On the mechanism of trailing vortex wandering

The mechanism of trailing vortex wandering has long been debated and is often attributed to either wind-tunnel effects or an instability. Using particle image velocimetry data obtained in the wake of a NACA0012 airfoil, we remove the effect of wandering from the measured velocity field and, through a triple decomposition, recover the coherent wandering motion. Based on this wandering motion, the most energetic structures are computed using the proper orthogonal decomposition (POD) and exhibit a helical mode with an azimuthal wavenumber of |m|=1 whose kinetic energy grows monotonically in the downstream direction. To investigate the nature of the vortex wandering, we perform a spatial stability analysis of a matched Batchelor vortex. The primary stability mode is found to be marginally stable and nearly identical in both size and structure to the leading POD mode. The strikingly similar structure, coupled with the measured energy growth, supports the proposition that the vortex wandering is the result of an instability. We conclude that the cause of the wandering is the non-zero radial velocity of the |m|=1 mode on the vortex centreline, which acts to transversely displace the trailing vortex, as observed in experiments. However, the marginal nature of the stability mode prevents a definitive conclusion regarding the specific type of instability

Reply to comment by Eduardo Garzanti on "When and where did India and Asia collide"

published_or_final_versio

Discussion on Quaternary sea-level change on the continental shelf of Hong Kong

Yim et al comment on Fyfe et al's sequence stratigraphical interpretation of the Quaternary inner shelf sediments of Hong Kong. Fyfe et al respond to the comments.published_or_final_versio

Requirements change: What's the alternative?

Numerous studies have shown that a software project's cost, schedule and defect density escalate as the rate of requirements change increases. Yet none of these studies have explored the effects of not making requirements changes in response to changes in user needs. This paper explains why a project incurs just as much, if not more, risk when requirements changes are suppressed. © 2008 IEEE

Disney's women: changes in depictions of femininity in Walt Disney's animated feature films, 1937-1999.

The animated films of Walt Disney have played an important role in American culture. Most Americans, either during childhood or adulthood, have been exposed to at least some of them. The films themselves have, in some respects, reflected American society and culture. They may also, at least to some extent, have influenced them. As academic scholarship on the history of Hollywood film has grown, various aspects of Disney's influence and cultural position have likewise come to be the focus of study. In recent decades, also, there has been a continually greater interest in the role of women in American society and how that role is constructed. Uniting both these scholarly interests, this thesis analyses how Disney films depict femininity, and the ways in which such depictions correspond with those in the larger arena of Hollywood film. To make these issues more comprehensible, it describes the beginnings of animated film in the United States, together with the early career and works of Walt Disney. In order to cast light on the manner in which such portrayals have changed over time, the films examined are analysed in relation to three particular time periods: 193 7-67, 1967-89, and 1989-99. By examining the depictions to be found within individual films, and comparing these depictions both with one another and with selected live-action, mainstream Hollywood films of the same eras, a better understanding of the make-up of the Disney films as a body of work is achieved, and a corrective offered to some of the misconceptions of Disney to be found within American society in general

Implementation of musculoskeletal Models of Care in primary care settings: Theory, practice, evaluation and outcomes for musculoskeletal health in high-income economies

Musculoskeletal conditions represent one of the largest causes of years lived with disability in high-income economies. These conditions are predominantly managed in primary care settings, and yet, there is a paucity of evidence on which approaches work well in increasing the uptake of best practice and in closing the evidence-to-practice gap. Increasingly, musculoskeletal models of service delivery (as components of models of care) such as integrated care, stratified care and therapist-led care have been tested in primary health care pathways for joint pain in older adults, for low back pain and for arthritis. In this chapter, we discuss why implementation of these models is important for primary care and how models are implemented using three case examples: we review implementation theory, principles and outcomes; we consider the role of health economic evaluation; and we propose key evidence gaps in this field. We propose the following research priorities for this area: investigating the generalisability of models of care across, for example, urban and rural settings, and for different musculoskeletal conditions; increasing support for self-management; understanding the importance of context in choosing a model of care; detailing how implementation has been undertaken; and evaluation of implementation and its impact

Can a falling tree make a noise in two forests at the same time?

