Given a C*-algebra A with a semicontinuous semifinite trace { acting on the Hilbert space H, we define the family A R of bounded Riemann measurable elements w.r.t. { as a suitable closure, a la Dedekind, of A, in analogy with one of the classical characterizations of Riemann measurable functions, and show that A R is a C*-algebra, and { extends to a semicontinuous semifinite trace on A R . Then, unbounded Riemann measurable operators are defined as the closed operators on H which are affiliated to A" and can be approximated in measure by operators in A R , in analogy with unbounded Riemann integration. Unbounded Riemann measurable operators form a {-a.e. bimodule on A R , denoted by A R , and such a bimodule contains the functional calculi of selfadjoint elements of A R under unbounded Riemann measurable functions. Besides, { extends to a bimodule trace on A R . Type II 1 singular traces for C*-algebras can be defined on the bimodule of unbounded Riemann-measurable operators. Noncommutative Riemann integration and singular traces for C*-algebras are then used to define Novikov Shubin numbers for amenable open manifolds, to show their invariance under quasiisometries, and to prove that they are (noncommutative) asymptotic dimensions.
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