Three-dimensional Monte Carlo Method Research Articles

Optimizing the administrated light dose during 5-ALA-mediated photodynamic therapy: Murine 4T1 breast cancer model.

Photodynamic therapy (PDT) is already used to treat many cancers, including breast cancer, the most common cancer in women worldwide. The destruction basis of this method is on produced singlet oxygen which is extremely reactive and is a major agent of tumor cell killing. The measurement of singlet oxygen produced within PDT is essential in predicting treatment outcomes and their optimization. This study aims to determine the optimal total light dose administered during PDT by calculating the singlet oxygen to facilitate the prediction of the treatment outcome in mice bearing 4T1 cell breast cancer. Monitoring the changes in photosensitizer fluorescence signals during PDT due to photobleaching can be one of the methods of determination of singlet oxygen generation in the PDT process. This study determined the oxygen singlet as a photodynamic dose from the three-dimensional Monte Carlo method and the photobleaching empirical dose constant. The photobleaching dose constant was established non-invasively by monitoring the invivo protoporphyrin IX (PpIX) fluorescence and photobleaching during PDT. The photobleaching dose constant (β) in J/cm2 was calculated using empirical fluorescence data. The invivo photobleaching dose constant of aminolevulinic acid was found to be 11.6 J/cm2 and based on this value, the optimal treatment light dose was estimated at 120 J/cm2 in mice bearing 4T1 breast cancer. It is concluded that information can be obtained regarding optimal treatment parameters by monitoring the invivo PpIX fluorescence and photobleaching during PDT.

Application and comparative analysis of radiative heat transfer models for coal-fired furnace

Thermal radiation is a crucial mode of heat transfer in the industrial furnace. The present article compares various radiative heat transfer models for non-gray gases environments with typical application to the pulverized coal-fired furnace. An open source CFD software OpenFOAM is used to implement a three-dimensional photon Monte Carlo (PMC) method for radiation from gray gases and first-order spherical harmonics (P 1-method), discrete ordinates method (DOM) and zonal method for radiation from non-gray gases. The non-gray radiation properties are calculated using the weighted-sum-of-gray-gases (WSGG) and full-spectrum k-distribution models. The PMC method is employed as a benchmark for comparing the accuracy of the P 1-method and the DOM for gray gas environment, and the zonal method is employed as a benchmark for comparing the accuracy of P 1-method and DOM for the non-gray gas environment. The zonal method and PMC are validated against the exact solution for plane-parallel medium filled with a gray gas. The accuracy of the P 1-method and DOM is analyzed and compared with the zonal method for non-gray gas radiation inside a cubical box of 1 m sides. The effect of coal and ash particle’s radiative properties on the radiative heat transfer has been analyzed. The k-distribution model along with radiation due to coal and ash particles is presented. The variation in absorption and scattering efficiency due to particle size and the complex index of refraction is analyzed for different types of coal and ash particles. Isotropic, forward scattering, and δ-Eddington approximation are compared with the anisotropic scattering using Mie-theory. The coal and ash particle’s radiative properties are calculated using the Mie-theory and are averaged using Planck intensity distribution. The particle size of the coal and ash is a more critical parameter compared to the complex index of refraction. The slight variation in projected area per unit coal and ash particle leads to a significant change in the radiative heat source and radiative heat flux at the wall of industrial furnace.

