Evaluation of proton density fat fraction (PDFF) obtained from a vendor-neutral MRI sequence and MRQuantif software.

OBJECTIVE: To validate the proton density fat fraction (PDFF) obtained by the MRQuantif software from 2D chemical shift encoded MR (CSE-MR) data in comparison with the histological steatosis data. METHODS: This study, pooling data from 3 prospective studies spread over time between January 2007 and July 2020, analyzed 445 patients who underwent 2D CSE-MR and liver biopsy. MR derived liver iron concentration (MR-LIC) and PDFF was calculated using the MRQuantif software. The histological standard steatosis score (SS) served as reference. In order to get a value more comparable to PDFF, histomorphometry fat fraction (HFF) were centrally determined for 281 patients. Spearman correlation and the Bland and Altman method were used for comparison. RESULTS: Strong correlations were found between PDFF and SS (rs = 0.84, p < 0.001) or HFF (rs = 0.87, p < 0.001). Spearman's coefficients increased to 0.88 (n = 324) and 0.94 (n = 202) when selecting only the patients without liver iron overload. The Bland and Altman analysis between PDFF and HFF found a mean bias of 5.4% ± 5.7 [95% CI 4.7, 6.1]. The mean bias was 4.7% ± 3.7 [95% CI 4.2, 5.3] and 7.1% ± 8.8 [95% CI 5.2, 9.0] for the patients without and with liver iron overload, respectively. CONCLUSION: The PDFF obtained by MRQuantif from a 2D CSE-MR sequence is highly correlated with the steatosis score and very close to the fat fraction estimated by histomorphometry. Liver iron overload reduced the performance of steatosis quantification and joint quantification is recommended. This device-independent method can be particularly useful for multicenter studies. CLINICAL RELEVANCE STATEMENT: The quantification of liver steatosis using a vendor-neutral 2D chemical-shift MR sequence, processed by MRQuantif, is well correlated to steatosis score and histomorphometric fat fraction obtained from biopsy, whatever the magnetic field and the MR device used. KEY POINTS: • The PDFF measured by MRQuantif from 2D CSE-MR sequence data is highly correlated to hepatic steatosis. • Steatosis quantification performance is reduced in case of significant hepatic iron overload. • This vendor-neutral method may allow consistent estimation of PDFF in multicenter studies.

Dissociation of GaN2+ and AlN2+ in APT: Electronic structure and stability in strong DC field.

We investigate from a theoretical point of view the stability of AlN2+ and GaN2+ dications produced under high static electric fields like those reached in Atom Probe Tomography (APT) experiments. By means of quantum chemical calculations of the electronic structure of these molecules, we show that their stability is governed by two independent processes. On the one hand, the spin-orbit coupling allows some molecular excited states to dissociate by inter-system crossing. On the other hand, the action of the electric field lowers the potential energy barrier, which ensures the dication stability in standard conditions. We present a detailed example of field emission dynamics in the specific case of the 11Δ states for a parabolic tip, which captures the essentials of the process by means of a simplified model. We show that the dissociation dynamics of AlN2+ and GaN2+ is completely different despite the strong resemblance of their electronic structure.

Dissociation of GaN2+ and AlN2+ in APT: Analysis of experimental measurements.

The use of a tip-shaped sample for the atom probe tomography technique offers the unique opportunity to analyze the dynamics of molecular ions in strong DC fields. We investigate here the stability of AlN2+ and GaN2+ dications emitted from an Al0.25Ga0.75N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN2+, while GaN2+ can only be observed as a transient species. We simulate the emission dynamics of these ions on field-perturbed potential energy surfaces obtained from quantum chemical calculations. We show that the dissociation is governed by two independent processes. For all bound states, a mechanical dissociation is induced by the distortion of the potential energy surface in the close vicinity of the emitting tip. In the specific case of GaN2+, the relatively small electric dipole of the dication in its ground 13Σ- and excited 11Δ states induces a weak coupling with the electric field so that the mechanical dissociation into Ga+ + N+ lasts for sufficient time to be observed. By contrast, the AlN2+ mechanical dissociation leads to Al2+ + N which cannot be observed as a correlated event. For some deeply bound singlet excited states, the spin-orbit coupling with lower energy triplet states gives another chance of dissociation by system inter-system crossing with specific patterns observed experimentally in a correlated time of flight map.

Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces.

The spin-orbit interaction couples the electrons' motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism-the Rashba effect-in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.

Role of a Neighbor Ion in the Fragmentation Dynamics of Covalent Molecules.

Fragmentation of molecular nitrogen dimers (N_{2})_{2} induced by collision with low energy 90 keV Ar^{9+} ions is studied to evidence the influence of a molecular environment on the fragmentation dynamics of N_{2} cations. Following the capture of three or four electrons from the dimer, the three-body N_{2}^{+}+N^{m+}+N^{n+} [with (m,n)=(1,1) or (1, 2)] fragmentation channels provide clean experimental cases where molecular fragmentation may occur in the presence of a neighbor molecular cation. The effect of the environment on the fragmentation dynamics within the dimer is investigated through the comparison of the kinetic energy release (KER) spectra for these three-body channels and for isolated N_{2}^{(m+n)+} monomer cations. The corresponding KER spectra exhibit energy shifts of the order of 10 eV, attributed to the deformation of the N^{m+}+N^{n+} potential energy curves in the presence of the neighboring N_{2}^{+} cation. The KER structures remain unchanged, indicating that the primary collision process is not significantly affected by the presence of a neighbor molecule.

Electronic structure and stability of the SiO2+ dications produced in tomographic atom probe experiments.

The molecular electronic states of the SiO2+ dication have been investigated in a joint theoretical and experimental analysis. The use of a tip-shaped sample for tomographic atom probe analysis offers the unique opportunity to produce and to analyze the lifetime of some excited states of this dication. The perturbation brought by the large electric field of the polarized tip along the ion trajectory is analyzed by means of molecular dynamics simulation. For the typical electric fields used in the experiment, the lowest energy triplet states spontaneously dissociate, while the lowest energy singlet states do not. We show that the emission process leads to the formation of some excited singlet state, which dissociates by means of spin-orbit coupling with lower-energy triplet states to produce specific patterns associated with Si+ + O+ and Si2+ + O dissociation channels. These patterns are recorded and observed experimentally in a correlated time-of-flight map.

Ultra-light extensometer for the assessment of the mechanical properties of the human skin in vivo.

BACKGROUND/PURPOSE: This paper aims to present an ultra-light extensometer device dedicated to the mechanical characterization of the human skin in vivo. METHODS: The device developed was conceived to be non-invasive, to work without any stand and to perform various uniaxial tensile tests with either effort or displacement control. We also use specific guarding tabs to make in vivo extension tests analogous to traction tests. RESULTS: Force-displacement curves are derived from the data provided by the device's sensors. The latter are converted into stress-strain curves thanks to complementary measurements of the skin thickness. We present typical experimental data and results that demonstrate the device ability to built stress-strain curves characteristic of the human skin behavior. An additional imaging unit records a sequence of images of the solicited skin area for further calculations of the displacement fields by digital image correlation. CONCLUSION: The analysis of the displacement and deformation fields validates the guarding tab efficiency and the capacity of the device to characterize the mechanical behavior of the human skin in vivo.

Intra- and inter-individual variability in the mechanical properties of the human skin from in vivo measurements on 20 volunteers.

BACKGROUND/PURPOSE: The mechanical properties and behavior of the human skin in vivo are of medical importance, particularly to surgeons who have to consider the skin extension capabilities in the preparation of surgical acts. Variable data can be found in literature that result from diverse kinds of tests (in vivo, ex vivo, and postmortem) performed with different instruments. METHODS: This paper presents the results of in vivo measurements performed on a cohort of 20 healthy volunteers with an ultralight homemade uniaxial extensometer. Different anatomical zones were explored under different directions of solicitation in order to document inter- and intra-individual variability as well as skin anisotropy. RESULTS: The experimental data obtained are fitted with a phenomenological exponential model allowing the identification of three parameters characteristic of the tested skin behavior. These parameters can be related to the concept of skin extensibility used by surgeons. CONCLUSION: The inter- and intra-variability observed on that cohort confirms the need for a patient-specific approach based on the in vivo measurement of the mechanical behavior of the human skin of interest. Even the direction of higher skin stiffness is found to be individual-dependent. The capability of the extensometer used in this study to fulfill such measurement needs is also demonstrated.

Electric-field control of magnetic order above room temperature.

Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.

