Search results for "Monte Carlo method."
showing 10 items of 1217 documents
Modeling of primary defect aggregation in tracks of swift heavy ions in LiF
2001
To simulate aggregation of primary F centers created along the path of swift heavy ions in LiF, Monte Carlo simulations were developed. Parameters relevant for defect aggregation as a result of their random hopping, such as the migration energy, temperature in the track, initial defect concentration, and diffusion time, were estimated from available experimental data. It is estimated that in the electronically excited state and under temperature locally increased up to 1200 K F centers are mobile enough to make several tens of hops. Most of the F aggregates formed are extremely small and consist only of two or three F centers. The fraction of larger F clusters ~with more than 10 defects! is…
Work in the field of BNCT using the Portuguese Research Reactor
1999
Abstract The goal of this work is to pursue the research activity in BNC and the installation of a therapy facility in the position presently occupied by the thermal column. With these objectives the experimental studies in mice and cells are continuing while improvements in the facilities are created or prepared. For this effect: (1) the installation of lead shield in the vertical access of the thermal column, which resulted in an enhancement of the Φ th toD γ ratio, was performed, (2) the adaptation of a beam tube to deliver a dominantly thermal or epithermal beam in two possible beam openings is being done and (3) Monte Carlo calculations aiming at the optimization of the conditions for…
Multiscale modeling of polymers at interfaces
2009
A brief review of modeling and simulation methods for a study of polymers at interfaces is provided. When studying truly multiscale problems as provided by realistic polymer systems, coarse graining is practically unavoidable. In this process, degrees of freedom on smaller scales are eliminated to the favor of a model suitable for efficient study of the system behavior on larger length and time scales. We emphasize the need to distinguish between dynamic and static properties regarding the model validation. A model which accurately reproduces static properties may fail completely, when it comes to the dynamic behavior of the system. Furthermore, we comment on the use of Monte Carlo method i…
Adsorption of CO and N 2 molecules at the surface of solid water. A grand canonical Monte Carlo study
2020
International audience; The adsorption of carbon monoxide and nitrogen molecules at the surface of four forms of solid water is investigated by means of grand canonical Monte Carlo simulations. The trapping ability of crystalline Ih and low-density amorphous ices, along with clathrate hy-drates of structures I and II, are compared at temperatures relevant for astrophysics. It is shown that, when considering a gas phase that contains mixtures of carbon monoxide and nitrogen, the trapping of carbon monoxide is favored with respect to that of nitrogen at the surface of all solids, irrespective of the temperature. The results of the calculations also indicate that some amounts of molecules can …
Stacking faults in close-packed clusters
2002
Ground state geometries of small hard sphere clusters were studied using two different type of contact interaction, a pair-potential and a many-atom interaction. Monte Carlo method in an FCC lattice with all possible (111) stacking faults was used to obtain the minimum energy geometries for clusters up to 59 atoms. Due to the surface energy, FCC packing is generally favoured as opposite to the HCP structure. However, in most cluster sizes the ground state obtained with the many-atom interaction has one or more stacking faults. The most symmetric geometry is usually not the ground state. Clusters with 59 and 100 atoms were studied due the possibility of a high symmetry cluster with stacking …
Smartphone snapshot mapping of skin chromophores under triple-wavelength laser illumination
2017
Abstract Chromophore distribution maps are useful tools for skin malformation severity assessment and for monitoring of skin recovery after burns, surgeries, and other interactions. The chromophore maps can be obtained by processing several spectral images of skin, e.g., captured by hyperspectral or multispectral cameras during seconds or even minutes. To avoid motion artifacts and simplify the procedure, a single-snapshot technique for mapping melanin, oxyhemoglobin, and deoxyhemoglobin of in-vivo skin by a smartphone under simultaneous three-wavelength (448–532–659 nm) laser illumination is proposed and examined. Three monochromatic spectral images related to the illumination wavelengths …
Monte Carlo calculation of dose rate distributions around 0.5 and 0.6 mm in diameter 192Ir wires
1999
Monte Carlo simulations of absolute dose rate in liquid water are presented in the form of away-along tables for 1 and 5 cm 192 Ir wires of 0.5 and 0.6 mm diameter. Simulated absolute dose rate values can be used as benchmark data to verify the calculation results of treatment planning systems or directly as input data for treatment planning. Best fit value of an attenuation coefficient suitable for use in Sievert integral-type calculations has been derived based on Monte Carlo simulation results. For the treatment planning systems that are based on the TG43 formalism we have also computed the required dosimetry parameters.
A Monte Carlo study of intersource effects in dome-type applicators loaded with LDR Cs-137 sources
2005
In this study, the dose rate distributions produced by low dose rate Cs-137 sources loaded in afterloadable dome applicators are studied using the Monte Carlo method. Dose differences between Monte Carlo results and calculations done using the superposition principle are within 1-3% in front of the applicator and between 3 and 10% near and along the longitudinal source axis. Consequently, the real doses to lateral vaginal wall, rectum and bladder are very close to the doses estimated applying the superposition principle, while the dose to the vaginal cuff has been overestimated by up to 10%.
Chain Conformations and Phase Behavior in Confined Polymer Blends
2007
We investigate the chain conformations and phase separation in binary polymer blends. Using large scale semi-grandcanonical Monte Carlo simulations and finite size scaling, we investigate the molecular extension and the intermolecular paircorrelation function in thin films with hard, non-preferentially adsorbing surfaces. The interplay between chain conformations, demixing and the validity of mean field theory is investigated for a large variation of chain lengths 16 ≤ N ≤ 512. Three regimes of film thickness D can be distinguished: (i) For film thicknesses much larger than the unperturbed chain extension R e, bulk behavior is observed, i.e., the critical temperature of demixing T c increas…
Spinodal Decomposition in Binary Polymer Blends: Monte Carlo Simulations and Dynamic Mean Field Theory
2001
Using large scale computer simulations we have investigated the interplay between single chain dynamics and the kinetics of phase separation in a symmetric binary polymer blend. In the framework of a coarse grained lattice model — the bond fluctuation model on a three dimensional lattice — we monitor the growth of concentration fluctuations after a quench from the one phase region into the miscibility gap. Chains of 64 effective segments are simulated in a cell of linear dimension L = 160, i.e., each simulation box contains 256 000 particles. The growth rate of composition fluctuations is averaged over 64 realizations of the temperature quench.