Spectral analysis of linearized stationary equations of a compressible viscous fluid

The spectrum of an operator on a torus described by linearized stationary equations of a compressible viscous fluid is considered. These equations are obtained by the linearization of non-linear equations of a compressible viscous fluid at an arbitrary solution depending on the $x$-variable. It is shown that the spectrum of the operator is a discrete point set, which lies in a sector of the complex plane that is symmetric relative to the real axis and has its vertex on the positive half-axis.
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