Approche des transferts de pollution bactérienne dans une crue karstique par l'étude des paramètres physico-chimiques

L'exploitation des systèmes aquifères karstiques est toujours effectuée sous des contraintes liées à leur forte vulnérabilité. Une étude complète d'un épisode de crue de la source du Lez a été réalisée grâce à une coopération entre les Services de Santé et l'Université. Cette étude comporte une observation des paramètres physico-chimiques et bactériologiques sur une période de 15 jours, correspondant à une réponse hydrodynamique impulsionnelle sur la totalité du bassin. Les pas de temps d'échantillonnage varient de 4 à 24 heures.L'interprétation des résultats physico-chimiques met en évidence une disjonction nette entre les variations piézométriques et le passage de différents volumes d'eau. L'écoulement des eaux plus chaudes (16,5 °C) observé lors de l'étiage, eaux d'origine profonde plus chargées chimiquement se poursuit jusque vers le milieu de la décrue pour faire place à l'arrivée d'eaux plus froides correspondant à des infiltrations rapides puis retardées. Les eaux les plus chaudes sont caractérisées par des variations des teneurs en magnésium, les teneurs en calcium restant à peu prés constantes. Inversement; les eaux froides de l'infiltration retardée ont de faibles variations des teneurs en magnésium et sont tracées par une forte augmentation des valeurs en calcium.Le risque sanitaire maximal est lié au début de l'arrivée des eaux froides. Les eaux d'étiage et les eaux profondes sont légèrement contaminées. Les eaux d'infiltration retardée sont peu contaminées. En dehors des zones de perte du réseau hydrographique et des axes d'infiltration rapide, la vulnérabilité de l'aquifère est faible à l'échelle du bassin.The exploitation of karstic aquifer systems for the supply of potable water raises the problem of the evaluation of sanitary risks, in view of their great vulnerability. To supply a great urban tenter, a yield as high as several cubic metres per hour is required, and this magnitude corresponds to that of an underground basin of several km2, so that it is difficult to monitor and protect.Analytical observations from sanitary control platforms on potable water catchments have shown the existence of periods of high bacteriological pollution synchronizing systematically with periods of a rise of water.These bacteriological pollution transfers depend on the general conditions in which the aquifer functions. It seemed interesting, for the prevention of contamination, to examine all these hydrogeologic functions observed during a water rise, using bacteriological parameters.This study was based on observations made during an overall flood period following a prolonged drought throughout the whole basin supplying the city of Montpellier (France). The aim was to carry out a correlation test on the functioning of a karstic aquifer, with regard to :- the variation of the main physico-chemical parameters,- the principal pathogenic germs,- the commonly observed indicators of faecal contamination.This operation, undertaken in close collaboration with the sanitation board and the university authorities, required considerable investment in human, materiat and financial resources.Montpellier, a city with a population of 250 000 inhabitants, is supplied with potable water from the source of the River Lez. The water catchment is-situated upstream of a. major resurgence (12 m3/s during the water rise), tapping water from a principal drainage channel at a depth of 40 metres.The area of the basin feeding the spring was evaluated to be 150 km2 by adjustment to the 450 km2 of Jurassic and Cretaceous outcropping certified limestone, north of Montpellier. Even if the limits of the basin are not precisely defined, some of its parameters are well known. The aquifer consists of different structural zones, almost like independent sub-systems, having in common a rapid drainage network. The response observed at the exurgence is compared globally with the pluviometric signs, as well as with the effects produced in each structural zone, the transfer time, chemistry, temperature, recession, etc.The whole aquifer must be considered under pressure and it is this state of pressure which is probably responsible for the directional flow of the water from the rock matrix and of that circulating in the major karstification areas. The aquifer may be either in a state of injection or drainage and this notion is supported by the chemical and thermal fluctuations at the exurgence point.A one-year experimental programme, based on our knowledge of this aquifer, has been set up in collaboration with forecasters at the National Meteorological Office. All have been on the alert and ready to intervene, equipped with all the necessary staff and apparatus to ensure reliable sampling and analyses. The following procedures were performed :- sampling every 4 hours during the first 48 hours ;- sampling every 12 hours during the following 48 hours.Then until the end of the study, sampling took place every 24 hours with :- 1 bacteriological sample in sterile condition,- 1 sample for physico-chemical analyses in the laboratory,- temperature measurements with a 1/10° mercury thermometer,- resistivity measurements,- pH measurements with two standards,- a limigraphic reading.This period of water rise, hydrologically homogeneous throughout the whote basin in the form of a single impulsive response tasting about 10 days, was characterised by the circulation of two types of water masses : from the rock matrix and resutting from rapid infiltration. The mixture of these two bodies, each with a distinct chemical character, is a function of the state of pressure in the aquifer. At the end of the rise, a third type of water intervenes, that of retarded infiltration.The best criteria for identifying these volumes of water are thermal ones. The most variable elements are magnesium and calcium. Deep waters with a temperature of 16 °5 are characterised by a variation in magnesium, and cold water, by a variation in calcium. The highest value of calcium is related to the passage of water bodies attributed to the influence of retarded infiltration.The geological observations and the processing of results by factorial analyses show a clear distinction between the chemical rise and the piezometric rise. The hydraulic rise point is constituted by water with the saure chemical characteristics as that of the lowest water level. The most important dilution due to rapid transfer in the basin is observed in the middle of the water fait. These synchronized with the highest batteriological pollution rate for most of the elements.This study has provided a global appreciation of the sanitary risks and shows how pollution mechanisms function. Risks are permanent, even during the passage of the deepest water with a long residence time. This phenomenon raises the question of the duration and mode of survive of non encystable bacteria indicators in the karst system. The survival time appeared to be about a year or more.There is always a covariation between the physico-chemical elements and bacteriological pollution where the aquifer is under high pressure and when the water rises or has reached its maximum level, or when the water starts to fall. It is when the level of the water starts to drop that the main peaks of bacteriological pollution are observed. From this moment onwards, the whole basin functions like a drained system and the absence of covariation in the physico-chemical and bacteriological parameters are signs that the flow has become heterogeneous.For sanitation purposes it may be sufficient to monitor temperature and other chemical elements, in order to determine when an additional treatment of the water is required to maintain its potability. An appropriate apparatus is being devised to this end

