مجله پژوهش فیزیک ایران
سال بیست و سوم شماره 1 (بهار 1402)

In this study, the effect of point defects on the thermal conductivity of UO2 is investigated. Especially, the effects of oxygen vacancy and interstitial are considered. Thermal conductivity of UO2, UO2+0.25 and UO2-0.25 is calculated by solving the phonon Boltzmann equation (BTE) under the relaxation time approximation (RTA). The results show that introducing any defects to the lattice structure of UO2 decreases thermal conductivity significantly. In addition, the results show that the variation of the thermal conductivity of UO2-0.25 is much lower than that of UO2+0.25 in the temperature interval of 300 to 1000 Kelvin.

Large magnetic resistance has been widely considered due to its many applications in various fields, including the manufacture of magnetic sensors. An important case of this type of resistance is the linear magnetoresistance caused by the inhomogeneity of charge distribution. The magnetoresistance of heterogeneous conductors is simulated by the two-dimensional resistance network model. In the network model, the resistance unit of a homogeneous circular disk with four current terminals and the potential difference between the terminals is considered, and the currents and potential differences are connected to each other by means of the impedance matrix, and the magnetic field is perpendicular to the lattice. In this work, we study and investigate the changes in magnetoresistance for a network including two subsystems with different resistances with a diagonal arrangement. The results show that the changes in the magnetic resistance of the heterogeneous system depend on the resistance ratio of the two materials as well as the location of the boundary between them. In addition, it was observed that for large values ​​of the resistance ratio or high inhomogeneity, there is the possibility of the existence of a peak of resistance variation.

In this article, we investigated electromagnetic oscillations in a quantum nonuniform electron-positron magnetoplasm interacting with a short pulse laser, in low frequency approximation, in two parallel and perpendicular directions. According to our investigations, the waves in the parallel direction are affected by ponderomotive force, vigorously. Quantum corrections cause the magnitude of this force to change and accordingly, cause the magnitude of phase and group velocities of the waves, as well as, their instability to change. In the parallel direction, initial quantities of number density and streaming velocity affect the waves directly, but the magnetic field affects these waves through the ponderomotive force, indirectly. As well, absorption of the laser pulse causes the plasma waves to grow in the laser direction and damp in the opposite direction. While, the amplification of the laser causes the waves to damp in the laser direction and grow in the opposite direction. In the perpendicular direction, the waves are influenced by the transverse gradient of initial quantities of number density, streaming velocity and external magnetic, in addition to their amounts, while these gradients don't have any effect on the parallel waves. Likewise, we investigate the behavior of the waves for different values of the transverse gradients. So that we indicate that the presence of each of gradients can completely change the behavior of the waves. As well, the investigations indicated that the presence of the transverse gradient of the initial density or streaming velocity couldn’t create the electromagnetic waves in the perpendicular direction but, the transverse gradient of the magnetic field could initiate these waves.

Different scattering processes have been yet studied in the noncommutative standard model (SM) and different limits on the noncommutative scale have been determined. In the present work we, for the first time, study the hadron production process through pair annihilation, in the noncommutative standard model. In the experimental studies of hadron production through pair annihilation a wide range of collision energy spectrum () has been considered. In our study, we restrict ourselves to the ranges  so having available experimental data from Belle Collaboration for B-meson production in the process  we shall determine a lower limit  for the noncommutative scale. In fact, by studying the effect of noncommutativity on the differential cross section at the parton level () as well as the fragmentation function of meson and comparing the theoretical results and experimental data the lower limit will be determined. Having analytical results for the pair annihilation cross section in the noncommutative SM it would be possible to specify the production cross section of each meson or baryon for various values of noncommutative scale.

In this article, electron transport has been studied for a system consisting of a double-stranded DNA molecule with a telomeric sequence attached to two semi-finite electrodes of silicic nanoribbons. This study has been investigated using the tight-binding model and Green's function approach. By placing the DNA molecule in the middle of two silicon nanorod electrodes, we can see the electron passing channels in the system, and also the type of organic base connected to the electrodes showed a significant effect on the electron transport of the system. Calculations show that telomeric sequences such as TAGGGT, TTAGGG, and GTTAGG have the highest electrical conductivity compared to other sequences. We found that by controlling the gate voltage in the system, It is possible to control the current or load delivery. Also, by increasing the number of organic base pairs in the system, we saw an increase in current, and by controlling the number of organic base pairs, the transport characteristics can be controlled. This ability to control has many uses and a significant role in the manufacture of electronic components.

