1,442 research outputs found

    Strategic Policy Choice in State-Level Regulation: The EPA's Clean Power Plan

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    The EPA's Clean Power Plan sets goals for COâ‚‚ emissions rate reductions by 2030 that vary substantially across states. States can choose the regulatory mechanism they use and whether or not to join with other states in implementing their goals. We analyze incentives to adopt rate standards versus cap-and-trade with theory and simulation. We show conditions where adoption of inefficient rate standards is a dominant strategy from both consumers' and generators' perspectives. Numerical simulations of the western electricity system highlight incentives for uncoordinated policies that lower welfare and increase emissions relative to coordination

    Use of stormwater impoundments near airports by birds recognizedas hazardous to aviation safety

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    Design of privately-owned stormwater impoundments within or near airport siting criteria has received little attention with regard to potential hazards posed to aviation safety. In particular, minimizing use of these impoundments by bird species recognized as hazardous to aviation poses an important challenge. Emergent vegetation, shoreline irregularity, and proximity of other water resources are linked to avian richness and diversity within wetlands, as well as bird use of stormwater impoundments on airports. We predicted also that impoundments with bank slope \u3e20% and those functioning as detention facilities, where water is periodically drawn down, would negatively influence use by birds; and that shoreline-vegetation diversity and local land-use diversity would be positively correlated with use. Over 104 weeks(March 2008 to March 2010), we surveyed bird use of 40 stormwater impoundments in the Auburn-Opelika Metropolitan area, Lee County, AL, USA, typical of privately-owned facilities located within or near airport siting criteria. We quantified local-scale and site-specific parameters possibly affecting bird use and evaluated fit for 17 a priori models relative to detection of 10 individual avian foraging guilds recognized as hazardous to aviation safety. Relative likelihoods of best-approximating models (Akaike weights) ranged from approximately 0.42 to 0.92. Based on best-approximating models for at least five of the 10 guilds, we suggest that broad reduction in use of stormwater impoundments, located within or near airport siting criteria, by bird species hazardous to aviation can be achieved via designs which minimize perimeter, surface area, and the ratio of open water to emergent vegetation

    Anterior temporal lobe is necessary for efficient lateralised processing of spoken word identity.

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    In the healthy human brain, the processing of language is strongly lateralised, usually to the left hemisphere, while the processing of complex non-linguistic sounds recruits brain regions bilaterally. Here we asked whether the anterior temporal lobes, strongly implicated in semantic processing, are critical to this special treatment of spoken words. Nine patients with semantic dementia (SD) and fourteen age-matched controls underwent magnetoencephalography and structural MRI. Voxel based morphometry demonstrated the stereotypical pattern of SD: severe grey matter loss restricted to the anterior temporal lobes, with the left side more affected. During magnetoencephalography, participants listened to word sets in which identity and meaning were ambiguous until word completion, for example PLAYED versus PLATE. Whereas left-hemispheric responses were similar across groups, patients demonstrated increased right hemisphere activity 174-294 msec after stimulus disambiguation. Source reconstructions confirmed recruitment of right-sided analogues of language regions in SD: atrophy of anterior temporal lobes was associated with increased activity in right temporal pole, middle temporal gyrus, inferior frontal gyrus and supramarginal gyrus. Overall, the results indicate that anterior temporal lobes are necessary for normal and efficient lateralised processing of word identity by the language network.The study was primarily funded by the MRC Cognition and Brain Sciences Unit with additional support from the Cambridge NIHR Biomedical Research Centre (the views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care). TEC was supported by the Association of British Neurologists, the Patrick Berthoud Charitable trust, and the NIHR. YS was supported by the Medical Research Council (MC-A060-5PQ90), Lundbeck Foundation (R164-2013-15801, project 18690), Danish Council for Independent Research (6110-00486, project 23776), HSE Basic Research Program and the RF Academic Excellence Project '5-100'. JBR was supported by the Wellcome Trust (103838), and the Medical Research Council (MC-A060-5PQ30 & SUAG/004 RG91365)

    Vibration Characteristics Determined for Stainless Steel Sandwich Panels With a Metal Foam Core for Lightweight Fan Blade Design

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    The goal of this project at the NASA Glenn Research Center is to provide fan materials that are safer, weigh less, and cost less than the currently used titanium alloy or polymer matrix composite fans. The proposed material system is a sandwich fan construction made up of thin solid face sheets and a lightweight metal foam core. The stiffness of the sandwich structure is increased by separating the two face sheets by the foam layer. The resulting structure has a high stiffness and lighter weight in comparison to the solid facesheet material alone. The face sheets carry the applied in-plane and bending loads (ref. 1). The metal foam core must resist the transverse shear and transverse normal loads, as well as keep the facings supported and working as a single unit. Metal foams have ranges of mechanical properties, such as light weight, impact resistance, and vibration suppression (ref. 2), which makes them more suitable for use in lightweight fan structures. Metal foams have been available for decades (refs. 3 and 4), but the difficulties in the original processes and high costs have prevented their widespread use. However, advances in production techniques and cost reduction have created a new interest in this class of materials (ref. 5). The material chosen for the face sheet and the metal foam for this study was the aerospace-grade stainless steel 17-4PH. This steel was chosen because of its attractive mechanical properties and the ease with which it can be made through the powder metallurgy process (ref. 6). The advantages of a metal foam core, in comparison to a typical honeycomb core, are material isotropy and the ease of forming complex geometries, such as fan blades. A section of a 17-4PH sandwich structure is shown in the following photograph. Part of process of designing any blade is to determine the natural frequencies of the particular blade shape. A designer needs to predict the resonance frequencies of a new blade design to properly identify a useful operating range. Operating a blade at or near the resonance frequencies leads to high-cycle fatigue, which ultimately limits the blade's durability and life. So the aim of this study is to determine the variation of the resonance frequencies for an idealized sandwich blade as a function of its face-sheet thickness, core thickness, and foam density. The finite element method is used to determine the natural frequencies for an idealized rectangular sandwich blade. The proven Lanczos method (ref. 7) is used in the study to extract the natural frequency

    Analysis of Stainless Steel Sandwich Panels with a Metal Foam Care for Lightweight Fan Blade Design

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    The quest for cheap, low density and high performance materials in the design of aircraft and rotorcraft engine fan and propeller blades poses immense challenges to the materials and structural design engineers. Traditionally, these components have been fabricated using expensive materials such as light weight titanium alloys, polymeric composite materials and carbon-carbon composites. The present study investigates the use of P sandwich foam fan blade made up of solid face sheets and a metal foam core. The face sheets and the metal foam core material were an aerospace grade precipitation hardened 17-4 PH stainless steel with high strength and high toughness. The stiffness of the sandwich structure is increased by separating the two face sheets by a foam core. The resulting structure possesses a high stiffness while being lighter than a similar solid construction. Since the face sheets carry the applied bending loads, the sandwich architecture is a viable engineering concept. The material properties of 17-4 PH metal foam are reviewed briefly to describe the characteristics of the sandwich structure for a fan blade application. A vibration analysis for natural frequencies and P detailed stress analysis on the 17-4 PH sandwich foam blade design for different combinations of skin thickness and core volume %re presented with a comparison to a solid titanium blade
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