Molecular/cluster statistical thermodynamics methods to simulate quasi-static deformations at finite temperature

AbstractThe rapid evolution of nanotechnology appeals for the understanding of global response of nanoscale systems based on atomic interactions, hence necessitates novel, sophisticated, and physically based approaches to bridge the gaps between various length and time scales. In this paper, we propose a group of statistical thermodynamics methods for the simulations of nanoscale systems under quasi-static loading at finite temperature, that is, molecular statistical thermodynamics (MST) method, cluster statistical thermodynamics (CST) method, and the hybrid molecular/cluster statistical thermodynamics (HMCST) method. These methods, by treating atoms as oscillators and particles simultaneously, as well as clusters, comprise different spatial and temporal scales in a unified framework. One appealing feature of these methods is their “seamlessness” or consistency in the same underlying atomistic model in all regions consisting of atoms and clusters, and hence can avoid the ghost force in the simulation. On the other hand, compared with conventional MD simulations, their high computational efficiency appears very attractive, as manifested by the simulations of uniaxial compression and nanoindenation

Muscovy duck reovirus p10.8 protein localizes to the nucleus via a nonconventional nuclear localization signal

BACKGROUND: It was previously report that the first open reading frame of Muscovy duck reocvirus S4 gene encodes a 95-amino-acid protein, designed p10.8, which has no sequence similarity to other known proteins. Its amino acid sequence offers no clues about its function. RESULTS: Subcellular localization and nuclear import signal of p10.8 were characterized. We found that p10.8 protein localizes to the nucleus of infected and transfected cells, suggesting that p10.8 nuclear localization is not facilitated by viral infection or any other viral protein. A functional non-canonical nuclear localization signal (NLS) for p10.8 was identified and mapped to N-terminus residues 1–40. The NLS has the ability to retarget a large cytoplasmic protein to the nucleus. CONCLUSIONS: p10.8 imported into the nucleus might via a nonconventional signal nuclear signal

Statistical modeling of damage evolution in spallation

In order to understand the mechanism of the incipient spallation in rolled metals, a one dimensional statistical mode1 on evolution of microcracks in spallation was proposed. The crack length appears to be the fundamental variable in the statistical description. Two dynamic processes, crack nucleation and growth, were involved in the model of damage evolution. A simplified case was examined and preliminary correlation to experimental observations of spallation was made.</span

Efficient and Reliable Nanoindentation Simulation by Dislocation Loop Erasing Method

Nanoindentation is a useful technique to measure material properties at microscopic level. However, the intrinsically multiscale nature makes it challenging for large-scale simulations to be carried out. It is shown that in molecular statics simulations of nanoindentation, the separated dislocation loops (SDLs) are trapped in simulation box which detrimentally affects the plastic behavior in the plastic zone (PZ); and the long-distance propagation of SDLs consumes much computational cost yet with little contribution to the variation of tip force. To tackle the problem, the dislocation loop erasing (DLE) method is proposed in the work to alleviate the influence of artificial boundary conditions on the SDL-PZ interaction and improve simulation efficiency. Simulation results indicate that the force-depth curves obtained from simulations with and without DLE are consistent with each other, while the method with DLE yields more reasonable results of microstructural evolution and shows better efficiency. The new method provides an alternative approach for large-scale molecular simulation of nanoindentation with reliable results and higher efficiency and also sheds lights on improving existing multiscale methods

closedtransscalestatisticalmicrodamage

Damage and failure due to distributed microcracks or microvoids are on the challenging frontiers of solid mechanics. This appeals strongly to tools not yet fully developed in continuum damage mechanics, in particular to irreversible statistical thermodynamics and a unified macroscopic equations of mechanics and kinetic equations of microstructural transformations. This review provides the state of the art in statistical microdamage mechanics. It clarifies on what level of approximation continuum damage mechanics works. Particularly, Z)-level approximation with dynamic function of damage appears to be a proper closed trans-scale formulation of the problem. It provides physical foundation of evolution law in damage mechanics. Es-sentially, the damage-dependent feature of the macroscopic evolution law is due to the movement of microdamage front, resulting from microdamage growth. It is found that intrinsic Deborah number D*, a ratio of nucleation rate over growth rate of microdamage, is a proper indication of critical damage in damage mechanics, based on the idea of damage localization. It clearly distinguishes the non-equilibrium damage evolution from equilibrium phase transition, like percolation. Finally, some comments on its limitations are made