Origin of the ν=1/2 fractional quantum Hall effect in wide quantum wells

The nature of the fractional quantum Hall effect at $\ensuremath{\nu}=1/2$, observed in wide quantum wells almost three decades ago, is still under debate. Previous studies have investigated it using the variational Monte Carlo method, which assumes that the transverse wave function and the gap between the symmetric and antisymmetric subbands obtained in a local density approximation at zero magnetic field remain valid even at high perpendicular magnetic fields; this method also ignores the effect of Landau level mixing. We develop in this work a three-dimensional fixed-phase diffusion Monte Carlo method, which gives, in a single framework, the total energies of various candidate states in a finite width quantum well, including Landau level mixing, directly in a large magnetic field. This method can be applied to one-component states and also to two-component states in the limit where the symmetric and antisymmetric bands are nearly degenerate. Our three-dimensional fixed-phase diffusion Monte Carlo calculations find that the one-component composite-fermion Fermi sea and the one-component Pfaffian states are very close in energy for a range of quantum-well widths and densities, suggesting that the observed 1/2 fractional quantum Hall state in wide quantum wells is likely to be the one-component Pfaffian state. We hope that this will motivate further experimental studies of this state.

A Simulation for the Electrical Conductivity of Nanocomposites Filled with Carbon Black Based on the Three-dimensional Monte Carlo Method

In this work, the electrical conductivity of nanocomposites filled with carbon black is simulated by the three-dimensional Monte Carlo method. First, three-dimensional model of the nanocomposites and carbon black is constructed and the conductive mechanism is studied. Then the calculation method of electrical conductivity of nanocomposites filled with carbon black is proposed according to the equivalent resistance of large-scale pure resistor network. Then the proposed electrical conductivity calculation method is verified by comparing with the simulation and experimental results. This result shows that it is feasible to directly obtain the conductivity of nanocomposites using the proposed conductivity calculation method. This study helps to estimate the electrical properties of nanocomposites filled with carbon black. And it also can help for studying nanocomposites filled with carbon nanotubes or graphene and the synergistic effect of hybrid fillers-filled nanocomposites.

Optimize Illumination Parameter of Low-Level Laser Therapy for Hemorrhagic Stroke by Monte Carlo Simulation on Visible Human Dataset

Stroke is the second leading cause of death and disability worldwide. The incidence of hemorrhagic stroke increases dramatically with the increasingly aging population. Recently, technology of low-level light/laser therapy (LLLT) is emerging as a novel noninvasive therapeutic approach to treat stroke based on effective photobiomodulation. To obtain optimal therapeutic effects, several LLLT illumination parameters such as beam size and beam type need to be optimized. However, the quantitative optimization of LLLT illumination parameters for stroke therapeutics is impractical to test directly on human subjects. In this paper, we employed a precise voxelized three-dimensional Monte Carlo method (MCVM) to simulate photon propagation within Visible Chinese human (VCH) head at different level of stroke with varied parameters of beams. By evaluation with criteria of the total fluence flux in lesion region and the maximal penetration depth, we found that Gaussian beam with larger or the same size of hemorrhagic region generates the highest and relative homogeneous therapeutic outcomes, while the Top-hat beam performed better when hemorrhagic region is much bigger than beam size. These results demonstrate the great potential of using VCH and MCVM in optimizing LLLT treatment parameters for stroke and in guiding future instrumentation of LLLT on hemorrhagic stroke.

Comprehensive Investigation of Multitraps-Induced Degradation in HfO2-Based nmosfets With Interfacial Layer by Three-Dimensional KMC Method

This paper investigates trap-induced degradation in nmosfets with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectric by three-dimensional Kinetic Monte Carlo method. Multiple microscopic mechanisms including trapping/detrapping, traps coupling, and trap generation/recombination are considered in simulation. The impacts of interfacial layer (IL) SiOx on positive bias temperature instability (PBTI) and trap-assisted tunneling (TAT) are comprehensively investigated. PBTI characteristics show the variations of power laws with time, and power laws are greatly affected by stress condition, trap density, and dielectric thickness. Therefore, impressionable power laws make much complexion in lifetime prediction. Meanwhile, it is found that IL markedly reduces PBTI effects. Significantly, TAT currents of fresh devices increase with IL thickening in the same effective oxide thickness (EOT), whereas TAT currents after stress decrease with IL thickening in a specific range. It can be concluded that the IL in the proper range of thickness can effectively suppress PBTI and TAT currents.

