Density probability distribution in one-dimensional polytropic gas dynamics

We discuss the generation and statistics of the density fluctuations in highly compressible polytropic turbulence, based on a simple model and one-dimensional numerical simulations. Observing that density structures tend to form in a hierarchical manner, we assume that density fluctuations follow a random multiplicative process. When the polytropic exponent $\gamma$ is equal to unity, the local Mach number is independent of the density, and our assumption leads us to expect that the probability density function (PDF) of the density field is a lognormal. This isothermal case is found to be singular, with a dispersion $\sigma_s^2$ which scales like the square turbulent Mach number $\tilde M^2$, where $s\equiv \ln \rho$ and $\rho$ is the fluid density. This leads to much higher fluctuations than those due to shock jump relations. Extrapolating the model to the case $\gamma \not =1$, we find that, as the Mach number becomes large, the density PDF is expected to asymptotically approach a power-law regime, at high densities when $\gamma<1$, and at low densities when $\gamma>1$. This effect can be traced back to the fact that the pressure term in the momentum equation varies exponentially with $s$, thus opposing the growth of fluctuations on one side of the PDF, while being negligible on the other side. This also causes the dispersion $\sigma_s^2$ to grow more slowly than $\tilde M^2$ when $\gamma\not=1$. In view of these results, we suggest that Burgers flow is a singular case not approached by the high-$\tilde M$ limit, with a PDF that develops power laws on both sides.Comment: 9 pages + 12 postscript figures. Submitted to Phys. Rev.

Advection of vector fields by chaotic flows

We have introduced a new transfer operator for chaotic flows whose leading eigenvalue yields the dynamo rate of the fast kinematic dynamo and applied cycle expansion of the Fredholm determinant of the new operator to evaluation of its spectrum. The theory hs been tested on a normal form model of the vector advecting dynamical flow. If the model is a simple map with constant time between two iterations, the dynamo rate is the same as the escape rate of scalar quantties. However, a spread in Poincar\'e section return times lifts the degeneracy of the vector and scalar advection rates, and leads to dynamo rates that dominate over the scalar advection rates. For sufficiently large time spreads we have even found repellers for which the magnetic field grows exponentially, even though the scalar densities are decaying exponentially.Comment: 12 pages, Latex. Ask for figures from [email protected]

Personal pack display and active smoking at outdoor café strips: assessing the impact of plain packaging 1 year postimplementation

Aims: We observed tobacco pack display and smoking at outdoor venues over three summers to assess changes in their prevalence following Australia's introduction of plain tobacco packaging with larger pictorial health warnings. Methods: Between January and April 2012 (preplain packaging (PP)), 2013 (early post-PP) and 2014 (1 year post-PP), we counted patrons, smokers and tobacco packs at cafés, restaurants and bars with outdoor seating. Pack type (branded, plain or unknown) and orientation were noted. Rates of active smoking, pack display and pack orientation were analysed using multilevel Poisson regression. Results: Prevalence of pack display among patrons declined from pre-PP (1 pack per 8.7 patrons) to early post-PP (1 pack per 10.4), and remained low 1 year post-PP (1 pack per 10.3). This appeared to be driven by a sustained decline in active smoking post-PP (pre-PP: 8.4% of patrons were smoking; early post-PP: 6.4%; 1 year post-PP: 6.8%). Notably, active smoking declined more in venues with children present than in those without. While early post-PP, plain packs were less often displayed face-up (74.0%) and more often concealed (8.9%) than branded packs pre-PP (face-up: 85.2%; concealed: 4.0%), this was not sustained 1 year post-PP (face-up: 85.7%; concealed: 4.4%). Also, external case use increased from pre-PP (1.2%) to early post-PP (3.5%), but returned to pre-PP levels 1 year post-PP (1.9%). Conclusions: This study demonstrated a sustained reduction in visibility of tobacco products and smoking in public, particularly in the presence of children, from pre-PP to 1 year post-PP. This effect is likely to reduce smoking-related social norms, thereby weakening an important influence on smoking uptake and better supporting quit attempts.Meghan Zacher, Megan Bayly, Emily Brennan, Joanne Dono, Caroline Miller, Sarah Durkin, Michelle Scollo, Melanie Wakefiel

