RT Journal T1 The Quadratic Numerical Range and the Spectrum of Some Unbounded Block Operator Matrices A1 Wenwen Qiu,Yaru Qi PB Acta mathematica scientia,Series A FD 2020-12-26 YR 2020 JF Acta mathematica scientia, Series A JO Acta mathematica scientia,Series A VO 40 IS 6 SP 1420 DO K1 ;Unbounded operator;Block operator matrices;Spectrum;Quadratic numerical range LK {http://121.43.60.238/sxwlxbA/EN/article/article_16256.shtml}