Electrostatic interactions mediated by polarizable counterions: weak and strong coupling limits

We investigate the statistical mechanics of an inhomogeneous Coulomb fluid composed of charged particles with static polarizability. We derive the weak- and the strong-coupling approximations and evaluate the partition function in a planar dielectric slab geometry with charged boundaries. We investigate the density profiles and the disjoining pressure for both approximations. Comparison to the case of non-polarizable counterions shows that polarizability brings important differences in the counterion density distribution as well as the counterion mediated electrostatic interactions between charged dielectric interfaces.Comment: 25 pages, 7 figure

Humanities doctoral education for a relational future:a Change Laboratory research intervention

Pressure to change the design of the doctorate is increasing, causing a tension between a politically driven emphasis to prepare PhD researchers for mobility beyond academia and current, scholarship-oriented, practices of traditional doctoral education. Research typically advocates that doctoral students need support to mobilise their expertise across boundaries, but there is a paucity of empirical studies investigating how such support could be provided and how different aspects of the required expertise might be developed. In this thesis, I therefore seek to understand and intervene in the development of boundary crossing collaborations, focusing on developing the forms of expertise required to prepare students for a relational future. My analysis draws on data from an 8-month long Change Laboratory research-intervention, which brought humanities doctoral students from a university together with non-academic professionals working for a UK charity. Applying relational working as an analytical framework, I trace the extent to which common knowledge, relational expertise and relational agency developed over the course of the intervention and highlight aspects of the intervention design that were most influential on that development. The findings suggest that incorporating additional practitioners, external but connected to the host organisation’s activity system, stimulated the development of common knowledge. Additionally, introducing the mediating stimulus of an activity system model, which participants perceived to be a ‘neutral’ focus for discussion, supported relational applications of individual expertise. Furthermore, the shared responsibility for producing data encouraged throughout the intervention seemingly fostered the internal and external verification of researcher expertise. Overall, I propose that interventions of this kind have the potential to become a new pedagogic medium, the Relational Change Laboratory (RCL), whose aim is to stimulate accelerated reciprocal learning within humanities doctoral education. Such an intervention, I argue, can alter the boundary crossing practices and outcomes for both students and host organisations

Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He

We have measured the ratio of the diffusion cross-section to the angular momentum reorientation cross-section in the colliding Fe-3He and Ni-3He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the helium temperature. The cross-section ratio is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine the cross-section ratio accurately, we introduce a model of Zeeman state dynamics that includes thermal excitations. We find the cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a 0.8 T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation as studied previously in transition metals and rare earth atoms.Comment: 10 pages, 5 figures; submitted to Phys. Rev.

Correcting the polarization effect in low frequency Dielectric Spectroscopy

We demonstrate a simple and robust methodology for measuring and analyzing the polarization impedance appearing at interface between electrodes and ionic solutions, in the frequency range from 1 to $10^6$ Hz. The method assumes no particular behavior of the electrode polarization impedance and it only makes use of the fact that the polarization effect dies out with frequency. The method allows a direct and un-biased measurement of the polarization impedance, whose behavior with the applied voltages and ionic concentration is methodically investigated. Furthermore, based on the previous findings, we propose a protocol for correcting the polarization effect in low frequency Dielectric Spectroscopy measurements of colloids. This could potentially lead to the quantitative resolution of the $\alpha$-dispersion regime of live cells in suspension

Theorising practices of relational working across the boundaries of higher education

Higher education research is replete with discussion of boundaries imagined as structural constraints in need of removal or circumvention. But, while foregrounding national-transnational frameworks, leadership strategising, and institutional structures, the scholarship is subdued about how boundaries are actually dealt with at ground level. How do practitioners come together, day by day, across higher education boundaries; and what is required for desirable practices to be nurtured? It is on this issue, and in particular the theorisation of this issue, that the present chapter will focus. The chapter presents and develops a relational working framework, based on the work of Anne Edwards. We highlight three core concepts (common knowledge, relational expertise and relational agency), disaggregating each into constituent features. We then apply the framework to re-interpret previously published empirical studies, to demonstrate its broad applicability. We argue that the framework usefully conceptualises how practitioners work with others across boundaries; that it helps us to notice how many boundaries are, in fact routinely permeated; and that it usefully highlights important aspects of local practices that are easily obscured

Diffusion, thermalization and optical pumping of YbF molecules in a cold buffer gas cell

We produce YbF molecules with a density of 10^18 m^-3 using laser ablation inside a cryogenically-cooled cell filled with a helium buffer gas. Using absorption imaging and absorption spectroscopy we study the formation, diffusion, thermalization and optical pumping of the molecules. The absorption images show an initial rapid expansion of molecules away from the ablation target followed by a much slower diffusion to the cell walls. We study how the time constant for diffusion depends on the helium density and temperature, and obtain values for the YbF-He diffusion cross-section at two different temperatures. We measure the translational and rotational temperatures of the molecules as a function of time since formation, obtain the characteristic time constant for the molecules to thermalize with the cell walls, and elucidate the process responsible for limiting this thermalization rate. Finally, we make a detailed study of how the absorption of the probe laser saturates as its intensity increases, showing that the saturation intensity is proportional to the helium density. We use this to estimate collision rates and the density of molecules in the cell.Comment: 20 pages, 11 figures, minor revisions following referee suggestion

Quantum Transition State Theory for proton transfer reactions in enzymes

We consider the role of quantum effects in the transfer of hyrogen-like species in enzyme-catalysed reactions. This study is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects imply that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We use a path integral approach which provides a general framework to understand tunneling in a quantum system which interacts with an environment at non-zero temperature. Here the quantum system is the active site of the enzyme and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature $T_0$ which is determined by the curvature of potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. For physically reasonable parameters quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of kinetic isotope effects for two classes of enzymes which have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction due to the environment is weak and only slightly modifies the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental degrees of freedom with frequencies much less than 1000 cm$^{-1}$ do not have a significant effect on quantum corrections to the reaction rate.Comment: Aspects of the article are discussed at condensedconcepts.blogspot.co

Offering weight management support to pregnant women with high body mass index: A qualitative study with midwives

Objective: The prevalence of pregnant women with high body mass index is increasing worldwide. High body mass index is associated with health risks for mother and baby and supporting healthy gestational weight gain is important. Midwives play an important role in supporting women to engage in behaviours such as healthy eating and physical activity. The aim of this study was to explore how midwives’ support pregnant women with high body mass index to establish a healthy lifestyle with emphasis on nutrition and physical activity in order to minimise gestational weight gain. Methods: Semi-structured interviews were conducted with 16 midwives working in antenatal health care in Sweden. Interviews were conducted shortly after new guidelines on care for pregnant women with high body mass index had been introduced. The interviews were recorded, transcribed and analysed by thematic analysis. Results: Three main themes were identified; use a conscious approach, invite to participate and have a long-term health perspective. Midwives built a relationship with a woman through identifying her concerns and circumstances, before sensitively discussing weight. Some midwives used Motivational Interviewing to help women identify their own resources. To reach long-term health benefits, midwives set achievable goals with the women. Conclusion: These study findings provide practical examples of how midwives can support women with weight management during pregnancy. Through being sensitive when developing a relationship, midwives enabled the women to identify their own resources and achievable goals. Support after the baby is born is needed subsequently to help women maintain their healthy behaviour changes