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

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

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

To plug-in or not to plug-in? Geomorphic analysis of rivers using the River Styles Framework in an era of big data acquisition and automation

n an era of big‐data acquisition and semiautomation of geomorphic river surveys, it is timely to consider how to better integrate this into existing and widely used conceptual frameworks and approaches to analysis. We demonstrate how Stage 1 of the River Styles Framework, which entails identification and interpretation of river character and behavior, patterns and controls, can be used as a “powerboard” into which available, developing and future semiautomated tools and workflows can be plugged (or unplugged). Prospectively, such approaches will increase the efficiency and scope of analyses, providing unprecedented insights into the diversity of rivers and their morphodynamics. We appraise the role of human decision‐making in conducting expert‐manual analyses and interpretations. Genuine integration of big‐data analytics, remote‐sensing based tools for semiautomated river analysis with expert‐manual interpretations including field insights, will be an essential ingredient to fully exploit emerging computational and remote sensing technologies to advance our understanding of river systems, to translate information into knowledge, and raise the standards of practice in river science and management

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

Multi-Qubit Systems: Highly Entangled States and Entanglement Distribution

A comparison is made of various searching procedures, based upon different entanglement measures or entanglement indicators, for highly entangled multi-qubits states. In particular, our present results are compared with those recently reported by Brown et al. [J. Phys. A: Math. Gen. 38 (2005) 1119]. The statistical distribution of entanglement values for the aforementioned multi-qubit systems is also explored.Comment: 24 pages, 3 figure

Classical Statistical Mechanics Approach to Multipartite Entanglement

We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over balanced bipartitions. We search for maximally multipartite entangled states, whose average purity is minimal, and recast this optimization problem into a problem of statistical mechanics, by introducing a cost function, a fictitious temperature and a partition function. By investigating the high-temperature expansion, we obtain the first three moments of the distribution. We find that the problem exhibits frustration.Comment: 38 pages, 10 figures, published versio

Setting a precautionary catch limit for Antarctic krill

A revised precautionary catch limit for Antarctic krill (Euphausia superba) in the Scotia Sea of 4 million tons was recently adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The limit was based on a total biomass of 44.3 million tons, as estimated from an acoustic and net survey of krill across the Scotia Sea sector of the Southern Ocean, and a harvest rate of 9.1%, as determined from an analysis of the risks of exceeding defined conservation criteria. We caution, however, that before the fishery can expand to the 4-inillion-ton level it will be necessary to establish mechanisms to avoid concentration of fishing effort, particularly in proximity to colonies of land-breeding krill predators, and to consider the effects of krill immigrating into the region from multiple sources

Modelling physical characteristics of river habitats

The physical characteristics of river habitats constitute the setting in which fluvial biota dwell and thrive. Determining the spatial and temporal patterns of physical habitat characteristics and the main factors that control them is extremely important to increase the efficiency of river management, conservation, and restoration. This study determined spatial patterns of physical habitat characteristics for Atlantic and Mediterranean rivers in northern Spain and developed a river classification based on hydromorphological characteristics. Data gathered from almost 600 sites following a modified version of the River Habitat Survey methodology were used. In addition to the usual River Habitat Survey variables, the sequence of hydromorphologic units (i.e., areas exhibiting similar hydraulic characteristics, in terms of water velocity and depth), water depths, and widths were recorded. Unmodified reaches were selected computing the Habitat Modification Score. Multiple Linear Regression models were employed to test relationships between Principal Component Analyses that summarized physical river habitat characteristics with ecological relevance and environmental variables (i.e., climate, topography, land cover, and geology) at different spatial scales and used to predict physical habitat attributes for all river reaches. The density of hydromorphologic units, flow turbulence, substrate size, and channel dimensions were able to discriminate river classes within the river network, with topography being the main environmental driver of habitat characteristics (although climate, geology, and land cover were also relevant). This classification scheme could constitute a useful tool to restore physical habitat conditions in modified river reaches.info:eu-repo/semantics/acceptedVersio

Multipartite Entanglement and Frustration

Some features of the global entanglement of a composed quantum system can be quantified in terms of the purity of a balanced bipartition, made up of half of its subsystems. For the given bipartition, purity can always be minimized by taking a suitable (pure) state. When many bipartitions are considered, the requirement that purity be minimal for all bipartitions can engender conflicts and frustration arises. This unearths an interesting link between frustration and multipartite entanglement, defined as the average purity over all (balanced) bipartitions.Comment: 15 pages, 7 figure