Incidence de la source de pollution sur la dissolution et la rétention sélective d'hydrocarbures en milieu poreux saturé en eau

Des expérimentations menées sur des modèles-colonnes de milieu poreux, se localisant sur des études de lessivage du corps d'imprégnation formé par des mélanges d'hydrocarbures et sur des essais de propagation de leurs parties solubles, ont été réalisées au laboratoire. Il est montré que le comportement des hydrocarbures en solution pendant le lessivage est fonction de la nature de la source de pollution, et que le transport des traces solubles d'alcanes est fortement freiné par les effets de l'échange liquide-gaz masquant les propriétés adsorbantes de la matrice solide, ou pouvant entraîner une modification du processus de sorption des hydrocarbures par la phase solide.La solubilité n'est pas un critère suffisant pour expliquer la dissolution sélective et progressive des constituants d'un corps d'imprégnation formé par un mélange de plusieurs espèces d'hydrocarbures, et lors du transport des parties solubles d'une telle source de contamination, l'influence des paramètres solubilité, constante de Henry et coefficient de distribution doivent être pris en compte simultanément pour étudier leur rétention sélective.In the case of groundwater contamination hy petroleum products, the constituents of the immiscible pollutant source will be selectively solubilized and transporled over large distances by the water movement. Then, long-term pollution of aquifers is essentially due to the transfer and transport of dissolved hydrocarbon traces. The behaviour of soluble hydrocarbons and the extent of pollution depend on hydrodynamical conditions of the infiltration area and phase partitioning between water, oil, gas and solid in the aquifer.This article deals with some aspects linked to the transfer mechanisms which take place during the selective dissolution of hydrocarbons and those relating to physico-chemicai exchanges accompanying the transport of soluble substances of the pollution source through saturated porous media. The experiments have been conducted with physical models constituted of glass columns : The glass column source of pollution (L = 75 cm, Ф = 10.4 cm) contained both natural quartz land and a motionless oil phase uniformly distributed in quantifies below residual saturation; it allows to study the selective dissolution of the constituents of the impregnation body. The exchange phenomena between phases were examined in a second glass column (L = 70 cm, Ф = 9.3 cm) which received the water charged with dissolved hydrocarbons coming from the glass column source, and filled with solid matrixes which were not contaminated at the beginning. The solid phase in the second glass column consisted of quartz sand or a mixture of agricultural soil and sand. The soil contained an average of 1.3 % of organic materials, 6.7 % of clay minerals and 27 % of limestone. The influence of the adsorbing properties of the solid material and the role of residual air on the transport and retention of soluble hydrocarbons were investigated. The variation of residual air content was obtained according to the filling method of the second glass column : “dry filling” favours the presence of the gaseous phase (water introduced by imbibition); “lifting by sedimentation” can reduce or partially avoid it (the second column is filled with the porous medium under water).For a pollutant source made of a mixture of hydrocarbons at equal fractions and belonging to a same homologous series (alkanes and aromatics), the experimental results allowed to establish the importance of solubility parameter as well on the mode of selective leaching of the impregnation body, as on the selective retention of soluble elements of the pollutant source.The behaviour of the constituents of the pollution source made of several hydrocarbon species appears differently and then, the solubility dues not constitute, for such a source, a sufficient criterion to apprehend the observed transfer and exchange mechanisms.- Selective dissolution : the modifications of behaviour especially result to the fact that some components of the pollution source are represented at very low proportions then, they can’t respect, during the partition phenomenon, the gradation of solubility values as well at the beginning of the leaching of the impregnation body, as at the decreasing stages of concentrations. This situation must be regarded for studying the transfer of soluble hydrocarbons after accidental spill of petroleum products because it will affect the transport and the contamination prediction.- Exchange phenomena : we observed that the liquid/gas exchange is the major factor of retention of soluble alkanes masking the effects of adsorbing materials. The influence of adsorbing character of the solid material appears clearly, only when the air content of the porous matrix is low. On the other band, the residual air content has no influence on the transport of soluble monoaromatics but the main phenomenon observed is in that case the liquid/solid exchange.Moreover, the impact of the gaseous phase on the alkanes involves a modification of sorption process of hydrocarbons by the solid phase : the selective retention of various constituents of a pollution source made of several hydrocarbon species should be interpreted by the knowledge at their respective distribution coefficient Kd as it was admitted by several authors, when the air content of the porous matrix is low. The sorption process should be more complex when the residual air content is great because the gaseous phase plays a preponderant role for the alkanes; in that case, the simultaneous effects of the solubility, the Henry's constant and the distribution coefficient must be taken into account together for getting a best understanding of each component behaviour of the pollution source and assessing their fate in the case of alluvial aquifer contamination

