Iranian Journal of Physics Research
https://ijpr.iut.ac.ir/
Iranian Journal of Physics Researchendaily1Tue, 20 Feb 2024 00:00:00 +0330Tue, 20 Feb 2024 00:00:00 +0330Machine learning and physical science
https://ijpr.iut.ac.ir/article_3478.html
-Finding larger tensor-to-scalar ratio in the framework of Trans-Planckian censorship conjecture
https://ijpr.iut.ac.ir/article_3437.html
Trans-Planckian censorship conjecture prohibits the sub-Planckian wavelengths during inflation to become classical. Under standard assumptions on the speeds of the tensor-to-scalar ratio, which set the speed of these perturbations equal to the light speed, the upper bound on the tensor-to-scalar ratio is reduced to the extent that there will be no prospect for the detection of tensor perturbations in the CMB. In this article, we show that with reducing the speed of tensor perturbations one can enhance the tensor-to-scalar ratio to an observable limit without violating the criteria of the effective field theory of inflation.&nbsp;3D wave expansion solution in spherical multilayer structures for acoustic illusion
https://ijpr.iut.ac.ir/article_3438.html
In this paper, a technique for creating an ideal acoustic illusion in three dimensions based on transformation acoustic theory and solutions of acoustic wave equations in terms of spherical harmonics is presented. The technique employs a three-dimensional structure consisting of concentric spherical shells made of homogeneous and isotropic materials that alter the scattering pattern of acoustic waves. To examine changes in the scattering pattern, the expansion coefficients in the scattered acoustic wave equation are calculated, and the scattering pattern in each layer of the structure is computed. By placing an object inside the core of this structure, the desired acoustic illusion is created. The foregoing acoustic illusion is identified by comparing the scattering pattern of this object inside the core structure to that of another object with different acoustic parameters and sizes (transformed). One of the advantages of this technique is the elimination of the limitation of cylindrical devices in the z-axis due to the spherical nature of the acoustic parameters of the structure and their independence of angles in spherical coordinates. This technique is a useful method for increasing accuracy in medical tissue imaging using ultrasound devices. In other words, by utilizing this technique, one can take advantage of higher-quality images of sensitive tissues in ultrasound devices.&nbsp;Hydrodynamic interaction between two beads in the presence of a temperature gradient: Effect of correlation of beads’ motion on the Soret effect
https://ijpr.iut.ac.ir/article_3417.html
To study the effect of internal structure of molecules on the Soret effect, we probe consequences of exerting a temperature gradient to a suspension of one single particle inside the fluid. The particle is modeled as two microspheres, loosely connected with a spring between them, or each trapped with an optical tweezers. For the later case, we calculate the net force, that the two beads system exerts on its surrounding fluid, due to the a temperature gradient. This result, lets us calculate the corresponding Soret coefficient of the two beads system. We further correct these calculations, considering the temperature dependence of the surrounding fluid&rsquo;s viscosity.Phase behavior of hard rods between two walls: Phase change of particles without occurring phase transition
https://ijpr.iut.ac.ir/article_3442.html
In this study, we investigated the phase behavior of rods with square ( ) and circular (diameter D) cross sections between two hard walls using the Parsons-Lee theory and applying the Zwanzig approximation. Our focus is to find wall-to-wall separations (H) and the size of particles in which the phase of the system changes without occurring a phase transition. It was determined that if the distance between the plates is smaller than the length of the particles, for any particle whose length (L) to diameter ratio is greater than 1, the second order phase transition occurs, and most of the particles are placed in a certain direction parallel to the plates, which this type of phase transition takes place at lower densities with increasing particle&rsquo;s aspect ratio. We also came to the conclusion that if the distance between the plates is greater than &nbsp;and , despite the phase change of the system with increasing particle density, no phase transition will occur. In addition, it was found that the cylindrical shaped particles show some unexpected behaviors, which could be due to the inappropriate performance of the applied theory or their real physical behavior, which requires more detailed studies to resolve the ambiguity.Hidden symmetry of three dimensional rotating black hole
https://ijpr.iut.ac.ir/article_3441.html
In this work, we study explicit and hidden symmetries of curved space-time. The explicit and hidden symmetries share the feature that their generators in the phase space of probe particle are constants of motion. Their difference is that the generator of hidden symmetry is given by the contraction of Killing tensor by two or more particle momenta while for the explicit symmetry, this generator is linear in particle momentum. Therefore, we can read the Killing tensors of a curved space-time using the constants of motions associated with its probe particle. The Killing tensors of four-dimensional and also higher-dimensional geometries have been studied. In this work, we answer the question about the existence of hidden symmetry in the three-dimensional rotating black hole. To this end, we independently analyze two types of probes: free particle and scalar field. Using the related constants of motion, we show that the Killing tensor of this three-dimensional black hole is trivial.Investigation of the beam loading effects in a constant-impedance traveling wave acceleration tube
https://ijpr.iut.ac.ir/article_3439.html
In a high- power acceleration structure, the friction factor is a limiting parameter and affects the energy gain of the particles. Beam can to excite acceleration modes and higher-order. The beam effects in the excitation of acceleration modes are known as beam loading. In this article, the beam loading effect for a constant impedance traveling wave accelerating tube in S band is simulated by CST software. The results are compared with the theoretical relation obtained from energy conservation. The main purpose of this article is to validate the theoretical relationship and investigate the effects of beam loading in constant impedance acceleration structures. The comparison of the results shows a good match between the simulation and the theoretical relationship. On the other hand, it can be claimed that the beam -loading effects cannot be compensated by changing the radio frequency design. The results of this study will be used to design a high-powered accelerator with an energy of 30 MeV and an average power of 30 kW in the S-band.Folding model potentials using the LOCV-DDAEI for 16O+16O elastic scattering
https://ijpr.iut.ac.ir/article_3418.html
The elastic scattering of 16O+16O systems at several incident energies are analyzed, in the framework of double folding model, using the density-dependent averaged effective two-body interaction (DDAEI). The DDAEI is generated via the lowest order constrained variational (LOCV) method for the symmetric nuclear matter (SNM), using the input bare Reid68 nucleon-nucleon (NN) potential. A new energy dependent factor, g(E), is introduced to the LOCV-DDAEI to get a more realistic description of heavy ion (HI) scattering, at the different incident energies. It is shown that a linear energy dependent function, provides a good agreement with the energy dependence of the nuclear optical potential, and causes to increase the convergence speed of iteration method in evaluating the exchange part of folded potential, such that the computing time is considerably decreased. The calculated cross sections of the 16O+16O systems in the above framework, are compared with the available experimental data. It is demonstrated that a quite good description of HI scattering can be obtained, using the above LOCV-DDAEI, by adjusting the parameters of the linear energy dependent factor, g(E).Investigating ion acoustic waves in dusty plasmas containing hot ions, electrons and non-thermal positrons with Cairns distribution
https://ijpr.iut.ac.ir/article_3445.html
This study investigated nonlinear ion acoustic solitons in a dusty plasma system, consisting of negatively charged dust particles, dynamic warms ions, electrons and positrons with non-thermal Cairns distributions. The nonlinear differential equation governing this system was obtained in two steps using the reductive perturbation method. In the first step, the nonlinear differential equation KdV was obtained considering lower-order exponents. The results showed the nonlinear coefficient of the mentioned equation was zero at the critical value &nbsp;in the desired system and this equation could not describe the solitons propagated in the system. In the next step, the modified KdV equation was obtained like the previous section using the reductive perturbation method, concerning higher-order exponents. The results showed scattering coefficients were the same in both cases. However, the nonlinear coefficient was a little more complicated in the modified case. In both cases, static solutions of solitons were investigated, and the effect of various parameters, including a non-equilibrium of electrons and positrons, on the wave structure was examined in detail. The results revealed unlike Maxwell&rsquo;s distribution, in which only positive solitons could be propagated, both positive and negative solitons could be propagated in this system. Also, the presence of non-equilibrium particles could increase the soliton amplitude and width. The obtained results could be used in space and laboratory plasma systems.Optimization of some input parameters of a pulsed TEA CO2 laser based on the generalized Landau-Teller equations
https://ijpr.iut.ac.ir/article_3440.html
In this paper, the six-temperature kinetic model based on the generalized Landau-Teller equations is used to optimize a pulsed TEA CO2 laser input parameters. This model was numerically solved by regarding the equations governing the electrical discharge media to obtain the density of electrons. In this study, for the first time, the dissociation of the CO2 molecule and the production of CO as a time evaluation equation were dynamically coupled with other rate equations. The time behavior of the discharge current and voltage and laser output pulse power was simulated for CO2:N2:He gases mixture ratio, which are 1:1:3, respectively. Also, the optimum values of the input parameters including the reflectivity of the output mirror, the capacity of the pre-ionization capacitor, and the capacity and charging voltage of the storage capacitor were calculated to obtain the maximum output peak power. The obtained results are significant in the optimum design of TEA CO2 oscillators.Study of the impact of polarization and shape factor on the nonlinear optical response of a hybrid molecule including a semiconductor quantum dot coupled two metallic nanoparticles: second harmonic generation
https://ijpr.iut.ac.ir/article_3451.html
In this paper, the generation of second-harmonic from a hybrid molecule composed of two metal nanoparticles with ellipsoidal shape coupled to a semiconductor quantum dot when a control laser field is applied to the system by using the density matrix approach is investigated. This applied field induces a polarization in the semiconductor quantum dot and both different plasmonic nanoparticles, and the polarized metal nanoparticles interact with the quantum dot through dipole&ndash;dipole interaction. We demonstrate that SHG strongly depends on the shape factor and the light polarization for oblate and prolate spheroidal plasmonic nanoparticles coupled with a quantum dot when the applied field is parallel or perpendicular to the axis of the system. The study of the light-matter interaction in such hybrid molecule can be useful to design the optical devices based on the plasmon-exciton-plasmon interaction.Behavior of the transition region on the wave propagation at the solar atmosphere
https://ijpr.iut.ac.ir/article_3443.html
Studying of megnetohydrodynamic waves in solar magnetic structures such as coronal loops, spicules, etc. can be very important for investigating the problem of heating the sun&rsquo;s outer atmosphere. For this purpose, a magnetic flux tube was considered in the presence of steady flow and sheared magnetic field in a stratified atmospheric layer. The transition region is a boundary layer between the solar chromosphere and the corona, which has very rapid changes in temperature and density. The effect of the transition region on the damping of Alfven waves and temperature changes with height were applied in the assumed flux tube. The Cartesian two-dimensional model was used to solve the magnetohydrodynamic equations, and the results were obtained from the damping in the form of graphs of temporal and spatial changes of the perturbed velocity and magnetic field. The graphs showed that the damping of Alfven waves is more visible with time than with space, so the more rapid the damping occurs, the more energy will be transferred to the corona.The effects of charge on the persistence length of biopolymers
https://ijpr.iut.ac.ir/article_3448.html
Flexibility and rigidity of biopolymers in mechanical structure have been investigated several times. Persistence length of a polymer is an exact factor to specify value of flexibility. No doubt that existence of charge on the polymers would have effect on the value of flexibility and therefore change in the persistence length of the polymer. In this study, by use of molecular dynamic simulation and Gaussian chain model (bead-spring model), we have investigated the effect of electric charge and salt concentration on the persistence length of the biopolymers in the cell. This simulation has been able to provide acceptable detail in the results.Investigation of entanglement of atomic systems near coherent perfect absorber materials
