Intrinsically disordered proteins (IDPs) do not possess well-defined three-dimensional structures in solution under physiological conditions. We develop all-atom, united-atom, and coarse-grained Langevin dynamics simulations for the IDP α-synuclein that include geometric, attractive hydrophobic, and screened electrostatic interactions and are calibrated to the inter-residue separations measured in recent single-molecule fluorescence energy transfer (smFRET) experiments. We find that α-synuclein is disordered, with conformational statistics that are intermediate between random walk and collapsed globule behavior. An advantage of calibrated molecular simulations over constraint methods is that physical forces act on all residues, not only on residue pairs that are monitored experimentally, and these simulations can be used to study oligomerization and aggregation of multiple α-synuclein proteins that may precede amyloid formation.
A simulation-based analysis is conducted of the ionic switching times for nanometer-scale binaryoxide "memristor" devices. This analysis is based upon a device model that incorporates nonlinear field-driven ionic transport within the bulk of the memristor. In contrast, prior models of charge transport in such devices have relied upon linear simplifications, or else they have included nonlinear effects only at the electrode interfaces. As shown here via simulation, the nonlinear model provides much closer quantitative agreement with experimentally observed device switching times. Also, this model predicts a distinct asymmetry between the "set" and "reset" switching behaviors of memristors that is not present in linear models. Thus, the model and the quantitative results derived using it suggest an experimental route by which the underlying device physics might be elucidated further. V
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