Instanton Calculus in Shell Models of Turbulence

It has been shown recently that intermittency of the Gledzer Ohkitani Yamada (GOY) shell model of turbulence has to be related to singular structures whose dynamics in the inertial range includes interactions with a background of fluctuations. In this paper we propose a statistical theory of these objects by modelling the incoherent background as a Gaussian white-noise forcing of small strength $\Gamma$. A general scheme is developed for constructing instantons in spatially discrete dynamical systems and the Cram\'er function governing the probability distribution of effective singularities of exponent $z$ is computed up to first order in a semiclassical expansion in powers of $\Gamma$. The resulting predictions are compared with the statistics of coherent structures deduced from full simulations of the GOY model at very high Reynolds numbers.Comment: 31 pages, 9 figures, submitted to Phys. Rev.

Towards a two-fluid picture of intermittency in shell models of turbulence

Intermittency in the Gledzer-Okhitani-Yamada (GOY) model of turbulence is explained in terms of collisions of coherent soliton-like structures with a random background issuing from the desintegration of their predecessors. This two-fluid picture is substantiated by the elucidation of local dynamical mechanisms leading to anomalous growth of coherent structures, their detection in true signals involving forcing and dissipation, and an investigation of their statistics.Comment: 4 pages Latex/RevTex, with 5 encapsulated postscript figures, submitted to Phys. Rev. Let

Tunable pinning of a superconducting vortex a by a magnetic vortex

The interaction between a straight vortex line in a superconducting film and a soft magnetic nanodisk in the magnetic vortex state in the presence of a magnetic field applied parallel to the film surfaces is studied theoretically. The superconductor is described by London theory and the nanodisk by the Landau-Lifshitz continuum theory of magnetism, using the approximation known as the rigid vortex model. Pinning of the vortex line by the nanodisk is found to result, predominantly, from the interaction between the vortex line and the changes in the nanodisk magnetization induced by the magnetic field of the vortex line and applied field. In the context of the rigid vortex model, these changes result from the displacement of the magnetic vortex. This displacement is calculated analytically by minimizing the energy, and the pinning potential is obtained. The applied field can tune the pinning potential by controlling the displacement of the magnetic vortex. The nanodisk magnetization curve is predicted to change in the presence of the vortex lineComment: 9 pages, 8 figures. Submitted to Phys. Rev.

Michael Lipsky, 'Street-Level Bureaucracy: Dilemmas of the Individual in Public Service'

This Handbook brings together a collection of leading international authors to reflect on the influence of central contributions, or classics, that have shaped the development of the field of public policy and administration. The Handbook reflects on a wide range of key contributions to the field, selected on the basis of their international and wider disciplinary impact. Focusing on classics that contributed significantly to the field over the second half of the 20th century, it offers insights into works that have explored aspects of the policy process, of particular features of bureaucracy, and of administrative and policy reforms. Each classic is discussed by a leading international scholars. They offer unique insights into the ways in which individual classics have been received in scholarly debates and disciplines, how classics have shaped evolving research agendas, and how the individual classics continue to shape contemporary scholarly debates. In doing so, this volume offers a novel approach towards considering the various central contributions to the field. The Handbook offers students of public policy and administration state-of-the-art insights into the enduring impact of key contributions to the fiel

Building the field of health policy and systems research: framing the questions.

In the first of a series of articles addressing the current challenges and opportunities for the development of Health Policy & Systems Research (HPSR), Kabir Sheikh and colleagues lay out the main questions vexing the field

The azimuthal component of Poynting's vector and the angular momentum of light

The usual description in basic electromagnetic theory of the linear and angular momenta of light is centred upon the identification of Poynting's vector as the linear momentum density and its cross product with position, or azimuthal component, as the angular momentum density. This seemingly reasonable approach brings with it peculiarities, however, in particular with regards to the separation of angular momentum into orbital and spin contributions, which has sometimes been regarded as contrived. In the present paper, we observe that densities are not unique, which leads us to ask whether the usual description is, in fact, the most natural choice. To answer this, we adopt a fundamental rather than heuristic approach by first identifying appropriate symmetries of Maxwell's equations and subsequently applying Noether's theorem to obtain associated conservation laws. We do not arrive at the usual description. Rather, an equally acceptable one in which the relationship between linear and angular momenta is nevertheless more subtle and in which orbital and spin contributions emerge separately and with transparent forms

Current Collegiate Experiences of Big-Time, Non-Revenue, NCAA Athletes

Over the past 30 years experiences of collegiate athletes have been a major focus of scholarly research. Through well-known works, student-athletes’ roles and personal development have been cornerstones of this new knowledge base (Adler & Adler, 1991; Lapchick, 1987). However, an understanding of the big-time athlete who also participates in nonrevenue sports1 is grossly under-represented in the literature. Thus, the purpose of this study was to examine the benefits and challenges that athletes in these sports (e.g., tennis, soccer, golf, track and field, etc.) currently experience. Interviews were conducted with 30 collegiate athletes—who were chosen at random from a sample pool of 9,231 athletes around the country—that focused on the types of benefits and the specific challenges that these athletes face while attending college. Results revealed current benefits of being a big-time, nonrevenue college athlete were very heterogeneous with a total of 24 distinct themes mentioned. The most popular of these included: academic benefits, being on a team, learning life skills, improved time management, and tangible benefits such as equipment, facilities, scholarship and travel. Current challenges that athletes face were much more homogenous, as only three lower order themes received more than two responses: missing out on things in college, lack of free time, and being stereotyped. As a whole, most athletes believed the challenges they face were worth the perceived benefits; and thus, big-time, non-revenue athletes do not receive an inferior overall college education experience (Potuto & O’Hanlon, 2007)