Spectral properties of unbounded Jacobi matrices with almost monotonic weights

Abstract: We present an unified framework to identify spectra of Jacobi matrices. We give applications to long-standing conjecture of Chihara concerning one-quarter class of orthogonal polynomials, to the conjecture posed by Roehner and Valent concerning continuous spectra of generators of birth and death processes and to spectral properties of operators studied by Janas, Moszy\'nski and Pedersen.