Richard B. Melrose
For a compact manifold without boundary a suspended algebra of pseudodifferential operators is considered; it is an algebra of pseudodifferential operators on, and translation-invariant in, an additional real variable. It is shown that the eta invariant, as defined by Atiyah, Patodi and Singer for admissible Dirac operators, extends to a homomorphism from the ring of invertible elements of the suspended algebra to the additive real line. The deformation properties of this extended eta homomorphism are discussed and a related `divisor flow' is shown to label the components of the set of invertible elements within each component of the elliptic set.