Étude par des paramètres globaux de la matière organique d'eaux brutes et clarifiée

Incluse dans une étude plus générale de caractérisation de la Matière Organique des eaux naturelles superficicielles, cette partie présente les résultats obtenus par ultrafiltration. Les différents paramètres analytiques suivis concernent le COT, COD, CODB, UV à 254 nm et le potentiel de formation des trihalométhanes (pTHM). Les méthodes expérimentales, mises en oeuvre sur les eaux brutes et clarifiées (notées eb et ec respectivement), comprennent l'ultrafiltration (seuils de coupure: 10, 1 et 0,5 kilodaltons), les demandes en chlore et en bioxyde de chlore ainsi que l'étape de clarification, si sur les usines une préoxydation existe.Le seuil de coupure de 10 kd ou 1 kd caractérise l'origine d'une eau brute. Les eaux de barrage, contrairement aux eaux « courantes », ont un classement logique des différentes fractions des masses moléculaires apparentes et ceci quel que soit le paramètre analytique suivi (COT ou absorbance UV). Sur toutes les eaux clarifiées ultrafiltrées, la fraction supérieure à 1 kd reste majoritaire. Dans nos conditions experimentales, ce seuil de coupure induit le changement le plus significatif entre une eau brute et son eau clarifiée. La valeur de l'absorbance UVec permet dans un premier temps d'approximer la valeur du COTec.Les autres paramètres analytiques (CODB, pTHM et demandes en oxydants) aussi bien sur les eaux brutes que clarifiées n'ont pas pû être corrélées avec un ou plusieurs autres paramètres physico-chimiques de ces mêmes eau.The following paper presents the work being carried out in a general study of natural organic matter. The three lines of work chosen by SAUR concern:- The fluorescence of natural waters or humic substances (SlMON et al., 1993); - The determination of dissolved hydrophobic and hydrophilic substances on each step of a water treatment plant (CROUE et al, 1992 a and b); - The molecular weight fractionation of dissolved organic matter, subject of this paper. The different raw or clarified waters (respectively rw and cw) were sampled in SAUR water plants. Some inorganic analytical characteristics of some raw waters are given in table 1. All raw and clarified water samples were characterized according to total organic carbon (TOC), UV absorbance (254 nm) and trihalomethane formation potential (THMFP) under the following conditions: about 20°C, 4 mg Cl2/mg TOC, and a 72-hour contact time in the dark. A Dohrmann DC80 and a Uvikon 930 were used for the determination of TOC (DOC) and UV-absorbance at 254 nm, respectively. When a preoxydation step was employed at the water plant, the clarification treatment was performed with a laboratory apparatus described in another paper (LEFEBVRE and LEGUBE, 1990). Bioeliminable Organic Dissolved Carbon in water was determined by the method described by JORET and LEVI (1986). Cl2 and ClO2 demands of raw and clarified waters were conducted as batch operations with oxidant doses of 1, 2 and 4 mg oxidant per mg TOC. Residual chlorine and chlorine dioxide in solutions were determined respectively by spectrophotometric measurements by two colorimetric methods: the DPD and ACVK methods.Ultrafiltration was conducted on raw and clarified waters to determine apparent molecular weight distribution (AMW). Organic matter distribution was determined with an Amicon system (stirred cell) with membranes characterized by nominal cutoff limits of 10, 1 and 0.5 kilodaltons. For each cutoff membrane, we took the initial water and a new membrane was used for each filtration. All permeates were characterized according to TOC and UV absorbance.In the case of clarified waters, the results included all the data, whatever the coagulant salt and its applied dosage.As shown in figures 1 and 2, no relation exists between UVrw absorbance or the ratio UVrw/TOCrw and TOCrw. For the same raw water, the ratio UVrw/TOCrw fluctuates according to a change between fulvic, humic and hydrophilic acids during the seasons (fg. 3). A better relation between UVcw and TOCcw was obtained: UVcw (254 nm, 5 cm)=0.1091 TOCrw - 0.0231 (r2=0 758), demonstrating that organic matter, which resists coagulation, has quite the same aromaticity whatever the water source (fig. 9). An approximation of TOCcw can be done by a simple measurement of UVcw at 254 nm. Figure 4 shows a correlation between DOCrw and TOCrw (DOCrw (mg/l)=0.888 TOCrw + 0.094; r2: 0.945). Except for 2 waters, UV absorbance removal was greater than TOC removal (fig. 13).The AMW distribution of all the studied waters was influenced in the same degree by clarification, with a shift in DOC and UV absorbance to the 10 kd fraction can represent at most 49.7% and 57.3% respectively of TOCcw and UVcw absorbance. All of the coagulants (ferric chloride, aluminium sulfate or prepolymerised alum salts) were completely in effective in removing dissolved organic matter with an AMW of legs than 500 daltons. The significant removal of high molecular weight compounds is followed by a small reduction in the THMFP expressed in µg per mg of TOC.The THM formation potential (THMFP) of raw waters is affected by the water source. Chloroform accounted for 85.4% of the THMFPrw and its average value was 63 µg per mg TOCrw. The clarified waters showed a marked difference in their THMFP distribution. Chloroform percentage was very different, ranging between 30 and 93% of THMFPcw.Clarification treatment slightly reduced the Cl2 and CIO2 demands of the waters: 2.7 mg Cl2/mg TOCrw and 23 mg Cl2/mg TOCcw; 25 mg ClO2/mg TOCrw amd 2.3 mg ClO2/mg TOCcw.An estimation of TOC removal by coagulation with aluminium salts can be done by ultrafiltration of this unknown water with a nominal cutoff of 10 kd (fig. 15).The value of the fraction above 10 kd or below 1 kd could be a useful parameter for the determination of the type of an unknown water, whatever the analytical parameters (tables 3a and 3b). In the case of reservoir raw waters, the order of fractions distribution was logical, whatever the analytical parameters (TOC or UV absorbance): the > 10 kd fraction; the 10 kd >> 1 kd fraction and the < 1 kd fraction (fig. 6 and 7). Figures 6 and 7 do not show the same sequence in the case of river water (e.g.: Mayenne, Garonne, Thames,.. .).No relation exists between BDOCrw and TOCrw or UVrw/TOCrw ratio (Fis. 5a and 5b). BDOCrw represents 0 to 36.4 percent of TOCrw. BDOC removal by coagulation is very different from one water to another (table 5), varying from 35% to 100%

