How does flow in a pipe become turbulent?

The transition to turbulence in pipe flow does not follow the scenario familiar from Rayleigh-Benard or Taylor-Couette flow since the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when the flow speed is high enough and the perturbation sufficiently strong such that turbulent flow is established, it can return to the laminar state without any indication of the imminent decay. In this parameter range, the lifetimes of perturbations show a sensitive dependence on initial conditions and an exponential distribution. The turbulence seems to be supported by three-dimensional travelling waves which appear transiently in the flow field. The boundary between laminar and turbulent dynamics is formed by the stable manifold of an invariant chaotic state. We will also discuss the relation between observations in short, periodically continued domains, and the dynamics in fully extended puffs.Comment: for the proceedings of statphys 2

The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8 figure

Giant rafted pumice blocks from the most recent eruption of Taupo volcano, New Zealand: Insights from palaeomagnetic and textural data

Giant blocks of pumice lie strewn along a former shoreline of intracaldera Lake Taupo, New Zealand, and are the sole subaerial evidence of the most recent volcanism at the Taupo supervolcano. Geochemically they are identical to material erupted during the complex and multiphase 1.8 ka Taupo eruption, which they post-date by one to two decades. The blocks, some of which are >10 m long, show complex jointing patterns indicative of both surface chilling and continued interior expansion, as well as heterogeneous vesicularity, with dense rims (mean density 917 kg/m3) grading via an intervening transition zone (mean density 844 kg/m3) into a more highly vesicular interior (mean density 815 kg/m3). Analysis of thermal demagnetisation data indicates significant reorientation of the blocks as they cooled through a series of blocking temperatures. Some parts of block rims cooled to below 580 °C well before emplacement on the shore, whereas other parts in the interior and transition zones, which cooled more slowly, acquired different orientations before stranding. Some block interiors cooled after blocks were finally deposited, and record the direction of the 1.8 ka field. The blocks are believed to be derived from one or both of a pair of rhyolitic lava domes that developed on the bed of Lake Taupo several decades after the climactic Taupo eruption over the inferred vent area.These, and similar giant rafted pumice blocks in other marine and lacustrine settings raise a number of questions about how volatile-rich felsic magma can be erupted underwater with only limited thermal fragmentation. Furthermore, the prolonged flotation of out-sized fragments of vesiculated magma formed during subaqueous dome-growth contrasts with the rapid sinking of smaller pieces of hot plinian pumice under laboratory conditions. The genesis of pumice forming the blocks is not entirely clear. Most simply the blocks may represent part of a vesiculated carapace of a growing lava dome, broken loose as the dome grew and deformed then rising buoyantly to the surface. Parts of the carapace could also be released by local magma-water explosions. Some textures of the pumice, however, suggest fresher magma released from beneath the carapace. This may suggest that silicic dikes and pillows/pods intruded into a growing mound of silicic hyaloclastite, itself formed by quench fragmentation and thermal granulation of the dike margins. This fragmental cover would have inhibited cooling of a still-hot and actively vesiculating interior, which was then released to float to the surface by gravitational destabilisation and collapse of the growing pile. Following their formation, the large fragments of pumice floated to the lake's surface, where they were blown ashore to become embedded in accumulating transgressive shoreface sediments and continue cooling

Energy loss due to defect formation from 206Pb recoils in SuperCDMS germanium detectors

The Super Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory studied energy loss associated with defect formation in germanium crystals at mK temperatures using in situ 210Pb sources. We examine the spectrum of 206Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of (6:08 ± 0:18)%, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of 19.7+0.6−0.5 eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches

Integrated analysis of environmental and genetic influences on cord blood DNA methylation in new-borns

