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

Biotin-independent strains of Escherichia coli for enhanced streptavidin production

Biotin is an archetypal vitamin used as cofactor for carboxylation reactions found in all forms of life. However, biotin biosynthesis is an elaborate multi-enzymatic process and metabolically costly. Moreover, many industrially relevant organisms are incapable of biotin synthesis resulting in the requirement to supplement defined media. Here we describe the creation of biotin-independent strains of Escherichia coli and Corynebacterium glutamicum through installation of an optimized malonyl-CoA bypass, which re-routes natural fatty acid synthesis, rendering the previously essential vitamin completely obsolete. We utilize biotin-independent E. coli for the production of the high-value protein streptavidin which was hitherto restricted because of toxic effects due to biotin depletion. The engineered strain revealed significantly improved streptavidin production resulting in the highest titers and productivities reported for this protein to date

E. coli surface display of streptavidin for directed evolution of an allylic deallylase

Artificial metalloenzymes (ArMs hereafter) combine attractive features of both homogeneous catalysts and enzymes and offer the potential to implement new-to-nature reactions in living organisms. Herein we present an E. coli surface display platform for streptavidin (Sav hereafter) relying on an Lpp-OmpA anchor. The system was used for the high throughput screening of a bioorthogonal CpRu-based artificial deallylase (ADAse) that uncages an allylcarbamate-protected aminocoumarin 1. Two rounds of directed evolution afforded the double mutant S112M-K121A that displayed a 36-fold increase in surface activity vs. cellular background and a 5.7-fold increased in vitro activity compared to the wild type enzyme. The crystal structure of the best ADAse reveals the importance of mutation S112M to stabilize the cofactor conformation inside the protein

‘This town’s a different town today’:: Policing and regulating the night-time economy

This article considers recent policing and regulatory responses to the night-time economy in England and Wales. Drawing upon the findings of a broader two-year qualitative investigation of local and national developments in alcohol policy, it identifies a dramatic acceleration of statutory activity, with 12 new or revised powers, and several more in prospect, introduced by the Labour Government within its first decade in office. Interview data and documentary sources are used to explore the degree to which the introduction of such powers, often accompanied by forceful rhetoric and high profile police action, has translated into a sustained expansion of control. Many of the new powers are spatially directed, as well as being focused upon the actions of distinct individuals or businesses, yet the willingness and capacity to apply powers to offending individuals in comparison to businesses is often variable and asymmetrical. The practice of negotiating order in the night-time economy is riddled with tensions and ambiguities that reflect the ad hoc nature and rapid escalation of the regulatory architecture. Night-time urban security governance is understood as the outcome of subtle organizational and interpersonal power-plays. Social orders, normative schemas and apportionments of blame thus arise as a byproduct of patterned (structural) relations

Infrared absorption analysis of organosilicon/oxygen plasmas in a microwave multipolar plasma excited by distributed electron cyclotron resonance

The dissociation of 4 groups of organosilicon monomers (such as hexamethydisiloxane, tetraethoxysilane, tetramethylsilane or tetramethoxysilane) in a MMP DECR reactor is analyzed by infrared absorption spectroscopy. The parent molecules are totally dissociated above 100 watts. The daughter stable molecules, such as C2H2, CH4, CO2, CO, C2H4 and OCH2 have been detected at low power but are dissociated at higher power. Each group exhibits its very own characteristics of dissociation as well as production of new species depending on its chemical composition. It seems that the DECR plasma at high energy dissociates the monomer molecule into its constituent atoms.La dissociation de 4 groupes de monomères organosiliciés (tels que l'hexaméthydisiloxane, le tétraéthoxysilane, le tétraméthylsilane ou encore le tétraméthoxysilane) dans un réacteur PMM RCER est analysée par spectroscopie d'absorption infrouge. Les molécules mères sont totalement dissociées au delà de 100 watts. Des molécules stables telles que C2H2, CH4, CO2, CO, C2H4 et OCH2 ont été détectées à faible puissance mais sont dissociées à plus forte énergie. Chaque groupe fait apparaitre ses propres charactéristiques au niveau de la dissociation ainsi que de la production de nouvelles espèces en fonction de sa composition chimique. Il semble que le plasma RCER dissocie les molécules en espèces atomiques

A Metabolic Prototype for Eliminating Tryptophan From The Genetic Code

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