physics

Kôdi Husimi

Kôdi Husimi is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Kôdi Husimi rather than just read about it. In short: 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, the Husimi Q representation in quantum mechanics, and Husimi's theorem in the mathematics of paper folding are named after him.

Key takeaways

Kôdi Husimi belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kôdi Husimi to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kôdi Husimi from memory before moving on to harder problems.

Reference excerpt

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, the Husimi Q representation 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 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.

Contributions

Physics 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.

Graph theory 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.

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

References

Further reading Konuma, Michiji; Otsuka, Masuhiko (May 2009), "Kodi Husimi and 'science and society'", Nippon Butsuri Gakkai-Shi (in Japanese), 64 (5): 357–362

Illustrations

Worked examples

Example 1 — a first encounter with Kôdi Husimi

Start with the simplest possible case. Write down what Kôdi Husimi claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Kôdi Husimi before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Kôdi Husimi ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Kôdi Husimi

In research: Kôdi Husimi appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Kôdi Husimi in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Kôdi Husimi is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1909 births, 2008 deaths, Academic staff of Nagoya University, so understanding it makes those chapters shorter.
In everyday life: Look for Kôdi Husimi outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Kôdi Husimi in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kôdi Husimi means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Kôdi Husimi out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kôdi Husimi in simple terms?

Why does Kôdi Husimi matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Kôdi Husimi?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Kôdi Husimi.