Obituary of Hirokazu Fujisaka

Professor Hirokazu Fujisaka of Kyoto University, internationally known and highly respected expert on the theory of nonlinear dynamics and chaos in complex systems, died suddenly and unexpectedly from massive brain hemorrhages on 21 August 2007. He was only 58 years old.

Born in Kagoshima in Southern Japan on 2 January 1949, Fujisaka received his undergraduate degree in Physics from Kyushu University in 1971. He earned his Ph.D. from the same institution in 1977 under the direction of Professor Hazime Mori.

Between 1976 and 1982 he performed research at Kyushu University and at the University of Marburg, supported in turn as a Research Fellow by the Japanese Society for the Promotion of Science (JSPS) and the Alexander von Humboldt-Stiftung. It was during this period that we both had the great pleasure of first learning to know him: P.A.R. as his office mate at Kyushu University, and S.G. as his mentor at the University of Marburg.

Upon his return to Japan in 1982, Dr. Fujisaka became Lecturer and was later promoted to Assistant Professor of Physics in the Faculty of Science at Kagoshima University. In 1989 he was appointed Assistant Professor of Physics in the Faculty of Science at Kyushu University, where he stayed until 1998. During this time he also served a period as Chair of the Kyushu Branch of the Physical Society of Japan.

In 1998 he became full Professor in the Department of Applied Analysis and Complex Dynamical Systems in the Graduate School of Informatics at Kyoto University. There he built and headed a productive research group specializing in theoretical and computational studies of complex systems. During several visits to his group, we were both always impressed by the combination of intellectual rigor and warm humanity with which he guided and encouraged his associates and apprentices.

During his much-too-short career, Professor Fujisaka contributed over 150 articles in international physics journals (including Physical Review). In addition, he reached out to audiences of students and general citizens in Japan with a single-author book and over twenty articles on nonlinear dynamics in Japanese.

His best known and most influential paper is probably his 1983 work with Tomoji Yamada, “Stability Theory of Synchronized Motion in Coupled-oscillator Systems” [Prog. Theor. Phys. 69, 32-47 (1983)], which still draws an average of over forty citations per year. Many more of his impressively often cited papers were published together with Professor Yamada over the years.

The name of Hirokazu Fujisaka will be connected forever with unique developments in the fields of deterministic chaos, fluctuations, large-deviation theory, and correlations in low-dimensional maps and coupled map systems. In particular he is known for his major and very original contributions on deterministic diffusion and on synchronization. Another focus is provided by several papers giving stimulating insight into the scaling and generalized extended self-similarity of turbulent fluctuations.

Hirokazu Fujisaka’s love and fascination over more than three decades were devoted to the rich variety of all types of fluctuations. He ever again impressed his colleagues and friends by his great competence and originality in a large variety of subfields of modern statistical physics, advancing the frontier of research by stimulating ideas and results. His papers cover transport properties, Ising systems, renormalization and scaling, chemical turbulence, phase transition physics, dissipative structures and as already emphasized coupled map systems, where he discovered chaos synchronization, synchron-nonsynchron coupling, and on-off-intermittency, followed by analysis of the implications for neural networks.

During the last decade, he took a strong interest in non-equilibrium phase transitions that occur in many spin systems driven by oscillating external fields, and his group became one of the most active in this field world-wide. After many years of personal friendship, this allowed P.A.R. the great pleasure of entering into a fruitful and fun collaboration with him and his group. S.G. is most grateful for the wonderful experience of working together with the young as well as the mature Hirokazu Fujisaka, profiting from and admiring his unique combination of outstanding originality and warmhearted personality.

Our friend, Hirokazu Fujisaka, was an excellent theoretical physicist and a truly fine human being, who was taken away from us much too early. He will be sorely missed by friends and colleagues world wide. We shall never forget him.