ABSTRACT
In this paper we use spontaneous flux production in annular superconductors to shed light on the Kibble-Zurek (KZ) scenario. In particular, we examine the effects of finite size and external fields, neither of which is directly amenable to the KZ analysis. Supported by 1D and 3D simulations, the properties of a superconducting ring are seen to be well represented by analytic Gaussian approximations which encode the KZ scales indirectly. Experimental results for annuli in the presence of external fields corroborate these findings.
Subject(s)
Electric Conductivity , Electromagnetic Fields , Models, Statistical , Scattering, Radiation , Computer SimulationABSTRACT
A public plan for eradicating Salmonella in Danish table-egg production was implemented in 1996. During 2002, the poultry industry took over the responsibility of the programme. The proportion of infected layer flocks was reduced from 13.4% in 1998 to 0.4% in 2006. The public-health impact of the plan has been quite marked. In 1997, 55-65% of the 5015 cases of human salmonellosis were estimated to be associated with eggs. In 2006, these figures were reduced to 1658 and 5-7%, respectively. Based on an assessment of the number of human cases attributable to table eggs, we used probabilistic modelling to estimate the avoided societal costs (health care and lost labour), and compared these with the public costs of control. The probable avoided societal costs during 1998-2002 were estimated to be 23.3 million euros (95% CI 16.3-34.9), and the results showed a continuous decreasing cost-benefit ratio reaching well below 1 in 2002. Further reductions in the primary production based on effective surveillance and control are required to ensure continued success.
Subject(s)
Chickens , Eggs/microbiology , Poultry Diseases/prevention & control , Salmonella Infections/economics , Salmonella Infections/prevention & control , Animals , Communicable Disease Control/economics , Communicable Disease Control/methods , Cost-Benefit Analysis , Denmark/epidemiology , Humans , Models, Biological , Models, Statistical , Poultry Diseases/economics , Public Health/economics , Time FactorsABSTRACT
New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb-Al/Al(ox)/Nb annular Josephson tunnel junctions (JTJs) as a function of the quench time, tau(Q). The probability f(1) to trap a single defect during the normal-metal-superconductor phase transition clearly follows an allometric dependence on tau(Q) with a scaling exponent sigma = 0.5, as predicted from the Zurek-Kibble mechanism for realistic JTJs formed by strongly coupled superconductors. This definitive experiment replaces one reported by us earlier, in which an idealized model was used that predicted sigma = 0.25, commensurate with the then much poorer data. Our experiment remains the only condensed matter experiment to date to have measured a scaling exponent with any reliability.
ABSTRACT
Phase transitions create a domain structure with defects, which has been argued by Zurek and Kibble (ZK) to depend in a characteristic way on the quench rate. We present an experiment to measure the ZK scaling exponent sigma. Using long symmetric Josephson tunnel junctions, for which the predicted index is sigma=0.25, we find sigma=0.27+/-0.05. Further, we agree with the ZK prediction for the overall normalization.
