93 research outputs found

    Hardening and Softening in Magnesium Alloys

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    Magnesium Alloys Based Composites

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    Metal matrix composites (MMCs) based on magnesium alloys are excellent candidates for engineering light structure materials, and have great potential in automotive, high performance defence and aerospace applications. In spite of relatively high number of papers dealing with microstructure and mechanical properties of MMCs based on Mg alloys, the deformation mechanisms and other physical properties of these materials are not known enough.The objective of this chapter is to reveal influence of various reinforcement types on the mechanical and physical behaviour of composites in which various magnesium alloys were reinforced with short alumina (Saffil®) fibres and/or SiC and Si particles.JRC.F.4-Safety of future nuclear reactor

    Superplastic Behaviour of an Mg-Ag-RE Magnesium Alloy

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    Fine-grained magnesium alloy QE22 (Mg-2.5wt.%Ag-2.5wt.%RE-0.6wt.%Zr) was prepared from cast ingot which was submitted to a two stages heat treatment. Subsequently the billet was overaged and extruded at high temperature. Samples were deformed at elevated temperatures from 380 °C up to 480 °C at various strain rates. Microstructure of deformed samples was studied using light and electron microscopy. Conditions for superplasticity of the investigated alloys have been estimated. Possible deformation mechanisms are discussed.JRC.F.4-Innovative Technologies for Nuclear Reactor Safet

    Data-Driven Motion Pattern Segmentation in a Crowded Environments

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    International audienceMotion is a strong clue for unsupervised grouping of individuals in a crowded environment. We show that collective motion in the crowd can be discovered by temporal analysis of points trajectories. First k-NN graph is constructed to represent the topological structure of point trajectories detected in crowd. Then the data-driven graph seg-mentation helps to reveal the interaction of individuals even when mixed motion is presented in data. The method was evaluated against the latest state-of-the-art methods and achieved better performance by more than 20 percent

    Effect of Short Saffil Fibres and SIC Particles on Mechanical Properties of Magnesium Alloys

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    The high temperature mechanical behaviour of composites with the AZ91 and AS21 magnesium alloys matrix, reinforced with short Saffil fibres and SiC particles were investigated. Samples were deformed in compression in the temperature range from room temperature to 300 °C. The yield stress and the maximum stress of true stress-true strain curves decrease with increasing temperature. Light and electron microscopy were used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The increased dislocation density and the shear stress at reinforcing phase/matrix interfaces were found as the most important contributions to the strengthening

    Multi-Object Tracking of Pedestrian Driven by Context

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    International audienceThe characteristics like density of objects, their contrast with respect to surrounding background, their occlu-sion level and many more describe the context of the scene. The variation of the context represents ambiguous task to be solved by tracker. In this paper we present a new long term tracking framework boosted by context around each track-let. The framework works by first learning the database of optimal tracker parameters for various context offline. During the testing, the context surrounding each tracklet is extracted and match against database to select best tracker parameters. The tracker parameters are tuned for each tracklet in the scene to highlight its discrimination with respect to surrounding context rather than tuning the parameters for whole scene. The proposed framework is trained on 9 public video sequences and tested on 3 unseen sets. It outperforms the state-of-art pedestrian trackers in scenarios of motion changes, appearance changes and occlusion of objects

    Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

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    Background: Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. // Methods: We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung's disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. // Findings: We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung's disease) from 264 hospitals (89 in high-income countries, 166 in middle-income countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in low-income countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. // Interpretation: Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between low-income, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

    Mechanical Properties and Strain Hardening Behaviour of Magnesium Alloys and Composites

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    Selected magnesium alloys and composites with magnesium alloy matrix were deformed at temperatures between room temperature and 300 °C at constant strain rate. The testing temperature influences significantly the deformation behaviour of the al/loys. The flow stress decreases with increasing temperature. The work hardening rate decreases with stress (strain) and temperature. Above about 200 °C, a dynamic balance between hardening and softening is observed. Stress relaxation tests were performed to identify thermally activated dislocation motion. The main thermally activated process is very probably the glide of dislocation in non-basal planes. The internal component of the applied stress decreases significantly with increasing temperature

    Enhanced Plasticity of a Mg-8Li Alloy Reinforced with SiC Particles

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    Mg-8Li alloy reinforced by 7 vol.% SiC particles was processed by a powder metallurgical method. Samples were deformed in tension at temperatures from room temperature up to 300 °C. The yield stress as well as the tensile strength decrease with increasing temperature. Decreasing stresses detected at temperatures higher than 150 °C indicate possible presence of recovery process/es. Estimated activation enthalpy is close to the activation enthalpy for the grain boundary sliding. Strain rate sensitivity was estimated at elevated temperatures. Enhanced plasticity was estimated at 300 °C. Light and scanning electron microscopy revealed the cavitations during the high temperature deformation.JRC.F.4-Safety of future nuclear reactor
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