Contents

Vestnik St. Petersburg University, Mathematics

Vol. 59, No. 1, 2026

TO THE 300th ANNIVERSARY OF SPbU

Research on the Qualitative Theory of Differential Equations at St. Petersburg University. The Center–Focus Problem. Phase Portraits of One Family of Cubic Systems

I. A. Andreeva, N. A. Begun, E. V. Vasil’eva, T. E. Zvyagintseva, and Y. A. Iljin p. 1  abstract

MATHEMATICS

On the Errors in the Correlogram of a Time Series Modeled by a Gaussian Random Process

R. V. Baluev and A. A. Fedotov p. 9  abstract

A Binary Inequality with Prime and Square-Free Number

S. I. Dimitrov p. 17  abstract

A Semiglobal Observer for the Korteweg–de Vries–Burgers Equation

M. V. Dolgopolik, A. L. Fradkov, and B. Andrievsky p. 29  abstract

TI-Groups in the Class of Quotient Divisible Abelian Groups

E. Kompantseva and T. Q. T. Nguyen p. 41  abstract

On A. N. Tikhonov’s Lemma and Its Generalization

V. N. Malozemov and A. V. Petrov p. 47  abstract

Change-Point Detection in Signal Parameters with Given Probability

E. A. Shapoval and N. E. Golyandina p. 56  abstract

MECHANICS

Dynamics Problems for Mechanical Systems with Geometric Singularities

S. N. Burian p. 66  abstract

On the Uniqueness of the Solution to the Problem of Determining the Parameters of a Mechanical Model of the Human Body under Vibration Exposure

N. K. Egorova p. 78  abstract

Modeling of a Vertical Tank on an Elastic Foundation According to Rod and Shell Theory

T. V. Zinovieva p. 83  abstract

Derivation of a Differential Equation for Finding a Control Force in the Generalized Chebyshev Problem and Application of the Stated Theory to the Suppression of Manipulator “Arm” Oscillations

M. P. Yushkov and S. O. Bondarenko p. 92  abstract

ASTRONOMY

Dynamics of a Single Secular Resonance in Planetary Systems

A. A. Berezina p. 101  abstract

Two Methods for Defining Jacobi Coordinates in the Planetary Problem

D. V. Mikryukov p. 115  abstract