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Search Results: 1 - 10 of 4895 matches for " Laurent Lebrun "
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Mn Effect on Nonlinear and Structural Properties of <110> Oriented PZN-4.5PT Single Crystals  [PDF]
Diouma Kobor, Modou Tine, Abdelowahed Hajjaji, Laurent Lebrun, Daniel Guyomar
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.35056
Abstract: Ferroelectric single crystals Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) are promising full materials for non resonant or large bandwidth transducers due to the large values of their piezoelectric properties (d ij , k ij ) and their low mechanical quality factor (Q ij ). Many studies on <001> oriented PZN-4.5PT single crystals were carried out but it is very difficult to find research findings on <110> oriented Mn doped PZN-PT. Thus, investigations were made using XRD, Raman and EPR characterization for <110> oriented PZN-4.5PT grown through the Flux method. Mn doping effect on structural, dielectric, mechanical and piezoelectric properties with two values of Mn percentage (1 and 2 mol%) are also reported in this paper. Through the XRD study, the lattice parameters of doped PZN-PT crystals are slightly increased compared to the undoped one but the Mn didn’t change its structure. The room temperature dielectric permittivity along <110> direction is about 1572 and 1626 (respectively 1% and 2% Mn doped crystals) which are much lower than that of the undoped PZN-4.5PT (2553). The remnant polarization and coercive field of <110> oriented doped crystal measured at 1 KHz are respectively 30 μC/cm2 and 4.30 kV/cm (PZN-4.5PT), 32 μC/cm2 and 6.10 kV/cm (PZN-4.5PT + 1% Mn) and 28 μC/cm2 and 7.30 kV/cm (for the 2% Mn doped crystal). The mechanical quality factor Qm changed from 139 to 441 respectively for the pure and 1% Mn doped single crystals at room temperature while it decreases slightly to 336 for the 2 mol% Mn doped.
Methyl Cholate and Resorcinarene New Carriers for the Recovery of Cr(III) Ions by Supported Liquid Membranes (SLM)s  [PDF]
Abdelkhalek Benjjar, Tarik Eljaddi, Oussama Kamal, Laurent Lebrun, Miloudi Hlaibi
Open Journal of Physical Chemistry (OJPC) , 2013, DOI: 10.4236/ojpc.2013.33013
Abstract:

The technique of supported liquid membranes was used to achieve the facilitated transport of Cr(III) ions, using tow amphiphilic carriers, the methyl cholate and resorcinarene. For prepared SLMs, toluene as organic phase and film of polyvinylidene difluoride, as hydrophobic polymer support with 100 μm in thickness and 0.45 μm as the diameter of the pores. The macroscopic parameters (P and J0) on the transport of these ions were determined for different medium temperatures. For these different environments, the prepared SLMs were highly permeable and a clear evolution of these parameters was observed. The parameter J0 depended on the temperature according to the Arrhenius equation. The activation parameters, Ea, ΔH and ΔS, for the transition state on the reaction of complex formation (ST) , were determined. To explain these results for this phenomenon, and achieve a better extraction of the substrate, a model based on the substrate complexation by the carrier and the diffusion of the formed complex (ST) was developed. The experimental results verify this model and determine the microscopic parameters (Kass and D*). These studies show that these parameters Kass and D* are specific to facilitated transport of Cr(III) ions by each of the carriers and they are changing significantly with temperature.

Dielectric and Mechanical Nonlinear Behavior of Mn Doped PMN-35PT Ceramics  [PDF]
Diouma Kobor, Abdelowahed Hajjaji, Jose E. Garcia, Rafel Perez, Alfons Albareda, Laurent Lebrun, Daniel Guyomar
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.14032
Abstract: This paper presents an investigation on dielectric and mechanical nonlinear properties in Mn-doped PMN-35PT ceramics. The structural study of the ceramics verifies that the 1% mol Mn doped PMN-35PT is a pure perovskite phase with a tetragonal symmetry. SEM micrograph shows the same microstructural mor- phology of an undoped ceramic. From the EPR spectra, it has been concluded that the major part of Mn is present in Mn2+ rather than in Mn4+ form. The addition of Mn2+ ions acts on the dielectric, piezoelectric and mechanical properties by decreasing the relative dielectric permittivity (3800 to 2074), the dielectric losses (0.60 to 0.53), the piezoelectric coefficient d33 (650 to 403 pC/N), and increasing the mechanical quality fac- tor Qm (78 to 317). It was found that in Mn2+ doped ceramics the dielectric response can not be described by Rayleigh law. This result can be understood taking into account that reversible motion of the domain wall is a relevant contribution to response of this material.
