Mathematical models for the electrical activity in cardiac cells are normally formulated as systems of ordinary differential equations (ODEs). The equations are nonlinear and describe processes occurring on a wide range of time scales. Under normal accuracy requirements, this makes the systems stiff and therefore challenging to solve numerically. As standard implicit solvers are difficult to im...

The notion of frequency response functions has been generalized to nonlinear systems in several ways. However, a relation between different approaches has not yet been established. In this paper, frequency domain representations for nonlinear systems are uniquely connected. Specifically, by means of novel analytical results, the generalized frequency response function (GFRF) and the higher orde...

This section is primarily concerned with developing the background of the describing function for a single sinusoidal signal and showing how it can be used in the analysis and possibly the design of a nonlinear feedback system. After the definition of the describing function, its value is obtained for several specific nonlinear characteristics and then it is shown how the information can be use...

In pulmonary hypertension and other conditions, such as acute respiratory distress syndrome and left heart failure, right ventricular dysfunction is a prognostic determinant. Therefore, functional parameters pertaining to the right heart alone, i.e. independent of its loading conditions, should be used to quantify right ventricular disease progression and the results of treatment. Two methods t...

neural mass models are computational nonlinear models that simulate the activity of a population of neurons as an average neuron, in such a way that different inhibitory post synaptic potential (ipsp) and excitatory post synaptic potential (epsp) signals could be reproduced. these models have been developed either to simulate the recognized neural mechanisms or to predict some physiological fac...

The robust control problem for nonlinear systems is discussed from the standpoint of the amplitude sensitivity of the nonlinear plant and nal control system. Failure to recognize and accommodate this factor may give rise to nonlinear control systems that behave diierently for small versus large input excitation, or perhaps exhibit limit cycles or instability. Sinusoidal-input describing functio...