Exact Study of the Effect of Level Statistics in Ultrasmall Superconducting Grains

The reduced BCS model that is commonly used for ultrasmall superconducting grains has an exact solution worked out long ago by Richardson in the context of nuclear physics. We use it to check the quality of previous treatments of this model, and to investigate the effect of level statistics on pairing correlations. We find that the ground state energies are on average somewhat lower for systems with non-uniform than uniform level spacings, but both have an equally smooth crossover from the bulk to the few-electron regime. In the latter, statistical fluctuations in ground state energies strongly depend on the grain's electron number parity.Comment: 4 pages, 3 eps figs, RevTe

Superconducting correlations in metallic nanoparticles: exact solution of the BCS model by the algebraic Bethe ansatz

Superconducting pairing of electrons in nanoscale metallic particles with discrete energy levels and a fixed number of electrons is described by the reduced BCS model Hamiltonian. We show that this model is integrable by the algebraic Bethe ansatz. The eigenstates, spectrum, conserved operators, integrals of motion, and norms of wave functions are obtained. Furthermore, the quantum inverse problem is solved, meaning that form factors and correlation functions can be explicitly evaluated. Closed form expressions are given for the form factors that describe superconducting pairing.Comment: revised version, 5 pages, revtex, no figure

Lesbian and bisexual women's human rights, sexual rights and sexual citizenship: negotiating sexual health in England.

Lesbian and bisexual women's sexual health is neglected in much Government policy and practice in England and Wales. This paper examines lesbian and bisexual women's negotiation of sexual health, drawing on findings from a small research project. Themes explored include invisibility and lack of information, influences on decision-making and sexual activities and experiences of services and barriers to sexual healthcare. Key issues of importance in this respect are homophobic and heterosexist social contexts. Drawing on understandings of lesbian, gay and bisexual human rights, sexual rights and sexual citizenship, it is argued that these are useful lenses through which to examine and address lesbian and bisexual women's sexual health and related inequalities

Extremes in benthic ecosystem services; Blue carbon natural capital shallower than 1000 m in isolated, small and young Ascension Island’s EEZ

Biodiversity tends to decrease with increasing isolation and reduced habitat size, and increase with habitat age. Ascension Island and its seamounts are small, isolated and relatively young, yet, within its soon-to-be designated major Marine Protected Area, harbour patchily dense life in the shallows and cold water corals in deeper waters. With few local threats, global climate related stressors (e.g. temperature and acidification) and arguably plastic pollution are key issues for its survival and continued provision of ecosystem services. We evaluate the accumulated carbon in benthos around Ascension Island’s EEZ shallower than 1000 m using data from two research cruises in 2015 and 2017 through seabed mapping, seabed camera imagery and collections of benthos using a mini-Agassiz trawl. Benthos shallower than 1000 m essentially comprises the coastal waters around Ascension Island and three seamounts (Harris-Stewart, Grattan and Un-named). There is considerable societal benefit from benthic carbon storage and sequestration through its mitigation value buffering climate change. This service is often termed ‘blue carbon’. Overall we estimate that there is at least 43,000 tonnes of blue carbon, on the 3% of Ascension Island EEZ’s seabed which is <1000 m, mainly in the form of cold coral reefs. Two thirds of that occurs around the main island of Ascension, but it is very unevenly distributed on the seabed. Seabed roughness (e.g. rocky outcrops) seems most important for the development of blue carbon hotspots. About 21% of the total blue carbon is considered to be sequestered (removed from the carbon cycle for 100+ years) = 9060 tonnes Carbon. At the 2019 Shadow Price of Carbon the proportion of CO2 considered sequestered is £29-59. As 9060 t C this is equivalent to 33,250 t CO2, which in 2019 is valued at approximately £1-2 million. With time, this increases with rising value of carbon, but also annual increment of carbon deposition, to £2-4 million by 2030. Thus even when biogeographic values of isolation, size and age are least favourable to biodiversity, the natural capital stock and future services of benthic ecosystems can be considerable and generate a quantifiable economic return on their conservation

