Monte Carlo Model Predictions Research Articles

Kinetic Modeling of Radiation Belt Electrons With Geant4 to Study Energetic Particle Precipitation in Earth's Atmosphere

AbstractWe present a new model designed to simulate the process of energetic particle precipitation, a vital coupling mechanism from Earth's magnetosphere to its atmosphere. The atmospheric response, namely excess ionization in the upper and middle atmosphere, together with bremsstrahlung X‐ray production, is calculated with kinetic particle simulations using the Geant4 Monte Carlo framework. Mono‐energy and mono‐pitch angle electron beams are simulated and combined using a Green's function approach to represent realistic electron spectra and pitch angle distributions. Results from this model include more accurate ionization profiles than previous analytical models, deeper photon penetration into the atmosphere than previous Monte Carlo model predictions, and predictions of backscatter fractions of loss cone electrons up to 40%. The model results are verified by comparison with previous precipitation modeling results, and validated using balloon X‐ray measurements from the Balloon Array for RBSP Relativistic Electron Losses mission and backscattered electron energy and pitch angle measurements from the Electron Loss and Fields Investigation with a Spatio‐Temporal Ambiguity‐Resolving CubeSat mission. The model results and solution techniques are developed into a Python package for public use.

Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 text {Te}text {V} with an integrated luminosity of 3.2~text{ fb }^{-1}. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.

Monte Carlo simulation of polarization-sensitive second-harmonic generation and propagation in biological tissue.

Polarization-sensitive second harmonic generation (p-SHG) is a nonlinear optical microscopy technique that has shown great promise in biomedicine, such as in detecting changes in the collagen ultrastructure of the tumor microenvironment. However, the complex nature of light-tissue interactions and the heterogeneity of biological samples pose challenges in creating an analytical and experimental quantification platform for tissue characterization via p-SHG. We present a Monte Carlo (MC) p-SHG simulation model based on double Stokes-Mueller polarimetry for the investigation of nonlinear light-tissue interaction. The MC model predictions are compared with experimental measurements of second-order nonlinear susceptibility component ratio and degree of polarization (DOP) in rat-tail collagen. The observed trends in the behavior of these parameters as a function of tissue thickness, as well as the overall extent of agreement between MC and experimental results, are discussed. High sensitivities of the susceptibility ratio and DOP are observed for the varying tissue thickness on the incoming fundamental light propagation pathway.

CHARACTERISATION OF THE GRAPHITE MODERATED THERMAL NEUTRON FIELD AT CMI

The graphite pile was set up at CMI to provide reference thermal neutron field for metrology and dosimetry purposes. It consists of three Pu-Be and three Am-Be radionuclide sources located in a 1.95 m (width) × 1.95 m (length) × 2.0 m (height) graphite moderator block. The neutron field in the volume of the experimental channel with dimensions of 40 cm × 40 cm × 135 cm (depth) was characterised experimentally and by Monte-Carlo calculations. Neutron fluence was determined by the activation of gold foils and Manganese tablets irradiated in nine different positions and by two 3He detectors of different construction irradiated in one position (bare and covered in three spherical PE moderators of 3, 3.5 and 4 inch diameter). Weighted mean value of the neutron fluence rate measured by all the abovementioned detectors in the pile centre was 2.91 × 104 cm-2 s-1 ± 1.8%. This value was used as a calibration factor for the Monte-Carlo model predictions. The neutron spectral fluence rate calculated by validated Monte-Carlo model was used to determine the conventionally true ambient and personal dose equivalent rates at different positions.

