2,146 research outputs found

    Numerical generation and study of synthetic bainitic microstructures

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    International audienceModels classically used to describe the probability of brittle fracture in nuclear power plants are written on the macroscopic scale. Its is not easy to surely capture the physical phenomena in such a type of approach, so that the application of the models far from their identification domain (temperature history, loading path) may become questionable. To improve the quality of the prediction of resistance and life time, microstructural information, describing the heterogeneous character of the material and its deformation mechanisms has to be taken into consideration. This paper is devoted to 16MND5 bainitic steel. Bainitic packets grow in former austenitic grains, and are not randomly oriented. Knowing the macroscopic stress is thus not sufficient to describe the stress-strain state in ferrite. An accurate model must take into account the actual microstructure, in order to provide realistic local stress and strain fields, to be used as inputs of a new class of cleavage models based on the local behavior. The paper shows the first two steps of the study: mesh generation and finite element computations using crystal plasticity

    An Enduring Platform for Public and Cooperative Economics Research: a Centennial Perspective

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    We introduce the special centennial issue of Annals of Public and Cooperative Economic

    Particle acoustic detection in gravitational wave aluminum resonant antennas

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    The results on cosmic rays detected by the gravitational antenna NAUTILUS have motivated an experiment (RAP) based on a suspended cylindrical bar, which is made of the same aluminum alloy as NAUTILUS and is exposed to a high energy electron beam. Mechanical vibrations originate from the local thermal expansion caused by warming up due to the energy lost by particles crossing the material. The aim of the experiment is to measure the amplitude of the fundamental longitudinal vibration at different temperatures. We report on the results obtained down to a temperature of about 4 K, which agree at the level of about 10% with the predictions of the model describing the underlying physical process.Comment: RAP experiment, 16 pages, 7 figure

    Evaluating humidity recovery efficiency of currently available heat and moisture exchangers: a respiratory system model study

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    OBJECTIVES: To evaluate and compare the efficiency of humidification in available heat and moisture exchanger models under conditions of varying tidal volume, respiratory rate, and flow rate. INTRODUCTION: Inspired gases are routinely preconditioned by heat and moisture exchangers to provide a heat and water content similar to that provided normally by the nose and upper airways. The absolute humidity of air retrieved from and returned to the ventilated patient is an important measurable outcome of the heat and moisture exchangers' humidifying performance. METHODS: Eight different heat and moisture exchangers were studied using a respiratory system analog. The system included a heated chamber (acrylic glass, maintained at 37°C), a preserved swine lung, a hygrometer, circuitry and a ventilator. Humidity and temperature levels were measured using eight distinct interposed heat and moisture exchangers given different tidal volumes, respiratory frequencies and flow-rate conditions. Recovery of absolute humidity (%RAH) was calculated for each setting. RESULTS: Increasing tidal volumes led to a reduction in %RAH for all heat and moisture exchangers while no significant effect was demonstrated in the context of varying respiratory rate or inspiratory flow. CONCLUSIONS: Our data indicate that heat and moisture exchangers are more efficient when used with low tidal volume ventilation. The roles of flow and respiratory rate were of lesser importance, suggesting that their adjustment has a less significant effect on the performance of heat and moisture exchangers

    Constrained caloric curves and phase transition for hot nuclei

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    Simulations based on experimental data obtained from multifragmenting quasi-fused nuclei produced in central 129^{129}Xe + nat^{nat}Sn collisions have been used to deduce event by event freeze-out properties in the thermal excitation energy range 4-12 AMeV [Nucl. Phys. A809 (2008) 111]. From these properties and the temperatures deduced from proton transverse momentum fluctuations, constrained caloric curves have been built. At constant average volumes caloric curves exhibit a monotonic behaviour whereas for constrained pressures a backbending is observed. Such results support the existence of a first order phase transition for hot nuclei.Comment: 14 pages, 5 figures, accepted in Physics Letters

    Etude des hétérogénéités des champs mécaniques dans un acier bainitique à l’aide de la diffraction des neutrons

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    Nous avons développé une méthodologie qui associe détermination de texture cristallographique et mesures de déformations élastiques par diffraction de neutrons afin d’analyser les contraintes dans des familles de grains de même orientation cristallographique au sein d’un matériau polycristallin. Nous présentons ici son application sur un acier bainitique constitutif des cuves des centrales nucléaires. Cette méthode semble être très prometteuse pour tester et valider les modèles de comportement mécanique
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