Epigenetic processes, including DNA methylation (DNAm), are among the mechanisms allowing integration of genetic and environmental factors to shape cellular function. While many studies have investigated either environmental or genetic contributions to DNAm, few have assessed their integrated effects. Here we examine the relative contributions of prenatal environmental factors and genotype on DNA methylation in neonatal blood at variably methylated regions (VMRs) in 4 independent cohorts (overall n = 2365). We use Akaike’s information criterion to test which factors best explain variability of methylation in the cohort-specific VMRs: several prenatal environmental factors (E), genotypes in cis (G), or their additive (G + E) or interaction (GxE) effects. Genetic and environmental factors in combination best explain DNAm at the majority of VMRs. The CpGs best explained by either G, G + E or GxE are functionally distinct. The enrichment of genetic variants from GxE models in GWAS for complex disorders supports their importance for disease risk

Defra Soil Protection Research in the Context of the Soil Natural Capital / Ecosystem Services Framework

Summary: "A Nation that destroys its soil destroys itself." This quote from, F.D. Roosevelt, 1937, from a letter written to all state Governors in the USA following the dust bowl, encapsulates the importance of soil protection. The dust bowl brought about legislation to protect and conserve soils as a fundamental natural resource in the USA between 1930 and 1936. In current times we are facing unprecedented pressure on land resources from multiple uses here in the UK and across Europe. In response to these increasing pressures Defra has produced soil protection reports and strategies including the report, ‘Safeguarding our Soils: A Strategy for England’ (PB13297). The vision statement of this document reads, ‘By 2030, all England’s soils will be managed sustainably and degradation threats tackled successfully. This will improve the quality of England’s soils and safeguard their ability to provide essential services for future generations.’ Similarly, the Welsh Assembly Government commissioned, ‘The Welsh Soils Action Plan’ (WSAP, 2009) which has a similar goal. These documents set out the pressing issues with regard to soils, their management and protection, and therefore serve as a useful contextual tool for synthesizing past Defra research with regard to current issues. This report synthesises soil protection research commissioned by Defra between 1990 and 2008, to provide the state of current Defra knowledge with regard to soil protection. Contextually, an attempt is made to fit the synthesized knowledge into the Natural Capital / Ecosystem Services framework. It offers a bold, fresh approach that will orient the report firmly in the context of strengthening the linking of science and policy through Natural Capital and Ecosystem Services, and firmly aligns the research with ongoing EU efforts. The report is comprised of 5 work packages for Defra project SP1607 “Defra research on soil protection 1990 - 2008: Synthesis of outputs’. Defra has made a firm commitment to adopt the ecosystems approach which is designed to convey the value of ecosystems, their capital, and their goods and services into the decision making / policy development process. The workpackages address the following: WP1: Chapter 1) Place England and Wales soil policy and research efforts in the wider context of European and International policy. Chapter 2) Identify and synthesize knowledge of needs of farmers, resource managers and the wider society. Chapter 3) Describe the soil natural capital / ecosystem services framework. WP2: Chapter 4) Evaluate current indicators and soil sampling/measurement strategy. Chapter 5) Evaluate work done on the quantification of soil capital. Chapter 6) Evaluate work done on the soil Ecosystem Services. WP3: Chapter 7) Identify Impact of climate change on soils, soil function, and threats to soil protection. Chapter 8) Identify threats to soils, for the England and Wales context; Evaluate research tackling threats that may degrade soil capital or reduce services. WP4: Chapter 9) Evaluate work done on the valuing of soil Natural Capital. WP5: Chapter 10) Future Vision

Serum leptin and cognitive function in people with Type 2 diabetes

People with obesity and type 2 diabetes are at increased risk of cognitive impairment. We aimed to investigate the association of leptin with cognitive abilities in an elderly population with type 2 diabetes. We performed a cross-sectional study of 1057 men and women aged 60–75 years with type 2 diabetes living in Lothian (Scotland). A cognitive battery was administered. Prior intelligence was estimated from vocabulary testing and adjustment for scores on this test was used to estimate lifetime cognitive change. Relationships between fasting morning leptin levels and cognitive ability and estimated cognitive change were tested. Higher leptin levels were associated with significantly poorer estimated overall cognitive decline, and poorer performance in 2 cognitive domains assessing mental flexibility and executive function, only amongst men (p < 0.05). High morning leptin levels in elderly men with type 2 diabetes are associated with estimated age-related cognitive change