The structure of vitreous binary oxides : silicate, germanate and plumbite networks

Structural aspects of three related binary oxide glass systems have been studied in detail using a combination of neutron and x-ray diffraction, empirical modelling techniques, and information from bulk property and spectroscopic measurements. The local Pb2+ environment in PbO SiO2 glasses changes only subtly with composition, having, on average 3.33 short (2:70 Å) and 1.3 long (2.70 <rPbO <3:27 Å) Pb- O bonds at 35 mol% PbO, and 3.57 short and 1.3(2) long Pb-O bonds at 80 mol% PbO. Therefore, over the entire series, lead behaves as a glass network forming cation, with highly asymmetric ligand distribution and stereochemically active electron lone-pair (LP), with gradual transition toward more axially symmetric environments (cf. crystalline PbO) as the PbO content increases. Structural modelling of the highest lead content oxide glass (80 PbO < 20 SiO2) to date reveals organisation of LPs to form voids, analogous to interlayer spaces in crystalline PbO polymorphs, and channels found within other crystalline lead oxide compounds such as Pb11Si3O17. The plumbite glass network is characterised by a high degree of intermediate-range ordering, evidenced by a very narrow first sharp diffraction peak (FSDP), as well as significant edge-sharing of Pb polyhedra and high oxygen-cation coordination numbers, e.g. [OPb4], [OPb3Si]. PbOGeO2 glass formation was found as high as 75 mol% PbO using rapid twinroller quenching. Such high lead glasses are analogues of the silicates, but with a 10% enhancement in correlation length derived from the FSDP. In the low PbO region a broad maximum in Ge-O coordination number of nGeO = 4:14(3) at 26:5(5) mol% PbO was observed. This is much smaller, and at higher metal oxide content than in Na, K and Cs germanate glasses and contradicts published results [N. Umesaki et al., Physica B 213, (1995), 490]. The weakness of the effect is attributed to Pb2+ playing a predominantly network forming role, although Ge-O and Pb-O coordination numbers showed positive correlation, such that the presence of [GeO5] or [GeO6] is indicative of Pb having some ‘modifying’ character. It was argued, based on empirical models and the known crystal chemistry, that Pb may occupy sites of intermediate character, with mixed s-p LP character, rather than invoking a bimodal distribution of network forming and modifying Pb sites. Homogeneous calcium germanate glasses were obtained in the region 21 to 41 mol% CaO by rapid twin-roller quenching, with glass-in-glass phase separation occuring in the low CaO region, and crystallisation around the CaGeO3 composition. A very broad maximum of nGeO = 4:30(3) at 28:0(5) mol% CaO was observed, correlating approximately with maxima in atomic number densities and glass transition temperatures. Nonbridging oxygen (NBO) are present in all glasses, again in contrast to alkali germanates. The position of the maximum is attributed to stabilisation of vertex sharing [GeOm>4] and/or [GeO6] units by divalent Ca2+. The presence of NBOs is related to the Ca-O coordination number of 7, with higher nGeO and less NBO predicted in Sr and Ba germanate glasses, where M-O coordination is expected to be larger. In both Ca and Pb germanate systems, the equilibrium crystals have much larger nGeO than the glasses, and this implies a decrease of nGeO with liquid, supercooled liquid and glass fictive temperatures. This tentative conclusion is supported by measurements on two 40 PbO 60 GeO2 glasses with different thermal histories

The roles of endolithic fungi in bioerosion and disease in marine ecosystems. II. Potential facultatively parasitic anamorphic ascomycetes can cause disease in corals and molluscs

Anamorphic ascomycetes have been implicated as causative agents of diseases in tissues and skeletons of hard corals, in tissues of soft corals (sea fans) and in tissues and shells of molluscs. Opportunist marine fungal pathogens, such as Aspergillus sydowii, are important components of marine mycoplankton and are ubiquitous in the open oceans, intertidal zones and marine sediments. These fungi can cause infection in or at least can be associated with animals which live in these ecosystems. A. sydowii can produce toxins which inhibit photosynthesis in and the growth of coral zooxanthellae. The prevalence of many documented infections has increased in frequency and severity in recent decades with the changing impacts of physical and chemical factors, such as temperature, acidity and eutrophication. Changes in these factors are thought to cause significant loss of biodiversity in marine ecosystems on a global scale in general, and especially in coral reefs and shallow bays

Water and Sodium in Heart Failure: A Spotlight on Congestion.

