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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]

Abstract: This work examines the utilization of Geant4 to practically achieve crucial corrections, in close geometry, for self-absorption and true coincidence summing in gamma-ray spectrometry of environmental samples, namely soil and water. After validation, different simulation options have been explored and compared. The simulation was used to correct for self-absorption effects, and to establish a summing-free efficiency curve, thus overcoming limitations and uncertainties imposed by conventional calibration standards. To be applicable in busy laboratories, simulation results were introduced into the conventional software Genie 2000 in order to be reliably used in everyday routine measurements. [Copyright &y& Elsevier]

Abstract: We will present Monte Carlo simulations of a soft-quadrumer model for diblock copolymer melts where each bead of the quadrumer has a size of the order of the gyration radius of half of a block. We will show that such a model captures the micro phase separation of diblock copolymers in the bulk as well as in confinement. For the confined system the form and strength of the interaction between the soft particles representing the diblock copolymers and the wall confining the melt are determined by iterative Boltzmann inversion techniques applied to chemically realistic Molecular Dynamics simulations. [Copyright &y& Elsevier]

The absolute K-shell ionization cross sections of K and Lα X-ray production cross sections of I by 10-30 keV electron impact have been measured. The target was prepared by evaporating a thin film of compound KI to a thick pure carbon substrate. The effects of multiple scattering of electrons penetrating the target films, electrons reflected from the thick pure carbon substrates and bremsstrahlung photons produced when incident electrons impacted on the targets were corrected by using the Monte Carlo method. For K K-shell and I L-shell X-ray characteristic peaks, the spectra were fitted using the spectrum-fitting program ALLFIT to extract the Kα and Kβ peak counts more accurately for element K, and Lα peak counts for element I. The experimental results were compared with some theoretical results developed recently and available experimental data from the literature. The experimental data for I L-shell X-ray production cross sections by 10-30 keV electron impact are given here for the first time. [ABSTRACT FROM AUTHOR]

Abstract: The expectation maximization algorithm is commonly used to reconstruct images obtained from positron emission tomography sinograms. For images with acceptable signal to noise ratios, iterations are terminated prior to convergence. A new quantitative and reproducible stopping rule is designed and validated on simulations using a Monte-Carlo generated transition matrix with a Poisson noise distribution on the sinogram data. Iterations are terminated at the solution which yields the most probable estimate of the emission densities while matching the sinogram data. It is more computationally efficient and more accurate than the standard stopping rule based on the Pearson''s χ 2 test. [Copyright &y& Elsevier]

Abstract: Control rods are activated by neutron reactions into the reactor. The activation is produced mainly in stainless steel and its impurities. The dose produced by this activity is not important inside the reactor, but it has to be taken into account when the rod is withdrawn from it. The neutron activation has been modeled with the MCNP5 code based on the Monte Carlo method. The number of reactions obtained with the code can be converted into activity. In this work, a detailed model of the control rod has been developed considering all its components: handle, tubes, gain, and central core. On the other hand, the rod has been divided into 5 zones in order to consider the different axial exposition to neutron flux into the reactor. Results of the Monte Carlo simulation for the neutron activation constitute a gamma source in the control rod. With this source, applying again the Monte Carlo method, doses at certain distance of the rod have been calculated. Comparison of calculated doses with experimental measurements leads to the validation of the model developed. [Copyright &y& Elsevier]

Abstract: A method is proposed to reproduce alpha-particle spectra measured with silicon detectors, combining analytical and computer simulation techniques. The procedure includes the use of the Monte Carlo method to simulate the tracks of alpha-particles within the source and in the detector entrance window. The alpha-particle spectrum is finally obtained by the convolution of this simulated distribution and the theoretical distributions representing the contributions of the alpha-particle spectrometer to the spectrum. Experimental spectra from 233U and 241Am sources were compared with the predictions given by the proposed procedure, showing good agreement. The proposed method can be an important aid for the analysis and deconvolution of complex alpha-particle spectra. [Copyright &y& Elsevier]