DFT calculation of the intermolecular exchange interaction in the magnetic Mn4_4 dimer

The dimeric form of the single-molecule magnet [Mn$_4$O$_3$Cl$_4$(O$_2$CEt)$_3$(py)$_3$]$_2$ recently revealed interesting phenomena: no quantum tunneling at zero field and tunneling before magnetic field reversal. This is attributed to substantial antiferromagnetic exchange interaction between different monomers. The intermolecular exchange interaction, electronic structure and magnetic properties of this molecular magnet are calculated using density-functional theory within generalized-gradient approximation. Calculations are in good agreement with experiment.Comment: 4 page

Performance over professional learning and the complexity puzzle: lesson observation in England’s further education sector

Attempts to measure the quality of teaching and learning have resulted in an overreliance on quantitative performance data and the normalisation of a set of reductionist practices in England’s further education sector in recent years. Focusing on lesson observation as an illustrative example and drawing on data from a national study, this article examines the application of observation and its impact on further education teachers’ practice. In viewing lesson observation through a complexity theory lens and contextualising it against the wider neoliberal backdrop of the marketisation of education, we seek to critique the inadequacies of current reductionist approaches to teacher evaluation, whilst simultaneously opening up a debate regarding the consequences of seeing classrooms as complex adaptive systems. In focusing on performative models of lesson observation in particular, the article exposes what we perceive as some of the epistemological and methodological shortcomings of neoliberalism in practice, but also offers an alternative way forward in dealing with the contested practice of evaluating the quality of teaching and learning

Interplay between pairing and exchange in small metallic dots

We study the effects of the mesoscopic fluctuations on the competition between exchange and pairing interactions in ultrasmall metallic dots when the mean level spacing is comparable or larger than the BCS pairing energy. Due to mesoscopic fluctuations, the probability to have a non-zero spin ground state may be non-vanishing and shows universal features related to both level statistics and interaction. Sample to sample fluctuations of the renormalized pairing are enlightened.Comment: 10 pages, 5 figure

User guide BGS Coastal Vulnerability Index version 1

Coastal vulnerability indexing is a GIS-based analysis tool for indicating multi-hazards and interdependencies within the coastal zone of Great Britain (GB). The mainland of Great Britain is surrounded by over 11 000 miles of coastline. It is a very diverse coastline both in terms of geology and geomorphology, ranging from the high chalk cliffs of Sussex to the flat expanses of The Wash and Morecambe Bay. The coast has been shaped by the continual forces of erosion from the wind, waves and tide and the characteristics and composition of the coastline dictate the degree of its vulnerability. The winter storms of 2013-14 starkly demonstrated the vulnerability of the GB coastline to erosion and overtopping but during media enquiries it became clear that a national picture of the sections of coastline susceptible to erosion didn’t exist. The Coastal Vulnerability Index (CVI) has been created to bring together a suite of data to fill this knowledge gap. With climate change forecasts of an increase in the frequency and intensity of winter storms, BGS has developed a coastal vulnerability index (CVI), drawing on existing BGS datasets and expertise, and we intend to work in collaboration with other organisations to help manage these changes in the future. The CVI will offer anyone with assets or an interest in the coastline around Great Britain access to easy-to use indexes linked to geohazard data. This will allow users to interpret potential interdependencies in terms of erosion, flooding, habitat and other vulnerabilities. Version 1 of the CVI represents the natural geological coastline (around the mainland of GB only) as if no coastal defences or made ground are present. Due to their complex geometry, the coastlines of N and W Scotland have not been included in version 1. This will be of particular value in areas where coastal defences are no longer maintained. Future versions of the CVI will include all coastal defences and made ground

User guide British Geological Survey Coastal Vulnerability Dataset (version 1)

This report describes the national scale BGS Coastal Vulnerability Dataset. The methods used to create the dataset have been critically assessed and its fitness for purpose determined by specialists in BGS. This document outlines the background to why the dataset was created, its potential uses and gives a brief description of the content. Technical information regarding the GIS and how the data was created is described and advice is provided on using the dataset