Mass spreading of non-reactive tracers in fractured bedrock can be described by a combination of molecular diffusion, hydrodynamic dispersion, and heterogeneous advection. These spreading mechanisms are fundamentally different in their behavior and, therefore, must be measured separately for reliable predictions of transport to be made. To separate the influence of these mechanisms, to the exte...

We study the rate of activated motion over multiple barriers, in particular the correlated double jump of an adatom diffusing on a missing-row reconstructed platinum (110) surface. We develop a transition path theory, showing that the activation energy is given by the minimum-energy trajectory which succeeds in the double jump. We explicitly calculate this trajectory within an effective-medium ...

Model reduction is an important systems task with a long history in traditional chemical engineering modeling. We discuss its interplay with modern data-mining tools (such as Local Feature Analysis and Diffusion Maps) through illustrative examples, and comment on important open issues regarding applications to large systems arising in molecular/atomistic simulations.

A molecular dynamics study on atomic self-diffusion in Frank-Kasper type dodecagonal quasicrystals is presented. It is found that the quasicrystal-specific flip mechanism for atomic diffusion, predicted by Kalugin and Katz, indeed occurs in this system. However, in order to be effective, this mechanism needs to be catalyzed by other defects, such as half-vacancies. For this reason, flip diffusi...

The Ludwig-Soret effect (that is, thermal diffusion) describes the concentration gradient in a mixture under a temperature gradient. The effect is quantified by the Soret coefficient, which is in turn related to the molecular and thermal diffusion coefficients of a mixture. Thermal diffusion is important in a myriad of applications, such as in petroleum reservoirs, material sciences, oceanograp...

In this study, the use of the three-layer feed forward neural network has been investigated for estimating of infinite dilute diffusion coefficient ( D12 ) of supercritical fluid (SCF), liquid and gas binary systems. Infinite dilute diffusion coefficient was spotted as a function of critical temperature, critical pressure, critical volume, normal boiling point, molecular volume in normal boilin...

Molecular diffusion of polymer chains and low molecular weight constituents and impurities can be an important process in the formation and application of polymer composites. Molecular diffusion in polymer systems is a complex process which can be a strong function of temperature, concentration, polymer molecular weight and polymer morphology. During the last decade, significant advances have b...

In chemistry and physics symmetry principles are all important, for example, leading to the selection rules governing optical transitions. We have investigated the influence of the molecular symmetry on the surface potential landscape of molecules in the limit of weak molecule-substrate binding. For this purpose, the induced lateral motion of Cu(II)-tetraazaphthalocyanine molecules, for which f...

A method-of-moments scheme is invoked to compute the asymptotic, long-time mean (or composite) velocity and dispersivity (effective diffusivity) of a two-state particle undergoing one-dimensional convectivediffusive motion accompanied by a reversible linear transition (“chemical reaction” or “change in phase”) between these states. The instantaneous state-specific particle velocity is assumed t...

We investigate through molecular dynamics the transition from Knudsen to molecular diffusion transport towards two-dimensional absorbing interfaces with irregular geometry. Our results indicate that the length of the active zone decreases continuously with density from the Knudsen to the molecular diffusion regime. In the limit where molecular diffusion dominates, we find that this length appro...