Finite momentum condensation in a pumped microcavity

We calculate the absorption spectra of a semiconductor microcavity into which a non-equilibrium exciton population has been pumped. We predict strong peaks in the spectrum corresponding to collective modes analogous to the Cooper modes in superconductors and fermionic atomic gases. These modes can become unstable, leading to the formation of off-equilibrium quantum condensates. We calculate a phase diagram for condensation, and show that the dominant instabilities can be at a finite momentum. Thus we predict the formation of inhomogeneous condensates, similar to Fulde-Ferrel-Larkin-Ovchinnikov states.Comment: 7 pages, 4 figures, updated to accepted versio

Reappraising the role of the vagus nerve in GLP-1-mediated regulation of eating.

Here, we provide a focused review of the evidence for the roles of the vagus nerve in mediating the regulatory effects of peripherally and centrally produced GLP-1 on eating behaviour and energy balance. We particularly focus on recent studies which have used selective genetic, viral, and transcriptomic approaches to provide important insights into the anatomical and functional organisation of GLP-1-mediated gut-brain signalling pathways. A number of these studies have challenged canonical ideas of how GLP-1 acts in the periphery and the brain to regulate eating behaviour, with important implications for the development of pharmacological treatments for obesity

An analysis of the distribution and abundance of sandeels in grey seals' foraging hotspots around the Inner Hebrides, West Scotland

Quantifying the abundance and distribution of sandeels in grey seal foraging areas will provide an improved understanding of habitat use of grey seals on the West Coast of Scotland. The lesser sandeel, Ammodytes marinus, is a key food for many seabirds and seals, and is also the target of the largest single-species fishery in the North Sea (Furness, 2002).Fisheries acoustic data were collected during 2 cruises in May 2004 and July 2004 around the Inner Hebrides, West Scotland. A fully calibrated EK500 echosounder was used, operating at two frequencies (38kHz and 120kHz). The collected data was processed using SonarData Echoview software. Acoustic identification of sandeels was established by using a dB difference algorithm (?MVBS = MVBS38 - MVBS120; where ?MVBS < -1 indicated sandeels). The resulting Nautical Area Backscattering Coefficient (NASC) was integrated for each 0.5 nmi interval and converted to a relative estimate of mean sandeel density in seal foraging areas. Information on the spatial distribution and movements of 34 grey seals around the West Coast of Scotland in 2003 and 2004 have been collected by SMRU using Satellite Relay Data Loggers (SDRL) and will be used to compare sandeel densities and distribution in areas of high seal usage.The results indicated that the distribution of sandeels was extremely patchy along transects and the cruise track. A comparison of the relative abundance of sandeels in foraging areas showed that densities vary extremely between these areas. Highest densities of sandeels were recorded East of Tiree on the 14th of May and in Stanton Banks on the 17th of July.Future research will involve establishing a correlation between seal usage of foraging areas and sandeel abundance and distribution. In addition, the analysis of other fish species and zooplankton in these areas will contribute to a further understanding of foraging strategies of grey seals. The capabilities of underwater acoustic research and their implementation in ecosystem-based studies are constantly evolving. Interdisciplinary research should be encouraged in order to provide useful insights in ecosystem dynamics but also to benefit fisheries and conservation management strategies

Uncertainty in the sensitivity of Arctic sea ice to global warming in a perturbed parameter climate model ensemble

The retreat of Arctic sea ice is a very likely consequence of climate change and part of a key feedback process, which can accelerate global warming. The uncertainty in predictions in the rate of sea ice retreat requires quantification and ultimately reduction via observational constraints. Here we analyse a climate model ensemble with perturbations to parameters in the atmosphere model. We find a large range of the sensitivity of Arctic sea-ice retreat to global temperature change, from 11 to 18% per degrees C. This is placed in the context of the uncertainty obtained by alternative model ensembles. Reasons for the different sensitivities are explored and we find that differences in the amount of ocean and atmospheric heat transported from low to high latitudes dominates over local radiative contributions to the heat budget. Furthermore, we find no significant relationship between the uncertainty in sea ice response to climate change and climate sensitivity

A study of senescence in the red raspberry cane

This archival publication may not reflect current scientific knowledge or recommendations

Hydromorphological frameworks: emerging trajectories

This paper forms a postscript to a Special Issue that reports on research funded through the European Union’s FP7 programme under Grant Agreement No. 282656 (REFORM)

Affine Constellations Without Mutually Unbiased Counterparts

It has been conjectured that a complete set of mutually unbiased bases in a space of dimension d exists if and only if there is an affine plane of order d. We introduce affine constellations and compare their existence properties with those of mutually unbiased constellations, mostly in dimension six. The observed discrepancies make a deeper relation between the two existence problems unlikely.Comment: 8 page

Statistical mechanics of multipartite entanglement

We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over all balanced bipartitions. We search for those (maximally multipartite entangled) states whose purity is minimum for all bipartitions and recast this optimization problem into a problem of statistical mechanics.Comment: final versio

Constructing Mutually Unbiased Bases in Dimension Six

The density matrix of a qudit may be reconstructed with optimal efficiency if the expectation values of a specific set of observables are known. In dimension six, the required observables only exist if it is possible to identify six mutually unbiased complex 6x6 Hadamard matrices. Prescribing a first Hadamard matrix, we construct all others mutually unbiased to it, using algebraic computations performed by a computer program. We repeat this calculation many times, sampling all known complex Hadamard matrices, and we never find more than two that are mutually unbiased. This result adds considerable support to the conjecture that no seven mutually unbiased bases exist in dimension six.Comment: As published version. Added discussion of the impact of numerical approximations and corrected the number of triples existing for non-affine families (cf Table 3

Climate-groundwater dynamics inferred from GRACE and the role of hydraulic memory

Groundwater is the largest store of freshwater on Earth after the cryosphere and provides a substantial proportion of the water used for domestic, irrigation and industrial purposes. Knowledge of this essential resource remains incomplete, in part, because of observational challenges of scale and accessibility. Here we examine a 14-year period (2002–2016) of GRACE observations to investigate climate-groundwater dynamics of 14 tropical and sub-tropical aquifers selected from WHYMAP's 37 large aquifer systems of the world. GRACE-derived changes in groundwater storage resolved using GRACE JPL Mascons and the CLM Land Surface Model are related to precipitation time series and regional-scale hydrogeology. We show that aquifers in dryland environments exhibit long-term hydraulic memory through a strong correlation between groundwater storage changes and annual precipitation anomalies integrated over the time series; aquifers in humid environments show short-term memory through strong correlation with monthly precipitation. This classification is consistent with estimates of Groundwater Response Times calculated from the hydrogeological properties of each system, with long (short) hydraulic memory associated with slow (rapid) response times. The results suggest that groundwater systems in dryland environments may be less sensitive to seasonal climate variability but vulnerable to long-term trends from which they will be slow to recover. In contrast, aquifers in humid regions may be more sensitive to seasonal climate disturbances such as ENSO-related drought but may also be relatively quick to recover. Exceptions to this general pattern are traced to human interventions through groundwater abstraction. Hydraulic memory is an important factor in the management of groundwater resources, particularly under climate change