Evidence of strong small-scale population structure in the Antarctic freshwater copepod Boeckella poppei in lakes on Signy Island, South Orkney Islands

Environmental conditions were particularly severe during the Last Glacial Maximum, altering the distribution of the Southern Hemisphere biota, particularly at higher latitudes. The copepod Boeckella poppei is the only macroscopic continental invertebrate species known to be distributed today across the three main biogeographic regions in Antarctica as well as in southern South America. Signy Island (South Orkney Islands) is a unique location for the study of Antarctic freshwater ecosystems due to its location and geographic isolation; it contains 17 lakes in several low altitude catchments. We conducted phylogeographic and demographic analyses using the cox1 gene on 84 individuals of B. poppei from seven lakes across Signy Island. We recorded low levels of genetic diversity and a strong genetic differentiation signal between the eastern and western valleys within the island. Phylogeographic structure and demographic inference analyses suggested at least one asymmetrical dispersal event from west to east. Demographic inference detected a strong signal of population growth during the deglaciation process, which may have followed either (1) a strong genetic bottleneck due to a reduction in population size during the last glacial period, or (2) a founder effect associated with postglacial recolonization of Signy Island from elsewhere. The genetic architecture of this island's populations of B. poppei shows that historical events, rather than continuous dispersal events, likely played a major role in the species' current distribution. Finally, our study considers possible mechanisms for dispersal and colonization success of the most dominant species in the Antarctic freshwater community

Halotolerant Copepoda in South American inland saline waters

The zooplankton in South American saline waters is mainly dominated by copepods at salinities lower than 90 g/l, whereas at salinities above 90 g/l Artemia sp. is totally dominant. The aim of the present study is to analyse the salinity range of halophilic copepods on the basis of a literature review for South American saline inland waters. The calanoid Boeckella poopoensis Marsh, 1906, is widespread on the South American Altiplano and southern Argentinian plains, and in southern Patagonian shallow ponds. In the upper part of the salinity range, 20-90 g/l, B. poopoensis is the only copepod in the zooplankton of southern Patagonian and Altiplano shallow lakes. In the salinity range 5-20 g/l B. poopoensis may co-exist with B. palustris (Harding, 1955), two cyclopoids and an harpacticoid, and at salinities lower than 5 g/l it may co-exist with an even wider range of copepod species. Ecological and biogeographical aspects are also discusse

Enablers and barriers to treatment adherence in heterozygous familial hypercholesterolaemia : a qualitative evidence synthesis

This evidence synthesis is funded by the National Institute for Health Research NIHR Bristol Biomedical Research Centre (Nutrition theme) at University Hospitals Bristol NHS Foundation Trust and The University of Bristol.Peer reviewedPublisher PD

Transient Shear Wave Propagation in a Viscoelastic Gel Cylinder: Comparison of Theory to MRI-Based Measurements

ABSTRACT Shear strain patterns in a cylindrical gelatin sample under transient angular acceleration were measured by tagged magnetic resonance imaging (MRI). Measured strain fields were compared to theoretical strain fields obtained by finite element (FE) simulation. Agreement between theory and experiment is very good. The current results support the utility of the experimental approach for tasks such as measurement of shear waves in brain tissue during angular acceleration of the skull. The results also show that a simple viscoelastic model is suitable to describe rapid shear deformation of a gel biomaterial

On waiting for something to happen

This paper seeks to examine two particular and peculiar practices in which the mediation of apparently direct encounters is made explicit and is systematically theorized: that of the psychoanalytic dialogue with its inward focus and private secluded setting, and that of theatre and live performance, with its public focus. Both these practices are concerned with ways in which “live encounters” impact on their participants, and hence with the conditions under which, and the processes whereby, the coming-together of human subjects results in recognizable personal or social change. Through the rudimentary analysis of two anecdotes, we aim to think these encounters together in a way that explores what each borrows from the other, the psychoanalytic in the theatrical, the theatrical in the psychoanalytic, figuring each practice as differently committed to what we call the “publication of liveness”. We argue that these “redundant” forms of human contact continue to provide respite from group acceptance of narcissistic failure in the post-democratic era through their offer of a practice of waiting