Transient dynamics of vulcanian explosions and column collapse

Several analytical and numerical eruption models have provided insight into volcanic eruption behaviour, but most address plinian-type eruptions where vent conditions are quasi-steady. Only a few studies have explored the physics of short-duration vulcanian explosions with unsteady vent conditions and blast events. Here we present a technique that links unsteady vent flux of vulcanian explosions to the resulting dispersal of volcanic ejecta, using a numerical, axisymmetric model with multiple particle sizes. We use observational data from well documented explosions in 1997 at the Soufrière Hills volcano in Montserrat, West Indies, to constrain pre-eruptive subsurface initial conditions and to compare with our simulation results. The resulting simulations duplicate many features of the observed explosions, showing transitional behaviour where mass is divided between a buoyant plume and hazardous radial pyroclastic currents fed by a collapsing fountain. We find that leakage of volcanic gas from the conduit through surrounding rocks over a short period (of the order of 10 hours) or retarded exsolution can dictate the style of explosion. Our simulations also reveal the internal plume dynamics and particle-size segregation mechanisms that may occur in such eruptions.     

The auroral footprint of Enceladus on Saturn

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity.     

Non-mitochondrial complex I proteins in a hydrogenosomal oxidoreductase complex

Trichomonas vaginalis is a unicellular microaerophilic eukaryote that lacks mitochondria yet contains an alternative organelle, the hydrogenosome, involved in pyruvate metabolism. Pathways between the two organelles differ substantially: in hydrogenosomes, pyruvate oxidation is catalysed by pyruvate:ferredoxin oxidoreductase (PFOR), with electrons donated to an [Fe]-hydrogenase which produces hydrogen. ATP is generated exclusively by substrate-level phosphorylation in hydrogenosomes, as opposed to oxidative phosphorylation in mitochondria. PFOR and hydrogenase are found in eubacteria and amitochondriate eukaryotes, but not in typical mitochondria. Analyses of mitochondrial genomes indicate that mitochondria have a single endosymbiotic origin from an alpha-proteobacterial-type progenitor. The absence of a genome in trichomonad hydrogenosomes precludes such comparisons, leaving the endosymbiotic history of this organelle unclear. Although phylogenetic reconstructions of a few proteins indicate that trichomonad hydrogenosomes share a common origin with mitochondria, others do not. Here we describe a novel NADH dehydrogenase module of respiratory complex I that is coupled to the central hydrogenosomal fermentative pathway to form a hydrogenosomal oxidoreductase complex that seems to function independently of quinones. Phylogenetic analyses of hydrogenosomal complex I-like proteins Ndh51 and Ndh24 reveal that neither has a common origin with mitochondrial homologues. These studies argue against a vertical origin of trichomonad hydrogenosomes from the proto-mitochondrial endosymbiont.     

Superconducting quantum bits

Superconducting circuits are macroscopic in size but have generic quantum properties such as quantized energy levels, superposition of states, and entanglement, all of which are more commonly associated with atoms. Superconducting quantum bits (qubits) form the key component of these circuits. Their quantum state is manipulated by using electromagnetic pulses to control the magnetic flux, the electric charge or the phase difference across a Josephson junction (a device with nonlinear inductance and no energy dissipation). As such, superconducting qubits are not only of considerable fundamental interest but also might ultimately form the primitive building blocks of quantum computers.     

Improved immunogenicity of a peptide epitope after fusion to hepatitis B core protein

Synthetic vaccines for viral diseases can use defined regions of viral proteins as immunogens: the peptide sequence of amino acids 141-160 of the VP1 protein of foot and mouth disease virus (FMDV) elicits virus-neutralizing antibodies to protect guinea pigs, cattle and pigs either when coupled to a carrier protein or when administered in liposomes or in incomplete Freund's adjuvant. The immune response to these peptides is much lower than that to complete virus particles and the same sequence fused to the N terminus of beta-galactosidase did not produce a more potent immunogen than synthetic peptide alone. We report here an expression system for immunogenic epitopes linked to a carrier protein, hepatitis B core antigen, to form part of a virus-like complex which can present these epitopes to the immune system at high density. The immunogenicity of these structures approaches that of FMDV particles.