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Search Results: 1 - 10 of 325299 matches for " S. Ravaine "
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Synthesis of non-spherical gold nanoparticles
M. Tréguer-Delapierre,J. Majimel,S. Mornet,E. Duguet,S. Ravaine
Gold Bulletin , 2008, DOI: 10.1007/BF03216597
Abstract: This article provides an overview of current research in the area of anisotropic gold nanoparticles. We begin by outlining key properties that they possess; we then describe how to control their morphology. Some of the most innovative synthetic strategies are highlighted together with an emphasis on recent results from our laboratories as well as future perspectives for anisotropic gold nanoparticles as novel materials.
Wall slip across the jamming transition of soft thermoresponsive particles
Thibaut Divoux,Véronique Lapeyre,Valérie Ravaine,Sébastien Manneville
Physics , 2015, DOI: 10.1103/PhysRevE.92.060301
Abstract: Flows of suspensions are often affected by wall slip, that is the fluid velocity $v_{f}$ in the vicinity of a boundary differs from the wall velocity $v_{w}$ due to the presence of a lubrication layer. While the slip velocity $v_s=\vert v_{f}-v_{w}\vert$ robustly scales linearly with the stress $\sigma$ at the wall in dilute suspensions, there is no consensus regarding denser suspensions that are sheared in the bulk, for which slip velocities have been reported to scale as a $v_s\propto\sigma^p$ with exponents $p$ inconsistently ranging between 0 and 2. Here we focus on a suspension of soft thermoresponsive particles and show that $v_s$ actually scales as a power law of the viscous stress $\sigma-\sigma_c$, where $\sigma_c$ denotes the yield stress of the bulk material. By tuning the temperature across the jamming transition, we further demonstrate that this scaling holds true over a large range of packing fractions $\phi$ on both sides of the jamming point and that the exponent $p$ increases continuously with $\phi$, from $p=1$ in the case of dilute suspensions to $p=2$ for jammed assemblies. These results allow us to successfully revisit inconsistent data from the literature and paves the way for a continuous description of wall slip above and below jamming.
Effects of confinement on the permanent electric-dipole moment of Xe atoms in liquid Xe
Boris Ravaine,Andrei Derevianko
Physics , 2004, DOI: 10.1103/PhysRevA.69.050101
Abstract: Searches for permanent electric-dipole moments (EDM) of atoms provide important constraints on competing extensions to the standard model of elementary particles. Recently proposed experiment with liquid $^{129}$Xe [M.V. Romalis and M.P. Ledbetter, Phys. Rev. Lett. \textbf{87}, 067601 (2001)] may significantly improve present limits on the EDMs. To interpret experimental data in terms of CP-violating sources, one must relate measured atomic EDM to various model interactions via electronic-structure calculations. Here we study density dependence of atomic EDMs. The analysis is carried out in the framework of the cell model of the liquid coupled with relativistic atomic-structure calculations. We find that compared to an isolated atom, the EDM of an atom of liquid Xe is suppressed by about 40%.
Quantum computing with magnetic atoms in optical lattices of reduced periodicity
Boris Ravaine,Andrei Derevianko,P. R. Berman
Physics , 2006, DOI: 10.1103/PhysRevA.74.022330
Abstract: We investigate the feasibility of combining Raman optical lattices with a quantum computing architecture based on lattice-confined magnetically interacting neutral atoms. A particular advantage of the standing Raman field lattices comes from reduced interatomic separations leading to increased interatomic interactions and improved multi-qubit gate performance. Specifically, we analyze a $J=3/2$ Zeeman system placed in $% \sigma _{+}-\sigma_{-}$ Raman fields which exhibit $\lambda /4$ periodicity. We find that the resulting CNOT gate operations times are in the order of millisecond. We also investigate motional and magnetic-field induced decoherences specific to the proposed architecture.
Atomic CP-violating polarizability
Boris Ravaine,M. G. Kozlov,Andrei Derevianko
Physics , 2005, DOI: 10.1103/PhysRevA.72.012101
Abstract: Searches for CP violating effects in atoms and molecules provide important constrains on competing extensions to the standard model of elementary particles. In particular, CP violation in an atom leads to the CP-odd (T,P-odd) polarizability $\beta^\mathrm{CP}$: a magnetic moment $\mu^\mathrm{CP}$ is induced by an electric field $\mathcal{E}_0$ applied to an atom, $\mu^\mathrm{CP} = \beta^\mathrm{CP} \mathcal{E}_0 $. We estimate the CP-violating polarizability for rare-gas (diamagnetic) atoms He through Rn. We relate betaCP to the permanent electric dipole moment (EDM) of the electron and to the scalar constant of the CP-odd electron-nucleus interaction. The analysis is carried out using the third-order perturbation theory and the Dirac-Hartree-Fock formalism. We find that, as a function of nuclear charge Z, betaCP scales steeply as Z^5 R(Z), where slowly-varying R(Z) is a relativistic enhancement factor. Finally, we evaluate a feasibility of setting a limit on electron EDM by measuring CP-violating magnetization of liquid Xe. We find that such an experiment could provide competitive bounds on electron EDM only if the present level of experimental sensitivity to ultra-weak magnetic fields [Kominis et al., Nature 422, 596 (2003)] is improved by several orders of magnitude.