Coupling the Six Flux Absorption–Scattering Model to the Henyey–Greenstein scattering phase function: Evaluation and optimization of radiation absorption in solar heterogeneous photoreactors

Robust and practical models describing the radiation field in heterogeneous photocatalytic systems, used in emerging environmental, photochemical and renewable energy applications, are fundamental for the further development of these technologies. The six-flux radiation absorption–scattering model (SFM) has shown to be particularly suitable for the modeling of the radiation field in solar pilot-plant photoreactors. In this study, the SFM was coupled to the Henyey–Greenstein (HG) scattering phase function in order to assemble the model with a more accurate description of the scattering phenomenon provided by this phase function. This new version of SFM, named as SFM-HG, was developed through fitting the Local Volumetric Rate of Photon Absorption (LVRPA) determined in a flat photoreactor to the “pseudo-experimental” LVRPA calculated by a Monte Carlo (MC) approach, which included the HG expression. As a result, simple mathematical correlations describing the SFM-HG scattering probabilities as function of the HG scattering parameter were determined. The SFM-HG was validated through a comparison with the MC model predictions of the Total Rate of Photon Absorption (TRPA) in the slab photoreactor. A RMSE% of approximately 5% demonstrated satisfactory agreement between the models. The SFM-HG was further applied to evaluate the impact of selected scattering phase functions on the absorption of radiation in solar photoreactors, operated with commercial TiO2 photocatalyst. The results have established that, the apparent optical thickness, τapp (or τapp,max for tubes) a parameter derived from the SFM approach, is the most appropriate for the design and optimization of photocatalytic reactors. This parameter is insensitive to scattering albedos and phase functions. CPC, tubular and flat-plate photoreactors should be designed with τapp,max=12, τapp,max=7 and τapp=4.5 respectively.

Application of a Monte Carlo model to predict space heating energy use of Belgrade's housing stock

Detailed domestic stock energy models can be used to help formulate optimum energy reduction strategies. However, there will always be considerable uncertainty related to their predictions due to the complexity of the housing stock and the many assumptions required to implement the models. This paper presents a simple Monte Carlo (MC) model that can be easily extended and/or transformed in relation to data available for investigating and quantifying uncertainties in both the housing stock model's predictions and scenario assumptions. While 90% of the MC model predictions fell within a range which is ±19% the mean value, 50% of them were within ±8% of the mean. The findings suggest that the uncertainties associated with the model predictions and scenario assumptions need to be acknowledged fully and – where possible – quantified as even fairly small variability in the influential variables may result in rather large uncertainty in the aggregated model's prediction.

Monte Carlo Model for Arborescent Polyisobutylene Production in the Batch Reactor

A Monte Carlo (MC) model is developed to predict molecular weight distribution and branching during the production of arborescent polyisobutylene. The model describes self‐condensing vinyl copolymerization (SCVCP) of isobutylene and inimer via living carbocationic polymerization. Six different propagation rate constants are required to account for two types of vinyl groups and three types of carbocations in the system. MC model predictions are better than predictions from a previous PREDICI material balance model because fewer simplifying assumptions are required. The MC model predictions reveal that reactions that were previously neglected have an important influence on polymer properties.

Underlying event studies and charged particle multiplicities in inelastic pp events with the ATLAS detector

Underlying event studies and charged particle multiplicities with the ATLAS detector in inelastic p– p collisions at center of mass energy of 900 GeV and 7 TeV are presented. The charged particle density, its dependence on pseudo-rapidity and transverse momentum and its correlation with the average transverse momentum are measured for events with at least two charged particles in the kinematic range | η | < 2.5 and p T > 100 MeV . For Underlying Event studies, the transverse momentum of charged tracks is required to be greater than 500 MeV. The measurements are compared with different Monte Carlo model predictions.

Assessment of Collisional-Energy-Based Models for Atmospheric Species Reactions in Hypersonic Flows

A recently proposed set of direct simulation Monte Carlo chemical reaction models, based solely on the collisional energy and the vibrational energy levels of the species involved, is applied to calculate equilibrium and nonequilibrium chemical reaction rates for atmospheric reactions in hypersonic flows. The direct simulation Monte Carlo model predictions are in good agreement with Park's model, several theoretical models, and experimental measurements. Physically plausible modifications to some of the direct simulation Monte Carlo models are presented that improve agreement. The observed agreement provides strong evidence that modeling of chemical reactions based on collisional energy and vibrational energy levels provides an accurate method for predicting equilibrium and nonequilibrium chemical reaction rates.

