Évolution de la qualité de l'eau dans le réseau de distribution de la ville de Montréal

Dans la présente étude, nous montrons l'évolution de l'eau dans un réseau de distribution. Ce réseau a été construit dans les années 70 à l'aide de conduites d'acier ou de fonte ductile munies d'un revêtement intérieur de ciment. Il est alimenté par des eaux de très bonne qualité qui circulent d'abord dans une suite de conduites maîtresses (de 2 700 mm à 900 mm) jusqu'à un secteur de petites conduites maillées (200 et 300 mm). Des échantillons d'eau ont été prélevés à 14 reprises durant une année, le long de la conduite maîtresse (le temps de séjour y varie de 0 h à 13,6 h) et dans le secteur de petites conduites (de 13,6 h à 18,4 h). Nous avons mesuré la température, le pH, plusieurs sous-produits de désinfection dont les trihalométhanes et les aldéhydes, le carbone organique total et biodégradable ainsi que les concentrations de bactéries hétérotrophes aérobies et anaérobies facultatives (BHA) et les comptes directs totaux mesurés en épifluorescence. Le réseau a très peu d'effet sur l'évolution des sous-produits de désinfection. En effet, les résultats obtenus à partir des échantillons témoins (eaux traitées conservées dans un flacon propre à la même température que dans le réseau) sont semblables à ceux obtenus à partir des eaux prélevées dans le réseau de distribution.Les concentrations de bactéries ainsi que les concentrations de CODB sont assez stables dans le réseau. Il est intéressant de noter qu'il y a de 0,2 à 0,45 mg/l de CODB, ce qui est supérieur à la concentration minimale de 0,15 mg/l requise pour la croissance des bactéries. Par contre, le chlore résiduel libre est toujours supérieur à 0,20 mg/l. Une seule exception, le 11 juillet 1994, dans le secteur de petites conduites, le chlore résiduel a baissé jusqu'à 0,16 mg/l. Durant cette journée, nous avons observé une légère augmentation des comptes directs totaux mesurés en épifluorescence.Studies were performed to follow the changes in water quality along a distribution system. The distribution system under study is divided into two parts: main pipes starting from the plant (from 2 700 mm to 900 mm diameter) feeding a small pipes sector (200 mm and 300 mm diameter). Residence times range from 0 to 13.6 hours in main pipes and from 13.6 h to 18.4 h in small pipes. All pipes are made of steel or ductile iron and their interior is lined with concrete; there is therefore little corrosion. Since the raw water is of such high quality, the treatment plant is very simple: a direct filtration on sand followed by ozonation and chlorine disinfection. Samples were taken on 14 occasions, during a full year period, in the distribution system and in the treatment plant after chlorination. These last samples were incubated in clean flasks at the network temperature. Measurements of temperature, pH, disinfection by-products (trihalomethanes, aldehydes, haloacetonitriles, haloacetones and chloropicrine), total organic carbon (TOC), biodegradable dissolved organic carbon (BDOC) and number of bacteria (heterotrophic plate count and total direct count by epifluorescence) were completed.The distribution network seems to have very little effect on chlorine demand and disinfection by-products. Results from water incubated in flasks are similar to those from distribution network. After more than 18 hours contact time, the chlorine residual is still higher than 0.2 mg/l in most of the samples taken in the distribution network and in the flask. It should be noted that the initial chlorine concentrations range from 0.65 mg/l (cold water) to 1.00 mg/l (warm water). Chlorine demand and trihalomethane (THM) curves are typical, a rapid increase with time followed by a relatively stable level. THM concentrations in the distribution network are low: a typical value of 14 µg/l after 13.6 hours contact time is detected. The maximum concentration of 43 µg/l of total THM was measured in a dead end. In this latter sample, 42 % of the THM was present as bromodichloromethane and 39 % as chloroform. Other by-products such as haloacetonitrile, haloacetone and chloropicrine were always detected in very small concentrations.Aldehyde concentrations in treated water were low, between 21 and 42 µg/l. These concentrations were stable throughout the distribution system. Fixed and free biomass seems to have very little effect on these biodegradable compounds. These results were confirmed by BDOC results. BDOC in treated water ranges from 0.2 to 0.45 mg/l and remains stable in the distribution system. These low BDOC concentrations and the chlorine residual of approximately 0.2 mg/l seem to be sufficient to prevent regrowth in the distribution system. Total direct counts by epifluorescence showed almost no increase of bacterial density except for the July 11th sample. This is the only day where the free chlorine residual dropped below 0.2 mg/l, with values of free chlorine residual dropping as low as 0.16 mg/l

Evidence for spin liquid ground state in SrDy2_2O4_4 frustrated magnet probed by muSR

Muon spin relaxation ($\mu$SR) measurements were carried out on SrDy$_2$O$_4$, a frustrated magnet featuring short range magnetic correlations at low temperatures. Zero-field muon spin depolarization measurements demonstrate that fast magnetic fluctuations are present from $T=300$ K down to 20 mK. The coexistence of short range magnetic correlations and fluctuations at $T=20$ mK indicates that SrDy$_2$O$_4$ features a spin liquid ground state. Large longitudinal fields affect weakly the muon spin depolarization, also suggesting the presence of fast fluctuations. For a longitudinal field of $\mu_0H=2$ T, a non-relaxing asymmetry contribution appears below $T=6$ K, indicating considerable slowing down of the magnetic fluctuations as field-induced magnetically-ordered phases are approached.Comment: 6 pages, 4 figures, to be published as a proceeding of HFM2016 in Journal of Physics: Conference Series (JPCS