Numerical Simulation of Nanorod Growth in REBa2Cu3Oy Superconducting Thin Films

Various nanostructures consisting of BaMO 3 (BMO) self-organize in REBa 2 Cu 3 Oy (REBCO) films prepared by vapor phase epitaxy. A numerical simulation of the BMO self-organization was developed using the three-dimensional Monte Carlo (3D-MC) method, and the effects of deposition parameters such as substrate temperature (T s ), deposition rate (v dep ), and BMO volume fraction (f BMO ) on BMO self-organization were investigated. We consider only the kinetic factors and ignore mismatch strain on the nanorods (NRs) morphology. 3D-MC simulations for various T s indicated that the number density of BMO NRs decreased with an increase in T s , and this tendency was similar to previous experimental results for BaHfO 3 -doped SmBCO films prepared by the pulsed laser deposition method. The effects of v dep and f BMO were also simulated to provide contour plots of the number density of NRs with respect to T s and f BMO at various v dep . Phase diagrams of nanostructures consisting of BMO with various v dep were also obtained. Although these results do not take into account degradation of the superconducting properties and crystalline defects induced by nonoptimized conditions, they are considered to be a useful guideline for control of the flux pinning landscape on REBCO-coated conductors.

Oxidative treatment, dispersion effect, and simulation of multi-walled carbon nanotubes in aqueous solution

In the present work, the multi-walled carbon nanotubes (MWCNTs) were modified by the treatment with concentrated nitric and sulfuric acid mixture (3: 1 vol/vol). The obtained material was characterized by X-ray diffraction (XRD). The effect of two surfactants, methylcellulose (MC) and cetyltrimethylammonium bromide (CTAB) on dispersing of MWCNTs in aqueous solution was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM). Also, the dispersing effect of the surfactants was simulated by three-dimensional Monte Carlo method. The results showed that the oxidative treatment leads to purification of the neat MWCNTs, and directly improved their dispersing. The mixture containing both MC and CTAB surfactants has better dispersing effect than individual surfactants. The optimum concentration ratio of MC, CTAB, and MWCNTs was 2: 3: 1. In the simulation model, MWCNTs were dispersed randomly. The simulation results may be helpful for the further research on mechanical and electrical properties of composites reinforced with MWCNTs.

Study on formation of step bunching on 6H-SiC (0001) surface by kinetic Monte Carlo method

The formation and evolution of step bunching during step-flow growth of 6H-SiC (0001) surfaces were studied by three-dimensional kinetic Monte Carlo (KMC) method and compared with the analytic model based on the theory of Burton-Cabera-Frank (BCF). In the KMC model the crystal lattice was represented by a structured mesh which fixed the position of atoms and interatomic bonding. The events considered in the model were adatoms adsorption and diffusion on the terrace, and adatoms attachment, detachment and interlayer transport at the step edges. In addition, effects of Ehrlich-Schwoebel (ES) barriers at downward step edges and incorporation barriers at upwards step edges were also considered. In order to obtain more elaborate information for the behavior of atoms in the crystal surface, silicon and carbon atoms were treated as the minimal diffusing species. KMC simulation results showed that multiple-height steps were formed on the vicinal surface oriented toward [11¯00] or [112¯0] directions. And then the formation mechanism of the step bunching was analyzed. Finally, to further analyze the formation processes of step bunching, a one-dimensional BCF analytic model with ES and incorporation barriers was used, and then it was solved numerically. In the BCF model, the periodic boundary conditions (PBC) were applied, and the parameters were corresponded to those used in the KMC model. The evolution character of step bunching was consistent with the results obtained by KMC simulation.

