Gheorghe Călugăreanu

Gheorghe Călugăreanu (16 June 1902 – 15 November 1976) was a Romanian mathematician, professor at Babeș-Bolyai University, and full member of the Romanian Academy.

Gheorghe Călugăreanu
Born(1902-06-16)June 16, 1902
Iași, Kingdom of Romania
DiedNovember 15, 1976(1976-11-15) (aged 74)
Cluj-Napoca, Socialist Republic of Romania
Resting placeBellu Cemetery, Bucharest
Alma materUniversity of Cluj
University of Paris
Known forWrithe of a knot
Călugăreanu invariant
Parent
Scientific career
FieldsMathematics
InstitutionsBabeș-Bolyai University
ThesisSur les fonctions polygènes d'une variable complexe (1928)
Doctoral advisorÉmile Picard
Doctoral studentsPetru Mocanu

He was born in Iași, the son of physician, naturalist, and physiologist Dimitrie Călugăreanu. From 1913 to 1921 he studied at the Gheorghe Lazăr High School in Bucharest, after which he attended University of Cluj, graduating in 1924. In 1926 he went to Paris to pursue his studies at the Sorbonne, supported by a scholarship from the Romanian government.[1] He obtained his Ph.D. in mathematics in 1929, with thesis Sur les fonctions polygènes d'une variable complexe written under the direction of Émile Picard[1][2] and defended before a jury that also included Édouard Goursat and Gaston Julia.[3] After returning to Romania, he was appointed assistant the University of Cluj in 1930; he was promoted to lecturer in 1934 and named professor in 1942. From 1953 to 1957 he served as Dean of the Faculty of Mathematics.[1][4] His Ph.D. students include Petru Mocanu.[2] He was elected a corresponding member of the Romanian Academy in 1955, and he became a full member in 1963.[5]

Călugăreanu studied the theory of functions of a complex variable (meromorphic functions, univalent functions, analytic extension invariants), as well as differential geometry and algebraic topology, especially in knot theory. In his best-known work,[6] he established in 1961 the following foundational result regarding the writhe of a knot: take a ribbon in three-dimensional space, let be the linking number of its border components, and let be its total twist; then the difference depends only on the core curve of the ribbon.[7] In a paper from 1959,[8] he showed how to calculate the writhe of a knot by means of a Gaussian double integral.[9] Călugăreanu's formula has since been pursued by James H. White[10] and F. Brock Fuller,[11] leading to applications in DNA topology, where writhe is used to describe the amount a piece of DNA is deformed as a result of torsional stress (a phenomenon known as DNA supercoiling).[12] The topological interpretation of helicity in terms of the Gauss linking number and its limiting form has been called the "Călugăreanu invariant" by Keith Moffatt and Renzo L. Ricca.[13]

He died of cancer in Cluj-Napoca in 1976; following his wishes, he was cremated and the urn was deposited at Bellu Cemetery in Bucharest.[5]

Publications

References
  1. O'Connor, John J.; Robertson, Edmund F., "Gheorghe Călugăreanu", MacTutor History of Mathematics Archive, University of St Andrews
  2. Gheorghe Călugăreanu at the Mathematics Genealogy Project
  3. Calugaréano, Georges (1928). Sur les fonctions polygènes d'une variable complexe (PDF) (Thesis). Thèses de sciences. Paris: Gauthier-Villars et Cie. JFM 54.0375.03. MR 3532954. OCLC 459041833.
  4. Mocanu, Petru T.; Sălăgean, Grigore. "Profesor Gheorghe Călugareanu" (in Romanian). Retrieved August 19, 2022.
  5. "Gheorghe Călugăreanu (1902–1976). Life and Work". ictp.acad.ro. Tiberiu Popoviciu Institute of Numerical Analysis. Retrieved August 18, 2022.
  6. Călugăreanu, Gheorghe (1961). "Sur les classes d'isotopie des nœuds tridimensionnels et leurs invariants". Czechoslovak Mathematical Journal (in French). 11 (4): 588–625. doi:10.21136/CMJ.1961.100486. MR 0149378.
  7. Cimasoni, David (2001). "Computing the writhe of a knot". Journal of Knot Theory and Its Ramifications. 10 (387): 387–395. arXiv:math/0406148. doi:10.1142/S0218216501000913. MR 1825964. S2CID 15850269.
  8. Călugăreanu, Gheorghe (1959). "L'intégrale de Gauss et l'analyse des nœuds tridimensionnels" (PDF). Revue de Mathématiques Pure et Appliquées (in French). 4: 5–20. MR 0131846.
  9. Vrănceanu, Gheorghe (1972). "On a geometrical interpretation of Călugăreanu's invariant". Revue Roumaine de Mathématiques Pures et Appliquées. 17: 1481–1486. MR 0324602.
  10. White, James H. (1969). "Self-linking and the Gauss integral in higher dimensions". American Journal of Mathematics. 91 (3): 693–728. doi:10.2307/2373348. JSTOR 2373348. MR 0253264.
  11. Fuller, F. Brock (1971). "The writhing number of a space curve". Proceedings of the National Academy of Sciences of the United States of America. 68 (4): 815–819. Bibcode:1971PNAS...68..815B. doi:10.1073/pnas.68.4.815. MR 0278197. PMC 389050. PMID 5279522.
  12. Bates, Andrew D.; Maxwell, Anthony (2005). DNA Topology (2nd ed.). Oxford: Oxford University Press. pp. 36–37. ISBN 978-0-19-850655-3. OCLC 64239232.
  13. Moffatt, Henry Keith; Ricca, Renzo L. (1992). "Helicity and the Călugăreanu invariant". Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences. 439 (1906): 411–429. Bibcode:1992RSPSA.439..411M. doi:10.1098/rspa.1992.0159. hdl:10281/20227. JSTOR 52228. MR 1193010. S2CID 122310895.
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