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A cost-effective method of experimentally determining rail vehicle dynamic parameters for use in analytical dynamic models has been developed by the Association of American Railroads (AAR). In this method, the rail vehicle’s rigid body modes of vibration are manually excited and the corresponding resonant frequencies are measured. Using these frequencies, the equations of motion for the system are solved for the vehicle’s mass moments of inertias, center of gravity location, and suspension stiffness. This method of dynamic parameter identification was developed at AAR’s Transportation Technology Center, Pueblo, Colorado. Compared to competing experimental methods, the AAR method offers the advantage of cost-effectiveness; it requires no expensive equipment and can be executed at remote locations. This paper describes the AAR method for rail vehicle parameter identification. An example of its use in the characterization of an iron ore rail vehicle is presented. In addition, dynamic simulation results for a transit vehicle, characterized using the AAR method, are compared to track test data for validation.

THE East Pacific Rise at 12°50' N (Fig. 1) is a fast-spreading ridge with intense hydrothermal activity1, and ophiolite studies2and thermal modelling3 indicate that this is a likely setting for a magma chamber. A recent seismic-reflection experiment4 imaged the top of the magma chamber at this site, at a depth of 1.4 km below the sea floor, and found that it is continuous for tens of kilometres along the rise axis. Here we examine a large set of accurate P-wave travel times from a detailed seismic refraction experiment at the same site5. The patterns observed in the travel times demonstrate that a zone of low seismic velocities exists beneath the rise axis throughout the region studied. The best-fitting two-dimensional structure, obtained from linear inversion of the travel times, includes an axial low-velocity zone (magma chamber) only ∼6 km wide, in which velocities are depressed by more than 0.5 km s-1

Animal and early clinical studies of gene therapy for tissue ischaemia suggested that this approach might provide benefit to patients with coronary artery disease not amenable to traditional revascularization. This enthusiasm was then tempered by the subsequent disappointing results of randomized clinical trials and led researchers to develop strategies using progenitor cells as an alternative to improve collateral function. However, the recent publication of several randomized clinical trials reporting either negative or weakly positive results using this approach have led to questions regarding its effectiveness. There are several factors that need to be considered in explaining the discordance between the positive studies of such treatments in animals and the disappointing results seen in randomized patient trials. Aside from the practical issues of arteriogenic therapies, such as effective delivery, vascular remodelling is an extraordinarily complex process, and the administration of a single agent or cell in the hope that it would lead to lasting physiological effects may be far too simplistic an approach. In addition, however, evidence now suggests that many of the traditional cardiovascular risk factors-such as age and hypercholesterolemia-may impair the host response not only to ischaemia but, critically, also to treatment as well. This review discusses the evidence and mechanisms for these observations and highlights future directions that might be taken in an effort to provide more effective therapies.