Spontaneous rotating vortex rings in a parametrically driven polariton fluid

We present the theoretical prediction of spontaneous rotating vortex rings in a parametrically driven quantum fluid of polaritons -- coherent superpositions of coupled quantum well excitons and microcavity photons. These rings arise not only in the absence of any rotating drive, but also in the absence of a trapping potential, in a model known to map quantitatively to experiments. We begin by proposing a novel parametric pumping scheme for polaritons, with circular symmetry and radial currents, and characterize the resulting nonequilibrium condensate. We show that the system is unstable to spontaneous breaking of circular symmetry via a modulational instability, following which a vortex ring with large net angular momentum emerges, rotating in one of two topologically distinct states. Such rings are robust and carry distinctive experimental signatures, and so they could find applications in the new generation of polaritonic devices.Comment: 6 pages, 4 figure

Supercooling and fragile glassiness in a dipolar kagome Ising magnet

We study equilibration and ordering in the classical dipolar kagome Ising antiferromagnet, which we show behaves as a disorder-free fragile spin glass. By identifying an appropriate order parameter, we demonstrate a transition to the ordered state proposed by Chioar et al. [Phys. Rev. B 93, 214410 (2016)] with a 12-site unit cell that breaks time-reversal and sublattice symmetries, and further provide evidence that the nature of the transition is first order. Upon approaching the transition, the spin dynamics slow dramatically. The system readily falls out of equilibrium, overshooting the transition and entering a supercooled liquid regime. Using extensive Monte Carlo simulations, we show that the system exhibits super-Arrhenius behaviour above the ordering transition. The relaxation time diverges according to a Vogel-Fulcher form at a finite `glass transition' temperature in the supercooled regime. Such behaviour, characteristic of fragile glasses, is particularly remarkable as the model is free of quenched disorder, does not straightforwardly conform to the avoided criticality paradigm, and is simple and eminently realisable in engineered nanomagnetic arrays

Emergent Coulombic criticality and Kibble-Zurek scaling in a topological magnet

When a classical system is driven through a continuous phase transition, its nonequilibrium response is universal and exhibits Kibble-Zurek scaling. We explore this dynamical scaling in the novel context of a three-dimensional topological magnet with fractionalized excitations, namely the liquid-gas transition of the emergent mobile magnetic monopoles in dipolar spin ice. Using field-mixing and finite-size scaling techniques, we place the critical point of the liquid-gas line in the three-dimensional Ising universality class. We then demonstrate Kibble-Zurek scaling for sweeps of the magnetic field through the critical point. Unusually slow microscopic time scales in spin ice offer a unique opportunity to detect this universal nonequilibrium physics in current experimental setups.This work was supported in part by Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/G049394/1 (C.C.), the Helmholtz Virtual Institute “New States of Matter and Their Excitations,” and the EPSRC NetworkPlus on “Emergence and Physics far from Equilibrium.” Research at Perimeter Institute is supported by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Economic Development and Innovation. The calculations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/) and the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk/, for which access was provided by the ARCHER Driving Test scheme). The authors are grateful to A. Sandvik for useful discussions and to S. L. Sondhi for advice and collaboration on several pieces of related work. J.O.H. is grateful to the EPSRC for funding, and to Michael Rutter for computing support.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.92.07514

Structural and Functional Analysis of Multi-Interface Domains

10.1371/journal.pone.0050821PLoS ONE71

Cooling of Quark Stars in the Color Superconductive Phase: Effect of Photons from Glueball decay

The cooling history of a quark star in the color superconductive phase is investigated. Here we specifically focus on the 2-flavour color (2SC) phase where novel process of photon generation via glueball (GLB) decay have been already investigated (Ouyed & Sannino 2001). The picture we present here can in principle be generalized to quark stars entering a superconductive phase where similar photon generation mechanisms are at play. As much as 10^{45}-10^{47} erg of energy is provided by the GLB decay in the 2SC phase. The generated photons slowly diffuse out of the quark star keeping it hot and radiating as a black-body (with possibly a Wien spectrum in gamma-rays) for millions of years. We discuss hot radio-quiet isolated neutron stars in our picture (such as RX J185635-3754 and RX J0720.4-3125) and argue that their nearly blackbody spectra (with a few broad features) and their remarkably tiny hydrogen atmosphere are indications that these might be quark stars in the color superconductive phase where some sort of photon generation mechanism (reminiscent of the GLB decay) has taken place. Fits to observed data of cooling compact stars favor models with superconductive gaps of Delta_2SC = 15-35 MeV and densities rho_2SC=(2.5-3.0)rho_N (rho_N being the nuclear matter saturation density) for quark matter in the 2SC phase. If correct, our model combined with more observations of isolated compact stars could provide vital information to studies of quark matter and its exotic phases.Comment: 7 journal pages, 4 figures, accepted for publication in MNRAS (more discussions on photon cooling versus neutrino cooling before and after pairing of quarks

