Interparticle friction leads to non-monotonic flow curves and hysteresis in viscous suspensions

Hysteresis is a major feature of the solid-liquid transition in granular materials. This property, by allowing metastable states, can potentially yield catastrophic phenomena such as earthquakes or aerial landslides. The origin of hysteresis in granular flows is still debated. However, most mechanisms put forward so far rely on the presence of inertia at the particle level. In this paper, we study the avalanche dynamics of non-Brownian suspensions in slowly rotating drums and reveal large hysteresis of the avalanche angle even in the absence of inertia. By using micro-silica particles whose interparticle friction coefficient can be turned off, we show that microscopic friction, conversely to inertia, is key to triggering hysteresis in granular suspensions. To understand this link between friction and hysteresis, we use the rotating drum as a rheometer to extract the suspension rheology close to the flow onset for both frictional and frictionless suspensions. This analysis shows that the flow rule for frictionless particles is monotonous and follows a power law of exponent $\alpha \!= \! 0.37 \pm 0.05$, in close agreement with the previous theoretical prediction, $\alpha\!=\! 0.35$. By contrast, the flow rule for frictional particles suggests a velocity-weakening behavior, thereby explaining the flow instability and the emergence of hysteresis. These findings show that hysteresis can also occur in particulate media without inertia, questioning the intimate nature of this phenomenon. By highlighting the role of microscopic friction, our results may be of interest in the geophysical context to understand the failure mechanism at the origin of undersea landslides.Comment: 10 pages, 8 figure

Characterization of a new 5' splice site within the caprine arthritis encephalitis virus genome: evidence for a novel auxiliary protein

<p>Abstract</p> <p>Background</p> <p>Lentiviral genomes encode multiple structural and regulatory proteins. Expression of the full complement of viral proteins is accomplished in part by alternative splicing of the genomic RNA. Caprine arthritis encephalitis virus (CAEV) and maedi-visna virus (MVV) are two highly related small-ruminant lentiviruses (SRLVs) that infect goats and sheep. Their genome seems to be less complex than those of primate lentiviruses since SRLVs encode only three auxiliary proteins, namely, Tat, Rev, and Vif, in addition to the products of <it>gag</it>, <it>pol</it>, and <it>env </it>genes common to all retroviruses. Here, we investigated the central part of the SRLV genome to identify new splice elements and their relevance in viral mRNA and protein expression.</p> <p>Results</p> <p>We demonstrated the existence of a new 5' splice (SD) site located within the central part of CAEV genome, 17 nucleotides downstream from the SD site used for the <it>rev </it>mRNA synthesis, and perfectly conserved among SRLV strains. This new SD site was found to be functional in both transfected and infected cells, leading to the production of a transcript containing an open reading frame generated by the splice junction with the 3' splice site used for the <it>rev </it>mRNA synthesis. This open reading frame encodes two major protein isoforms of 18- and 17-kDa, named Rtm, in which the N-terminal domain shared by the Env precursor and Rev proteins is fused to the entire cytoplasmic tail of the transmembrane glycoprotein. Immunoprecipitations using monospecific antibodies provided evidence for the expression of the Rtm isoforms in infected cells. The Rtm protein interacts specifically with the cytoplasmic domain of the transmembrane glycoprotein <it>in vitro</it>, and its expression impairs the fusion activity of the Env protein.</p> <p>Conclusion</p> <p>The characterization of a novel CAEV protein, named Rtm, which is produced by an additional multiply-spliced mRNA, indicated that the splicing pattern of CAEV genome is more complex than previously reported, generating greater protein diversity. The high conservation of the SD site used for the <it>rtm </it>mRNA synthesis among CAEV and MVV strains strongly suggests that the Rtm protein plays a role in SRLV propagation <it>in vivo</it>, likely by competing with Env protein functions.</p

Sedimentation of active colloidal suspensions

In this paper, we investigate experimentally the non-equilibrium steady state of an active colloidal suspension under gravity field. The active particles are made of chemically powered colloids, showing self propulsion in the presence of an added fuel, here hydrogen peroxide. The active suspension is studied in a dedicated microfluidic device, made of permeable gel microstructures. Both the microdynamics of individual colloids and the global stationary state of the suspension under gravity - density profiles, number fluctuations - are measured with optical microscopy. This allows to connect the sedimentation length to the individual self-propelled dynamics, suggesting that in the present dilute regime the active colloids behave as 'hot' particles. Our work is a first step in the experimental exploration of the out-of-equilibrium properties of artificial active systems.Comment: 4 pages, 4 figure

Evaluation quantitative de l’adhérence de colles chirurgicales par la technique de gonflement-décollement

Nous avons mesuré l’adhérence de membranes de péricarde équin collées par un adhésif chirurgical par gonflement-décollement, par injection d’eau distillée sous pression. La pression critique de décollement permet d’estimer une énergie de propagation de la fissure interfaciale. Les valeurs d’énergie d’adhérence mesurées sont faibles par rapport aux collages industriels, mais assez fiables pour permettre une comparaison entre différents adhésifs et une étude de l’effet des conditions de collage

