261 research outputs found
Gear error induced impact in a multiple take-off textile drive system operating under light loading
A combined theoretical and experimental investigation is made
into the causes of premature gear failures which had occurred in the
complex and lighly loaded gear trains of an industrial textile
machine. A comprehensive review of previous relevant work identifies
the problem as one of torsional vibratory impact excited by gear
transmission errors.
An extension of the dynamic stiffness method is developed for
the analysis of forced vibration response due to relative displacement,
harmonic excitation imparted by transmission error components. The
technique is then applied to a generalised mathematical model of the
complete machine in which typical production distributions of gear
error magnitude and relative phasing are inserted. Gear-tooth
dynamic loads are computed at every mesh for a number of different
machine configurations over the operating speed range. The influence
of selected inertia, flexibility and damping elements is demonstrated.
A novel technique employing magnetic drums is devised and
evaluated for the direct measurement of-relative motions in a meshed
pair of oscillating gears. Automatic compensation is provided for
transmission error and mounting eccentricity. A further direct
technique is reported for the detection of tooth impacts and is based
on the change in electrical resistance between meshing teeth as the
contact pressure varies.
Measurements in a multi-gearbox experimental rig demonstrated
that the gears described non-linear motions, involving excursions
through the backlash and heavy impacts on both drive and reverse faces.
Theoretical predictibns of dynamic loading distribution within
machines show reasonable compatibility with patterns of gear
failure recorded in service, even though the analysis does not allow for system non-linearities.
Machine design considerations are examined in retrospect from
a dynamics standpoint. Past and present designs are appraised and
possible alternatives to these are briefly discussed.
Finally, the salient factors identified in the investigation
are summarised and recommendations made for future work
Coverage with evidence development: applications and issues
Copyright © Cambridge University Press, 2010OBJECTIVES: The aim of this study was to describe the current issues surrounding Coverage with Evidence Development (CED). CED is characterized by restricted coverage for a new technology in parallel with targeted research when the stated goal of the research or data collection is to provide definitive evidence for the clinical or cost-effectiveness impact of the new technology. METHODS: Presented here is information summarized and interpreted from presentations and discussions at the 2008 Health Technology Assessment International (HTAi) meeting and additional information from the medical literature. This study describes the differences between CED and other conditional coverage agreements, provides a brief history of CED, describes real-world examples of CED, describes the areas of consensus between the stakeholders, discusses the areas for future negotiation between stakeholders, and proposes criteria to assist stakeholders in determining when CED could be appropriate. RESULTS: Payers could interpret the evidence obtained from a CED program either positively or negatively, and a range of possible changes to the reimbursement status of the new technology may result. Striking an appropriate balance between the demands for prompt access to new technology and acknowledging that some degree of uncertainty will always exist is a critical challenge to the uptake of this innovative form of conditional coverage. CONCLUSIONS: When used selectively for innovative procedures, pharmaceuticals, or devices in the appropriate disease areas, CED may provide patients access to promising medicines or technologies while data to minimize uncertainty are collected.The development of the manuscript was funded by Medicines Australi
Can whole-drawer images measure up? A reply to Johnson et al. (2013)?
Johnson et al. (2013) found that morphometric measurements of dragonfly wings taken from actual specimens and measurements taken from whole-drawer images of those specimens were equally accurate. We do not believe that their conclusions are justified by their data and analysis. Our reasons are, first, that their study was constrained in ways that restrict the generalisability of their results, but second, and of far greater significance, their statistical approach was entirely unsuited to their data and their results misled them to erroneous conclusions. We offer an alternative analysis of their data as published. Our reanalysis demonstrates, contra Johnson et al., that measurements from scanned images are not a reliable substitute for direct measurement
Locations of marine animals revealed by carbon isotopes
Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available
Economic Geology Models 4. Tantalum and Niobium: Deposits, Resources, Exploration Methods and Market â A Primer for Geoscientists
The worldâs main tantalum (Ta) resources are in pegmatites (e.g. Wodgina, Australia), rare element-enriched granites (e.g. Abu Dabbab, Egypt), peralkaline complexes (e.g. Nechalacho, Canada), weathered crusts overlying the previously mentioned deposit types, and in placers. Niobium (Nb) resources with the highest economic potential are in weathered crusts that overlie carbonatite complexes (e.g. CatalĂŁo I and II, Brazil). Brazil accounts for 90% of the global Nb mine production with another 9% coming from the Niobec Mine, Canada (a hard-rock underground mine). However, at least 17 undeveloped carbonatite complexes outside of Brazil have NI-43-101 compliant Nb resource estimates (e.g. Aley carbonatite, Canada). Concentrates from most carbonatites are used to produce ferroniobium (FeâNb alloy), and Ta is not recovered. The Ta and Nb contents of some carbonatites (e.g. Upper Fir deposit and Crevier dyke, Canada) are of the same order of magnitude as that of pegmatite ores; however, concentrates from carbonatites have a higher Nb/Ta ratio. Historically, 10â12% Ta2O5 in Nb concentrates has not been recovered in âwesternâ smelters because of the hydrofluoric acid cost. Western countries perceive Ta and Nb supplies to be at risk. Tantalum market downturns resulted in several mines in Australia and Canada closing, at least temporarily, and a resultant shortfall has been filled by what is now recognized as âconflict-free columbite-tantaliteâ from Central Africa. The lack of ore will not be a key factor in future Ta and Nb supply disruption. For example, more than 280 Nb- and 160 Ta-bearing occurrences are known in Canada alone, and more resources will likely to be discovered as geophysical and geochemical exploration methods are optimized.RĂSUMĂLes principales sources mondiales en tantale (Ta) sont les pegmatites (par ex. Wodgina, Australie), les granites enrichis en Ă©lĂ©ments rares (par ex. Abu Dabbab, Ăgypte), les complexes hyperalcalins (par ex. Nechalacho, Canada), les croĂ»tes altĂ©rĂ©es recouvrant les types de gisements dĂ©jĂ mentionnĂ©s, et les placers. Les sources en niobium (Nb) ayant le meilleur potentiel Ă©conomique se trouvent dans les croĂ»tes altĂ©rĂ©es qui recouvrent les complexes de carbonatite (par ex. CatalĂŁo I et II, BrĂ©sil). Le BrĂ©sil est la source de 90% de la production miniĂšre mondiale de Nb, et 9% provient de la mine Niobec, au Canada (une mine souterraine). Cela dit, il existe au moins 17 complexes de carbonatite non dĂ©veloppĂ©s Ă l'extĂ©rieur du BrĂ©sil dont les estimations de ressources en Nb sont conformes Ă la norme NI-43-101 (par ex. Aley carbonatite, Canada). Les concentrĂ©s de la plupart des carbonatites sont utilisĂ©s pour produire du ferroniobium (alliage Fe-Nb), et le Ta n'est pas rĂ©cupĂ©rĂ©. Les teneurs en Ta et Nb de certaines carbonatites (par ex. le gisement de Upper Fir et le dyke Crevier, Canada) sont du mĂȘme ordre de grandeur que celles des minerais depegmatite; cependant, les concentrĂ©s de carbonatites ont une proportion Nb/Ta plus Ă©levĂ©e. Historiquement, 10 Ă 12% du Ta2O5 des concentrĂ©s de Nb n'ont pas Ă©tĂ© rĂ©cupĂ©rĂ©s dans les fonderies de l'Ouest en raison du coĂ»t de lâacide fluorhydrique. Les pays occidentaux estiment que les approvisionnements en Ta et Nb sont Ă risque. Le flĂ©chissement du marchĂ© du tantale a entraĂźnĂ© la fermeture, au moins temporaire, de plusieurs mines en Australie et au Canada, et la pĂ©nurie qui en rĂ©sulte a Ă©tĂ© comblĂ©e par ce qui est maintenant reconnu comme Ă©tant du minerai de colombite-tantalite «sans conflit» d'Afrique centrale. Le manque de minerai ne sera pas un facteur clĂ© des perturbations Ă venir de l'approvisionnement en Ta et Nb. Par exemple, plus de 280 occurrences minĂ©rales contenant du Nb et 160 occurrences minĂ©rales contenant du Ta sont connues au Canada seulement, et davantage de ressources seront probablement dĂ©couvertes Ă mesure que les mĂ©thodes d'exploration gĂ©ophysique et gĂ©ochimique seront optimisĂ©es
Lickometry: A novel and sensitive method for assessing functional deficits in rats after stroke
The need for sensitive, easy to administer assessments of long-term functional deficits is crucial in pre-clinical stroke research. In the present study, we introduce lickometry (lick microstructure analysis) as a precise method to assess sensorimotor deficits up to 40 days after middle cerebral artery occlusion in rats. Impairments in drinking efficiency compared to controls, and a compensatory increase in the number of drinking clusters were observed. This highlights the utility of this easy to administer task in assessing subtle, long-term deficits, which could be likened to oral deficits in patients
Asymptotics of Feynman Diagrams and The Mellin-Barnes Representation
It is shown that the integral representation of Feynman diagrams in terms of
the traditional Feynman parameters, when combined with properties of the
Mellin--Barnes representation and the so called {\it converse mapping theorem},
provide a very simple and efficient way to obtain the analytic asymptotic
behaviours in both the large and small ratios of mass scales.Comment: References added. This is the version published in Physics Letters
DNA barcoding identifies a cosmopolitan diet in the ocean sunfish
The ocean sunfish (Mola mola) is the worldâs heaviest bony fish reaching a body mass of up to 2.3 tonnes. However, the prey M. mola consumes to fuel this prodigious growth remains poorly known. Sunfish were thought to be obligate gelatinous plankton feeders, but recent studies suggest a more generalist diet. In this study, through molecular barcoding and for the first time, the diet of sunfish in the north-east Atlantic Ocean was characterised. Overall, DNA from the diet content of 57 individuals was successfully amplified, identifying 41 different prey items. Sunfish fed mainly on crustaceans and teleosts, with cnidarians comprising only 16% of the consumed prey. Although no adult fishes were sampled, we found evidence for an ontogenetic shift in the diet, with smaller individuals feeding mainly on small crustaceans and teleost fish, whereas the diet of larger fish included more cnidarian species. Our results confirm that smaller sunfish feed predominantly on benthic and on coastal pelagic species, whereas larger fish depend on pelagic prey. Therefore, sunfish is a generalist predator with a greater diversity of links in coastal food webs than previously realised. Its removal as fisheriesâ bycatch may have wider reaching ecological consequences, potentially disrupting coastal trophic interactions
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