Cuntz semigroups of compact-type Hopf C*-algebras

The classical Cuntz semigroup has an important role in the study of C*-algebras, being one of the main invariants used to classify recalcitrant C*-algebras up to isomorphism. We consider C*-algebras that have Hopf algebra structure, and find additional structure in their Cuntz semigroups, thus generalizing the equivariant Cuntz semigroup. We develop various aspects of the theory of such semigroups, and in particular, we give general results allowing classification results of the Elliott classification program to be extended to classification results for C*-algebraic quantum groups.Comment: Keywords: Cuntz semigroup, Hopf algebras, equivariant Cuntz semigroup, C*-algebraic quantum groups, multiplicative unitarie

Relative double commutants in coronas of separable C*-algebras

We prove a double commutant theorem for separable subalgebras of a wide class of corona C*-algebras, largely resolving a problem posed by Pedersen. Double commutant theorems originated with von Neumann, whose seminal result evolved into an entire field now called von Neumann algebra theory. Voiculescu later proved a C*-algebraic double commutant theorem for subalgebras of the Calkin algebra. We prove a similar result for subalgebras of a much more general class of so-called corona C*-algebras

Monotonicity Analysis over Chains and Curves

Chains are vector-valued signals sampling a curve. They are important to motion signal processing and to many scientific applications including location sensors. We propose a novel measure of smoothness for chains curves by generalizing the scalar-valued concept of monotonicity. Monotonicity can be defined by the connectedness of the inverse image of balls. This definition is coordinate-invariant and can be computed efficiently over chains. Monotone curves can be discontinuous, but continuous monotone curves are differentiable a.e. Over chains, a simple sphere-preserving filter shown to never decrease the degree of monotonicity. It outperforms moving average filters over a synthetic data set. Applications include Time Series Segmentation, chain reconstruction from unordered data points, Optical Character Recognition, and Pattern Matching.Comment: to appear in Proceedings of Curves and Surfaces 200

Exact Solutions for a Class of Matrix Riemann-Hilbert Problems

Consider the matrix Riemann-Hilbert problem. In contrast to scalar Riemann-Hilbert problems, a general matrix Riemann-Hilbert problem cannot be solved in term of Sokhotskyi-Plemelj integrals. As far as the authors know, the only known exact solutions known are for a class of matrix Riemann-Hilbert problems with commutative and factorable kernel, and a class of homogeneous problems. This article employs the well known Shannon sampling theorem to provide exact solutions for a class of matrix Riemann-Hilbert problems. We consider matrix Riemann-Hilbert problems in which all the partial indices are zero and the logarithm of the components of the kernels and their nonhomogeneous vectors are functions of exponential type (equivalently, band-limited functions). Then, we develop exact solutions for such matrix Riemann-Hilbert problems. Several well known examples along with a remark on the case of functions not of exponential type are given

Generalized Coefficients for Hopf Cyclic Cohomology

A category of coefficients for Hopf cyclic cohomology is defined. It is shown that this category has two proper subcategories of which the smallest one is the known category of stable anti Yetter-Drinfeld modules. The middle subcategory is comprised of those coefficients which satisfy a generalized SAYD condition depending on both the Hopf algebra and the (co)algebra in question. Some examples are introduced to show that these three categories are different. It is shown that all components of Hopf cyclic cohomology work well with the new coefficients we have defined

Constructive Gelfand duality for C*-algebras

We present a constructive proof of Gelfand duality for C*-algebras by reducing the problem to Gelfand duality for real C*-algebras.Comment: 6page

Classifying C∗C^*-algebras with both finite and infinite subquotients

We give a classification result for a certain class of $C^{*}$-algebras $\mathfrak{A}$ over a finite topological space $X$ in which there exists an open set $U$ of $X$ such that $U$ separates the finite and infinite subquotients of $\mathfrak{A}$. We will apply our results to $C^{*}$-algebras arising from graphs.Comment: Version III: No changes to the text. We only report that Lemma 4.5 is not correct as stated. See arXiv:1505.05951 for the corrected version of Lemma 4.5. As noted in arXiv:1505.05951, the main results of this paper are true verbatim. Version II: Improved some results in Section 3 and loosened the assumptions in Definition 4.