Furthermore, the excessive use of TCS is suspected to increase the risk of emergence of TCS-resistant bacteria and the selection of resistant strains.

We use the Richtmyer-Meshkov instability (RMI) at a metal-gas interface to infer the metal's yield stress (Y) under shock loading and release. We first model how Y stabilizes the RMI using hydrodynamics simulations with a perfectly plastic constitutive relation for copper (Cu). The model is then tested with molecular dynamics (MD) of crystalline Cu by comparing the inferred Y from RMI simulations with direct stress-strain calculations, both with MD at the same conditions. Finally, new RMI experiments with solid Cu validate our simulation-based model and infer Y~0.47 GPa for a 36 GPa shock.

The authors show using atomistic simulations that stress-driven grain growth can be obtained in the athermal limit during nanocrystalline aluminum indentation. They find that the grain growth results from rotation of nanograins and propagation of shear bands. Together, these mechanisms are shown to lead to the unstable migration of grain boundaries via process of coupled motion. An analytical model is used to explain this behavior based on the atomic-level shear stress acting on the interfaces during the shear band propagation. This study sheds light on the atomic mechanism at play during the abnormal grain coarsening observed at low temperature in nanocrystalline metals.

We have investigated the conformational effects of modifying the amide group in model dipeptides. The N‐methyl amide ψ[CO‐NMe], N‐hydroxy amide ψ[CO‐N(OH)], N‐amino amide ψ[ CO‐N (NH2)], retro amide ψ[ NH‐CO], reduced amide in the neutral ψ[CH2‐NH] and protonated ψ[CH2‐N + H2] state, and hydrazide ψ[CO‐NH‐NH] have been introduced as surrogates of the amide link in pseudopeptide derivatives of the Pro‐Gly or Ala‐Gly model dipeptides protected on both termini by an amide group. These compounds have been studied in solution by proton nmr and ir spectroscopy, and in the solid state by x‐ray diffraction, giving an extended data set of experimental structural and conformational information on pseudopeptide sequences. The conformational effects depend both on the nature and the position of the modified amide link. Some modifications appear to have no intrinsic conformational induction (N‐amino and retro amide), but destabilize any local folded structure by hydrogen‐bond breaking. Because of the formation of strong intramolecular interactions, others are capable of stabilizing a β‐turn (for example protonated reduced amide), or of inducing a particular local conformation such as a β‐ or γ‐like turn (for example N‐hydroxy amide). The particular geometry of the cis N‐methyl amide and of the “hydrazino” proline favors the formation of a sharp turn of the main chain. All these structural data are of interest to the design of bioactive peptide mimics. © 1993 John Wiley & Sons, Inc.