Strain distribution in the porcine lumbar laminae under asymmetric loading

If the articular facets of the vertebra grow in an asymmetric manner, the developed geometry causes an asymmetry of loading. When the loading environment is altered by way of increased activity, the likelihood of acquiring a stress fracture may be increased. The combination of geometric asymmetry and increased activity is hypothesised to be the precursor to the stress fracture under investigation in this study, spondylolysis. This vertebral defect is an acquired fracture with 7% prevalence in the paediatric population. This value increases to 21% among athletes who participate in hyperextension sports. Tests were carried out on porcine lumbar vertebrae, on which the effect of facet angle asymmetry was simulated by offsetting the load laterally by 7mm from the mid-point. The aim of the study is to investigate whether an increase in the coronal orientation of one facet leads to an increase in strain in the corresponding vertebral lamina. Strain in the laminae was recorded using six 3-element stacked rosette strain gauges placed bilaterally. Results show that a significant linear predictive relationship exists between load offset and average strain level in the vertebral laminae with p values of 0.006 and 0.045 for principal strains e1 and e2 on the right-hand side, and p-values of 0.009 and 0.001 for principal strains e1 and e2 on the left-hand side (R2 all .0.9). This study concludes that facet angle asymmetry does lead to a difference in strain in the vertebral laminae. Change in principal strain as a result of facet asymmetry has a linear relationship and an asymmetry threshold exists beyond which compressive strain on the more coronally oriented facet can be increased by up to 15%

On implementing omega in systems with weak reliability and synchrony assumptions

We study the feasibility and cost of implementing Omega --- a fundamental failure detector at the core of many algorithms ---in systems with weak reliability and synchrony assumptions. Intuitively, Omega allows processes to eventually elect a common leader. We first give an algorithm that implements Omega in a weak system S where (a) except for some unknown timely process s, all processes may be arbitrarily slow or may crash, and (b) only the output links of s are eventually timely (all other links can be arbitrarily slow and lossy). Previously known algorithms for Omega worked only in systems that are strictly stronger than S in terms of reliability or synchrony assumptions. We next show that algorithms that implement $\Omega$ in system S are necessarily expensive in terms of communication complexity: all correct processes (except possibly one) must send messages forever; moreover, a quadratic number of links must carry messages forever.This result holds even for algorithms that tolerate at most one crash. Finally, we show that with a small additional assumption to system S--- the existence of some unknown correct process whoselinks can be arbitrarily slow and lossy but fair ---there is a communication-efficient algorithm for Omega such that eventually only one process (the elected leader) sends messages. Some recent experimental results indicate that two of the algorithms for Omega described in this paper can be used in dynamically-changing systems and work well in practice~ST0

On deadlocks of exclusive AND-requests for resources

10.1007/s004460050011Distributed Computing9277-94DICO