جستجوی مقالات مرتبط با کلیدواژه « شبیه سازی » در نشریات گروه « فیزیک »

Inductively coupled plasma (ICP) is widely used in applications such as material processing and In this comparative study, we aim to design a dielectric barrier discharge (DBD) reactor under atmospheric pressure. The current requirement is to characterize the plasma and optimize the designed plasma system under variable circumstances. A one-dimensional time-dependent simulation of a DBD tool, driven by a sinusoidal RF voltage with an amplitude of 755 kV at 52 kHz, in argon gas is shown. The DBD device with two electrodes, covered by dielectric material and with variable dielectric constant between 2, 5 and 8 was considered, and the discharge parameters were simulated in terms of time across the plasma space to find an optimal dielectric constant for delivering maximum power deposition. Using a sinusoidal voltage to DBD device with different dielectric constant, electric field profiles, electron density, electron temperature, mass fraction of argon atoms, average electron energy, ion current density, electron current density, plasma, and power deposition are shown.

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.

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.

One popular method to produce 2D materials is the physical method of liquid phase exfoliation (LPE) utilizing ultrasound technique. In this research, our aim is to obtain the optimum conditions for the exfoliation of 2D materials of graphene from graphite utilizing LPE by simulation of ultrasonic waves irradiation and the pressure difference in the solution using COMSOL physics interactive. These simulations are carried on for the probe of 14 mm in diameter and 22 kHz in frequency, and then for the probe of 22 mm and 40 mm in diameter and 20 kHz frequency to obtain the maximum acoustic pressure difference in the solution. Then the probe, which the simulation shows produces the maximum acoustic pressure difference is used for the experimental investigation of the volume and the density of the graphite solution, which is irradiated by ultrasound for graphene, produced. The numerical simulations give an expectation to have more graphene exfoliation when the pressure difference in solution sonication is more. This expectation is verified by the experimentation. The experimental results which are analyzed using UV-visible spectroscopy, FESEM, TEM, and Raman spectrum show the probes with 14 mm and 22 mm produce less flakes which are in smaller size compared to the probe with diameter 40 mm which few-layer and even bilayer graphene with larger size are observed. Also we observed the density and the volume of the solution has importance in the layer number of the flakes production.

In this research, using the characteristic matrix theory, the three-layer V2O5/Ag/WO3 (VAW) electrode as a transparent conductive structure is designed and its optimal structure is determined. Then, a perovskite solar cell based on a VAW three-layer electrode with Glass/V2O5/Ag/WO3/PEDOT:PSS/CH3NH3PbI3/PCBM/Al structure is considered and the optical properties of the perovskite solar cell are investigated using the transfer matrix method (TMM). In the following, it is shown that the effects of changing the thickness of the WO3 layer on the optical properties of the three-layer VAW and the perovskite solar cell based on the VAW electrode are more significant than the effects of changing the thickness of the layer V2O5. The maximum short circuit current density (19.3 mA/cm2) in the perovskite solar cell based on the VAW electrode was obtained for the thicknesses of the V2O5 layer of 40 nm and WO3 layer of 55 nm, which is 12.2% higher than the calculated value for perovskite solar cell based on ITO electrode (17.2 mA/cm2). Finally, the perovskite solar cell based on the optimized VAW electrode was fabricated and the results showed that this solar cell has better performance than solar cell based on the commercial ITO electrode.

In a polywell reactor, it is critical to have a stable and energetic virtual cathode that is necessary to accelerate ions and create fusion interactions. Increasing the confinement time of virtual cathode electrons is of critical importance in the performance of polywell reactors. In this paper, COMSOL Multiphysics software was used to perform a three-dimensional numerical simulation in order to investigate the impacts of effective variables of a polywell on the virtual cathode. The findings indicated that the confinement time depends on the distance between the coils, coil radius, coil current, and the kinetic energy of the injected electrons. In addition, by using the simulation results, the dependence of the mentioned parameters on the confinement time is obtained, and then a mathematical model was developed.

