The mathematical model of a simplest quasi-one-dimensional quantum network constructed of relatively narrow waveguides (the width of the waveguide is less than the de Broghlie wavelength of the electron in the material) is developed. This model allows to reduce the problem of calculating the current through the quantum network to the construction of scattered waves for some Schr"{o}dinger equation on the corresponding one-dimensional graph. We consider a graph consisting of a compact part and few semiinfinite rays attached to it via some boundary condition depending on a parameter $beta$ (analog of the inverse exponential hight $e^{-bH}$ of a potential barrier $H$ separating the rays from the compact part). This parameter regulates the connection between the rays and the compact part. Spectral properties of the Schr"{o}dinger operator on this graph are described with a special emphasis on the resonance case when the Fermi level in the rays coincides with one of eigenvalues of the nonperturbed Schr"{o}dinger operator on the ring. An explicit expression is obtained for the scattering matrix in the resonance case for weakening connection between the rays and the compact part. |

__Keywords__

__Math Review Classification__

__Last Updated__

March 1999

__Length__

16 pages

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