The following are my papers, preprints and publications. They are provided in DVI, PDF and PostScript formats.
- Corran Webster and Adam Winchester, Busemann Points of Metric Spaces, preprint, 2005.
(DVI)
(PDF)
(PostScript forthcoming)
We provide a geometric condition which says precisely when the metric boundary of a proper separable metric space has no Busemann points. This result generalizes an earlier result which applied only to graph metrics.
- Corran Webster and Adam Winchester, Boundaries of Hyperbolic
Metric Spaces, preprint, 2003 (to appear Pacific J. Math).
(DVI)
(PDF)
(PostScript)
We investigate the relationship between the metric boundary and the Gromov boundary of a hyperbolic metric space. We show that the Gromov boundary is a quotient of the metric boundary and the quotient map is continuous, and that therefore a word-hyperbolic group has an amenable action on the metric boundary of its Cayley graph. Furthermore, if the space is 0-hyperbolic, the boundaries agree, and as a consequence there are no non-Busemann points on the boundary of such spaces. These results have significance for the study of Lip-norms on group C*-algebras.
- Corran Webster and Adam Winchester, Busemann Points of Infinite
Graphs, Preprint, 2003 (to appear Trans. AMS).
(DVI)
(PDF)
(PostScript)
We provide a geometric condition which determines whether or not every point on the metric boundary of a graph with the standard path metric is a Busemann point, that is it is the limit point of a geodesic ray. We apply this and a related condition to investigate the structure of the metric boundary of Cayley graphs. We show that groups such as the braid group and the discrete Heisenberg group have boundary points of the Cayley graph which are not Busemann points when equipped with their usual generators.
- Corran Webster, On Unbounded Operators Affiliated with
C*-Algebras, J. Operator Theory, 51 (2004), 237-244.
(DVI) (PDF)
(PostScript)
We show that the multipliers of Pedersen's ideal of a C*-algebra A correspond to the densely defined operators on A which are affiliated with A in the sense defined by Woronowicz, and whose domains contain Pedersen's ideal. We also extend the theory of q-continuity developed by Akemann to unbounded operators and show that these operators correspond to self-adjoint operators affiliated with A.
- Corran Webster and Soren Winkler, The Krein-Milman Theorem in Operator Convexity, Trans. Amer. Math. Soc. 351 (1999), no. 1, 307--322. (DVI) (PDF) (PostScript)
- Edward G. Effros and Corran Webster, Operator Analogues of Locally Convex Spaces, Operator Algebras and Applications (Samos 1996), (NATO Adv. Sci. Inst. Ser. C Math. Phys. Sci., 495), Kluwer, 1997 (DVI) (PDF) (PostScript)
- Corran Webster, Local Operator Spaces and Applications,
PhD Thesis, University of California, Los Angeles, 1997
(DVI) (PDF) (PostScript) - Corran Webster, Harmonic Analysis and Representation Theory
of Automorphism Groups of Homogeneous Trees, Honours Thesis,
University of New South Wales, 1991.
(DVI) (PDF) (PostScript)
We generalize the Krein-Milman theorem to the setting of matrix convex sets of Effros-Winkler, extending the work of Farenick-Morenz on compact C*-convex sets of complex matrices and the matrix state spaces of C*-algebras. An essential ingredient is to prove the non-commutative analogue of the fact that a compact convex set K may be thought of as the state space of the space of continuous affine functions on K.
Local operator spaces are defined to be projective limits of operator spaces. These limits arise when one considers linear spaces of unbounded operators, and may be regarded as the "quantized" or "operator" analogues of locally convex spaces. It is shown that for nuclear spaces, the maximal and minimal quantizations coincide. Thus, in a striking contrast to normed spaces, a nuclear space has precisely one quantization. Furthermore, it is shown that a local operator space is nuclear in the operator sense if and only if its underlying locally convex space is nuclear. Operator versions of bornology and duality are also considered.