Proton-Air Cross Section and Extensive Air Showers

Hadronic cross sections at ultra-high energy have a significant impact on the development of extensive air shower cascades. Therefore the interpretation of air shower data depends critically on hadronic interaction models that extrapolate the cross section from accelerator measurements to the highest cosmic ray energies. We discuss how extreme scenarios of cross section extrapolations can affect the interpretation of air shower data. We find that the theoretical uncertainty of the extrapolated proton-air cross section at ultra-high energies is much larger than suggested by the existing spread of available Monte Carlo model predictions. The impact on the depth of the shower maximum is demonstrated.

Inclusive production of the [formula omitted] meson in hadronic decays of the Z boson

The inclusive production rate of the ρ±(770) vector meson in hadronic Z decays is measured with the ALEPH detector at the LEP collider. A total of 3.2 million hadronic events are selected from data recorded between 1991 and 1995. Decays of ρ±→π0+π± are reconstructed for xE>0.05 and xp>0.05 where xp=pρ/pbeam and xE=Eρ/Ebeam. The average ρ± multiplicity per hadronic event is evaluated to be N(ρ±)=2.59±0.03±0.15±0.04 where the first error is statistical and the second systematic. The third error is from the uncertainty in the extrapolation to xp=xE=0. The rates and differential cross-section are compared with Monte Carlo model predictions and OPAL measurements. Residual Bose–Einstein correlations are found to be an important component in the analysis.

A Monte Carlo simulation model for vacuum membrane distillation process

Vacuum membrane distillation (VMD) process received a great deal of attention by many investigators because of its promising applications in many separation areas. Theoretical models published in literature describe vapor flux through membrane pores ignoring membrane pore space interconnectivity. Those models, in most cases are restricted to Knudsen type of flow and in a less extent to the combined Knudsen-viscous mechanism also described by the dusty gas model. This paper is one of a series of papers in which a Monte Carlo simulation model is developed to describe the vapor flux across the membrane in association with membrane distillation process. Unlike earlier paper in the series, this paper deals with VMD for the first time. The membrane pore space is described by a three-dimensional network of interconnected cylindrical pores, having a pore size distribution. The model can take into account all related mass transport mechanisms based on the kinetic theory of gases. When this model was applied to VMD process, it was assumed that water vapor is the only permeant, the VMD process is in an isothermal condition and there is no surface effect. The effects of the bulk feed temperature, downstream pressure and membrane pore size on the simulated VMD flux were discussed. The Monte Carlo model predictions were found to be in qualitative agreement with available experimental data when Knudsen type of flow was considered. When viscous type of flow is considered, the simulation results indicate that the higher feed solution temperature and higher pore size do not necessarily increase the vapor flux.

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of pi0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of sqrt(s) = 91.2 GeV. Neutral pions are reconstructed using photons from conversion pairs and photons measured in the electromagnetic calorimeter. The inclusive pi0 momentum spectrum is measured in the range from 0.025 < x(p) = p/p(beam) < 1 to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi0 cross section has also been measured as a function of transverse momentum with respect to the event plane (p_T^in and p_T^out_T).

Inclusive production of neutral vector mesons in hadronic Z decays

Data on the inclusive production of the neutral vector mesonsρ 0(770),ω(782), K*0(892), andφ(1020) in hadronic Z decays recorded with the ALEPH detector at LEP are presented and compared to Monte Carlo model predictions. Bose-Einstein effects are found to be important in extracting a reliable value for theρ 0 production rate. An averageρ 0 multiplicity of 1.45±0.21 per event is obtained. Theω is detected via its three pion decay modeω→π + π − π 0 and has a total rate of 1.07±0.14 per event. The multiplicity of the K*0 is 0.83±0.09, whilst that of theφ is 0.122±0.009, both measured using their charged decay modes. The measurements provide information on the relative production rates of vector and pseudoscalar mesons, as well as on the relative probabilities for the production of hadrons containing u, d, and s quarks.