3,063 research outputs found

    The analysis of thermal stress involving non-linear material behaviour

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    Transport processes of particles in dilute suspensions in turbulent water flow—phase II

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    This work was concerned with an improved and more practical understanding of particle motion in a turbulent fluid field. It is felt that such an increased understanding has been achieved both in an analytical and in an experimental sense. Analytically, a theory simplified by the restrictive constraints of isotropy and Stokesian drag has been developed. Assumption of a reasonable particle energy spectrum allowed calculation of various statistical quantities important in the determination of the particle's turbulent motion. By such an analysis three characterizing parameters were found. Two describe inertial effects due to the particle's size and density. They were found to be of prime importance in the determination of the ratio of the particle's fluctuating velocity variance to that of the fluid. The crossing of the particle from one region of correlated fluid turbulence to another by virtue of its free fall velocity is described by the third parameters. This parameter was shown to be of particular importance in limiting the particle's velocity correlation. The two effects, of inertia and of free fall velocity, together act to determine dispersion. A well parameterized particle experiment was undertaken. Analysis of the particles' behavior in the turbulent flow gave a three dimensional characterization of their motion. In particular calculation of velocity variances, autocorrelations, and energy spectra were made. These measurements in conjunction with measurements on the turbulent fluid field allowed comparison between theory and experiment. Comparison of theoretical prediction to experimental observation showed good agreement provided the underlying assumptions inherent in the theoretical derivation were valid. Agreement suffered when these assumptions proved less valid. In particular non-Stokesian drag and anisotropic effects caused. disagreement between theory and experiment.U.S. Department of the InteriorU.S. Geological SurveyOpe

    Three dimensional optical imaging of blood volume and oxygenation in the neonatal brain

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    Optical methods provide a means of monitoring cerebral oxygenation in newborn infants at risk of brain injury. A 32-channel optical imaging system has been developed with the aim of reconstructing three-dimensional images of regional blood volume and oxygenation. Full image data sets were acquired from 14 out of 24 infants studied; successful images have been reconstructed in 8 of these infants. Regional variations in cerebral blood volume and tissue oxygen saturation are present in healthy preterm infants. In an infant with a large unilateral intraventricular haemorrhage, a corresponding region of low oxygen saturation was detected. These results suggest that optical tomography may provide an appropriate technique for investigating regional cerebral haemodynamics and oxygenation at the cotside. (c) 2006 Elsevier Inc. All rights reserved

    A flexible framework for assessing the quality of crowdsourced data

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    Ponencias, comunicaciones y pĂłsters presentados en el 17th AGILE Conference on Geographic Information Science "Connecting a Digital Europe through Location and Place", celebrado en la Universitat Jaume I del 3 al 6 de junio de 2014.Crowdsourcing as a means of data collection has produced previously unavailable data assets and enriched existing ones, but its quality can be highly variable. This presents several challenges to potential end users that are concerned with the validation and quality assurance of the data collected. Being able to quantify the uncertainty, define and measure the different quality elements associated with crowdsourced data, and introduce means for dynamically assessing and improving it is the focus of this paper. We argue that the required quality assurance and quality control is dependent on the studied domain, the style of crowdsourcing and the goals of the study. We describe a framework for qualifying geolocated data collected from non-authoritative sources that enables assessment for specific case studies by creating a workflow supported by an ontological description of a range of choices. The top levels of this ontology describe seven pillars of quality checks and assessments that present a range of techniques to qualify, improve or reject data. Our generic operational framework allows for extension of this ontology to specific applied domains. This will facilitate quality assurance in real-time or for post-processing to validate data and produce quality metadata. It enables a system that dynamically optimises the usability value of the data captured. A case study illustrates this framework

    Gelatine backing affects the performance of single-layer ballistic-resistant materials against blast fragments

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    Penetrating trauma by energized fragments is the most common injury from explosive devices, the main threat in the contemporary battlefield. Such devices produce projectiles dependent upon their design, including preformed fragments, casings, glass, or stones; these are subsequently energized to high velocities and cause serious injuries to the body. Current body armor focuses on the essential coverage, which is mainly the thoracic and abdominal area, and can be heavy and cumbersome. In addition, there may be coverage gaps that can benefit from the additional protection provided by one or more layers of lightweight ballistic fabrics. This study assessed the performance of single layers of commercially available ballistic protective fabrics such as Kevlar®, Twaron®, and Dyneema®, in both woven and knitted configurations. Experiments were carried out using a custom-built gas-gun system, with a 0.78-g cylindrical steel fragment simulating projectile (FSP) as the impactor, and ballistic gelatine as the backing material. FSP velocity at 50% risk of material perforation, gelatine penetration, and high-risk wounding to soft tissue, as well as the depth of penetration (DoP) against impact velocity and the normalized energy absorption were used as metrics to rank the performance of the materials tested. Additional tests were performed to investigate the effect of not including a soft-tissue simulant backing material on the performance of the fabrics. The results show that a thin layer of ballistic material may offer meaningful protection against the penetration of this FSP. Additionally, it is essential to ensure a biofidelic boundary condition as the protective efficacy of fabrics was markedly altered by a gelatine backing
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