Universal Rim Thickness in Unsteady Sheet Fragmentation

Unsteady fragmentation of a fluid bulk into droplets is important for epidemiology as it governs the transport of pathogens from sneezes and coughs, or from contaminated crops in agriculture. It is also ubiquitous in industrial processes such as paint, coating, and combustion. Unsteady fragmentation is distinct from steady fragmentation on which most theoretical efforts have been focused thus far. We address this gap by studying a canonical unsteady fragmentation process: the breakup from a drop impact on a finite surface where the drop fluid is transferred to a free expanding sheet of time-varying properties and bounded by a rim of time-varying thickness. The continuous rim destabilization selects the final spray droplets, yet this process remains poorly understood. We combine theory with advanced image analysis to study the unsteady rim destabilization. We show that, at all times, the rim thickness is governed by a local instantaneous Bond number equal to unity, defined with the instantaneous, local, unsteady rim acceleration. This criterion is found to be robust and universal for a family of unsteady inviscid fluid sheet fragmentation phenomena, from impacts of drops on various surface geometries to impacts on films. We discuss under which viscous and viscoelastic conditions the criterion continues to govern the unsteady rim thickness.United States. Department of Agriculture (Award MDW-2016-04938

Gene functionalities and genome structure in Bathycoccus prasinos reflect cellular specializations at the base of the green lineage

Background: Bathycoccus prasinos is an extremely small cosmopolitan marine green alga whose cells are covered with intricate spider's web patterned scales that develop within the Golgi cisternae before their transport to the cell surface. The objective of this work is to sequence and analyze its genome, and to present a comparative analysis with other known genomes of the green lineage. Research: Its small genome of 15 Mb consists of 19 chromosomes and lacks transposons. Although 70% of all B. prasinos genes share similarities with other Viridiplantae genes, up to 428 genes were probably acquired by horizontal gene transfer, mainly from other eukaryotes. Two chromosomes, one big and one small, are atypical, an unusual synapomorphic feature within the Mamiellales. Genes on these atypical outlier chromosomes show lower GC content and a significant fraction of putative horizontal gene transfer genes. Whereas the small outlier chromosome lacks colinearity with other Mamiellales and contains many unknown genes without homologs in other species, the big outlier shows a higher intron content, increased expression levels and a unique clustering pattern of housekeeping functionalities. Four gene families are highly expanded in B. prasinos, including sialyltransferases, sialidases, ankyrin repeats and zinc ion-binding genes, and we hypothesize that these genes are associated with the process of scale biogenesis. Conclusion: The minimal genomes of the Mamiellophyceae provide a baseline for evolutionary and functional analyses of metabolic processes in green plants

Plankton networks driving carbon export in the oligotrophic ocean

The biological carbon pump is the process by which CO 2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterized. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria and alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of a few bacterial and viral genes can predict a significant fraction of the variability in carbon export in these regions

Epsilon toxin from Clostridium perfringens acts on oligodendrocytes without forming pores, and causes demyelination.

Epsilon toxin (ET) is produced by Clostridium perfringens types B and D and causes severe neurological disorders in animals. ET has been observed binding to white matter, suggesting that it may target oligodendrocytes. In primary cultures containing oligodendrocytes and astrocytes, we found that ET (10(-9) M and 10(-7) M) binds to oligodendrocytes, but not to astrocytes. ET induces an increase in extracellular glutamate, and produces oscillations of intracellular Ca(2+) concentration in oligodendrocytes. These effects occurred without any change in the transmembrane resistance of oligodendrocytes, underlining that ET acts through a pore-independent mechanism. Pharmacological investigations revealed that the Ca(2+) oscillations are caused by the ET-induced rise in extracellular glutamate concentration. Indeed, the blockade of metabotropic glutamate receptors type 1 (mGluR1) prevented ET-induced Ca(2+) signals. Activation of the N-methyl-D-aspartate receptor (NMDA-R) is also involved, but to a lesser extent. Oligodendrocytes are responsible for myelinating neuronal axons. Using organotypic cultures of cerebellar slices, we found that ET induced the demyelination of Purkinje cell axons within 24 h. As this effect was suppressed by antagonizing mGluR1 and NMDA-R, demyelination is therefore caused by the initial ET-induced rise in extracellular glutamate concentration. This study reveals the novel possibility that ET can act on oligodendrocytes, thereby causing demyelination. Moreover, it suggests that for certain cell types such as oligodendrocytes, ET can act without forming pores, namely through the activation of an undefined receptor-mediated pathway.journal articleresearch support, non-u.s. gov't2015 Mar2014 10 31importe

The Tara Pacific expedition—A pan-ecosystemic approach of the “-omics” complexity of coral reef holobionts across the Pacific Ocean

