Deconvoluting Reversal Modes in Exchange Biased Nanodots

Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been deconvoluted into local, microscopic, bias separately experienced by nanodots going through different reversal modes. The relative fraction of dots in each mode can be modified by exchange bias. Single domain dots exhibit a simple loop shift, while vortex state dots have asymmetric shifts in the vortex nucleation and annihilation fields, manifesting local incomplete domain walls in these nanodots as magnetic vortices with tilted cores.Comment: 17 pages, 3 figures. Phys. Rev. B in pres

Numerical Simulations of Dynamos Generated in Spherical Couette Flows

We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculiar regime where dynamo action may be obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner core might explain the decrease of the dynamo threshold. For lower $E$ ($E=10^{-4}$) this internal shear layer becomes unstable, leading to small scales fluctuations, and the favorable dynamo regime is lost. We also model the effect of ferromagnetic boundary conditions. Their presence have only a small impact on the dynamo onset but clearly enhance the saturated magnetic field in the ferromagnetic parts. Implications for experimental studies are discussed

Observation of correlations up to the micrometer scale in sliding charge-density waves

High-resolution coherent x-ray diffraction experiment has been performed on the charge density wave (CDW) system K$_{0.3}$MoO$_3$. The $2k_F$ satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the $2k_F$ satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge density wave systems. Several scenarios are discussed.Comment: 4 pages, 3 figures Typos added, references remove

Knee Kinematics Estimation Using Multi-Body Optimisation Embedding a Knee Joint Stiffness Matrix: A Feasibility Study

The use of multi-body optimisation (MBO) to estimate joint kinematics from stereophotogrammetric data while compensating for soft tissue artefact is still open to debate. Presently used joint models embedded in MBO, such as mechanical linkages, constitute a considerable simplification of joint function, preventing a detailed understanding of it. The present study proposes a knee joint model where femur and tibia are represented as rigid bodies connected through an elastic element the behaviour of which is described by a single stiffness matrix. The deformation energy, computed from the stiffness matrix and joint angles and displacements, is minimised within the MBO. Implemented as a “soft” constraint using a penalty-based method, this elastic joint description challenges the strictness of “hard” constraints. In this study, estimates of knee kinematics obtained using MBO embedding four different knee joint models (i.e., no constraints, spherical joint, parallel mechanism, and elastic joint) were compared against reference kinematics measured using bi-planar fluoroscopy on two healthy subjects ascending stairs. Bland-Altman analysis and sensitivity analysis investigating the influence of variations in the stiffness matrix terms on the estimated kinematics substantiate the conclusions. The difference between the reference knee joint angles and displacements and the corresponding estimates obtained using MBO embedding the stiffness matrix showed an average bias and standard deviation for kinematics of 0.9±3.2° and 1.6±2.3 mm. These values were lower than when no joint constraints (1.1±3.8°, 2.4±4.1 mm) or a parallel mechanism (7.7±3.6°, 1.6±1.7 mm) were used and were comparable to the values obtained with a spherical joint (1.0±3.2°, 1.3±1.9 mm). The study demonstrated the feasibility of substituting an elastic joint for more classic joint constraints in MBO

Type II and IV radio bursts in the active period October-November 2003

In this report we present the Type II and IV radio bursts observed and analyzed by the radio spectrograph ARTEMIS IV1, in the 650-20MHz frequency range, during the active period October-November 2003. These bursts exhibit very rich fine structures such fibers, pulsations and zebra patterns which is associated with certain characteristics of the associated solar flares and CMEs.Comment: Recent Advances in Astronomy and Astrophysics: 7th International Conference of the Hellenic Astronomical Society. AIP Conference Proceedings, Volume 848, pp. 199-206 (2006

Integration of OpenCalphad thermo-chemical solver in PLEIADES/ALCYONE fuel performance code

International audienceThe ALCYONE fuel performance code, co-developed by CEA, EDF and Framatome, within the PLEIADES software environment provides a multidimensional modeling for detailed analysis of PWR fuel elements behavior under irradiation [1]. Iodine-Stress Corrosion Cracking is one of the physical phenomena of major interest for cladding design and long term operation of PWRs. In a first step towards I-SCC simulations, the thermochemical code ANGE was integrated in PLEIADES [2]. ANGE, a modified version of SOLGASMIX, enables to compute thermo-chemical equilibria using the TBASE database [3] and associate species description [4] but has some limitations and cannot be used to solve chemical systems based on the Compound Energy Formalism, such as the one proposed in the TAF-ID [5]. Consequently, a robust, efficient and free numerical tool, OpenCalphad [6], was introduced in PLEIADES. In this work, we focus our presentation on the calculation of complex multi-component systems representative of fuel elements behavior under irradiation. From the results of in-reactor power transient calculations (1D-2D-3D), we show that ALCYONE/OpenCalphad is much faster than ALCYONE/ANGE. We note a decrease of the CPU time by almost a factor 4 that can be explained by the OpenCalphad solver itself and by a set of numerical strategies implemented to start a thermodynamic calculation on a mesh node by using another calculated equilibrium as an initial solution. We also show through first results the capacity and the robustness of the ALCYONE/OpenCalphad coupling to do in-reactor power transients calculations (1D-2D-3D) using the TAF-ID. In the latter, the models are more complicated and the possible phases are greater in number than in the TBASE database. For calculations performed in the same conditions as those done with the TBASE database, we note a slight increase of the CPU time that can be reduced by calculating several thermodynamic equilibria simultaneously with a multithread approach.References[1] V. Marelle, et al. New developments in ALCYONE 2.0 fuel performance code, Top Fuel, Boise ID (2016)[2] B. Baurens, et al., J. Nucl. Mater. 452 (2014) 578[3] E.H.P. Cordfuncke, R.J.M. Konings, J. Phase Equilibria 14 [4] (1993)[4] T.M. Besmann, Comprehensive Nucl. Mater. 1.17 (2012)[5] C. Gueneau et al., J. Nucl. Mater. 419 (2011) 147[6] B. Sundman, et al, Integ. Mater. Manuf. Innov. 4 (2015)

