Energy spectra of vortex distributions in two-dimensional quantum turbulence

We theoretically explore key concepts of two-dimensional turbulence in a homogeneous compressible superfluid described by a dissipative two-dimensional Gross-Pitaeveskii equation. Such a fluid supports quantized vortices that have a size characterized by the healing length $\xi$. We show that for the divergence-free portion of the superfluid velocity field, the kinetic energy spectrum over wavenumber $k$ may be decomposed into an ultraviolet regime ($k\gg \xi^{-1}$) having a universal $k^{-3}$ scaling arising from the vortex core structure, and an infrared regime ($k\ll\xi^{-1}$) with a spectrum that arises purely from the configuration of the vortices. The Novikov power-law distribution of intervortex distances with exponent -1/3 for vortices of the same sign of circulation leads to an infrared kinetic energy spectrum with a Kolmogorov $k^{-5/3}$ power law, consistent with the existence of an inertial range. The presence of these $k^{-3}$ and $k^{-5/3}$ power laws, together with the constraint of continuity at the smallest configurational scale $k\approx\xi^{-1}$, allows us to derive a new analytical expression for the Kolmogorov constant that we test against a numerical simulation of a forced homogeneous compressible two-dimensional superfluid. The numerical simulation corroborates our analysis of the spectral features of the kinetic energy distribution, once we introduce the concept of a {\em clustered fraction} consisting of the fraction of vortices that have the same sign of circulation as their nearest neighboring vortices. Our analysis presents a new approach to understanding two-dimensional quantum turbulence and interpreting similarities and differences with classical two-dimensional turbulence, and suggests new methods to characterize vortex turbulence in two-dimensional quantum fluids via vortex position and circulation measurements.Comment: 19 pages, 8 figure

Suburban Sydney

Sydney has been described as a `City of Suburbs.1 Indeed, the process of suburbanisation is arguably one of the most important developments in Australias post-invasion history. Kilometre after kilometre of suburb has for decades dominated the cultural landscape of Sydney and other Australian capital cities, while suburbia has formed the heartland of the bourgeois ideology that has been dominant for more than two generations. Metropolitan Sydneys phenomenal suburban expansion during much of the twentieth century has been explored by a small number of urban historians.2 But the impact and importance of suburbanisation in and around Sydney by far the largest annual metropolitan investment item has still to attract the attention it deserves.34

'The birthplace of Australian multiculturalism?' Retrospective commemoration, participatory memoralisation and official heritage

In Australia, the authorised heritage discourse contributes to shaping the stereotypically Australian. It actively engages in creating a contemporary national story which glosses over the more shameful or distasteful episodes and themes in Australian colonial and post-colonial history which is presented as being by-and-large progressive and benign. While the process of forging national history has become more complex and increasingly fraught, given globalisation and the emergence of new histories, nation and nationalism remain culturally persistent. The turn to multiculturalism from the 1970s as the principal way of defining Australianness and the nation lead some conservatives in politics and the heritage industry to appropriate the new social history, using it to present diversity as an indicator of a fair and open society. In this process, both history - an evolving academic discipline - and the past - lived experience which has meanings and uses in the present - were transformed into heritage. © 2009 Taylor & Francis

An Examination of Foodborne Outbreaks of Salmonella Enteritidis in the United States, 1973-2008

Salmonella is a common enteric pathogen and is the most frequently reported bacterial infection in the United States. The two most commonly reported serotypes causing human illness in the United States are Salmonella serotype Typhimurium and Salmonella serotype Enteritidis (SE). The incidence and number of foodborne outbreaks of SE started to increase in the 1970s and by 1994, SE was the most common Salmonella serotype reported to the Centers for Disease Control and Prevention (CDC). SE has been most commonly associated with consumption of shell eggs. Outbreak reports were obtained from the Foodborne Disease Outbreak Surveillance System (FDOSS) and analyzed. The number of outbreaks of SE has declined by 67% since 1990, likely as a result of the combined effect of on-farm interventions, public health policies, and food safety education messages. In addition to the decline in SE outbreaks, study findings demonstrate that there have been changes in the geographical distribution of SE outbreaks in the US. “Simple egg” foods and retail food settings have been the most commonly and consistently associated vehicles and food consumption and preparation settings with SE outbreaks in the US from 1973 to 2008

Ford\u27s Venture in Mexico

Ford announced in April 2016 that it was planning on investing $1.6 billion to build a Focus manufacturing plant in San Luis Potosi, Mexico. In January 2017, the company announced that it will be withdrawing from the project and pursuing alternative operations. This paper serves as an exploration of the social, cultural, political, and economic factors that influenced Ford’s decision, with an in depth analysis of the impact of Ford’s withdrawal on the company, its stakeholders, and the U.S. and Mexico regions

Snell's Law for a vortex dipole in a Bose-Einstein condensate

A quantum vortex dipole, comprised of a closely bound pair of vortices of equal strength with opposite circulation, is a spatially localized travelling excitation of a planar superfluid that carries linear momentum, suggesting a possible analogy with ray optics. We investigate numerically and analytically the motion of a quantum vortex dipole incident upon a step-change in the background superfluid density of an otherwise uniform two-dimensional Bose-Einstein condensate. Due to the conservation of fluid momentum and energy, the incident and refracted angles of the dipole satisfy a relation analogous to Snell's law, when crossing the interface between regions of different density. The predictions of the analogue Snell's law relation are confirmed for a wide range of incident angles by systematic numerical simulations of the Gross-Piteavskii equation. Near the critical angle for total internal reflection, we identify a regime of anomalous Snell's law behaviour where the finite size of the dipole causes transient capture by the interface. Remarkably, despite the extra complexity of the surface interaction, the incoming and outgoing dipole paths obey Snell's law.Comment: 16 pages, 7 figures, Scipost forma

Three-body interactions in complex fluids: virial coefficients from simulation finite-size effects

A simulation technique is described for quantifying the contribution of three-body interactions to the thermodynamical properties of coarse-grained representations of complex fluids. The method is based on comparing the third virial coefficient $B_3$ for a complex fluid with that of an approximate coarse-grained model described by a pair potential. To obtain $B_3$ we introduce a new technique which expresses its value in terms of the measured volume-dependent asymptote of a certain structural function. The strategy is applicable to both Molecular Dynamics and Monte Carlo simulation. Its utility is illustrated via measurements of three-body effects in models of star polymer and highly size-asymmetrical colloid-polymer mixtures.Comment: 13 pages, 8 figure

Town Planning

From an accidental city without a plan, Sydney has become a city with many plans. Some would say too many, and there have been endless rounds of planning system reform since the 1980s. The central city and suburbs no longer grow âlike topsyâ but with the greater metropolitan area still being propelled by market forces towards a population of seven million by the mid twenty-first century, there are new sets of pressures around both old (development versus environment, local-state tensions, congestion) and new (affordability, social polarisation, impacts of climate change) problems which inescapably challenge the first Australian city and the one most connected to the global economy