perturbation of energy-level system
51Egypt — /ee jipt/, n. 1. Arab Republic of. a republic in NE Africa. 64,791,891; 386,198 sq. mi. (1,000,252 sq. km). Cap.: Cairo. Arabic, Misr. Formerly (1958 71), United Arab Republic. 2. an ancient kingdom in NE Africa: divided into the Nile Delta… …
52Tsunami — For other uses, see Tsunami (disambiguation) …
53United Nations Framework Convention on Climate Change — UNFCCC logo. The United Nations Framework Convention on Climate Change (UNFCCC or FCCC) is an international environmental treaty produced at the United Nations Conference on Environment and Development (UNCED), informally known as the Earth… …
54Density functional theory — Electronic structure methods Tight binding Nearly free electron model Hartree–Fock method Modern valence bond Generalized valence bond Møller–Plesset perturbation theory …
55climate change — Introduction periodic modification of Earth s climate brought about as a result of changes in the atmosphere as well as interactions between the atmosphere and various other geologic, chemical, biological, and geographic factors within the Earth …
56Neptune — This article is about the planet. For other uses, see Neptune (disambiguation). Neptune   …
57Big Bang — This article is about the cosmological model. For the sitcom, see The Big Bang Theory. For other uses, see Big Bang (disambiguation) …
58Black hole — For other uses, see Black hole (disambiguation). Simulated view of a black hole (center) in front of the Large Magellanic Cloud. Note the gravitat …
59Mitigation of global warming — involves taking actions to reduce greenhouse gas emissions and to enhance sinks aimed at reducing the extent of global warming. [ [http://www.ipcc.ch/pdf/glossary/ar4 wg3.pdf IPCC Glossary Working Group III, p. 818] ] This is in distinction to… …
60Biology — For other uses, see Biology (disambiguation). Biology deals with the study of the many varieties of living organisms. Cloc …
