Tham khảo tài liệu 'dictionary of material science and high energy physics part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | subsonic flow Flow in which the local Mach number is less than unity. The governing differential equations in subsonic flow are elliptic. substitutional defects Defects arising out of substitution of some atoms in a crystal by atoms of a different element although the basic structure remains the same. Sudbury neutrino observatory SNO The first detector capable of distinguishing electron neutrinos from muon or tauon neutrinos. The detector contains 1000 T of heavy water D2O surrounded by 9500 photo multiplier tubes. Using heavy water gives an advantage over using ordinary water Kamioka detector because deuteron in heavy water is sensitive to the neutral current reaction ve d p n ve . A neutron realized in this reaction can be captured by another nucleus through a n y reaction. A scintillation counter can detect Y quanta. The minimum neutrino energy to activate this reaction is MeV sum-frequency generation When two laser beams of frequencies and 2 are incident on a non-linear material a new beam with frequency sum 1 2 is generated. This occurs via simultaneous absorption of an incident photon from each field followed by emission of a photon at the sum-frequency. summing over histories Richard Feynman devised this method. This method of string theories has been fully developed by Stanley Mandelstam and Alexandar Polyakov. sum rule A formula which establishes the equality between some quantity or expression to the sum over all states of another quantity. The most prominent example is the Thomas-Reiche-Kuhn sum rule. sunspots Magnetic regions roughly the same diameter as the earth which appear as dark spots on the surface of the sun and can last anywhere from a few days to several weeks in the case of the larger ones. The temperature at the center of a sunspot is about 4500 K whereas the photosphere is normally 6000 K. The number of sunspots varies cyclically with an 11 year period related to the solar magnetic cycle. During the sunspot cycle the activity ranges .
