Effect of combining a DC bias current with an AC transport current on AC losses in a High Temperature Superconductor

Creating complex flux configurations by superposing a dc current or magnetic field onto the ac current in a type II superconducting tape should lead to a variety of peculiar behaviors. An example is the appearance of the Clem valley, a minimum in the ac losses as a function of the dc bias amplitude, which has been theoretically studied by LeBlanc et al., in the continuation of Clem's calculations. These situations have been investigated by applying a dc current to a silver-gold sheathed Bi-2223 tape at 77 K (critical current 29 A), in addition to the usual ac transport current. The ac losses were measured by the null calorimetric method to ensure that the total losses were being accounted for. These were recorded for different values of the ac and dc currents, leading to the observation of two different behaviors depending on the ac current. Our revelation of the Clem valley is, to our knowledge, the first experimental validation of this phenomenon in high temperature superconductors, and may provide a simple way of reducing the ac loss in industrial applications of these materials.Comment: 4 pages,4 figures - ASC 9

Short review on porous metal membranes—Fabrication, commercial products, and applications

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Porous metal membranes have recently received increasing attention, and significant progress has been made in their preparation and characterisation. This progress has stimulated research in their applications in a number of key industries including wastewater treatment, dairy processing, wineries, and biofuel purification. This review examines recent significant progress in porous metal membranes including novel fabrication concepts and applications that have been reported in open literature or obtained in our laboratories. The advantages and disadvantages of the different membrane fabrication methods were presented in light of improving the properties of current membrane materials for targeted applications. Sintering of particles is one of the main approaches that has been used for the fabrication of commercial porous metal membranes, and it has great advantages for the fabrication of hollow fibre metal membranes. However, sintering processes usually result in large pores (e.g., >1 µm). So far, porous metal membranes have been mainly used for the filtration of liquids to remove the solid particles. For porous metal membranes to be more widely used across a number of separation applications, particularly for water applications, further work needs to focus on the development of smaller pore (e.g., sub-micron) metal membranes and the significant reduction of capital and maintenance costs

Silver metal nano-matrixes as high efficiency and versatile catalytic reactors for environmental remediation

Nano-porous metallic matrixes (NMMs) offer superior surface to volume ratios as well as enhanced optical, photonic, and electronic properties to bulk metallic materials. Such behaviours are correlated to the nano-scale inter-grain metal domains that favour the presence of electronic vacancies. In this work, continuous 3D NMMs were synthesized for the first time through a simple diffusion-reduction process whereby the aerogel matrix was functionalized with (3-Mercaptopropyl)trimethoxysilane. The surface energy of the silica monolith templates was tuned to improve the homogeneity of the reduction process while thiol functionalization facilitated the formation of a high density of seeding points for metal ions to reduce. The diameter of NMMs was between 2 and 1000 nm, corresponding to a silver loading between 1.23 and 41.16 at.%. A rates of catalytic degradation kinetics of these NMMS which is three orders of magnitude higher than those of the non-functionalized silver-silica structures. Furthermore, the enhancement in mechanical stability at nanoscale which was evaluated by Atomic Force Microscopy force measurements, electronic density and chemical inertness was assessed and critically correlated to their catalytic potential. This strategy opens up new avenues for design of complex architectures of either single or multi-metal alloy NMMs with enhanced surface properties for various applications

Assessing the temporal stability of surface functional groups introduced by plasma treatments on the outer shells of carbon nanotubes

Plasma treatments are emerging as superior efficiency treatment for high surface to volume ratio materials to tune functional group densities and alter crystallinity due to their ability to interact with matter at the nanoscale. The purpose of this study is to assess for the first time the long term stability of surface functional groups introduced across the surface of carbon nanotube materials for a series of oxidative, reductive and neutral plasma treatment conditions. Both plasma duration dose matrix based exposures and time decay experiments, whereby the surface energy of the materials was evaluated periodically over a one-month period, were carried out. Although only few morphological changes across the graphitic planes of the carbon nanotubes were found under the uniform plasma treatment conditions, the time dependence of pertinent work functions, supported by Raman analysis, suggested that the density of polar groups decreased non-linearly over time prior to reaching saturation from 7 days post treatment. This work provides critical considerations on the understanding of the stability of functional groups introduced across high specific surface area nano-materials used for the design of nano-composites, adsorptive or separation systems, or sensing materials and where interfacial interactions are key to the final materials performance

Vincent Leglaive. Marcel Proust, tel qu’en son labyrinthe littéraire

L’exposition « Marcel Proust. La Fabrique de l’œuvre » présentée jusqu’au 22 janvier 2023 à la Bibliothèque Nationale de France est l’occasion de commémorer le centenaire de la mort de l’auteur de A La Recherche du Temps Perdu survenue le 18 novembre 1922, en offrant au visiteur une plongée sans précédent au cœur même de la production du roman. Ainsi, à travers d’un nombre impressionnant de manuscrits, d’épreuves de correction, d’éditions originales, mais aussi d’œuvres d’art, d’objets précie..

Étude des pertes CA dans un ruban supraconducteur à haute température critique à l'aide de la méthode calorimétrique par annulation

Ce mémoire est consacré aux pertes alternatives dans les supraconducteurs à haute température critique. Ces pertes sont provoquées par le mouvement des tubes de flux au sein d'un supraconducteur provoquées par la partie alternative du courant de transport qui le parcourt. Dans un premier temps nous présenterons quelques aspects théoriques reliés aux mécanismes à l'origine des pertes dans les supraconducteurs à haute température critique. Ensuite, à l'aide du modèle de l'état critique nous verrons en détail comment simuler les pertes hystérétiques: le mode de fonctionnement de notre programme de simulation, utilisé par la suite, sera exposé. Nous présenterons les mesures réalisées grâce à la méthode calorimétrique par annulation utilisée avec un échantillon monofilamentaire réalisé suivant la technique de la poudre en tube. L'étude portera essentiellement sur la variation des pertes à courant alternatif fixé et à courant continu variable. L'étude des pertes en fonction de la fréquence sera également abordée ainsi que la granularité de l'échantillon. Le bon accord entre expériences et simulations nous permettra de mieux comprendre le phénomène des pertes hystérétiques ce qui nous amènera à nous interroger sur le courant d'écrantage Meissner. Ceci nous permettra alors de définir une grandeur caractéristique, similaire à ce dernier dans ses effets mais pas dans ses causes, reliée d'une part à la barrière de surface entre les grains et le matériau intergrain et, d'autre part, au courant critique du matériau intergrain