Abstract: Based on the Vicanek and Urbassek theory [M. Vicanek, H.M. Urbassek, Phys. Rev. B 44 (1991) 7234] combined to a home-made Monte Carlo simulation, the present work deals with backscattering coefficients, mean penetration depths and stopping profiles for 1–4keV electrons normally incident impinging on Al and Cu thin film targets. The cross-sections used to describe the electron transport are calculated via the appropriate analytical expression given by Jablonski [A. Jablonski, Phys. Rev. B 58 (1998) 16470] whose new improved version has been recently given [Z. Rouabah, N. Bouarissa, C. Champion, N. Bouaouadja, Appl. Surf. Sci. 255 (2009) 6217]. The behavior of the backscattering coefficient, mean penetration depth and stopping profiles versus the metallic film thickness at the nanometric scale and beyond is here analyzed and discussed. [Copyright &y& Elsevier]

Abstract: An empirical stopping criterion for the 2D-maximum-likelihood expectation–maximization (MLEM) iterative image reconstruction algorithm in positron emission tomography (PET) has been proposed. We have applied the MLEM algorithm on Monte Carlo generated noise-free projection data and studied the properties of the pixel updating coefficients (PUC) in the reconstructed images. Appropriate fitting lead to an analytical expression for the parameterization of the minimum value in the PUC vector for all non-zero pixels for a given number of detected counts, which can be employed as basis for the stopping criterion proposed. These results have been validated with simulated data from real PET images. [Copyright &y& Elsevier]

Abstract: We propose an adaptive hybrid method suitable for stochastic simulation of diffusion dominated reaction–diffusion processes. For such systems, simulation of the diffusion requires the predominant part of the computing time. In order to reduce the computational work, the diffusion in parts of the domain is treated macroscopically, in other parts with the tau-leap method and in the remaining parts with Gillespie’s stochastic simulation algorithm (SSA) as implemented in the next subvolume method (NSM). The chemical reactions are handled by SSA everywhere in the computational domain. A trajectory of the process is advanced in time by an operator splitting technique and the timesteps are chosen adaptively. The spatial adaptation is based on estimates of the errors in the tau-leap method and the macroscopic diffusion. The accuracy and efficiency of the method are demonstrated in examples from molecular biology where the domain is discretized by unstructured meshes. [Copyright &y& Elsevier]

Abstract: Recently, a series of quaternary Zr-based bulk metallic glasses (BMGs), i.e., Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3, have been developed and their glass-forming ability (GFA) increases with Cu concentration. In this work, atomic structures of the three BMGs were rebuilt by reverse Monte Carlo simulations based on the reduced pair distribution functions measured by high energy X-ray diffraction. The results show that a certain amount of substitution of short Zr–Cu, Cu–Cu pairs with long Zr–Zr and Zr–Al pairs enhances the local denser packing of Kasper polyhedral centered by Zr and Al atoms. A cell sub-divided method is proposed to describe the fluctuation of local number density which is found to follow the normal distribution function. The largest possible free volume in the three alloys is found to approaches to 3.8Å. For the three alloys, the enhancement of GFA with increasing Cu content is due to the increase in the fluctuation degree of local density instead of the dense packing. [Copyright &y& Elsevier]

Thin films Backscattering Coefficients ( BSCs) for 1 to 4 keV electron and positron normally incident beams are stochastically modeled and calculated by the Monte Carlo method. We suggest a new function BSC( δ) depending only of one free parameter (to be determined) and which can describe very well the variation of the backscattering coefficient versus the film thickness ( δ). Moreover, this paper aims at discussing the observed differences between the electron and positron properties impinging on solid targets. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of bremsstrahlung spectra generated by 5–25keV electron impact on thick targets of aluminium, titanium, zirconium, molybdenum and tungsten are reported. The experimental data are compared with the simulation results of X-ray spectra obtained from the general-purpose Monte Carlo code PENELOPE, which implements accurate cross-sections for ordinary bremsstrahlung emission but disregards polarization bremsstrahlung. The agreement between the experimental and simulation results is satisfactory. This is in contrast with a recent study in which large discrepancies were observed between experimental and Monte Carlo simulation results. Our results provide evidence for the reliability of the combined choices of the interaction cross-sections and of the simulation algorithms implemented in PENELOPE for bremsstrahlung emission. [Copyright &y& Elsevier]

