A disease is any condition which results in the disorder of a structure or function in a living organism that is not due to any external injury. The study of disease is called pathology, which includes the study of cause. Disease is often construed as a medical condition associated with specific symptoms and signs. It may be caused by external factors such as pathogens or by internal dysfunctions, particularly of the immune system, such as an immunodeficiency, or by a hypersensitivity, including allergies and autoimmunity.
Harnessing the Sun's unlimited (for all practical purposes) energy supply is one of the most promising alternatives to combustion of fossil fuels. Improved characterisation of coatings for concentrating solar power (CSP) systems will speed development.