Bragg spectroscopy of an accelerating condensate with solitary-wave behaviour

We present a theoretical treatment of Bragg spectroscopy of an accelerating condensate in a solitary-wave state. Our treatment is based on the Gross-Pitaevskii equation with an optical potential representing the Bragg pulse and an additional external time-dependent potential generating the solitary-wave behaviour. By transforming to a frame translating with the condensate, we derive an approximate set of equations that can be readily solved to generate approximate Bragg spectra. Our analytic method is accurate within a well defined parameter regime and provides physical insight into the structure of the spectra. We illustrate our formalism using the example of Bragg spectroscopy of a condensate in a time-averaged orbiting potential trap.Comment: 9 pages, 3 figure

Solitary-wave description of condensate micro-motion in a time-averaged orbiting potential trap

We present a detailed theoretical analysis of micro-motion in a time-averaged orbiting potential trap. Our treatment is based on the Gross-Pitaevskii equation, with the full time dependent behaviour of the trap systematically approximated to reduce the trapping potential to its dominant terms. We show that within some well specified approximations, the dynamic trap has solitary-wave solutions, and we identify a moving frame of reference which provides the most natural description of the system. In that frame eigenstates of the time-averaged orbiting potential trap can be found, all of which must be solitary-wave solutions with identical, circular centre of mass motion in the lab frame. The validity regime for our treatment is carefully defined, and is shown to be satisfied by existing experimental systems.Comment: 12 pages, 2 figure

The insect pathogen Serratia marcescens Db10 uses a hybrid non-ribosomal peptide synthetase-polyketide synthase to produce the antibiotic althiomycin

There is a continuing need to discover new bioactive natural products, such as antibiotics, in genetically-amenable micro-organisms. We observed that the enteric insect pathogen, Serratia marcescens Db10, produced a diffusible compound that inhibited the growth of Bacillis subtilis and Staphyloccocus aureus. Mapping the genetic locus required for this activity revealed a putative natural product biosynthetic gene cluster, further defined to a six-gene operon named alb1-alb6. Bioinformatic analysis of the proteins encoded by alb1-6 predicted a hybrid non-ribosomal peptide synthetase-polyketide synthase (NRPS-PKS) assembly line (Alb4/5/6), tailoring enzymes (Alb2/3) and an export/resistance protein (Alb1), and suggested that the machinery assembled althiomycin or a related molecule. Althiomycin is a ribosome-inhibiting antibiotic whose biosynthetic machinery had been elusive for decades. Chromatographic and spectroscopic analyses confirmed that wild type S. marcescens produced althiomycin and that production was eliminated on disruption of the alb gene cluster. Construction of mutants with in-frame deletions of specific alb genes demonstrated that Alb2-Alb5 were essential for althiomycin production, whereas Alb6 was required for maximal production of the antibiotic. A phosphopantetheinyl transferase enzyme required for althiomycin biosynthesis was also identified. Expression of Alb1, a predicted major facilitator superfamily efflux pump, conferred althiomycin resistance on another, sensitive, strain of S. marcescens. This is the first report of althiomycin production outside of the Myxobacteria or Streptomyces and paves the way for future exploitation of the biosynthetic machinery, since S. marcescens represents a convenient and tractable producing organism

The ‘Interior World’ of the Nineteenth-Century Maloti-Drakensberg Mountains

Over the last four decades researchers have cast the Maloti-Drakensberg Mountains as a marginal refuge for ‘Bushmen’ amidst constricting nineteenth-century frontiers. Rock art scholarship has expanded on this characterisation of mountains as refugia, focusing on heterogeneous raiding bands forging new cultural identities. Here, we propose another view of the Maloti-Drakensberg: a dynamic political theatre in which polities that engaged in illicit or ‘heterodox’ activities like cattle raiding and hunter-gatherer lifeways set the terms of colonial encounters. We employ the concept of the ‘interior world’ to refigure the region as one fostering subsistence and political behaviours that did not conform to the expectations of colonial authority. Paradoxically, such heterodoxies over time constituted widespread social logics within the Maloti-Drakensberg, and thus became commonplace and meaningful. We synthesise historical and archaeological evidence (new and existing) to illustrate the significance of the nineteenth-century Maloti-Drakensberg, offering a revised southeast-African colonial landscape and directions for future research

Discussion required for correct interpretation

Thank you for the opportunity to comment on the editorial by Romero and colleagues [1], which raises a number of important and interesting questions. Such discussion is mandatory if results of scientific techniques such as gene array are to be correctly interpreted and used as the basis for future improvements in patient care

PS1-10jh Continues to Follow the Fallback Accretion Rate of a Tidally Disrupted Star

We present late-time observations of the tidal disruption event candidate PS1-10jh. UV and optical imaging with HST/WFC3 localize the transient to be coincident with the host galaxy nucleus to an accuracy of 0.023 arcsec, corresponding to 66 pc. The UV flux in the F225W filter, measured 3.35 rest-frame years after the peak of the nuclear flare, is consistent with a decline that continues to follow a $t^{-5/3}$ power-law with no spectral evolution. Late epochs of optical spectroscopy obtained with MMT ~ 2 and 4 years after the peak, enable a clean subtraction of the host galaxy from the early spectra, revealing broad helium emission lines on top of a hot continuum, and placing stringent upper limits on the presence of hydrogen line emission. We do not measure Balmer H\delta absorption in the host galaxy strong enough to be indicative of a rare, post-starburst "E+A" galaxy as reported by Arcavi et al. (2014). The light curve of PS1-10jh over a baseline of 3.5 yr is best modeled by fallback accretion of a tidally disrupted star. Its strong broad helium emission relative to hydrogen (He II \lambda 4686/H\alpha > 5) could be indicative of either the hydrogen-poor chemical composition of the disrupted star, or certain conditions in the tidal debris of a solar-composition star in the presence of an optically-thick, extended reprocessing envelope.Comment: Accepted for publication in ApJ Letter

Gut-seeded α-synuclein fibrils promote gut dysfunction and brain pathology specifically in aged mice

Parkinson’s disease is a synucleinopathy that is characterized by motor dysfunction, death of midbrain dopaminergic neurons and accumulation of α-synuclein (α-Syn) aggregates. Evidence suggests that α-Syn aggregation can originate in peripheral tissues and progress to the brain via autonomic fibers. We tested this by inoculating the duodenal wall of mice with α-Syn preformed fibrils. Following inoculation, we observed gastrointestinal deficits and physiological changes to the enteric nervous system. Using the AAV-PHP.S capsid to target the lysosomal enzyme glucocerebrosidase for peripheral gene transfer, we found that α-Syn pathology is reduced due to the increased expression of this protein. Lastly, inoculation of α-Syn fibrils in aged mice, but not younger mice, resulted in progression of α-Syn histopathology to the midbrain and subsequent motor defects. Our results characterize peripheral synucleinopathy in prodromal Parkinson’s disease and explore cellular mechanisms for the gut-to-brain progression of α-Syn pathology