In this paper, the electrical control of the lateral shift of the reflected beams from a pseudo-isotropic nanocomposite structurally chiral slab is investigated, theoretically. The medium is made of a pseudo-isotropic chiral material where the silver nanoparticles are dispersed randomly inside it. The results show that the structure does not have any photonic bandgap in the absence of a low-frequency electric field and the lateral shift of the reflected beam from the structure is negligible. By the application of a low-frequency electric field, a photonic bandgap appears in the transmission spectra of the structure which only prevents the propagation of the right-handed circularly polarized waves. The giant positive and negative lateral shifts are observed at the edges of this bandgap. The mentioned properties of the structure have been used in the design of the electro-optical switches. Also, it has been shown that the lateral shifts can be controlled by varying the light incidence angle, the filling fraction of metallic nanoparticles, and the thickness of the slab.

Due to physical and chemical interactions with the cell DNA, ionizing radiations induce early and late damage to the genetic material. This type of damage, which is mainly caused by single-stranded and double-stranded breaks in DNA, and if not repaired by the cell, can lead to genetic mutations or cell death. In this research, the DNA damage of living cells, induced by protons and carbon ions, which are of great importance in radiation therapy studies, has been investigated with the MCDS code. In order to check the accuracy of the MCDS code results in this research, the probability of each type of damage and the yields have been calculated and compared with the results of previous works with Geant4-DNA. The results of this research, especially double-strand breaks, are very close to the results calculated with the Geant4-DNA code. There are also differences in the results due to the difference in the cross-sections of the two codes, especially in ionization and excitation interactions, as well as the reaction rates of chemical radicals. The results of this research regarding the efficiency of double-strand breaks can be very useful in the planning of treatment with protons and carbon ions.

Nowadays, convolution/superposition(C/S) is used to calculate absorbed dose distribution by using the absorbed dose kernel(ADK). ADK describes the absorbed dose distribution per number of interaction at a small volume around the point of photon interaction. The purpose of this study is to calculate ADK and investigate its angular and radial behavior. In this study, ADK is calculated in a homogeneous water phantom in the polar coordinates by using the Monte Carlo Geant4 toolkit for monoenergetic photons with energies in the range 0.3MeV-5MeV. To study accurately, ADK is divided into several groups in order of produced charged particle set in motion at each photon interaction. Our result shows ADK rapidly decreases as the polar angle, with respect to the incident photon direction, is increased. As the radial distance from the interaction point increases, ADK is raised and then strongly decreased. ADK is symmetrically distributed around the point of interaction for low incident photon energy while forward distributed for high incident energy photons.

In this research, firstly, the structure of a double-layer phosphorene nanoribbon is introduced. Then, for the simplified structure of this system in the presence of a void, the substituted wave function which has a topological origin is analyzed analytically and the analytical results are compared with the numerical method. The Landauer-Buttiker approach is used in the numerical calculation of the substituted probability density (LDOS). Finally, for bilayer phosphorene, by considering more parameters, the wave function and the energy of the substituted state in the presence of a vacancy have been reported numerically.

Strong and long-range coupling of the magnetization dynamics of the two antiferromagnetic layers mediated by the phonons transferred through a nonmagnetic insulator has been investigated. The magnetization dynamics in one of the antiferromagnetic layers via a magnetoelastic interaction leads to the excitation of phonons and their pumping to the nonmagnetic layer. The transfer of phonons, which carry angular momentum, through a nonmagnetic insulator from one antiferromagnetic layer to another, leads to an interference pattern in the absorption spectrum, which represents the coupling of magnetization dynamics of two layers.

In this paper, we consider the four-dimensional electrodynamics with SIM(2) symmetry in a very special relativity framework. First, we examine the charge-conjugation symmetry of the action at the tree (classical) level and show that the action in this framework is charge-conjugation invariant. Then, to investigate perturbatively the preservation of charge-conjugation symmetry at the loop (quantum) level, we shall focus on one-loop graphs with an odd number of photon external lines. To this end, we use the effective action approach to obtain the general form of the photon odd-point function and study the behavior of the one and three-point function of the photon under the charge-conjugation transformation. Our analysis shows that the total amplitude of the one and three-point function vanishes and hence the charge-conjugation symmetry is preserved at the quantum level. Next, we use a non-perturbative method to show that this symmetry exists at the quantum level (to all orders) and the total amplitude of all photon's odd-point functions vanishes.

