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

‘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

The politics of coproduction during Latin America’s ‘Pink Tide’: Water, housing, and waste in comparative perspective

Coproduction brings together a diverse range of state and non-state actors to create and deliver public services. These processes, which occur across the Global South, have been widely studied. However, insufficient critical attention has been paid to their politics. We address this gap in the literature by analysing the politics of coproduction in Latin America during the ‘pink tide’ of the early twenty-first century. Drawing on original qualitative research, this article explores the coproduction of three distinct public services—water, housing, and waste—in three countries where left-leaning presidents and governments were elected into office—Ecuador, Bolivia, and Uruguay. We argue that coproduction is intrinsically political in these three cases; that is, the ‘political’ is internal to, and inherent in, coproduction. Our comparative analysis centres on two political dimensions—subject-making and collective autonomy—and shows that tensions around these two issues were central to coproduction in Ecuador, Bolivia, and Uruguay . The article demonstrates the importance of not treating politics as a mere contextual concern in coproduction analysis and shows that coproduction has the capacity to reshape political relationships and subjectivities. Taking politics into account is essential to understanding the dynamics and potential of coproduction in the Global South. Our comparative analysis also provides new insights into Latin American politics, especially concerning 'pink tide' governments and the provisioning of public services