Ni uptake by a green alga. 2. Validation of equilibrium models for competition effects

It is generally admitted that the presence of major cations and H+ can attenuate trace metal uptake. Recent models such as the biotic ligand model (BLM) aim to quantify and predict this effect by determining stability constants for each of the major competitors for any given interaction of a trace metal with a biological organism. In this study, short-term Ni internalization fluxes (J(int)) were used to quantitatively assess the binding of H+, Mg2+, Ca2+ (K(H-Rs), K(Mg-Rs), K(Ca-Rs)), and trace metals to transport sites (R(s)) leading to Ni biouptake by Chlamydomonas reinhardtii. H+ and Mg2+ are shown to compete directly for the entry of Ni with affinity constants that are of the same order of magnitude (K(Mg-Rs) = 10(5.1) M(-1); K(H-Rs) = 10(5.3) M(-1)) as that measured for Ni (K(Ni-Rs) = 10(5.1) M(-1)). The Ni internalization fluxes were also strongly linked to the Mg cell status. In contrast, the role of Ca2+ could not be explained by a simple competitive equilibrium with the Ni transport sites. Aluminum (K(Al-Rs) = 10(8) M(-1)), Zn (K(Zn-Rs) = 10(6.5) M(-1)), and Cu (K(Cu-Rs) = 10(6.6) M(-1)) were all shown to compete strongly with Ni for uptake. In addition to the determination of uptake constants, these studies provide insight into the transport mechanisms of Ni by the green alga, C. reinhardtii.     

TRANSPORT MEASUREMENTS THROUGH MEMBRANES BY DRYING

Drying porous asymmetric ultrafiltration membranes can be accomplished either through the dense skin or the porous bottom side. In both cases the opposite side of the membranes is made tight by a flat plate. When the water is transported through the dense skin only one constant drying period and one period of falling rate can be observed, whereas for the drying through the porous sublayer two constant and two falling rate periods can be seen. Using a modified two capillary model for the drying behavior the water transport through both sides of the membranes and the surface porosity can be estimated.     

Structural studies of the phase separation in the UO2–PuO2–Pu2O3 ternary system

In the oxygen hypo-stoichiometric range of (U_1?yPu_y)O_2?x mixed oxide MOX fuels, the U–Pu–O phase diagram is known to exhibit a large biphasic domain depending on the Pu content. However, the phase equilibria are still to be fully described as various representations are proposed in the literature.In the present work, we notify new insights into the phase separation occurring in the UO₂–PuO₂–Pu₂O₃ domain at room temperature. Our microstructural and X-ray diffraction results are compared to the different representations reported in the literature. We provide, for the first time in the hypo-stoichiometric domain, an indisputable experimental observation of a triphasic region at high Pu content, composed of two fluorite-type structures and of one α-Pu₂O₃ sesquioxyde type structure. These results are in contradiction with previous experimental representations of the U–Pu–O ternary system.     

Suspended sediment concentration in relation to forestry operations in Catamaran Brook and its tributaries (Canada)

The Catamaran Brook Habitat Research Project is a 15‐year investigation of river processes and potential impacts of forestry activities on Atlantic salmon (Salmo salar) and its freshwater lotic habitats. Suspended sediments have been sampled in Catamaran Brook and its tributaries from 1990 to 1997. Data on total event precipitation and hourly peak discharge were related to suspended sediment concentration (SSC) under different catchment conditions (dry vs. wet) and treatment (absence or occurrence of timber harvesting). Although SSC generally showed a good correlation to total event precipitation and hourly peak discharge, there was no clear evidence that forestry operations were an important factor within the main Catamaran Brook during the timber harvesting year and the year that followed. Such was not the case for SSC in small tributaries draining directly from cut blocks during logging. In fact, the highest concentrations of suspended sediment were measured in small tributaries draining cut blocks during timber harvesting (with a maximum SSC of 404 mg L⁻¹ in Tributary 1). Within the main Catamaran Brook, a dilution effect rapidly decreased these values downstream of affected tributaries. Processes related to the transfer of sediment to the streams are discussed. Potential improvements in river management and operational timing with respect to the timing of harvesting activities as it relates to precipitation, discharge, catchment conditions (dry vs. wet), freezing/thawing, and salmon migration are also discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