Despite all available therapies, the rates of hospitalization and death from heart failure (HF) remain unacceptably high. The most common reasons for hospital admission are symptoms related to congestion. During hospitalization, most patients respond well to standard therapy and are discharged with significantly improved symptoms. Post-discharge, many patients receive diligent and frequent follow-up. However, rehospitalization rates remain high. One potential explanation is a persistent failure by clinicians to adequately manage congestion in the outpatient setting. The failure to successfully manage these patients post-discharge may represent an unmet need to improve the way congestion is both recognized and treated. A primary aim of future HF management may be to improve clinical surveillance to prevent and manage chronic fluid overload while simultaneously maximizing the use of evidence-based therapies with proven long-term benefit. Improvement in cardiac function is the ultimate goal and maintenance of a ‘‘dry’’ clinical profile is important to prevent hospital admission and improve prognosis. This paper focuses on methods for monitoring congestion, and strategies for water and sodium management in the context of the complex interplay between the cardiac and renal systems. A rationale for improving recognition and treatment of congestion is also proposed

Tourism and toponymy: Commodifying and Consuming Place Names

Academic geographers have a long history of studying both tourism and place names, but have rarely made linkages between the two. Within critical toponymic studies there is increasing debate about the commodification of place names, but to date the role of tourism in this process has been almost completely overlooked. In some circumstances, toponyms can become tourist sights based on their extraordinary properties, their broader associations within popular culture, or their role as metanyms for some other aspect of a place. Place names may be sights in their own right or ‘markers’ of a sight and, in some cases, the marker may be more significant than the sight to which it refers. The appropriation of place names through tourism also includes the production and consumption of a broad range of souvenirs based on reproductions or replicas of the material signage that denote place names. Place names as attractions are also associated with a range of performances by tourists, and in some cases visiting a place name can be a significant expression of fandom. In some circumstances, place names can be embraced and promoted by tourism marketing strategies and are, in turn, drawn into broader circuits of the production and consumption of tourist space

‘The longest suicide vote in history’: the Labour Party leadership election of 2015

The Labour leadership contest of 2015 resulted in the election of the veteran Left-wing backbencher, Jeremy Corbyn, who clearly defeated the early favourite, Andy Burnham. Yet Corbyn enjoyed very little support among Labour MPs, and his victory plunged the PLP into turmoil, particularly as he was widely viewed as incapable of leading the Party to victory in the 2020 general election. Given that, much of the established academic literature on Party leadership contests emphasises the ability to foster unity, and thereby render a party electable, as two of the key criteria for electing a new leader, coupled with overall competence, important questions are raised about how and why the Labour Party chose someone to lead them who clearly does not meet these criteria. We will argue that whilst these are the natural priorities of MPs when electing a new leader, in Corbyn’s case, much of the extra-parliamentary Labour Party was more concerned about ideological conviction and purity of principles, regardless of how far these diverged from public opinion. This was especially true of those who signed-up to the Labour Party following the 2015 general election defeat. Indeed, many of these only did so after Corbyn had become a candidate. This clearly suggests a serious tension between maximising intra-party democracy and ensuring the electability of the parliamentary party itself

