Roentgen (unit) this derivative quantity the roentgen equivalent physical (rep) to distinguish it from the ICR roentgen. The introduction of the roentgen measurement unit, which relied upon measuring the ionisation of air, replaced earlier less accurate practices that relied on timed exposure, film exposure, or fluorescence. This led the way to setting exposure limits,and the National Council on Radiation Protection and Measurements of the United States established the first formal dose limit in 1931 as 0.1 roentgen per day. The International X-ray and Radium Protection Committee, now known as the International Commission on Radiological Protection (ICRP) soon followed with a limit of
Wilhelm Barthlott (Geodiversity), including migration and globalization. His Biodiversity Distribution Map has been published in numerous textbooks in addition to being the foundation for many postgraduate studies. In the framework of the BMBF-BIOTA-AFRICA project led by him, biodiversity patterns in Africa as a model continent are analyzed and potential impacts of climate change are investigated. Wilhelm Barthlott was the first botanist to use high resolution in scanning electron microscopy systematically in the research of biological surfaces since 1970. Most prominent among his results was the discovery of the self-cleaning effect of superhydrophobic micro- and nanostructured surfaces, which were technically realized with the