Antiviral Activities of Sulfated Polysaccharides Isolated from Sphaerococcus coronopifolius (Rhodophytha, Gigartinales) and Boergeseniella thuyoides (Rhodophyta, Ceramiales)

Water-soluble sulfated polysaccharides isolated from two red algae Sphaerococcus coronopifolius (Gigartinales, Sphaerococcaceae) and Boergeseniella thuyoides (Ceramiales, Rhodomelaceae) collected on the coast of Morocco inhibited in vitro replication of the Human Immunodeficiency Virus (HIV) at 12.5 μg/mL. In addition, polysaccharides were capable of inhibiting the in vitro replication of Herpes simplex virus type 1 (HSV-1) on Vero cells values of EC50 of 4.1 and 17.2 μg/mL, respectively. The adsorption step of HSV-1 to the host cell seems to be the specific target for polysaccharide action. While for HIV-1, these results suggest a direct inhibitory effect on HIV-1 replication by controlling the appearance of the new generations of virus and potential virucidal effect. The polysaccharides from S. coronopifolius (PSC) and B. thuyoides (PBT) were composed of galactose, 3,6-anhydrogalactose, uronics acids, sulfate in ratios of 33.1, 11.0, 7.7 and 24.0% (w/w) and 25.4, 16.0, 3.2, 7.6% (w/w), respectively

Models of marine fish biodiversity : assessing predictors from three habitat classification schemes

Prioritising biodiversity conservation requires knowledge of where biodiversity occurs. Such knowledge, however, is often lacking. New technologies for collecting biological and physical data coupled with advances in modelling techniques could help address these gaps and facilitate improved management outcomes. Here we examined the utility of environmental data, obtained using different methods, for developing models of both uni- and multivariate biodiversity metrics. We tested which biodiversity metrics could be predicted best and evaluated the performance of predictor variables generated from three types of habitat data: acoustic multibeam sonar imagery, predicted habitat classification, and direct observer habitat classification. We used boosted regression trees (BRT) to model metrics of fish species richness, abundance and biomass, and multivariate regression trees (MRT) to model biomass and abundance of fish functional groups. We compared model performance using different sets of predictors and estimated the relative influence of individual predictors. Models of total species richness and total abundance performed best; those developed for endemic species performed worst. Abundance models performed substantially better than corresponding biomass models. In general, BRT and MRTs developed using predicted habitat classifications performed less well than those using multibeam data. The most influential individual predictor was the abiotic categorical variable from direct observer habitat classification and models that incorporated predictors from direct observer habitat classification consistently outperformed those that did not. Our results show that while remotely sensed data can offer considerable utility for predictive modeling, the addition of direct observer habitat classification data can substantially improve model performance. Thus it appears that there are aspects of marine habitats that are important for modeling metrics of fish biodiversity that are not fully captured by remotely sensed data. As such, the use of remotely sensed data to model biodiversity represents a compromise between model performance and data availability

Acoustics of monodisperse open-cell foam: An experimental and numerical parametric study

International audienceThis article presents an experimental and numerical parametric study of the acoustical properties of monodisperse open-cell solid foam. Solid foam samples are produced with very good control of both the pore size (from 0.2 to 1.0 mm) and the solid volume fraction (from 6% to 35%). Acoustical measurements are performed by the threemicrophone impedance tube method. From these measurements, the visco-thermal parameters-namely, viscous permeability, tortuosity, viscous characteristic length, thermal permeability, and thermal characteristic length-are determined for an extensive number of foam samples. By combining Surface Evolver and finite-element method calculations, the visco-thermal parameters of body centered cubic (bcc) foam numerical samples are also calculated on the whole range of solid volume fraction (from 0.5% to 32%), compared to measured values and to theoretical model predictions [Langlois et al. (2019). Phys. Rev. E 100(1), 013115]. Numerical results are then used to find approximate formulas of visco-thermal parameters. A systematic comparison between measurements and predictions of the Johnson-Champoux-Allard-Lafarge (JCAL) model using measured visco-thermal parameters as input parameters, reveals a consistent agreement between them. From this first step, a calculation of the optimal microstructures maximizing the sound absorption coefficient is performed.

Permeability of polydisperse solid foams

International audienceThe effect of polydispersity on foam permeability is investigated by numerical simulations. Foam structures are first generated by Laguerre tessellations via the Neper software and relaxed to minimize the surface energy via the Surface Evolver software. The fluid flow and permeability are then calculated by means of pore-network simulations, by considering either fully open-cell foams or foams with randomly selected closed windows. Different configurations of window aperture are used, including identical window aperture size, identical window aperture ratio, or random window aperture ratio. The main results are obtained for the case of foams having identical and uniform window aperture ratios. For such foams and at constant mean pore size, foam permeability is found to strongly increase with the polydispersity degree. The numerical results are employed to discuss the validity of the mean pressure field assumption used to calculate the foam permeability, the effect of small pores, and the definition of an equivalent Kelvin foam size. We show that as long as the fluctuations of the window aperture ratio remain low, foam permeability can be estimated by using the mean pressure field hypothesis. The weak effect of small pores on permeability is related to their small contribution to the overall fluid volume fraction. Finally, various estimations of the equivalent Kelvin foam size based on pore-size distribution are propose

