University Joseph Fourier - Grenoble 1
Recent publications
Polycrystalline compound Pr0.67Sr0.16Ca0.17Mn0.75Fe0.25O3 was prepared by the conventional solid-state reaction. Structural, magnetic and electrical measurements were investigated. The XRD data have been analyzed by Rietveld refinement technique which reveals that the sample is crystallized in an orthorhombic structure with Pbnm space group. Temperature dependences of the magnetization in both field cooled and zero field cooled modes show the coexistence of ferromagnetic and antiferromagnetic interactions for Pr0.67Sr0.16Ca0.17Mn0.75Fe0.25O3. The analysis of electrical resistivity data shows the semiconductor behavior in all temperatures, which can be explained by small polaron hopping and Mott’s variable range hopping (VRH) models. It was found that the transport mechanism is dominated by the VRH model.
The structure, magnetic properties, and critical behavior of Nd0.6Sr0.2K0.2MnO3 compound are investigated. Rietveld refinement of the X-ray diffraction pattern shows that the examined sample is a pure single phase, crystallized in an orthorhombic Pnma structure. The nanometric size of crystallites calculated using Williamson-Hall method is validated by transmission electron microscopy micrographs. Magnetic measurements indicate a second-order ferromagnetic (FM)/paramagnetic (PM) transition at the Curie point Tc. Various techniques are used such as modified Arrott plot (MAP), Kouvel-Fisher method (KF), and critical isotherm analysis (CIA) to identify critical properties from isothermal magnetization data near critical regions. The deduced values are close to the 3D Ising model, proving the existence of a short-range ferromagnetic order in Nd0.6Sr0.2K0.2MnO3 sample. The results fully meet the requirements of the universal scaling assumption, further confirming its accuracy.
Background While evidence concerning Quality of Life (QoL) in youth with cerebral palsy (CP) in comparison to the general population has been accumulating, there is a lack of studies exploring differences on a wider range of positive and negative mental health outcomes in emerging adults. Methods This binational case control study is part of the SPARCLE cohort study on QoL and participation of youth with CP. QoL (WHOQOL-BREF), depression (PHQ-9), anxiety (GAD-7) and self-efficacy (GSE) were assessed in 198 emerging adults with CP and 593 emerging adults from the general population, matched for country of residence, age and gender. ANCOVAs with impairment and pain as covariates were run. Results Similar levels of QoL were found in both samples, except for the environmental domain, with better QoL for emerging adults with CP compared to the general population. There were significant descriptive differences regarding depression with worse levels in the CP sample, however, also worse levels of self-efficacy. Pain as a covariate had a significant negative impact on all measures, leading to poorer self-efficacy while worsening depression and anxiety; impairment had a significant worsening impact on physical QoL and self-efficacy only. Conclusion Similar expressions of mental health outcomes in emerging adults with CP and the general population indicate the high adaptive capability of emerging adults with CP.
An investigation was conducted to understand the electrical behavior of the double-layered perovskite LaCaBiMn2O7 at temperatures varying from 2 to 400 K under a magnetic field range 0–5 T. At metal-insulator peak temperature (TMI), the data reveal a metal-insulator transition. The compound exhibits a strong magnetoresistance (MR) effect (∼55%) around TMI at a field of 5 T, while the highest value of temperature coefficient of resistance (TCR) is 0.89% K⁻¹ was found at zero-field. In order to analyze the electrical behavior as well as the magnetic properties, a simulation was established with the resistivity (ρ) data using a mathematical model based on the percolation theory. The mutual relationship between transport properties and magnetic behavior has been exploited to predict the magnetic entropy change by analysis of ρ(H, T), It is demonstrated that the magnetic entropy change acquired from ρ(H, T) data is in accordance with those determined by magnetization measurements.
