On Algorithms Based on Joint Estimation of Currents and Contrast in Microwave Tomography

This paper deals with improvements to the contrast source inversion method which is widely used in microwave tomography. First, the method is reviewed and weaknesses of both the criterion form and the optimization strategy are underlined. Then, two new algorithms are proposed. Both of them are based on the same criterion, similar but more robust than the one used in contrast source inversion. The first technique keeps the main characteristics of the contrast source inversion optimization scheme but is based on a better exploitation of the conjugate gradient algorithm. The second technique is based on a preconditioned conjugate gradient algorithm and performs simultaneous updates of sets of unknowns that are normally processed sequentially. Both techniques are shown to be more efficient than original contrast source inversion.Comment: 12 pages, 12 figures, 5 table

Breakthrough infections due to SARS-CoV-2 Delta variant: relation to humoral and cellular vaccine responses

IntroductionCOVID-19 vaccines are expected to provide effective protection. However, emerging strains can cause breakthrough infection in vaccinated individuals. The immune response of vaccinated individuals who have experienced breakthrough infection is still poorly understood.MethodsHere, we studied the humoral and cellular immune responses of fully vaccinated individuals who subsequently experienced breakthrough infection due to the Delta variant of SARS-CoV-2 and correlated them with the severity of the disease.ResultsIn this study, an effective humoral response alone was not sufficient to induce effective immune protection against severe breakthrough infection, which also required effective cell-mediated immunity to SARS-CoV-2. Patients who did not require oxygen had significantly higher specific (p=0.021) and nonspecific (p=0.004) cellular responses to SARS-CoV-2 at the onset of infection than those who progressed to a severe form.DiscussionKnowing both humoral and cellular immune response could allow to adapt preventive strategy, by better selecting patients who would benefit from additional vaccine boosters.Trial registration numbershttps://clinicaltrials.gov, identifier NCT04355351; https://clinicaltrials.gov, identifier NCT04429594

Can Trees and Forests Contribute to Environmental Noise Abatement?

Dans le présent article, nous abordons le contrôle du bruit des transports terrestres, et plus particulièrement celui issu des routes. Notre objectif est de déterminer, à partir des résultats de la littérature scientifique ainsi que de notre propre retour d’expérience, dans quels cas l’impact de la plantation d’arbres ou de bandes boisées est bénéfique sur la réduction du bruit environnemental, ceci pour quelle efficacité acoustique attendue et avec quelles bonnes pratiques. Nous commençons notre propos par un bref rappel réglementaire sur la gestion du bruit routier, et nous présentons une revue synthétique des principaux effets d’atténuation observés lors de la propagation sonore en présence d’arbres : effets de sol, de diffusion et de réfraction météorologique. Puis, nous envisageons certaines configurations paysagères typiques étudiées dans la littérature scientifique et nous donnons pour chacune d’elles l’impact acoustique attendu : bande de forêt le long d’une infrastructure routière, rangée d’arbres le long d’une protection antibruit et l’arbre dans la ville. Nous donnons finalement un ensemble de recommandations sur l’usage des arbres et des bandes de forêt comme élément pouvant améliorer l’environnement sonore extérieur. Nous conseillons notamment de planter des feuillus persistants ou un mélange de feuillus persistants et de conifères, avec une densité d’au moins 0,25 arbre/m2. Concernant le sol, nous recommandons de le cultiver avant les plantations d’arbres et d’y adjoindre de la matière organique décomposée. Nous déconseillons d’autre part de planter des arbres en partie haute d’un merlon antibruit.In this article, we focus on ground transportation noise abatement and more precisely road traffic noise control. From the literature as well as our own experience in this field we aim at determining which are the planting schemes for trees or forest strips that are most effective for environmental noise abatement, the expected noise attenuation and associated good practices. Beginning with a brief reminder of French regula-tions on road noise management, we then present a summary review of main attenuation processes obser-ved when sounds propagate through woodland areas: ground, diffusion and refraction effects. Then we consider some typical landscape configurations studied in the scientific literature, specifying their respective expected acoustic impact: a forest strip along a road infrastructure, a row of trees along noise barriers and trees in the city. Finally, a set of recommendations is provided for the correct use of trees and forest strips as elements that improve the outdoor sound environment. Our advice is to plant broadleaved evergreens or a mixture of broadleaved evergreens and conifers, at a minimum density of 0.25 tree/m2. We also advise culti-vating the ground before trees planting and distributing well-composted organic matter. On the other hand we advise against planting trees at the top of earth berms

Characterization and sampling of a deep and heterogeneous aquifer -An application to the Paleocene -Eocene aquifer in the Aquitaine basin, France

International audienceGroundwater sampling in boreholes has been carried out for decades according to well-established protocols and regulations. An important requirement in this context is the need to purge the borehole prior to any sampling action, the volume of the purge being adapted to the water flow and the regulatory context. Contaminated site investigations have introduced the concept of water column heterogeneity in the screened section of boreholes, which also occurs in some uncontaminated boreholes or in long-screened boreholes. Specific guidelines and practices were thus introduced, in particular the concept of discrete sampling. This type of sampling can be advantageously used in deep boreholes, provided that there is some renewal of water at the screens or the perforated intervals. The present study aims to take a step forward in the characterization of deep boreholes set up in the Aquitaine basin in France, by defining a protocol for relatively short boreholes (depth < 170 m) and applying it to much deeper boreholes, formerly drilled for oil and gas exploration (sampling up to 1035 m deep). Acquisitions were performed to better characterize water chemistry, including some isotope considerations. They were based on physico-chemical logging and endoscopic inspections where technically possible. After a review of the information provided by the investigations on the characterization of the Paleocene – Eocene aquifer in southwestern France, a methodology is proposed to make sampling in deep boreholes with low-yield more reliable, by combining the abstraction of a reduced water volume and the use of a downhole sampling system

Contrast source inversion method applied to relatively high contrast objects

International audienceThis paper presents a contrast source inversion method for microwave tomography with improved performance with respect to the popular multiplicative regularized contrast source inversion (MR-CSI) method when the contrast of the object under study is relatively high. More precisely, some shortcomings of MR-CSI which may prevent it from performing adequately on higher contrast objects are outlined. The proposed method does not suffer from such shortcomings, but necessitates the tuning of parameters. However, a unique set of parameters can be used in a wide variety of experimental conditions related to a given application. Simple guidelines to determine their values are provided

Fast solutions of the 2D inverse scattering problem based on a TSVD approximation of the internal field for the forward model

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A 3-TERM OPTIMIZATION CRITERION FOR FASTER INVERSION IN MICROWAVE TOMOGRAPHY

The problem of microwave tomography consists of finding the electrical characteristics (permittivity and conductivity) of a medium using scattered fields measured under various conditions of illumination. Such inversion can be achieved with a variety of techniques based upon the minimization of an appropriate criterion. The popular current source inversion (CSI) technique is one of those. In this paper, the CSI technique is presented and its main limitations are underlined. Then, in order to overcome these limitations, a generalized form of CSI is developed. An analysis of the time consuming operations of this new algorithm is done, and a new technique is proposed; it proves to be faster than the other two methods, the speed increase ranging between factors of 2 and 5. Performance of the algorithms is illustrated with examples based on synthetic data

Oxic and post-oxic chemical changes related to eogenesis and mesogenesis in a Miocene paleolake

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