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Slime molds response to carbon nanotubes exposure: from internalization to behavior
Get PDFCarbon nanotubes (CNTs) offer attractive opportunities due to their physical, electrical, mechanical, optical, and thermal properties. They are used in a wide range of applications and are found in numerous consumer products. On the downside, their increasing presence in the environment poses potential threats to living organisms and ecosystems. The aim of this study was to evaluate the toxicity of double-walled carbon nanotubes (DWCNTs) on a new model system: the acellular slime mold Physarum polycephalum. Despite its ecological significance, its simplicity of organization, and its behavioral complexity, exposure of such organisms to nanoparticles has been poorly investigated. Slime molds were exposed to DWCNTs using three routes of exposure (topical, food, environment). We first demonstrated that DWCNTs were rapidly internalized by slime molds especially when DWCNTs were mixed with the food or spread out in the environment. Secondly, we showed that a 6-week exposure to DWCNTs did not lead to bioaccumulation nor did it lead to persistence in the slime molds when they entered a resting stage. Thirdly, we revealed that 2 days following exposure, DWCNTs were almost entirely excreted from the slime molds. Lastly, we uncovered that DWCNTs exposure altered the migration speed, the pseudopods formation, and the expansion rate of the slime molds. Our results extend our current knowledge of CNTs cytotoxicity and introduce P. polycephalum as an ideal organism for nanotoxicology
Why comparison between different chemical extraction procedures is necessary to better assess the metals availability in sediments
Get PDFSingle and sequential extractions are current and useful tools for estimating the availability of metals in soils or sediments. Many chemical extraction procedures have been proposed in the literature, making the comparison difficult. This study compares the data consistency of the potential availability given by four chemical extractions commonly found in the literature:
➢two single procedures (using dilute HCl or EDTA as reactant)
➢two sequential procedures (the modified standardized 3-steps procedure of the Standards, Measurements and Testing Programme (SMTP), namely BCR-extraction, and the 7-steps procedure of Leleyter and Probst (1999), namely LP-extraction).
The leaching procedures are all performed on the reference lake sediment CRM BCR-701, used as a reference to assess the accuracy of the modified standardized procedure of Rauret et al. (1999). The results show similar availabilities between HCl and EDTA single leaches for Zn, Cu, Cr and Pb and between HCl and the BCR procedures for Zn, Cu, Cr and Ni. The LP-extraction is the most aggressive of the four tested procedures (except for Pb extraction), mainly due to a better extraction of the exchangeable fraction, by a better dissolution of the acido-soluble phase and particularly to a better dissolution of the amorphous and crystalline Fe-oxides. The comparison between the four procedures reveals a major problem of Pb extraction, potentially due to the formation of lead precipitates during HCl and the LP-extractions, even if an overestimation of the lead availability by the BCR procedure cannot be excluded
Low‐density insulation blocks and hardboards from amaranth (Amaranthus cruentus) stems, a new perspective for building applications
Get PDFNowadays, amaranth appears as a promising source of squalene of vegetable origin. Am‐aranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for the formulation of moisturizing creams. It is almost exclusively extracted from the liver of sharks, causing their overfishing. Thus, providing a squalene of renewable origin is a major challenge for the cosmetic industry. The ama‐ranth plant has thus experienced renewed interest in recent years. In addition to the seeds, a stem is also produced during cultivation. Representing up to 80% (w/w) of the plant aerial part, it is composed of a ligneous fraction, the bark, on its periphery, and a pith in its middle. In this study, a fractionation process was developed to separate bark and pith. These two fractions were then used to produce renewable materials for building applications. On the one hand, the bark was used to produce hardboards, with the deoiled seeds acting as natural binder. Such boards are a viable al‐ternative to commercial wood‐based panels. On the other hand, the pith was transformed into co‐hesive and machinable low‐density insulation blocks revealing a low thermal conductivity value
Study of the densification and grain growth mechanisms occurring during spark plasma sintering of different submicronic yttria-stabilized zirconia powders
Get PDFDensification and grain growth mechanisms of Yttria-Stabilized Zirconia sintered by Spark Plasma Sintering are
investigated. Sintering trajectories of four commercial submicronic powders with different average particle sizes
and yttria amounts have been established and sintering regimes determined. Densification mechanisms are
determined in the regime where densification is occurring without grain growth using a model derived from hotpressing.
