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SourceAvailable from: Jacques Huot[Show abstract] [Hide abstract]
ABSTRACT: In this paper we report the role of morphology and severe plastic deformation on the hydrogen storage properties of magnesium. Samples were prepared in air at room temperature by accumulative roll-bonding, filing and a combination of both processes. Accumulative roll-bonding drastically refined the microstructure of magnesium but resulted in a limited hydrogen capacity. Filing accelerated the activation of magnesium without compromising hydrogen capacity. Combining both techniques enhanced or worsened the hydrogen storage properties depending on the processing sequence. These results are explained in terms of microstructure and morphology of the samples.International Journal of Hydrogen Energy 08/2014; 39(24):12778–12783. DOI:10.1016/j.ijhydene.2014.06.042
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ABSTRACT: The selection of a copula that appropriately describes the dependence structure of a bivariate distribution function is an issue of a prime interest in multivariate statistical analysis. The most popular methods of testing are those based on the empirical copula and on Kendall’s process; these tests require the use of the parametric bootstrap, which is computationally heavy. This paper introduces the concept of CC-power functions associated to bivariate copulas. In a first step, their theoretical properties are explored and computations for many popular dependence models are provided. Then, empirical counterparts of these functions are proposed and the weak convergence of suitably normalized versions are obtained from an application of the functional delta method. In addition, a multiplier bootstrap method for these CC-power processes is described and validated. While of an independent interest to treat many hypotheses related to copulas, these newly introduced tools are used to develop a goodness-of-fit test for bivariate multi-parameter copula models. The recursive nature of the CC-power functions induces easily computable formulas for the test statistics and suggests a sequential method of testing. The sample properties of this goodness-of-fit test are investigated and compared to those of competing procedures, and its usefulness is illustrated on some pairs of the multivariate Uranium exploration data set.Journal of Multivariate Analysis 08/2014; 129. DOI:10.1016/j.jmva.2014.03.018
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ABSTRACT: We present a study of the effects of para–ortho conversion on performance of an adsorption-based hydrogen storage system using finite element methods implemented in COMSOL Multiphysics 4.3a platform. The base model which does not take into account the para–ortho conversion is validated using the experimental data of Maxsorb activated carbon measured with a test bench at room and cryogenic temperatures. The validated model is subsequently applied to simulate the storage system filled with MOF-5 and then extended to investigate the effects of endothermic para–ortho conversion of hydrogen isomers on storage and thermal performances during hydrogen charging/discharging cycle for four inlet temperatures, 35, 50, 77 and 100 K. Our results show that the endothermic conversion reduces the system temperature and increases the net storage capacity. The temperature changes due to the different heat sources are used to investigate the effect of conversion on the temperature reduction. The adsorbed and gas phase masses in the storage system with and without conversion at the end of the charging time are used to determine the effect of conversion on the storage system capacity. Even though the conversion is more significant at low temperature (35 K), the gains are larger at high temperature (100 K).International Journal of Hydrogen Energy 07/2014; 39(22):11651–11660. DOI:10.1016/j.ijhydene.2014.05.101
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