Bifurcation analysis of a van der Pol-Duffing circuit with parallel resistor.
Mean directionally curved lines on surfaces immersed in R.
The notion of principal configuration of immersions of surfaces into R, due to Sotomayor and Gutierrez [16] for lines of curvature and umbilics, is extended to that of mean directional configuration for immersed surfaces in R. This configuration consists on the families of mean directionally curved lines, along which the second fundamental form points in the direction of the mean curvature vector, and their singularities, called here H-singularities.
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