Crafting the magnonic and spintronic response of BiFeO3 films by epitaxial strain.

Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property--antiferromagnetism--has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mössbauer and Raman spectroscopies combined with Landau-Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves.

Potential energy curves and spin-orbit coupling of light alkali-heavy rare gas molecules.

The potential energy curves of the X, A, and B states of alkali-rare gas diatomic molecules, MKr and MXe, are investigated for M = Li, Na, K. The molecular spin-orbit coefficients a(R)=<(2)Π(½)|H(SO)|(2)Π(½)> and b(R)=<(2)Π(-½)|H(SO)|(2)Σ(½)> are calculated as a function the interatomic distance R. We show that a(R) increases and b(R) decreases as R decreases. This effect becomes less and less important as the mass of the alkali increases. A comparison of the rovibrational properties deduced from our calculations with experimental measurements recorded for NaKr and NaXe shows the quality of the calculations.

Anisotropic mechanical characterization of human skin by in vivo multi-axial ring suction test.

Human skin is a soft tissue behaving as an anisotropic material. The anisotropy emerges from the alignment of collagen fibers in the dermis, which causes the skin to exhibit greater stiffness in a certain direction, known as Langer's line. The importance of determining this anisotropy axis lies in assisting surgeons in making incisions that do not produce undesirable scars. In this paper, we introduce an open-source numerical framework, MARSAC (Multi-Axial Ring Suction for Anisotropy Characterization: https://github.com/aflahelouneg/MARSAC), adapted to a commercial device CutiScan CS 100® that applies a suction load on an annular section, causing a multi-axial stretch in the central zone, where in-plane displacements are captured by a camera. The presented framework receives inputs from a video file and converts them into displacement fields through Digital Image Correlation (DIC) technique. From the latter and based on an analytical model, the method assesses the anisotropic material parameters of human skin: Langer's line ϕ, and the elastic moduli E1 and E2 along the principal axes, providing that the Poisson's ratio is fixed. The pipeline was applied to a public data repository, https://search-data.ubfc.fr/femto/FR-18008901306731-2021-08-25_In-vivo-skin-anisotropy-dataset-for-a-young-man.html, containing 30 test series performed on a forearm of a Caucasian subject. As a result, the identified parameter averages, ϕˆ=40.9±8.2∘ and the anisotropy ratio E1ˆ/E2ˆ=3.14±1.60, were in accordance with the literature. The intra-subject analysis showed a reliable assessment of ϕ and E2. As skin anisotropy varies from site to site and from subject to subject, the novelty of the method consists in (i) an optimal utilization of CutiScan CS 100® probe to measure the Langer's line accurately and rapidly on small areas with a minimum diameter of 14mm, (ii) validation of an analytical model based on deformation ellipticity.

Electronic subband reconfiguration in a d0-perovskite induced by strain-driven structural transformations.

It is well known that transport in lightly n-doped SrTiO(3) involves light and heavy electron bands. We have found that upon application of moderate quasi-isotropic pressures, the relative positions of these subbands are changed by a few meV and, eventually, a band inversion occurs at ~1 kbar. Such effects are, however, suppressed in the closely related KTaO(3) perovskite. We show that the extremely subtle electronic reconfiguration in SrTiO(3) is triggered by strain-induced structural transformations that are accompanied by remarkable mobility enhancements up to about Δµ/µ≈300%. Our results provide a microscopic rationale for the recently discovered transport enhancement under strain and underscore the role of the internal structural degrees of freedom in the modulation of the perovskite electronic properties.

Multiferroic phase transition near room temperature in BiFeO3 films.

In multiferroic BiFeO(3) thin films grown on highly mismatched LaAlO(3) substrates, we reveal the coexistence of two differently distorted polymorphs that leads to striking features in the temperature dependence of the structural and multiferroic properties. Notably, the highly distorted phase quasiconcomitantly presents an abrupt structural change, transforms from a standard to a nonconventional ferroelectric, and transitions from antiferromagnetic to paramagnetic at 360±20 K. These coupled ferroic transitions just above room temperature hold promises of giant piezoelectric, magnetoelectric, and piezomagnetic responses, with potential in many applications fields.

Nonadiabatic molecular dynamics of photoexcited Li2(+) Ne(n) clusters.

