Kōji Husimi (June 29, 1909 – May 8, 2008, ja, 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, the

Husimi Q representation The Husimi Q representation, introduced by Kôdi Husimi in 1940, is a quasiprobability distribution commonly used in quantum mechanics to represent the phase space distribution of a quantum state such as light in the phase space formulation. It i ...

in quantum mechanics, and Husimi's theorem in the mathematics of paper folding are named after him.

Education and career

Husimi studied at the University of Tokyo, graduating in 1933. He spent a year there as an assistant, and then moved to

Osaka University , abbreviated as , is a public research university located in Osaka Prefecture, Japan. It is one of Japan's former Imperial Universities and a Designated National University listed as a "Top Type" university in the Top Global University Project. ...

in 1934, where he soon began working with

Seishi Kikuchi was a Japanese physicist, known for his explanation of the Kikuchi lines that show up in diffraction patterns of diffusely scattered electrons. Biography Seishi Kikuchi was born and grew up in Tokyo. He graduated in 1926 from Tokyo Imperial Un ...

. At Osaka, he became Dean of the Faculty of Science. He moved to

Nagoya University , abbreviated to or NU, is a Japanese national research university located in Chikusa-ku, Nagoya. It was the seventh Imperial University in Japan, one of the first five Designated National University and selected as a Top Type university of T ...

in 1961, and directed the plasma institute there. He retired in 1973, and became a professor emeritus of both Nagoya and Osaka.

Contributions

Physics

A 1940 paper by Husimi introduced the

in quantum mechanics. Husimi also gave the name to the kagome lattice, frequently used in statistical mechanics.

Graph theory

In the mathematical area of graph theory, the name "Husimi tree" has come to refer to two different kinds of graphs:

cactus graph In graph theory, a cactus (sometimes called a cactus tree) is a connected graph in which any two simple cycles have at most one vertex in common. Equivalently, it is a connected graph in which every edge belongs to at most one simple cycle, or ( ...

s (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 Frank Harary (March 11, 1921 – January 4, 2005) was an American mathematician, who specialized in graph theory. He was widely recognized as one of the "fathers" of modern graph theory. Harary was a master of clear exposition and, together with ...

and

George Eugene Uhlenbeck George Eugene Uhlenbeck (December 6, 1900 – October 31, 1988) was a Dutch-American theoretical physicist. Background and education George Uhlenbeck was the son of Eugenius and Anne Beeger Uhlenbeck. He attended the Hogere Burgerschool (High S ...

. 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.

Pacifism and world affairs

Husimi was an early member of the Science Council of Japan, joining it in 1949, and it was largely through his efforts that the Science Council in 1954 issued a statement proposing principles for the peaceful use of nuclear power and opposing the continued existence of nuclear weapons. This statement, in turn, led to the Japanese law outlawing military uses of nuclear technology. Later, he served as president of the Science Council of Japan from 1977 to 1982. He was also a frequent participant in the Pugwash Conferences on Science and World Affairs and a leader of the Committee of Seven for World Peace.

Recreational mathematics

Husimi's recreational interests included origami; he designed several variations of the traditional

orizuru The ''orizuru'' (折鶴 ''ori-'' "folded," ''tsuru'' "crane"), or paper crane, is a design that is considered to be the most classic of all Japanese origami.Jccc Origami Crane Project – Materials For Teachers & Students. MEANING OF THE ORIGAM ...

(paper crane), folded on paper shaped as a rhombus instead of the usual square, and studied the properties of the

bird base Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight s ...

that allow it to be varied within a continuous family of deformations. With his wife, Mitsue Husimi, he wrote a book on the mathematics of origami,. 2nd ed., 1984, . which included a theorem characterizing the folding patterns with four folds meeting at a single vertex that may be folded flat. The generalization of this theorem to arbitrary numbers of folds at a single vertex is sometimes called Husimi's theorem..