Search results for "Monte carlo method"
showing 10 items of 1234 documents
Kramers potential study of the Rouse-like dynamics of short alkane chains.
1999
In this work we present a Kramers potential study of the orientational dynamics and shear viscosity of short chain alkanes. In this approach the determination of the orientational relaxation time is reduced to the calculation of static moments of single chain conformations. We study a chemically realistic alkane model that asymptotically produces Gaussian chain conformations by means of a Monte Carlo simulation. Our results are applicable to single chain descriptions of polymer melt dynamics and to the intrinsic viscosity of molecules in a Theta solvent. When we map the unknown time unit of our relaxation time result for one particular chain length and temperature to the value obtained for …
Monte Carlo Simulation of a Homopolymer−Copolymer Mixture Interacting with a Surface: Bulk versus Surface Micelles and Brush Formation
2008
Using Monte Carlo simulations of the bond fluctuation model, we study the formation of micelles in a confined mixture of asymmetric AB-diblock copolymers and homopolymers. The composition of the sphere-forming AB-diblock copolymers is fA = 1/8. The mixture is confined into a thin film. The film surfaces attract the minority component of the diblock with strength, eW. To efficiently sample the micelle size distribution and establish equilibrium between the surface and the bulk, we work in the semigrandcanonical ensemble, i.e. at fixed density and fixed chemical potential difference between the two types of chains, choosing a large incompatibility χN ≃ 100 (strong segregation regime). The com…
Quasi-isoactinic reactor for photocatalytic kinetics studies
2007
Photochemical reactors characterized by almost uniform values of the local volumetric rate of photon absorption (LVRPA), i.e., quasi-isoactinic photoreactors, are particularly suitable for assessing the influence of radiant field intensity in kinetic studies. In this work, Monte Carlo simulations have been performed to obtain LVRPA values in a flat photoreactor irradiated on both sides. This configuration appears to be particularly suitable for obtaining quasi-isoactinic conditions. The influence of catalyst albedo and scattering phase function is assessed, and the conditions for obtaining iso-actinicity are discussed. Finally, these conditions are related to an easy-to-measure parameter, n…
Methods to Compute Pressure and Wall Tension in Fluids containing Hard Particles
2011
Colloidal systems are often modelled as fluids of hard particles (possibly with an additional soft attraction, e.g. caused by polymers also contained in the suspension). in simulations of such systems, the virial theorem cannot be straightforwardly applied to obtain the components of the pressure tensor. In systems confined by walls, it is hence also not straightforward to extract the excess energy due to the wall (the "wall tension") from the pressure tensor anisotropy. A comparative evaluation of several methods to circumvent this problem is presented, using as examples fluids of hard spheres and the Asakura-Oosawa model of colloid-polymer mixtures with a size ratio $q=0.15$ (for which th…
On the origin of the halo stabilization
2012
Monte Carlo simulations show that charge-regulation alone can cause highly charged zirconium nanoparticles to adsorb to a similarly charged or neutral silica particle and thereby stabilizing the latter. This mechanism, referred to as halo stabilization, is quite general and applicable in a range of systems provided that pH, van der Waals forces, and dissociation constants of the charge-regulating particles are properly chosen. In our modeling we see an overall attraction at low volume fractions of nanoparticles, while at higher a repulsive barrier is created, stabilizing the microparticles and protecting them from aggregation. The charge-regulation mechanism also turns the silica surface fr…
Methodology for assessment of measuring uncertainties of articulated arm coordinates measuring machine
2014
International audience; The Articulated Arm Coordinate Measuring Machines (AACMM) have gradually evolved and are increasingly used in mechanic industry. At present, measurement uncertainties relating to the use of these devices are not yet well-quantified. The work carried out consists on determining the measurement uncertainties of a mechanical part by an Articulated Arm Coordinate Measuring Machine. The studies aiming to develop a model of measurement uncertainties are based on the Monte Carlo method developed in Supplement 1 of the Guide to Expression of Uncertainty in Measurement [1] but also identifying and characterizing the main sources of uncertainty. A Multi-level Monte Carlo appro…
Using of a uncertainty model of an polyarticulated coordinates measuring arm to validate the measurement in a manufacturing processsus
2014
International audience; Coordinates Measuring Arms (CMA) are increasingly used to control industrial parts and are often an alternative to CMM controls that require conditions of laboratory measurement and involve significant costs. However, the control of uncertainties is often not guaranteed because the measurement process is complex and there is no standard for setting a framework qualification process of the measurement process.The proposed study, in this paper, is a first approach to model the measurement uncertainties of a CMA with contact sensor. The problem is complex because there are many sources of uncertainty, largely due to variability in the handling carried out by the operato…
The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray Showers detected by the Pierre Auger Observatory
2011
In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an Extensive Air Shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 1017 and 1019 eV and zenith angles up to 65. A parametrization combining a step function with an exponenti…
Radial electron fluence around ion tracks as a new physical parameter for the detection threshold of PADC using Geant4-DNA toolkit
2018
International audience; The detection threshold of poly(allyl dyglycol carbonate), PADC, for C ions is determined as 55 eV/nm in stopping power, which is significantly higher than that for proton and He ions. The stopping power is not a universal parameter for expressing the detection threshold of PADC. A new physical parameter of Radial Electron Fluence around Ion Tracks, REFIT, is proposed to describe the detection threshold of PADC. It is defined as the number density of electrons passing through the surface of a cylinder of a certain radius that is co-axial with the trajectory. Furthermore, preliminary calculations are presently being performed using the Monte Carlo simulation code of G…
Zenith distribution and flux of atmospheric muons measured with the 5-line ANTARES detector
2010
The ANTARES high energy neutrino telescope is a three-dimensional array of about 900 photomultipliers distributed over 12 mooring lines installed in the Mediterranean Sea. Between February and November 2007 it acquired data in a 5-line configuration. The zenith angular distribution of the atmospheric muon flux and the associated depth-intensity relation are measured and compared with previous measurements and Monte Carlo expectations. An evaluation of the systematic effects due to uncertainties on environmental and detector parameters is presented.