THE EFFECT OF SELECTED SPORT SURFACES ON VERTICAL LANDING FORCES IN JUMPING

Introduction: The jump for height has received much attention as an important element in many sport activities, but less attention is given to the impact of landing, which may result in injuries due to the large forces involved (Miller, 1976). Therefore, activities that involve landings are potentially more harmful to the joint when there is inefficient absorptive material within the shoes and/or the sport surface. Cavanagh and Lafortune (1980) found that vertical forces, with magnitudes 2.5 times those found in running, were generated when landing from a vertical jump. Nigg, Denoth and Neukomm (1981) reported a force of magnitude 3.5 times the body weight when landing from a vertical jump. Knowing the magnitude of the vertical reaction forces to human beings, when jumping on different sport surfaces, could assist surface manufacturers and shoe designers in producing products that will reduce impact and therefore reduce injuries

THE EFFECT OF SELECTED SPORT SURFACES ON GROUND REACTION FORCES IN WALKING AND RUNNING

Introduction During physical activity, the human body exerts force against its environment. Previous research indicates that the body is exposed to magnitudes of force equaling 2 to 3 times body weight in running (Bates, 1985 & Dickinson, Cook & Leinhardt, 1985) and 1.1 to 1.3 times body weight in walking (Cavanagh, 1980). The magnitude and duration of these forces are a potential source of physical injury. Most biomechanical research in locomotion has examined the role offootwear. However, there is not enough information on the absorption capacity of shoes to determine their safety limit and the ground reaction force is relatively unaffected by footwear changes (Clarke, Frederick & Hamill, 1984)

Does Income Mobility Equalize Longer-term Incomes? New Measures of an Old Concept

This paper develops a new class of measures of mobility as an equalizer of longer-term incomes – a concept different from other notions such as mobility as time-independence, positional movement, share movement, income flux, and directional income movement. A number of properties are specified leading to a class of indices, one easily-implementable member of which is applied to data for the United States and France. Using this index, income mobility is found to have equalized longer-term earnings among U.S. men in the 1970s but not in the 1980s or 1990s. In France, though, income mobility was equalizing throughout, and it has attained its maximum in the most recent period

Quantum Fields and Extended Objects in Space-Times with Constant Curvature Spatial Section

The heat-kernel expansion and $\zeta$-regularization techniques for quantum field theory and extended objects on curved space-times are reviewed. In particular, ultrastatic space-times with spatial section consisting in manifold with constant curvature are discussed in detail. Several mathematical results, relevant to physical applications are presented, including exact solutions of the heat-kernel equation, a simple exposition of hyperbolic geometry and an elementary derivation of the Selberg trace formula. With regards to the physical applications, the vacuum energy for scalar fields, the one-loop renormalization of a self-interacting scalar field theory on a hyperbolic space-time, with a discussion on the topological symmetry breaking, the finite temperature effects and the Bose-Einstein condensation, are considered. Some attempts to generalize the results to extended objects are also presented, including some remarks on path integral quantization, asymptotic properties of extended objects and a novel representation for the one-loop (super)string free energy.Comment: Latex file, 122 page

Systematic and Controllable Negative, Zero, and Positive Thermal Expansion in Cubic Zr1–xSnxMo2O8

We describe the synthesis and characterization of a family of materials, Zr1–xSnxMo2O8 (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, αl, ranging from −7.9(2) × 10–6 to +5.9(2) × 10–6 K–1 (12–500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of “cubic” SnMo2O8, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material