In this study, the 199Au nanoparticles production parameters have been investigated by a two-part study.The first part is about the indirect method for production of non-carrier-added (NCA) 199Au radionuclide which was investigated both theoretically and experimentally. We applied MCNPX-2.6 code, TALYS-1.9, and ALICE code, aiming to simulate the reactor core of Tehran Research Reactor (TRR) and determining the activity of 199Au by MCNPX code using cross-sections calculated by TALYS-1.9 and specifying the production yield of 199Au. Also, the excitation function of 199Au was calculated via  reaction by TALYS-1.9 and ALICE/ASH-0.1 codes. As the corresponding experimental approach, we worked on the reactor production of 199Au by utilizing  thermal neutron flux through irradiation of natural Pt target for a specified irradiation time of 21 hours and 10 minutes in TRR. Regarding our facilities for evaluating the production yield, two samples of 11 mg and 15.5 mg natural Pt targets were bombarded in TRR. Because the natural Pt target, consists of five different stable isotopes (192Pt, 194Pt, 195mPt, 196Pt, 198Pt), some radionuclides as impurities will be produced during the reactor bombardment. So, using an enriched Pt target will increase the production yield together with a reduction of the impurity production. To separate 199Au radionuclide from the impurities mentioned above, and also to calculate both the chemical yield and the radionuclide purity of 199Au, two chemical separation techniques were applied. In the first technique, 199Au radionuclide was separated from impurities by employing liquid-liquid extraction (LLX) using ethyl acetate. As a result of this separation, the chemical yield of 199Au radionuclide was more than 99%. In the second technique, 199Au was separated by employing LLX using liquid cation exchanger, Di-(2-Ethylhexyl) phosphoric acid (HDEHP). By applying this technique, the chemical yield of 199Au radionuclide was more than 80% consequently. We calculated the theoretical findings and compared the results with the related experimental values.In the second part of the present study, the synthesis of radioactive 199Au nanoparticles (199AuNPs) have been investigated by the Turkevich method with the aim of produce citrate-gold nanoparticles with different sizes of approximately 50 nm. Possible uses and applications of 199Au nanoparticles in medicine are also discussed.

In this study, calculations related to the mass attenuation coefficient (µ/ρ) of Polyethylene/Bismuth Oxide composite (HDPE-Bi2O3) for different weight percentages of Bi2O3 in the polymer matrix, namely 0 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt% and 8 wt% for photons with 59 keV energy that can be used in dental radiography centers were simulated using the MCNP code and results were compared with XCOM data. The simulation results of the mass attenuation coefficient of the composite in different weight fractions via the methods of MCNP and XCOM at 59 keV showed a good agreement with each other. The results of this study showed that the Polyethylene/Bismuth Oxide composite material in optimal weight fraction and thickness can be used as a radiation shield in dental radiography centers.

Patient dosimetry plays the essential role in nuclear medicine performed with various method in clinical and research approaches. There are many methods for internal dosimetry which Monte Carlo code with high accuracy has the crucial place compare to others. The principle reason that Monte Carlo couldn’t performed as the clinical method is the high computation time. This method could be use in the complex geometry such as patient but before the implementation of the code, accreditation should be done. This paper aim to present the method of validation the Gate Monte Carlo codes in PET nuclear medicine. The researches were carried out with experimental tests by head and TLD dosimeters and the results were compared with GATE outputs at the same geometry. In the second steps, ICRP110 phantom in two state of lunge to lunge as a source to target organ and liver to lung considered the MIRD internal dosimetry method had been simulated. The S factor were the results of the simulation codes compared with MCNPX Monte Carlo results in the same conditions. The result has shown the accordance between the simulation and experimental data with high accuracy and highlights the role of Monte Carlo in complex geometry as the high accurate and validate methods.

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

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

In this paper, the variations of particles distribution function (DF) in a one-dimensional collisionless plasma expansion are studied. It is shown that, for the self-similar cases the initial Maxwellian distribution function of ions gradually converse to a δ-like one. So, the dynamic of the ions could be considered with fluid equations. On the other hand, for the effects of charge separation that occurs assuming the expansion of finite plasma, the process of plasma expansion imposes variations on electrons DF which causes it to change from Maxwellian to a non-Maxwellian one. In order to investigate the electrons DF at each moment, a particle simulation is used. In this simulation, the electrons dynamic is determined by Vlasov equation. Ions dynamic is given by fluids equations. Finally, it is indicated that, the higher energy tails of electrons DF in the main body of plasma are descended due to the motion of high energy electrons into vacuum and the electrons DF transforms to a super-Maxwellian DF. In the opposite side, at ion front zone which is the place of high energy electrons presence, electrons DF transform from Maxwellian to Lorentzian case with the high energy tails

One of the driving factors for creating axial flow inside the gas centrifuge rotor to increase the separation performance is the scoop. Due to the exposure of the scoop to the high Mach gas flow, the flow will be shocked, and strong gradients will occur in the flow.  In this research, the gas flow around the scoop in a two-dimensional state (r-θ) is simulated by the Direct Simulation Monte Carlo method (DSMC) using the dsmcFoam solver at different distances of the scoop from the rotor wall. The results show that increasing the distance of the scoop from the rotor wall and decreasing the contact angle of the gas flow with the scoop reduces the maximum temperature and drag force. For instance, increasing the distance of the scoop from the wall by 31% (from 8 to 10.5 mm) in 3800 Pa wall pressure and 85° contact angle, causing a maximum temperature decrease of 1.3% (from 596 to 588 K) and also the drag force is reduced by 49.4% (2412 to 1221 dyn). Furthermore, reducing the angle of the gas flow with the scoop by 11.8% (from 85 ° to 75 °) in 3800 Pa wall pressure and at the distance of the scoop from the wall equal to 10.5 mm causes a maximum temperature decrease of 6.8% (from 588 To 548 K) and the drag force is reduced by 50.3% (1552 to 771 dyn).

In this research, squeezing fragility due to thermal bath, in quantum squeezed state generation, is simulated. For this purpose, single mode dissipative cavity with non-zero second-order susceptibility is used. Cavity nonlinear medium is driving by laser pump with known frequency, and pairs of identical photons are created, with one-half frequency of driving pump. This process known as degenerate parametric down conversion. In the absence of any dissipation, simulation shows linear time dependent squeezing parameter, which is in agreement with theoretical results. In two photon loss of cavity in contact with cold reservoir, competition between gain and two photon loss, results in stable squeezing of initial vacuum, in steady state of system. At the end, has been shown that, non-zero thermal reservoir, omits the squeezing and leads the final cavity field to the thermal mixture of Fock states.

Supercapacitors as electrical energy storage systems are widely known devices and due to the complexity of these systems, the numerical simulation is a fundamental approach to investigate their charging mechanism. Geometric effects of the pore are important on the electrical capacitance properties of supercapacitors. In this paper, the effects of linear pores width on their ion-philic behaviors are investigated. For this purpose similar linear pore systems that only differ in the pores’ width are simulated by using the PLT algorithm implemented in CAVIAR. The systems are simulated at two different applied voltages: 0 and 2 V.  It was shown that the width is an important factor, that is, a larger pore width shows more ion-philic behaviors.

Radiation therapy, the most common and successful treatment used after surgery, plays an important role in the treatment of cancer. In proton therapy, the tumor is irradiated by proton beam. To increase the treatment efficacy of breast tumors, gold nanoparticles (GNP) and boron-sodium boron (BSH) solution containing boron-11 can be injected separately into the tumor and then irradiated with proton beam. In this study, using Geant4 / Gate7 simulation, confirming the increase in the dose reached the breast tumor tissue in proton therapy was performed through two separate stages, so that in the first stage, in order to maximize the received dose by protons in the tumor, injection of sodium boron captate (BSH) containing boron-11 was used in the presence of proton beam irradiation. Also, based on the injection of different concentrations of sodium boron captate solution containing boron-11 into the breast phantom, using the Monte Carlo code Geant4 / Gate7, the number of emitted alpha particles caused by the reaction  11Bp,α 8Be estimated. As a result of alpha-proton-alpha avalanche reaction, the amount of alpha particles produced by p+ 16O→α+ 13N  more than the alpha particles produced by the reaction produced due to the  11B+p→3α+8.7MeV The findings of the simulations show that the location of the Bragg peak inside the tumor changes with increasing energy to higher depths. Also, by injecting gold nanoparticles in different amounts of 25, 50 and 75 mg / ml with simultaneous irradiation of proton beam, the absorbed dose is up to 1.75% compared to the absorbed dose due to the injection of sodium boron captate solution containing boron-11 with the same values increase. In other words, the results of this study confirm the ability of gold nanoparticles to increase the effectiveness of treatment by increasing the absorption dose in breast tumors using proton therapy.