Abstract: The absorption enhancement observed on the CPM spectra of nanotextured silicon thin films should be attributed to light scattering effects. A detailed numerical simulation based on Monte Carlo method is presented to calculate the absorption spectra of hydrogenated nanocrystalline silicon films according to the CPM setup. The calculated spectra of apparent optical absorption coefficient depend mainly on the characteristic parameters of nano-Si:H thin film, denoted crystalline/amorphous fraction which favors bulk light scattering phenomena and the film thickness which leads to the light scattering at the rough surface. [Copyright &y& Elsevier]

Abstract: We investigate the short-time critical dynamics of the Baxter–Wu (BW) and Turban (3TU) models to estimate their global persistence exponent . We conclude that this new dynamical exponent can be useful in detecting differences between the critical behavior of these models which are very difficult to obtain in usual simulations. In addition, we estimate again the dynamical exponents of the four-state Potts (FSP) model in order to compare them with results previously obtained for the BW and 3TU models and to decide between two sets of estimates presented in the current literature. We also revisit the short-time dynamics of the 3TU model in order to check if, as already found for the FSP model, the anomalous dimension of the initial magnetization could be equal to zero. [Copyright &y& Elsevier]

Abstract: A general method is presented to explicitly compute autocovariance functions for non-Poisson dichotomous noise based on renewal theory. The method is specialized to a random telegraph signal of Mittag-Leffler type. Analytical predictions are compared to Monte Carlo simulations. Non-Poisson dichotomous noise is non-stationary and standard spectral methods fail to describe it properly as they assume stationarity. [Copyright &y& Elsevier]

Abstract: The current status of the Geant4 toolkit and the recent developments for the geometry, electromagnetic and hadronic physics for medium and high energy are presented. The focus of many recent improvements of the toolkit are key applications including the simulation of large Hadron collider (LHC) experiments at CERN. These developments and physics model extensions provide new capabilities and improvements for other applications of the toolkit for radiation studies in high energy physics (HEP), space and medical research. [Copyright &y& Elsevier]

Abstract: The trapping effect of self-interstitial atom (SIA) clusters in neuron-irradiated Fe was analyzed in terms of generic traps. The effect of the cut-off size between sessile and glissile SIA clusters was investigated. The accumulation of SIA clusters decreased drastically as the cut-off size increased, which originated from the elimination of the SIA clusters at a grain boundary through its one-dimensional motion. When the immobile generic traps were introduced to the kinetic Monte Carlo simulation model, the effect of trap parameters was assessed. An increase in the binding energy between the trap and SIA-species resulted in a decrease in the number of mono-SIAs that were dissociated from the trap and a corresponding delay in visible SIA clusters. The size-dependent prefactor for the dissociation rate of trapped SIA clusters was necessary for a realistic accumulation behavior of SIA clusters. The trap density affects the density and size of the accumulated SIA cluster density during irradiation. This parameterization of generic traps provided insight into the mechanism of accumulation of SIA and SIA cluster. [Copyright &y& Elsevier]

Abstract: A Monte Carlo scheme is described where the secondary electron generation has been incorporated. The initial position of a secondary electron due to Fermi sea excitation is assumed to be where the inelastic collision took place, while the polar and azimuth angles of secondary electrons can be calculated in two different ways. The first one assumes a random direction of the secondary electrons, corresponding to the idea that slow secondary electrons should be generated with spherical symmetry. Such an approach violates momentum conservation. The second way of calculating the polar and azimuth angles of the secondary electrons takes into account the momentum conservation rules within the classical binary collision model. The aim of this paper is to compare the results of these two different approaches for the determination of the energy distribution of the secondary electrons emitted by solid targets. [Copyright &y& Elsevier]

Abstract: The implantation and retention of Cs atoms during low-energy irradiation of different materials (Si, Ge, and InP) was investigated by dynamic computer simulations using the Monte-Carlo code T-DYN that takes into account the gradual change of the target composition due to the Cs irradiation. The Cs incorporation was studied for four impact energies (0.2, 0.5, 1, and 3keV) and for incidence angles ranging from 0° to 85°. For selected irradiation conditions, different values of the Cs surface binding energy U Cs (0.4, 0.8, and 2.4eV) were used. The total implantation fluences were chosen to lie well above the values required to reach a stationary state. The steady-state Cs surface concentration, c Cs, exhibits a distinct dependence on impact energy and angle, and on U Cs; it decreases with increasing incidence energy and angle. Furthermore, increasing U Cs results in a pronounced increase of c Cs. The computed values of c Cs appear to be higher than corresponding data from experiment. Under equilibrium, the partial sputtering yields of the target, Y X, depend only weakly on U Cs, but vary with the Cs energy and angle. Y X exhibits the usual dependence on incidence angle, first increasing up to a maximum value (at ∼65°–75°) and declining sharply for larger angles. For all bombardment conditions a clear preferential sputtering of Cs atoms as compared to the target atoms is found; typically, preferential sputtering of Cs increases with decreasing irradiation energy and incidence angle, and with decreasing U Cs. [Copyright &y& Elsevier]

