J. T. Chalker

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We examine bosons hopping on a one-dimensional lattice in the presence of a random potential at zero temperature. Bogoliubov excitations of the Bose-Einstein condensate formed under such conditions are localized, with the localization length diverging at low frequency as l(omega) approximately 1/omega(alpha). We show that the well-known result alpha=2(More)
We examine the statistical mechanics of spin-ice materials with a [100] magnetic field. We show that the approach to saturated magnetization is, in the low-temperature limit, an example of a 3D Kasteleyn transition, which is topological in the sense that magnetization is changed only by excitations that span the entire system. We study the transition(More)
The decline of Viet Nam's once highly effective commune health stations has resulted in the over-prescription of drugs and the danger of lower public health standards. It must be recognized that private and public activities form part of the same health system, and need firm supervision if it is to flourish.
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We study the vortex lines that are a feature of many random or disordered three-dimensional systems. These show universal statistical properties on long length scales, and geometrical phase transitions analogous to percolation transitions but in distinct universality classes. The field theories for these problems have not previously been identified, so that(More)
  • J Chalker
  • Bulletin of the World Health Organization
  • 2001
OBJECTIVE To improve the use and dosage of antibiotics prescribed at Commune Health Stations in Viet Nam, and in so doing find out whether antibiotic dosage can be easily and reliably measured as a drug-use indicator. METHODS All commune health workers from the 217 commune health stations in Hai Phong Province, Viet Nam, were enlisted over an 18-month(More)
We study the consequences of disorder in the Kitaev honeycomb model, considering both site dilution and exchange randomness. We show that a single vacancy binds a flux and induces a local moment. This moment is polarized by an applied field h: in the gapless phase, for small h the local susceptibility diverges as χ(h)∼ln(1/h); for a pair of nearby vacancies(More)
The effect on prescribing habits of a drug supply and cost sharing system was studied in a hill district in Nepal. In this district the inadequate yearly supply of drugs from the government was supplemented by an extra supply from the project. Drugs were sold at a fixed prescription charge which covered all drugs for one episode of illness. The prescribing(More)