An all-optical velocity filter and beam splitter for generating cold molecular beams: a proposal and simulation

In order to generate one or two cold molecular beams that have neither a permanent electric dipole moment nor a magnetic dipole one, a controllable scheme to form an all-optical velocity filter and molecular beam splitter by using two red-detuned, crossing and cavity-enhanced guiding laser beams is proposed, and both the dynamic velocity filtering and beam splitting processes of the guided cold I2 molecular beam are studied by using the three-dimensional Monte Carlo method. Our study shows that by adjusting the laser power difference between the two guiding laser beams from −124 W to 124 W, a splitting ratio of the two-arm output molecular beams from about 10.3% to 89.7% can be obtained. Also, by adjusting the intersection angle between the two standing wave cavities from 80° to 10°, an adjustable splitting ratio from about 1.6% to 98.4% can be obtained. If the intersection angle between the guided oblique beam and the guided straight beam is set to 80°, a cold I2 molecular beam with a full-width at half-maximum longitudinal velocity of 1 m s−1 and a longitudinal temperature of 8 mK can be generated by using an all-optical velocity filter.

Numerical Simulation of Bearing Force Over Bit-Patterned Media using 3-D DSMC Method

Nowadays, the hard disk drive (HDD) filling with helium have emerged to achieve highly stable magnetic recording. The bearing force in helium is different from that in air. This paper uses the three-dimensional (3D) direct simulation Monte Carlo (DSMC) method to investigate the bearing force over bit patterned media (BPM) in the filling gases of air and helium under different conditions, including ambient temperature, rotation speed of disk, slider surface temperature, flying attitude of slider, and velocity loss during the collision process between gas molecules and slider in the HDD.

Analysis of Low Intensity Laser Therapy as adjuvant to Photodynamic Therapy in Nonmelanoma Skin Cancer.

The combination of Low Intensity Laser Therapy and Photodynamic Therapy constitutes a minimal invasive and highly selective alternative for the treatment of skin tumors. Photodynamic effectiveness, specially the absence of recurrence, highly depends on the type of tumor, as well as on several parameters such as those related with the optical source. Therefore it is important to have predictive tools to provide an appropriate treatment planning. This work proposes the use of a complex predictive model that includes a three-dimensional meshing of the considered tumor geometry and the optical propagation therein by a three-dimensional Monte Carlo method. The proposed tool is applied to three different types of skin tumors, squamous cell carcinoma, nodular and infiltrative basal cell carcinomas. The estimated volume of treatment, depending on the tumor type and source parameters, allows an appropriate treatment planning in order to avoid undesirable tumor recurrence.

Efficient and Accurate Simulation of Light Propagation in Bio-Tissues Using the Three-Dimensional Geometric Monte Carlo Method

Energy deposition in bio-tissues is a prerequisite for the calculation of heat transfer during laser–tissue interactions. We calculated light propagation and energy deposition in bio-tissues using a three-dimensional (3D) geometric Monte Carlo (MC) method, which uses the mathematically defined geometrical relationship between photons and tissue structures. We demonstrated the accuracy and efficiency of this method compared with the voxel-based MC method: it was 25 times faster than the VMC with a voxel size of 10 µm. Results of light propagation in the multi-coaxial vessel cluster proved that an artificial vessel distribution could be used to predict the absorption characteristics in real tissues with a similar blood volume fraction.

Characterisation and simulation of highly dispersed carbon nanofibre-reinforced cement materials

In this work, carbon nanofibres (CNFs) were incorporated into ordinary Portland cement matrices. The mechanical behaviour of these composites and the effect of CNFs on cement hydration and microstructure of cement paste were compared with a plain cement sample by means of mercury intrusion porosimetry, X-ray diffraction, thermal analysis and scanning electron microscopy. The random distribution of CNFs in cement matrices was simulated by three-dimensional Monte Carlo method. The results showed that the added 0·1 wt% CNFs increased the maximum flexural, compressive strength, toughness and impermeability performance of blended cement compared with the samples. The incorporation of CNFs into cement paste accelerated the rate of the hydration reaction and increased the amount of hydration products. The use of CNFs also improved pore parameters, and the pore size distribution of these composites shifted towards smaller pore size scope. In addition, scanning electron micrographs showed that good interaction between CNFs and the cement matrix occurs, with CNFs acting as fillers, resulting in a denser microstructure.

