Understanding why metal-on-metal hip arthroplasties fail: a comparison between patients with well-functioning and revised birmingham hip resurfacing arthroplasties. AAOS exhibit selection.

A large proportion of metal-on-metal hip arthroplasty failures are due to unexplained pain. The mechanism of failure has been thought to be associated with factors that increase material loss, including specific design features and surgical positioning of components. However, recent evidence suggests that there is not a simple dose-response relationship. An analysis of failed metal-on-metal hip arthroplasties involving a single design was performed in an attempt to help resolve this issue. Our aim was to identify the clinical and component variables associated with failure of metal-on-metal hip arthroplasties, particularly in patients undergoing revision arthroplasty because of unexplained hip pain, and to clarify the role of material loss

Chaos in the Takens-Bogdanov bifurcation with O(2) symmetry

The Takens–Bogdanov bifurcation is a codimension two bifurcation that provides a key to the presence of complex dynamics in many systems of physical interest. When the system is translation invariant in one spatial dimension with no left-right preference the imposition of periodic boundary conditions leads to the Takens–Bogdanov bifurcation with O(2) symmetry. This bifurcation, analyzed by G. Dangelmayr and E. Knobloch, Phil. Trans. R. Soc. London A 322, 243 (1987), describes the interaction between steady states and traveling and standing waves in the nonlinear regime and predicts the presence of modulated traveling waves as well. The analysis reveals the presence of several global bifurcations near which the averaging method (used in the original analysis) fails. We show here, using a combination of numerical continuation and the construction of appropriate return maps, that near the global bifurcation that terminates the branch of modulated traveling waves, the normal form for the Takens–Bogdanov bifurcation admits cascades of period-doubling bifurcations as well as chaotic dynamics of Shil’nikov type. Thus chaos is present arbitrarily close to the codimension two point

Green, circular, bio economy : A comparative analysis of sustainability avenues

Despite their evidently different assumptions and operationalization strategies, the concepts of Circular Economy, Green Economy and Bioeconomy are joined by the common ideal to reconcile economic, environmental and social goals. The three concepts are currently mainstreamed in academia and policy making as key sustainability avenues, but a comparative analysis of such concepts is missing. The aim of this article is thus to comprehensively analyse the diversity within and between such concepts. The results are drawn from a bibliometric review of almost two thousand scientific articles published within the last three decades, coupled with a conceptual analysis. We find that, for what concerns environmental sustainability, Green Economy acts as an 'umbrella' concept, including elements from Circular Economy and Bioeconomy concepts (e.g. eco-efficiency; renewables), as well as additional ideas, e.g. nature-based solutions. In particular, Circular Economy and Bioeconomy are resource-focused, whereas in principle Green Economy acknowledges the underpinning role of all ecological processes. Regarding the social dimension, Green Economy is more inclusive of some aspects at local level (e.g. eco-tourism, education), while there is an emerging discussion in Bioeconomy literature around local processes in terms of biosecurity and rural policies. When considering weak/strong sustainability visions, all concepts remain limited in questioning economic growth. By comparing the different sustainability strategies promoted by these concepts we do not advocate for their substitutability, but for their clarification and reciprocal integration. The findings are discussed in light of the concepts' synergies and limits, with the purpose to inform research and policy implementation. (C) 2017 The Authors. Published by Elsevier Ltd.Peer reviewe

Charactering taper junction wear helps understand the mechanism of failure of metal on metal hip replacements.

Introduction: Taper junction material loss is the result of corrosion and mechanical wear. The significance of the taper junction material loss is highlighted by studies that compared resurfacing and total hip replacements of the same type and size. High volumes of material loss are reported, especially from the head taper, but the pattern of wear is unknown. One report characterized the material loss pattern of five tapers (n=5) into axisymmetrical and asymmetrical, along the long axis of the taper. We noticed more than two patterns on our retrievals and we set out to characterize these types and relate them to clinical variables. Methods: We retrospectively analysed retrieved cobalt-chromium tapers (n=146) using a roundness measurement machine. We also performed a corrosion classification and collected clinical data (metal ion levels, time to revision, component sizes). A non-blinded author devised a four-group classification (table). Two blinded authors classified the material loss patterns derived from the roundness measurement machine. Results: The four groups of material loss patterns Low wear (n= 62), Open-end band (n=29), Stripped material loss (n=51) and Coup-Countercoup (n=4). Kappa was 0.78 (p<0.001) in the assessment of interobserver reliability. Kruskal-Wallis test revealed: - Significantly higher volumes of wear on the taper of Stripped material loss compared to Low wear (p<0.001) and Open-end band compared to Low wear (p<0.001) groups. - Significantly higher chromium ion blood levels in the open-end band compared to the Stripped material loss group. - Significantly higher Cobalt ion blood levels in the Stripped material loss compared to the Low wear group - Significantly higher Cobalt/Chromium ration in the Open-end band compared to the Low wear group One-way ANOVA analysis revealed: - Significant difference between in the head sizes between the groups (p=0.01). Post-hoc analysis located the difference between the Low wear (median=40, range=20) and Open-end band (median=49, range=20) groups (p<0.001). - Significantly higher time to revision in the Stripped material loss compared to the Low wear group (p=0.05), in the post-hoc analysis. - Significantly higher corrosion scores in the Stripped material loss compared to the Low wear group (p<0.001) and the Open-end band compared to the Low wear group (p<0.001). Discussion: The results suggests that corrosion becomes worse over time and that the material loss pattern evolves gradually from the Low wear to Open-end band and finally to Stripped. Further analysis is required to assess the factors that affect the Coup-countercoup group

Design of an Agile Unmanned Combat Vehicle - A Product of the DARPA UGCV Program

The unmanned ground combat vehicle (UGCV) design evolved by the SAIC team on the DARPA UGCV Program is summarized in this paper. This UGCV design provides exceptional performance against all of the program metrics and incorporates key attributes essential for high performance robotic combat vehicles. This performance includes protection against 7.62 mm threats, C130 and CH47 transportability, and the ability to accept several relevant weapons payloads, as well as advanced sensors and perception algorithms evolving from the PerceptOR program. The UGCV design incorporates a combination of technologies and design features, carefully selected through detailed trade studies, which provide optimum performance against mobility, payload, and endurance goals without sacrificing transportability, survivability, or life cycle cost. The design was optimized to maximize performance against all Category I metrics. In each case, the performance of this design was validated with detailed simulations, indicating that the vehicle exceeded the Category I metrics. Mobility metrics were analyzed using high fidelity VisualNastran vehicle models, which incorporate the suspension control algorithms and controller cycles times. DADS/Easy 5 3-D models and ADAMS simulations were also used to validate vehicle dynamics and control algorithms during obstacle negotiation