Raphaël Weil

Magnetic domain walls displacement: Automotion versus spin-transfer torque

From the magnetization dynamics equation, a domain wall that changes structure is predicted to undergo a displacement by itself, a phenomenon called automotion. We experimentally demonstrate this effect in soft nanostrips, by transforming under spin-transfer torque a metastable asymmetric transverse wall into a vortex wall. Displacements more than three times larger than under spin-transfer torque only are measured for 1 ns pulses. The results are explained by analytical and numerical micromagnetics. Their relevance to domain-wall motion under spin-transfer torque is emphasized.

Mechanical tuning of adhesion through micro-patterning of elastic surfaces

We present an investigation of the role of micropatterning on adhesion properties at soft deformable polydimethylsiloxane (PDMS)/acrylic adhesive interfaces. Contrary to what has been observed for low aspect ratio rigid patterns, where the adhesion enhancement was found to only result from the increase of the interfacial area due to patterning, we show that for soft elastic arrays of cylindrical pillars, the elastic deformation of the patterns can lead to a noticeable extra adhesion increase. The effect of the geometrical characteristics of the patterning for hexagonal arrays of PDMS micropillars on the adhesion energy is presented. We show that varying the size of the pattern allows one to tune the adhesion energy, and that this adhesion enhancement saturates when the pillars become too close to each other, due a coupling of the elastic deformation fields inside the underlying substrate. A mechanical model has been developed and found in good quantitative agreement with experimental data, with a unique fitting parameter, the rupture criteria for the adhesive on the top of the pillars. Such a rupture criterion can thus be extracted from systematic experiments on controlled patterned surfaces. This criterion remains sensitive to the chemistry of the surfaces.

Diversité chimique des calculs prostatiques : une investigation par MEB et spectroscopie infrarouge

OBJECTIVE Revisiting the chemical diversity of the crystalline phases of prostatic calculi by means of SEM and FT-IR analysis. METHODS A set of 32 prostatic calculi has been studied by FT-IR and SEM. RESULTS FT-IR analysis has determined the chemical composition of each prostatic calculus and the SEM observation has described the morphology of the calculi surfaces and layers. Infrared analysis revealed that 90.7% of the stones were mainly composed of calcium phosphates. However, several mineral phases previously not reported in prostatic calculi were observed, as brushite or octocalcium phosphate pentahydrate. CONCLUSION Prostatic calculi exhibited a diversity of crystalline composition and morphology. As previously reported for urinary calculi, relationships between composition and morphology of prostatic stones and étiopathogenic conditions could be of interest in clinical practice.

FAM20A Gene Mutation: Amelogenesis or Ectopic Mineralization?

Background and objective: FAM20A gene mutations result in enamel renal syndrome (ERS) associated with amelogenesis imperfecta (AI), nephrocalcinosis, gingival fibromatosis, and impaired tooth eruption. FAM20A would control the phosphorylation of enamel peptides and thus enamel mineralization. Here, we characterized the structure and chemical composition of unerupted tooth enamel from ERS patients and healthy subjects. Methods: Tooth sections were analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and X-Ray Fluorescence (XRF). Results: SEM revealed that prisms were restricted to the inner-most enamel zones. The bulk of the mineralized matter covering the crown was formed by layers with varying electron-densities organized into lamellae and micronodules. Tissue porosity progressively increased at the periphery, ending with loose and unfused nanonodules also observed in the adjoining soft tissues. Thus, the enamel layer covering the dentin in all ERS patients (except a limited layer of enamel at the dentino-enamel junction) displayed an ultrastructural globular pattern similar to one observed in ectopic mineralization of soft tissue, notably in the gingiva of Fam20a knockout mice. XRD analysis confirmed the existence of alterations in crystallinity and composition (vs. sound enamel). XRF identified lower levels of calcium and phosphorus in ERS enamel. Finally, EDS confirmed the reduced amount of calcium in ERS enamel, which appeared similar to dentin. Conclusion: This study suggests that, after an initial normal start to amelogenesis, the bulk of the tissue covering coronal dentin would be formed by different mechanisms based on nano- to micro-nodule aggregation. This evocated ectopic mineralization process is known to intervene in several soft tissues in FAM20A gene mutant.

Efficient spin-to-charge conversion in the 2D electron liquid at the LAO/STO interface

Spin-to-charge conversion using the inverse Rashba-Edelstein effect is measured in the 2D electron liquid existing at the interface between LaAlO3 and SrTiO3. The effect is found to be larger than in the highly Rashba split Bi/Ag interface which we attribute to an amplifying effect due to a long carriers momentum lifetime. The explanation is supported by temperature measurements and the Rashba field is also shown to be anisotropic in the interface plane.