https://ijpr.iut.ac.ir/article_3419.html
Recently, coherent perfect absorbers have received much attention from researchers in the field of classical optics. Such absorbers, known as a time-reversal of lasers, provide perfect absorption of the incident light. Considering the very attractive features of these materials, in this paper, we investigate the quantum optics of these materials. To do this, we consider two coherent perfect absorber structures and assume two identical two-level atoms; one of which is prepared in its ground state and the other in the excited state, are placed on both sides of the coherent perfect absorber slabs. We compute the spontaneous emission rate, Lamb shift, and collective decay of atoms near two slabs, and then investigate the entanglement dynamics of the atomic system using the concurrence. We find that these parameters exhibit a damped oscillatory behavior with increasing the distance between the atoms and the slabs. In contrast to the classical regime, we also observe that these structures are not the perfect absorbers in the quantum regime.g-SiC and g-SiC2 siligraphenes as two multifunctional H2S sensing materials
https://ijpr.iut.ac.ir/article_3446.html
The main purpose of this article is to investigate the capability of g-SiC and g-SiC2 siligraphenes in detecting H2S gas through diverse sensing mechanisms, using density functional theory. Our calculations demonstrate that the adsorption of H2S molecules onto both siligraphenes is a physical and exothermic process. The physical adsorption process helps sensing materials to recover soon (a few nanoseconds) after gas removal at room temperature. Investigation of geometric and electronic properties of g-SiC and g-SiC2 in combination with H2S molecule shows that both materials have the gas-detection ability through thermal- and resistance-based mechanisms. For example, the electrical conductance of g-SiC changes by 38% due to gas adsorption. In addition, the presence of H2S molecule on the g-SiC surface, changes the type of its majority carriers and makes it possible to use this material in Seebeckeffect-based H2S sensors. Overall, various sensing mechanisms besides short recovery time, make g-SiC and g-SiC2 great candidates to be used in H2S gas sensor as sensing material.Encoding and transmission of information based on radial carpet beams and convolutional neural network detection
https://ijpr.iut.ac.ir/article_3449.html
Radial carpet beams are a novel form of structured light that falls under the category of combined half-integer Bessel-like beams. This study introduces the radial carpet beam as a means of information transmission and a solution for expanding the information encoding freedoms. The method employed for detecting and classifying these beams is the convolutional neural network (CNN). To conduct the study, a dataset consisting of 16 different classes of radial carpet modes was prepared. These modes were propagated through underwater turbulence conditions over a distance of 120 cm. The convolutional neural network used in the study was based on the widely recognized DenseNet-201 architecture, utilizing transfer learning techniques. The trained model achieved a 97% accuracy in mode detection and classification. Subsequently, the performance of the proposed model was evaluated by transmitting and receiving a 4-bit grayscale image measuring 150 x 200 pixels through an underwater communication link based on radial carpet modes. The evaluation results clearly demonstrate the potential for achieving new encoding options with radial carpet beams. Moreover, the convolutional neural network method proves to be an optimal approach for detecting and classifying structured light beams. This method alleviates the challenges of&nbsp; using multiple optical components in coherent detection techniques, which traditionally rely on diffraction gratings. In addition to simplifying optical system configuration, it also reduces implementation costs and volume, particularly in optical communication applications.Anisotropic magnetoresistance in La0.4Pr0.3Ca0.3MnO3 thin films
https://ijpr.iut.ac.ir/article_3447.html
The paper presents a study on the magnetoresistance (MR) and anisotropic magnetoresistance (AMR) properties of La0.4Pr0.3Ca0.3MnO3 (LPCMO) thin films. The thin films were grown using pulsed laser deposition method on LaAlO3 (LAO) (111) and MgO (MGO) (100) substrates, with a thickness of approximately 90 nm as estimated by X-Ray reflectometry (XRR) method. The LPCMO sample on the LAO substrate exhibited a lower metal-insulation transition than the one on &nbsp;the MgO substrate due to high compressive stress. The MR was found to be 57% and 98% for LPCMO/LAO and the LPCMO/MGO films, respectively. The LPCMO/MGO sample also showed a significantly higher MR (80%) compared to LPCMO/LAO sample (32%), indicating its potential application.Comparison of direct DNA damage by protons and oxygen, carbon, and helium ions using Geant4-DNA code
