F. S. Rofe-Beketov
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Methods Funct. Anal. Topology 18 (2012), no. 2, 176-188
A relation is established between spectral and oscillation properties of the problem on a finite interval and a semi-axis for second order differential equations with block-triangular matrix coefficients.
Inverse scattering problem on the axis for the triangular $2\times 2$ matrix potential with a virtual level
Methods Funct. Anal. Topology 15 (2009), no. 4, 301-321
The characteristic properties of scattering data for the Schrodinger operator on the axis with a triangular $2\times 2$ matrix potential are obtained under the simple or multiple virtual levels being possibly present. Under a multiple virtual level, a pole for the reflection coefficient at $k=0$ is possible. For this case, the modified Parseval equality is constructed.