Elaboration and dielectric property of modified PZT/epoxy nanocomposites

Composites of lead zirconate titanate (PZT) 50 nm nanoparticles and epoxy resins have been produced with various PZT contents from 0 to 20 wt%. The morphology and thermal properties of prepared composites were characterized using scanning electron microscopy and differential scanning calorimetry. The PZT nanoparticles were found to be well dispersed in the epoxy resin matrix. The glass transition temperature (T_g) value of the nanocomposites increases from 164 to 178°C with increasing the PZT weight fraction. The dielectric composites properties dependences were studied via a wide range of frequency from 10 Hz to 100 kHz. The dielectric constant of PZT/epoxy composite was increased from 5.56 to 6.29 (at f = 1 kHz, T = 30°C), respectively to the incorporated PZT amount, and these values are higher than that the dielectric constant of pure cured epoxy resin, ε = 4.86. POLYM. COMPOS., 37:455–461, 2016. © 2014 Society of Plastics Engineers     

Treatment of odorous sulphur compounds by chemical scrubbing with hydrogen peroxide--stabilisation of the scrubbing solution

To slow down the hydrogen peroxide decomposition in basic aqueous conditions, the addition of stabilizers and co-stabilizers in the scrubbing solution was investigated. Results found with sodium silicate (Na2SiO3) were quite promising but several problems still remained. Based on these observations, this study focused on the research of a better stabilizer. Several ways were investigated: the use of silicate solutions employed in pulp industries, the addition of co-stabilizers to sodium silicate, or the use of an another stabilizer (the poly-alpha-hydroxyacrylic acid). Experiments revealed that the poly-alpha-hydroxyacrylic acid is the best stabilizing compound.     

Determination of aroma compound diffusion in model food systems: Comparison of macroscopic and microscopic methodologies

Diffusion properties at macroscopic and microscopic scales for three aroma compounds (in solution and gel systems) were characterized using three different methodologies: the diffusion cell and the Volatile Air Stripping Kinetic methods for the determination of apparent diffusion coefficients and the pulsed-field-gradient Nuclear Magnetic Resonance method for the determination of self-diffusion coefficients. The accuracy of the methods was established by comparing ethyl hexanoate diffusion coefficient in water or D₂O solution and in 1%-agar gel system at 25 and 30 °C. The robustness of the three methodologies was also investigated in 1%-iota-carrageenan system with different NaCl content leading to gel strengthening.     

Retention/release equilibrium of aroma compounds in fat‐free dairy gels

BACKGROUND: The replacement of fat by thickeners in fat‐free yoghurts leads to an important modification of aroma compound partitioning, with an impact on aroma perception. Investigation of retention/release equilibria allows a good understanding of aroma compound behaviour depending on food composition. RESULTS: Vapour/liquid equilibria of ten aroma compounds (two esters, two ketones, three aldehydes and three alcohols) in several media were studied to investigate the influence of pectin addition to fat‐free dairy gel on the retention/release equilibrium. The partition coefficient of each aroma compound was measured by headspace analysis at equilibrium in six media (pure water, low‐methoxylated pectin gels and dairy gels with or without added pectin). The release of aroma compounds was similar in the aqueous media (pure water and pectin gels) on the one hand and in the dairy gels on the other hand. However, a trend to greater release occurred with the addition of pectin in both cases. Four aroma compounds were more retained in dairy gels than in water and pectin gels. No relationship appeared between retention and either the chemical function or hydrophobicity (logP values) for the entire set. However, several subsets showed a linear correlation between K and logP values. CONCLUSION: These results suggest that other structural properties than hydrophobicity are probably involved, changing the retention/release behaviour of aroma compounds according to the matrix composition. In order to probe the interactions, further experiments with a larger set of aroma compounds followed by molecular modelling interpretation are needed. Copyright © 2010 Society of Chemical Industry