Iranian Journal of Physics Research
Year:2023 | Volume:23 | Issue:3(پیاپی 93)|Papers Count:21

Scattering matrix formalism is employed to calculate the spin transfer torque in a graphene-based domain wall (DW) in the ballistic regime. We have suggested a new method for manipulating the direction of domain wall motion by both the length of the DW and magnetic barrier that is the ratio of induced exchange field to Fermi energy. It has also shown that spin current density gives us more insight into the transmission of spin-polarized electrons.

In this study, TiO2 nanotube arrays (TNTAs) are produced using an efficient, low-cost, and ecofriendly environmental anodization process in an electrolyte containing Glycerin. The TNTAs were annealed for 2 hours at 500 °C. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and photoelectrochemical properties (PEC) were used to analyze the sample. According to the obtained findings, the photoelectrochemical response of the TiO2 film was accomplished with a current density (Jph) of 0.196 mAcm-2 and photoconversion efficiency of 0.14 %.

The morphological and structural properties of NiO films have been studied to find out the possibility of exploit (exploiting) it as a gas sensor. The thin film of the nickel oxide has been obtained by a chemical spray pyrolysis technique on glass substrates using various concentrations of nickel nitrate hexahydrate [Ni(NO3)2:6H2O] aqueous solution. The produced films were characterized using X-Ray diffraction and atomic force microscopy. The investigations revealed that the crystal structure are a cubic polycrystalline with preferential orientation along the (111) plane. The topographical analyse (AFM) shows that the values of the grain size increasing with increase the concentration, where average of the grain diameter raised from 42.04-110.058 nm of 0.01 M and 0.1M concentrations respectively. The gas sensing results demonstrate that sensitivity of nickel oxide semiconductor films to the hydrogen sulfide gas are affected by the size of the growing crystallites and the operating temperature.

In this study, we have investigated the optical and high-temperature thermochromic properties of yttrium iron garnet powder and paint. The powders were produced using the solid-state reaction technique, and the thermochromic paint was sprayed over an Al alloy substrate. X-ray diffraction patterns, optical and field emission scanning electron microscopes, and UV-Vis and FTIR spectrophotometers were used to assess the structural, surface morphology and optical characteristics of the materials. The thermochromic characteristics of the samples were investigated by extracting the chromatic coordinates L*b*a* from digital pictures taken at temperatures ranging from 25 to 210 °C. The results reveal that when the temperature rises, the color of the paint changes from dark green to dark brown. The charge transfer between oxygen and iron ions, as well as the electron transition across the orbitals of the d layer, could be responsible for the observed reversible color change. The paint has strong thermal stability up to 350 °C which is suitable for high-temperature thermochromic applications.

In this paper we have studied the squeezing and entanglement properties of the cavity light generated by a three-level laser. In this quantum optical system, N three-level atoms available in an open cavity, coupled to a two-mode vacuum reservoir, are pumped to the top level by means of electron bombardment at constant rate. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, we have calculated the mean, variance of the photon number, the quadrature squeezing, entanglement amplification as well as the normalized second-order correlation function for the cavity light. In addition, we have shown that the presence of the spontaneous emission process leads to a decrease in the mean and variance of the photon number. We have observed that the two-mode cavity light is in a squeezed state and the squeezing occurs in the minus quadrature. In addition, we have found that the effect of the vacuum reservoir noise is to increase the photon-number variance and to decrease the quadrature squeezing of the cavity light. However, the vacuum reservoir noise does not have any effect on the mean photon number. Moreover, the maximum quadrature squeezing of the light generated by the laser, operating far below threshold, is found to be below the vacuum-state level. In addition, our result indicates that the quadrature squeezing is greater for than that for for 0.01 < < 0.35 and is smaller for than that for for 0.35 < < 1. We have also noted that the squeezing and entanglement in the two-mode light are directly related. As a result, an increase in the degree of squeezing directly leads to an increase in the degree of entanglement and vice versa. This shows that, whenever there is squeezing in the two-mode light, there exists an entanglement in the system.

In this paper, Ni-doped ZnO nanorods (NRs) with concentrations of (0%, 1%, 2%, and 4%) were successfully grown on glass slides by Chemical bath deposition CBD at (85-90) °C. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and UV- Vis spectrum were performed to characterize the prepared films. The results of the X-ray diffraction measurements of the samples showed that all the prepared films were of a crystalline structure of the hexagonal type with the dominance of growth in the (002) direction and a decrease in the intensity of the peak characteristic with increased Ni-doped. The FESEM images show the average diameters of ZnO NRs, Ni (1%) NRs, Ni (2%) NRs and Ni (4%) NRs, there is a clear increase in the rate of the average diameters by increasing the percentage of doping. The band gap of seed layers ZnO and undoped ZnO nanorods /glass was found to be 3.25 eV and 3.2 eV respectively. The values of the optical energy gap of Ni-doped ZnO are about (3.12, 3.09, 3) eV with an increase in the rate of doping. The results of the optical and structure measurements also included calculating parameters micro strain (ε), about the Ni doped ZnO (0%, 1%, 2%, and 4%) films for (100), (002), and (101).