Calibration and performances of the integrated Mach-Zehnder (iMZ) wavefront sensor for extreme adaptive optics

International audienceWe describe new results obtained with the integrated Mach-Zehnder (iMZ) self referenced wavefront sensor (WFS) allowing to extract independently phase and amplitude from intensity variations in the pupil images produced by the interferometer. This kind of wavefront sensor meets extreme adaptive optics requirements, high speed (1 kHz) and high accuracy (< 10 nm at 5-10 cm spatial scale), as well as the reconstruction of phasing errors on segmented telescopes and scintillation measurements. In this paper we present the calibration method we have developed and validated experimentally to accurately extract the phase and the amplitude of the wavefront from the Mach-Zehnder signal, using several diversities in the phase patterns. We also present a new phase modulation method which combined with an unwrapping algorithm increases the dynamical range of the wavefront sensor up to several microns, otherwise limited to ± lambda/4 without these new strategies. Numerical simulations of the Mach-Zehnder performances for various turbulence phase will be presented to address the ultimate sensor accuracy. We will also report on our latest laboratory calibration results, using a deformable mirror and a spatial light modulator to introduce the required phase modulations

Predicting permeability via statistical descriptors of morphology on polydisperse foams including membranes

International audienceQuantitative structure-property relationships are crucial for the understanding and prediction of the acoustical properties of complex foams. For fluid flow in polydisperse foams, characterizing the pore size distribution and membrane content facilitates prediction of permeability, a key property that has been extensively studied in material science, geophysics and chemical engineering. In this work, we propose a formula to predict the permeability of polydisperse foams including membranes via microstructural descriptors which can be derived from X-ray microtomography and scanning electron micrographs

Tuning membrane content of sound absorbing cellular foams: Fabrication, experimental evidence and multiscale numerical simulations

International audienceThis work is focused on tailoring cellular foam membranes for sound absorption. Several foam configurations with a constant porosity and varying membrane content were first fabricated by using milli-fluidic techniques. This approach allows transport and sound absorbing properties to be continuously tuned on purpose, from open-cell to closed-cell foams. The morphology of these foams was then investigated using optical micrography. Microstructural descriptors such as the proportions of closed and open windows and aperture size were specifically analyzed. The associated transport and sound absorbing properties were subsequently characterized using airflow resistivity and three-microphone standing wave tube measurements. The numerical reconstruction of foam samples was next addressed by considering a Periodic Unit Cell (PUC) approach on Kelvin cells. The transport properties of these virtual samples were determined by numerical homogenization, performing sequential evaluations of the parameters that govern visco-thermal losses. To overcome the limitation induced by the size of the numerical model at the pore scale, an averaging procedure was proposed. The results show that the PUC model can be used to accurately predict the transport and sound absorbing behavior of interest. The relevance of the multiscale estimations for acoustic properties is demonstrated over the entire range of membrane content

Permeability of solid foam: Effect of pore connections

International audienceIn this paper, we study how the permeability of solid foam is modified by the presence of membranes that close partially or totally the cell windows connecting neighboring pores. The finite element method (FEM) simulations computing the Stokes problem are performed at both pore and macroscopic scales. For foam with fully interconnected pores, we obtain a robust power-law relationship between permeability and aperture size. This result is due to the local pressure drop mechanism through the aperture as described by Sampson for fluid flow through a circular orifice in a thin plate. Based on this local law, pore-network simulation of simple flow is used and is shown to reproduce FEM results. Then this low computational cost method is used to study in detail the effect of an open window fraction on the percolation properties of the foam pore space. The results clarify the effect of membranes on foam permeability. Finally, Kirkpatrick’s model is adapted to provide analyticalexpressions that allow for our simulation results to be successfully reproduced

Micro-macro acoustic modeling of heterogeneous foams with nucleation perturbation

International audienceThe properties of a polyurethane foam are greatly influenced by the addition of graphite particles during the manufacturing process, initially used as a fire retardant. These thin solid particles perturbate the nucleation process by generating bubbles in their immediate vicinity. A large body of work has focused on foams that are reasonably homogeneous. In this work, we propose a modeling approach for inhomogeneous foams that includes membrane effects and allows pore size distributions to be accounted for. The cellular structure of the foam is obtained through a random Laguerre tessellation optimized from experimental properties. The structure of real foam samples is analyzed using X-ray computed tomography and scanning electron microscopy, followed by image processing, to create three-dimensional, digital models of the samples. The corresponding effective material parameters, including the permeability, the tortuosity and the viscous characteristic length, are subsequently computed by applying a numerical homogenization approach. All the numerical data are presented, discussed and gauged against experimental results