Coral reefs are the most diverse habitats in the marine realm. Their productivity, structural complexity, and biodiversity critically depend on ecosystem services provided by corals that are threatened because of climate change effects—in particular, ocean warming and acidification. The coral holobiont is composed of the coral animal host, endosymbiotic dinoflagellates, associated viruses, bacteria, and other microeukaryotes. In particular, the mandatory photosymbiosis with microalgae of the family Symbiodiniaceae and its consequences on the evolution, physiology, and stress resilience of the coral holobiont have yet to be fully elucidated. The functioning of the holobiont as a whole is largely unknown, although bacteria and viruses are presumed to play roles in metabolic interactions, immunity, and stress tolerance. In the context of climate change and anthropogenic threats on coral reef ecosystems, the Tara Pacific project aims to provide a baseline of the “-omics” complexity of the coral holobiont and its ecosystem across the Pacific Ocean and for various oceanographically distinct defined areas. Inspired by the previous Tara Oceans expeditions, the Tara Pacific expedition (2016–2018) has applied a pan-ecosystemic approach on coral reefs throughout the Pacific Ocean, drawing an east–west transect from Panama to Papua New Guinea and a south–north transect from Australia to Japan, sampling corals throughout 32 island systems with local replicates. Tara Pacific has developed and applied state-of-the-art technologies in very-high-throughput genetic sequencing and molecular analysis to reveal the entire microbial and chemical diversity as well as functional traits associated with coral holobionts, together with various measures on environmental forcing. This ambitious project aims at revealing a massive amount of novel biodiversity, shedding light on the complex links between genomes, transcriptomes, metabolomes, organisms, and ecosystem functions in coral reefs and providing a reference of the biological state of modern coral reefs in the Anthropocene

Biosurfactants Change the Thinning of Contaminated Bubbles at Bacteria-Laden Water Interfaces

Bubbles reside at the water surface before bursting, emitting droplets that can contain chemicals and pathogens linked to disease and contamination. We discover that bacterial secretions enhance the lifetime of bubbles. We also reveal and elucidate two distinct regimes of thinning for such contaminated bubbles. Initially, marginal regeneration governs their thinning rate, similarly to clean water bubbles. However, due to their enhanced lifetime, it is eventually evaporation that governs their thinning, thus also dramatically decreasing their thickness at burst. We derive and experimentally validate the expression for the critical timescale at which the transition between the two regimes occurs. The shift in thinning law makes the droplets produced by contaminated bubbles smaller, faster, and more numerous than those produced by clean bubbles. Our findings suggest that microorganisms can manipulate the aging physics of surface bubbles to enhance their own water-to-air dispersal.United States. Department of Agriculture (Award MDW-2016-04938

Disease transmission via drops and bubbles

Seasonal influenza was responsible for nearly a million hospitalizations in the US in 2018, and tuberculosis killed more than a million people around the world. Those and other infectious diseases are spread by pathogens, such as bacteria and viruses. An important part of the pathogens' life cycle occurs in liquids, whose fluid dynamics influences transmission from one infected host or environmental reservoir to another. A cough or sneeze, for instance, produces a turbulent cloud of hot, moist air and droplets, as shown in figure 1. That cloud and its droplet payload can span a room up to 8 m long in a few seconds. Droplets can also be spread from bursting bubbles or splashed from a wet, contaminated surface. To predict and model disease transmission at both population and individual scales, and to develop efficient mitigation innovations and strategies against the spread of infectious diseases, understanding the role of the underlying fluid dynamics is critical. Yet little is known about the factors affecting the source, transport, and persistence of pathogen-bearing droplets. This Quick Study focuses on the example of bursting air bubbles to illustrate the rich physics and close coupling of biology and fluid dynamics in the context of disease transmission

Bursting bubbles and water-to-air-transfer : interplay between underlying physics and microbial contamination

Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 87-94).Surface bubbles are very efficient at transporting microorganisms and chemicals from water bodies to the atmosphere: upon burst, they release a multitude of droplets known to shape climate and to participate to airborne disease transmission. In this thesis, we combined controlled laboratory experiments with theoretical modelling to study the environmental and in-situ factors that control the droplet population emitted by large surface bubbles. First, we showed that a global Marangoni flow on bubbles cap due to temperature differences, evaporation, and presence of chemicals such as in saltwater can significantly alters the thinning and lifetime of bubbles. This Marangoni dynamics shapes the drainage and thickness evolution of bubbles, until they eventually rupture by nucleation of a hole in their cap. Second, we then proposed a physical picture that explains how and why micrometer-thick bubbles puncture naturally: we showed how local perturbations due to minute contaminants or intrusions can lead to hole nucleation. These findings explain the evolution of the cap thickness and the lifetime of bubbles in relatively clean water. We then studied the influence of microorganism contamination. We discovered that bacterial secretions can make bubbles live longer and indirectly enhance their thinning. As a consequence, bubbles in contaminated water emit smaller, faster, and more numerous droplets than in clean water: microorganisms can alter the physics of bubble ageing and burst to enhance their own water-to-air transfer.by Stephane Poulain.S.M.S.M. Massachusetts Institute of Technology, Department of Civil and Environmental Engineerin

An electron diffraction and bond valence sum investigation of oxygen/fluorine ordering in Nb n O 2 n -1 F n +2 , n =3

The n=3 member of the NbnO2n-1Fn+2 family of oxyfluoride compounds has been carefully investigated by electron diffraction. This compound was previously believed to have a random distribution of oxygen and fluorine ions at each of the anion sites. Electron diffraction experiments have revealed the presence of strong planar diffuse scattering perpendicular to the a and b directions at the G±[qkl]* and G±[hql]* regions of reciprocal space, where G represents a Bragg reflection of the I4/mmm average structure, h and k are continuous variables and q=0.39±0.08. The continuous planes of diffuse intensity imply the existence of strings of ordered oxygen and fluorine atoms for equatorial anion sites along [100] and [010] albeit without correlation from one such string to the next. A bond valence sum argument has been used to derive a plausible site occupation model for the remaining apical and median anion sites