66 research outputs found
Separation between coherent and turbulent fluctuations. What can we learn from the Empirical Mode Decomposition?
The performances of a new data processing technique, namely the Empirical
Mode Decomposition, are evaluated on a fully developed turbulent velocity
signal perturbed by a numerical forcing which mimics a long-period flapping.
First, we introduce a "resemblance" criterion to discriminate between the
polluted and the unpolluted modes extracted from the perturbed velocity signal
by means of the Empirical Mode Decomposition algorithm. A rejection procedure,
playing, somehow, the role of a high-pass filter, is then designed in order to
infer the original velocity signal from the perturbed one. The quality of this
recovering procedure is extensively evaluated in the case of a "mono-component"
perturbation (sine wave) by varying both the amplitude and the frequency of the
perturbation. An excellent agreement between the recovered and the reference
velocity signals is found, even though some discrepancies are observed when the
perturbation frequency overlaps the frequency range corresponding to the
energy-containing eddies as emphasized by both the energy spectrum and the
structure functions. Finally, our recovering procedure is successfully
performed on a time-dependent perturbation (linear chirp) covering a broad
range of frequencies.Comment: 23 pages, 13 figures, submitted to Experiments in Fluid
Etude cinétique de la dégradation de l’Endosufane en solution
Les pesticides sont fréquemment utilisés en Côte d’Ivoire. Leur détection dans les eaux de forage témoigne de leur mauvais usage et d’un grave problème agroenvironnemental. La photolyse directe ou la photocatalyse sont de nouvelles techniques d’oxydation, envisageables pour résoudre ce problème, avec l’avantage d’utiliser à terme les UV-A solaires. L’ a-endosulfane et le b-endosulfane ont été sélectionnés pour cette étude. Leurs dégradations dans l’eau de forage et dans l’eau déionisée ont été respectivement effectuées dans un réacteur muni d’une lampe basse pression de 6 watts ou par exposition à la lumière solaire. La photodégradation dans l’eau de forage est plus rapide que celle observée dans l’eau déionisée. On observe cependant une stabilité relative des isomères d’endosulfane sous irradiation solaire avec des temps de demi-vie de 770 h pour a endosulfane et 407 h pour b endosulfane. L’utilisation du photocatalyseur (Fe3+/H2O2) a accéléré la dégradation de l’endosulfane quelque soit la source d’irradiation. Sous irradiation solaire, les temps de demi-vie passent à 56,34 minutes et à 41,74 minutes respectivement pour l’a et le b endosulfane
Reactivity of neonicotinoid insecticides with carbonate radicals
“NOTICE: this is the author’s version of a work that was accepted for
publication in Water Research. Changes resulting from the
publishing process, such as peer review, editing, corrections,
structural formatting, and other quality control mechanisms may not be
reflected in this document. Changes may have been made to this work
since it was submitted for publication. A definitive version was
subsequently published in WATER RESEARCH, [VOL46, ISSUE11, jul 2012]
DOI10.1016/j.watres.2012.03.051¨
©IWA Publishing 2012. The definitive peer-reviewed and edited version of this
article is published in Water Research 46 11 3476-3489 2012 10.1016/j.watres.2012.03.051
and is available at www.iwapublishing.comThe reaction of three chloronicotinoid insecticides, namely Imidacloprid (IMD), Thiacloprid (THIA) and Acetamiprid (ACT), with carbonate radicals (CO3 center dot-) was investigated. The second order rate constants (4 +/- 1) x 10(6), (2.8 +/- 0.5) x 10(5), and (1.5 +/- 1) x 10(5) M-1 s(-1) were determined for IMD, THIA and ACT, respectively. The absorption spectra of the organic intermediates formed after CO3 center dot- is approximately equal to attack to IMD is in line with those reported for alpha-aminoalkyl radicals. A reaction mechanism involving an initial charge transfer from the amidine nitrogen of the insecticides to CO3 center dot- is proposed and further supported by the identified reaction products. The pyridine moiety of the insecticides remains unaffected until nicotinic acid is formed. CO3 center dot- radical reactivity towards IMD, ACT, and THIA is low compared to that of HO center dot radicals, excited triplet states, and O-1(2), and is therefore little effective in depleting neonicotinoid insecticides. (C) 2012 Elsevier Ltd. All rights reserved.This research was financially supported by Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Agencia Nacional de Promocion Cientifica y Tecnologica (Argentina, project PICT 2007 number 00308), and Agencia Espanola de Cooperacion Internacional (project A/8199/07). M.L.D. thanks CONICET for a graduate studentship. M.C.G. is a research member of CONICET. D.O.M. is a research member of Comision de Investigaciones Cientificas de la Provincia de Buenos Aires (CIC), Argentina. L.S.J. acknowledges Ministerio de Ciencia e Innovacion for his Juan de la Cierva scholarship.Dell'arciprete, ML.; Soler Escoda, JM.; Santos-Juanes Jordá, L.; Arques Sanz, A.; Martire, DO.; Furlong, JP.; González, MC. (2012). Reactivity of neonicotinoid insecticides with carbonate radicals. Water Research. 46(11):3476-3489. https://doi.org/10.1016/j.watres.2012.03.051S34763489461
