Cavitation hydrodynamique de nanofluides dans des microcanaux

La réalisation de micro diaphragmes et de micro Venturis dont la section de passage est de quelques dizaines de µm2 nous a permis d'obtenir des écoulements cavitants à des débits inférieurs au µl/h. Des liquides disponibles en quantité limitée peuvent ainsi être caractérisés. Nous avons étudié des nanofluides constitués de nanoparticules dispersées dans de l'eau DI. Les phénomènes de métastabilité de l'eau pure et de nucléation hétérogène causée par la phase dispersée ont été observés et analysés

Predicting Venous Thromboembolic Events in Patients with Coronavirus Disease 2019 Requiring Hospitalization: an Observational Retrospective Study by the COVIDIC Initiative in a Swiss University Hospital.

Coronavirus disease 2019 (COVID-19) can result in profound changes in blood coagulation. The aim of the study was to determine the incidence and predictors of venous thromboembolic events (VTE) among patients with COVID-19 requiring hospital admission. Subjects and Methods. We performed a retrospective study at the Lausanne University Hospital with patients admitted because of COVID-19 from February 28 to April 30, 2020. Among 443 patients with COVID-19, VTE was diagnosed in 41 patients (9.3%; 27 pulmonary embolisms, 12 deep vein thrombosis, one pulmonary embolism and deep vein thrombosis, one portal vein thrombosis). VTE was diagnosed already upon admission in 14 (34.1%) patients and 27 (65.9%) during hospital stay (18 in ICU and nine in wards outside the ICU). Multivariate analysis revealed D-dimer value > 3,120 ng/ml (P < 0.001; OR 15.8, 95% CI 4.7-52.9) and duration of 8 days or more from COVID-19 symptoms onset to presentation (P 0.020; OR 4.8, 95% CI 1.3-18.3) to be independently associated with VTE upon admission. D-dimer value ≥ 3,000 ng/l combined with a Wells score for PE ≥ 2 was highly specific (sensitivity 57.1%, specificity 91.6%) in detecting VTE upon admission. Development of VTE during hospitalization was independently associated with D-dimer value > 5,611 ng/ml (P < 0.001; OR 6.3, 95% CI 2.4-16.2) and mechanical ventilation (P < 0.001; OR 5.9, 95% CI 2.3-15.1). VTE seems to be a common COVID-19 complication upon admission and during hospitalization, especially in ICU. The combination of Wells ≥ 2 score and D - dimer ≥ 3,000 ng/l is a good predictor of VTE at admission

Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection

International audienceModern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technolog

Étude du transport tunnel dépendant du spin dans des jonctions tunnels magnétiques épitaxiées Fe/MgO/Fe bcc

Many possible applications have arisen in the domain of spin electronics since the prediction and experimental observation of high tunneling magneto-resistance (TMR) values in MgO-based tunnel junctions. These high TMR values are due to the crystallinity of the stack, which allows the electronic transport to be described by Bloch wave functions and gives a symmetry dependence of the spin filtering in the tunnel barrier. An original experimental set-up has been developed during this PhD that is able to measure the electronic properties of nano-objects under an applied magnetic field. It combines fast electronic acquisition cards and an atomic force microscope (AFM) equipped with a full metallic tip. This set-up is highly versatile and allows nano-objects to be electrically contacted without difficult nano-fabrication steps. This set-up has been used in order to study the influence of the interfaces on the electronic properties of the fully epitaxial magnetic tunnel junction Fe/MgO/Fe (100). Two interface resonant states (IRS) have been observed for the first time in this system at 0.2 eV and 1.1 eV above the Fermi energy of the minority spin electrons. These IRS drastically modify the tunnel transport and even reverse the dynamic TMR. The transport symmetry of the IRS has been found from a study of samples with different MgO thicknesses.La prédiction et l'observation de très forts taux de magnétorésistance tunnel (TMR) dans des jonctions tunnel magnétiques à base de MgO a ouvert de nouvelles perspectives d'applications dans le domaine de l'électronique de spin. Ces forts taux de TMR ne peuvent s'expliquer qu'en prenant en compte la structure cristalline des électrodes et le filtrage de la barrière tunnel dépendant des symétries. Un dispositif original de mesures de transport sous champ magnétique d'objets de taille nanométrique a été développé au cours de cette thèse. Il associe une électronique d'acquisition rapide et un Microscope à Force Atomique (AFM) muni d'une pointe métallique. Ce dispositif très versatile permet de contacter électriquement et d'étudier de différents types de nano-objets sans étapes compliquées de nanofabrication. Ce dispositif a été utilisé pour étudier l'influence des interfaces sur le transport dans des jonctions tunnel Fe/MgO/Fe (100) cristallines obtenues par épitaxie. Deux états résonants d'interface (IRS) ont été observés pour la première fois dans ce système à 0.2eV et 1.1eV au dessus du niveau de Fermi pour les électrons minoritaires. Ces IRS modifient fortement le transport tunnel et le dominent autour de 1V avec une inversion de la TMR dynamique. Une étude en fonction de l'épaisseur de MgO a permis de trouver la symétrie dominant le transport de ces IRS

Étude du transport tunnel dépendant du spin dans des jonctions tunnels magnétiques épitaxiées Fe/MgO/Fe bcc