Abstract: The implantation of Cs atoms in silicon was investigated by dynamic computer simulations using the Monte-Carlo code T-DYN that takes into account the gradual change of the target composition due to the Cs irradiation. The incorporation of Cs atoms was studied for incidence angles ranging from 0° to 85° and for four impact energies (0.2, 0.5, 1 and 3keV). The total implantation fluences were (1–2)×1017 Cs/cm2, well above the values required to reach a stationary state. The steady-state Cs surface concentrations exhibit a pronounced dependence on impact angle and energy. At normal incidence, they vary between ∼0.57 (at 0.2keV) and ∼0.18 (3keV), but decrease with increasing incidence angle. Under equilibrium, the partial sputtering yield of Si exhibits the typical dependence on incidence angle, first increasing up to a maximum value (at ∼70°–75°) and declining sharply for larger angles. For all irradiation conditions a strongly preferential sputtering of Cs as compared to Si atoms is found, increasing with decreasing irradiation energy (from 4.6 at 3keV to 7.2 at 0.2keV) and for nearer-normal incidence. [Copyright &y& Elsevier]

Abstract: A new sample component is presented for the Monte Carlo, ray-tracing program, McStas, which is widely used to simulate neutron scattering instruments. The new component allows the sample to be described by its material dynamic structure factor, which is separated into coherent and incoherent contributions. The effects of absorption and multiple scattering are treated and results from simulations and previous experiments are compared. The sample component can also be used to treat any scattering material which may be close to the sample and therefore contaminates the total, measured signal. [Copyright &y& Elsevier]

Abstract: The phase separation dynamics in two-dimensional binary mixtures is studied by means of a dynamic lattice liquid (DLL) model. In contrast to other methods, a simulation based on a DLL model works properly for dense systems characterized by full occupation of the lattice sites. The DLL model is a base for the first parallel algorithm which takes into account coincidences of elementary molecular movements resulting in a local cooperative structural transformation. It permits observation of a phase separation process in a system where movements of particles are highly correlated. We have investigated the influence of the proposed dynamics on a critical temperature value of TC , the domain growth and diffusion above and below TC . [Copyright &y& Elsevier]

Abstract: The thermodynamic and critical properties of two dimensional dilute XY spin magnets on a triangular lattice are studied by using a hybrid Monte Carlo method. The critical temperatures of different non-magnetic impurity densities are obtained by two types of methods, including finite-size scaling of plane magnetic susceptibility and helicity modulus. It is found that the dilution plays an important effect on the critical temperature and thermodynamic equilibrium properties. The critical temperature decreases with the increase of magnetic impurity density and the BKT phase transition vanishes at the site percolation threshold . [Copyright &y& Elsevier]

Abstract: A new algorithm is presented to improve the efficiency of neutral particle Monte Carlo radiation transport. When a radiation quantum is produced from a source or undergoes a scattering event, it is divided into two parts. One continues to undergo the normal analogue transport process. The other is deterministically transported to a randomly selected point on the surface of an arbitrary convex region, from where it continues normal transport. Application of this approach substantially improves efficiency in cases where particles must reach small geometric regions in order to make tally contributions. The algorithm is demonstrated in a simulation of X-ray scattering in a radiographic imaging application. [Copyright &y& Elsevier]

Abstract: The relative dielectric constant of three-phase porous composite materials was calculated by finite element methods, in which the geometric model was established by Monte Carlo technique and three kinds of materials were distributed in fixed proportion randomly. The variation of relative dielectric constant for three-phase materials coincided with the logarithm model very well, but for three-phase porous composite materials, changes of relative dielectric constant were different with that of three-phase materials. After careful consideration and trying, a calculation model was induced according to the computational solution. The values calculated by this model were in good agreement with the experimental findings. [Copyright &y& Elsevier]

