2019
Том 71
№ 7

# Nudel'man A. A.

Articles: 3
Article (Russian)

### Extension of the Stieltjes moment sequence to the left and related problems of the spectral theory of inhomogeneous string

Ukr. Mat. Zh. - 2007. - 59, № 6. - pp. 815–825

For a nonhomogeneous string with the known mass distribution (the full mass is assumed to be infinite), the known finite length, and the unknown spectral measure $d\sigma(t)$, we construct an analogous string with spectral measure $d\sigma(t)/t$. This allows to calculate the moments of all negative orders of the measure $d\sigma(t)$. The mechanical interpretation of the Stieltjes investigations on the moment problem proposed by M. G. Krein enables one to solve the following problem: for given Stieltjes moment sequence with unique solution, calculate the moments of negative orders. This problem is equivalent to the following one: establish the asymptotic behavior of the associate Stieltjes function near zero if its asymptotic behavior near infinity is given.

Article (Russian)

### Criterion of unitary similarity of minimal passive scattering systems with a given transfer function

Ukr. Mat. Zh. - 2000. - 52, № 2. - pp. 147-156

We establish necessary and sufficient conditions under which all minimal passive scattering systems that have a given transfer operator function are unitarily equivalent. These conditions can be significantly simplified in special cases important for applications, in particular, in the case where a transfer function is rational and in a more general case where this function is pseudoextendable.

Article (Ukrainian)

### On M. G. Krein's contribution to the moment problem

Ukr. Mat. Zh. - 1994. - 46, № 1-2. - pp. 63–75