PORE-SCALE SIMULATION OF FLUID FLOW IN PACKED-BED REACTORS VIA RIGID-BODY SIMULATIONS AND CFD

The problem of fluid flow in porous media is of paramount importance in the process, oil and metallurgical industries, since it is involved in the extraction of minerals and oil, in aquifer dynamics, as well as chemical reactions carried out in fixed bed catalytic reactors. Its CFD simulation is particularly interesting, as it offers the possibility of reducing the extent of costly experimental investigations, but presents a number of technical challenges. One of the main issues is the generation of a geometrical model that realistically represents the porous medium/particle packing. Its derivation from experiments (i.e. micro-computer tomography) is complicated and packing codes are often limited to simple convex (mainly spherical) objects. In this work a computational tool developed in computer graphics, and integrated with the Bullet Physic Library, is used to generate realistic packings of polydisperse catalytic spheres and trilobes. The geometrical model is then meshed with SnappyHexMesh and then simulated with Ansys Fluent. Results show excellent agreement with experiments, demonstrating the great potentiality of the approac

Long-term cellular immunity of vaccines for Zaire Ebola Virus Diseases

Recent Ebola outbreaks underscore the importance of continuous prevention and disease control efforts. Authorized vaccines include Merck’s Ervebo (rVSV-ZEBOV) and Johnson & Johnson’s two-dose combination (Ad26.ZEBOV/MVA-BN-Filo). Here, in a five-year follow-up of the PREVAC randomized trial (NCT02876328), we report the results of the immunology ancillary study of the trial. The primary endpoint is to evaluate long-term memory T-cell responses induced by three vaccine regimens: Ad26–MVA, rVSV, and rVSV–booster. Polyfunctional EBOV-specific CD4+ T-cell responses increase after Ad26 priming and are further boosted by MVA, whereas minimal responses are observed in the rVSV groups, declining after one year. In-vitro expansion for eight days show sustained EBOV-specific T-cell responses for up to 60 months post-prime vaccination with both Ad26-MVA and rVSV, with no decline. Cytokine production analysis identify shared biomarkers between the Ad26-MVA and rVSV groups. In secondary endpoint, we observed an elevation of pro-inflammatory cytokines at Day 7 in the rVSV group. Finally, we establish a correlation between EBOV-specific T-cell responses and anti-EBOV IgG responses. Our findings can guide booster vaccination recommendations and help identify populations likely to benefit from revaccination

Long-term cellular immunity of vaccines for Zaire Ebola Virus Diseases

Recent Ebola outbreaks underscore the importance of continuous prevention and disease control efforts. Authorized vaccines include Merck’s Ervebo (rVSV-ZEBOV) and Johnson & Johnson’s two-dose combination (Ad26.ZEBOV/MVA-BN-Filo). Here, in a five-year follow-up of the PREVAC randomized trial (NCT02876328), we report the results of the immunology ancillary study of the trial. The primary endpoint is to evaluate long-term memory T-cell responses induced by three vaccine regimens: Ad26–MVA, rVSV, and rVSV–booster. Polyfunctional EBOV-specific CD4+ T-cell responses increase after Ad26 priming and are further boosted by MVA, whereas minimal responses are observed in the rVSV groups, declining after one year. In-vitro expansion for eight days show sustained EBOV-specific T-cell responses for up to 60 months post-prime vaccination with both Ad26-MVA and rVSV, with no decline. Cytokine production analysis identify shared biomarkers between the Ad26-MVA and rVSV groups. In secondary endpoint, we observed an elevation of pro-inflammatory cytokines at Day 7 in the rVSV group. Finally, we establish a correlation between EBOV-specific T-cell responses and anti-EBOV IgG responses. Our findings can guide booster vaccination recommendations and help identify populations likely to benefit from revaccination

Evaluation of waning of IgG antibody responses after rVSVΔG-ZEBOV-GP and Ad26.ZEBOV, MVA-BN-Filo Ebola virus disease vaccines: a modelling study from the PREVAC randomized trial.