Digital Technology To Support Organic Growers ? Mesclun: A Web App To Help Designing Complex Organic Vegetable Production

For organic vegetable growers, combining long rotations involving a high level of plant diversity with intercropping can bring economic and ecological benefits but often increase management complexity and workload. To support the decision making of farmers facing such challenges, the research-action objective of the MESCLUN programme is to develop a web application based on the innovative computer technologies of knowledge graphs and semantic web. In this French transdisciplinary project, we articulate methods and frameworks from different fields (agronomy, economy, design, knowledge and computer engineering) with expertise of agricultural practitioners (organic growers, advisors, teachers, organic farming students). Through an iterative and participatory approach based on co-innovation workshops in 4 contrasted regions of France, we design, develop and test web app prototypes to help farmers to appropriate systemic thinking, explore and assess their “own” solutions in the organisation of complex organic vegetables systems. We will present functionalities/interface of the first web app prototype. We will for example show how the web app can help growers to plan their crops in space and time considering contrasted fertility and plants health strategies as well as marketing requirements. We will also illustrate how different simulations can be assessed from a socio-economic perspective (workload and income). Based on those first results, we will examine the specificities, added value and blind spots of our web app compared to other decision making tools in the organic agricultural sector. To feed a more general debate, we will provide critical discussion points on the potentialities and limitations of innovative digital solutions to support decision making in complex organic farming systems

HSAF-induced antifungal effects in Candida albicans through ROS-mediated apoptosis

Heat-stable antifungal factor (HSAF) belongs to polycyclic tetramate macrolactams (PTMs), which inhibits many fungal pathogens and is effective in inhibiting Candida albicans (C. albicans). In this study, we found that HSAF induced the apoptosis of C. albicans SC5314 through inducing the production of reactive oxygen species (ROS). Nevertheless, we validated the efficacy of HSAF against candidiasis caused by C. albicans in a murine model in vivo,and HSAF significantly improved survival and reduced fungal burden compared to vehicles. A molecular dynamics (MD) simulation was also investigated, revealing the theoretical binding mode of HSAF to the β-tubulin of C. albicans. This study first found PTMs-induced fungal apoptosis through ROS accumulation in C. albicans and its potential as a novel agent for fungicides

Characteristics of primary care practices associated with patient education during COVID-19: Results of the PRICOV-19 cross-sectional study in 38 countries

editorial reviewedAbstract: - Background During the COVID-19 pandemic, prevention was at the heart of the management of the health crisis with an important component related to citizen health education and therapeutic education for both the covid infected patient and the patient at risk. Primary care practices (PCPs) played a crucial role in these educational activities. - Questions / Objectives This paper aims to explore which PCP configurations enabled responsiveness to the patient education component during the COVID-19 pandemic. - Methods A "Patient Education - PE" score was created based on responses to six self-reported questionnaire items, such as staff involvement in providing information to patients by telephone. These were compiled by PRICOV, a multi-country cross-sectional study in Europe and Israel. A linear mixed model (LMM) analysis was performed with continuous PE score and PCP characteristics with 3638 respondents. - Results The mean PE score was 2.55 (SD. 0.68) with a maximum of 4 and varies suite widely between countries. Among all PCP characteristics, the following factors significantly (p < 0.05) increasing the PE score are main payment system (with a capitation payment system or another system compared to the fee for service), perception of the same or above average PCP with patients with chronic conditions and perception of adequate government support. - Conclusion The results highlight some levers that will overcome some barriers and enable the development of the educational approach appropriate to primary care; the model presented is still incomplete and requires further investigation to identify additional configuration elements favorable to educational activities.PRICO

Travelling in time with networks: revealing present day hybridization versus ancestral polymorphism between two species of brown algae, Fucus vesiculosus and F. spiralis

Background: Hybridization or divergence between sympatric sister species provides a natural laboratory to study speciation processes. The shared polymorphism in sister species may either be ancestral or derive from hybridization, and the accuracy of analytic methods used thus far to derive convincing evidence for the occurrence of present day hybridization is largely debated. Results: Here we propose the application of network analysis to test for the occurrence of present day hybridization between the two species of brown algae Fucus spiralis and F. vesiculosus. Individual-centered networks were analyzed on the basis of microsatellite genotypes from North Africa to the Pacific American coast, through the North Atlantic. Two genetic distances integrating different time steps were used, the Rozenfeld (RD; based on alleles divergence) and the Shared Allele (SAD; based on alleles identity) distances. A diagnostic level of genotype divergence and clustering of individuals from each species was obtained through RD while screening for exchanges through putative hybridization was facilitated using SAD. Intermediate individuals linking both clusters on the RD network were those sampled at the limits of the sympatric zone in Northwest Iberia. Conclusion: These results suggesting rare hybridization were confirmed by simulation of hybrids and F2 with directed backcrosses. Comparison with the Bayesian method STRUCTURE confirmed the usefulness of both approaches and emphasized the reliability of network analysis to unravel and study hybridization