Dielectric and Ferroelectric Properties of PZN-4.5PT Nanoparticles Thin Films on Nanostructured Silicon Substrate for Ferrophotovoltaic and Energy Storage Application  [PDF]
Rémi Ndioukane, Moussa Touré, Diouma Kobor, Laurence Motte, Jeanne Solard, Laurent Lebrun
Journal of Modern Physics (JMP) , 2019, DOI: 10.4236/jmp.2019.106043
Abstract: The integration of ferroelectric materials as thin films has attracted considerable attention these last years thanks to their outstanding performances that allow considering new features for the realization of photovoltaic devices. Our study focuses on investigating structural, dielectric and ferroelectric properties of undoped and Mn doped PZN-4.5PT nanoparticles thin films on Silicon substrate. We fabricate very stable PZN-4.5PT nanoparticles thin films deposited on nanostructured silicon substrate with giant relative dielectric permittivity of 2.76 × 104 and 17.7 × 104 for respectively the undoped and Mn doped thin films. These values are very large compared to those found in single crystals and might be explained by the influence of the gel in which nanoparticles were dispersed. The SEM images show the crystallization of new hexagonal phases on the film surface probably coming from interaction between Si and the gel. The hysteresis loops permitted to determine the spontaneous polarization (Ps), remnant polarization (Pr) and coercive field Ec which are equal to 11.73 μC/cm2, 10.20 μC/cm2 and 20 V/cm, respectively for the undoped nanoparticles thin film and 22.22 μC/cm2, 19.32 μC/cm2 and 20 V/cm respectively for the Mn doped one. These values are high and correspond to the best ones found in literature compared to typical ferroelectric thin films.
The IBIS view of the galactic centre: INTEGRAL's imager observations simulations
P. Goldoni,A. Goldwurm,P. Laurent,F. Lebrun
Physics , 1997, DOI: 10.1063/1.54071
Abstract: The Imager on Board Integral Satellite (IBIS) is the imaging instrument of the INTEGRAL satellite, the hard-X/soft-gamma ray ESA mission to be launched in 2001. It provides diagnostic capabilities of fine imaging (12' FWHM), source identification and spectral sensitivity to both continuum and broad lines over a broad (15 keV--10 MeV) energy range. It has a continuum sensitivity of 2~10^{-7} ph cm^{-2} s^{-1} at 1 MeV for a 10^6 seconds observation and a spectral resolution better than 7 % at 100 keV and of 6 % at 1 MeV. The imaging capabilities of the IBIS are characterized by the coupling of the above quoted source discrimination capability with a very wide field of view (FOV), namely 9 x 9 degrees fully coded, 29 x 29 degrees partially coded FOV. We present simulations of IBIS observations of the Galactic Center based on the results of the SIGMA Galactic Center survey. They show the capabilities of this instrument in discriminating between different sources while at the same time monitoring a huge FOV. It will be possible to simultaneously take spectra of all of these sources over the FOV even if the sensitivity decreases out of the fully coded area. It is envisaged that a proper exploitation of both the FOV dimension and the source localization capability of the IBIS will be a key factor in maximizing its scientific output.
Hard X-Rays from the Galactic Nucleus: Present and Future Observations
A. Goldwurm,P. Goldoni,P. Laurent,F. Lebrun,J. Paul
Physics , 1999,
Abstract: In spite of increasing evidences of the presence of a massive Black Hole at the Galactic Center, its radio counterpart, Sgr A*, shows little activity at high energies, and recent models involving energy advection (ADAF) have been proposed to explain this difficulty. We present results on the hard X-ray emission from the galactic central square degree obtained from the SIGMA/GRANAT 1990-1997 survey of this region. The best upper limits available today on the Sgr A* 30-300 keV emission are presented and compared to X-ray data and to the predictions of ADAF models. We also present simulations of Sgr A* observations with the future ESA gamma-ray Observatory INTEGRAL, which show that the imager instrument (20 keV-10 MeV) will be able either to detect the expected ADAF emission from the accreting Galactic Nucleus black hole or set tight upper limits which will constrain the physical parameters of such system.