Resetting in stochastic systems is defined in different ways. In this research, a 1D non-Markovian random walk is considered. In this process, the reset changes the dynamics in a way where the random walker, after losing its memory, goes back to a fixed point in space and starts again. In this study we investigate time evolution and also the long-time limit of displacement moments in the presence of resetting. Our calculations in the long-time limit show that the probability distribution function for displacement reaches a steady-state. On the other hand, this distribution never gets to a Gaussian form for any values of the resetting rate. We will show that, in contrast to the case where the process does not undergo resetting, the moments accumulate to finite values. This is confirmed by doing Monte Carlo simulations.

Nowadays, by expanding the application of thin layers in industry and medical sciences, their fabrication methods have also received attention. One of those methods is the vaporizing material method with the help of an electron gun. The most important part in the electron gun is the electron optic, which is responsible for producing and accelerating electrons, so that it becomes possible to vaporize refractory materials in a shorter period of time by better modifying and controlling the electron beam (the shape and diameter of the electron beam) at the target location. The reduction and control of the beam diameter in this evaporation source depends on various parameters such as device geometry, magnetic field intensity, electric power, etc. Therefore, in this research, the effect of those parameters was investigated by conducting experiments and using finite element and modeling software. The simulation results revealed that the effect of the effective parameters on the beam diameter can be predicted to a good extent, so that the diameter of the electron beam decreases by changing the geometrical shape, size and displacement of the output beam components. Then, the new electron gun, compared to the existing prototype, is optimized by applying these changes in the construction of the device and conducting experiments, and its beam diameter is reduced by 40% to be more focused.

The most important nonlinear feature in the EEG response to external stimuli is the harmonic generation and entrainment which is due to the interaction between stimuli and ongoing brain oscillations. In this paper, we study the nonlinear brain dynamics and harmonic generation responses to the periodic external stimuli by employing continuum neural field model. A compact dynamical model of brain activity is first introduced, and the governing equations for the evolution of potential are obtained. Then, using the perturbation method and multiple time scales, we show brain response oscillations in harmonic drive frequency consistent with the recorded scalp EEGs from awake human subjects. Finally, to confirm the experimentally observed results of interaction between photic driving and brain dynamics, we have numerically simulated the full neural field model equations, and have shown harmonic frequency generation over a range of external frequencies.

One of the on-line range verification techniques in proton therapy is time -of-flight (TOF) measurement for prompt gamma. In this technique, the prompt gamma timing spectra is measured using the time difference between passage of the particle bunch through the target entrance of the beam and the arrival time of the corresponding prompt γ-ray at the detector.In this study, homogeneous PMMA phantom and PMMA phantoms with a slice of bone or air cavity were simulated in GEANT4 simulation. These targets were irradiated with a proton pencil beam with an initial energy of 150 MeV, and the resulting PGT spectra was recorded by scintillation detectors.Then, a code was programmed in MATLAB software to analytically solve the kinematics of proton movement in the phantom, and the PGT spectrum obtained from GEANT4 was given as an input to this software code and the prompt gamma-ray emission profiles was obtained in the phantom. In this study, the effect of the type and position of the heterogeneous slice on the PGT spectrum and the prompt gamma-ray emission profiles resulting from the PGT transformation was investigated. From the comparison of the prompt gamma-ray emission profile resulting from PGT spectra conversion, with the energy deposition spectra resulting from GEANT4 simulation, it was observed that the range shift and the shift of energy deposition location resulting from an inhomogeneity in PMMA have a significant relationship compared to the reference phantom.The presence of an inhomogeneous slice of bone and air cavity with a thickness of 10 mm shifts the range of the proton compared to its range in the reference phantom by 4 mm and 9.6 mm, respectively, and the spectra of energy deposition for these states are respectively 4.8 mm and 9.9 mm shifted relative to the energy deposition spectra of the reference phantom. Therefore, the PGT spectra reflects the proton transit time in the target material and provides the possibility of determining the prompt gamma-ray emission profiles and the possibility of confirming the delivery of the dose to the patient's body.