Many possible applications have arisen in the domain of spin electronics since the prediction and experimental observation of high tunneling magneto-resistance (TMR) values in MgO-based tunnel junctions. These high TMR values are due to the crystallinity of the stack, which allows the electronic transport to be described by Bloch wave functions and gives a symmetry dependence of the spin filtering in the tunnel barrier. An original experimental set-up has been developed during this PhD that is able to measure the electronic properties of nano-objects under an applied magnetic field. It combines fast electronic acquisition cards and an atomic force microscope (AFM) equipped with a full metallic tip. This set-up is highly versatile and allows nano-objects to be electrically contacted without difficult nano-fabrication steps. This set-up has been used in order to study the influence of the interfaces on the electronic properties of the fully epitaxial magnetic tunnel junction Fe/MgO/Fe (100). Two interface resonant states (IRS) have been observed for the first time in this system at 0.2 eV and 1.1 eV above the Fermi energy of the minority spin electrons. These IRS drastically modify the tunnel transport and even reverse the dynamic TMR. The transport symmetry of the IRS has been found from a study of samples with different MgO thicknesses.La prédiction et l'observation de très forts taux de magnétorésistance tunnel (TMR) dans des jonctions tunnel magnétiques à base de MgO a ouvert de nouvelles perspectives d'applications dans le domaine de l'électronique de spin. Ces forts taux de TMR ne peuvent s'expliquer qu'en prenant en compte la structure cristalline des électrodes et le filtrage de la barrière tunnel dépendant des symétries. Un dispositif original de mesures de transport sous champ magnétique d'objets de taille nanométrique a été développé au cours de cette thèse. Il associe une électronique d'acquisition rapide et un Microscope à Force Atomique (AFM) muni d'une pointe métallique. Ce dispositif très versatile permet de contacter électriquement et d'étudier de différents types de nano-objets sans étapes compliquées de nanofabrication. Ce dispositif a été utilisé pour étudier l'influence des interfaces sur le transport dans des jonctions tunnel Fe/MgO/Fe (100) cristallines obtenues par épitaxie. Deux états résonants d'interface (IRS) ont été observés pour la première fois dans ce système à 0.2eV et 1.1eV au dessus du niveau de Fermi pour les électrons minoritaires. Ces IRS modifient fortement le transport tunnel et le dominent autour de 1V avec une inversion de la TMR dynamique. Une étude en fonction de l'épaisseur de MgO a permis de trouver la symétrie dominant le transport de ces IRS

Hydrodynamic cavitation in microsystems. I. Experiments with deionized water and nanofluids

International audienceAn experimental study of hydrodynamic cavitation downstream microdiaphragms and microventuris is presented. Deionized water and nanofluids have been characterized within silicon-Pyrex micromachined devices with hydraulic diameters ranging from 51 μm to 104 μm. The input pressure could reach up to 10 bars, and the flow rate was below 1 liter per hour. The output pressure of the devices was fixed at values ranging from 0.3 bar to 2 bars, so that it was possible to study the evolution of the cavitation number as a function of the Reynolds number in the orifice of the diaphragms or in the throat of the venturis. A delay on the onset of cavitation has been recorded for all the devices when they are fed with deionized water, because of the metastability of the liquid and because of the lack of roughness of the walls. For the first time, hydrodynamic cavitation of nanofluids (nanoparticles dispersed into the liquid) has been considered. The presence of nano-aggregates in the liquid does not exhibit any noticeable effect on the cavitation threshold through the venturis. However, such a presence has a strong influence on the cavitation onset in microdiaphragms: above a critical volume solid concentration of ≈10−5, the metastability is broken and the nanofluids behave as tap water filled up with large nuclei. These microdevices, where a low amount of fluid is required to reach cavitating flows, appear to be useful tools in order to study cavitating phenomena in localized area with specific fluids

Cavitation in microchannels

International audienc

Bias dependence of tunneling magnetoresistance in magnetic tunnel junctions with asymmetric barriers

Equipe 101 : Nanomagnétisme et électronique de spinInternational audienceThe transport properties of magnetic tunnel junctions (MTJs) are very sensitive to interface modifications. In this work we investigate both experimentally and theoretically the effect of asymmetric barrier modifications on the bias dependence of tunneling magnetoresistance (TMR) in single crystal Fe/MgO-based MTJs with (i) one crystalline and one rough interface, and (ii) with a monolayer of O deposited at the crystalline interface. In both cases we observe an asymmetric bias dependence of TMR and a reversal of its sign at large bias. We propose a general model to explain the bias dependence in these and similar systems reported earlier. The model predicts the existence of two distinct TMR regimes: (i) a tunneling regime when the interface is modified with layers of a different insulator, and (ii) a resonant regime when thin metallic layers are inserted at the interface. We demonstrate that in the tunneling regime, negative TMR is due to the high voltage which overcomes the exchange splitting in the electrodes, while the asymmetric bias dependence of TMR is due to the interface transmission probabilities. In the resonant regime, inversion of TMR could happen at zero voltage depending on the alignment of the resonance levels with the Fermi surfaces of the electrodes. Moreover, the model predicts a regime in which TMR has different signs at positive and negative bias, suggesting possibilities of combining memory with logic functions

High-resolution imaging of cells using metal clad waveguides (MCWG)

International audienc

High-resolution imaging of cells using metal clad waveguides (MCWG)

International audienc