Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (109–1012 s-1) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the and directions and Al shocked/compressed along the direction.This article is published as Levitas, Valery I., and Ramon Ravelo. "Virtual melting as a new mechanism of stress relaxation under high strain rate loading." Proceedings of the National Academy of Sciences 109, no. 33 (2012): 13204-13207. 10.1073/pnas.1203285109. Posted with permission.</p

Large-scale Climate and Land Cover Influences on Blackbird Populations in the Prairie Pothole Region of the United States and Canada

Blackbirds are ubiquitous members of the avian fauna in the Prairie Pothole Region of the United States and Canada. Their abundance combined with their food habitats make blackbirds significant agricultural pests on sunflower. Cost estimates for blackbird damage to sunflower in the northern Great Plains range from 4-11 million dollars per year. Because of their economic impact on agriculture, it is imperative to understand the environmental factors that influence their abundance. This study attempts to quantify the effects of landscape-level climatic and land use patterns on blackbird population dynamics in the Prairie Pothole Region of the United States and Canada

Isospin-asymmetric nuclear matter

This study uses classical molecular dynamics to simulate infinite nuclear matter and study the effect of isospin asymmetry on bulk properties such as energy per nucleon, pressure, saturation density, compressibility, and symmetry energy. The simulations are performed on systems embedded in periodic boundary conditions with densities and temperatures in the ranges ρ=0.02to 0.2fm−3 and T=1, 2, 3, 4, and 5 MeV, and with isospin content of x=Z/A=0.3, 0.4, and 0.5. The results indicate that symmetric and asymmetric matter are self-bound at some temperatures and exhibit phase transitions from a liquid phase to a liquid-gas mixture. The main effect of isospin asymmetry is found to be a reduction of the equilibrium densities, a softening of the compressibility and a disappearance of the liquid-gas phase transition. A procedure leading to the evaluation of the symmetry energy and its variation with the temperature was devised, implemented and compared to mean field theory results

Buffer Capacity Allocation: A method to QoS support on MPLS networks

This paper describes an optimized model to support QoS by mean of Congestion minimization on LSPs (Label Switching Path). In order to perform this model, we start from a CFA (Capacity and Flow Allocation) model. As this model does not consider the buffer size to calculate the capacity cost, our model- named BCA (Buffer Capacity Allocation)- take into account this issue and it improve the CFA performance. To test our proposal, we perform several simulations; results show that BCA model minimizes LSP congestion and uniformly distributes flows on the networ

Dislocation nucleation induced by a shock wave in a perfect crystal: Molecular dynamics simulations and elastic calculations

info:eu-repo/semantics/publishe

Plasticity induced by a shock wave: large scale molecular dynamics simulations

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Uniaxial Hugoniostat: A method for atomistic simulations of shocked materials

An new equilibrium molecular-dynamics method (the uniaxial Hugoniostat) is proposed to study the energetics and deformation structures in shocked crystals. This method agrees well with nonequilibrium molecular-dynamics simulations used to study shock-wave propagation in solids and liquids.Journal Articleinfo:eu-repo/semantics/publishe

Dislocation structure behind a shock front in fcc perfect crystals: Atomistic simulation results

Large-scale molecular dynamics simulations are used to investigate the dislocation structure behind a shock front in perfect fcc crystals. Shock compression in both the (100) and (111) directions induces dislocation loop formation via a sequential emission of partial dislocations, but in the (100) case, this process is arrested after the first partial, resulting in stacking-fault loops. The large mobility of the bounding partial dislocations results in a plastic wave that is always overdriven in the (100) direction; the leading edges of the partials are traveling with the plastic front, as in the models of Smith and Hornbogen. In contrast, both partials are emitted in (111) shock compression, resulting in perfect dislocation loops bounded only by thin stacking fault ribbons due to the split partial dislocations. These loops grow more slowly than the plastic shock velocity, so new loops are periodically nucleated at the plastic front, as suggested by Meyers.SCOPUS: ar.jinfo:eu-repo/semantics/publishe