We study the two-dimensional kinetic Ising model below its equilibrium critical temperature, subject to a square-wave oscillating external field. We focus on the multi-droplet regime where the metastable phase decays through nucleation and growth of many droplets of the stable phase. At a critical frequency, the system undergoes a genuine non-equilibrium phase transition, in which the symmetry-broken phase corresponds to an asymmetric stationary limit cycle for the time-dependent magnetization. We investigate the universal aspects of this dynamic phase transition at various temperatures and field amplitudes via large-scale Monte Carlo simulations, employing finite-size scaling techniques adopted from equilibrium critical phenomena. The critical exponents, the fixed-point value of the fourth-order cumulant, and the critical order-parameter distribution all are consistent with the universality class of the two-dimensional equilibrium Ising model. We also study the cross-over from the multi-droplet to the strong-field regime, where the transition disappears.

Abstract:In this study, we investigate the interaction of jets with their environment at a microscopic level, which is a key open question in the study of relativistic jets. Using small simulation systems during past research, we initially studied the evolution of both electron-proton and electron-positron relativistic jets containing helical magnetic fields, by focusing on their interactions with an ambient plasma. Here, using larger jet radii, we have performed simulations of global jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities, such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the mushroom instability (MI). We found that the evolution of global jets strongly depends on the size of the jet radius. For example, phase bunching of jet electrons, in particular in the electron-proton jet, is mixed with a larger jet radius as a result of the more complicated structures of magnetic fields with excited kinetic instabilities.Galaxies 2017, 5, 58; doi:10.3390/galaxies5040058 www.mdpi.com/journal/galaxies Galaxies 2017, 5, 58 2 of 7In our simulation, these kinetic instabilities led to new types of instabilities in global jets. In the electron-proton jet simulation, a modified recollimation occurred, and jet electrons were strongly perturbed. In the electron-positron jet simulation, mixed kinetic instabilities occurred early, followed by a turbulence-like structure. Simulations using much larger (and longer) systems are required in order to further thoroughly investigate the evolution of global jets containing helical magnetic fields.

We briefly introduce hysteresis in spatially extended systems and the dynamic phase transition observed as the frequency of the oscillating field increases beyond a critical value. Hysteresis and the decay of metastable phases are closely related phenomena, and a dynamic phase transition can occur only for field amplitudes, temperatures, and system sizes at which the metastable phase decays through nucleation and growth of many droplets. We present preliminary results from extensive Monte Carlo simulations of a two-dimensional kinetic Ising model in a square-wave oscillating field and estimate critical exponents by finite-size scaling techniques adapted from equilibrium critical phenomena. The estimates are consistent with the universality class of the two-dimensional equilibrium Ising model and inconsistent with two-dimensional random percolation. However, we are not aware of any theoretical arguments indicating why this should be so. Thus, the question of the universality class of this nonequilibrium critical phenomenon remains open.

It is estimated that 2.3 million people in the UK are living with coronary heart disease (CHD) (ONS 2014a). It is therefore important to have a deeper understanding of the pathophysiology of the condition and an awareness of the complex interplay of contributory factors. Written from the perspective of a student ODP, this article investigates the aetiology, presentation and progression of the disease, and puts CHD into the context of the emerging anaesthetic practitioner's practice.