Kôdi Husimi

Kôdi Husimi (June 29, 1909 – May 8, 2008, Japanese: 伏見康治) was a Japanese theoretical physicist who served as the president of the Science Council of Japan.Husimi trees in graph theory, and the Husimi Q representation in quantum mechanics, are named after him.

Husimi studied at the University of Tokyo, graduating in 1933. He spent a year there as an assistant, and then moved to Osaka University in 1934, where he soon began working with Seishi Kikuchi. At Osaka, he became Dean of the Faculty of Science. He moved to Nagoya University in 1961, and directed the plasma institute there. He retired in 1973, and became a professor emeritus of both Nagoya and Osaka.

A 1940 paper by Husimi introduced the Husimi Q representation in quantum mechanics. Husimi also gave the name to the kagome lattice, frequently used in statistical mechanics.

In the mathematical area of graph theory, the name "Husimi tree" has come to refer to two different kinds of graphs: cactus graphs (the graphs in which each edge belongs to at most one cycle) and block graphs (the graphs in which, for every cycle, all diagonals of the cycle are edges). Husimi studied cactus graphs in a 1950 paper, and the name "Husimi trees" was given to these graphs in a later paper by Frank Harary and George Eugene Uhlenbeck. Due to an error by later researchers, the name came to be applied to block graphs as well, causing it to become ambiguous and fall into disuse.

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