By using the fixed point theory in cones,we obtained the existence of positive solutios for the third-order two-point semipositive boundary value problems in which nonlinearity f(t,u)does not have to be continuous and lower bounded but only have to meet Carathéodory s conditions.

A study on root-locus of third order systems was conducted by polar root-locus equation, come to a conclusion that basic root-locus graphs of third order system are hyperbolas, and a discuss of every concrete thing was conducted.

Step response to the second-order system with zero;

Analysis and application of performance index for transient responseof second-order system;

This system includes oscilla-tor, second-order system, counter, decoder,circuit and Helmholtz coils etc.

Existence of periodic solutions of a class of second order systems at resonance;

Standard second order system index mark form and the interaction between time-frequency performance and system characteristic parameter are discussed;the correlation of system time-frequency performance index is founded;all of these show the practical significance in different analytical domains reflecting system dynamic performance.