Given a simple polygon in the plane, a deflation is defined as the inverse of a flip in the Erd˝ os-Nagy sense. In 1993 Bernd Wegner conjectured that every simple polygon admits only a finite number of deflations. In this note we describe a counterexample to this conjecture by exhibiting a family of polygons on which deflations go on forever.
Forward dynamic models suggest that muscle-induced joint motions depend on dynamic coupling between body segments. As a result, biarticular muscles may exhibit non-intuitive behavior in which the induced joint motion is opposite to that assumed based on anatomy. Empirical validation of such predictions is important for models to be relied upon to… (More)
Individuals who have suffered cerebral insults often exhibit stiff-knee gait, a condition characterized by reduced knee flexion during swing. We investigated the effect that an increment in normal rectus femoris (RF) activity can have on hip and knee joint angles during swing, as a first step to determining this muscle's involvement in stiff-knee gait. For… (More)
The objective of this study was to investigate the effects of age and speed on body center of mass (COM) motion over a gait cycle. Whole body kinematics and ground reactions were recorded for 21 healthy young (21-32 y) and 20 healthy older adults (66-81 y) walking at 80%, 100% and 120% of preferred speed. The limb-induced COM accelerations and the work done… (More)
This article presents a method for recommending scientific articles taking into consideration their degree of generality or specificity. This approach is based on the idea that less expert people in a specific topic prefer to read more general articles to be introduced into it, while people with more expertise prefer to read more specific articles. Compared… (More)
The exact solution of the anti-symmetric quadratic truly nonlinear oscillator is derived from the first integral of the nonlinear differential equation which governs the behaviour of this oscillator. This exact solution is expressed as a piecewise function including Jacobi elliptic cosine functions. The Fourier series expansion of the exact solution is also… (More)
The hamstrings are often associated with the development of crouch gait, a fatiguing form of walking characterized by excessive hip flexion, knee flexion and ankle dorsiflexion during stance. However, recent studies have called into question whether abnormally active hamstrings induce the limb to move into a crouch posture. The purpose of this study was to… (More)