Grain growth mechanisms are determined using the conventional power law in the regime where ceramics
are fully densified. Densification occurs by grain boundary sliding accommodated by an in-series interface-
reaction/lattice diffusion of cations or by an overlapping of surface diffusion and grain boundary sliding
mechanisms for tetragonal stabilized zirconia and by dislocation climbing for fully stabilized zirconia. A normal
grain growth occurs for each ceramic, all composed of a single phase, contrary to the two-phased ceramics
obtained in literature where grain growth occurs by segregation at grain boundaries
Shock motion inside a varying cross-section channel and consequences on the downstream flow
Get PDFShock wave propagation in a variable cross-section channel is a recurrent issue in the literature. Seminal work regarding this flow configuration has been proposed by~\citeapos{whitham_propagation_1958} through the derivation of a one-dimensional approach connecting the shock Mach number and the area channel: the A-M relation. It is based on strong theoretical restrictions: (i) shock equations applied on a , (ii) omission of the post-shock influence, and (iii) initial conditions at rest. It has been the focus of many studies aimed at generalizing it. However, very little attention has been paid to the study of the shock motion outside the varying cross-sectional region since~\citeapos{russell_shock-wave_2018}. The objective of the current work is to describe and to explain the shock wave behaviour in a constant area channel behind a convergent or divergent channel. It is found that the shock propagation in the downstream uniform area region is influenced by the post-shock flow unsteadinesses. Thence, the Whitham model is not suited to the shock motion study in a constant area region downstream of a convergent or divergent area region. A detailed flow description is provided and a quasi-steady model for determining the waves intensity at large times is proposed. This model gives accurate results without any assumptions on the shock strength, area variation or the shock upstream state. Finally, this study points out the limits of the use of Whitham's theory in a variable area channel with increasing section variation rate (where )
Influence of Hybrid Sol-Gel Crosslinker on Self-Healing Properties for Multifunctional Coatings
Get PDFSelf-healing polymers are a new class of material that has recently received a lot of attention because of the lifespan improvement it could bring to multiple applications. One of the major challenges is to obtain multifunctional materials which can self-heal and exhibit other interesting properties such as protection against corrosion. In this paper, the effect of the incorporation of an aminosilane on the properties of a self-healing organic polymer containing disulfide bond is studied on films and coatings for aluminium AA2024-T3 using simple one step in situ synthesis. Hybrid coatings with enhanced anticorrosion properties measured by EIS were obtained thanks to the formation of a protective oxide interface layer, while exhibiting wound closure after exposition at 75 °C. The thermal, mechanical and rheological properties of the films with different aminosilane amounts were characterized in order to understand the influence of the slight presence of the inorganic network. Stiffer and reprocessable hybrid films were obtained, capable to recover their mechanical properties after healing. The nanocomposite structure, confirmed by TEM, had a positive effect on the self-healing and stress relaxation properties. These results highlight the potential of sol-gel chemistry to obtain efficient anticorrosion and self-healing coatings
Development and validation of QuEChERS-based extraction for quantification of nine micropollutants in wastewater treatment plant
Get PDFA modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was established for simultaneous quantification of eight pharmaceutical molecules (2-hydroxyibuprofen, diclofenac, ibuprofen, propranolol, ofloxacin, oxazepam, sulfamethoxazole, carbamazepine) and caffeine in environmental matrices. Analysis was performed by ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS-MS). Quantification was performed by using the 13C internal standard method for each molecule. Two methods were firstly optimized on freeze-dried waste activated sludge and then applied and validated on real complex matrices, which have contrasted physicochemical properties, i.e., clarified wastewater and primary sludge. The combination of acetate buffer with MgSO4 (protocol A) and citrate buffer with Na2SO4 (protocol B) was found necessary to recover the nine targeted compounds. Adding a higher salts quantity of Na2SO4 (protocol B) compared to MgSO4 (protocol A) is crucial to increase the ionic strength of the aqueous solution and to obtain comparable extraction recoveries of the targetedmolecules. Adding two times solvent volume to the aqueous phase leads to increased absolute recovery for all molecules and both protocols. After demonstration of the final protocol’s performance on the control matrix, its robustness was tested on the matrices of interest. As a result, the two proposed detection methods exhibit good reproducibility, high sensitivity, and high reliability