SANS from Salt-Free Aqueous Solutions of Hydrophilic and Highly Charged Star-Branched Polyelectrolytes

International audienceScattering functions of sodium sulfonated polystyrene (NaPSS) star-branched polyelectrolytes with high sulfonation degrees were measured from their salt-free aqueous solutions, using the Small Angle Neutron Scattering (SANS) technique. Whatever the concentration c, they display two maxima. The first, of abscissa q 1 *, is related to a position order between star cores and scales as q 1 * 9 c 1/3. The second, of abscissa q 2 *, is also observed in the scattering function of a semi-dilute solution of NaPSS linear polyelectrolytes. In the dilute regime (c < c*, non-overlapping stars), peak abscissa does not depend on concentration c and is just an intramolecular characteristic associated with the electrostatic repulsion between arms of the same star. In the semi-dilute regime, due to the star interpenetration, the scattering function – through the peak position, reflects repulsion between arms of the same star or of different stars. The c threshold between these distinct c-dependencies of q 2 * in the dilute and semi-dilute regimes is estimated as c*. Just as simple is the measurement of the geometrical radius R of the star obtained from the q 1 * value at c* through the relation 2R = 2π/q 1 *. By considering NaPSS stars of the same functionality with different degrees of polymerization per arm N a , we find R scaling linearly with N a , suggesting an elongated average conformation of the arms. This is in agreement with theoretical predictions and simulations. Meanwhile the value of q 2 * measured in the dilute regime does not allow any inhomogeneous counterion distribution inside the stars to be revealed

Cutaneous Burn Injury Modulates Urinary Antimicrobial Peptide Responses and the Urinary Microbiome

OBJECTIVES: Characterization of urinary bacterial microbiome and antimicrobial peptides after burn injury to identify potential mechanisms leading to urinary tract infections and associated morbidities in burn patients. DESIGN: Retrospective cohort study using human urine from control and burn subjects. SETTING: University research laboratory. PATIENTS: Burn patients. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Urine samples from catheterized burn patients were collected hourly for up to 40 hours. Control urine was collected from "healthy" volunteers. The urinary bacterial microbiome and antimicrobial peptide levels and activity were compared with patient outcomes. We observed a significant increase in urinary microbial diversity in burn patients versus controls, which positively correlated with a larger percent burn and with the development of urinary tract infection and sepsis postadmission, regardless of age or gender. Urinary psoriasin and β-defensin antimicrobial peptide levels were significantly reduced in burn patients at 1 and 40 hours postadmission. We observed a shift in antimicrobial peptide hydrophobicity and activity between control and burn patients when urinary fractions were tested against Escherichia coli and Enterococcus faecalis urinary tract infection isolates. Furthermore, the antimicrobial peptide activity in burn patients was more effective against E. coli than E. faecalis. Urinary tract infection-positive burn patients with altered urinary antimicrobial peptide activity developed either an E. faecalis or Pseudomonas aeruginosa urinary tract infection, suggesting a role for urinary antimicrobial peptides in susceptibility to select uropathogens. CONCLUSIONS: Our data reveal potential links for urinary tract infection development and several morbidities in burn patients through alterations in the urinary microbiome and antimicrobial peptides. Overall, this study supports the concept that early assessment of urinary antimicrobial peptide responses and the bacterial microbiome may be used to predict susceptibility to urinary tract infections and sepsis in burn patients

The Benefits of an Innovative Literacy Assessment Field Experience

In many fields of study, an internship or experiential practice is an essential part of learning the discipline. In education, those experiences are often clinical field placements in methods courses or student teaching. The combination of field work while learning the content has many benefits, which we sought to determine. This research study explores the benefits of an embedded field experience in a university literacy assessment course for preparing pre- and in-service teachers as they implement effective literacy assessments and instruction. Based on Kolb’s Experiential Learning Theory (1984), pre- and in-service teachers interacted with elementary students over a ten week span to administer an informal literacy assessment, analyze the data, and apply instructional strategies to support the literacy strengths and needs of the students. This mixed-methods research was conducted using the triangulation of four data points – an online survey and three course assignments – and findings are conclusive with previous research

Draft Genome Sequence of Clinical Isolate Alcaligenaceae sp. Strain 429

Here, we present the 3.53-Mb genome for Alcaligenaceae sp. strain 429, isolated from a patient with unknown etiology. While the 16S rRNA gene most closely resembles Paenalcaligenes species, average amino acid identity (AAI) analysis did not meet the threshold to classify our strain as a species of this family

La critique d'auteur dans les lettres françaises L'homme aux figures de cire de Champfleury

Periodista, dramaturgo y novelista, Champfleury es también famoso por su importante contribución a la crítica literaria. Considerado jefe del realismo, sus ideas se encuentran en sus textos de investigación, sobre todo en El realismo, pero también en sus obras de ficción. Es el caso de El hombre de las figuras de cera, relato corto que ilustra perfectamente sus ideas acerca de la representación estética.46 página

Early stages of leaf decomposition are mediated by aquatic fungi in the hyporheic zone of woodland streams

1. Leaf litter constitutes the major source of organic matter and energy in woodland stream ecosystems. A substantial part of leaf litter entering running waters may be buried in the streambed as a consequence of flooding and sediment movement. While decomposition of leaf litter in surface waters is relatively well understood, its fate when incorporated into river sediments, as well as the involvement of invertebrate and fungal decomposers in such conditions, remain poorly documented. 2. We tested experimentally the hypotheses that the small interstices of the sediment restrict the access of the largest shredders to buried organic matter without compromising that of aquatic hyphomycetes and that fungal decomposers in the hyporheic zone, at least partly, compensate for the role of invertebrate detritivores in the benthic zone. 3. Alder leaves were introduced in a stream either buried in the sediment (hyporheic), buried after 2 weeks of exposure at the sediment surface (benthic-hyporheic), or exposed at the sediment surface for the entire experiment (benthic). Leaf decomposition was markedly faster on the streambed surface than in the two other treatments (2.1- and 2.8-fold faster than in the benthic-hyporheic and hyporheic treatments, respectively). 4. Fungal assemblages were generally less diverse in the hyporheic habitat with a few species tending to be relatively favoured by such conditions. Both fungal biomass and sporulation rates were reduced in the hyporheic treatment, with the leaves subject to the benthic-hyporheic treatment exhibiting an intermediate pattern. The initial 2-week stage in the benthic habitat shaped the fungal assemblages, even for leaves later subjected to the hyporheic conditions. 5. The abundance and biomass of shredders drastically decreased with burial, except for Leuctra spp., which increased and was by far the most common leaf-associated taxon in the hyporheic zone. Leuctra spp. was one of the rare shredder taxa displaying morphological characteristics that increased performance within the limited space of sediment interstices. 6. The carbon budgets indicated that the relative contributions of the two main decomposers, shredders and fungi, varied considerably depending on the location within the streambed. While the shredder biomass represented almost 50% of the initial carbon transformed after 80 days in the benthic treatment, its contribution was <0.3% in the hyporheic one and 2.0% in the combined benthic-hyporheic treatment. In contrast, mycelial and conidial production in the permanently hyporheic environment accounted for 12% of leaf mass loss, i.e. 2–3 times more than in the two other conditions. These results suggest that the role of fungi is particularly important in the hyporheic zone. 7. Our findings indicate that burial within the substratum reduces the litter breakdown rate by limiting the access of both invertebrate and fungal decomposers to leaves. As a consequence, the hyporheic zone may be an important region of organic matter storage in woodland streams and serve as a fungal inoculum reservoir contributing to further dispersal. Through the temporary retention of litter by burial, the hyporheic zone must play a significant role in the carbon metabolism and overall functioning of headwater stream ecosystems

Soviet arms control policy: A means toward what end

Thesis (B.A.) in Russian and East European Studies--University of Illinois at Urbana-Champaign, 1983.Bibliography: leaves 62-64.Microfiche of typescript. [Urbana, Ill.] : Photographic Services, University of Illinois, U of I Library, [1983]. 2 microfiches (70 frames) : negative ; 11 x 15 cm