Quasimonoenergetic electron beams produced by colliding cross-polarized laser pulses in underdense plasmas

The interaction of two laser pulses in an underdense plasma has proven to be able to inject electrons in plasma waves, thus providing a stable and tunable source of electrons. Whereas previous works focused on the "beatwave" injection scheme in which two lasers with the same polarization collide in a plasma, this present letter studies the effect of polarization and more specifically the interaction of two colliding cross-polarized laser pulses. It is shown both theoretically and experimentally that electrons can also be pre-accelerated and injected by the stochastic heating occurring at the collision of two cross-polarized lasers and thus, a new regime of optical injection is demonstrated. It is found that injection with cross-polarized lasers occurs at higher laser intensities.Comment: 4 pages, 4 figure

Repetition and difference: Lefebvre, Le Corbusier and modernity's (im)moral landscape: a commentary

This article engages with the relationship between social theory, architectural theory and material culture. The article is a reply to an article in a previous volume of the journal in question (Smith, M. (2001) ‘Repetition and difference: Lefebvre, Le Corbusier and modernity’s (im)moral landscape’, Ethics, Place and Environment, 4(1), 31-34) and, consequently, is also a direct engagement with another academic's scholarship. It represents a critique of their work as well as a recasting of their ideas, arguing that the matter in question went beyond interpretative issues to a direct critique of another author's scholarship on both Le Corbusier and Lefebvre. A reply to my article from the author of the original article was carried in a later issue of the journal (Smith, M. (2002) ‘Ethical Difference(s): a Response to Maycroft on Le Corbusier and Lefebvre’, Ethics, Place and Environment, 5(3), 260-269)

High-quality ion beams by irradiating a nano-structured target with a petawatt laser pulse

We present a novel laser based ion acceleration scheme, where a petawatt circularly polarized laser pulse is shot on an ultra-thin (nano-scale) double-layer target. Our scheme allows the production of high-quality light ion beams with both energy and angular dispersion controllable by the target properties. We show that extraction of all electrons from the target by radiation pressure can lead to a very effective two step acceleration process for light ions if the target is designed correctly. Relativistic protons should be obtainable with pulse powers of a few petawatt. Careful analytical modeling yields estimates for characteristic beam parameters and requirements on the laser pulse quality, in excellent agreement with one and two-dimensional Particle-in Cell simulations.Comment: 18 pages, 7 figures, accepted in New. J. Phy

Early out-of-equilibrium beam-plasma evolution

We solve analytically the out-of-equilibrium initial stage that follows the injection of a radially finite electron beam into a plasma at rest and test it against particle-in-cell simulations. For initial large beam edge gradients and not too large beam radius, compared to the electron skin depth, the electron beam is shown to evolve into a ring structure. For low enough transverse temperatures, the filamentation instability eventually proceeds and saturates when transverse isotropy is reached. The analysis accounts for the variety of very recent experimental beam transverse observations.Comment: to appear in Phys. Rev. Letter

Comment on “Electron Temperature Scaling in Laser Interaction with Solids”

International audienceA Comment on the Letter by T. Kluge et al., Phys. Rev. Lett. 107, 205003 (2011). The authors of the Letter offer a Reply

Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure