929 research outputs found

    Development of a new generation of high-temperature composite materials

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    Intermetallic matrix composites proposed to meet advanced aeropropulsion requirements are discussed. The powder metallurgy fabrication process currently being used to produce these intermetallic matrix composites will be presented, as will properties of one such composite, SiC/Ti3Al+Nb. In addition, the direction of future research will be outlined, including plans for enhanced fabrication of intermetallic composites by the arc-spray technique and fiber development by the floating-zone process

    High temperature fatigue behavior of a SiC/Ti-24Al-11Nb composite

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    A series of tension-tension strain- and load-controlled tests were conducted on unidirectional SiC/Ti-24Al-11Nb (at percent) composites at 425 and 815 C. Several regimes of damage were identified using Talrega's concept of fatigue life diagrams. Issues of test technique, test control mode, and definition of failure were also addressed

    Investigation of a SiC/Ti-24Al-11Nb composite

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    A summary of ongoing research on the characterization of a continuous fiber reinforced SiC/Ti-24Al-11Nb (at percent) composite is presented. The powder metallurgy fabrication technique is described as are the nondestructive evaluation results of the as-fabricated composite plates. Tensile properties of the SiC fiber, the matrix material, and the 0-deg SiC/Ti-24Al-11Nb composite (fibers oriented unidirectionally, parallel to the loading axis) from room temperature to 1100 C are presented and discussed with regard to the resultant fractography. The as-fabricated fiber-matrix interface has been examined by scanning transmission electron microscopy and the compounds present in the reaction zone have been identified. Fiber-matrix interaction and stability of the matrix near the fiber is characterized at 815, 985, and 1200 C from 1 to 500 hr. Measurements of the fiber-matrix reaction, the loss of C-rich coating from the surface of the SiC fiber, and the growth of the Beta depleted zone in the matrix adjacent to the fiber are presented. These data and the difference in coefficient of thermal expansion between the fiber and the matrix are discussed in terms of their likely effects on mechanical properties

    Nanomechanical and thermophoretic analyses of the nucleotide-dependent interactions between the AAA+ subunits of magnesium chelatase

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    In chlorophyll biosynthesis, the magnesium chelatase enzyme complex catalyzes the insertion of a Mg2+ ion into protoporphyrin IX. Prior to this event, two of the three subunits, the AAA+ proteins ChlI and ChlD, form a ChlID− MgATP complex. We used microscale thermophoresis to directly determine dissociation constants for the I-D subunits from Synechocystis, and to show that the formation of a ChlID− MgADP complex, mediated by the arginine finger and the sensor II domain on ChlD, is necessary for the assembly of the catalytically active ChlHID−MgATP complex. The N-terminal AAA+ domain of ChlD is essential for complex formation, but some stability is preserved in the absence of the C-terminal integrin domain of ChlD, particularly if the intervening polyproline linker region is retained. Single molecule force spectroscopy (SMFS) was used to determine the factors that stabilize formation of the ChlID−MgADP complex at the single molecule level; ChlD was attached to an atomic force microscope (AFM) probe in two different orientations, and the ChlI subunits were tethered to a silica surface; the probability of subunits interacting more than doubled in the presence of MgADP, and we show that the N-terminal AAA+ domain of ChlD mediates this process, in agreement with the microscale thermophoresis data. Analysis of the unbinding data revealed a most probable interaction force of around 109 pN for formation of single ChlID−MgADP complexes. These experiments provide a quantitative basis for understanding the assembly and function of the Mg chelatase complex

    Urban centre green metrics in Great Britain: a geospatial and socioecological study

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    Green infrastructure plays a vital role in urban ecosystems. This includes sustaining biodiversity and human health. Despite a large number of studies investigating greenspace disparities in suburban areas, no known studies have compared the green attributes (e.g., trees, greenness, and greenspaces) of urban centres. Consequently, there may be uncharacterised socioecological disparities between the cores of urban areas (e.g., city centres). This is important because people spend considerable time in urban centres due to employment, retail and leisure opportunities. Therefore, the availability of––and disparities in––green infrastructure in urban centres can affect many lives and potentially underscore a socio-ecological justice issue. To facilitate comparisons between urban centres in Great Britain, we analysed open data of urban centre boundaries with a central business district and population of ≥100,000 (n = 68). Given the various elements that contribute to ‘greenness’, we combine a range of different measurements (trees, greenness, and accessible greenspaces) into a single indicator. We applied the normalised difference vegetation index (NDVI) to estimate the mean greenness of urban centres and the wider urban area (using a 1 km buffer) and determined the proportion of publicly accessible greenspace within each urban centre with Ordnance Survey Open Greenspace data. Finally, we applied a land cover classification algorithm using i-Tree Canopy to estimate tree coverage. This is the first study to define and rank urban centres based on multiple green attributes. The results suggest important differences in the proportion of green attributes between urban centres. For instance, Exeter scored the highest with a mean NDVI of 0.15, a tree coverage of 11.67%, and an OS Greenspace coverage of 0.05%, and Glasgow the lowest with a mean NDVI of 0.02, a tree cover of 1.95% and an OS Greenspace coverage of 0.00%. We also demonstrated that population size negatively associated with greenness and tree coverage, but not greenspaces, and that green attributes negatively associated with deprivation. This is important because it suggests that health-promoting and biodiversity-supporting resources diminish as population and deprivation increase. Disparities in green infrastructure across the country, along with the population and deprivation-associated trends, are important in terms of socioecological and equity justice. This study provides a baseline and stimulus to help local authorities and urban planners create and monitor equitable greening interventions in urban/city centres

    Intercalation-enhanced electric polarization and chain formation of nano-layered particles

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    Microscopy observations show that suspensions of synthetic and natural nano-layered smectite clay particles submitted to a strong external electric field undergo a fast and extended structuring. This structuring results from the interaction between induced electric dipoles, and is only possible for particles with suitable polarization properties. Smectite clay colloids are observed to be particularly suitable, in contrast to similar suspensions of a non-swelling clay. Synchrotron X-ray scattering experiments provide the orientation distributions for the particles. These distributions are understood in terms of competing (i) homogenizing entropy and (ii) interaction between the particles and the local electric field; they show that clay particles polarize along their silica sheet. Furthermore, a change in the platelet separation inside nano-layered particles occurs under application of the electric field, indicating that intercalated ions and water molecules play a role in their electric polarization. The resulting induced dipole is structurally attached to the particle, and this causes particles to reorient and interact, resulting in the observed macroscopic structuring. The macroscopic properties of these electro-rheological smectite suspensions may be tuned by controlling the nature and quantity of the intercalated species, at the nanoscale.Comment: 7 pages, 5 figure

    Receptor for Fc on the surfaces of schistosomes

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    Schistosoma mansoni masks its surface with adsorbed host proteins including erythrocyte antigens, immunoglobulins, major histocompatibility complex class I, and beta (2)-microglobulin (beta (2)m), presumably as a means of avoiding host immune responses, How this is accomplished has not been explained. To identify surface receptors for host proteins, we biotinylated the tegument of live S, mansoni adults and mechanically transformed schistosomula and then removed the parasite surface with detergent, Incubation of biotinylated schistosome surface extracts witt l human immunoglobulin G (IgG) Fc-Sepharose resulted in purification of a 97-kDa protein that was subsequently identified as paramyosin (Pmy), using antiserum specific for recombinant Pmy, Fc also bound recombinant S. mansoni Pmy and native S. japonicum Pmy, Antiserum to Pmy decreased the binding of Pmy to Fc-Sepharose, and no proteins bound after removal of Pmy from extracts. Fluoresceinated human Fe bound to the surface, vestigial penetration glands, and nascent oral cavity of mechanically transformed schistosomula, and rabbit anti-Pmy Fab fragments ablated the binding of Fc to the schistosome surface, Pmy coprecipitated with host IgG from parasite surface extracts, indicating that complexes formed on the parasite surface as well as in vitro. Binding of Pmy to Fe was not inhibited by soluble protein A, suggesting that Pmy does not bind to the region between the CH2 and CH3 domains used by many other Fc-binding proteins. beta (2)m did not bind to the schistosome Fc receptor (Pmy), a finding that contradicts reports from earlier workers but did bind to a heteromultimer of labeled schistosomula surface proteins, This is the first report of the molecular identity of a schistosome Fc receptor; moreover it demonstrates an additional aspect of the unusual and multifunctional properties of Pmy from schistosomes and other parasitic flatworms

    Shmapped: development of an app to record and promote the well-being benefits of noticing urban nature

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    The majority of research to date on the links between well-being and green spaces comes from cross-sectional studies. Shmapped is an app that allows for the collection of well-being and location data live in the field and acts as a novel dual data collection tool and well-being intervention, which prompts users to notice the good things about their surroundings. We describe the process of developing Shmapped from storyboarding, budgeting, and timescales; selecting a developer; drawing up data protection plans; and collaborating with developers and end-user testers to ultimately publishing Shmapped. The development process and end-user testing resulted in a highly functional app. Limitations and future uses of such novel dual data collection and intervention apps are discussed and recommendations are made for prospective developers and researchers

    Where the wild things are! Do urban green spaces with greater avian biodiversity promote more positive emotions in humans?

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    Urban green space can help mitigate the negative impacts of urban living and provide positive effects on citizens’ mood, health and well-being. Questions remain, however, as to whether all types of green space are equally beneficial, and if not, what landscape forms or key features optimise the desired benefits. For example, it has been cited that urban landscapes rich in wildlife (high biodiversity) may promote more positive emotions and enhance well-being. This research utilised a mobile phone App, employed to assess people’s emotions when they entered any one of 945 green spaces within the city of Sheffield, UK. Emotional responses were correlated to key traits of the individual green spaces, including levels of biodiversity the participant perceived around them. For a subsample of these green spaces, actual levels of biodiversity were assessed through avian and habitat surveys. Results demonstrated strong correlations between levels of avian biodiversity within a green space and human emotional response to that space. Respondents reported being happier in sites with greater avian biodiversity (p < 0.01, r = 0.78) and a greater variety of habitats (p < 0.02, r = 0.72). Relationships were strengthened when emotions were linked to perceptions of overall biodiversity (p < 0.001, r = 0.89). So, when participants thought the site was wildlife rich, they reported more positive emotions, even when actual avian biodiversity levels were not necessarily enhanced. The data strengthens the arguments that nature enhances well-being through positive affect, and that increased ‘engagement with nature’ may help support human health within urban environments. The results have strong implications for city planning with respect to the design, management and use of city green spaces

    Characterization of dust emission from alluvial sources using aircraft observations and high-resolution modeling

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    International audienceWe investigate mineral dust emission from alluvial sediments within the upland region in northern Mauritania in the vicinity of a decaying nocturnal low-level jet (LLJ). For the first time, the impact of valleys that are embedded in a rather homogeneous surrounding is investigated with regard to their role as dust source. Measures for local atmospheric dust burden were retrieved from airborne observations, satellite observations, and model simulations and analyzed in order to provide complementary information at different horizontal scales. Observations by the LEANDRE Nouvelle Generation backscatter lidar system flying aboard the French Falcon 20 aircraft were taken along five parallel flight legs perpendicular to the orientation of the main valley system dominating the topography of the study area. Results from a comparison of lidar-derived extinction coefficients with topography and aerial photographs confirm the relevance of (1) alluvial sediments at the valley bottoms as a dust source, and (2) the break-down of the nocturnal LLJ as a trigger for dust emission in this region. An evaluation of the AROME regional model, forecasting dust at high resolution (5 km grid), points toward an under-representation of alluvial dust sources in this region. This is also evident from simulations by the MesoNH research model. Although MesoNH simulations show higher dust loadings than AROME, which are more comparable to the observations, both models underestimate the dust concentrations within the boundary layer compared to lidar observations. A sensitivity study on the impact of horizontal grid spacing (5 km versus 1 km) highlights the importance of spatial resolution on simulated dust loadings
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