TY  - JOUR
AU  - Hatamleh, Raéd 
PY  - 2007
TI  - On a Class of Nonhomogeneous Fields in Hilbert Space
JF  - Journal of Mathematics and Statistics
VL  - 3
IS  - 4
DO  - 10.3844/jmssp.2007.207.210
UR  - https://thescipub.com/abstract/jmssp.2007.207.210
AB  - Two-parametric semigroups of operators in Hilbert space with bounded infinitesimal doubly commuting operators are studied. The characteristics describing deviation of a semigroup from unitary one, when infinitesimal operators are unitary, in particular, nonunitary index, have been introduced. Necessary and sufficient conditions for nonunitary index finiteness have been obtained.