We study energy and spin transport in a one-dimensional Ising chain which is connected to two separate heat baths on both sides. By applying the Born-Markov approximation, within the global approach, we derive the Markovian master equation of the system, and also the explicit form of the Lindblad operators and the steady state. Thereafter, we investigate the behavior of energy and spin dynamics of the system in the global regime. Finally, we solve the problem with the local approach, and we show that the results are not the same for both approaches.

Brain cancer has the lowest survival percentage among different cancers and it has caused the death of people under  40 more than others. Therefore, in this paper, the treatment of brain cancer with non-invasive photothermal therapy is investigated and the effect of various treatment factors including laser power full width at half maximum (FWHM) of the laser beam profile on the success of the treatment is evaluated. The simulations are performed by solving the three-dimensional Pennes bioheat transfer equation, Beer–Lambert law, and by considering the presence of gold nanorods, the Gaussian laser profile, as well as the initial and boundary conditions with the finite element method (FEM). The results of the investigations demonstrate that the laser power and radius of the laser spot are two important quantities in the success of the treatment. These two quantities affect the dose of thermal energy received by the cancerous tissue and control the temperature and fraction of tumour and tissue damage in different positions. Also, smaller and larger radii of laser spot than 1.1R (R is the radius of the brain tumour) lead to more and less temperature differences, respectively, in different parts of the tumour. However, the highest temperature and temperature rate can be obtained at the upper center point of the cancerous tissue in all treatment conditions. In addition, increasing the laser power from 0.5 to 1 W causes an increase in the temperature in different points of the tumour and irreversible destruction continues even after turning off the laser due to the tumor temperature in a different position beeing higher than 42 °C, as well as heat transfer due to conduction and convection.

In this paper, zirconium carbide (ZrC) thin films were deposited on glass and aluminum substrates using DC magnetron sputtering. It was found that different ratios of acetylene gas (C2H2, as a reactive gas) in the gas mixture of acetylene and argon (Ar, as a sputtering gas) affect the microstructural properties, corrosion behavior, and protection efficiency of ZrC thin films. X-ray diffraction (XRD) was used to characterize the microstructural properties of thin films. The corrosion behavior of thin films in a 3.5% NaCl solution was evaluated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). FESEM was also employed to examine thin films' surface morphology and thickness.

In this article, we first introduce a system consisting of two dissipative cavities, in each of which there is a two-level atom. Each of the atoms is under the influence of a classical laser field, which causes the displacement of their energy levels. The correlation between two cavities is given by the field-field interaction term. We use the Gardiner-Collet model to describe the dissipation in this research. After introducing the Hamiltonian of the system, we simplify the Hamiltonian by using the Fano technique and introducing two sets of new operators. Also, with introducing the atomic bare bases, the Hamiltonian of the system will become a solvable form. Then, by using the technique of Laplace transforms, we solve the time-dependent Schrödinger equation and find the explicit form of the system's wave function at every moment of time. Having the wave function of the atom-atom system and using the concurrence criterion, we investigate the entanglement dynamics of the system in two strong and weak interaction regimes corresponding to the non-Markovian and Markovian regimes. The results show that there will be no stable state of entanglement in this system. We will also show that the classical laser field will play a constructive role in maintaining the initial entanglement as well as the generated entanglement.

Isotopic yields and half-lives for  (_ 104^266)Rf and (_104^268)Rfisotopes of the superheavy nucleus Rutherfordium are calculated and compared with the experimental data. For each fragmentation, the probability of tunneling through the fission barrier and the fission decay constant are obtained using the WKB approximation. Then, by summation over all partial fission constants, total fission constant and half-lives of two isotopes are obtained. In order to calculate the fission barrier, proximity nuclear and Coulomb potentials are considered (because of even-even isotopes, their ground state spin is zero, so centrifugal potential becomes zero.). The fission barrier as a function of fragment mass number is plotted for two isotopes. Usually, spontaneous fission occurs in superheavy nuclei in such a way that the excitation energy of the parent nucleus is low and therefore the number of neutrons emitted along with the fission is small and can be ignored. Therefore, in this method, which is known as cold spontaneous fission, instantaneous emission of neutrons along with fission is ignored. Isotopic yields of (_ 104^266)Rf and (_104^268)Rf for all possible splitting indicated that the production of two fragments  (_ 52^134)Te and (_52^132)Te have the highest partial yields for fission of  (_ 104^266)Rf and (_104^268)Rf isotopes, respectively. The existence of a small difference between the calculated and measured half-lives confirms the relative success of our method.
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In this work, the single ionization of helium atoms from the ground and the first excited state by bare carbon ions () impact at the incident energy of 100 MeV has been studied. The post form of CDW-4B formalism is used in the calculations. The correlated Silverman wave function as the ground state of the helium atom has been used to consider the effects of static electron correlation. The results, as the fully differential cross section in the azimuthal plane for different angles and the ejected electron energy 6.5 eV and momentum transfer 0.75 a.u, are compared with experimental and three-body formalism results from theory. Also, the variations of the fully differential cross section in the scattering plane for the various ejected electron energies and momentum transfers have been studied.

