André Boivin (1955-2014) passed away at University Hospital on Friday, October 17, 2014, as a result of heart failure.

Professor Boivin completed his PhD at the Université de Montréal in 1984 under the direction of Paul Gauthier. He came to the University of Western Ontario as an Assistant Professor in 1986, after holding postdoctoral fellowships at UCLA and University College, London. He was promoted to Associate Professor in 1991, and then to Professor in 2004. He was appointed as Chair of Western's Department of Mathematics in 2011.

His research specialties were complex analysis and approximation theory, and he was the author of multiple papers in these areas. He gave tireless service to granting agencies and selection committees in Québec and Ontario, and was a frequent conference organizer.

He served with distinction as Graduate Student Chair before becoming Chair of the Department, and supervised many graduate students during the course of his career at Western. Caring, warmth and passion were the hallmarks of his relationships with students and colleagues.

André Boivin is survived by his wife Yinghui Jiang, son Alexandre, daughter Melanie and step son JP. He was well loved and respected by his colleagues, students and coworkers throughout the University, and he will be sorely missed.

Each week the Department of Mathematics hosts a wide variety of seminars and events. For a comprehensive list of events, please consult our departmental calendar.

In this talk we investigate the Witt equivalence of certain types of
fields. In particular, we show that for two Witt equivalent function fields
over global fields there is a natural bijection between certain Abhyankar
valuations of these fields, that corresponds to Witt equivalence of
respective residue fields. We also examine to what extent this result
carries over to Abhyankar valuations with finite residue field.

To each differential-graded algebra and element a\in A^1,
we associate a cochain complex, where the map is defined by
the multiplication by a. The degree l resonance variety is
the set of elements a in A^1 such that the l-th cohomology
is not zero. It is shown that The degree l resonance
variety, up to ambient linear isomorphism, is an invariant
of A. The characteristic varieties of a space are the jump loci for homology
of rank 1 local systems. The main motivation for the study of resonance
varieties comes from the tangent cone, which there is a close relation
between the degree-one resonance varieties to the characteristic varieties,
where the tangent cone of W at 1 is the algebraic subset
TC_1(W) of C^n defined by the initial ideal in(J) \subset S.
In this talk we describe the degree-one resonance variety.
We will be particularly interested in the resonance varieties of graphical
arrangements.