This study looks at the material gain and enhanced spontaneous emission of CdSe(1-x)S(x)/ZnS and CdSe(1-x)S(x)/ZnO quantum dot (QD) structures. (remove dot) cadmium selenide (CdSe) QDs, cadmium sulfide (CdS) wetting layer (WL), zinc oxide (ZnO) and zinc sulfide (ZnS) as a barrier layers were investigated to achieve QDs semiconductor with active region (B). The energy levels and band alignment between layers are predicted using the quantum disk model. Gain is an estimation for the transverse electric (TE) and magnetic (TM) modes in QDs structures, taking into consideration the momentum matrix element. The mole-fraction (x) and contributions of the barriers (ZnO and ZnS) material in enhanced gain and spontaneous emission were investigated in this manuscript. When ZnS is used as a barrier material, the spontaneous emission is found to be 11.75×10^19 (eV.sec.cm^3 )^(-1) at x~0.69 and wavelength 324 nm, and the material gain has maximum values of order 5.671×10^4 cm^(-2) for TM and 3.743×10^7for TE modes, respectively. Whenever the barrier is changed to ZnO, the results are different; at x~0.438 and wavelength 365 nm, the spontaneous emission becomes 2.965×10^19 (eV.sec.cm^3 )^(-1) and the gain has maximum values of order 2.118×10^4 cm^(-2) for TM and 1.242×10^5 cm^(-2)for TE mode.

Structural, electronic, mechanical and optical properties of half-Heusler alloy TiPdSn were investigated from first-principles calculation as well as the structural phase transition under pressure. The projected augmented wave (PAW) type of pseudopotential within the generalized gradient approximation (GGA) was used during the calculation. The obtained results revealed that TiPdSn is a semiconductor with an indirect band gap. Also the results from the mechanical property showed that TiPdSn is ductile and mechanically stable. TiPdSn is seen to undergo structural phase transition from cubic to two different structures namely type1 and type2 which crystallize in hexagonal structure and the transition pressures recorded were 4.53GPa for type 1 and 25.3 GPa for type 2. Optical properties revealed that TiPdSn has a static dielectric function of 21.47 and a refractive index of 4.63. The band gap of the alloy decreases and later increases as pressure increases.

A spherically symmetric matter collapses under its own gravity. For the Milky Way, the time scale of collapse for a spherical halo with NFW density is ∼ 26 My which is very small compared to the age of the Milky Way. The effect of a pressure, obeying a polytrope equation of state is investigated. It is shown that for p ∝ ρ9/8, the time scale would be of the order of 1 Gy. It is also argued that such a polytrope, if considered to be in equilibrium, could explain the rotation curve of the milky way.

In the present research, g-C3N4/MIL-88B(Fe) nanocomposite photocatalyst was successfully synthesized by the solvothermal method. The morphology, crystal structure, chemical functionalities, and optical properties of the obtained nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV-Vis diffuse reflectance spectroscopy (DRS), respectively. According to the SEM and TEM images, spindle-shaped MIL-88B(Fe) nanostructures were synthesized with an average length and width of 2 and 1 μm, respectively. Furthermore, g-C3N4 nanoparticles with an average diameter of 30 nm were observed on the surface of the MIL-88B(Fe). Based on the XRD results, the presence of both g-C3N4 and MIL-88B(Fe) nanostructures in the prepared composite was confirmed. Also, the presence of functional groups of the MIL-88B(Fe) and g-C3N4 was determined by FTIR. Based on DRS analysis and Tauc's plot, the band gap energy of the prepared composite was measured as 2.1 eV, which indicated that the prepared composite could absorb light in the visible region. The degradation of organic pollutant methylene blue (MB) in the g-C3N4/MIL- 88B(Fe)+light+H2O2 system was investigated to evaluate the photo-Fenton activity of the prepared composite in comparison with light and light+H2O2 systems. The results showed that the presence of g-C3N4/MIL-88B(Fe) composite increased the degradation rate of MB pollutant under the photo-Fenton process by 8.1 and 2.8 times higher than the mentioned systems, respectively. Thus, MB removal efficiency reached 100% within 20 min of illumination. The superiority of the g-C3N4/MIL-88B(Fe)+light+H2O2 system can be attributed to the retardation of electron-hole recombination due to the presence of two nanostructures of g-C3N4 and MIL-88B(Fe) in heterojunction, which has led to an increase in the efficiency of the photo-Fenton reaction.