Fermi-surface topology of the iron pnictide LaFe2_2P2_2

We report on a comprehensive de Haas--van Alphen (dHvA) study of the iron pnictide LaFe$_2$P$_2$. Our extensive density-functional band-structure calculations can well explain the measured angular-dependent dHvA frequencies. As salient feature, we observe only one quasi-two-dimensional Fermi-surface sheet, i.e., a hole-like Fermi-surface cylinder around $\Gamma$, essential for $s_\pm$ pairing, is missing. In spite of considerable mass enhancements due to many-body effects, LaFe$_2$P$_2$ shows no superconductivity. This is likely caused by the absence of any nesting between electron and hole bands.Comment: 5 pages, 4 figure

Evolution of shell structure in neutron-rich calcium isotopes

We employ interactions from chiral effective field theory and compute the binding energies and low-lying excitations of calcium isotopes with the coupled-cluster method. Effects of three-nucleon forces are included phenomenologically as in-medium two-nucleon interactions, and the coupling to the particle continuum is taken into account using a Berggren basis. The computed ground-state energies and the low-lying 2+ states for the isotopes 42,48,50,52Ca are in good agreement with data, and we predict the excitation energy of the first 2+ state in 54Ca at 1.9 MeV, displaying only a weak sub-shell closure. In the odd-mass nuclei 53,55,61Ca we find that the positive parity states deviate strongly from the naive shell model.Comment: 5 pages, 4 figures; small correction of effective 3NF and slight change of the corresponding parameters; updated figures and tables; main results and conclusions unchange

Structures of a deAMPylation complex rationalise the switch between antagonistic catalytic activities of FICD.

The endoplasmic reticulum (ER) Hsp70 chaperone BiP is regulated by AMPylation, a reversible inactivating post-translational modification. Both BiP AMPylation and deAMPylation are catalysed by a single ER-localised enzyme, FICD. Here we present crystallographic and solution structures of a deAMPylation Michaelis complex formed between mammalian AMPylated BiP and FICD. The latter, via its tetratricopeptide repeat domain, binds a surface that is specific to ATP-state Hsp70 chaperones, explaining the exquisite selectivity of FICD for BiP's ATP-bound conformation both when AMPylating and deAMPylating Thr518. The eukaryotic deAMPylation mechanism thus revealed, rationalises the role of the conserved Fic domain Glu234 as a gatekeeper residue that both inhibits AMPylation and facilitates hydrolytic deAMPylation catalysed by dimeric FICD. These findings point to a monomerisation-induced increase in Glu234 flexibility as the basis of an oligomeric state-dependent switch between FICD's antagonistic activities, despite a similar mode of engagement of its two substrates - unmodified and AMPylated BiP

Liposome Co-sedimentation and Co-flotation Assays to Study Lipid-Protein Interactions

A large proportion of proteins are expected to interact with cellular membranes to carry out their physiological functions in processes such as membrane transport, morphogenesis, cytoskeletal organization, and signal transduction. The recruitment of proteins at the membrane-cytoplasm interface and their activities are precisely regulated by phosphoinositides, which are negatively charged phospholipids found on the cytoplasmic leaflet of cellular membranes and play critical roles in membrane homeostasis and cellular signaling. Thus, it is important to reveal which proteins interact with phosphoinositides and to elucidate the underlying mechanisms. Here, we present two standard in vitro methods, liposome co-sedimentation and co-flotation assays, to study lipid-protein interactions. Liposomes can mimic various biological membranes in these assays because their lipid compositions and concentrations can be varied. Thus, in addition to mechanisms of lipid-protein interactions, these methods provide information on the possible specificities of proteins toward certain lipids such as specific phosphoinositide species and can hence shed light on the roles of membrane interactions on the functions of membrane-associated proteins.Peer reviewe

Refractive index matched, nearly hard polymer colloids

Refractive index matched particles serve as essential model systems for colloid scientists, providing nearly hard spheres to explore structure and dynamics. The poly(methyl methacrylate) latexes typically used are often refractive index matched by dispersing them in binary solvent mixtures, but this can lead to undesirable changes, such as particle charging or swelling. To avoid these shortcomings, we have synthesized refractive index matched colloids using polymerization-induced self-assembly (PISA) rather than as polymer latexes. The crucial difference is that these diblock copolymer nanoparticles consist of a single core-forming polymer in a single non-ionizable solvent. The diblock copolymer chosen was poly(stearyl methacrylate)-poly(2,2,2trifluoroethyl methacrylate) (PSMA-PTFEMA), which self-assembles to form PTFEMA core spheres in n-alkanes. By monitoring scattered light intensity, n-tetradecane was found to be the optimal solvent for matching the refractive index of such nanoparticles. As expected for PISA syntheses, the diameter of the colloids can be controlled by varying the PTFEMA degree of polymerization. Concentrated dispersions were prepared, and the diffusion of the PSMA-PTFEMA nanoparticles as a function of volume fraction was measured. These diblock copolymer nanoparticles are a promising new system of transparent spheres for future colloidal studies

Beyond paradigm : The ‘what’ and the ‘how’ of classroom research

This article reviews studies in second language classroom research from a cross-theoretic perspective, arguing that the classroom holds the potential for bringing together researchers from opposing theoretical orientations. It shows how generative and general cognitive approaches share a view of language that implicates both implicit and explicit knowledge, and that holds a bias towards implicit knowledge. Arguing that it is implicit knowledge that should be the object of research, it proposes that classroom research would benefit from incorporating insights from a generative understanding of language. Specifically, there is a need for a more nuanced view of the complexity of language in terms of linguistic domain, and the interaction between those domains. Generative second language acquisition research that shows developmental differences in terms of both linguistic domain and interface is reviewed. The core argument is a call for more attention to the ‘what’ of language development in classroom research and, by implication, teaching practice. As such, the language classroom is seen to offer potential for research that goes beyond paradigm to address both the ‘what’ and the ‘how’ of language development