Search results for "ExAC"
showing 10 items of 1440 documents
The Dirichlet-Bohr radius
2015
[EN] Denote by Ω(n) the number of prime divisors of n ∈ N (counted with multiplicities). For x ∈ N define the Dirichlet-Bohr radius P L(x) to be the best r > 0 such that for every finite Dirichlet polynomial n≤x ann −s we have X n≤x |an|r Ω(n) ≤ sup t∈R X n≤x ann −it . We prove that the asymptotically correct order of L(x) is (log x) 1/4x −1/8 . Following Bohr’s vision our proof links the estimation of L(x) with classical Bohr radii for holomorphic functions in several variables. Moreover, we suggest a general setting which allows to translate various results on Bohr radii in a systematic way into results on Dirichlet-Bohr radii, and vice versa
Fabrication and characterization of magnetic FePt nanoparticles prepared by extraction–pyrolysis method
2018
We are grateful to Prof. E. Kotomin for useful discussions. The research leading to these results has received funding from the ERAF (2017) Project, while A. I. Popov thanks IMIS-2 for the funding support.
Reversible oxidation of WOx and MoOx nano phases
2012
International audience; WOx and MoOx nano phases were prepared on TiO2(1 1 0) surfaces by a CVD procedure consisting of adsorption and decomposition of W(CO)(6) or Mo(CO)(6) precursors followed by annealing under UHV. Metal amount involved in each elaborated sample is in the fractional range from 0.1 to 0.35 equivalent monolayer (eqML) of W or Mo. Evolution of sample stoichiometry as a function of subsequent treatment is followed by valence band and core level photoemission as well as work function measurement. In each case, exposure of samples to molecular oxygen at room temperature induces an increase of sample work function in a range of several tenth of eV. Such a work function change i…
Synthesis and Characterization of Nanostructured Cobalt Hexacyanoferrate
2010
Cobalt hexacyanoferrate (CoHCF) nanoparticles have been synthesized by mixing aqueous solutions of K3Fe(CN)6 and CoCl2 under vigorous stirring at different temperatures and following two different procedures, drop-by-drop or immediate mixing. The resulting CoHCF nanoparticles, with dimensions of several tens of nanometers, were characterized using TEM, SEM-EDX, IR, and XRD. Their electrochemical behavior was investigated in comparison with the CoHCF powder bulk compound. The CoHCF nanoparticles exhibit an electrochemically driven conversion to the bulk one that has been investigated by a chemometric approach in order to establish the best synthetic parameters. The rate and the degree of con…
Heterogeneous nucleation of a droplet pinned at a chemically inhomogeneous substrate: A simulation study of the two-dimensional Ising case
2018
Heterogeneous nucleation is studied by Monte Carlo simulations and phenomenological theory, using the two-dimensional lattice gas model with suitable boundary fields. A chemical inhomogeneity of length b at one boundary favors the liquid phase, while elsewhere the vapor is favored. Switching on the bulk field Hb favoring the liquid, nucleation and growth of the liquid phase starting from the region of the chemical inhomogeneity are analyzed. Three regimes occur: for small fields, Hb bcrit, the critical droplet radius is so large that a critical droplet having the contact angle θc required by Young's equation in the region of the chemical inhomogeneity does not yet "fit" there since the base…
Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials
2018
In this work a model was developed that allows to understand the behavior of a chirped fiber Bragg grating for the detection and characterization of cracks in materials. In addition to the amplitude response, we show that the group delay of the grating provides useful information for the characterization of the crack. The position of the crack can be determined thanks to the linear chirp of the grating that fixes a correlation between the spatial position and both, the wavelength and the group delay. However, our analysis shows that this simple approach has a source of error, which can be overcome if a controllable external strain can be applied to the embedded grating, additional to the st…
Q-switching of an erbium-doped fibre laser modulated by a Bragg grating fixed to a piezoelectric
2003
The performance of the Q-switched erbium-doped fibre laser with two fibre Bragg gratings as cavity mirrors was theoretically analysed, employing a set of rate equations for the ion populations and the photon flux inside the cavity. The simulation considers a system where the pulsed laser emission is produced by the temporal modulation of a Bragg grating fixed to a piezoelectric and operating in the 1550 nm spectral region. The temporal evolution of different frequency components of the laser emission produced is governed by the instantaneous overlap between the two gratings. Theoretical results are in agreement with previously reported experimental values.
Exact solution of ‘‘hot dimer’’ adsorption in one-dimensional lattices
1993
An analytical solution for the kinetics of the ``hot-dimer'' adsorption in a one-dimensional lattice is reported. Hot dimers are molecules that dissociate after deposition, and each of the remaining monomers fly apart up to a maximum distance R from the original adsorption sites. The kinetics of this process is strongly dependent on the flying distance R. We find a particular behavior of the jamming coverage as a function of R. Monte Carlo simulation results are in agreement with such a calculation.
Curvature as a Guiding Field for Patterns in Thin Block Copolymer Films
2018
Experimental data on thin films of cylinder-forming block copolymers (BC)—free-standing BCmembranes as well as supported BC films—strongly suggest that the local orientation of the BC patternsis coupled to the geometry in which the patterns are embedded. We analyze this phenomenon using generalsymmetry considerations and numerical self-consistent field studies of curved BC films in cylindricalgeometry. The stability of the films against curvature-induced dewetting is also analyzed. In goodagreement with experiments, we find that the BC cylinders tend to align along the direction of curvature athigh curvatures. At low curvatures, we identify a transition from perpendicular to parallel alignm…
A photoemission study of molybdenum hexacarbonyl adsorption and decomposition on TiO2(110) surface.
2007
International audience; The adsorption and decomposition of molybdenum hexacarbonyl on (110) TiO2 surfaces were studied using both core levels and valence band photoemission spectroscopies. It was found that after an adsorption at 140 K, when going back to room temperature, only a small part of molybdenum compounds, previously present at low temperature, remained on the TiO2 surface. This indicates that the desorption temperature on such a surface is lower than the decomposition one. The use of photon irradiation to decompose the hexacarbonyl molecule was also studied. It was shown that during such a decomposition molecular fragments were chemisorbed on the surface allowing a higher amount …