The secure transfer of keys between two parties, is one of the primary problems in cryptography. The possibility that the key can be manipulated or intercepted by way of an eavesdropper is the cause for the concern. A promising way to this problem is Quantum Key Distribution (QKD). The secure distribution of keys that may be used to encrypt and decrypt messages is made feasible by this approach, which makes use of the idea of quantum mechanics. QKD offers a degree of protection that can not be done by means of classical cryptography techniques, and has remarkable capability for application in a scope of fields in which secure correspondence is crucial. QKD is a field of study that has brought various conventions pointed toward empowering the safe alternate of cryptographic keys between two parties, Alice and Bob. Two key protocols within this field are the BB84 which was designed by Bennett and Brassard and E91 which was proposed by Ekert. While other protocols have been developed, many draw inspiration from these two foundational approaches. We focused specifically on the E91 protocol and explored its potential for the safe transfer of entangled pairs within computer networks. This protocol utilizes entanglement between particles as a means of verifying the security of the key exchange. Our investigation centered around testing the entanglement swapping for two particles using the E91 protocol, with the aim of developing a novel method for the secure transmission of entangled pairs via computer networks. Our findings suggest promising avenues for future work in implementing secure entanglement swapping in practical applications.

Mass composition of cosmic rays and thus determining their sources, especially at high energies, is one of the most important parts of astroparticle physics and cosmic ray science which also can help to know the universe better. Many different methods have been used to estimate the mass composition so far, which the most important of them has been done by Pierre Auger observatory group. In present work, in order to estimate the mass composition of cosmic rays, two different ways (first using from muonic component and second, maximum atmospheric depth) are used which they have been done by comparing experimental data and simulated ones. An increase in the mass composition and low flux of photons is observed at high energies. The diagram of maximum atmospheric depth in terms of energy, which is produced by extrapolation and interpolation statistical method, raises and falls meaningfully that is compatible to the results of Pierre Auger observatory. At higher energies, the percentage of primary particles have a tendency to heavier particles and in low energies the primary particles are lighter. Also, the most important breaks in the energy spectrum of cosmic rays are seen.

Considering bulk viscosity as (i) constant quantity and (ii) functions of cosmic time, the field equations in 5-dimensional Bianchi type-I model in the context of general theory of relativity, has been obtained and solved in this paper by the use of certain physical assumptions, which are agreeing with the present observational findings. In both cases, the model represents an exponentially expanding and accelerating Universe that starts with volume 0 and stops with infinite volume. The model has an initial singularity and will eventually approach the de-Sitter phase ( ). It also satisfies the energy conditions and . This model represents a matter-dominated Universe that agrees with current observational data. The model is anisotropic one and shearing throughout its evolution for . Considering bulk viscosity as (i) constant quantity and (ii) functions of cosmic time, the field equations in 5-dimensional Bianchi type-I model in the context of general theory of relativity, has been obtained and solved in this paper by the use of certain physical assumptions, which are agreeing with the present observational findings. In both cases, the model represents an exponentially expanding and accelerating Universe that starts with volume 0 and stops with infinite volume. The model has an initial singularity and will eventually approach the de-Sitter phase ( ). It also satisfies the energy conditions and . This model represents a matter-dominated Universe that agrees with current observational data. The model is anisotropic one and shearing throughout its evolution for .

In current work, new hybrid composite have been prepared by mixing gold nanocolloid physically with PVA-Fe2O3. Morphological, compositional, structure and optical properties of hybrid composites were studied by transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and UV-visible spectroscopy (UV-VIS). XRD results showed that both Au and Fe2O3 have peaks in the structure and that confirmed by EDS and FTIR results. Microscopes results indicated the nanosized nature of prepared materials. UV–vis spectrum show absorption edge at 440 nm which relates to PVA-Fe2O3 mixed with Au which means there is a red shift after incorporation of Au in the composites. And the energy gap of composite became equal to 2.48 eV after adding Au solution.

Electrons of orbitals near to nuclei of heavy atoms acquire speeds comparable to the speed of light in vacuum. Therefore, to study the properties of crystals containing heavy atoms, it is necessary to take into account the relativistic effects. In this work, using the first-principles DFT+U method, we have calculated the electronic structure and geometric properties of uranium dioxide UO2 within full-relativistic, scalar-relativistic, and non-relativistic formulations, and compared the results. It is shown that: (i) the non-relativistic scheme gives results very far form experimental values for both lattice constant and bang gap; (ii) in full-relativistic case which the spin-orbit effects are included, the Kohn-Sham band-gap is increased by 6.2% and the lattice constant decreases by 0.05% compared to scalar-relativistic one. Therefore, in the study of geometric properties of UO2, using the scalar-relativistic regime is quite accurate and one does not need to perform much more expensive full-relativistic calculations whenever one does not study the electronic excitation properties.