一种模拟生物组织内光传播的三维几何蒙特卡洛方法

一种模拟生物组织内光传播的三维几何蒙特卡洛方法

Trajectory-based analysis of low-energy electrons and photocurrents generated in strong-field ionization

The three-dimensional classical-trajectory Monte Carlo method is employed to investigate low-energy photoelectron spectra in above-threshold ionization by strong laser fields. By connecting the tunneling coordinates with the final momentum-energy spectra, we identify the effects of the Coulomb potential on electron trajectories and the final energy spectra. In addition, we verify that the photoelectron spectra, depending on the energy region, can be controlled with a two-color laser pulse by varying the phase delay. The modulations of the electron spectra and yields as well as the generated photocurrents reveal the connections among them, which support our previous work [Phys. Rev. Lett. 109, 243002 (2012)] on terahertz wave generation from two-color laser pulses.

Influence of the Sintering of Electrocatalysts and Decrease of Proton Conductivity on the Current-Voltage Performance in the High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC)

The relevance of the sintering of electrocatalysts and voltage drops of HT-PEMFC was theoretically evaluated under the non-humid conditions at 150 °C, 170 °C and 190 °C. The degree of agglomeration of electrocatalysts over time simulated by three-dimensional kinetic Monte Carlo method was compared and quantitatively agreed with experimentally measured Transmission Electron Microscopy (TEM) results. Agglomeration of electrocatalysts leads to the loss of the electrochemically active surface area. It was found to be occurred more severe as temperature increased. Decreasing rate of the proton conductivity was calculated based on the tortuosity of the proton pass. The more the phosphoric acid was evaporated, the more tortuous the proton path became. A theoretical breakdown of the voltage drops indicated that the deterioration of electrocatalysts impacted on the earlier several hundreds of hours. The decrease in the voltage at the latter stage was due to mainly the decrease in the proton conductivity.

Three-dimensional Monte Carlo calculation of gas production in structural material of APEX reactor for some evaluated data files

Proton and He-4 gas production rates in the structural material of a fusion-fission hybrid reactor were calculated with the three-dimensional Monte Carlo method by the MCNPX-2.5.0 code. We examined these reaction rates with five nuclear data libraries: ENDF/B-VII.0 T=300K, JEFF-3.1 T=300K, JENDL-4.0 T=300K, ROSFOND T=300K and CENDL-3.1 T=300K. The production from each isotope of structural material made of ferritic steel was calculated. The neutron flux load is assumed to be 10MW/m2.

Effective Resistance of Gas Flow in Microchannels

The resistance of gas flow in microchannels is higher because of the relatively more importance of interfacial effects at microscale. We studied the effective resistance of gas from the wall interactions, the ends effect, and the rarefication effect quantitatively using the three-dimensional (3D) direct simulation Monte Carlo (DSMC) method. The effective resistance is enhanced by the wall interactions, increasing exponentially as the concerned walls distance decreases. For short microchannels, the ends effects from both inlet and outlet also raise the effective resistance of gas flow in microchannels following a reciprocal exponential relationship with the aspect ratio of length to height. The gas rarefication strengthens the effective resistance enhancement by either the wall interaction effects or the ends effects. This work turns a complicated micromechanical problem into simple available formulae for designs and optimization of microengineering.

Influence of Deposition Temperature and Rate on the Surface Morphology of Sc Thin Film

The growth peculiarity of Sc thin film is simulated by a three-dimensional kinetic Monte Carlo method. The simulation results show that the surface root-mean-square roughness of Sc thin films is increased with the increasing of the deposition rate. The number of initial nucleus of Sc thin films is decreased gradually with the increasing of deposition temperature, and the size of the Sc grains gets larger with the increasing of the deposition temperature. The optimal deposition rate and deposition temperature of Sc thin film are predicted to be 10 ML/s or 3.308 nm/s, and 700 K, respectively.