This is an expository thesis which addresses the requirements for an operator algebra to be similar to a <em>C</em>*-algebra. It has been conjectured that this similarity condition is equivalent to either amenability or total reductivity; however, the problem has only been solved for specific types of operators. <br /><br /> We define amenability and total reductivity, as well as present some of the implications of these properties. For the purpose of establishing the desired result in specific cases, we describe the properties of two well-known types of operators, namely the compact operators and quasitriangular operators. Finally, we show that if A is an algebra of compact operators or of triangular operators then A is similar to a <em>C</em>* algebra if and only if it has the total reduction property.

The invariant subspace problem is the long-standing question whether every operator on a Hilbert space of dimension greater than one has a non-trivial invariant subspace. Although the problem is unsolved in the Hilbert space case, there are counter-examples for operators acting on certain well-known non-reflexive Banach spaces. These counter-examples are constructed by considering a single orbit and then extending continuously to a hounded linear map on the entire space. Based on this process, we introduce an operator which has properties closely linked with an orbit. We call this operator the orbit operator. In the first part of the thesis, examples and basic properties of the orbit operator are discussed. Next, properties linking invariant subspaces to properties of the orbit operator are presented. Topics include the kernel and range of the orbit operator, compact operators, dilation theory, and Rotas theorem. Finally, we extend results obtained for strict contractions to contractions.

Techn. Univ., Diss.--München, 2006.

Thesis (M.S.)--University of Akron, Dept. of Mathematics, 2008. / "May, 2008." Title from electronic thesis title page (viewed 07/12/2008) Advisor, Jeffrey M. Riedl; Faculty Readers, Ethel Wheland, Stuart Clay; Department Chair, Joseph Wilder; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (M.S.)--University of Akron, Dept. of Mathematics, 2008. / "May, 2008." Title from electronic thesis title page (viewed 07/12/2008) Advisor, Jeffrey M. Riedl; Faculty Readers, William S. Clary, Ethel R. Wheland; Department Chair, Joseph W. Wilder; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (M.Eng.(Faculty of Engineering, The Built Environment and Information Technology))--University of Pretoria, 2009. / Abstracts in English and Afrikaans. Includes bibliographical references (leaves 180-187).

by J.M. Schumacher. / Bibliography: p. 33. / "April, 1982." Research supported by the Netherlands Organization for the Advancement of Pure Scientific Research (ZWO).

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