52,157 research outputs found
A Turbulent Constitutive Law for the Two-Dimensional Inverse Energy Cascade
We develop a fundamental approach to a turbulent constitutive law for the 2D
inverse cascade, based upon a convergent multi-scale gradient (MSG) expansion.
To first order in gradients we find that the turbulent stress generated by
small-scale eddies is proportional not to strain but instead to `skew-strain,'
i.e. the strain tensor rotated by The skew-strain from a given
scale of motion makes no contribution to energy flux across eddies at that
scale, so that the inverse cascade cannot be strongly scale-local. We show that
this conclusion extends a result of Kraichnan for spectral transfer and is due
to absence of vortex-stretching in 2D. This `weakly local' mechanism of inverse
cascade requires a relative rotation between the principal directions of strain
at different scales and we argue for this using both the dynamical equations of
motion and also a heuristic model of `thinning' of small-scale vortices by an
imposed large-scale strain. Carrying out our expansion to second-order in
gradients, we find two additional terms in the stress that can contribute to
energy cascade. The first is a Newtonian stress with an `eddy-viscosity' due to
differential strain-rotation, and the second is a tensile stress exerted along
vorticity contour-lines. The latter was anticipated by Kraichnan for a very
special model situation of small-scale vortex wave-packets in a uniform strain
field. We prove a proportionality in 2D between the mean rates of differential
strain-rotation and of vorticity-gradient stretching, analogous to a similar
relation of Betchov for 3D. According to this result the second-order stresses
will also contribute to inverse cascade when, as is plausible, vorticity
contour-lines lengthen on average by turbulent advection.Comment: 24 pages, 1 figur
Electracy: the Internet as fifth estate
This account of an experimental approach to apparatus invention is offered as an introduction to apparatus study in general (grammatology), and electracy as the digital apparatus in particular. The approach is that of the Florida Research Ensemble (FRE), working through the EmerAgency, a virtual consultancy developed to translate Arts & Letters pedagogy into institutional consulting. The term 'electracy' (modeled on 'literacy,' a portmanteau of 'electricity' and Derrida's 'trace') was adopted to clarify that digital technologies are not reducible to a 'media literacy,' but include, besides technological innovations, inventions in the dimensions of institution formation and related skill sets, and identity behaviors individual and collective (ethics and politics). Current members of the FRE include Gregory Ulmer (University of Florida), John Craig Freeman (Emerson College), Barbara Jo Revelle (University of Florida), Jack Stenner (University of Florida), Jan Holmevik (Clemson University)
Br(e)king the Exploitation of Labor?: Tensions Regarding the Welfare Workforce
This Article examines the deep human rights concerns within the transmogrifying world of work, focusing on the integral part that work plays in the definition, construction, maintenance, and enhancement of the social contract in the context of the New York City welfare workforce. Part I reviews the employee /partner/independent contractor distinctions, focusing on recent case law, the regulatory tax regime, and related issues. Part II examines the complex pressures that workfare legislation will exert throughout most sectors of the workforce and the unemployed. Part III explores the role of Catholic social teachings on workers\u27 rights as well as the reemergence of the living wage initiative. This Article concludes that the situation is grim, perhaps inexorably Malthusian. As huge pools of surplus labor bid unsuccessfully for increasingly scarce jobs, all but the most educated and technologically adept face unrelenting downward pressures on wage compensation
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