The determination of crystal structure by means of X-rays

Thesis (M.A.)--Boston University This item was digitized by the Internet Archive

Kinetics of shape equilibration for two-dimensional islands

We study the relaxation to equilibrium of two dimensional islands containing up to 20000 atoms by Kinetic Monte Carlo simulations. We find that the commonly assumed relaxation mechanism - curvature-driven relaxation via atom diffusion - cannot explain the results obtained at low temperatures, where the island edges consist in large facets. Specifically, our simulations show that the exponent characterizing the dependence of the equilibration time on the island size is different at high and low temperatures, in contradiction with the above cited assumptions. Instead, we propose that - at low temperatures - the relaxation is limited by the nucleation of new atomic rows on the large facets : this allows us to explain both the activation energy and the island size dependence of the equilibration time.Comment: 9 pages, revte

Automating agent-based modeling : data-driven generation and application of innovation diffusion models

Simulation modeling is useful to understand the mechanisms of the diffusion of innovations, which can be used for forecasting the future of innovations. This study aims to make the identification of such mechanisms less costly in time and labor. We present an approach that automates the generation of diffusion models by: (1) preprocessing of empirical data on the diffusion of a specific innovation, taken out by the user; (2) testing variations of agent-based models for their capability of explaining the data; (3) assessing interventions for their potential to influence the spreading of the innovation. We present a working software implementation of this procedure and apply it to the diffusion of water-saving showerheads. The presented procedure successfully generated simulation models that explained diffusion data. This progresses agent-based modeling methodologically by enabling detailed modeling at relative simplicity for users. This widens the circle of persons that can use simulation to shape innovation

Den fatale streg ----------

Rusens inspiration er tema for Louis Jensens bidrag om Johannes Ewalds “Højen”. “Højen” er, ifølge Jensen, en berusende tekst, der beskriver digterensinspirerede rus; en inspiration der udspringer af såvel ungdom, et følsomt sind som en flaske vin. Det er digterens lod og længsel, siger Jensen med Ewald, at løfte og blive løftet, at blive opfyldt, at se verden som den er, at møde den gennem inspirationens berusende klarhed. Og at udtrykke det sete og følte i poesien. For i beruselsen er også sandheden, om end kun for et øjeblik

Forvent mindre, arbejd mere!

Forvent mindre, arbejd mere