Mitochondrial effects of dexamethasone imply both membrane and cytosolic-initiated pathways in HepG2 cells

Glucocorticoid treatment is often linked to increased whole-body energy expenditure and hypermetabolism. Glucocorticoids affect mitochondrial energy production, notably in the liver, where they lead to mitochondrial uncoupling reducing the efficacy of oxidative phosphorylation. However, the signaling pathways involved in these phenomena are poorly understood. Here we treated HepG2 cells with dexamethasone for different times and, by using different combinations of inhibitors, we showed that dexamethasone treatment leads to recruitment of two main signaling pathways. The first one involves a G-protein coupled membrane glucocorticoid binding site and rapidly decreases complexes I and II activities while complex III activity is upregulated in a p38MAPK dependent mechanism. The second one implies the classical cytosolic glucocorticoid receptor and triggers long-term transcriptional increases of respiration rates and of complex IV activity and quantity. We concluded that mitochondria are the target of multiple dexamethasone-induced regulatory pathways that are set up gradually after the beginning of hormone exposure and that durably influence mitochondrial oxidative phosphorylation

Erratum. Maternal ageing impairs mitochondrial DNA kinetics during early embryogenesis in mice

STUDY QUESTION: Does ageing affect the kinetics of the mitochondrial pool during oogenesis and early embryogenesis? SUMMARY ANSWER: While we found no age-related change during oogenesis, the kinetics of mitochondrial DNA content and the expression of the factors involved in mitochondrial biogenesis appeared to be significantly altered during embryogenesis. WHAT IS KNOWN ALREADY: Oocyte mitochondria are necessary for embryonic development. The morphological and functional alterations of mitochondria, as well as the qualitative and quantitative mtDNA anomalies, observed during ovarian ageing may be responsible for the alteration of oocyte competence and embryonic development. STUDY DESIGN, SIZE, DURATION: The study, conducted from November 2016 to November 2017, used 40 mice aged 5-8 weeks and 45 mice aged 9-11 months (C57Bl6/CBA F(1)). A total of 488 immature oocytes, with a diameter ranging from 20 μm to more than 80 μm, were collected from ovaries, and 1088 mature oocytes or embryos at different developmental stages (two PN, one-cell, i.e. syngamy, two-cell, four-cell, eight-cell, morula and blastocyst) were obtained after ovarian stimulation and, for embryos, mating. PARTICIPANTS/MATERIALS, SETTING, METHODS: Mitochondrial DNA was quantified by quantitative PCR. We used quantitative reverse transcriptase PCR (RT-PCR) (microfluidic method) to study the relative expression of three genes involved in the key steps of embryogenesis, i.e. embryonic genome activation (HSPA1) and differentiation (CDX2 and NANOG), two mtDNA genes (CYB and ND2) and five genes essential for mitochondrial biogenesis (PPARGC1A, NRF1, POLG, TFAM and PRKAA). The statistical analysis was based on mixed linear regression models applying a logistic link function (STATA v13.1 software), with values of P < 0.05 being considered significant. MAIN RESULTS AND THE ROLE OF CHANCE: During oogenesis, there was a significant increase in oocyte mtDNA content (P < 0.0001) without any difference between the two groups of mice (P = 0.73). During the first phase of embryogenesis, i.e. up to the two-cell stage, embryonic mtDNA decreased significantly in the aged mice (P < 0.0001), whereas it was stable for young mice (young/old difference P = 0.015). The second phase of embryogenesis, i.e. between the two-cell and eight-cell stages, was characterized by a decrease in embryonic mtDNA for young mice (P = 0.013) only (young/old difference P = 0.038). During the third phase, i.e. between the eight-cell and blastocyst stage, there was a significant increase in embryonic mtDNA content in young mice (P < 0.0001) but not found in aged mice (young/old difference P = 0.002). We also noted a faster expression of CDX2 and NANOG in the aged mice than in the young mice during the second (P = 0.007 and P = 0.02, respectively) and the third phase (P = 0.01 and P = 0.008, respectively) of embryogenesis. The expression of mitochondrial genes CYB and ND2 followed similar kinetics and was equivalent for both groups of mice, with a significant increase during the third phase (P < 0.01). Of the five genes involved in mitochondrial biogenesis, i.e. PPARGC1A, NRF1, POLG, TFAM and PRKAA, the expression of three genes decreased significantly during the first phase only in young mice (NRF1, P = 0.018; POLGA, P = 0.002; PRKAA, P = 0.010), with no subsequent difference compared to old mice. In conclusion, during early embryogenesis in the old mice, we suspect that the lack of a replicatory burst before the two-cell stage, associated with the early arrival at the minimum threshold value of mtDNA, together with the absence of an increase of mtDNA during the last phase, might potentially deregulate the key stages of early embryogenesis. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Because of the ethical impossibility of working on a human, this study was conducted only on a murine model. As superovulation was used, we cannot totally exclude that the differences observed were, at least partially, influenced by differences in ovarian response between young and old mice. WIDER IMPLICATIONS OF THE FINDINGS: Our findings suggest a pathophysiological explanation for the link observed between mitochondria and the deterioration of oocyte quality and early embryonic development with age. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the University of Angers, France, by the French national research centres INSERM and the CNRS and, in part, by PHASE Division, INRA. There are no competing interests