The paper by Falk and Langer proposes a dynamical theory of low-temperature shear deformation in amorphous solids, based on molecular dynamics simulations of a two-dimensional, two-component noncrystalline system. The simulations reveal typical behaviors of metallic glasses and other viscoplastic materials, including reversible elastic deformation at low stresses, irreversible plastic deformation at higher stresses, a stress threshold for unbounded plastic flow, and a strong dependence on the history of deformations. Microscopic observations suggest that a complete description of the macroscopic state requires specifying additional features of shear transformation zones, which are small regions susceptible to inelastic rearrangements. The authors introduce new state variables into the constitutive equations, extending earlier models of creep in metallic glasses. The theory is based on the assumption that irreversible motions are governed by local entropic fluctuations in the volumes of these transformation zones. The theory accounts for many simulation results but is limited by its mean-field nature, which does not account for spatial correlations. The paper also discusses the experimental setup, including the algorithm used for molecular dynamics simulations and the model solid used in the simulations. The results show that the system exhibits a well-defined critical stress for plastic deformation, with a significant Bauschinger effect observed during reverse loading. The theoretical interpretation of the simulations is detailed, including hypotheses about the probabilities of volume fluctuations and the equations of motion for the densities of shear transformation zones.The paper by Falk and Langer proposes a dynamical theory of low-temperature shear deformation in amorphous solids, based on molecular dynamics simulations of a two-dimensional, two-component noncrystalline system. The simulations reveal typical behaviors of metallic glasses and other viscoplastic materials, including reversible elastic deformation at low stresses, irreversible plastic deformation at higher stresses, a stress threshold for unbounded plastic flow, and a strong dependence on the history of deformations. Microscopic observations suggest that a complete description of the macroscopic state requires specifying additional features of shear transformation zones, which are small regions susceptible to inelastic rearrangements. The authors introduce new state variables into the constitutive equations, extending earlier models of creep in metallic glasses. The theory is based on the assumption that irreversible motions are governed by local entropic fluctuations in the volumes of these transformation zones. The theory accounts for many simulation results but is limited by its mean-field nature, which does not account for spatial correlations. The paper also discusses the experimental setup, including the algorithm used for molecular dynamics simulations and the model solid used in the simulations. The results show that the system exhibits a well-defined critical stress for plastic deformation, with a significant Bauschinger effect observed during reverse loading. The theoretical interpretation of the simulations is detailed, including hypotheses about the probabilities of volume fluctuations and the equations of motion for the densities of shear transformation zones.