rVSVΔG-ZEBOV-GP and Ad26.ZEBOV, MVA-BN-Filo are WHO-prequalified vaccination regimens against Ebola virus disease (EVD). Challenges associated with measuring long-term clinical protection warrant the evaluation of immune response kinetics after vaccination. Data from a large phase 2 randomized double-blind clinical trial (PREVAC) were used to evaluate waning of anti-Ebola virus (EBOV) glycoprotein (GP1,2) antibody concentrations after rVSVΔG-ZEBOV-GP or Ad26.ZEBOV, MVA-BN-Filo vaccination with linear mixed-effect regression models. After a post-vaccination peak, each vaccination strategy was associated with a decrease of anti-EBOV GP1,2 antibody concentrations with distinct kinetics, highlighting a less-rapid decline in antibody levels after vaccination by rVSVΔG-ZEBOV-GP. One year after administration of the vaccine, antibody concentrations were higher in children compared to adults for both vaccines, although with different effect sizes: 1.74-fold higher concentrations (95% confidence interval [CI] [1.48; 2.02]) for children 12-17 years old to 3.10-fold higher concentrations (95% CI [2.58; 3.69]) for those 1-4 years old compared to adults for Ad26.ZEBOV, MVA-BN-Filo versus 1.36-fold (95% CI [1.12; 1.61]) to 1.41-fold (95% CI [1.21; 1.62]) higher than these values for adults, with relatively small changes from one age category of children to another, for rVSVΔG-ZEBOV-GP. Antibody concentrations also differed according to geographical location, pre-vaccination antibody concentration, and sex. In combination with knowledge on memory response, characterization of the major determinants of immune response durability of both vaccinations may guide future EVD control protocols.Trial registration: ClinicalTrials.gov identifier: NCT02876328

Mixing induced by an homogeneous bubbly flow

Colloque avec actes et comité de lecture. Internationale.International audienceBubble columns are commonly used for chemical processes because of their good mixing and transfer capabilities. This work aims at understanding and modelling the mixing of a passive scalar at high Schmidt number in a homogeneous bubbly flow for gas volume fraction ranging from 1 to 13%

Mixing by a bubbly flow in a Hele-Shaw cell: time-resolved measurements and modelling

International audienceThe present work investigates the mixing of a low diffusivity fluorescent dye within a homogeneous swarm of high-Re air bubbles rising in a vertical Hele-Shaw cell filled with water, for gas volume fractions from 1.4 to 5.4%. A given amount of Rhodamine WT is injected at a given location within the bubble swarm during a finite time at the beginning of the experiment. The bubbles motion generates liquid agitation, which causes a specific mixing of the dye. The local dye concentration at a given location is measured by an original Laser Induced Fluorescence (LIF) technique. On one side of the cell, a first optical fibre connected to a laser is used to light up a volume of 0.2 mm³. On the other side of the cell, a second optical fibre collects the emitted light in an observation volume of 7 mm³. Thanks to a spectrophotometer connected to this fibre, the fluoresced light, which intensity is proportional to the dye concentration, is separated from the incident light. This system allows us to record the time evolution of the local dye concentration at a frequency of 250 Hz. Concurrently, the distribution of the bubbles around the measurement volume is imaged with a high speed camera synchronized with the spectrometer. This camera is used to assess the LIF technique in bubbly flow. At a certain distance above the injection point, the dye concentration signal is characterized by rapid and intense fluctuations corresponding to the passages of patches of dye carried by individual bubbles superimposed to a slow global evolution. The global time evolution of the concentration shows two stages. It first increases as the injected dye is transported by the bubbles towards the measurement volume and then decreases as it moves farther. At large time, the global decrease is observed to be exponential, which is incompatible with a Fickian diffusive process but consistent with the transport of the dye by the mean wakes and the wake vortices that are quickly damped out by wall friction. The mixing by the bubble swarm is a convective intermittent process

Utilisation des capteurs de pression en colonne à bulles industrielle : des mesures fiables et complètes

International audienc