The standard model of cosmology,, has been successful in describing many observations. With the improvement of the number and the accuracy of observations, some inconsistencies among key cosmological parameters of the model have emerged. Many alternative models are proposed to alleviate these tensions. On the other hand, some observations of peculiar velocity show higher values than expected in a  universe which may contradict the cosmological principle. In this work, we used linear perturbation theory to measure bulk flow and  parameter in two alternative cosmological models  and XCDM. We compared measured bulk flows with the  predictions and some observations. We did a   analysis to see which model is preferred by data. We find that  model predicts higher bulk flows and is more consistent with observational data but does not reduce  tension. Bulk flows measured in the XCDM model are lower compared to  . However, this model can reconcile  tension.

Cadmium telluride nanoparticles (CdTe NPs) were deposited by the thermal evaporation method on glass substrates at a temperature of 373 K and a vacuum pressure of 2.7 mPa, and thin films with the thickness of 100 nm were fabricated. The prepared films were subjected to ultraviolet-visible (UV-Vis) spectroscopy to study the optical properties of thin films. To investigate the effect of annealing temperature on the optical properties of cadmium telluride thin films, these films were annealed at temperatures (323-373) K. The light absorption spectra of films before and after annealing were recorded using UV-Vis spectroscopy at a wavelength range of 600-1600 nm shows that the value of light absorption by films  increased with the increased annealing temperature. The optical energy bandgap of the grown films has a decrement process from 1.519 eV after annealing. The results of the Tauc plot show the decrease in energy bandgap with annealing. Extinction and refractive indices increase with increment of photon energy and annealing temperature. The relative density and electronic polarizability of grown films increase after annealing. Other optical parameters obtained in this work, including the real and imaginary parts of the dielectric constant, increase, while the surface and volume energy loss functions decrease with increase of the annealing temperature. The results of this work indicate that the deposited cadmium telluride thin films annealed at 373 K have better optical properties for photoelectronic applications.

In this research we introduce a model by adding two singlet scalars to the Higgs potential of the Standard Model and imposing scale symmetry to address the hierarchy problem. The scale symmetry plays a crucial role here. In the classical limit, all the scalars are massless. Only one of the singlet scalars and the Higgs doublet acquire non-zero expectation value. After diagonalization of the mass matrix, we have a massless singlet scalar, the so-called scalon, and two massive scalars. From quantum corrections, the scalon gets mass. Besides theoretical constraints on the parameters of the model, we impose bounds on the triple Higgs interactions provided by ATLAS and CMS detectors at the LHC.

In spite of the incredible evolutions of advanced material characterization methods, this field of research faces different technical and scientific challenges. Thermal lens spectroscopy is known as a sensitive and nondestructive optical based technique to characterize the opto-thermal properties of materials and also to diagnose the impurities in the solutions. In this research, by engaging thermal lens spectroscopy, we investigate the thermal diffusivity coefficient of ultrathin silver layers, prepared by magnetron sputtering. For this propose, the Shen theoretical model is fitted to the obtained empirical signal and subsequently, the thermal diffusivity coefficient will be extracted. The results clearly show that, in the investigated interval thickness (<15nm), the thermal diffusivity coefficient increases by increasing the thickness. Furthermore, our findings reveal that in the very fine thickness region, the thermal diffusivity coefficient shows a fair dependence on the thickness of the silver layers. This might be explained by 2D behavior of the thermal diffusivity for ultrathin metal nanolayers.