Analysis of elevated temperature data for thermodynamic properties of selected radionuclides

This report is a review of chemical thermodynamic data for Ni, Zr, Tc, U, Np, Pu and Am in aqueous solutions at elevated temperatures. Thermodynamic data for aqueous reactions over the temperature range 20-150{degrees}C are needed for geochemical modeling studies of the Yucca Mountain Project. The present review is focused on the aqueous complexes relevant to expected conditions in the Yucca Mountain region: primarily the hydroxide, carbonate, sulfate and fluoride complexes with the metal ions. Existing thermodynamic data are evaluated, and means of extrapolating 25{degrees}C data to the temperatures of interest are discussed. There will be a separate review of solubility data for relevant Ni, Zr, Tc, Np, Pu and Am compounds

Glider observations of enhanced deep water upwelling at a shelf break canyon: a mechanism for cross-slope carbon and nutrient exchange

Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf-break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons. As the slope current reverts to poleward flow, the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region. The upwelled features are identified by the presence of sub-pycnocline high salinity water on the shelf, and are upwelled from a depth of 300 m on the slope, thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf

Magnetic Reconnection in Extreme Astrophysical Environments

Magnetic reconnection is a basic plasma process of dramatic rearrangement of magnetic topology, often leading to a violent release of magnetic energy. It is important in magnetic fusion and in space and solar physics --- areas that have so far provided the context for most of reconnection research. Importantly, these environments consist just of electrons and ions and the dissipated energy always stays with the plasma. In contrast, in this paper I introduce a new direction of research, motivated by several important problems in high-energy astrophysics --- reconnection in high energy density (HED) radiative plasmas, where radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. I identify the key processes distinguishing HED reconnection: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and Compton resistivity); and, at the most extreme end, QED effects, including pair creation. I then discuss the main astrophysical applications --- situations with magnetar-strength fields (exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares and magnetically-powered central engines and jets of GRBs. Here, magnetic energy density is so high that its dissipation heats the plasma to MeV temperatures. Electron-positron pairs are then copiously produced, making the reconnection layer highly collisional and dressing it in a thick pair coat that traps radiation. The pressure is dominated by radiation and pairs. Yet, radiation diffusion across the layer may be faster than the global Alfv\'en transit time; then, radiative cooling governs the thermodynamics and reconnection becomes a radiative transfer problem, greatly affected by the ultra-strong magnetic field. This overall picture is very different from our traditional picture of reconnection and thus represents a new frontier in reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic reconnection). Article is based on an invited review talk at the Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA; February 8-12, 2010). 30 pages, no figure

Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland

Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG’s terminus occupies a large overdeepening. HG’s retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°C a–1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG’s northern lateral margin. Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72 km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century

The Flow Country: The peatlands of Caithness and Sutherland

This NCC publication is one of two which describes the nature conservation interest and importance of the Flow Country, in Caithness and Sutherland, northern Scotland. This area is now recognised as the largest expanse of blanket bog in Europe and the report provided the first global review of the extent of this peatland type. The Flow Country is of outstanding importance, both nationally and internationally. These peatlands are three times larger than any other in either Britain or Ireland. The scale and diversity of the habitat is unique, and the total size and range of bird species present, and other aspects of the fauna, is of international importance. At the time of publication, in the mid-1980s, this area was suffering from widespread afforestation. This 1988 review summarised NCC’s detailed surveys of peatland vegetation in the Flow Country, and is complementary to a 1987 publication Birds, bogs and forestry: the peatlands of Caithness and Sutherland which outlined the ornithological importance of this area, and documented and called for a halt to the destructive afforestation which was then occurring

Suppression of Quantum Phase Interference in Molecular Magnets Fe₈ with Dipolar-Dipolar Interaction

Renormalized tunnel splitting with a finite distribution in the biaxial spin model for molecular magnets is obtained by taking into account the dipolar interaction of enviromental spins. Oscillation of the resonant tunnel splitting with a transverse magnetic field along the hard axis is smeared by the finite distribution which subsequently affects the quantum steps of hysteresis curve evaluated in terms of the modified Landau-Zener model of spin flipping induced by the sweeping field. We conclude that the dipolar-dipolar interaction drives decoherence of quantum tunnelling in molcular magnets Fe₈, which explains why the quenching points of tunnel spliting between odd and even resonant tunnelling predcited theoretically were not observed experimentally.Comment: 5 pages including 3 figure and 1 table. To appear in Physical Review

Magnetar outbursts: an observational review

Transient outbursts from magnetars have shown to be a key property of their emission, and one of the main way to discover new sources of this class. From the discovery of the first transient event around 2003, we now count about a dozen of outbursts, which increased the number of these strongly magnetic neutron stars by a third in six years. Magnetar outbursts might involve their multi-band emission resulting in an increased activity from radio to hard X-ray, usually with a soft X-ray flux increasing by a factor of 10-1000 with respect to the quiescent level. A connected X-ray spectral evolution is also often observed, with a spectral softening during the outburst decay. The flux decay times vary a lot from source to source, ranging from a few weeks to several years, as also the decay law which can be exponential-like, a power-law or even multiple power-laws can be required to model the flux decrease. We review here on the latest observational results on the multi-band emission of magnetars, and summarize one by one all the transient events which could be studied to date from these sources.Comment: 34 pages, 6 figures. Chapter of the Springer Book ASSP 7395 "High-energy emission from pulsars and their systems", proceeding of the Sant Cugat Forum on Astrophysics (12-16 April 2010). Review updated to January 201

Using Genetic Variation to Explore the Causal Effect of Maternal Pregnancy Adiposity on Future Offspring Adiposity: A Mendelian Randomisation Study

Background: It has been suggested that greater maternal adiposity during pregnancy affects lifelong risk of offspring fatness via intrauterine mechanisms. Our aim was to use Mendelian randomisation (MR) to investigate the causal effect of intrauterine exposure to greater maternal body mass index (BMI) on offspring BMI and fat mass from childhood to early adulthood. Methods and Findings: We used maternal genetic variants as instrumental variables (IVs) to test the causal effect of maternal BMI in pregnancy on offspring fatness (BMI and dual-energy X-ray absorptiometry [DXA] determined fat mass index [FMI]) in a MR approach. This was investigated, with repeat measurements, from ages 7 to 18 in the Avon Longitudinal Study of Parents and Children (ALSPAC; n = 2,521 to 3,720 for different ages). We then sought to replicate findings with results for BMI at age 6 in Generation R (n = 2,337 for replication sample; n = 6,057 for total pooled sample). In confounder-adjusted multivariable regression in ALSPAC, a 1 standard deviation (SD, equivalent of 3.7 kg/m2) increase in maternal BMI was associated with a 0.25 SD (95% CI 0.21–0.29) increase in offspring BMI at age 7, with similar results at later ages and when FMI was used as the outcome. A weighted genetic risk score was generated from 32 genetic variants robus

Temporal fluctuations of waves in weakly nonlinear disordered media

We consider the multiple scattering of a scalar wave in a disordered medium with a weak nonlinearity of Kerr type. The perturbation theory, developed to calculate the temporal autocorrelation function of scattered wave, fails at short correlation times. A self-consistent calculation shows that for nonlinearities exceeding a certain threshold value, the multiple-scattering speckle pattern becomes unstable and exhibits spontaneous fluctuations even in the absence of scatterer motion. The instability is due to a distributed feedback in the system "coherent wave + nonlinear disordered medium". The feedback is provided by the multiple scattering. The development of instability is independent of the sign of nonlinearity.Comment: RevTeX, 15 pages (including 5 figures), accepted for publication in Phys. Rev.