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Different deterministic solution methods are being used to solve the criticality problem of the reflected systems with different anisotropic behaviours for both fission neutrons and neutrons undergoing scattering. In the present study, the criticality problem is simulated using the developed Monte Carlo algorithm. Different angular distributions, such as Inönü, Anlı–Güngör and tetra-anisotropic kernels are taken into account. For each anisotropic kernel, the sampling method of the direction cosine of either newborn fission neutrons or scattered neutrons is presented by extracting the required probability distribution function (PDF). The simulation starts with an initial guess and following the presented procedure, the criticality thickness of the system is estimated with a certain convergence criterion. Different variance reduction methods, such as implicit capture, Russian-roulette and splitting, are also implemented to get more precise results with a reasonable computational time cost. The validity of the presented method is verified by comparing with the results of different deterministic methods. Finally, using an exact scattering function, the three considered kernels are compared with each other. It is seen that the tetra-anisotropic kernel is the best among the considered kernels. [ABSTRACT FROM AUTHOR]

Structural properties, such as mechanical and electrical properties of materials irradiated with γ-rays are affected by displacement damage. Successive processes with different behaviours ultimately lead to the formation of sets of ‘defects’ within the material, and as an example, it may cause the substance to become brittle. In this study, Monte Carlo codes provide information using a code-based simulation method on primary knock-on atoms, or PKAs, that cause damage. Also, the rate of damage caused by the gamma radiation from the cobalt-60 source on the structural properties of iron is calculated. To access PKA information, a program called GAMMATRACK has been developed. This software provides information about the rejected atoms' properties and the interaction kinematics. The theoretical calculation method has also been used to confirm the results of the Monte Carlo method. Using the generated secondary electrons, the stopping and range of ions in matter (SRIM) code can calculate the damage caused by gamma radiation. PKA data were extracted by the GAMMATRACK program, which can be used as input for the SRIM code for the systematic analysis of gamma damage. The obtained PKA spectrum for iron agrees with the previous works. It is realised that only monovacancies are produced, and under cobalt-60 irradiation, the possibility of the atom–atom collision is negligible. Therefore, creating PKA cascades will be ruled out. Also, the damage rate for an iron target is calculated at ~10−7, 10−8 (displacement per atom (DPA) / year) for both theoretical and Monte Carlo method (MCNPX + SRIM code) computations. [ABSTRACT FROM AUTHOR]

This work examines the origin of the abnormal magnetism exhibited by CuMnFe–PBAs modified with multi-walled carbon nanotubes (MWCNTs). The system of CuMnFe–PBAs@MWCNTs coexists with both large and small clusters. CuMnFe–PBAs clusters have an average particle size of 28 nm, and some of the smaller particles are adsorbed on the surface of MWCNTs. Surprisingly, the magnitude of magnetization increases linearly with decreasing temperature. When above the Curie temperature, the magnitude of magnetization is significantly greater than that of PBAs without being modified. This phenomenon can be attributed to magnetostatic interactions between ultra-fine magnetic nanoparticles adsorbed on the surface of MWCNTs. Using the Monte Carlo method, we simulated the magnetostatic interaction of cylindrical adsorbed particles, and the simulation results are almost identical to those observed experimentally. The results indicate that 0.089 CuMnFe–PBAs clusters per 1 nm2 can be adsorbed onto the surface area of MWCNTs. We demonstrate that MWCNTs adsorbing magnetic particles exhibit magnetic behavior, and suggest a method for producing ultrafine materials. It also introduces a new method of calculating the adsorption efficiency of carbon nanotubes, offering theoretical guidance for future research on nanomaterials with enhanced adsorption efficiency. [ABSTRACT FROM AUTHOR]

We study canonical and affine versions of the quantized covariant Euclidean free real scalar field-theory on four dimensional lattices through the Monte Carlo method. We calculate the two-point function near the continuum limit at finite volume. Our investigation shows that affine quantization is able to give meaningful results for the two-point function for which is not available an exact analytic result and therefore numerical methods are necessary. [ABSTRACT FROM AUTHOR]

Swarm intelligence method is an effective way to improve the particle degradation and sample depletion of the traditional particle filter. This paper proposes a particle filer based on the gravitation field algorithm (GF-PF), and the gravitation field algorithm is introduced into the resampling process to improve particle degradation and sample depletion. The gravitation field algorithm simulates the solar nebular disk model, and introduces the virtual central attractive force and virtual rotation repulsion force between particles. The particles are moves rapidly to the high-likelihood region under action of the virtual central attractive force. The virtual rotation repulsion force makes the particles keep a certain distance from each other. These operations improve estimation performance, avoid overlapping of particles and maintain the diversity of particles. The proposed method is applied into INS/gravity gradient aided navigation, by combining the sea experimental data of an inertial navigation system. Compared with the particle swarm optimization particle filter(PSO-PF) and artificial physics optimized particle filter (APO-PF), the GF-PF has higher position estimate accuracy and faster convergence speed with the same experimental conditions.

