Comparing dynamical systems concepts and techniques for biomechanical analysis

Traditional biomechanical analyses of human movement are generally derived from linear mathematics.While these methods can be useful in many situations,they do not describe behaviors in human systems that are predominately nonlinear.For this reason,nonlinear analysis methods based on a dynamical systems approach have become more prevalent in recent literature.These analysis techniques have provided new insights into how systems(1) maintain pattern stability,(2) transition into new states,and(3) are governed by short-and long-term(fractal) correlational processes at different spatio-temporal scales.These different aspects of system dynamics are typically investigated using concepts related to variability,stability,complexity,and adaptability.The purpose of this paper is to compare and contrast these different concepts and demonstrate that,although related,these terms represent fundamentally different aspects of system dynamics.In particular,we argue that variability should not uniformly be equated with stability or complexity of movement.In addition,current dynamic stability measures based on nonlinear analysis methods(such as the finite maximal Lyapunov exponent) can reveal local instabilities in movement dynamics,but the degree to which these local instabilities relate to global postural and gait stability and the ability to resist external perturbations remains to be explored.Finally,systematic studies are needed to relate observed reductions in complexity with aging and disease to the adaptive capabilities of the movement system and how complexity changes as a function of different task constraints.

Study and Application of New Polyamine Polymer Drilling Fluid

Adding the polyamine inhibitor into drilling fluid can effectively strengthen the rejection capability and improve the rheological behavior of drilling fluid system. According to the analysis of the comparison of the physiochemical properties of the polyamine inhibitor, a polyamine polymer drilling fluid system was established by means of adding UAE polyamine into traditional polymer drilling fluid. Conventional properties and environmental influence of this system have been evaluated in this paper. The result indicates that the polymer drilling fluid system optimized by polyamine shows a high-performance, such as excellent rejection performance, better rheological and filtration properties, better environmental protection functions. Thus it can be used in high water-sensitive, high temperature, high pressure or vulnerable formation drilling operations.

DYNAMICS OF A DIFFUSIVE PREDATOR-PREY MODEL WITH ADDITIVE ALLEE EFFECT

In this paper, we investigate the dynamics of a diffusive predator prey model with Holling-II functional response and the additive Allee effect in prey. We show the local and global asymptotical stability of the positive equilibrium, and give the conditions of the existence of the Hopf bifurcation. By carrying out global qualitative and bifurcation analysis, it is shown that the weak and strong Allee effects in prey can induce different dynamical behavior in the predator-prey model. Furthermore, we use some numerical simulations to illustrate the dynamics of the model. The results may be helpful for controlling and managing the predator-prey system.