**Sun-Yung Alice Chang** was born in China at the time when the Communists were rapidly taking control of the country. By late 1949 the Communists were in control of almost all of China, the main exception being Taiwan which continued to be controlled by the Nationalist government. Soon after this Chang's family moved from mainland China to the Republic of China in Taiwan. She grew up in Taiwan, attending school there and then studying at the National University of Taiwan. She received her B.S. from the National University in 1970 and then went to the United States to study for her doctorate. In 1974 she was awarded a Ph.D. from the University of California, Berkeley, for a thesis written with Donald Sarason as her advisor. In her thesis, Chang worked on problems in classical analysis, in particular the study of boundary behaviour of bounded analytic functions on the unit disc.

After receiving her doctorate, Chang was appointed as an assistant professor at the State University of New York at Buffalo for the academic year 1974-1975. Following this she was appointed Hedrick Assistant Professor at the University of California at Los Angeles until 1977 when she moved to the University of Maryland as an assistant professor. She was a Sloan Fellow during the year 1979-1980.

In 1980 Chang returned to the University of California at Los Angeles as an associate professor, being later promoted to full professor. She was an invited speaker at the International Congress of Mathematicians at Berkeley in 1986. During 1988-1989 she was also a full professor at the University of California, Berkeley.

Chang's research interests include the study of certain geometric types of nonlinear partial differential equations. She also studies the related extremal inequalities and problems in isospectral geometry.

Perhaps Chang's greatest honour was the award of the 1995 Ruth Lyttle Satter Prize in Mathematics. The prize is awarded every two years to a woman who has made an outstanding contribution to mathematics research in the previous five years. The award is valued at $4,000. Chang received the prize at the American Mathematical Society meeting in San Francisco in January 1995. The citation for the prize read:-

The Ruth Lyttle Satter Prize is awarded to Sun-Yung Alice Chang for her deep contributions to the study of partial differential equations on Riemannian manifolds and in particular for her work on extremal problems in spectral geometry and the compactness of isospectral metrics within a fixed conformal class on a compact3-manifold.

On receiving the prize Chang spoke about her work (see [1]):-

It is an honor for me to receive the prize. Since all the work cited above is joint work with my coauthors (Paul Yang for the most part, but also Tom Branson and Matt Gursky), I would like to express my indebtedness to them.

The problems which I have been working on in the past few years are mainly connected with the study of extremal functions of Sobolev inequalities. Such functions play an important role in the study of the blow-up phenomenon in a number of problems in geometry. Following the early work of J Moser and influenced by the work of T Aubin and R Schoen on the Yamabe problem, P. Yang and I have solved the partial differential equation of Gaussian/scalar curvatures on the sphere by studying the extremal functions for certain variation functionals. We have also applied this approach in conformal geometry to the isospectral compactness problem on3-manifolds when the metrics are restricted in any given conformal class. More recently we have been studying the extremal metrics for these functionals. We are working to derive further geometric consequences. This latter piece of work is a natural extension of the earlier work by Osgood-Phillips-Sarnak on the log-determinant functional on compact surfaces.

Chang also spoke about the position of women in mathematics research and how things are changing rapidly:-

Since the Satter Prize is an award for women mathematicians, one cannot help but to reflect on the status of women in our profession now. Compared to the situation when I was a student, it is clear that there are now many more active women research mathematicians. I can personally testify to the importance of having role models and the companionship of other women colleagues. However, I think we need even more women mathematicians to prove good theorems and to contribute to the profession.

In 1998, in addition to her Professorship at the University of California, Los Angeles, Chang was appointed Professor at Princeton University. The appointment at the University of California ended in 2000. Chang is married to Paul Yang, also a Professor of Mathematics at Princeton University; they have one daughter and one son.

Chang has received many honours in addition to the Ruth Lyttle Satter Prize in Mathematics which we described above. She was an Invited Speaker at the International Congress of Mathematicians held in Berkeley in 1986, and a Plenary Speaker at the International Congress of Mathematicians held in Beijing in 2002. She held a John Simon Guggenheim Memorial Foundation Fellowship in 1999-2000 and served on the Steel Prize Selection Committee of the American Mathematical Society during 2001-2004. On 28 April 2009 the National Academy of Sciences announced that Chang had been elected a member.

In June 2009 Chang was one of the organisers of '2009 the Program for Women and Mathematics' held at the Institute for Advanced Study at Princeton. The course was entitled "Geometric PDE" and described using analytic tools like that of partial differential equations to solve problems in geometry. Chang gave the Advanced Lecture Course which studied:-

... model differential equations like that of the Gaussian curvature equations on compact surfaces, the prescribing curvature equations and the evolution equations related to the curvature flows.

As to her hobbies, Chang lists reading novels, taking walks and listening to music.

**Article by:** *J J O'Connor* and *E F Robertson*

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