Coupled Ostrovsky equations for internal waves in a shear flow

In the context of fluid flows, the coupled Ostrovsky equations arise when two distinct linear long wave modes have nearly coincident phase speeds in the presence of background rotation. In this paper, nonlinear waves in a stratified fluid in the presence of shear flow are investigated both analytically, using techniques from asymptotic perturbation theory, and through numerical simulations. The dispersion relation of the system, based on a three-layer model of a stratified shear flow, reveals various dynamical behaviours, including the existence of unsteady and steady envelope wave packets.Comment: 47 pages, 39 figures, accepted to Physics of Fluid

Transformation of a shoaling undular bore

We consider the propagation of a shallow-water undular bore over a gentle monotonic bottom slope connecting two regions of constant depth, in the framework of the variable-coefficient Korteweg-de Vries equation. We show that, when the undular bore advances in the direction of decreasing depth, its interaction with the slowly varying topography results, apart from an adiabatic deformation of the bore itself, in the generation of a sequence of isolated solitons - an expanding large-amplitude modulated solitary wavetrain propagating ahead of the bore. Using nonlinear modulation theory we construct an asymptotic solution describing the formation and evolution of this solitary wavetrain. Our analytical solution is supported by direct numerical simulations. The presented analysis can be extended to other systems describing the propagation of undular bores (dispersive shock waves) in weakly non-uniform environments

Anonymity and its Prospects in the Digital World

"This work­ing paper traces the changes under­gone by anonymity - and by the dis­courses sur­rounding it - in liberal Western societies. The author asks whether the current politi­cization of the issue is likely to have any impact on the gra­dual dis­appearance of oppor­tunities for anonymity that we are currently witnes­sing and argues that anonymity is an ambi­valent but critical feature of the demo­cratic public sphere. The argu­ment proceeds in three stages. It begins with a number of concep­tual ob­ser­vations on anonymity. From these, a heuristic frame­work emerges with which the changes in anony­mous communi­cation, and in the role this communi­cation plays in society, can be described. The author then analyses the extent to which options for anonymity have been affected by the rev­olution in infor­mation and communi­cation techno­logies and concludes by con­sidering how anonymity is framed in public dis­course and what impacts this has." (author's abstract)"Das Working Paper unter­sucht die Ver­änderungen von Anonymität und den Diskursen über Anonymität in liberalen west­lichen Gesell­schaften. Der Autor fragt, in­wiefern die gegen­wärtige Politi­sierung des Themas einen Einfluss auf das gra­duelle Ver­schwinden der Möglich­keiten anonymer Kom­munikation haben wird und welche Be­deutung Anonymität für die demo­kratische Öffen­tlich­keit hat. Die Analyse voll­zieht sich in drei Schritten: Zunächst wird konzep­tuell ge­klärt, was Anonymität ist und darauf auf­bauend ein heur­istisches Instru­ment ent­wickelt mittels dessen sich die Ver­änderung anonymer Kom­muni­kations­mög­lich­keiten in der Gesell­schaft be­schreiben lassen. Im zweiten Schritt wird dieses Instru­ment zur An­wendung gebracht, um die sich wandelnden Möglich­keiten anonymer Komm­uni­kation im digitalen Struktur­wandel zu porträtieren. Der dritte Teil des Papiers fragt schließ­lich nach der Art und Weise, wie Anonymität im öffent­lichen Diskurs politi­siert wird - und sucht die Erfolgs­aus­sichten ab­zu­schätzen, die diese Thema­tisierung hat, der Ent­wicklung zu be­gegnen oder sie gar um­zu­kehren." (Autorenreferat

Combined effect of rotation and topography on shoaling oceanic internal solitary waves

Internal solitary waves commonly observed in the coastal ocean are often modeled by a nonlinear evolution equation of the Korteweg-de Vries type. Because these waves often propagate for long distances over several inertial periods, the effect of Earth's background rotation is potentially significant. The relevant extension of the Kortweg-de Vries is then the Ostrovsky equation, which for internal waves does not support a steady solitary wave solution. Recent studies using a combination of asymptotic theory, numerical simulations, and laboratory experiments have shown that the long time effect of rotation is the destruction of the initial internal solitary wave by the radiation of small-amplitude inertia-gravity waves, and the eventual emergence of a coherent, steadily propagating, nonlinear wave packet. However, in the ocean, internal solitary waves are often propagating over variable topography, and this alone can cause quite dramatic deformation and transformation of an internal solitary wave. Hence, the combined effects of background rotation and variable topography are examined. Then the Ostrovsky equation is replaced by a variable coefficient Ostrovsky equation whose coefficients depend explicitly on the spatial coordinate. Some numerical simulations of this equation, together with analogous simulations using the Massachusetts Institute of Technology General Circulation Model (MITgcm), for a certain cross section of the South China Sea are presented. These demonstrate that the combined effect of shoaling and rotation is to induce a secondary trailing wave packet, induced by enhanced radiation from the leading wave. © 2014 American Meteorological Society

Language and the development of intercultural competence in an 'internationalised' university: staff and student perspectives

Within the currently diverse UK higher education environment, one important aspect of learning is the development of intercultural competence. The study that informs this paper investigated the ways intercultural competence was perceived as being enhanced or inhibited through current language and educational practices at a university that positions itself as internationally engaged and globally recognised. The project employed a multiple-case study design, examining eight academic programmes drawn from four different broad disciplinary groupings: social sciences, science, engineering, and management. Data were collected through individual, focus group and stimulated recall interviews, the latter using class observation recordings as a stimulus. The study revealed the ways in which language was exploited by both staff and students to convey particular meanings within an intercultural context. It was found that language choices, register and style were perceived as contributing to the pragmatic impact of either reinforcing barriers to or promoting intercultural competence development