It is a commonplace to claim that quantum mechanics supports the old idea that a tree falling in a forest makes no sound unless there is a listener present. In fact, this conclusion is far from obvious. Furthermore, if a tunnelling particle is observed in the barrier region, it collapses to a state in which it is no longer tunnelling. Does this imply that while tunnelling, the particle can not have any physical effects? I argue that this is not the case, and moreover, speculate that it may be possible for a particle to have effects on two spacelike separate apparatuses simultaneously. I discuss the measurable consequences of such a feat, and speculate about possible statistical tests which could distinguish this view of quantum mechanics from a ``corpuscular'' one. Brief remarks are made about an experiment underway at Toronto to investigate these issues.Comment: 9 pp, Latex, 3 figs, to appear in Proc. Obsc. Unr. Conf.; Fig 2 postscript repaired on 26.10.9

Probabilistic Analysis of Optimization Problems on Generalized Random Shortest Path Metrics

Simple heuristics often show a remarkable performance in practice for optimization problems. Worst-case analysis often falls short of explaining this performance. Because of this, "beyond worst-case analysis" of algorithms has recently gained a lot of attention, including probabilistic analysis of algorithms. The instances of many optimization problems are essentially a discrete metric space. Probabilistic analysis for such metric optimization problems has nevertheless mostly been conducted on instances drawn from Euclidean space, which provides a structure that is usually heavily exploited in the analysis. However, most instances from practice are not Euclidean. Little work has been done on metric instances drawn from other, more realistic, distributions. Some initial results have been obtained by Bringmann et al. (Algorithmica, 2013), who have used random shortest path metrics on complete graphs to analyze heuristics. The goal of this paper is to generalize these findings to non-complete graphs, especially Erd\H{o}s-R\'enyi random graphs. A random shortest path metric is constructed by drawing independent random edge weights for each edge in the graph and setting the distance between every pair of vertices to the length of a shortest path between them with respect to the drawn weights. For such instances, we prove that the greedy heuristic for the minimum distance maximum matching problem, the nearest neighbor and insertion heuristics for the traveling salesman problem, and a trivial heuristic for the $k$-median problem all achieve a constant expected approximation ratio. Additionally, we show a polynomial upper bound for the expected number of iterations of the 2-opt heuristic for the traveling salesman problem.Comment: An extended abstract appeared in the proceedings of WALCOM 201

Probabilistic Analysis of Facility Location on Random Shortest Path Metrics

The facility location problem is an NP-hard optimization problem. Therefore, approximation algorithms are often used to solve large instances. Such algorithms often perform much better than worst-case analysis suggests. Therefore, probabilistic analysis is a widely used tool to analyze such algorithms. Most research on probabilistic analysis of NP-hard optimization problems involving metric spaces, such as the facility location problem, has been focused on Euclidean instances, and also instances with independent (random) edge lengths, which are non-metric, have been researched. We would like to extend this knowledge to other, more general, metrics. We investigate the facility location problem using random shortest path metrics. We analyze some probabilistic properties for a simple greedy heuristic which gives a solution to the facility location problem: opening the $\kappa$ cheapest facilities (with $\kappa$ only depending on the facility opening costs). If the facility opening costs are such that $\kappa$ is not too large, then we show that this heuristic is asymptotically optimal. On the other hand, for large values of $\kappa$, the analysis becomes more difficult, and we provide a closed-form expression as upper bound for the expected approximation ratio. In the special case where all facility opening costs are equal this closed-form expression reduces to $O(\sqrt[4]{\ln(n)})$ or $O(1)$ or even $1+o(1)$ if the opening costs are sufficiently small.Comment: A preliminary version accepted to CiE 201

Elastic-plastic solutions for expanding cavities embedded in two different cohesive-frictional materials

An analytical solution of cavity expansion in two different concentric regions of soil is developed and investigated in this paper. The cavity is embedded within a soil with finite radial dimension and surrounded by a second soil, which extends to infinity. Large-strain quasi-static expansion of both spherical and cylindrical cavities in elastic-plastic soils is considered. A non-associated Mohr–Coulomb yield criterion is used for both soils. Closed-form solutions are derived, which provide the stress and strain fields during the expansion of the cavity from an initial to a final radius. The analytical solution is validated against finite element simulations, and the effect of varying geometric and material parameters is studied. The influence of the two different soils during cavity expansion is discussed by using pressure–expansion curves and by studying the development of plastic regions within the soils. The analytical method may be applied to various geotechnical problems, which involve aspects of soil layering, such as cone penetration test interpretation, ground-freezing around shafts, tunnelling, and mining