[1] H. K. Du and J. Pan, “Perturbation of Spectrums of 2 × 2 Operator Matrices,” Proceedings of the American Mathematical Society, Vol. 121, 1994, pp. 761-766.
http://dx.doi.org/10.1090/S0002-9939-1994-1185266-2
[2] H. Y. Zhang and H. K. Du, “Browder Spectra of Upper Triangular Operator Matrices,” Journal of Mathematical Analysis and Applications, Vol. 323, No. 1, 2006, pp. 700-707. http://dx.doi.org/10.1016/j.jmaa.2005.10.073
[3] M. Barrua and M. Boumazgour, “A Note on the Spectra of an Upper Triangular Operator Matrix,” Proceedings of the American Mathematical Society, Vol. 131, 2003, pp. 3083-3088. http://dx.doi.org/10.1090/S0002-9939-03-06862-X
[4] X. H. Cao and B. Meng, “Essential Appoximate Point Spectra and Weyl’s Theorem for Operator Matices,” Journal of Mathematical Analysis and Applications, Vol. 304, No. 2, 2005, pp. 759-771.
http://dx.doi.org/10.1016/j.jmaa.2004.09.053
[5] D. S. Djordjevic, “Perturbations Spectra of Operator Matrices,” Journal of Operator Theory, Vol. 48, 2002, pp. 467-486.
[6] J. K. Han, H. Y. Lee and W. Y. Lee, “Invertible Completions of 2 × 2 Operator Matrices,” Proceedings of the American Mathematical Society, Vol. 128, 2000, pp. 119123. http://dx.doi.org/10.1090/S0002-9939-99-04965-5
[7] Y. Li, X. H. Sun and H. K. Du, “Inversctions of the Left and Right Essential Spectra of 2 × 2 Upper Triangular Operator Matrices,” Bulletin London Mathematical Society, Vol. 36, 2004, pp. 811-819.
[8] H. Y. Zhang, X. H. Zhang and H. K. Du, “Drazin Spectra of 2 × 2 Upper Triangular Operator Matrices,” Acta Mathematica Scientia, Vol. 29, 2009, pp. 272-282.
[9] J. B. Conwey, “A Course in Functional Analysis,” Springer-verlag, New York, Heidelberg, Berlin, Tokyo, 1985.
http://dx.doi.org/10.1007/978-1-4757-3828-5