22 research outputs found
Biodiversity conservation: history, protected areas and hotspots
Angola is a large country of great physiographic, climatic and habitat
diversity, with a corresponding richness in animal and plant species. Legally protected
areas (National Parks and Game Reserves) were established from the 1930s
and occupied 6% of the country’s terrestrial area at the time of independence in
1975. As a consequence of an extended war, the Protected Areas were exposed to
serious neglect, poaching and land invasions. Many habitats of biogeographic
importance, and many rare and endemic species came under threat. The recently
strengthened administration gives cause for optimism that a new era for biodiversity
conservation is at hand. The Protected Areas system was greatly expanded in 2011,
and increasing resources are being made available towards achieving management
effectivenessinfo:eu-repo/semantics/publishedVersio
YinYang bipolar dynamic organizational modeling for equilibrium-based decision analysis: Logical transformation of an indigenous philosophy to a global science
Sources of labour productivity: a panel investigation of the role of military expenditure
Colonization of tree xylem by Phytophthora ramorum, P. kernoviae and other Phytophthora species
A simple quality assurance test tool for the visual verification of light and radiation field congruent using electronic portal images device and computed radiography
<p>Abstract</p> <p>Background</p> <p>The radiation field on most megavoltage radiation therapy units are shown by a light field projected through the collimator by a light source mounted inside the collimator. The light field is traditionally used for patient alignment. Hence it is imperative that the light field is congruent with the radiation field.</p> <p>Method</p> <p>A simple quality assurance tool has been designed for rapid and simple test of the light field and radiation field using electronic portal images device (EPID) or computed radiography (CR). We tested this QA tool using Varian PortalVision and Elekta iViewGT EPID systems and Kodak CR system.</p> <p>Results</p> <p>Both the single and double exposure techniques were evaluated, with double exposure technique providing a better visualization of the light-radiation field markers. The light and radiation congruency could be detected within 1 mm. This will satisfy the American Association of Physicists in Medicine task group report number 142 recommendation of 2 mm tolerance.</p> <p>Conclusion</p> <p>The QA tool can be used with either an EPID or CR to provide a simple and rapid method to verify light and radiation field congruence.</p