On unitarizability in the case of classical p-adic groups

In the introduction of this paper we discuss a possible approach to the unitarizability problem for classical p-adic groups. In this paper we give some very limited support that such approach is not without chance. In a forthcoming paper we shall give additional evidence in generalized cuspidal rank (up to) three.Comment: This paper is a merged and revised version of ealier preprints arXiv:1701.07658 and arXiv:1701.07662. The paper is going to appear in the Proceedings of the Simons Symposium on Geometric Aspects of the Trace Formul

Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions

The weak nucleon axial-vector form factor for quasi-elastic interactions is determined using neutrino interaction data from the K2K Scintillating Fiber detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of which half are charged-current quasi-elastic interactions nu-mu n to mu- p occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for oxygen and assume the form factor is approximately a dipole with one parameter, the axial vector mass M_A, and fit to the shape of the distribution of the square of the momentum transfer from the nucleon to the nucleus. Our best fit result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated vector form factors from recent electron scattering experiments and a discussion of the effects of the nucleon momentum on the shape of the fitted distributions.Comment: 14 pages, 10 figures, 6 table

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde

Inclusive search for same-sign dilepton signatures in pp collisions at root s=7 TeV with the ATLAS detector

An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from p p collisions at root s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb(-1). The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, e mu and mu mu channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation d-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. A lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks

Measurement of inclusive two-particle angular correlations in pp collisions with the ATLAS detector at the LHC

We present a measurement of two-particle angular correlations in proton- proton collisions at s√=900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum p T  > 100 MeV and pseudorapidity |η| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to pythia 8 and herwig++ as well as to the AMBT2B, DW and Perugia 2011 tunes of pythia 6. The data are not satisfactorily described by any of these models

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Position resolution and particle identification with the ATLAS EM calorimeter

In the years between 2000 and 2002 several pre-series and series modules of the ATLAS EM barrel and end-cap calorimeter were exposed to electron, photon and pion beams. The performance of the calorimeter with respect to its finely segmented first sampling has been studied. The polar angle resolution has been found to be in the range 50-60 mrad/sqrt(E (GeV)). The neutral pion rejection has been measured to be about 3.5 for 90% photon selection efficiency at pT=50 GeV/c. Electron-pion separation studies have indicated that a pion fake rate of (0.07-0.5)% can be achieved while maintaining 90% electron identification efficiency for energies up to 40 GeV.Comment: 32 pages, 22 figures, to be published in NIM

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal