Produit de solubilité de la calcite et constantes de dissociation de CaHCO3+ et CaCO30 entre 5 et 75 °C

Les valeurs du produit de solubilité de la calcite et des constantes de dissociation de CaHCO3+ et CaCO30, notées K3 et K4, ont été déterminées à différentes températures comprises entre 5 et 75 °C (la calcite est instable aux températures plus élevées) à partir des mesures [(Ca2+)T, pH] de solubilité de ce sel dans l'eau carboniquement pure. Les résultats obtenus ont permis d'établir les relations empiriques suivantes :pKs= 7,8156 + 0,03111 T + (1 502/T) - 5,518 log TpK3= 6,2447 + 0,00437 T + (864,479/T) - 0,363 log TpK4= 2,89636 + 0,00707 T + (102,87/T) - 0,44176 log Texpressions dans lesquelles T désigne la température absolue (K) et log le logarithme décimal.Des variations de pKS avec la température nous avons déduit, à 25 °C, les grandeurs thermodynamiques relatives à la dissolution de la calcite :∆H0 = -2510 cal. mol-1, ∆S0 = -47,2 cal. mol-1. K-1et ∆C∘p = -73,9 cal. mol-1. K-1The values of the solubility product of calcite and dissociation constants of CaHCO3+ and CaCO30, K3 and K4 respectively, were determined at several temperatures between 5 and 75 °C (calcite becomes unstable at higher temperatures) from measurements [(Ca2+)T, pH] of calcite solubility using carbonically pure water. The results obtained lead to the following empirical expressions for the dependence of equilibrium constants on the temperature :pKs= 7,8156 + 0,03111 T + (1 502/T) - 5,518 log TpK3= 6,2447 + 0,00437 T + (864,479/T) - 0,363 log TpK4= 2,89636 + 0,00707 T + (102,87/T) - 0,44176 log Twhere log T is the common logarithm of the absolute temperature T(K).Using this expression of pKS, the calculated thermodynamic properties of the calcite dissolution reaction at 25 °C are :∆H0 = -2510 cal. mol-1, ∆S0 = -47,2 cal. mol-1. K-1et ∆C∘p = -73,9 cal. mol-1. K-

Élimination des cations métalliques divalents : complexation par l'alginate de sodium et ultrafiltration

Depuis quelques années la pollution par les métaux lourds et devenue un problème important pour la protection de l'environnement et de nombreuses méthodes ont été développées pour éliminer les métaux toxiques présents dans l'eau.Parmi les différents procédés utilisés, la complexation-ultrafiltration est bien connue et de nombreuses études sur ce sujet sont décrites dans la littérature. Cependant, le choix de nouveaux macroligands hydrosolubles demeure important pour développer cette technologie.L'un des objectifs de ce travail était de montrer que dans ce procédé un biopolymère peut remplacer un macroligand de synthèse. Les expériences ont été menées avec de l'alginate de sodium, polysaccharide extrait des algues brunes, et porteur de groupements carboxyliques et hydroxydes capables de complexer les cations.Notre étude se divise en trois parties. Après avoir décrit, dans la première, le matériau et les méthodes utilisées, nous étudions dans la seconde les conditions de l'ultrafiltration (seuil de coupure, pression appliquée, pH, concentration ), avant de discuter dans la troisième les résultats obtenus dans le traitement de solutions contenant Cd2+, Cu2+, Mn2+ and Pb2+.For some years past, pollution by heavy metals has become one of the main problems for environmental protection. A number of methods have been developed to remove toxic metals from water. Among the various processes used, complexation-ultrafiltration is well known and numerous studies on this subject are described in the literature. However, the choice of new water-soluble macroligands remains important for developing this technology.One aim of the present work was to prove that biopolymers can replace synthetic macroligands in the process. The experiments have been conducted with sodium alginate, a polysaccharide extracted from brown seaweeds and containing carboxylic and hydroxyl groups able to complex heavy cations. Filtration experiments were performed with a frontal system, equipped with a polysulfone membrane with a 20000 Daltons cut-off . The solutions studied were prepared by diluting in demineralized water either sodium alginate or "Titrisol Merck" for cations. Before filtration the two solutions were mixed and stirred for 20 min. The pH of the feed solutions was adjusted with HCl (or HNO3 for Pb) or NaOH and determined accurately using a calibrated probe.The molecular weight of sodium alginate was determined by liquid chromatography and the viscosity was measured with either a viscosimeter for low values or a capillary method for concentrated solutions. Cation concentrations were measured by atomic absorption spectrophotometryBoth permeate and retentate macroligands concentrations were estimated from measurements of total organic carbon (TOC). Following each experiment, chemical cleaning was performed by filtration of HCl, NaOH and water. This procedure was followed by demineralized water filtration, to ensure that the initial permeability was restored.In the first part of the work the ultrafiltration of sodium alginate solutions for different concentrations and various pressures was studied. Experimental results for macroligand retention, deduced from the TOC values, show a total rejection. All the curves, permeate flux versus time, present the same profile which indicates a significant concentration polarization. According to the obtained results we chose the value of 5 10-2 g L-1 for the ligand concentration and one bar for the applied pressure.In the second part of the study, the retention of cations (Cd2+, Cu2+, Mn2+ and Pb2+) was investigated. The observed results show that the removal rates are close to 100%. These values depend both on the total concentration of cation and on the pH value. The retention of cations is shown to depend strongly on pH: a variation of pH between 3 and 5 leads to changes in retention efficiency from 0 to 100%. This can be explained by the dissociation of alginic acid as a function of pH. For lower pH values the macroligand is in a molecular form and the metallic cation remains free; for higher values metal complexation is possible, increasing the rejection. If coordination number, rejection rate and pH are known, the various association constants can be determined using a graphical method. It can be seen from the results that the stability of the complexes formed decreases in the sequence Pb>Cu>Mn>Cd.In order to investigate the retention of these cations in a fresh water, the influence of calcium hardness was studied. The results indicate that cation removal decreases when the calcium concentration increases. This observation is an important restriction for fresh water treatment but does not affect the elimination of metals from a solution or an industrial waste containing cations

Nanofiltration de solutions de nitrate d'ammonium. Etude des paramètres influents

Cet article propose une étude de la rétention du nitrate d'ammonium par une membrane commerciale de nanofiltration (Nanomax 50). Les effets de la pression, de la concentration et de la vitesse d'écoulement tangentiel ont été étudiés avec le souci d'une meilleure compréhension du mécanisme de transport des ions nitrate et en vue d'une optimisation de la rétention. Le taux de rétention des ions nitrate augmente dans un premier temps avec la pression, atteint un maximum puis diminue. La rétention, pour des pressions élevées, peut cependant être améliorée en augmentant la vitesse d'écoulement tangentiel. La séparation résulterait d'un rapport de différentes forces : une force d'entraînement radial dans le pore (illustrée par l'effet de la pression transmembranaire), une force d'entraînement tangentiel vers le rétentat (illustrée par l'effet de la vitesse d'écoulement tangentiel) et une force de surface traduisant les interactions membrane-soluté (illustrée par l'effet de la concentration). L'équation de Spiegler et Kedem est proposée en première approche de modélisation pour une valeur limite de pression.Many water sources deal with the problem of increasing nitrate concentrations above authorised levels for drinking water. In order to minimise this amount of pollution and to achieve high quality of water and reused water in the distribution system, membrane processes are becoming a promising technology. Indeed, they present the major advantages of a small land area requirement, low temperature operation, continuous separation, better effluent quality, little or no sludge production and a large reduction in the quantities of chemical additives. Reverse osmosis has already been used to remove most of the nitrates together with the other solutes, but the disadvantage is that this technique induces a total demineralisation of the treated water. Another possible filtration process, nanofiltration, has been investigated in this study while no extensive research has been carried out on its nitrate removal potential. Theories cannot adequately predict the influence of operating parameters on membrane performance. Consequently, new membranes and modules must be experimentally evaluated for each new application. The main objective of this study was to provide fundamental data for designing an operation of nanofiltration under various operating conditions such as transmembrane pressure, cross-flow velocity and initial feed concentration for drinking water and water reuse purposes.The retention rate rises with an increase of the applied pressure, reaches a maximum and then decreases. Such a result is quite different from those usually mentioned in the literature where the retention increases and reaches a plateau when the pressure grows. The singular decrease of the retention rate observed in this study could be explained in terms of a concentration polarization phenomenon. However, since the volumetric flux increased linearly with the pressure and remained close to the pure water flux, it might be thought that such an assumption is not valid in the case of this work. Therefore, another hypothesis has to be provided to explain the variation of the retention with transmembrane pressure. As the size of NH4+ ion (ionic radius=0.148 nm) is lower than that of the pore of membrane (diameter=1 nm), cations can enter the pores where they are partially retained due to surface forces (electrostatic and friction forces). When the pressure increases, these forces remain constant while drag forces increase due to the flux in the pore. At low pressure (∆P < 5 bars), the surface forces are stronger than the drag forces. Therefore, the solute flux remains low while the solvent flux increases with the pressure, leading to an increase in the solute retention. Above a given pressure (≅ 5 bars), the drag forces become higher than the surface forces. Consequently, the retention rate decreases.As can be observed in the obtained results, the retention rate decreased when the feed concentration was increased regardless of the operating pressure. This effect is mainly attributed to the cation shielding of the effective charge of the membrane. This characteristic can be explained by the fact that the electric repulsion becomes less efficient at higher concentration. It has been recognized that the effective charge density of the membrane decreases with an increase in the feed concentration of an ionic solution. Consequently, the retention rate of the co-ion due to charge effect is reduced. It follows that a greater amount of nitrate ions could permeate when feed solutions of higher concentration are applied.The effect of cross-flow velocity on the fluxes is insignificant since the permeate flux depends only on transmembrane pressure. However, the retention performance increases with velocity. The lower the cross-flow velocity, the higher the interaction between the solute and the membrane. Therefore, at low cross-flow rate, the solute amount that enters the membrane pores is high. When the drag forces become stronger than the surface forces, as explained above, the retention sharply decreases. At high cross-flow velocity, the feed circulation transports a large solute amount and therefore, the solute amount that enters the pores is reduced and is less sensitive to operating pressure. In consequence, the sensitivity of the retention to transmembrane pressure is not so marked. It might be thought that for a very high cross-flow velocity, the retention increases and then remains constant.It was demonstrated in this work that nanofiltration can be successfully used to remove nitrates from water. The retention was shown to depend strongly on operating parameters such as feed solution concentration, applied pressure and circulation cross-flow rate. In fact, the retention is mainly determined by the intensity of the solute / membrane interaction. This interaction comes from two main forces: a tangential one due to the feed solute flow (illustrated by the cross-flow velocity effect) and a radial one in the pores due to drag forces (illustrated by the transmembrane pressure effect). Moreover, it was observed that the valence of the associated ions is an important factor that can affect nitrate retention. It can be expected that the optimization of the separation performance will result of the best combination of all these parameters. Therefore, with a view to a future industrial application, it will be necessary to take into consideration the chemical composition of the resource and to adapt the operating conditions to the desired objectives

Reusability of filtering facepiece respirators after decontamination through drying and germicidal UV irradiation.

During pandemics, such as the SARS-CoV-2, filtering facepiece respirators plays an essential role in protecting healthcare personnel. The recycling of respirators is possible in case of critical shortage, but it raises the question of the effectiveness of decontamination as well as the performance of the reused respirators. Disposable respirators were subjected to ultraviolet germicidal irradiation (UVGI) treatment at single or successive doses of 60 mJ/cm &lt;sup&gt;2&lt;/sup&gt; after a short drying cycle (30 min, 70°C). The germicidal efficacy of this treatment was tested by spiking respirators with two staphylococcal bacteriophages (vB_HSa_2002 and P66 phages). The respirator performance was investigated by the following parameters: particle penetration (NaCl aerosol, 10-300 nm), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry and mechanical tensile tests. No viable phage particles were recovered from any of the respirators after decontamination (log reduction in virus titre &gt;3), and no reduction in chemical or physical properties (SEM, particle penetrations &lt;5%-6%) were observed. Increasing the UVGI dose 10-fold led to chemical alterations of the respirator filtration media (FTIR) but did not affect the physical properties (particle penetration), which was unaltered even at 3000 mJ/cm &lt;sup&gt;2&lt;/sup&gt; (50 cycles). When respirators had been used by healthcare workers and undergone decontamination, they had particle penetration significantly greater than never donned respirators. This decontamination procedure is an attractive method for respirators in case of shortages during a SARS pandemic. A successful implementation requires a careful design and particle penetration performance control tests over the successive reuse cycles

Morphological and functional evaluation of the bioresorption of the bioresorbable everolimus-eluting vascular scaffold using IVUS, echogenicity and vasomotion testing at two year follow-up: a patient level insight into the ABSORB A clinical trial

The aim of this study was to describe vaso-reactivity (by Acetylcholine and Methergine tests) at 2 year follow-up in parallel with the individual changes in the echogenicity characteristics of the polymer struts of the everolimus eluting bioresorbable vascular scaffold (BVS), from post-treatment to 2 year follow-up, in patients enrolled in the ABSORB Cohort A study. Intravascular ultrasound assessment was performed with a phased array catheter (EagleEye, Volcano Corporation, Cordova, CA, USA) with automated pullback at 0.5 mm per second. The % ratio at 6 months and 2 years [(Scaffold Area post PCI- Lumen Area)/Scaffold Area post PCI] was calculated as a measure of scaffold shrinkage. The % change of hyperechogenicity was defined as: ([post-procedural hyperechogenicity] - [2 year follow up hyperechogenicity])/[post-procedural hyperechogenicity]) × 100. The vasomotion test with intracoronary acetylcholine (10-6M) or intravenous methergine (0.4 mg) was performed at 2 years. Overall nine patients received all these analyses and were enrolled in the present analysis. A 50-96% reduction in hyperechogenicity was observed between baseline and 2 years, which corresponded to a change in vasoreactivity between 2 and 22%. A vasoconstriction of the scaffolded segment was observed in the 5 patients, who underwent the methergine test, with a mean decrease in lumen diameter after met

Development of an in vitro culture method for cells and tissues from the zebra mussel (dreissena polymorpha)

Despite the successful transfer of mammalian in vitro techniques for use with fish and other vertebrates, little progress has been made in the area of invertebrate tissue culture. This paper describes the development of an in vitro technique for the culture of both cells in suspension and tissue explants from the gill, digestive gland and mantle of the zebra mussel (Dreissena polymorpha) and their successful maintenance in culture for up to 14 days. Cell suspensions from the gills and digestive gland were the most successful technique developed with viability &amp;gt; 80% maintained for up to 8 days in culture, suitable for use in short term toxicity tests. Tissue explants from the mantle were also maintained in culture for up to 14 days. This paper describes the challenges involved in the development of a novel in vitro culture technique for aquatic invertebrates

Mechanisms of the sensory effects of tacrolimus on the skin

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Sodium channel Na(V)1.5 expression is enhanced in cultured adult rat skeletal muscle fibers.

International audienceThis study analyzes changes in the distribution, electrophysiological propertiesand proteic composition of voltage-gated sodium channels (Na(V)) in cultured adult rat skeletal muscle fibers. Patch clamp and molecular biology techniques were carried out in flexor digitorum brevis (FDB) adult rat skeletal muscle fibers maintained in vitro after cell dissociation with collagenase. After 4 days of culture, an increase of the Na(V)1.5 channel type was observed. This was confirmed by an increase in TTX-resistant channels and by Western blot test. These channels exhibited increased activation time constant (tau(m)) and reduced conductance, similar to what has been observed in denervated muscles in vivo, where the density of Na(V)1.5 was increasing progressively after denervation. By real-time polymerase chain reaction, we found that the expression of beta subunits was also modified, but only after 7 days of culture: increase in beta(1) without beta(4) modifications. beta(1) subunit is known to induce a negative shift of the inactivation curve, thus reducing current amplitude and duration. At day 7, tau(h) was back to normal and tau(m) still increased, in agreement with a decrease in sodium current and conductance at day 4 and normalization at day 7. Our model is a useful tool to study the effects of denervation in adult muscle fibers in vitro and the expression of sodium channels. Our data evidenced an increase in Na(V)1.5 channels and the involvement of beta subunits in the regulation of sodium current and fiber excitability