Identifying Anticyclonic Vortex Features Produced by the Rossby Wave Instability in Protoplanetary Disks

Several nearby protoplanetary disks have been observed to display large scale crescents in the (sub)millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby wave instability within the gaseous disk. Such vortices have local gas over-densities and are expected to concentrate dust particles with Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescent are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counter-rotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculation of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and 12CO emission around the frequency of 345 GHz. We find that the anticyclonic features of vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability to detect such vortex features and present an analysis procedure to infer their kinematic properties.Comment: 14 pages, 8 figures, Accepted for publication in Astrophysical Journa

Prethermal nematic order and staircase heating in a driven frustrated Ising magnet with dipolar interactions

Many-body systems subject to a high-frequency drive can show intriguing thermalization behavior. Prior to heating to a featureless infinite-temperature state, these systems can spend an exponentially long time in prethermal phases characterized by various kinds of order. Here, we uncover the rich non-equilibrium phase diagram of a driven frustrated two-dimensional Ising magnet with competing short-range ferromagnetic and long-range dipolar interactions. We show that the ordered stripe and nematic phases, which appear in equilibrium as a function of temperature, underpin subsequent prethermal phases in a new multi-step heating process en route towards the ultimate heat death. We discuss implications for experiments on ferromagnetic thin films and other driving induced phenomena in frustrated magnets.Comment: 4 pages + 2 figure

A Generalized Birkhoff-Rott Equation for Two-Dimensional Active Scalar Problems

In this paper we derive evolution equations for the two-dimensional active scalar problem when the solution is supported on one-dimensional curves. These equations are a generalization of the Birkhoff–Rott equation when vorticity is the active scalar. The formulation is Lagrangian and it is valid for nonlocal kernels K that may include both a gradient and an incompressible term. We develop a numerical method for implementing the model which achieves second order convergence in space and fourth order in time. We verify the model by simulating classic active scalar problems such as the vortex sheet problem (in the case of inviscid, incompressible flow) and the collapse of delta ring solutions (in the case of pure aggregation), finding excellent agreement. We then study two examples with kernels of mixed type, i.e., kernels that contain both incompressible and gradient flows. The first example is a vortex density model which arises in superfluids. We analyze the effect of the added gradient component on the Kelvin–Helmholtz instability. In the second example, we examine a nonlocal biological swarming model and study the dynamics of density rings which exhibit complicated milling behavior

Green procurement in the private sector: a state of the art review between 1996 and 2013

NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Cleaner Production. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Cleaner Production, Volume 85, 15 December 2014, Pages 122–133. DOI 10.1016/j.jclepro.2014.08.106The purpose of this paper is to identify the main themes of Green Procurement (GP) in the private sector through a literature review of papers published between 1996 and 2013 and to develop some future research directions. GP research has garnered interest from academics and industry alike. This is demonstrated by the increasing number of academic papers published in recent years. This literature review builds on the three themes in the adoption of GP identified from the literature: 1) the motivation and drivers for the implementation of GP; 2) barriers to the implementation of GP; 3) the performance impacts of the adoption of GP. Given that there are distinctive features of the private sector, compared to the public sector, this analysis focuses on GP in the private sector. The approach to GP holds important implications for managers, by directing limited resources towards projects which intersect both environmental performance and economic performance. The article discusses interesting findings, develops a conceptual framework of GP and suggests a number of directions for future research