- PublicationAccès librePerfect vortex modes for nondestructive characterization of mode dependent loss in ring core fibers(New York, N.Y. : Institute of Electrical and Electronics Engineers, 2022-08-02)Ring core fibers (RCF) enable high-performance modal multiplexing with low crosstalk and can support orbital angular momentum (OAM) modes. RCFs are challenging to characterize due to the lack of commercial multiplexers, especially for high OAM orders. For fibers supporting large numbers of modes, typical cutback techniques for characterization are extremely wasteful of fiber, especially as one cutback is required for each mode. We show the differential modal loss across modes 3 to 10 was significantly underestimated using an OTDR when exciting modes individually or when exciting all modes indiscriminately. We exploit perfect vortex beams to achieve reliable and nondestructive characterization of mode-dependent loss (MDL) for OAM modes. Perfect vortex beams allow us to maximize the coupling efficiency at each mode launch, increasing the accuracy of MDL estimate. We fabricated fiber with a refractive index difference between the ring core and the cladding of a 5.1×10⁻². For this fiber, mode orders 3 to 10 are the most suitable for data transmission and were the focus of our work (the fiber support up to OAM order 13). Such a high index difference can lead to MDL. We demonstrate that the modal loss spans from 2.14 to 4.38 dB/km for orders 3 to 10.
- PublicationRestriction temporaireNiobium addition improves the corrosion resistance of TiHfZrNbₓ high-entropy alloys in Hanks’ solution(Amsterdam : Elsevier, 2022-06-02)High-strength TiHfZrNbₓ high-entropy alloys could become the ideal materials for small-diameter endovascular stents once their corrosion resistance in the physiological milieu is confirmed. This work aims at evaluating the corrosion resistance of a TiHfZrNbₓ high-entropy-alloys family in Hanks’ solution at 37 °C and revealing the influence of niobium on the mechanisms of dissolution and passivation. The alloys were subjected to a series of static and dynamic electrochemical tests and surface characterization, employing the static/dynamic/cyclic polarizations, impedance spectroscopy, XPS, AFM, and SEM. Results confirm a higher corrosion resistance of the alloys compared to that of CP-Ti and Ti6Al4V. The addition of niobium considerably improves the microstructural homogeneity that ensures a low dissolution rate and a greater resistance of the film due to the lower concentration of point defects. The passive film behaves as an n-type semiconductor and is composed of a mixture of TiO₂, Nb₂O₅, ZrO₂, and HfO₂ oxides, with the presence of metallic hydroxides on the outermost layer. A detailed description of the niobium influence on the mechanisms of the dissolution and passivation is presented in this work.
- PublicationAccès libreNative plant turnover and limited exotic spread explain swamp biotic differentiation with urbanization(Uppsala, Sweden : Opulus Press, 2020-11-27)Questions: Does urbanization promote biotic differentiation or homogenization of swamp plant communities? What is the contribution of natives and exotics to swamp response to urbanization? Location: Quebec City, Canada. Methods: Plant communities of 34 swamps located in low, moderately or highly urbanized landscapes were sampled, and species classified into three exclusive groups: native wetland, native upland and exotic plants. Urbanization's influence on the richness of each plant group was assessed using mixed models. Between-site compositional similarities were calculated to identify variations in beta diversity with urbanization level using tests for homogeneity in multivariate dispersion. Beta diversity was further partitioned into species replacement and richness difference for each plant group. Finally, the relationships of ten environmental variables representing soil water saturation and microtopography with plant assemblages were determined by redundancy analysis. Results: Although the richness of exotics increased with urbanization intensity, revealing increasing propagule pressure, it remained six to 27 times lower compared to the richness of natives, which remained stable with urbanization. On the other hand, beta diversity increased with urbanization, with higher dissimilarities in species composition between highly urbanized swamps than between low-urbanized ones. This pattern resulted from high species replacement among natives, while richness difference mainly contributed to exotic beta diversity. Changes in plant assemblages were mostly associated with bryophyte cover and soil drainage and red mottle size, suggesting that hydrological conditions likely acted as a strong driver of swamp plant community response to urbanization. Conclusions: Swamp plant communities experienced biotic differentiation with increasing urbanization. This differentiation pattern likely was linked to the unpredict-able effect of urbanization on hydrological regimes, which promoted high native turnover while limiting exotic spread. Long-term monitoring is recommended to ensure that exotics do not outcompete natives through time. Designing sustainable cities requires a greater understanding of the multifaceted effect of urbanization on biodiversity.
- PublicationRestreintTransverse permeability in Eucalyptus nitens wood specimens(Essex, England : Taylor and Francis, 2022-07-27)Permeability functionalities are noticeable in the wood drying and impregnation processes because it has an effect on the bulk flow of a fluid through the wood structure. The aim of this work was to measure the radial and tangential specific gas permeability of Eucalyptus nitens wood for 10 different provenances. Furthermore, the effect of the radial position (defined as inner-wood, middle-wood, and outer-wood) on the measurements was investigated. The specific gas permeability of E. nitens ranged in order of magnitude from 10−20 to 10−16 m2. The results showed that the radial position had a statistically significant effect on the specific permeability in both flow directions and, in general, the permeability values increased from inner-wood to outer-wood. Moreover, the scanning electron microscopy images showed obstruction of vessels by tyloses which explained the lower permeability values obtained in the inner-wood of E. nitens. Differences in the magnitude of the permeability values could explain the diverse drying and impregnation behavior according to the wood zones, the low permeability values in the internal wood-zone could suggest an opportunity for improving it, through chemical modification or structural changes to introduce new functionalities of this radial wood-zone in Eucalyptus nitens.
- PublicationAccès libreGrowth response of cuttings to drought and intermittent flooding for three Salix species and implications for riverbank soil bioengineering(New York : Springer, 2021-04-12)Willows are used as cuttings or in fascines for riverbank soil bioengineering, to control erosion with their high resprouting ability and rapid growth. However, water availability is highly variable along riverbanks both in time and space and constitutes a major stress limiting willow establishment. A species-specific understanding of willow cutting response to water stress is critical to design successful riverbank soil bioengineering projects given exclusive use of local species is often recommended. In a three-month greenhouse experiment, we investigated the effects of three soil moisture treatments (drought—soil saturation—intermittent flooding) on survival, biomass production and root growth of cuttings of three willow species used for soil bioengineering along NE American streams (Salix discolor—S. eriocephala—S. interior). Cutting survival was high for all species and treatments (>89%). Biomass production and root volume only differed between species. S. eriocephala produced the highest biomass and root volume, and S. discolor invested more in belowground than aboveground biomass. Root length responded to soil moisture differently between species. Under intermittent flooding, S. eriocephala produced shorter roots, while S. interior produced longer roots. For riverbank soil bioengineering, S. eriocephala should be favored at medium elevation and S. interior at lower elevation.