Transform marginal Plateaus (TMPs) are large and flat structures commonly found in deep oceanic domains, but origin and relationship to adjacent oceanic lithosphere remain poorly understood. This paper focuses on two conjugate TMPs, the Demerara Plateau off Suriname and French Guiana and the Guinea Plateau, located at the junction of the Jurassic Central Atlantic and the Cretaceous Equatorial Atlantic Oceans. The study helps to understand (1) the tectonic history of both Demerara and Guinea Plateaus, (2) the relationship between the Demerara Plateau and the adjacent oceanic domains and finally, (3) to throw light on the formation of Transform Marginal Plateaus (TMPs). We analyze two existing wide-angle seismic derived velocity models from the MARGATS seismic experiment (Demerara Plateau), and adjacent composite industrial seismic lines covering the Demerara and Guinea Plateaus. The Demerara Plateau displays a 30 km thick crust, subdivided into 3 layers, including a high velocity lower crust (HVLC). The velocities and velocity gradients do not fit values of typical continental crust but instead correspond to volcanic margin or Large Igneous Province (LIP) type crusts. We propose that the, possibly continental, lower crust is intruded by magmatic material and that the upper crustal layer is made of extrusive volcanic rocks of the same magmatic origin, forming thick seaward (westward) dipping reflectors (SDRs) sequences. This SDR complex extends to the Guinea Plateau as well and was emplaced during hotspot (Sierra Leone)-related volcanic rifting preceding the Jurassic opening of the Central Atlantic and forming the western margin of the plateau. N-S composite lines linking Demerara and Guinea plateaus reveal the spatial extent of the SDR complex but also a preexisting basement ridge separating the two plateaus. The entire Demerara-Guinea margin would therefore be an inherited Jurassic volcanic margin bordering the Central Atlantic Ocean to the east, with as a possible conjugate being the Bahamas Plateau on the other side of the ocean. This margin was then reworked during a non-coaxial Cretaceous second phase of rifting potentially accompanied by a magmatic event. Opening of the northern margin occurs in a transform mode splitting the Jurassic volcanic margin in two parts (Guinea and Demerara TMPs), conceivably along a pre-existing basement ridge. Rifting of the eastern part of the Demerara Plateau occurred surprisingly along the eastern limit of the Jurassic SDR complex, forming the present-day eastern divergent margin of the Demerara Plateau. After that stage, the Demerara and Guinea plateaus are individualized on each side of the Equatorial Atlantic. This study also highlights the major contribution of thermal anomalies related to hotspots and superposed tectonic phases in the case of other TMPs which share numerous characteristics with the Demerara Plateau.
The main idea of this paper is to incorporate and solidify magnetic nanoparticles of CoFe2O4 with a size less than 20 nm in a synthesized porous alumina membrane. In such a configuration, all the magnetic particles are oriented according to an external magnetic field and stay in this orientation even without a magnetic field after the solidification of the matrix. The procedure consists of three preliminary steps. First, we mixed the well-dispersed CoFe2O4 nanoparticles in a hexane solvent, to have a state transition from the liquid (CoFe2O4 nanoparticles surrounded by organic layer and dispersed in hexane) to the solid one of CoFe2O4. Second, we incorporate CoFe2O4 nanoparticles into the alumina membrane pores. Finally, a step of a heat treatment compatible with the magnetic nanoparticles is necessary to evaporate all the organic compounds. The insertion of nanoparticles has been done with the help of an external magnetic field. This work presents a new technique to synthesis a solid regular array of cobalt ferrite nanorods. After the removal of AAO membrane, cobalt ferrite nanorods can be used as a host for another material to prepare a nanocomposite material like extrinsic multiferroic.