Marked influence of the nature of chemical bond on CP-violating signature in molecular ions $\mathrm{HBr}^{+}$ and $\mathrm{HI}^{+}$
Boris Ravaine,Sergey G. Porsev,Andrei Derevianko
Physics , 2004, DOI: 10.1103/PhysRevLett.94.013001
Abstract: Heavy polar molecules offer a great sensitivity to the electron Electric Dipole Moment(EDM). To guide emerging searches for EDMs with molecular ions, we estimate the EDM-induced energy corrections for hydrogen halide ions $\mathrm{HBr}^{+}$ and $\mathrm{HI}^{+}$ in their respective ground $X ^2\Pi_{3/2}$ states. We find that the energy corrections due to EDM for the two ions differ by an unexpectedly large factor of fifteen. We demonstrate that a major part of this enhancement is due to a dissimilarity in the nature of the chemical bond for the two ions: the bond that is nearly of ionic character in $\mathrm{HBr}^{+}$ exhibits predominantly covalent nature in $\mathrm{HI}^{+}$. We conclude that because of this enhancement the HI$^+$ ion may be a potentially competitive candidate for the EDM search.
Relaxation effect and radiative corrections in many-electron atoms
Andrei Derevianko,Boris Ravaine,W. R. Johnson
Physics , 2004, DOI: 10.1103/PhysRevA.69.054502
Abstract: We illuminate the importance of a self-consistent many-body treatment in calculations of vacuum polarization corrections to the energies of atomic orbitals in many-electron atoms. Including vacuum polarization in the atomic Hamiltonian causes a substantial re-adjustment (relaxation) of the electrostatic self-consistent field. The induced change in the electrostatic energies is substantial for states with the orbital angular momentum $l &;gt; 0$. For such orbitals, the relaxation mechanism determines the sign and even the order of magnitude of the total vacuum polarization correction. This relaxation mechanism is illustrated with numerical results for the Cs atom.
Elaboración de Membranas Poliméricas Porosas a partir de Cristales Coloidales
Casis,Natalia; Fidalgo,Maria M; Ravaine,Serge; Estenoz,Diana A;
Información tecnológica , 2010, DOI: 10.4067/S0718-07642010000100002
Abstract: polymeric porous membranes with a high control of morphology and porous size were fabricated from colloidal crystals made of silica particles. this fabrication process allows different morphologies according to the particle sizes and number of layers on the templates. silica particles with a narrow size distribution were synthesized by two methods. colloidal crystals were obtained by vertical deposition of the particles on a glass substrate and by the langmuir-blodgett technique to create templates of different particle sizes. to produce the membrane, polystyrene (ps) and styrene (st)-vinyl benzyl thymine (vbt) copolymers were used. the procedure involved the infiltration of monomers in the templates and then, the polymerization by uv radiation. the proposed method represents a relatively simple alternative, both versatile and economically attractive to manufacture macroporous polymers.
Elaboración de Membranas Poliméricas Porosas a partir de Cristales Coloidales Elaboration of Porous Polymeric Membranes from Colloidal Crystals
Natalia Casis,Maria M Fidalgo,Serge Ravaine,Diana A Estenoz
Información Tecnológica , 2010,
Abstract: Se elaboraron membranas poliméricas porosas con elevado control de la morfología y de los tama os de poros a partir de cristales coloidales constituidos por partículas de sílice. El método empleado permite obtener diferentes morfologías dependiendo del tama o de las partículas y del número de capas involucradas en los depósitos. Para la síntesis de las partículas se emplearon dos métodos, originándose distintos tama os. Los cristales coloidales se obtuvieron por deposición vertical de las partículas sobre un sustrato de vidrio y por la técnica de Langmuir-Blodgett. Se fabricaron membranas de poliestireno (PS) y de copolímero de estireno (St)-vinil bencil timina (VBT). El procedimiento involucró la infiltración de los monómeros seguida por la polimerización por irradiación con luz UV. El método propuesto provee una alternativa relativamente simple, muy versátil y a la vez económica para la elaboración de polímeros macroporosos. Polymeric porous membranes with a high control of morphology and porous size were fabricated from colloidal crystals made of silica particles. This fabrication process allows different morphologies according to the particle sizes and number of layers on the templates. Silica particles with a narrow size distribution were synthesized by two methods. Colloidal crystals were obtained by vertical deposition of the particles on a glass substrate and by the Langmuir-Blodgett technique to create templates of different particle sizes. To produce the membrane, polystyrene (PS) and styrene (St)-vinyl benzyl thymine (VBT) copolymers were used. The procedure involved the infiltration of monomers in the templates and then, the polymerization by UV radiation. The proposed method represents a relatively simple alternative, both versatile and economically attractive to manufacture macroporous polymers.
Study of the Structural and Electrical Properties of Cr-Doped BiFeO3 Ceramic  [PDF]
S. S. Arafat, S. Ibrahim
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.810051
Abstract: Multiferroic BiFe1-xCrxO3 (x = 0.2 and 0.4) ceramics were synthesized in a single phase. The effects of Cr3+ substitution on the crystal structure, dielectric permittivity and leakage current were investigated. Preliminary X-ray structural studies revealed that the samples had a rhombohedral perovskite crystal structure. The dielectric constant ε' significantly increased while the dielectric loss tanδ was substantially decreased with the increase in Cr3+ substitution. The temperature effect on the dielectric properties exhibited an anomaly corresponding to magneto-electric coupling in the samples and was shifted to lower temperatures with the increase in Cr3+ substitution. The leakage current density also reduced in magnitude with the increase in the Cr3+ substitution.
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