Helicity and alpha-effect by current-driven instabilities of helical magnetic fields

Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\alpha$-effect scale with the current helicity of the background field. The $\alpha$-tensor is highly anisotropic as the components $\alpha_{\phi\phi}$ and $\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\alpha\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.Comment: 6 pages, 7 figures, submitted to MNRA

School-based educational and on-site vaccination intervention among adolescents: study protocol of a cluster randomised controlled trial

INTRODUCTION: Childhood vaccination programmes have been established in all Organisation for Economic Co-operation and Development (OECD) countries; however, measles, mumps and rubella (MMR) as well as diphtheria, tetanus, pertussis and polio (Tdap-IPV) vaccination rates are not optimal in adolescents. Education in combination with easy access vaccination may be a promising approach to improve vaccination rates. We aim at improving MMR and Tdap-IPV rates in a school setting in the context of a planned cluster randomised controlled trial (cRCT), the present paper describes the detailed protocol of this trial. METHODS AND ANALYSIS: We will conduct a school-based cRCT, where schools will be randomised to either an educational condition addressing knowledge, risk communication and enhancing self-efficacy regarding vaccination or a low-intensity information condition. In both conditions, a bus equipped with medical staff and materials, will be delivering MMR and Tdap-IPV vaccine directly after the intervention. Schools in the city centre of Berlin, Germany, will be stratified by percentage of migration and type of school. Primary outcome is the number of students who receive vaccination in the bus. Secondary outcomes are knowledge and self-efficacy. An estimated sample size of 355 school classes with approximately 25 students per class is required. The planned analyses will take the nested structure of students, classes and schools into account. ETHICS AND DISSEMINATION: The study will be performed according to the principles of Good Clinical Practice and the Declaration of Helsinki. Approval was obtained by the local ethics committee. Parents of all students will be informed in advance. Their written consent will be obtained, in case students are underage. For dissemination, we will engage with governmental organisations to create potential of our educational unit to be included in future public health prevention schemes