Diffusion Monte Carlo Simulations Research Articles

Monte Carlo simulation of simultaneous gas flow and diffusion in an asymmetric distal pulmonary airway model.

In order to evaluate the effect of anatomic asymmetries on the gas concentration distribution in the pulmonary airways, a Monte Carlo simulation of combined bulk flow and molecular diffusion was carried out in a realistic distal airway model (Parkeret al., 1971). This airway model, composed of branches distal to the 0.5-ram diameter airways, contained an upper symmetric segment consisting of four generations of conducting airways and a lower asymmetric segment of alveolar ducts and sacs arranged in five transport paths of varying lengths. In accounting for the volume increases of these ducts and sacs occurring during normal respiration, uniform alveolar filling rates and a fixed length-to-diameter ratio of all airways were assumed. For a pulse injection of inert tracer gas, the simulation was employed to determine the longitudinal concentration profiles in the conducting airways. In the alveolated airways, not only were the longitudinal profiles determined along each path, but radial transport from the core to the periphery of the airways was considered.

Monte carlo simulation of simulateous gas flow and diffusion in an asymmetric distal pulmonary airway model

Monte carlo simulation of simulateous gas flow and diffusion in an asymmetric distal pulmonary airway model

Approximate Integration of Stochastic Differential Equations

Approximate Integration of Stochastic Differential Equations

Monte Carlo simulation of simultaneous bulk, grain boundary, and surface diffusion

The diffusion of a sorbate in a solid body bisected by a narrow straight grain boundary has been simulated using a combination of the so-called floating random walk Monte Carlo technique and a modified technique of that sort, particularly applicable to the study of random walks inside narrow grain boundaries. The results have been compared to the published solutions obtained from deterministic methods. Complex composite processes involving simultaneous bulk, grain boundary, and surface diffusion have been simulated as well, using the techniques so developed, so as to show that the computations are quite feasible, even though at this point the results cannot always be verified by comparison to known solutions.