Integral/IBIS Observations of persistent black hole spectral states during the Core Program
P. Laurent,P. Goldoni,A. Goldwurm,F. Lebrun
Physics , 2001,
Abstract: The Imager on Board the Integral Satellite (IBIS) is one of the two main telescopes of Integral, the ESA soft gamma-ray mission to be launched in 2002. The Integral Core Program will be divided into two main parts, the Galactic Centre Deep Exposure program and the Galactic Plane Scan for a total amount of around 6 .6 10^6 seconds each year. In this paper, we will study the visibility of persist ent galactic black holes as observed by IBIS during these two phases of the Core Program. We will also present what information may be derived from the IBIS observations of spectral/temporal properties (variation of the spectral index, presence/absence of a spectral break, ...) of these binary systems in different spectral states, in particular in the framework of the bulk motion Comptonization model.
Variable polarization measured in the prompt emission of GRB 041219A using IBIS on board INTEGRAL
D. Gotz,P. Laurent,F. Lebrun,F. Daigne,Z. Bosnjak
Physics , 2009, DOI: 10.1088/0004-637X/695/2/L208
Abstract: Polarization measurements provide direct insight into the nature of astrophysical processes. Unfortunately, only a few instruments are available for this kind of measurements at gamma-ray energies, and the sources need to be very bright. Gamma-Ray Bursts (GRBs) are ideal candidates due to their large flux over limited time intervals, maximizing the available signal-to-noise ratio. To date a few polarization measurements have been reported, claiming of a high degree of polarization in the prompt emission of GRBs but with low statistical evidence. We used the IBIS telescope on board the INTEGRAL satellite to measure the polarization of the prompt gamma-ray emission of the long and bright GRB 041219A in the 200-800 keV energy band. We find a variable degree of polarization ranging from less than 4% over the first peak to 43+/-25% for the whole second peak. Time resolved analysis of both peaks indicates a high degree of polarization, and the null average polarization in the first peak can be explained by the rapid variations observed in the polarization angle and degree. Our results are consistent with different models for the prompt emission of GRBs at these energies, but they favor synchrotron radiation from a relativistic outflow with a magnetic field which is coherent on an angular size comparable with the angular size of the emitting region (~1/Gamma) . Indeed this model has the best capabilities to maintain a high polarization level, and to produce the observed variability.
Observation of a Black-Hole X-ray Nova in Outburst with INTEGRAL
P. Goldoni,A. Goldwurm,P. Laurent,F. Lebrun,B. Cordier
Physics , 2001,
Abstract: We simulate the observation of a bright Nova Musca-like X-ray nova during outburst with INTEGRAL, the next ESA gamma-ray space observatory. We will show how performances of the INTEGRAL instruments allow deep study of X-ray Novae and will evaluate the scientific output that INTEGRAL will provide on this class of transient gamma-ray sources, which are now believed to contain black holes in low mass binary systems. The variable high-energy feature around 511 keV observed from X-ray Nova Musca in 1991 by the SIGMA telescope would be detected by INTEGRAL at very high significance level. INTEGRAL data will permit to set important constraints on the models and allow to distinguish between electron-positron or nuclear de-excitation origin of the line. Characteristic spectral and timing features detected by INTEGRAL instruments over a very large energy band will also provide clues to understand physics of accretion in these black holes binaries and in particular to distinguish between thermal and non-thermal origin of radiation and to assess the role of bulk motion comptonization.
Hystricognathy vs Sciurognathy in the Rodent Jaw: A New Morphometric Assessment of Hystricognathy Applied to the Living Fossil Laonastes (Diatomyidae)
Lionel Hautier,Renaud Lebrun,Soonchan Saksiri,Jacques Michaux,Monique Vianey-Liaud,Laurent Marivaux
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0018698
Abstract: While exceptional for an intense diversification of lineages, the evolutionary history of the order Rodentia comprises only a limited number of morphological morphotypes for the mandible. This situation could partly explain the intense debates about the taxonomic position of the latest described member of this clade, the Laotian rock rat Laonastes aenigmamus (Diatomyidae). This discovery has re-launched the debate on the definition of the Hystricognathi suborder identified using the angle of the jaw relative to the plane of the incisors. Our study aims to end this ambiguity. For clarity, it became necessary to revisit the entire morphological diversity of the mandible in extant and extinct rodents. However, current and past rodent diversity brings out the limitations of the qualitative descriptive approach and highlights the need for a quantitative approach. Here, we present the first descriptive comparison of the masticatory apparatus within the Ctenohystrica clade, in combining classic comparative anatomy with morphometrical methods. First, we quantified the shape of the mandible in rodents using 3D landmarks. Then, the analysis of osteological features was compared to myological features in order to understand the biomechanical origin of this morphological diversity. Among the morphological variation observed, the mandible of Laonastes aenigmamus displays an intermediate association of features that could be considered neither as sciurognathous nor as hystricognathous.
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