Glass breaks like metals, but at the nanometer scale

We report in situ Atomic Force Microscopy experiments which reveal the presence of nanoscale damage cavities ahead of a stress-corrosion crack tip in glass. Their presence might explain the departure from linear elasticity observed in the vicinity of a crack tip in glass. Such a ductile fracture mechanism, widely observed in the case of metallic materials at the micrometer scale, might be also at the origin of the striking similarity of the morphologies of fracture surfaces of glass and metallic alloys at different length scales.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Lett, few minor corrections, Fig. 1b change

A Tractable Experimental Model for Study of Human and Animal Scabies

Scabies, a neglected parasitic disease caused by the microscopic mite Sarcoptes scabiei, is a major driving force behind bacterial skin infections in tropical settings. Aboriginal and Torres Strait Islander peoples are nearly twenty times more likely to die from acute rheumatic fever and rheumatic heart disease than individuals from the wider Australian community. These conditions are caused by bacterial pathogens such as Group A streptococci, which have been linked to underlying scabies infestations. Community based initiatives to reduce scabies and associated disease have expanded, but have been threatened in recent years by emerging drug resistance. Critical biological questions surrounding scabies remain unanswered due to a lack of biomedical research. This has been due in part to a lack of either a suitable animal model or an in vitro culture system for scabies mites. The pig/mite model reported here will be a much needed resource for parasite material and will facilitate in vivo studies on host immune responses to scabies, including relations to associated bacterial pathogenesis, and more detailed studies of molecular evolution and host adaptation. It represents the missing tool to extrapolate emerging molecular data into an in vivo setting and may well allow the development of clinical interventions

Free speech versus marginalized groups: Public and newspaper responses to the Charlie Hebdo attack

© 2019 NOND of AEJMC. This study explores how British and American newspapers covered the 2015 terrorist attack on Charlie Hebdo. British newspapers prioritize free speech and the protection of marginalized groups compared with American ones, but both countries differentiate Muslims from radical terrorists. Attention to news media coverage of the attack is positively related to public approval of publishing the cartoons, supporting press freedom. Implications for free speech debate over Charlie Hebdo are discussed

A Metabolic Prototype for Eliminating Tryptophan From The Genetic Code

We set out to reduce the chemical constitution of a living organism to 19 amino acids. A strain was constructed for reassigning the tryptophan codon UGG to histidine and eliminating tryptophan from Escherichia coli. Histidine codons in the gene for an essential enzyme were replaced with tryptophan codons and the restoration of catalytic activity by missense suppressor His-tRNA bearing a CCA anticodon was selected. We used automated cultivation to assess the stability of this genetic construct during evolution. Histidine to tryptophan mutation at codon 30 in the transketolase gene from yeast and its cognate suppressor tRNA were stably propagated in a tktAB deletant of E. coli over 2500 generations. The ratio of histidine misincorporation at tryptophan sites in the proteome increased from 0.0007 to 0.03 over 300 days of continuous culture. This result demonstrated that the genetic code can be forced to evolve by permanent metabolic selection

Facies analyses, chronostratigraphy and paleoenvironemental reconstructions of jurassic to cetaceous sequence of the Congo basin

International audienceThe Congo Basin is characterized by an extensive and relatively thick (ca. 1 km) succession of Jurassic-Cretaceous sedimentary sequences that preserves a unique record of the tectonic and climatic evolution of central Africa during the main period of break-up of Gondwana and the emergence of the Indian and South Atlantic Oceans. New facies analysis and detailed correlations of these ‘Congo’ sequences are described from field observations in the southwestern Congo Basin and by re-logging cores and well logs from four deep boreholes drilled in the center of the basin in the 1950s and 1970s. The lowermost Upper Jurassic sequence (the Stanleyville Group) records a short marine incursion of the proto-Indian Ocean into the northern Congo Basin, and is in turn overlain to the south by widespread aeolian dune deposits (the Lower Kwango Group), which correlate well with other Upper Jurassic to Lower Cretaceous aeolian sequences in Namibia and eastern Brazil, attesting to a giant ‘Sahara-like’ paleo-desert across central West Gondwana, just before the separation of Africa from South America. U-Pb detrital zircons geochronology from this aeolian sequence in the Congo Basin dates mid-Silurian (ca. 430 Ma), Permian-Triassic (ca. 240 and 290 Ma) and Jurassic (ca. 190 Ma) magmatic zircons, here proposed to have been sourced from abundant volcanic activity along the proto-Andes, in southernmost Gondwana. Two successive middle Cretaceous lacustrine sequences in the center of the Congo Basin (the Loia and Bokungu Groups), first analcime-rich and episodically anoxic, and then more carbonated, are interpreted to record an episode of basin stagnation following the eruption of the Paraná-Etendeka Large Igneous Province and a subsequent hot/humid climate maximum during the opening of the South Atlantic Ocean. Late Cretaceous sedimentation in the Congo Basin terminated with fluvial sediments (the Upper Kwango Group) suggesting marginal uplifts during the Kalahari epeirogeny. The top of these sequences is truncated by a regional Cenozoic peneplanation surface

Cell wall as a target for bacteria inactivation by pulsed electric fields

International audienceThe integrity and morphology of bacteria is sustained by the cell wall, the target of the main microbial inactivation processes. One promising approach to inactivation is based on the use of pulsed electric fields (PEF). The current dogma is that irreversible cell membrane electro-permeabilisation causes the death of the bacteria. However, the actual effect on the cell-wall architecture has been poorly explored. Here we combine atomic force microscopy and electron microscopy to study the cell-wall organization of living Bacillus pumilus bacteria at the nanoscale. For vegetative bacteria, exposure to PEF led to structural disorganization correlated with morphological and mechanical alterations of the cell wall. For spores, PEF exposure led to the partial destruction of coat protein nanostructures, associated with internal alterations of cortex and core. Our findings reveal for the first time that the cell wall and coat architecture are directly involved in the electro-eradication of bacteria

Toward an orthogonal central dogma

The central dogma processes of DNA replication, transcription, and translation are responsible for the maintenance and expression of every gene in an organism. An orthogonal central dogma may insulate genetic programs from host regulation and allow expansion in the roles of these processes within the cell

Aerogel Processing

International audienceOne of the problems largely commented in the sol-gel science is how to make large bodies, because gels tend to crack during drying. The drying stresses are attributed to capillary phenomena and differential strain which result from a pressure gradient in the pore liquid. By the supercritical drying (SCD), the capillary stresses are eliminated and monolithic aerogel can be obtained. This chapter focuses on silica aerogel, the most studied aerogel. It presents an overview of the supercritical drying techniques, but also some of the remarkable aerogel properties (optical, mechanical, thermal and acoustical, etc.) with respect to its peculiar microstructure. The chapter briefly presents other kinds of aerogels (oxides and chalcogenideaerogels, composite aerogels, organic aerogels, etc.) and a panel of potential applications