Tales of the unexpected: the selection of British party leaders since 1963

Jeremy Corbyn’s election as Leader of the Labour Party in 2015 stunned observers and practitioners of British politics alike. In this article, we first outline a theoretical framework that purports to explain why political parties operating in parliamentary systems choose the leaders they do. We then examine 32 leadership successions involving five major British parties since 1963, and note that many of these were unexpected, in that they were triggered by unforeseen circumstances, such as the sudden death or resignation of the incumbent. Examining each party in turn, we briefly explain why the winners won and identify at least eight cases (a quarter of our sample) where a candidate widely expected to prevail at the outset was ultimately defeated by a ‘dark horse’, ‘second favourite’ or even ‘rank outsider’. Of these, Corbyn’s election in 2015 was the most unexpected and, consistent with the findings of studies of party leadership conventions in other parliamentary systems, namely Canada and Spain, suggests that ideological and policy concerns are sometimes more important than considerations of party unity and electability, especially when a leadership contest is dominated by party activists

Lead silicate glass structure : new insights from diffraction and modeling of probable lone pair locations

Structures of binary PbO‐SiO2 glasses have been studied in detail over the compositional range 35 to 80 mol% PbO using high‐resolution neutron diffraction, high‐energy X‐ray diffraction, static 207Pb NMR, and structural modeling. The changes in the local environment of Pb(II) are subtle; it has a low coordination to oxygen (∼3 to 4) plus a stereochemically active electron lone pair and, thus, behaves as a glass network forming (or intermediate) cation over the entire composition range. This conclusion contradicts previous reports that Pb(II) is a network modifier at low concentrations, and is supported by an analysis of lead and alkaline earth silicate glass molar volumes. The Pb‐O peak bond length shortens by 0.04 Å with increasing PbO content, indicating stronger, more covalent bonding, and consistent with an increase in the number of short (≤ 2.70 Å) Pb‐O bonds, from 3.3 to 3.6. This is accompanied by increased axial symmetry of the Pb(II) sites, and is interpreted as a gradual transition toward square pyramidal [PbO4] sites such as those found in crystalline PbO polymorphs. An attendant decrease in the periodicity associated with the first sharp diffraction peak (FSDP) toward that of β‐PbO, accompanied by increases in the correlation lengths associated with the plumbite network (FSDP) and silicate anions (neutron prepeak), provides evidence of increased intermediate‐range order and has implications for the glass forming limit imposed by crystallization. Pb(II) electron lone pairs occupy the natural voids within the silicate network at low PbO contents, while at high PbO contents they aggregate to create voids that form part of the plumbite network, analogous to the open channels in Pb11Si3O17 and the layered structures of α‐ and β‐PbO. Si‐O and Pb‐O bond lengths have been correlated with 29Si and 207Pb NMR chemical shifts, respectively. This is the first time that such correlations have been demonstrated for glasses and attests to the accuracy with which pulsed neutron total scattering can measure average bond lengths

Evolutionary factors affecting the cross-species utility of newly developed microsatellite markers in seabirds

Microsatellite loci are ideal for testing hypotheses relating to genetic segregation at fine spatio-temporal scales. They are also conserved among closely related species, making them potentially useful for clarifying interspecific relationships between recently diverged taxa. However, mutations at primer binding sites may lead to increased non-amplification, or disruptions that may lead to decreased polymorphism in non-target species. Furthermore, high mutation rates and constraints on allele size may also lead, with evolutionary time, to an increase in convergently evolved allele size classes, biasing measures of interspecific genetic differentiation. Here, we used next-generation sequencing to develop microsatellite markers from a shotgun genome sequence of the sub-Antarctic seabird, the thin-billed prion (Pachyptila belcheri), that we tested for cross-species amplification in other Pachyptila and related sub-Antarctic species. We found that heterozygosity decreased and the proportion of non-amplifying loci increased with phylogenetic distance from the target species. Surprisingly, we found that species trees estimated from interspecific FST provided better approximations of mtDNA relationships among the studied species than those estimated using DC, even though FST was more affected by null alleles. We observed a significantly non-linear second order polynomial relationship between microsatellite and mtDNA distances. We propose that the loss of linearity with increasing mtDNA distance stems from an increasing proportion of homoplastic allele size classes that are identical in state, but not identical by descent. Therefore, despite high cross-species amplification success and high polymorphism among the closely related Pachyptila species, we caution against the use of microsatellites in phylogenetic inference among distantly related taxa