Singular Quadratic Forms in Perturbation Theory 87 miRNAs as biomarkers Domänen und Ministerium für Landwirtschaft miRNAs as biomarkers the first of the Methods in Molecular Biology volumes from Humana Press was published with its step by step recipe approach Typical examples of such expressions are Schrodin ger operators with O potentials ( ~ + AD) and Hamiltonians in quantum field theory with perturbations given in terms of operators of creation and annihilation (P( The notion of singular quadratic form appears in mathematical physics as a tool for the investigation of formal expressions corresponding to perturbations devoid of operator sense