Abstract: Three reconstruction methods based on Tikhonov regularization are used to solve the ill-posed inverse problem when incorporating Monte Carlo calculations into the β-ray induced X-ray spectrometry (BIXS) for analyzing the tritium content and depth distribution in the material surface. These methods are implemented by the GENEREG, CONTIN and REGUTOOLS codes, respectively. The tritium sample is assumed to be a molybdenum slab of 5μm thickness, and an argon gas of 5mm thickness is filled in front of the molybdenum slab. The Monte Carlo code PENELOPE is used to simulate the X-ray energy spectra induced by tritium’s β-decays. The reconstruction results for tritium depth distributions by these three codes are compared and the comparison shows that the code GENEREG can give satisfactory results. Some discussions are made. [Copyright &y& Elsevier]

Abstract: The material model presented in this paper describes elasto-plastic behaviour of the material under a cyclic load application. It takes into account damage occurrence and accumulation in the material and it’s relation to isotropic and kinematic hardening or softening. The material constitutive model for description of low-cycle fatigue behaviour is highly non-linear and therefore its parameter identification requires complex numerical procedure, such as genetic algorithm (GA). Because of its complexity, the unique genetic operators’ routines in GA calculation procedure are developed to make possible fast and reliable convergence to the results. These routines are incorporated in developed software solution. The calculation resulted in identification of material parameters that are validated in comparing material response of numerical solution with experimental data. [Copyright &y& Elsevier]

Simulations show that a phenomenon of coplanarity of most energetic subcores of γ-ray–hadron families found in mountain-based and stratospheric X-ray–emulsion chamber experiments requires to introduce a coplanar particle generation with large transverse momenta in hadron interactions at superhigh energies. Some physical mechanisms are considered. A phenomenological model, which makes it possible to simulate the coplanar particle generation, is presented. Different versions of this model are considered, their features are described and compared with those of models applied by the CORSIKA package. Cosmic-ray experimental data and simulated results are compared. Conclusion on features of hadron interactions at superhigh energies and some predictions with respect to LHC experiments are made. [ABSTRACT FROM AUTHOR]

Abstract: In this work, an evolutionary type global optimization method for identifying the stable geometries of atomic clusters is developed and applied to carbon clusters for testing purpose. Monte Carlo (MC) type local optimization is used between genetic algorithm (GA) steps together with a special mutation operation designed for the cluster geometry optimization problem. Cluster geometries and the corresponding potential energies for carbon obtained with this GA–MC hybrid method are compared with available results in the literature and reliability of the method is justified for moderate sized carbon clusters. [Copyright &y& Elsevier]

Abstract: Darwinian and Lamarckian schemes within evolutionary algorithms have been implemented and optimised. We compare the performance of these two approaches applied to the problem of structure prediction of the titania polymorphs. A number of well-known phases have thus been reproduced as well as several plausible novel microporous and dense structures. Two different potential parameter sets, within the Born model description of a solid, were employed. Following the Lamarckian concept in a genetic or more generally in an evolutionary algorithm, all new candidate structures are immediately relaxed (analogous to the ageing process in nature); consequently, competition within any current population to procreate only occurs between mature candidate structures, which correspond to local minima on the energy landscape. In the Darwinian scheme, no local optimisation is performed, which should result in significant saving in CPU time per candidate structure considered. We show, however, that the Lamarckian scheme (which ultimately searches for the global minimum on a simplified landscape) is more successful and efficient at generating the target structures. Analysis of why the Lamarckian scheme produced a perfect success rate uncovered a weakness in the Darwinian approach when diversity of the population is allowed to reduce, and further methodological developments are suggested. [Copyright &y& Elsevier]

Abstract: In transported probability density function and filtered density function methods, micromixing models are required to close the molecular mixing term. The accuracy and computational efficiency of improved versions of the parameterized scalar profile (PSP) model are assessed and compared with commonly used mixing models such as Curl, modified Curl, interaction by exchange with the mean and Euclidean minimum spanning tree. Different generalizations of the PSP mixing model for spatially inhomogeneous flow configurations are presented. The selected test cases focus on molecular mixing and avoid interference with other models. Simulation results for a three-stream problem, involving two inert scalars, and a multi-scalar test case with mean-scalar-gradients are presented. [Copyright &y& Elsevier]