certain temperature, while one of its longitudinal modes is optically pumped by an external laser. By writing the Heisenberg-Lanjevin dynamical equations for the longitudinal modes inside the cavity and solving them, we obtain the time evolution of the internal optical field in the steady state. Then, using the input-output theory in quantum optics, we obtain the optical field of the cavity output in the steady state and calculate the power spectrum of the cavity output from that. The result appears as the sum of a coherent part and an incoherent part in the output power spectrum, where the former is related to the mean field and the latter is related to the quantum fluctuations of the field inside the cavity, which is the source of thermal radiation. Finally, we show that in the continuum limit, the quantum fluctuations of the cavity output lead to the emergence of the one-dimensional Planck spectrum, which at the low-frequency limit leads to the one-dimensional form of the Rayleigh-Jeans relation. Then, by calculating the total output energy density, we obtain the Stefan-Boltzmann law for one-dimensional blackbody radiation.