The heat of atomization of sulfur trioxide, SO3_3 - a benchmark for computational thermochemistry

Calibration ab initio (direct coupled cluster) calculations including basis set extrapolation, relativistic effects, inner-shell correlation, and an anharmonic zero-point energy, predict the total atomization energy at 0 K of SO$_3$ to be 335.96 (observed 335.92$\pm$0.19) kcal/mol. Inner polarization functions make very large (40 kcal/mol with $spd$, 10 kcal/mol with $spdfg$ basis sets) contributions to the SCF part of the binding energy. The molecule presents an unusual hurdle for less computationally intensive theoretical thermochemistry methods and is proposed as a benchmark for them. A slight modification of Weizmann-1 (W1) theory is proposed that appears to significantly improve performance for second-row compounds.Comment: Chem. Phys. Lett., in pres

Theoretical studies of positronium formation in positron collisions with lithium and hydrogen atoms

The Kohn variational method has been used to study elastic scattering and positronium (Ps) formation in positron collisions with atomic hydrogen and lithium, in the energy region where only these two channels are open. In common with other alkali metals, lithium is interesting in that its valence electron is sufficiently weakly bound that positronium formation is exothermic, and hence an open channel for incident positrons of zero energy. For such a process, Wigner's threshold theory predicts an s-wave cross section which has an inverse dependence on the wavenumber, k, of the projectile as k→0. Using a model potential and very elaborate trial functions, a detailed investigation of s- and p-wave positron-lithium scattering has been made in the energy range 0-1.84eV, and preliminary results have also been obtained for d-wave scattering. The s-wave Ps formation cross section, as calculated variationally, appears to be in accordance with the Wigner theory, although this partial wave contributes negligibly to the Ps channel across most of the energy range considered. The p and d partial waves make a much more substantial contribution to the rearrangement process. New cross sections for positron-hydrogen scattering have been calculated for the energy region close to the positronium formation threshold, and results have been compared with the predictions of R-matrix threshold theory

Disrupting the dynamics of oppression in intercultural research and practice

In this special issue we focus on exploring the tensions, challenges and possibilities for working in contexts where relationships between groups are characterized by dominance and resistance. Some of the impetus lies in our own struggles and frustrations with models, guidelines and ‘recipes’ that have been developed to guide sensitive, competent and empowering research and practice across boundaries of ‘race’, ethnicity and culture. These models and guidelines are often framed as tools that will enable culturally competent transactions across these boundaries

The social context of gender-based violence, alcohol use and HIV risk among women involved in high-risk sexual behaviour and their intimate partners in Kampala, Uganda.

This paper explores the interaction between gender-based violence and alcohol use and their links to vulnerability to HIV-infection in a population of women and their regular male partners in Kampala, Uganda. Data derive from 20 life history interviews (10 women and 10 men). Participants were drawn from a cohort of women at high risk of sexually transmitted infection (including HIV). Six of the women were current or former sex workers. Findings reveal that life histories are characterised by recurrent patterns of gender inequity related to violence, limited livelihood options and socioeconomic disadvantage. Overall, findings suggest women are able to negotiate safer sex and protect themselves better against abuse and violence from clients than from their intimate partners, although the status of men as 'client' or 'partner' is transitory and fluid. Among male respondents, alcohol led to intimate partner violence and high levels of sexual-risk taking, such as engagement with sex workers and reduced condom use. However, male partners are a heterogeneous group, with distinct and contrasting attitudes towards alcohol, condom use and violence. Actions to address gender-based violence need to be multi-pronged in order to respond to different needs and circumstances, of both women and men

The influence of floral traits on specialisation and modularity of plant-pollinator networks in a biodiversity hotspot in the Peruvian Andes

Background and Aims: Modularity is a ubiquitous and important structural property of ecological networks which describes the relative strengths of sets of interacting species and gives insights into the dynamics of ecological communities. However, this has rarely been studied in species-rich, tropical plant–pollinator networks. Working in a biodiversity hotspot in the Peruvian Andes we assessed the structure of quantitative plant–pollinator networks in nine valleys, quantifying modularity among networks, defining the topological roles of species and the influence of floral traits on specialization. Methods: A total of 90 transects were surveyed for plants and pollinators at different altitudes and across different life zones. Quantitative modularity (QuanBiMo) was used to detect modularity and six indices were used to quantify specialization. Key Results: All networks were highly structured, moderately specialized and significantly modular regardless of size. The strongest hubs were Baccharis plants, Apis mellifera, Bombus funebris and Diptera spp., which were the most ubiquitous and abundant species with the longest phenologies. Species strength showed a strong association with the modular structure of plant–pollinator networks. Hubs and connectors were the most centralized participants in the networks and were ranked highest (high generalization) when quantifying specialization with most indices. However, complementary specialization d' quantified hubs and connectors as moderately specialized. Specialization and topological roles of species were remarkably constant across some sites, but highly variable in others. Networks were dominated by ecologically and functionally generalist plant species with open access flowers which are closely related taxonomically with similar morphology and rewards. Plants associated with hummingbirds had the highest level of complementary specialization and exclusivity in modules (functional specialists) and the longest corollas. Conclusions: We have demonstrated that the topology of networks in this tropical montane environment was non-random and highly organized. Our findings underline that specialization indices convey different concepts of specialization and hence quantify different aspects, and that measuring specialization requires careful consideration of what defines a specialist