The effect of rare regions on a disordered itinerant quantum antiferromagnet with cubic anisotropy

We study the quantum phase transition of an itinerant antiferromagnet with cubic anisotropy in the presence of quenched disorder, paying particular attention to the locally ordered spatial regions that form in the Griffiths region. We derive an effective action where these rare regions are described in terms of static annealed disorder. A one loop renormalization group analysis of the effective action shows that for order parameter dimensions $p<4$ the rare regions destroy the conventional critical behavior. For order parameter dimensions $p>4$ the critical behavior is not influenced by the rare regions, it is described by the conventional dirty cubic fixed point. We also discuss the influence of the rare regions on the fluctuation-driven first-order transition in this system.Comment: 6 pages RevTe

Smeared phase transition in a three-dimensional Ising model with planar defects: Monte-Carlo simulations

We present results of large-scale Monte Carlo simulations for a three-dimensional Ising model with short range interactions and planar defects, i.e., disorder perfectly correlated in two dimensions. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. This is caused by effects similar to but stronger than Griffiths phenomena. In an infinite-size sample there is an exponentially small but finite probability to find an arbitrary large region devoid of impurities. Such a rare region can develop true long-range order while the bulk system is still in the disordered phase. We compute the thermodynamic magnetization and its finite-size effects, the local magnetization, and the probability distribution of the ordering temperatures for different samples. Our Monte-Carlo results are in good agreement with a recent theory based on extremal statistics.Comment: 9 pages, 6 eps figures, final version as publishe

Modeling infection risk and energy use of upper-room Ultraviolet Germicidal Irradiation systems in multi-room environments

The effectiveness of ultraviolet irradiation at inactivating airborne pathogens is well proven, and the technology is also commonly promoted as an energy-efficient way of reducing infection risk in comparison to increasing ventilation. However, determining how and where to apply upper-room Ultraviolet Germicidal Irradiation devices for the greatest benefit is still poorly understood. This article links multi-zone infection risk models with energy calculations to assess the potential impact of a Ultraviolet Germicidal Irradiation installation across a series of inter-connected spaces, such as a hospital ward. A first-order decay model of ultraviolet inactivation is coupled with a room air model to simulate patient room and whole-ward level disinfection under different mixing and ultraviolet field conditions. Steady-state computation of quanta-concentrations is applied to the Wells–Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative influence of different design factors for susceptible patients co-located with an infectious source or in nearby rooms. In each case, energy requirements are calculated and compared to achieving the same level of infection risk through improved ventilation. Ultraviolet devices are seen to be most effective where they are located close to the infectious source; however, when the location of the infectious source is not known, locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones. Results show an ultraviolet system may be an energy-efficient solution to controlling airborne infection, particularly in semi-open hospital environments, and considering the whole ward rather than just a single room at the design stage is likely to lead to a more robust solution

Quantum walks: a comprehensive review

Quantum walks, the quantum mechanical counterpart of classical random walks, is an advanced tool for building quantum algorithms that has been recently shown to constitute a universal model of quantum computation. Quantum walks is now a solid field of research of quantum computation full of exciting open problems for physicists, computer scientists, mathematicians and engineers. In this paper we review theoretical advances on the foundations of both discrete- and continuous-time quantum walks, together with the role that randomness plays in quantum walks, the connections between the mathematical models of coined discrete quantum walks and continuous quantum walks, the quantumness of quantum walks, a summary of papers published on discrete quantum walks and entanglement as well as a succinct review of experimental proposals and realizations of discrete-time quantum walks. Furthermore, we have reviewed several algorithms based on both discrete- and continuous-time quantum walks as well as a most important result: the computational universality of both continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing Journa

The MeerKAT Galaxy Cluster Legacy Survey: I. Survey overview and highlights

Please abstract in the article.The South African Radio Astronomy Observatory (SARAO), the National Research Foundation (NRF), the National Radio Astronomy Observatory, US National Science Foundation, the South African Research Chairs Initiative of the DSI/NRF, the SARAO HCD programme, the South African Research Chairs Initiative of the Department of Science and Innovation.http://www.aanda.orghj2022Physic