The indoor absorbed gamma dose rate in air is calculated by a simple theoretical model. The dose inside any room is put in a relation to that of some reference room by using some correction factors that are estimated by the MCNP5 simulation code. These correction factors reflect the effect of the different elements that control the value of the dose. The radiation considered in this study is the natural one due to the uranium series 238U, the thorium series 232Th and the potassium radionuclide 40K. The affecting elements include the main ones like the thickness, density and dimensions of the different parts of the room, in addition to some other factors, e.g., the division of some walls and the existence of adjacent rooms, doors, windows and partial inner walls. A special factor is the exhalation of radon from building materials. The scheme of studying that last factor is utilized to calculate radon exhalation rates from both the building materials and the soil. [ABSTRACT FROM AUTHOR]

Determination of the thickness of a nanometer thin film is an important topic in the nanostructure characterization field. Currently, the X-ray photoelectron spectroscopy and the ellipsometer have been used to analyze the film thickness. This work proposes another thickness measurement method based on secondary electron (SE) and backscattered electron (BE) yields which are produced by an electron beam with a certain energy. Through comprehensively analyzing a lot of simulated data of the ratio of SE to BE yields at different primary energies and overlayer thicknesses for a variety of overlayer/substrate structures, a semiempirical formula was obtained for the film thickness determination (up to 5 nm). According to the formula, the film thickness can be obtained based on the measured ratio of SE to BE yields. A specific example shows a good agreement is reached between the simulated and experimental measurements in the case of the Be/Pt systems. [ABSTRACT FROM AUTHOR]

Previous works have highlighted the suitability of the concept of fractal structure, which derives from asymmetric topology, to propound generalized definitions of fractal dimension. The aim of the present article is to collect some results and approaches allowing to connect the self-similarity index and the fractal dimension of a broad spectrum of random processes. To tackle with, we shall use the concept of induced fractal structure on the image set of a sample curve. The main result in this paper states that given a sample function of a random process endowed with the induced fractal structure on its image, it holds that the self-similarity index of that function equals the inverse of its fractal dimension.

Variational Monte Carlo method was employed to investigate the total energies of the excited states 210+, 310+, 110-, 130+, 130-, 230+, 11-1+ and 13-1+ of the helium atom. Strong magnetic field effect on the energy is investigated and illustrated graphically. The point of transition from the ground state to 13-1+ state was obtained and comparisons with previous works were introduced. The results concluded comply with the most recent, accurate and the exact values. [ABSTRACT FROM AUTHOR]

Positron implantation profiles in various materials for 22Na isotope source are discussed. The spatial distribution of positrons in materials with densities from 1 to 21 g/cm³ are simulated using GEANT4 code. The results indicate that depth distributions of thermalized positrons in any homogeneous medium can be described by the sum of two exponential functions. Contribution of the short-range exponent is about 11% in the materials. The both absorption coefficients can be well represented as a function of material density and atomic number. Proposed empirical model agrees well with available experimental data. [ABSTRACT FROM AUTHOR]

One of the key aspects regarding the technological development of nuclear fusion reactors is the understanding of the interaction between high-energy ions coming from the confined plasma and the materials that the plasma-facing components are made of. Among the multiple issues important to plasma–wall interactions in fusion devices, physical erosion and composition changes induced by energetic particle bombardment are considered critical due to possible material flaking, changes to surface roughness, impurity transport and the alteration of physicochemical properties of the near surface region due to phenomena such as redeposition or implantation. A Monte Carlo code named MATILDA (Modeling of Atomic Transport in Layered Dynamic Arrays) has been developed over the years to study phenomena related to ion beam bombardment such as erosion rate, composition changes, interphase mixing and material redeposition, which are relevant issues to plasma-aided manufacturing of microelectronics, components on object exposed to intense solar wind, fusion reactor technology and other important industrial fields. In the present work, the code is applied to study three cases of plasma material interactions relevant to fusion devices in order to highlight the code’s capabilities: (1) the Be redeposition process on the ITER divertor, (2) physical erosion enhancement in castellated surfaces and (3) damage to multilayer mirrors used on EUV diagnostics in fusion devices due to particle bombardment. [ABSTRACT FROM AUTHOR]

Metastable Fe-Cu alloys are of considerable scientific interest, and an efficient interatomic potential is crucial for reliable atomistic simulations. Interatomic potentials developed for pure Fe and pure Cu are difficult to mix for the Fe-Cu alloys since the analytic function form of pure Fe is not of the same type of pure Cu potential. Additionally, elemental potentials taken from alloy descriptions may not work well for the pure species. This is particularly true if the elements were fit for compounds instead of being optimised separately. In this article, we present compatible analytic function forms that work for pure species and are easily mixed with two adjustable parameters for their alloys. We tested the proposed potentials to make sure that the performance is adequate for pure species as well as their alloys. The predicted values were in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The ground state energy of hydrogen molecular ion confined by a hard prolate spheroidal cavity is calculated. The case in which the nuclear positions are clamped at the foci is considered. Our calculations are based on using the variational Monte Carlo method with an accurate trial wave function depending on many variational parameters. The results were extended to also include the HeH++ molecular ion. The obtained results are in good agreement with the most recent results. [ABSTRACT FROM AUTHOR]

We have focused on temperature changes in the collimator at the TARLA bremsstrahlung photon facility. One of the important parameters during the design of an ideal collimator, especially for high-energy photons, is temperature rise in the collimator material. For this purpose, energy deposition in the collimator materials was simulated using the FLUKA Monte Carlo code. Depending on energy deposition values, temperature rise in the collimator materials of Al, Cu and Fe was calculated for photon beams with 8-32 MeV energies. [ABSTRACT FROM AUTHOR]

A collection of six novel bootstrap algorithms, applied to probability-proportional-to-size samples, is explored for variance estimation, confidence interval andp-value production. Developed according to bootstrap fundamentals such as themimickingprinciple and theplug-inrule, these algorithms make use of an empirical bootstrap population informed by sampled units each with assigned weight. Starting from the natural choice of Horvitz–Thompson (HT)-type weights, improvements based on calibration to known population features are fostered. Focusing on the population total as the parameter to be estimated and on the distribution of the HT estimator as the target of bootstrap estimation, simulation results are presented with the twofold objective of checking practical implementation and of investigating the statistical properties of the bootstrap estimates supplied by the algorithms explored. [ABSTRACT FROM AUTHOR]