Excited levels in Sr90, Sr92, Sr94, and Sr96 nuclei were reinvestigated using high-statistics multiple-γ coincidence data from neutron-induced fission of U235 and spontaneous fission of Cf252, measured using Exogam at Institut Laue Langevin and Gammasphere arrays, respectively. The experimental goal was the search for new excited levels and firm spin-parity assignments to known levels. A total of 23 new levels with 30 new or corrected decays and 39 new or improved spin-parity assignments were obtained in the four nuclei. Negative-parity structures on top of 3− excitation were firmly identified and extended to higher spins. New positive-parity structures in Sr94 and Sr96 were observed with 3+ excitations characteristic of γ collectivity. The 277.7-keV, E2 decay from the 1507.0-keV level to the second 0+ level in Sr96, found in this paper, completes the coexisting deformed band in this nucleus. To learn about the microscopic structure of levels in the Sr88−96 nuclei, we performed large-scale shell-model calculations. The calculations compared to the experiment, helped the discussion of the evolution of collectivity in strontium isotopes, highlighting the important role of various single-particle excitations in phase transitions and shape coexistence in the region. The special role of the neutron 9/2+[404] extruder as a catalyst of the deformation change in the region is highlighted.
The electrical and magnetoresistance behaviors of La0.8−xoxNa0.2−xoxMnO3 [with x = 0 (N0) and 0.1 (N0.1)] polycristalline samples were investigated. Resistance measurements versus temperature under different magnetic applied fields were performed to investigate the electronic transport as well as the magnetoresistance properties. The metal/insulator transition temperature decreases from 280 K for x = 0 to 275 K for x = 0.1. The electrical conduction in these compounds has been well described in the context of the percolation model based on the phase separation of ferromagnetic metallic regions with paramagnetic insulating ones. The temperature-dependent resistance shows the existence of a minimum at low temperature. This behavior is due to the existence of a competition between inelastic and elastic interactions expressed by Kondo-like spin-dependent scattering. An empirical model was used to describe the variation of the magetoresistance and normalized resistance as a function of the magnetic applied field. The model was successfully widely tested on several magnetic specimens and the evolution of the fitting parameters was discussed in detail.
In this research paper, we have carried out an in-depth study of the critical phenomena at the FM–PM phase transition for Nd0.5Ba0.5CoO3 (NBCO). The FM–PM phase transition is identified as second order for our material. Moreover, the critical exponents of NBCO compound were estimated based on multiple techniques such as Kouvel–Fisher, modified Arrott plot method, and critical isotherm analysis. Therefore, the average values of the critical exponent and the critical temperature obtained by the various methods are (βmoy = 0.506; γmoy = 1.011; δmoy = 3.042; TC = 125.543). The obtained critical exponents are in agreement with the mean-field model. Furthermore, the exponent n as a function of temperature reveals the non-homogeneous nature of NBCO compound. According to the mean field theory, the magnetic entropy change (ΔSM vs. M²) was invested to determine the spontaneous magnetization (Mspont) values. Results match reasonably well with those obtained from the classical extrapolation of Arrott plots (μ0H/M vs. M²).
The change of the shell structure in atomic nuclei, so-called “nuclear shell evolution”, occurs due to changes of major configurations through particle-hole excitations inside one nucleus, as well as due to variation of the number of constituent protons or neutrons. We have investigated how the shell evolution affects Gamow-Teller (GT) transitions that dominate the β decay in the region below ¹³²Sn using the newly obtained experimental data on a long-lived isomer in ¹²⁷Ag. The T1/2=67.5(9) ms isomer has been identified with a spin and parity of (27/2+) at an excitation energy of 1942−20+14 keV, and found to decay via an internal transition of an E3 character, which competes with the dominant β-decay branches towards the high-spin states in ¹²⁷Cd. The underlying mechanism of a strong GT transition from the ¹²⁷Ag isomer is discussed in terms of configuration-dependent optimization of the effective single-particle energies in the framework of a shell-model approach.
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1,346 members
Jean-Pierre Bachy
  • UFR Médecine
Sibylle Anderl
  • Institut de Planétologie et Astrophysique de Grenoble
Pierre Y Chavant
  • Département de chimie moléculaire
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Grenoble, France