Non-linear conductivity and quantum interference in disordered metals

We report on a novel non-linear electric field effect in the conductivity of disordered conductors. We find that an electric field gives rise to dephasing in the particle-hole channel, which depresses the interference effects due to disorder and interaction and leads to a non-linear conductivity. This non-linear effect introduces a field dependent temperature scale $T_E$ and provides a microscopic mechanism for electric field scaling at the metal-insulator transition. We also study the magnetic field dependence of the non-linear conductivity and suggest possible ways to experimentally verify our predictions. These effects offer a new probe to test the role of quantum interference at the metal-insulator transition in disordered conductors.Comment: 5 pages, 3 figure

Experiencing smallpox in eighteenth-century England

This thesis explores eighteenth-century smallpox to investigate the course, management and control of the disease by communities, families and individuals. It focusses first on the prevalence of smallpox in Oxfordshire demonstrating that smallpox mortality in the county reduced during the century because, even before inoculation was practised, the disease was clearly being controlled through community and familial responsibility; containment and isolation practices were successful in impeding the disease. Secondly, the thesis uses the combination of parish register data and family reconstitution to reconstruct three catastrophic outbreaks in the county. It ascertains a causal relationship between adult and child deaths and presents new knowledge on pathways of smallpox transmission and the nature of familial proximity. Moreover it establishes a direct relationship between changes in behavioural patterns and adult smallpox deaths. Drawing from a national body of life-writings the roles of smallpox carers are also scrutinised, revealing their high levels of stress but also their resilience thanks to integrated and reciprocal support. Spousal, parental and kinship networks were vital components of this care. Thirdly, the thesis explores how inoculation was practised in Oxfordshire from the 1760s onwards. Despite the difficulties and conflicts encountered by practitioners, it is clear that local provision was characterised by demand-led and well-organised programmes, conclusions that help to explain the high levels of local immunity. It also argues that inoculation was a likely factor in the rise in smallpox mortality in the late 1760s and early 1770s, although the absence of major outbreaks of smallpox in Oxfordshire after the 1770s and the high level of inoculation activity in the county and its regions indicate that the practice was reducing smallpox mortality by that time. The procedure was generally more accepted by the younger generation despite the sometimes irreconcilable family differences. This helps explain reduced infant mortality in the later eighteenth century since it is shown that infants were most at risk of smallpox from the home environment and thus the immunity of parents to smallpox through inoculation was a key factor in reducing overall infant mortality

Animal suffering calls for more than a bigger cage

Ng (2016) argues for incremental welfare biology partly because it would be impossible to demonstrate conclusively that animals are sentient. He argues that low cost changes in industrial practices and working collaboratively may be more effective in advancing animal welfare than more adversarial approaches. There is merit in some of Ng’s recommendations but a number of his arguments are, in my view, misdirected. The fact that nonhuman animals feel has already been adequately demonstrated. Cruelty to animals is intrinsic to some industries, so the only way to oppose it is to oppose the industry

Urbanisation is associated with reduced Nosema sp. infection, higher colony strength and higher richness of foraged pollen in honeybees

Bees are vital pollinators, but are faced with numerous threats that include loss of floral resources and emerging parasites amongst others. Urbanisation is a rapidly expanding driver of land-use change that may interact with these two major threats to bees. Here we investigated effects of urbanisation on food store quality and colony health in honeybees (Apis mellifera) by sampling 51 hives in four different land-use categories: urban, suburban, rural open and rural wooded during two seasons (spring and autumn). We found positive effects of urban land use on colony strength and richness of stored pollen morphotypes, alongside lower late-season Nosema sp. infection in urban and suburban colonies. Our results reveal that honeybees exhibit lower colony performance in strength in rural areas, adding to the growing evidence that modern agricultural landscapes can constitute poor habitat for insect pollinators

Semiclassical description of resonant tunneling

We derive a semiclassical formula for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The calculations idealize an experimental situation where a strong magnetic field tilted with respect to an electric field is used. The resulting semiclassical expression is written as the sum over special periodic orbits which hit both walls of the quantum well and are perpendicular to the first wall.Comment: LaTeX, 8 page

Bioprospecting halotolerant lignocellulolytic enzymes from salt marsh ecosystems

Lignocellulose is an abundant agricultural waste product presenting an attractive renewable feedstock for ethanol production. Currently, lignocellulosic bioprocessing is economically constrained requiring expensive pretreatments, high enzyme loadings and large volumes of freshwater imposing water security concerns. Seawater is an abundant and inexpensive prospective replacement solvent. The discovery of highly active halotolerant enzymes with novel tolerances may enable seawater incorporation in bioprocessing; sustainably improving process economics and mitigating water security concerns. Salt marshes are intertidal ecosystems where lignocellulose is remineralised within the predominantly marine organic rich sediments; representing model ecosystems for targeted bioprospecting of highly active, halotolerant and inhibitor resistant enzymes. In this thesis, salt marsh carbon cycling is explored using an in situ degradation experiment. Metatranscriptomics in conjunction with metasecretome proteomics enabled the identification of the lignocellulose-associated enzymatic profile at the ecosystem level and their most likely taxonomic origin. Amplicon sequencing was conducted to reveal the abundance profile for key taxa. Investigations revealed 11,268 identifiable biomass associated proteins, 410 of which were annotated as putative carbohydrate active domains within 307 proteins. The ecosystem level profile displayed a preference for cellulose over matrix polysaccharide deconstruction. Carbohydrate esterase family 1 enzymes were highly abundant; however, lignin modifying enzymes were not, suggesting a decoupling mechanism for accessibility in lieu of oxidative modification. Fungi made no contribution to the lignocellulolytic library; the dominant lignocellulolytic producing taxa were bacteria, identified as the Proteobacteria and Bacteroidetes families Flavobacteriaceae, Alteromonadaceae, Cytophagaceae, Saccharospirillaceae, Marinilabiaceae, Flammeovirgaceae, Bacteroidaceae and Vibrionaceae and Sphingobacteriaceae. A spectrum of potential enzymes were selected for expression in a heterologous system; two enzymes were characterised in depth and both demonstrated halotolerance. This included a putative GH6; identified as an exo-ß-1,4-glucanase with significant activity on crystalline cellulose. A second protein displayed a product profile representative of a ß-1,4-glucosidase with significant transglycosylase activity on oligosaccharide substrates

Creation of solitons and vortices by Bragg reflection of Bose-Einstein condensates in an optical lattice

We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion.Comment: 5 pages including 5 figures (for higher resolution figures please email the authors