Crystalline Ultrastructures, Inflammatory Elements, and Neoangiogenesis Are Present in Inconspicuous Aortic Valve Tissue

Morbidity from calcific aortic valve disease (CAVD) is increasing. Recent studies suggest early reversible changes involving inflammation and neoangiogenesis. We hypothesized that microcalcifications, chemokines, and growth factors are present in unaffected regions of calcific aortic valves. We studied aortic valves from 4 patients with CAVD and from 1 control, using immunohistochemistry, scanning electron microscopy, and infrared spectrography. We revealed clusters of capillary neovessels in calcified (ECC), to a lesser extent in noncalcified (ECN) areas. Endothelial cells proved constant expression of SDF-1 in ECC, ECN, and endothelial cells from valvular surface (ECS). Its receptor CXCR4 was expressed in ECC. IL-6 expression correlated with CXCR4 staining and presence of lymphocytes. VEGF was expressed by ECS, its receptor by ECC and ECN. Crystalline ultrastructures were found on the surface of histologically noncalcified areas (HNCAs), spectrography revealed calcium hydroxylapatite. Our results demonstrate that crystalline ultrastructures are present in HNCAs, undergoing neoangiogenesis in an inflammatory context. These alterations could be an early witness of disease and an opening to therapy.

Cassie-Wenzel–like transition in patterned soft elastomer adhesive contacts

In this paper, we presented an experimental and theoretical analysis of the formation of the contact between a smooth elastomer lens and an elastomer substrate micropatterned with hexagonal arrays of cylindrical pillars. We show using a JKR model coupled with a full description of the deformation of the substrate between the pillars that the transition between the top to the full contact is obtain when the normal load is increased above a well predicted threshold. We have also shown that above the onset of full contact, the evolution of the area of full contact was obeying a simple scaling.We present an experimental and theoretical analysis of the transition from top to mixed top and full contacts between a smooth elastomer sphere and an elastomer substrate micropatterned with hexagonal arrays of cylindrical pillars. We show that surprisingly the overall behavior of the apparent radius of contact vs. the applied load obeys JKR contact mechanics, whatever the nature of the contact (top or mixed). This allows us to propose a mechanical description predicting quantitatively the evolution of the critical load for the onset of full contact with the pattern geometry and qualitatively that of the area of full contact above this threshold. We emphasize the role of the mechanical coupling between the pillars induced by the deformation of the substrate for large enough densities of pillars.

Self-hybridization within non-Hermitian localized plasmonic systems

The orthogonal eigenmodes are well-defined solutions of Hermitian equations describing many physical situations from quantum mechanics to acoustics. However, a large variety of non-Hermitian problems, including gravitational waves close to black holes or leaky electromagnetic cavities, require the use of a bi-orthogonal eigenbasis with consequences challenging our physical understanding1–4. The need to compensate for energy losses made the few successful attempts5–8 to experimentally probe non-Hermiticity extremely complicated. We overcome this problem by considering localized plasmonic systems. As the non-Hermiticity in these systems does not stem from temporal invariance breaking but from spatial symmetry breaking, its consequences can be observed more easily. We report on the theoretical and experimental evidence for non-Hermiticity-induced strong coupling between surface plasmon modes of different orders within silver nanodaggers. The symmetry conditions for triggering this counter-intuitive self-hybridization phenomenon are provided. Similar observable effects are expected to exist in any system exhibiting bi-orthogonal eigenmodes.A combined theoretical and experimental study of plasmonic nanostructures reveals a self-hybridization effect that arises from the non-Hermitian eigenmodes of localized surface plasmons.

Bi-orthogonality allows observation of self-hybridization in plasmonic system

Surface plasmons resonances occur when a metallic nano-particle is excited by an external electric field. Within the quasi-static limit, Ouyang and Isaacson [1] have shown that the plasmon modes are the solutions of an eigenvalue problem. This boundary element method (BEM) [2] has been extensively used to compute nano-particle plasmon resonances [3,4]. Depending on the geometry of the particle, the solutions of this eigenproblem can form a bi-orthogonal basis in which left and right eigenvectors are different. Apart from bringing additional mathematical difficulties, this particularity of the plasmonic eigenproblem has always been considered as a mere computation detail [6].