Analysis and modeling of magnetocaloric effect near magnetic phase transition temperature

International audienceMagnetocaloric behavior of gadolinium near room temperature can be correctly described by the Weiss molecular field theory especially in the paramagnetic state. In this paper, this approach is generalized for binary rare earth alloys which present as Gd a second order phase transition. The magnetic entropy variation can be calculated as a function of the temperature and the applied field. This model was tested on a laboratory synthesized samples of Gd-Tb. The agreement between calculations and experiments shows that this model can be easily used for these alloys in order to optimize their composition and adjust their Curie temperatures. For first order transition materials, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to the spontaneous crystal deformation and the structure transformation. A model based on the phenomenological approach of Bean Rodbell is developed to describe such a behavior. It highlights the link between the nature of magnetic transition and the magnetocaloric effect. It can be identified by only two parameters: T 0 the Curie temperature without deformation and η an order parameter which characterizes the transition nature. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by the new Mn 1-x (Ti 0.5 V 0.5) x As materials

A new method for air exchange efficiency assessment including natural and mixed mode ventilation

The COVID-19 health crisis highlighted the correlation between air exchange efficiency and virus airborne transmission. Air exchange efficiency is a performance index able to characterize ventilation effectiveness in buildings. Some standards, such as ASHRAE 129, clearly define assessment procedures of air exchange efficiency for mechanical ventilation, adopting tracer gas techniques. However, standardized procedures are based on measurements at the exhaust and cannot be adopted for natural and mixed mode ventilation strategies. In the ‘80s, Sandberg suggested that tracer gas decay technique enables to measure simultaneously the nominal time constant (through air change rate measurements) and the mean age of air in several points of the ventilated zone. This paper aims to present practical issues and uncertainty analysis related to the implementation of this approach, in a new commissioning protocol. For this purpose, we compare the new procedure, based on Sandberg's observation, with the ASHRAE 129 protocol for mechanical ventilation. Results coming from field campaigns show that the difference between air exchange efficiency values obtained using ASHRAE 129 protocol (51.8%) and the new procedure (47.4%) are usually negligible in low airflow rate, considering an average uncertainty of ± 7.0%. Results show that the procedure is robust and that it is technically possible to implement it to natural and mixed-mode ventilation

MECANISME DE LA REACTION 14N(3He, p)16O A E3He = 3 MeV

Les sections efficaces différentielles des réactions 14N(3He, p)16O ont été mesurées à E3He = 3 MeV. Les distributions angulaires de la plupart des groupes de protons de cette réaction montrent une allure caractéristique de processus d'interaction directe et ont été analysées en termes de la théorie élémentaire de l'onde plane en supposant la capture d'un deuton. La possibilité d'autres types de mécanisme direct de réaction (diagrammes rectangulaires) a été envisagée pour certains groupes.Differential cross-section measurements were made for the 14N(3He, p)16O reaction at a bombarding energy of 3 MeV. Angular distributions of some proton groups suggesting a direct process have been analysed with the PWBA theory assuming a deuteron capture. The possible manifestation of the four-point graphs is discussed

A magnetic field source system for magnetic refrigeration and its interaction with magnetocaloric material

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On the magnetocaloric effect in d-metal pnictides

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Bi-clustering continuous data with self-organizing map

International audienceIn this paper, we present a new SOM-based bi-clustering approach for continuous data. This approach is called Bi-SOM (for Bi-clustering based on Self-Organizing Map). The main goal of bi-clustering aims to simultaneously group the rows and columns of a given data matrix. In addition, we propose in this work to deal with some issues related to this task: (1) the topological visualization of bi-clusters with respect to their neighborhood relation, (2) the optimization of these bi-clusters in macro-blocks and (3) the dimensionality reduction by eliminating noise blocks, iteratively. Finally, experiments are given over several data sets for validating our approach in comparison with other bi-clustering methods