Necessary conditions for normal solvability in duals of LF-spaces. Manfred Möller (1987) Manuscripta mathematica
Nonhermitian systems and pseudospectra Lloyd N. Trefethen (2005/2006) Séminaire Équations aux dérivées partielles Four applications are outlined of pseudospectra of highly nonnormal linear operators.
Norm inequalities in star algebras. Gaur, A.K. (2002) JIPAM. Journal of Inequalities in Pure & Applied Mathematics [electronic only]