An artificial dielectric slab for ultra high-field MRI: proof of concept

High-permittivity dielectric pads, i.e., thin, flexible slabs, usually consisting of mixed ceramic powders and liquids, have been previously shown to increase the magnetic field at high and ultra high-fields in regions of low efficiency of transmit coils, thus improving the homogeneity of images. However, their material parameters can change with time, and some materials they contain are bio incompatible. This article presents an alternative approach replacing ceramic mixtures with a low-cost and stable artificial dielectric slab. The latter comprises a stack of capacitive grids realized using multiple printed-circuit boards. Results in this article show that the proposed artificial dielectric structure can obtain the same increase in the local transmit radiofrequency magnetic field distribution in a head phantom at 7 T as the conventional dielectric pad. (C) 2020 The Authors. Published by Elsevier Inc.Radiolog

Effect of a Near Fault on the Seismic Response of a Base-Isolated Structure with a Soft Storey

This study focuses on the soft-storey behavior of RC structures with lead core rubber bearing (LRB) isolation systems under near and far-fault motions. Under near-fault ground motions, seismic isolation devices might perform poorly because of large isolator displacements caused by large velocity and displacement pulses associated with such strong motions. In this study, four different structural models have been designed to study the effect of soft-storey behavior under near-fault and far-fault motions. The seismic analysis for isolated reinforced concrete buildings is carried out using a nonlinear time history analysis method. Inter-story drifts, absolute acceleration, displacement, base shear forces, hysteretic loops and the distribution of plastic hinges are examined as a result of the analysis. These results show that the performance of a base isolated RC structure is more affected by increasing the height of a story under nearfault motion than under far-fault motion

Seismic vibration control using a novel inerto-elastic damper

The use of advanced structural control devices is an effective engineering solution to reduce earthquake induced damages to structures. Owing to rapid advancement in technology and persistent research efforts, a variety of control devices have been developed and successfully implemented. Quite recently, a new passive damper, called inerter has been introduced, which is capable of developing a fictive mass. This study presents a novel inerto-elastic damper, which combines the inerter devices with classical elastic springs, and demonstrates the effectiveness of these devices in achieving seismic response reduction. The inerto-elastic device employs the inerter and elastic spring in parallel to control the seismic structural response. The effectiveness of the inerto-elastic dampers has been demonstrated through the response of a multi-degree of freedom system subjected to seismic excitations. The results of the analysis show a significant reduction in the response of the structure with novel inerto-elastic damper, as compared to those of structures with normal elastic spring as well as no dampers. The response quantities of interest, considered for this study are top floor displacement, inter-storey drift and base shear. The study also underlines optimal parameters for the inerter fictive mass and the elastic spring stiffness on the basis of the results obtained

A metamaterial-inspired MR antenna independently tunable at two frequencies

International audienc

Optical properties of metamaterials: Influence of electric multipoles, magnetoelectric coupling, and spatial dispersion

International audienc

Hybridized eigenmodes of periodic wire arrays and their application in radiofrequency coils for preclinical MRI

International audienc

Zoledronic acid and interleukin-2 treatment improves immunocompetence in HIV-infected persons by activating Vγ9Vδ2 T cells

Objective: γδ T cells bearing the Vγ9Vδ2 T-cell receptor exert many antiviral effector functions in humans, including release of anti-HIV factors and direct cytotoxicity against virus-infected cells. Moreover, they are known to activate dendritic cells, improving antigen presentation function. After HIV infection, Vγ9Vδ2 T-cell number and reactivity are rapidly affected and they decrease upon disease progression. Bisphosphonate drugs such as zoledronic acid (Zol), used to treat bone diseases, have been shown to induce in vivo, in combination with interleukin-2, Vγ9Vδ2 T-cells' activation. The aim of this work was to verify whether the administration of Zol in combination with interleukin-2 in HIV-infected patients might improve Vγ9Vδ2 T-cell function, including immune adjuvancy mediated by 78-dendritic cell cross-talk. Design and methods: In HIV patients naive to antiretroviral therapy, we analyzed the effect of combined Zol and interleukin-2 treatment, in comparison to Zol alone, on Vγ9Vδ2 T-cell number, maturation and function, on dendritic cell activation and on HIV-specific CD8 T-cell response. Results: Zol and interleukin-2-combined treatment induced in-vivo Vγ9Vδ2 T-cell expansion and maturation. Paralleling Vγ9Vδ2 T-cell activation, increased dendritic cell maturation and HIV-specific CD8 T-cell responses were found. Conclusion: The specific modulation of Vγ9Vδ2 T-cell number and responsiveness after HIV infection may be at least transiently restored in vivo by Zol and interleukin-2 treatment. In this way, the immune effector mechanisms, secondary to Vγ9Vδ2 T-cell activation, were improved, suggesting a possible adjuvancy role of Zol and interleukin-2 treatment in restoring innate and specific competence in HIV-infected persons. © 2009 Wolters Kluwer Health