Kinematics of a bubble freely rising in a thin-gap cell with additional in-plane confinement
Get PDFWe analyze the behavior of air bubbles freely rising at high Reynolds numbers in a planar thin-gap cell filled with distilled water. The gap thickness of the cell is fixed to h≃2.8 mm (or h≃1 mm in additional experiments) and its in-plane width W is varied from 2.4 to 21 cm. This allows us to investigate the evolution from unconfined thin-gap situations (i.e., large W and h≪W) controlled by the bubble characteristic lengths (diameter in the cell plane d>h and thickness close to the gap size h) to doubly confined situations controlled by the channel dimensions. As the bubble size d increases, and beyond a critical value that depends on W, we observe a mean rise velocity of the bubble, Vb, lower than that for larger W, along with a modification of the bubble shape. The departure occurs for oscillating bubbles of approximate elliptical shape, which becomes closer to circular as the lateral confinement increases. We further investigate how the bubble oscillatory motion is impacted by the transverse confinement. Assuming that the wall effect is related to the strength of the downward flow generated by the bubble, we introduce the relative velocity Urel=Vb/ξ, where ξ=1−d/W is the confinement ratio and found Urel≃Vb,∞ for all the cell widths considered, where Vb,∞ is the mean rise velocity in the absence of the transverse confinement (i.e., for W sufficiently large). This provides an estimation, at leading order, of the bubble velocity, that generalizes the expression proposed by Filella et al. J. Fluid Mech. 778, 60 (2015) and accounts for the additional drag experienced by the bubble due to the lateral walls. We then show that, for given d and ξ, the frequency and amplitudes of the oscillatory motion can be predicted using the characteristic length and velocity scales, d and Urel. As the bubble size is increased further, the bubble behavior becomes fully dominated by the channel dimensions. Cylindrical-capped shapes emerge, corresponding to a radius of curvature Rc at the front of the bubble, Rc≃0.31W, independent of the bubble size and of the gap thickness. At the same time, the mean rise velocity of the bubble saturates at a constant value, corresponding to a constant Froude number, Fr=Vb/√gW, that depends on the gap thickness h of the cell
Bubble fragmentation dynamics in a subsonic Venturi tube for the design of a compact microbubble generator
Get PDFMicrobubble generators are in wide demand in industry following the discovery of a number of new functions of microbubble mixtures. This paper deals with a Venturi tube microbubble generator in which air bubbles at the inlet are fragmented in the diverging part of the tube. In contrast with past studies, we here regulated the flow subsonic so that fragmentation occurred without the help of pressure shock waves. Counting the microbubbles in image processing, we found that a single bubble fragmented into 20–400 microbubbles depending on the Weber number. The power efficiency is found to range from 30 to 50 percent and insensitive to the liquid viscosity. The mechanism of subsonic fragmentation is elucidated adopting particle tracking velocimetry, in association with a theoretical description of the translational motion and the shape oscillation of the bubble. The key event was found to be the bubble’s rapid slipback in the diverging part of the Venturi tube due to a positive pressure gradient. This provides a function that prevents large bubbles from being released from the subsonic Venturi tube
Mesoscopic simulations of the in situ NMR spectra of porous carbon based supercapacitors: electronic structure and adsorbent reorganisation effects
Get PDFIn situ NMR spectroscopy is a powerful technique to investigate charge storage mechanisms in carbon-based supercapacitors thanks to its ability to distinguish ionic and molecular species adsorbed in the porous electrodes from those in the bulk electrolyte. The NMR peak corresponding to the adsorbed species shows a clear change of chemical shift as the applied potential difference is varied. This variation in chemical shift is thought to originate from a combination of ion reorganisation in the pores and changes in ring current shifts due to the changes of electronic density in the carbon. While previous Density Functional Theory calculations suggested that the electronic density has a large effect, the relative contributions of these two effects is challenging to untangle. Here, we use mesoscopic simulations to simulate NMR spectra and investigate the relative importance of ion reorganisation and ring currents on the resulting chemical shift. The model is able to predict chemical shifts in good agreement with NMR experiments and indicates that the ring currents are the dominant contribution. A thorough analysis of a specific electrode/electrolyte combination for which detailed NMR experiments have been reported allows us to confirm that local ion reorganisation has a very limited effect but the relative quantities of ions in pores of different sizes, which can change upon charging/discharging, can lead to a significant effect. Our findings suggest that in situ NMR spectra of supercapacitors may provide insights into the electronic structure of carbon materials in the future