https://ijpr.iut.ac.ir/article_3450.html
Ionizing radiations can directly affect cells by inducing DNA breaks. This impact includes single-stranded and double-stranded failures; which may cause cell death and mitotic failure. In the present study, with the help of an atomic DNA model built in the Geant4-DNA code and its initial validation, direct DNA damage by interaction with carbon ions 114/u2 MeV, 134/21 MeV/u oxygen, 62/83 MeV/u helium and radiation 62MeV protons have been investigated. For this purpose, after the initial validation, the results of single-stranded, double-stranded fractures and double-stranded fracture efficiency at depths of 5 to 30.7 mm were evaluated for the mentioned ions. The ratio of single strand breaks for oxygen ions at 5 mm (and the location of the Bragg peak: 30.7 mm), 1.85 (1.55), 4.19 (9.42), and 10.6, respectively. (22/24) is more than carbon ions, helium and proton rays. On the other hand; The two-strand break at a depth of 5 mm for oxygen, carbon, helium and proton ions is equal to 0.09, 0.05, 0.01 and 0.005 respectively. These values were calculated as 2.09, 1.34, 0.22, and 0.03 at the place of the Bragg peak (with a significant increase). The results show heavy ions behave much more effective than light ions and protons in terms of biological effects (in the form of single- and double-strand breaks), therefore, they are more effective options for inhibiting or controlling cancer cells.Study of temperature distribution in a metallic nanograting based on a Kerr nonlinear material irradiated by a nanosecond pulsed laser
https://ijpr.iut.ac.ir/article_3452.html
In this article, we investigate the temperature distribution in a one-dimensional metallic nanograting heated by a nanosecond Gaussian pulse laser using the finite element method. It is assumed that the nanograting slits are filled with a Kerr-type nonlinear material. The results indicate a strong dependency of the system's temperature distribution on the incident laser fluence. Also, the temperature distributions are completely different for linear and nonlinear regimes at high laser fluences around the pulse peak and after that. Indeed, exciting the nonlinear optical Kerr effect, especially at high laser fluences, leads to a change in the temperature response of the nonlinear regime compared to the linear one. Moreover, depending on the applied laser wavelength, there is a possibility of increasing or decreasing the temperature compared to the linear case. On the other hand, one can not enhance the laser fluence to any amount, as this may raise the temperature even higher than the melting point of the materials. Therefore, as the strong laser pulses are applied, temperature investigations should be conducted to prevent excessive heating and damage to the system.Investigating parameters affecting the rotational motion of optically trapped metal nanoparticles
https://ijpr.iut.ac.ir/article_3458.html
Controlling the position and motion of small objects using light offers an attractive means of manipulating tiny microscopic samples, such as biological cells or microscopic particles. Optical tweezers enable the trapping of gold nanoparticles, and by employing circular polarization of the laser, they can be rotated at a frequency of several kHz. This study aims to investigate the rotational dynamics of particles in a two-dimensional optical trap and experimentally study the factors affecting it, including laser power, numerical aperture of the focusing lens, and the medium viscosity. The rotational dynamics were analyzed using two methods, namely the power spectrum method and autocorrelation of particle movement. Experimental results on 400 nm gold particles reveal that, under a laser wavelength of 1064 nm and a numerical aperture of 1, the maximum rotation speed reaches 1470 Hz. Additionally, the observed changes in rotation speed within different liquids with different viscosity agree with the theory prediction.Anti-Kibble-Zurek behavior in Su–Schrieffer–Heeger (SSH) model with noisy coupling crossing the quantum critical point
https://ijpr.iut.ac.ir/article_3460.html
In this paper we show that if we impose noise to the time varying coupling parameter of a closed system, then the system exhibits anti-Kibble-Zurek behavior leading to growth of excitations. Furthermore, our finding indicates that to minimize excitations, there is optimal ramp time, which is proportional to the noise strength but the exponent does not show agreement with the results of previous works. It is demonstrated there are restrictions of adiabatic protocols, like quantum annealing, and the rate of optimal ramp time is universal.Local disentanglers for the equivalence of two-dimensional topological quantum codes
https://ijpr.iut.ac.ir/article_3456.html
Studying equivalence classes under local unitary transformations is one of the most important approaches for the classification of topological quantum states. It has specially attracted much attention for topological quantum codes due to their application in quantum computing. In particular, It has been shown that each D dimensional color code is local unitary equivalence to many copies of D dimensional toric codes. In this paper, we consider such transformations for two- dimensional (2D) topological codes by introducing GHZ disentanglers. We apply the above disentanglers on qubits corresponding to one particular color in the color code defined on a three-colorable honeycomb lattice. Then, we show that it leads to disentangling other colors because the initial color code is converted to two copies of the triangular toric codes. Furtheremore we extend the above transformations for color codes on different three-colorable lattices. We show that by applying GHZ disentanglers corresponding to one particular color, the color code is converted to two toric codes defined on dual lattices corresponding to other colors. This result is also useful for comparing color codes on different lattices regarding the difference between their dual lattices.The study of θφ component of the viscous stress tensor in the protoplanetary discs
https://ijpr.iut.ac.ir/article_3444.html
Observation and numerical documents have shown that the protoplanetary discs (PPDs) around the young stellar objects (YSOs) to be gravitationally unstable. The self-gravity can be important in PPDs . The gravitational instability and outflow (mass-loss) are dominant mechanisms for transporting outward angular momentum and inward accretion in the disc cold mid-plane. The structure of the self-gravitating accretion discs depends strongly on the rate at which it cools. In this paper, we have studied the hydrodynamical equations in the presence of &theta;&phi; component of the viscous stress tensor (t_&theta;&phi;) in the spherical coordinates (r,&theta;,&phi;) by using the semi analytical self similar solutions in the steady state and axisymmetric assumptions. This component of the viscous stress tensor is related to transport outward angular momentum by outflows. The solutions indicate that the disc is gravitationally instable. The gravitational instability as a viscose source leads to heat the disc. Our results have shown the Toomre parameter (Q) decreases by increasing the cooling rate because the heating supplied by gravitational instability is not enough to counteract cooling and so the disk will fragment and produce planets. The results have shown that t_&theta;&phi; makes the disc colder and thinner and outflows form in the regions with lower latitude. We have shown that the effect of t_&theta;&phi; in the mid-plane of the disc is more effective than t_r&phi; (turbulent viscosity).Controllability in nonlinear dynamical systems: a compartmental model
https://ijpr.iut.ac.ir/article_3455.html
Controlling non-linear systems and steering the system to a stable state is a significant issue in complex systems. Controllability is our ability to steer a dynamical system to a desired final state in finite time. A compartmental model is general mathematical modeling used to predict the time evolution of complex systems. We consider a three-dimensional nonlinear system with a transition threshold that has only one steady state (equilibrium fixed point) that is reached in a long time. Our goal is to drive this system towards the desired stable fixed point at the beginning of the dynamics (finite time). The nonlinear System was investigated as a compartmental model. We used the control strategy of multidimensional dynamical systems and proposed the canonicaltransformation from which the control function was obtained. In order to show that the fixed points of the system are stable, we used the linear stability method and the Gershgorin circle theorem. By numerically solving the differential equations after control, the system reached the desired fixed points in a finite time. We plotted the state space for different fixed points and four regions were obtained. We found the points where the control function can steer the system to a stable state in a finite time. We found fixed points that are non-physical.