Symmetry breaking in MAST plasma turbulence due to toroidal flow shear

The flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up-down symmetry of the magnetic equilibrium. Using experimental Beam-Emission-Spectroscopy (BES) measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating density field. The tilt is a statistical expression of the "shearing" of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the nonlinear stability threshold. Away from the threshold, the symmetry is effectively restored

Of Remedies and Poisons: Recreational Use of Antiretroviral Drugs in the Social Imagination of South African Carers

During an ethnographic study of barriers to, and compliance with, antiretroviral (ARV) treatment in the South Africa’s West Coast region, our team came across a general sense amongst heath care providers that there was a lively illicit trade in antiretroviral medications. In itself, this is seen to be a barrier to adherence for many of their patients whose medication is traded to, or stolen by, drug dealers. Independent anecdotal evidence is emerging about this trade, though there has been little hard data verifying the existence of a recreational market for ARVs. While there are rumours that Efavirenz (some of whose side effects are hallucinogenic) is being used in the manufacture of crystal methamphetamine (locally ‘tik’), such reports, in themselves, do not seem able to explain the ubiquity (and the confidence) of the belief in this trade amongst the health care providers with whom we have interacted. This paper explores aspects of the off-label trade of ARVs (as we have come to know it) and, as importantly, how rumor and knowledge of this trade has gained increasing currency in the social imagination of health and social care workers. This, we argue, could precipitate a real crisis in the Government’s public rollout programme.Keywords: Social Imagination, South Africa, antiretroviral treatment, Recreational drugs, HIV/AID

UBV(RI)C JHK observations of Hipparcos-selected nearby stars

We present homogeneous, standardized UBV(RI)C photometry for over 700 nearby stars selected on the basis of Hipparcos parallaxes. Additionally, we list JHK photometry for about half of these stars, as well as L photometry for 86 of the brightest. A number of stars with peculiar colours or anomalous locations in various colour–magnitude diagrams are discussed.Web of Scienc

Metal Concentrations in Grape Spirits

Metals are a necessity for human health as they play significant roles in biological systems. However,contamination of food and beverages by heavy metals such as lead (Pb), iron (Fe), chromium (Cr), cadmium(Cd), copper (Cu), cobalt (Co), Nickel (Ni) and zinc (Zn) is a major public health problem in developingcountries. In this study we evaluated the levels of Li, Be, B, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr,Mo, Cd, Sb, Ba, Hg and Pb in grape spirits, including pot still spirit, neutral wine spirit and commercialbrandies. Interesting variations in the levels of metals was observed. Factors such as origin and type ofspirits influenced levels of metals in spirits. These differences in some metal levels such as copper canbe used to determine possible adulteration and in authenticity assessments of brandies. Surprisingly thecommercial brandies had higher metal concentrations when compared to pot still spirit and neutral winespirit. Unmatured pot still spirit had the highest copper levels. Our study shows that generally the metallevels in most of the commercial brandies were within permissible limits

Further observations of Hipparcos red stars and standards for UBV(RI)C photometry

We present homogeneous and standardized UBV(RI)C JHK photometry for over 100 M stars selected from an earlier paper on the basis of apparent photometric constancy. L photometry has been obtained for stars brighter than about L = 6. Most of the stars have a substantial number of UBV(RI)C observations and, it is hoped, will prove useful as red supplementary standards. Additionally,we list JHK photometry for nearly 300 Hipparcos red stars not selected as standards, as well as L photometry for the brightest stars.Web of Scienc

Ion-scale turbulence in MAST: anomalous transport, subcritical transitions, and comparison to BES measurements

We investigate the effect of varying the ion temperature gradient (ITG) and toroidal equilibrium scale sheared flow on ion-scale turbulence in the outer core of MAST by means of local gyrokinetic simulations. We show that nonlinear simulations reproduce the experimental ion heat flux and that the experimentally measured values of the ITG and the flow shear lie close to the turbulence threshold. We demonstrate that the system is subcritical in the presence of flow shear, i.e., the system is formally stable to small perturbations, but transitions to a turbulent state given a large enough initial perturbation. We propose that the transition to subcritical turbulence occurs via an intermediate state dominated by low number of coherent long-lived structures, close to threshold, which increase in number as the system is taken away from the threshold into the more strongly turbulent regime, until they fill the domain and a more conventional turbulence emerges. We show that the properties of turbulence are effectively functions of the distance to threshold, as quantified by the ion heat flux. We make quantitative comparisons of correlation lengths, times, and amplitudes between our simulations and experimental measurements using the MAST BES diagnostic. We find reasonable agreement of the correlation properties, most notably of the correlation time, for which significant discrepancies were found in previous numerical studies of MAST turbulence.Comment: 67 pages, 37 figures. Submitted to PPC

Transition to subcritical turbulence in a tokamak plasma

Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.Comment: 16 pages, 5 figures, accepted to Journal of Plasma Physic

Between the Clinic and the Community: Temporality and Patterns of ART Adherence in the Western Cape Province, South Africa

In an ethnographic study conducted over thirty months in South Africa’s Western Cape Province ending in 2012, we explored ART adherence amongst almost 200 patients attending three clinics. This setting contained significant political, structural, economic and socio cultural barriers to the uptake of, and adherence to, treatment. Such barriers certainly impacted patient drug use and the labelling of clients as ‘adherent’ or ‘non-adherent’. Yet, as our fieldwork developed, it became apparent that these labels also bore little relationship to the amount and regularity of drug consumption outside the clinic. Indeed, the people that we knew moved through these labels in ways that could not simply be explained by brute socio-economic circumstances, poor understanding of the functions of the drugs, or varying levels of family and community support, which themselves often changed over time. This paper presents four on-going ‘patterns of adherence’, which are clearly discernible in the communities in which we worked. Each pattern is demonstrated through the life of an ‘index patient’ whose case is seen to be representative of the range of experiences and practices observed under the terms ‘adherent’ and ‘non-adherent’. We argue that such terms are deeply contextual and, crucially, temporally situated. The complex intertwining of political, economic, socio cultural, gender, and biological factors that constitute the lives of participants exists in time and we call for a focus on evolving lives in relationship to changing health systems that can follow (and respond to) such developments to better deliver both information and services.Keywords: ART adherence, community, health systems, socio-cultural barriers drug consumptio

A search for previously unrecognised metal-poor subdwarfs in the Hipparcos astrometric catalogue

We have identified 317 stars included in the Hipparcos astrometric catalogue which have parallaxes measured to a precision of better than 15%, and whose location in the (M_V, (B-V)_T) diagram implies a metallicity comparable to or less than that of the intermediate-abundance globular cluster, M5. We have undertaken an extensive literature search to locate Stromgren, Johnson/Cousins and Walraven photometry for over 120 stars. In addition, we present new UBVRI photometry of 201 of these candidate halo stars, together with similar data for a further 14 known metal-poor subdwarfs. Those observations provide the first extensive dataset of RI photometry of metal-poor, main-sequence stars with well-determined trigonometric parallaxes. Finally, we have obtained intermediate-resolution optical spectroscopy of 175 stars. We are able to estimate abundances for 270 stars. The overwhelming majority have near-solar abundance, with their inclusion in the present sample stemming from errors in the colours listed in the Hipparcos catalogue. Only 44 stars show consistent evidence of abundances below [Fe/H]= -1.0. Nine are additions to the small sample of metal-poor subdwarfs with accurate photometry. We consider briefly the implication of these results for cluster main-sequence fitting.Comment: to appear in Monthly Notices of the Royal Astronomical Society (some tables appear out of order in the text