We investigate the relaxation of photoexcited Li(2)(+) chromophores solvated in Ne(n) clusters (n = 2-22) by means of molecular dynamics with surface hopping. The simplicity of the electronic structure of these ideal systems is exploited to design an accurate and computationally efficient model. These systems present two series of conical intersections between the states correlated with the Li+Li(2s) and Li+Li(2p) dissociation limits of the Li(2)(+) molecule. Frank-Condon transition from the ground state to one of the three lowest excited states, hereafter indexed by ascending energy from 1 to 3, quickly drives the system toward the first series of conical intersections, which have a tremendous influence on the issue of the dynamics. The states 1 and 2, which originate in the Frank-Condon area from the degenerated nondissociative 1(2)Π(u) states of the bare Li(2)(+) molecule, relax mainly to Li+Li(2s) with a complete atomization of the clusters in the whole range of size n investigated here. The third state, which originates in the Frank-Condon area from the dissociative 1(2)Σ(u)(+) state of the bare Li(2)(+) molecule, exhibits a richer relaxation dynamics. Contrary to intuition, excitation into state 3 leads to less molecular dissociation, though the amount of energy deposited in the cluster by the excitation process is larger than for excitation into state 1 and 2. This extra amount of energy allows the system to reach the second series of conical intersections so that approximately 20% of the clusters are stabilized in the 2(2)Σ(g)(+) state potential well for cluster sizes n larger than 6.

Spectroscopic properties of alkali atoms embedded in Ar matrix.

We present a theoretical investigation of visible absorption and related luminescence of alkali atoms (Li, Na, and K) embedded in Ar matrix. We used a model based on core polarization pseudopotentials, which allows us to determine accurately the gas-to-matrix shifts of various trapping sites. The remarkable agreement between our calculated results and the experimental spectra recorded by several authors allows us to establish a clear assignment of the observed spectra, which are made of contributions from crystalline sites on the one hand, and of grain boundary sites on the other hand. Our study reveals remarkably large Stokes shifts, up to 9000 cm(-1), which could be observed experimentally to identify definitely the trapping sites.

Bridging multiferroic phase transitions by epitaxial strain in BiFeO3.

We report the influence of epitaxial strain on the multiferroic phase transitions of BiFeO3 films. Using advanced characterization techniques and calculations we show that while the magnetic Néel temperature hardly varies, the ferroelectric Curie temperature TC decreases dramatically with strain. This is in contrast with the behavior of standard ferroelectrics where strain enhances the polar cation shifts and thus TC. We argue that this is caused by an interplay of polar and oxygen tilting instabilities and that strain can drive both transitions close together to yield increased magnetoelectric responses.

Structure and photoabsorption properties of cationic alkali dimers solvated in neon clusters.

We present a theoretical investigation of the structure and optical absorption of M(2)(+) alkali dimers (M=Li,Na,K) solvated in Ne(n) clusters for n=1 to a few tens Ne atoms. For all these alkali, the lowest-energy isomers are obtained by aggregation of the first Ne atoms at the extremity of the alkali molecule. This particular geometry, common to other M(2)(+)-rare gas clusters, is intimately related to the shape of the electronic density of the X (2)Σ(g)(+) ground state of the bare M(2)(+) molecules. The structure of the first solvation shell presents equilateral Ne(3) and capped pentagonal Ne(6) motifs, which are characteristic of pure rare gas clusters. The size and geometry of the complete solvation shell depend on the alkali and were obtained at n=22 with a D(4h) symmetry for Li and at n=27 with a D(5h) symmetry for Na. For K, our study suggests that the closure of the first solvation shell occurs well beyond n=36. We show that the atomic arrangement of these clusters has a profound influence on their optical absorption spectrum. In particular, the XΣ transition from the X (2)Σ(g)(+) ground state to the first excited (2)Σ(u)(+) state is strongly blueshifted in the Frank-Condon area.

[Hereditary iron overload]. / Surcharges héréditaires en fer.

The field of hereditary iron overload has known, in the recent period, deep changes mainly related to major advances in molecular biology. It encompasses now a series of genetic entities. The mechanistic understanding of iron overload development and iron toxicity has greatly improved. The diagnostic approach has become essentially noninvasive with a major role for biological tests. From the therapeutic viewpoint, the phlebotomy treatment is now enriched by the possibility of resorting to oral chelation and by innovative perspectives directly linked to our improvement in the molecular understanding of these diseases.