This study assessed the suitability of a new portable system that is based on Hertz's contact theory for evaluating internal gluteal muscle stresses under the ischial tuberosities of wheelchair users in real-time as a risk indicator for a deep tissue injury. Sitting in a wheelchair was monitored and processed with the portable system for six control subjects and five individuals with paraplegia...

Experimentally it is known that the bulk modulus K and shear modulus m of a granular assembly of elastic spheres increase with pressure p faster than the p1 3 law predicted by effective medium theory (EMT) based on Hertz-Mindlin contact forces. To understand the origin of these discrepancies, we perform numerical simulations of granular aggregates under compression. We show that EMT can describ...

We present a theory of sur ng in web rings, common link structures observed on the World Wide Web. In particular, we determine an optimum ring size for sur ng, and show how to organize rings in a hierarchy so as to maximize the probability that a user will nd the information he seeks. Given the sur ng characteristics of users, which can be obtained from usage data, we then determine how to orga...

We calculate the coefficient of restitution, ǫ, starting from a microscopic model of elastic disks. The theory is shown to agree with the approach of Hertz in the quasistatic limit, but predicts inelastic collisions for finite relative velocities of two approaching disks. The velocity dependence of ǫ is calculated numerically for a wide range of velocities. The coefficient of restitution furthe...

We simulate static model sandpiles in two dimensions (2D) and focus on the stresses inside the pile. In this study tangential forces, e.g. friction, are neglected. We compare the simplest possible interaction model, i.e. a linear spring and a linear dashpot, with a nonlinear law based on Hertz' theory. Furthermore, we present data obtained by a simulation of frictionless polygons with twelve si...