Nonequilibrium Phase Transition in the Kinetic Ising model: Critical Slowing Down and Specific-heat Singularity

The nonequilibrium dynamic phase transition, in the kinetic Ising model in presence of an oscillating magnetic field, has been studied both by Monte Carlo simulation and by solving numerically the mean field dynamic equation of motion for the average magnetisation. In both the cases, the Debye 'relaxation' behaviour of the dynamic order parameter has been observed and the 'relaxation time' is found to diverge near the dynamic transition point. The Debye relaxation of the dynamic order parameter and the power law divergence of the relaxation time have been obtained from a very approximate solution of the mean field dynamic equation. The temperature variation of appropiately defined 'specific-heat' is studied by Monte Carlo simulation near the transition point. The specific-heat has been observed to diverge near the dynamic transition point.Comment: Revtex, Five encapsulated postscript files, submitted to Phys. Rev.

Characterizing the boundary lateral to the shear direction of deformation twins in magnesium

The three-dimensional nature of twins, especially the atomic structures and motion mechanisms of the boundary lateral to the shear direction of the twin, has never been characterized at the atomic level, because such boundary is, in principle, crystallographically unobservable.We thus refer to it here as the dark side of the twin. Here, using high-resolution transmission electron microscopy and atomistic simulations, we characterize the dark side of {1012} deformation twins in magnesium. It is found that the dark side is serrated and comprised of {1012} coherent twin boundaries and semi-coherent twist prismatic–prismatic {2110} boundaries that control twin growth. The conclusions of this work apply to the same twin mode in other hexagonal close-packed materials, and the conceptual ideas discussed here should hold for all twin modes in crystalline materials

Three-dimensional character of the deformation twin in magnesium

Deformation twins are three-dimensional domains, traditionally viewed as ellipsoids because of their two-dimensional lenticular sections. In this work, we performed statistical analysis of twin shapes viewing along three orthogonal directions: the ‘dark side’ (DS) view along the twin shear direction (η1), the twinning plane normal (TPN) view (k1) and the ‘bright side’ (BS) view along the direction λ(=k1 × η1). Our electron back-scatter diffraction results show that twins in the DS and BS views normally exhibit a lenticular shape, whereas they show an irregular shape in the TPN view. Moreover, the findings in the TPN view revealed that twins grow faster along λ the lateral direction than along η1 the forward propagation direction at the initial stages of twin growth. These twin sections are irregular, indicating that growth is locally controlled and the overall shape is not perfectly ellipsoidal. We explain these findings using atomistic models, and ascribe them to differences in the mobility of the edge and screw components of the twinning dislocations

Characterizing the boundary lateral to the shear direction of deformation twins in magnesium

The three-dimensional nature of twins, especially the atomic structures and motion mechanisms of the boundary lateral to the shear direction of the twin, has never been characterized at the atomic level, because such boundary is, in principle, crystallographically unobservable.We thus refer to it here as the dark side of the twin. Here, using high-resolution transmission electron microscopy and atomistic simulations, we characterize the dark side of {1012} deformation twins in magnesium. It is found that the dark side is serrated and comprised of {1012} coherent twin boundaries and semi-coherent twist prismatic–prismatic {2110} boundaries that control twin growth. The conclusions of this work apply to the same twin mode in other hexagonal close-packed materials, and the conceptual ideas discussed here should hold for all twin modes in crystalline materials

Effect of martensitic phase transformation on the behavior of 304 austenitic stainless steel under tension

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Nonequilibrium phase transition in the kinetic Ising model: Is transition point the maximum lossy point ?

The nonequilibrium dynamic phase transition, in the kinetic Ising model in presence of an oscillating magnetic field, has been studied both by Monte Carlo simulation (in two dimension) and by solving the meanfield dynamical equation of motion for the average magnetization. The temperature variations of hysteretic loss (loop area) and the dynamic correlation have been studied near the transition point. The transition point has been identified as the minimum-correlation point. The hysteretic loss becomes maximum above the transition point. An analytical formulation has been developed to analyse the simulation results. A general relationship among hysteresis loop area, dynamic order parameter and dynamic correlation has also been developed.Comment: 8 pages Revtex and 4 Postscript figures; To appear in Phys. Rev.

Centrality, rapidity and transverse momentum dependence of J/ψ suppression in Pb–Pb collisions at √sNN = 2.76 TeV

The inclusive J/ψ nuclear modification factor (RAA) in Pb–Pb collisions at √sNN = 2.76 TeV has been measured by ALICE as a function of centrality in the e+e− decay channel at mid-rapidity (|y| < 0.8) and as a function of centrality, transverse momentum and rapidity in the μ+μ− decay channel at forward-rapidity (2.5 < y < 4). The J/ψ yields measured in Pb–Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAA integrated over a centrality range corresponding to 90% of the inelastic Pb–Pb cross section is 0.72±0.06(stat.)±0.10(syst.) at mid- rapidity and 0.58 ± 0.01(stat.) ± 0.09(syst.) at forward- rapidity. At low transverse momentum, significantly larger values of RAA are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/ψ yield originates from charm quark (re)combination in the deconfined partonic medium

Suppression of Υ (1S) at forward rapidity in Pb– Pb collisions at √sNN = 2.76 TeV

We report on the measurement of the inclusive Υ (1S) production in Pb–Pb collisions at √sNN = 2.76 TeV carried out at forward rapidity (2.5 < y < 4) and down to zero transverse momentum using its μ+μ− decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive Υ (1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon– nucleon collisions. The nuclear modification factor, for events in the 0–90% centrality range, amounts to 0.30 ± 0.05(stat) ± 0.04(syst). The observed Υ (1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence