2,372 research outputs found
Analysis and Insights from a Dynamical Model of Nuclear Plant Safety Risk
In this paper, we expand upon previously reported results of a dynamical systems model for the impact of plant processes and programmatic performance on nuclear plant safety risk. We utilize both analytical techniques and numerical simulations typical of the analysis of nonlinear dynamical systems to obtain insights important for effective risk management. This includes use of bifurcation diagrams to show that period doubling bifurcations and regions of chaotic dynamics can occur. We also investigate the impact of risk mitigating functions (equipment reliability and loss prevention) on plant safety risk and demonstrate that these functions are capable of improving risk to levels that are better than those that are represented in a traditional risk assessment. Next, we analyze the system response to the presence of external noise and obtain some conclusions with respect to the allocation of resources to ensure that safety is maintained at optimal levels. In particular, we demonstrate that the model supports the importance of management and regulator attention to plants that have demonstrated poor performance by providing an external stimulus to obtain desired improvements. Equally important, the model suggests that excessive intervention, by either plant management or regulatory authorities, can have a deleterious impact on safety for plants that are operating with very effective programs and processes. Finally, we propose a modification to the model that accounts for the impact of plant risk culture on process performance and plant safety risk. We then use numerical simulations to demonstrate the important safety benefits of a strong risk culture.Nonlinear Dynamical Systems, Process Model, Risk Management
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Modeling Dynamic Stall for a Free Vortex Wake Model of a Floating Offshore Wind Turbine
Floating offshore wind turbines in deep waters offer significant advantages to onshore and near-shore wind turbines. However, due to the motion of floating platforms in response to wind and wave loading, the aerodynamics are substantially more complex. Traditional aerodynamic models and design codes do not adequately account for the floating platform dynamics to assess its effect on turbine loads and performance. Turbines must therefore be over designed due to loading uncertainty and are not fully optimized for their operating conditions. Previous research at the University of Massachusetts, Amherst developed the Wake Induced Dynamics Simulator, or WInDS, a free vortex wake model of wind turbines that explicitly includes the velocity components from platform motion. WInDS rigorously accounts for the unsteady interactions between the wind turbine rotor and its wake, however, as a potential flow model, the unsteady viscous response in the blade boundary layer is neglected. To address this concern, this thesis presents the development of a Leishman-Beddoes dynamic stall model integrated into WInDS. The stand-alone dynamic stall model was validated against two-dimensional unsteady data from the OSU pitch oscillation experiments and the coupled WInDS model was validated against three-dimensional data from NRELâs UAE Phase VI campaign. WInDS with dynamic stall shows substantial improvements in load predictions for both steady and unsteady conditions over the base version of WInDS. Furthermore, use of WInDS with the dynamic stall model should provide the necessary aerodynamic model fidelity for future research and design work on floating offshore wind turbines
Incidental Cutaneous Reaction Patterns: Epidermolytic Hyperkeratosis, Acantholytic Dyskeratosis, and Hailey-Hailey-Like Acantholysis: A Potential Marker of Premalignant Skin Change
Focal acantholytic dyskeratosis (FAD), epidermolytic hyperkeratosis (EHK), and Hailey-Hailey-like acantholysis (HH) represent unique histology reaction patterns, which can be associated with defined phenotypic and genotypic alterations. Incidental microscopic foci demonstrating these patterns have been identified in skin and mucosal specimens in association with a gamut of disease processes. These changes, when secondary, are of unclear etiology and significance. The following study further analyzes the incidence and association of these histologic patterns in a routine pathology/dermatopathology practice
Instalacion de un sistema de bitacoras para la pesca atunera de superficie en Venezuela y analisis de los primeros resultados
Dans le cadre des recommandations faites par le SCRS de la C.I.C.T.A. un nouveau systĂšme de livres de bord a Ă©tĂ© mis en place au VĂ©nĂ©zuela en avril 1986. L'analyse des premiers rĂ©sultats montre que les dĂ©clarations faites par les canneurs et les senneurs divergent pour les espĂšces de thon peu abondantes dans les eaux vĂ©nĂ©zueliennes comme le patudo (#Thunnus obesus) ou le thon noir (#Thunnus atlanticus). La comparaison des dĂ©clarations rĂ©alisĂ©es par un senneur et un canneur sur un mĂȘme banc confirme l'existence de biais qui affecte Ă©galement les deux principales espĂšces qui sont l'albacore (#Thunnus albacares) et le listao (#Katsuwonus pelamis) et en particulier les estimations du poids moyen des individus de ces deux espĂšces ... L'observation d'oiseaux, accompagnĂ©e (95,5 % des cas), ou non (50 %), par d'autres indices est la principale source de dĂ©tection des bancs de thon
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Considerations for the Design Optimization of Floating Offshore Wind Turbine Blades
Floating offshore wind turbines are an immature technology with relatively high costs and risk associated with deployment. Of the few floating wind turbine prototypes and demonstration projects deployed in real metocean conditions, all have used standard turbines design for onshore or offshore fixed bottom conditions. This neglects the unique unsteady aerodynamics brought on by floating support structure motion. While the floating platform has been designed and optimized for a given rotor, the global system is suboptimal due to the rotor operating in conditions outside of which it was design for. If the potential offered by floating wind turbines is to be realized, offering access to deep water near-shore, costs need to continue to be reduced. This dissertation is the first known design study that considers the optimization of wind turbine rotors specifically for floating conditions.
Two design optimization methodologies are presented using different analysis fidelity levels. A relatively computationally efficient, state-state blade element moment optimization of floating wind turbine blades is presented that will be useful for future systems level optimization studies. A higher fidelity methodology is then presented, using time-domain aeroelastic simulations to fully capture the unsteady aerodynamics and dynamic couplings between the rotor and platform motion throughout the optimization process. The principal finding of these studies is that low induction rotors are a promising technology pathway for future FOWT systems, reducing the severity of cyclical loading due to platform motion
Ajuste de una curva de crecimiento a frecuencias de tallas de atun listado (Katsuwonus pelamis) pescado en el mar Caribe suroriental
La croissance du thon listao provenant de la pĂȘcherie de surface vĂ©nĂ©zuĂ©lienne de la Mer des CaraĂŻbes a Ă©tĂ© estimĂ©e Ă partir de distributions de tailles mensuelles obtenues entre 1988 et 1993. Le logiciel MULTIFAN, qui emploie la mĂ©thode de maximum de vraisemblance, a Ă©tĂ© utilisĂ© pour ajuster les donnĂ©es observĂ©es au modĂšle de von Bertalanffy, donnant pour rĂ©sultat L(infini) = 94,9 cm et K = 0,340. La signification statistique de l'ajustement, et la comparaison des estimations obtenues avec celles estimĂ©es dans d'autres ocĂ©ans, semblent indiquer l'existence de deux recrutements annuels dans cette pĂȘcherie. D'autre part, les rĂ©sultats obtenus, et le fait de pouvoir observer une apparente progression des modes pendant plusieurs annĂ©es, rendent crĂ©dible l'utilisation des techniques de maximum de vraisemblance avec des distributions de tailles pour l'Ă©tude de la croissance du listao de cette pĂȘcherie. (RĂ©sumĂ© d'auteur
Experimental observation of four-photon entanglement from down-conversion
We observe polarization-entanglement between four photons produced from a
single down-conversion source. The non-classical correlations between the
measurement results violate a generalized Bell inequality for four qubits. The
characteristic properties and its easy generation with high interferometric
contrast make the observed four-photon state well-suited for implementing
advanced quantum communication schemes such as multi-party quantum key
distribution, secret sharing and telecloning.Comment: 4 pages, 3 figure
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Should neurologists initiate treatment for hypertension and hyperlipidemia to reduce cardiovascular risk in epilepsy?
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