Skin Cancer Prevention, Tanning and Vitamin D: A Content Analysis of Print Media in Germany and Switzerland.

BACKGROUND: Print media are a major source of health information. OBJECTIVES: To analyse press coverage related to skin cancer prevention. METHODS: We conducted a content analysis of print media articles pertaining to skin cancer prevention, solaria and vitamin D published in Germany and Switzerland over a 1-year period between 2012 and 2013. RESULTS: Overall, 2,103 articles were analysed. Applying sunscreen was by far the most common sun protection recommendation. A considerable number of articles on solaria and vitamin D advocated exposure to ultraviolet radiation to enhance physical appearance and vitamin D photosynthesis, often without mentioning any precaution measures. In total, 26.8% of the articles contained misleading or erroneous statements mostly related to sunscreen use and vitamin D issues. CONCLUSIONS: Print media can serve as powerful education tools to foster skin cancer prevention. However, misleading or erroneous reports may negatively impact sun-safe behaviour.

Self-similar wave produced by local perturbation of the Kelvin-Helmholtz shear-layer instability.

We show that the Kelvin-Helmholtz instability excited by a localized perturbation yields a self-similar wave. The instability of the mixing layer was first conceived by Helmholtz as the inevitable growth of any localized irregularity into a spiral, but the search and uncovering of the resulting self-similar evolution was hindered by the technical success of Kelvin's wavelike perturbation theory. The identification of a self-similar solution is useful since its specific structure is witness of a subtle nonlinear equilibrium among the forces involved. By simulating numerically the Navier-Stokes equations, we analyze the properties of the wave: growth rate, propagation speed and the dependency of its shape upon the density ratio of the two phases of the mixing layer.