Operator's and organizational maintenance manual : intercommunication stations LS-147A/FI, LS-147B/FI, LS-147C/FI, and LS-147D/FI.

"5 June 1961."

Intercommunication stations, LS-200/FI, LS-201/FI, LS-202/FI, and LS-125B/FI.

"August 1955."

DS, GS, and depot maintenance manual : control, intercommunication set C-1611D/AIC and discriminator, discrete signal MD-736/A.

"May 1970."

Field and depot maintenance manual : intercommunication stations LS-147A/FI, LS-147B/FI, LS-147C/FI, and LS-147D/FI.

"20 July 1961."

Operator's and organizational maintenance manual : intercommunication stations LS-147A/FI, LS-147B/FI, LS-147C/FI, and LS-147D/FI.

"5 June 1961."

Organizational maintenance manual : control, intercommunication set C-1611D/AIC and discriminator, discrete signal MD-736/A.

"January 1970."

On the zeros of the Abelian integrals for a class of Liénard systems

A planar polynomial differential system has a finite number of limit cycles. However, finding the upper bound of the number of limit cycles is an open problem for the general nonlinear dynamical systems. In this paper, we investigated a class of Liénard systems of the form x'=y, y'=f(x)+y g(x) with deg f=5 and deg g=4. We proved that the related elliptic integrals of the Liénard systems have at most three zeros including multiple zeros, which implies that the number of limit cycles bifurcated from the periodic orbits of the unperturbed system is less than or equal to 3.