Plasmonic science has been noticed by researchers, with the increasing development of knowledge and technology in nanometer dimensions. Gold and silver ellipsoidal metal nanoparticles can exhibit unique optical properties due to their ellipsoidal structure with special symmetry and are therefore very suitable options for use in the new generation of optical sensors. Therefore, in this work, the optical properties of gold and silver metal ellipsoidal nanoparticles were simulated in different dielectric environments as well as in different sizes with using the MATLAB program. The results show that with increasing the diameter of the ellipsoidal nanoparticles (flattened state) of gold, the peak of the absorption, scattering and extinction spectra increases, which can be a good option for plasmonic applications and optical devices. Also, compared to ellipsoidal nanoparticles (elongated state), the absorption and extinction efficiencies intensity are higher and the scattering peak appears at higher wavelengths, while for the elongated state, ellipsoidal nanoparticles do not show such a case. Due to the small number of conducting electrons in nanoparticles and the homogeneous displacement of free charges within the nanoparticle, it is only the bipolar distribution of free charges that causes single peaks in the extinction and absorption spectrum of ellipsoidal gold and silver nanoparticles.

Dual-energy X-ray radiography is an important inspection technology in imaging large cargos for finding illegal materials such as explosives, narcotics, weapons, etc. A useful aspect of dual-energy X-ray radiography is the possibility of discriminating and identifying materials with different atomic numbers which can be obtained by imaging large cargos at two different X-ray energies (normally above 3 MeV). In the present work, first a dual-energy X-ray radiography system including X-ray sources, collimator, and detector array was simulated using MCNPX code. Then, the obtained data from this radiography system for four step wedges of graphite, aluminum, steel, and lead materials were gathered and material discrimination curves were obtained using four algorithms including log-log, R-T, r-θ, and α2-α1. The results show that among the proposed algorithms for material discrimination, R-T, r-θ, and α2-α1 algorithms have better performance and due to the less overlap of material discrimination curves for low sample thicknesses, R-T algorithm can be a better choice for obtaining material discrimination curves in dual-energy radiography systems.

Among the four stable isotopes of sulfur, the heaviest isotope, 36S, has found many applications in radioisotope production and neutron activation. In the present work, due to the very low natural abundance of 36S, the single withdrawal cascades are used to separate this isotope. The concentration distribution equations in the transient state are separated using the Laasonen method and linearized by the q iteration method to simulate the cascade. The code is validated using existing experimental results. To separate the 36S isotope to a high concentration of 90% by a fixed number of centrifuge machines, different arrangements of the square single withdrawal cascades, the feed stage location, and the feed flow rate were investigated. In the arrangement with 15 stages and eight centrifuge machines at each stage, the concentration of 36S in the reservoir reaches 95% after 1460 hours. The results showed that reducing the feed flow of the cascade and increasing the distance of the feed stage from the reservoir leads to an increment in the concentration of 36S in the reservoir.

The use of metal matrix composites can provide a combination of desirable properties of metals as well as the special physical properties of neutron absorber reinforcing particles such as boron carbide, which alone may be brittle. Therefore, in the present study on neutron attenuation power of composite shielding, several Al-B4C composite samples with weight fractions of 5, 10 and 20% B4C have been used. In order to investigate the neutron absorption properties of the studied samples, the MCNP Monte Carlo code and the neutron source of the dry channel of the MNSR reactor with a flux of 2.13E+5 n.cm-2.s-1 have been used  ,which provided in nominal reactor power of 30 kW. The results show that the neutron flux in the presence of 5, 10 and 20% boron carbide samples is predicted to be 1.32E+05 n.cm-2.s-1,1.12E+05 n.cm-2.s-1 and 1.07E+05 n.cm-2.s-1, respectively. With this increase in the percentage of reinforcement phase, neutron flux is reduced down to 50%.