This paper investigates the influence of temperature anisotropy on the ignition criterion of deuterium-tritium fuel in fast ignition fusion schemes that rely on short-pulse lasers-generated shock waves. The results show that increasing the temperature anisotropy parameter, β = T⊥/T∥, unexpectedly increases the fraction of alpha particles created and deposited into the ignition domain. For β < 1, the maximum confinement parameter remains below 4 g/cm2, whereas for β > 1, it exceeds 4 g/cm2. The fusion energy fraction, fα, decreases throughout the laser pulse irradiation of the fuel (1 picosecond). A 100-fold increase in the temperature anisotropy parameter, β, leads to a 38% increase in the required plasma density times the hot spot dimension for fuel ignition. However, for β less than 1, the fusion energy fraction deposited decreases with time and reaches its minimum value of about 0.1 at the end of the laser pulse.

By specifying the electric susceptibility tensor and the magnetic permeability tensor , we introduce two isotropic but inhomogeneous media which are analogous to the Rindler space-time and the Poincaré ‎half-space‎. The propagation of electromagnetic waves in these media is investigated

The main objective of this work is to investigate a new material based on fluorine doped NiO thin films by spray deposition technique. Nickel nitrate hexahydrate Ni(NO3)2.6H2O and ammonium fluoride (NHF4) with a ratio of F/Ni = 0.04 were used to prepare F doped NiO. The structural, optical and electrical properties of F doped NiO thin films were investigated with different NiO:F solution volumes of 5, 10, 15 and 20 ml using the spray technique. The prepared F doped NiO thin films have a monocrystalline nature with a cubic structure; the (111) diffraction peak is the preferred orientation; the maximum crystallite size is 19.21 nm obtained for 20 ml. The optical property shows that the all the prepared F doped NiO thin films have a good transmittance of about 80 % in the visible region. The F doped NiO thin films deposited with 20 ml have a minimum optical gap energy of 3.51 eV and the highest value of Urbach energy of 0,689 meV. However, the thin film prepared with 5 ml has a minimum electrical resistivity of 231 Ω.cm, which can be used as a gas sensing.

In this study, we present a discrete-time non-Markov process, referred to as an Elephant Random Walk, implemented on an infinite one-dimensional lattice, with the inclusion of random memory resetting. Upon each random resetting event, the walker completely loses its memory. Through analytical calculations, we determine the moments of displacement in the presence of random resetting. Our findings demonstrate that the process does not attain a steady state. However, the long-time behavior of the moments reveals that, under specific conditions, the displacement distribution follows a Gaussian distribution. By manipulating the resetting mechanism, the transition from diffusive to superdiffusive behavior, or vice versa, can be induced in the process.

Controlling tokamak plasmas is a complex process that is affected by structured uncertainties and unmodeled dynamics. To overcome these challenges and achieve a well-defined robust behavioral outcome, it is crucial to develop standard controllers. The decoupling control theory for Multiple-Input Multiple-Output (MIMO) processes is a powerful technique that allows the mitigation or elimination of undesirable cross-coupling terms in tokamaks, making it superior to the Single-Input Single-Output (SISO) control scheme. Our study proposes two types of controllers, PID-tuned and cascaded-robust controllers, that exploit decoupling and robustness for horizontal position and current control of plasma in IR-T1 tokamak. We compare the controllers through simulations and study the impact of changing the vertical field coil voltage on the cross-coupling of these two plasma parameters. The results demonstrate that the PID-tuned controller outperforms the robust controller in terms of meeting control requirements, disturbance rejection, reference value tracking, and disruption mitigation, especially in cross-coupling controls. Of course, the definitive confirmation requires experimental studies with more diverse conditions and, finally construction and operation of these controllers in tokamaks.

Correct prediction of the behavior of UO2 crystal, which is an anti-ferromagnetic system with strongly correlated electrons, is possible by using a modified density functional theory, the DFT+U method. In the context of DFT+U, the energy of the crystal turns out to be a function with several local minima, the so-called meta-stable states, and the lowest energy state amongst them is identified as the ground state. OMC was a method that was used in DFT+U to determine the ground state. The SMC method, by leveraging only the oxygen electronic spin-polarization degrees of freedom, has indeed uncovered the multi-minima energy structure within the DFT+U approach and produced results consistent with the experimental data. In this work, we compare the SMC and OMC results and show that although the ground states of the two methods have similar energies and geometries, the electronic structures have significant differences. Moreover, we show that the GS obtained from SMC is by 0.0022 Ry/(formula unit) above that of OMC. The discrepancy in GS results between the two methods suggests that they explore minimum-energy states across different electron densities subspaces. Neither method alone is sufficient to identify the global minimum energy state. Therefore, to obtain the global-minimum state of energy one has to search over larger subspaces that involve both occupation matrices of U atoms and starting magnetization of O atoms.