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The effect of flux in a wide range from 1.39×10−10 to 1.39 ×10−3 dpa/s has been studied by the cluster dynamics (CD) simulation for pure iron neutron irradiated at a temperature of 300°C for the two fluences. The critical flux values which mark the regimes of flux dependence of average size, number density and irradiation induced hardening for vacancy clusters (VC) and self-interstitial atoms clusters (SIAC) are found. It was found that the effect of neutron irradiation on average size of SIAC was similar for low and high fluxes in the case of the same fluence. [ABSTRACT FROM AUTHOR]

Characterization of helium-implanted Fe–(2.5–12.5)at% Cr alloys with the flux of 7 × 10–6 dpa/s at a temperature of 343 K has been performed by means of cluster dynamics simulations. We have suggested a model for simulating an Fe–C–Cr system under helium implantation based on a selection of the latest data from atomistic studies and available experiments. Kinetics of carbon-vacancy and helium-vacancy complexes has been studied. Only one parameter is used to guarantee the best reproduction possible of experimental positron annihilation lifetime spectroscopy data for Fe–Cr alloys on dependences of vacancy cluster size on chromium content and irradiation dose via fitting. This is an effective binding energy of self-interstitial atoms to dislocation loops decorated by chromium atoms. It has a “snaky” dependence of chromium content with a minimum of about 9%Cr. [ABSTRACT FROM AUTHOR]

Cluster dynamics (CD) study of damage accumulation has been performed for helium-implanted Fe–2.5 at%Cr alloy with the flux of 7 × 10−6 dpa/s at the temperature of 343 K. Findings confirm the non-monotonic dose dependence of the vacancy clusters mean size for irradiation doses from 0.15 to 0.74 dpa, observed in the positron annihilation spectroscopy experiment. The effect of the chromium and carbon atoms on the formation and kinetics of point defects clusters has been taken into account. The ratio of vacancies formed to cluster to the total number of surveillance vacancies at the end of the cascade stage (irradiation parameterfvcl) and migration energy of vacancies in bcc iron (material parameterEmv) have been varied to provide the best fit of CD simulation results to positron annihilation spectroscopy data on the positron lifetime in defects. The calibrated CD model has been used to study the effect of the presence of vacancy clusters in the non-irradiated state Fe–2.5at%Cr alloy on the evolution of point defect clusters in this material due to helium implantation. [ABSTRACT FROM PUBLISHER]

A comparison between object kinetic Monte Carlo (OKMC) and cluster dynamics (CD) simulations of damage accumulation has been made in the domain of low (77–150 K) temperatures for electron-irradiated and then annealed pure iron as well as at 573 K temperature for neutron-irradiated high concentrated Fe–12.5 at% Cr alloy. Findings indicate that an increase in the size of the simulation box up to 300 nm×300 nm×300 nm in OKMC simulation and direct integration of master equation of CD provide the quantitative agreement results of these methods among themselves as well as with the experimental data of microstructure evolution of Fe–12.5 at% Cr alloy and qualitative agreement for the case of pure iron electron irradiated at 77 K and then annealed at temperatures between 77 and 150 K. [ABSTRACT FROM AUTHOR]

The numerical modelling of concentrated alloy precipitation kinetics remains a challenge at all scales. At the microscopic scale, kinetic Monte Carlo (KMC) simulations can cope with nucleation and early growth whatever the solute concentration may be; it cannot, however, address coarsening. At the mesoscopic scale, the advantage of cluster dynamics (CD) is its ability to describe the whole kinetics of precipitation but lacks of reliability for nucleation in concentrated alloys. Finally, analytical models are preferred at the macroscopic scale for their simplicity, their flexibility and their ability to be incorporated within more general approaches, to predict mechanical properties, for instance. The present work aims at examining the ability of CD and classical analytical models to describe the growth of an isolated precipitate in a concentrated binary alloy, by comparison with KMC simulations taken as the reference. [ABSTRACT FROM AUTHOR]

Kinetic Monte Carlo simulations of precipitation in AlZr alloys are compared with predictions of cluster dynamics based on an enhanced thermodynamic model. A methodology and various tools are proposed to learn as much as possible from such comparisons. Important deviations between the two methods are investigated and interpreted through the role of different mechanisms. [ABSTRACT FROM AUTHOR]

The effect of the size dependence of the production rate of point defect clusters is taken into account in the cluster dynamics (CD) modeling of the simultaneous formation of vacancy clusters and self-interstitial atom clusters in neutron-irradiated pure iron. The calibration of material parameters has been carried out. The correspondence between small angle neutron scattering, transmission electron microscopy and positron annihilation spectroscopy and CD data is studied. [ABSTRACT FROM AUTHOR]

Bramwell A., Nelles J. and Wolfe D. A. Knowledge, innovation and institutions: global and local dimensions of the ICT cluster in Waterloo, Canada, Regional Studies. This paper presents research findings on the information and communication technology (ICT) cluster in Waterloo, Ontario. Cluster dynamics in Canada do not conform to some of the key assumptions in the literature on clusters that emphasize the importance of local intra-cluster dynamics based on inter-firm linkages at the local level. The results of this case study indicate that many inter-firm linkages in the Waterloo ICT cluster are non-local, and that extra-firm institutional supports, such as the local university and industry association, are critical in sustaining and strengthening the cluster. Knowledge-based cluster theories that emphasize the role of local and global knowledge flows and learning processes, and the interaction effect of civic capital and local institutions in supporting the development of a local 'learning economy', provide more compelling explanations for the resilience of the ICT cluster in Waterloo, Ontario... [ABSTRACT FROM AUTHOR]

The problem of the star cluster in the Galactic tidal field is briefly discussed. A sufficient condition for star escape is obtained. [ABSTRACT FROM AUTHOR]