Mathematical modeling of the dynamic behavior of physical systems, gives computers that mimic the capabilities to intelligently monitor and predict their evolutionary characteristics. In this paper, we present a syste...
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Mathematical modeling of the dynamic behavior of physical systems, gives computers that mimic the capabilities to intelligently monitor and predict their evolutionary characteristics. In this paper, we present a system for tracking the time-varying features of non-rigid objects in images of evolving scenes, using the elastic string model of planar contours, which permits the inference and prediction of the quantitative parameters that characterize evolutionary behavior. The goal of our work is to dynamically track non-rigid objects in video sequences, using object alignment techniques based on the properties of the elastic string. We present experimental results of growth cone and neurite tracking in cell growth and motion studies.
To obtain information describing the postfailure behavior of human proximal tibial trabecular bone, cube specimens of bone were mechanically tested in compression beyond the point of failure. Tests were performed in t...
This paper extends the systematic approach described in Winters and Stark (62) for developing muscle models. The underlying motivation is our finding that for larger scale shoulder and head-neck postural systems to be...
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This paper extends the systematic approach described in Winters and Stark (62) for developing muscle models. The underlying motivation is our finding that for larger scale shoulder and head-neck postural systems to be mechanically stable, open-loop muscle properties are often not sufficient. There are three primary contributions. First, the previous muscle mechanical model structure and parameter estimation process of (62) is updated to reflect recent experimental findings. Second, an intrafusal (IF) muscle model is developed that includes a gamma(static) motoneuron (MN) drive, a Hill muscle model, and a muscle spindle sensor across the IF series element;this provides a more appropriate muscle spindle output signal, especially for studies of posture. Third, the conceptual cut between the neurocontrol input and the actuator is raised from just below the MN summing junction to a higher location, allowing a muscle-reflex actuator'' to be defined that satisfies the formal theoretical requirement for possessing passive spring-like behavior when the neurocontrol input is constant, alpha-gamma MN coactivation is assumed, and three types of intrinsic autogenic reflex responses (spindle, Golgi tendon organ, Rhenshaw cell) are developed. Default feedback gains are set based on the criteria that inherent feedback should not sculpt the feedforward excitation drive by more than +/- 10% of maximum. This new actuator model only mildly affects voluntary goal-directed dynamic performance, but enhances spring-like performance around the postural equilibrium state, in line with available animal and human studies and with several theories on postural regulation.
An intrafusal (IF) muscle model is developed that includes a γstatic motoneuron (MN) drive, a Hill muscle model, and a muscle spindle sensor across the IF series element. This provides a more appropriate muscle spind...
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An intrafusal (IF) muscle model is developed that includes a γstatic motoneuron (MN) drive, a Hill muscle model, and a muscle spindle sensor across the IF series element. This provides a more appropriate muscle spindle output signal, especially for studies of posture. The conceptual cut between the neurocontrol input and the actuator is raised from just below the MN summing junction to a higher location, allowing a 'muscle-reflex actuator' to be defined that satisfies the formal theoretical requirement for possessing passive spring-like behavior when the neurocontrol input is constant. α- γ MN coactivation is assumed.
By analyzing cardiac beat-to-beat intervals and interbeat increments, we find that—unlike adults—the difference in the pattern of interbeat increments in healthy and sick newborn infants is more due to a change in t...
By analyzing cardiac beat-to-beat intervals and interbeat increments, we find that—unlike adults—the difference in the pattern of interbeat increments in healthy and sick newborn infants is more due to a change in the amplitude and much less to a change in the ordering of the interbeat increments. This suggests that very low-frequency elements of neonatal and adult heart rate variability rise from fundamentally different mechanisms.
A finite element algorithm to simulate two dimensional flows of viscous and inviscid compressible fluids for a wide range of Mach numbers is presented in this work. This model is coupled to immersed deformable structu...
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A finite element algorithm to simulate two dimensional flows of viscous and inviscid compressible fluids for a wide range of Mach numbers is presented in this work. This model is coupled to immersed deformable structures through equilibrium and compatibility conditions in order to analyze its dynamic behavior. For the fluid, time integration is performed by a two-step Taylor-Galerkin explicit scheme and Newmark’s method is used to obtain the dynamic response of the structure. An arbitrary mixed Euler-Lagrange description is used to re-define a new finite element mesh in the presence of the immersed structure displacements. Finally, several examples are included showing the model behavior and possibilities for future expansions.
A network thermodynamic model has been devised to describe the coupled movement of water and glycerol molecules within the kidney during perfusion with solutions of time-varying glycerol and impermeant comcentrations....
A network thermodynamic model has been devised to describe the coupled movement of water and glycerol molecules within the kidney during perfusion with solutions of time-varying glycerol and impermeant comcentrations. Both flows are governed by a combination of the individual osmotic potential differences between compartments, the viscoelastic behavior of the tissue, and the momentum transferred between the two flows. The system is modelled using the bond graph technique and simulated with the ENPORT7 package (Rosencode Associates, 1993).
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