The development of a treadle pump: Lessons from the South African experience

Manual pumps / Design / South Africa

Explicit correlation and intermolecular interactions: Investigating carbon dioxide complexes with the CCSD(T)-F12 method

We have optimized the lowest energy structures and calculated interaction energies for the CO₂–Ar, CO₂–N₂, CO₂–CO, CO₂–H₂O, and CO₂–NH₃ dimers with the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)]-F12 methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. For a given cardinal number, we find that results obtained with the CCSD(T)-F12 methods are much closer to the CCSD(T) complete basis set limit than the conventional CCSD(T) results. The relatively modest increase in the computational cost between explicit and conventional CCSD(T) is more than compensated for by the impressive accuracy of the CCSD(T)-F12 method. We recommend use of the CCSD(T)-F12 methods in combination with the VXZ-F12 basis sets for the accurate determination of equilibrium geometries and interaction energies of weakly bound electron donor acceptor complexes

Quantifying cooperative intermolecular interactions for improved carbon dioxide capture materials

We have optimized the geometry and calculated interaction energies for over 100 different complexes of CO₂ with various combinations of electron accepting (Lewis acid) and electron donating (Lewis base) molecules. We have used the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)-F12] methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. We observe only modest changes in the geometric parameters of CO₂ upon complexation, which suggests that the geometry of CO₂ adsorbed in a nanoporous material should be similar to that of CO₂ in gas phase. When CO₂ forms a complex with two Lewis acids via the two electron rich terminal oxygen atoms, the interaction energy is less than twice what would be expected for the same complex involving a single Lewis acid. We consider a series of complexes that exhibit simultaneous CO₂-Lewis acid and CO₂-Lewis base intermolecular interactions, with total interaction energies spanning 14.1–105.9 kJ mol⁻¹. For these cooperative complexes, we find that the total interaction energy is greater than the sum of the interaction energies of the constituent complexes. Furthermore, the intermolecular distances of the cooperative complexes are contracted as compared to the constituent complexes. We suggest that metal-organic-framework or similar nanoporous materials could be designed with adsorption sites specifically tailored for CO₂ to allow cooperative intermolecular interactions, facilitating enhanced CO₂ adsorption

Word contexts enhance the neural representation of individual letters in early visual cortex

Visual context facilitates perception, but how this is neurally implemented remains unclear. One example of contextual facilitation is found in reading, where letters are more easily identified when embedded in a word. Bottom-up models explain this word advantage as a post-perceptual decision bias, while top-down models propose that word contexts enhance perception itself. Here, we arbitrate between these accounts by presenting words and nonwords and probing the representational fidelity of individual letters using functional magnetic resonance imaging. In line with top-down models, we find that word contexts enhance letter representations in early visual cortex. Moreover, we observe increased coupling between letter information in visual cortex and brain activity in key areas of the reading network, suggesting these areas may be the source of the enhancement. Our results provide evidence for top-down representational enhancement in word recognition, demonstrating that word contexts can modulate perceptual processing already at the earliest visual regions

A two-loop relation between inclusive radiative and semileptonic B-decay spectra

A shape-function independent relation is derived between the partial B->X_u+l+nu decay rate with a cut on P_+=E_X-P_X<Delta and a weighted integral over the normalized B->X_s+gamma photon-energy spectrum. The leading-power contribution to the weight function is calculated at next-to-next-to-leading order in renormalization-group improved perturbation theory, including exact two-loop matching corrections at the scale mu_i^2 ~ m_b*Lambda_{QCD}. The overall normalization of the weight function is obtained up to yet unknown corrections of order [alpha_s(m_b)]^2. Power corrections from phase-space factors are included exactly, while the remaining subleading contributions are included at first order in 1/m_b. At this level unavoidable hadronic uncertainties enter, which are estimated in a conservative way. The combined theoretical accuracy in the extraction of |V_{ub}| is at the level of 5% if a value of Delta near the charm threshold can be achieved experimentally.Comment: 22 pages, 4 figures; few comments and one reference added; version to appear in JHE

Reflections on methodology and interdisciplinarity in the postmodern dialogue between theology and the natural sciences

Postmodern interdisciplinarity provides a more flexible and productive methodological framework for the age-old dialogue between theology and the natural sciences than did the modern more rigid and oppositional disciplinary framework. Taking the work of Wentzel van Huyssteen as basis, the author focuses on developing an understanding of the roles of interdisciplinarity, foundationalism, non-foundationalism, and postfoundationalism in the dialogue between theology and science, and highlights the methodological changes resulting from the change-over from modernity to postmodernity.Acta Theologica Vol. 2 2007: pp. 44-6

Youth envisioning safe schools: a participatory video approach

Gender-based violence is pervasive in South African society and is often seen as the driver of HIV, particularly affecting youth. Rural KwaZulu-Natal, where we have been working in a district in an on-going university-school partnership, is noted as the epicentre of the epidemic. The two secondary schools in this study were therefore conveniently chosen while the 30 Grade 9 learners, 7 boys and 23 girls between the ages of 13&#8211;16, were purposively selected. The use of participatory visual methodologies,which is the focus of this special issue, taps into the notion of &#8216;research asintervention&#8217; and speaks to the potential of educational research contributing to social change. In this qualitative study we used participatory video to explore youths&#8217; understanding of gender-based violence, as well as how they envision making schools safe. Power theory is used as theoretic lens to frame the study and to make meaning of the findings, namely, that girls&#8217; bodies are sites for gender-based violence at unsafeschools; that the &#8216;keepers of safety&#8217; are perpetuating gender-based violence at school; and that learners have a sound understanding of what can be done to address gender-based violence. This study, with its &#8216;research as intervention&#8217; approach, enabled learners to make their voices heard and to reflect on what it is that they as youth can do to contribute to safe schooling