Diamagnetism of doped two-leg ladders and probing the nature of their commensurate phases

We study the magnetic orbital effect of a doped two-leg ladder in the presence of a magnetic field component perpendicular to the ladder plane. Combining both low-energy approach (bosonization) and numerical simulations (density-matrix renormalization group) on the strong coupling limit (t-J model), a rich phase diagram is established as a function of hole doping and magnetic flux. Above a critical flux, the spin gap is destroyed and a Luttinger liquid phase is stabilized. Above a second critical flux, a reentrance of the spin gap at high magnetic flux is found. Interestingly, the phase transitions are associated with a change of sign of the orbital susceptibility. Focusing on the small magnetic field regime, the spin-gapped superconducting phase is robust but immediately acquires algebraic transverse (i.e. along rungs) current correlations which are commensurate with the 4k_F density correlations. In addition, we have computed the zero-field orbital susceptibility for a large range of doping and interactions ratio J/t : we found strong anomalies at low J/t only in the vicinity of the commensurate fillings corresponding to delta = 1/4 and 1/2. Furthermore, the behavior of the orbital susceptibility reveals that the nature of these insulating phases is different: while for delta = 1/4 a 4k_F charge density wave is confirmed, the delta = 1/2 phase is shown to be a bond order wave.Comment: 15 pages, 17 figure

Double formation de voies pour l'estimation de temps de trajet en contexte fortement bruité

La tomographie acoustique océanique a pour objectif l'estimation des variations de la vitesse des ondes dans l'océan à partir des temps de trajet de ces ondes. L'identification des différentes ondes est rarement possible sur le signal enregistré entre une source et un capteur dans des configurations réelles : mélange des ondes, faible rapport signal sur bruit. Cependant, en tenant compte de la structure multidimensionnelle de l'acquisition, des alternatives existent. Dans ce papier, nous proposons une nouvelle méthode : la double formation de voies (en émission et en réception) permettant d'extraire les ondes se propageant dans le milieu océanique et nous étudions sa robustesse face au bruit sur des données simulées

Localisation de source par filtrage modal : Application à des données petites échelles en ASM

- Dans les environnements océaniques peu profonds, la propagation peut être modélisée, à grande distance, par une somme de modes. En utilisant les coefficients d'excitation de ces modes, le filtrage modal permet de localiser une source acoustique située dans le guide d'ondes océanique. Un méthode permettant l'extraction de ces coefficients à partir d'un réseau horizontal de capteurs a été développée [6]. Celle-ci est appliquée sur un ensemble de données "petites échelles" réalisées en cuve et reproduisant un guide d'ondes océanique. Ses performances sont étudiées et une amélioration est proposée

Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4

We have studied the onset temperature of the superconductivity Tc_onset of the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction of the magnetic field H. We compare the results of two samples with nearly the same onset temperature but with different scattering relaxation time tau. We revealed a complicated interplay of a variety of pair-breaking effects and mechanisms that overcome these pair-breaking effects. In low fields, the linear temperature dependences of the onset curves in the H-T phase diagrams are governed by the orbital pair-breaking effect. The dips in the in-plane field-angle phi dependence of Tc_onset, which were only observed in the long-tau sample, provides definitive evidence that the field-induced dimensional crossover enhances the superconductivity if the field direction is more than about 19-degrees away from the a axis. In the high-field regime for H//a, the upturn of the onset curve for the long-tau sample indicates a new superconducting state that overcomes the Pauli pair-breaking effect but is easily suppressed by impurity scatterings. The Pauli effect is also overcome for H//b' by a realization of another state for which the maximum of Tc_onset(phi) occurs in a direction different from the crystalline axes. The effect on Tc_onset of tilting the applied field out of the conductive plane suggests that the Pauli effect plays a significant role in determining Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4 is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77, 2008

Pairing competition in a quasi-one-dimensional model of organic superconductors (TMTSF)2X_{2}X in magnetic field

We microscopically study the effect of the magnetic field (Zeeman splitting) on the superconducting state in a model for quasi-one-dimensional organic superconductors (TMTSF)$_{2}X$. We investigate the competition between spin singlet and spin triplet pairings and the Fulde-Ferrell-Larkin-Ovchinnikov(FFLO) state by random phase approximation. While we studied the competition by comparison with the eigenvalue of the gap equation at a fixed temperature in our previous study (Phys. Rev. Lett. \textbf{102} (2009) 016403), here we obtain both the $T_c$ for each pairing state and a phase diagram in the $T$(temperature)-$h_z$(field)-$V_y$(strength of the charge fluctuation) space. The phase diagram shows that consecutive transitions from singlet pairing to the FFLO state and further to $S_z=1$ triplet pairing can occur upon increasing the magnetic field when $2k_{F}$ charge fluctuations coexist with $2k_{F}$ spin fluctuations. In the FFLO state, the singlet d-wave and $S_{z}=0$ triplet $f$-wave components are strongly mixed especially when the charge fluctuations are strong.Comment: 11 pages, 9 figure

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Multi-objective Dynamic Optimization of Crops Irrigated with Reused Treated Wastewater

International audienc

Séparation d'ondes par double formation de voies : Application à la campagne FAF03 de tomographie acoustique océanique

En tomographie acoustique, la formation de voies est souvent appliquée sur des données obtenus sur une antenne de récepteurs, dans le but de mieux identifier les arrivées des différents rayons et de pouvoir mesurer ensuite leurs temps de propagation. Dans ce papier, nous proposons une nouvelle méthode pour des données obtenues à partir d'une antenne d'émetteurs et une antenne de récepteurs: la double formation de voies (en émission et en réception). Nous analysons son utilité sur des données réelles obtenues dans un chenal acoustique sous-marin

Imaging visceral adhesion to polymeric mesh using pneumoperitoneal-MRI in an experimental rat model

International audienceBackground: Intraperitoneal mesh implantation is often associated with formation of adhesion to the mesh. This experimental study examines the potential of minimally invasive pneumoperitoneal-MRI to assess these adhesions in a preclinical context. Methods: Uncoated polyethylene terephthalate meshes were placed intraperitoneally in rats, in regard to the caecum previously scraped to promote petechial bleeding and subsequent adhesions. Examinations were performed 2-weeks post mesh implantation using a rodent dedicated high field MRI. Respiratory-triggered T2 weighted images were acquired prior to and after intraperitoneal injection of ~8-10mL gas to induce a mechanical stress on the abdominal wall. Results Adhesions are occasionally seen in sham operated rats as opposed to rats receiving polyethylene terephthalate meshes. On high-resolution images, meshes can be detected due to their characteristic net-shape. Angers.. However, evidence of adherence is only found if intraperitoneal gas injection is performed, when a ~1-cm elevation of the abdominal wall is observed. When adherence occurs between the mesh and the caecum, the latter remains in contact with the wall. Looser adherences between visceral tissue and meshes are also observed. Conclusions T2-weighted pneumoperitoneal-MR imaging is a powerful tool for assessing adherence after intraperitoneal mesh implantation. According to the mini-invasive procedure adopted here, this approach may allow a temporal follow-up of adherence fate