# American Institute of Mathematical Sciences

December  2013, 6(4): iii-iii. doi: 10.3934/krm.2013.6.4iii

## Seiji Ukai

 1 Division of Applied Mathematics, Brown University, Providence, RI 02812

Published  November 2013

Seiji Ukai has made fundamental contributions to the mathematical study for the Boltzmann equation. His seminal construction of global solutions near Maxwellian opens the era for the study of non-homogeneous Boltzmann solutions, his work on a gas passing an obstacle remains a penetrating classical result, and his study of inverse power laws without angular cutoff marks a breakthrough in the field.
I first met Seiji in 1995 at Oberwolfach. I remember that he smoked a lot and we had to stand in the cold for discussions. He was gentle and soft-spoken, paused and thought carefully before answering my questions. We met several years later again at Oberwolfach, when I presented my construction of global smooth solutions to the compressible Euler-Poisson system. He was excited and relaxed, and with Bob Glassey, we talked a lot about problems in fluids.
Motivated by my desire to understand collision effects in a plasma, I decided to learn and work on the Boltzmann equation. I was greatly influenced by his elegant survey paper Solutions of the Boltzmann Equation', and later found a different way to control the macroscopic part of Boltzmann solutions. I was very encouraged by the positive feedbacks from the Boltzmann community, in particular, Desvillettes, Illner, Ukai and Villani, among others.
In 2001, I visited Japan, passing through Tokyo. Seiji insisted meeting with me at my hotel in Tokyo (he had to travel for two hours for that!). He took me out for dinner and we chatted a lot about everything. As with many of my Japanese friends, when conversations go deeper, sometimes we resort to Chinese characters for better communications. His knowledge in Chinese characters was so impressive, and I remember clearly our discussion about the Chinese character head'. He was shocked to learn its simplified form currently in use, which is so much different from its traditional counterpart. Shooking his head in disbelief, he wanted to know the exact reason behind such a simplification. A true scholar, Seiji was so meticulous about every detail! It got quite late and I stood outside my hotel, watching him walking quickly towards the subway station.
I have not seen Seiji too much in recent years. I am always grateful for his encouragements and mathematical insights, and will always remember the lovely evening we spent together in 2001.
Citation: Yan Guo. Seiji Ukai. Kinetic & Related Models, 2013, 6 (4) : iii-iii. doi: 10.3934/krm.2013.6.4iii

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