Stabilizing a graphene platform toward discrete components
© 2016 Author(s).We report on statistical analysis and consistency of electrical performances of devices based on a large scale passivated graphene platform. More than 500 graphene field effect transistors (GFETs) based on graphene grown by chemical vapor deposition and transferred on 4 in. SiO2/Si substrates were fabricated and tested. We characterized the potential of a two-step encapsulation process including an Al2O3 protection layer to avoid graphene contamination during the lithographic process followed by a final Al2O3 passivation layer subsequent to the GFET fabrication. Devices were investigated for occurrence and reproducibility of conductance minimum related to the Dirac point. While no conductance minimum was observed in unpassivated devices, 75% of the passivated transistors exhibited a clear conductance minimum and low hysteresis. The maximum of the device number distribution corresponds to a residual doping below 5 × 1011 cm−2 (0.023 V/nm). This yield shows that GFETs integrating low-doped graphene and exhibiting small hysteresis in the transfer characteristics can be envisaged for discrete components, with even further potential for low power driven electronics.This study was partly funded by the European Union through the projects Grafol (No. 285275) and Graphene Flagship (No. 604391 and Core1 No. 696656)
Photo-Fenton process for treating biological laboratory wastewater containing formaldehyde
The Critical Richardson Number and Limits of Applicability of Local Similarity Theory in the Stable Boundary Layer
Measurements of atmospheric turbulence made over the Arctic pack ice during
the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to
determine the limits of applicability of Monin-Obukhov similarity theory (in
the local scaling formulation) in the stable atmospheric boundary layer. Based
on the spectral analysis of wind velocity and air temperature fluctuations, it
is shown that, when both of the gradient Richardson number, Ri, and the flux
Richardson number, Rf, exceed a 'critical value' of about 0.20 - 0.25, the
inertial subrange associated with the Richardson-Kolmogorov cascade dies out
and vertical turbulent fluxes become small. Some small-scale turbulence
survives even in this supercritical regime, but this is non-Kolmogorov
turbulence, and it decays rapidly with further increasing stability. Similarity
theory is based on the turbulent fluxes in the high-frequency part of the
spectra that are associated with energy-containing/flux-carrying eddies.
Spectral densities in this high-frequency band diminish as the
Richardson-Kolmogorov energy cascade weakens; therefore, the applicability of
local Monin-Obukhov similarity theory in stable conditions is limited by the
inequalities Ri < Ri_cr and Rf < Rf_cr. However, it is found that Rf_cr = 0.20
- 0.25 is a primary threshold for applicability. Applying this prerequisite
shows that the data follow classical Monin-Obukhov local z-less predictions
after the irrelevant cases (turbulence without the Richardson-Kolmogorov
cascade) have been filtered out.Comment: Boundary-Layer Meteorology (Manuscript submitted: 16 February 2012;
Accepted: 10 September 2012
Hydrolysis and photolysis of two organophosphorus pesticides in dilute aqueous solutions: kinetics and by products
The transformation of two selected organophophorus pesticides (OPs) by hydrolysis and photolysis processes has been studied in aqueous solution. Because of their extensive use profenofos and isazofos were chosen for this study. Hydrolysis and photolysis experiments were performed in purified water at pH = 8.0 and ionic strength equal to 2.5 mM. The irradiation was obtained with a polychromatic light starting at 285 nm. Kinetic investigations coupled with analytical studies (identification of degradation products) were performed. Apparent first order rate constants were determined for hydrolysis and photolysis processes. For each organophosphorus pesticide, experiments have been performed to identify the photodegradation products. The proposed structures will be discussed
Etude de l'association MOD - trifluraline par microextraction en phase solide (SPME) couplée à la spectrométrie de masse
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