Pricing European Options with a Log Student's t-Distribution: a Gosset Formula

The distribution of the returns for a stock are not well described by a normal probability density function (pdf). Student's t-distributions, which have fat tails, are known to fit the distributions of the returns. We present pricing of European call or put options using a log Student's t-distribution, which we call a Gosset approach in honour of W.S. Gosset, the author behind the nom de plume Student. The approach that we present can be used to price European options using other distributions and yields the Black-Scholes formula for returns described by a normal pdf.Comment: 12 journal pages, 9 figures and 3 tables (Submitted to Physica A

Processfolio: uniting Academic Literacies and Critical Emancipatory Action Research for practitioner-led inquiry into EAP writing assessment

This paper reports on the design and implementation of an alternative form of writing assessment on a UK English for Academic Purposes (EAP) presessional course. The assessment, termed processfolio, was a response to research inquiry into how writing assessment in a local context negated student agency and inculcated disempowering models of teaching and learning academic writing. The project merged an Academic Literacies approach to writing (Lea and Street, 1998) with a Critical Emancipatory Action Research (Carr and Kemmis, 1986) framework and a Critical Realist(Bhaskar, 1989) perspective. Data collected from the folios and interviews with students and teachers on their experiences of the processfolio found that a small scale intervention has potential for agency to be exercised within the highly constrained context of a UK EAP pre-sessional. New directions in research are proposed which can engage students and teachers to work for change in UK EAP assessment within their internal and external constraints

The Impact of a SIG on Assessment Literacy

A major aim of professional associations is to provide opportunities for professionals to interact with others, share ideas and develop in their chosen profession. Professional associations exist to provide specialized networking and development opportunities to a specific profession, group of individuals or field of study. To promote and support specialized research and communication, smaller subgroups within an association are often chartered or developed. These subgroups are typically known as Special Interest Groups. According to Jacob et al. (2013), association members join SIGs because they want to go deeper into a specialized content area and they enjoy networking with others who ‘speak the same language.’ The TESOL Arabia Testing, Assessment and Evaluation SIG (TAE SIG) has focused their professional development activities on an important trend in the field, that of language assessment literacy (LAL). Language assessment literacy has been a critical topic in English language teaching since the late 1990s. Unfortunately, this is mainly due to the fact that so many English language teachers are not assessment literate. In other words, many English language teachers lack the knowledge and skills to write effective language tests, evaluate the effectiveness of their tests, and use their test results in meaningful ways. The purpose of this chapter is to critically examine the status of LAL in the Middle East and North Africa (MENA) region and report on activities that the TAE SIG has implemented to increase LAL

Factors in AIDS Dementia Complex Trial Design: Results and Lessons from the Abacavir Trial

OBJECTIVES: To determine the efficacy of adding abacavir (Ziagen, ABC) to optimal stable background antiretroviral therapy (SBG) to AIDS dementia complex (ADC) patients and address trial design. DESIGN: Phase III randomized, double-blind placebo-controlled trial. SETTING: Tertiary outpatient clinics. PARTICIPANTS: ADC patients on SBG for ≥8 wk. INTERVENTIONS: Participants were randomized to ABC or matched placebo for 12 wk. OUTCOME MEASURES: The primary outcome measure was the change in the summary neuropsychological Z score (NPZ). Secondary measures were HIV RNA and the immune activation markers β-2 microglobulin, soluble tumor necrosis factor (TNF) receptor 2, and quinolinic acid. RESULTS: 105 participants were enrolled. The median change in NPZ at week 12 was +0.76 for the ABC + SBG and +0.63 for the SBG groups (p = 0.735). The lack of efficacy was unlikely related to possible limited antiviral efficacy of ABC: at week 12 more ABC than placebo participants had plasma HIV RNA ≤400 copies/mL (p = 0.002). There were, however, other factors. Two thirds of patients were subsequently found to have had baseline resistance to ABC. Second, there was an unanticipated beneficial effect of SBG that extended beyond 8 wk to 5 mo, thereby rendering some of the patients at baseline unstable. Third, there was an unexpectedly large variability in neuropsychological performance that underpowered the study. Fourth, there was a relative lack of activity of ADC: 56% of all patients had baseline cerebrospinal fluid (CSF) HIV-1 RNA <100 copies/mL and 83% had CSF β-2 microglobulin <3 nmol/L at baseline. CONCLUSIONS: The addition of ABC to SBG for ADC patients was not efficacious, possibly because of the inefficacy of ABC per se, baseline drug resistance, prolonged benefit from existing therapy, difficulties with sample size calculations, and lack of disease activity. Assessment of these trial design factors is critical in the design of future ADC trials