Strain-Modified RKKY Interaction in Carbon Nanotubes

For low-dimensional metallic structures, such as nanotubes, the exchange coupling between localized magnetic dopants is predicted to decay slowly with separation. The long-range character of this interaction plays a significant role in determining the magnetic order of the system. It has previously been shown that the interaction range depends on the conformation of the magnetic dopants in both graphene and nanotubes. Here we examine the RKKY interaction in carbon nanotubes in the presence of uniaxial strain for a range of different impurity configurations. We show that strain is capable of amplifying or attenuating the RKKY interaction, significantly increasing certain interaction ranges, and acting as a switch: effectively turning on or off the interaction. We argue that uniaxial strain can be employed to significantly manipulate magnetic interactions in carbon nanotubes, allowing an interplay between mechanical and magnetic properties in future spintronic devices. We also examine the dimensional relationship between graphene and nanotubes with regards to the decay rate of the RKKY interaction.Comment: 7 pages, 6 figures, submitte

Water calcium concentration modifies whole-body calcium uptake in sea bream larvae during short-term adaptation to altered salinities

Whole-body calcium uptake was studied in gilthead sea bream larvae (9–83·mg) in response to changing environmental salinity and [Ca2+]. Calcium uptake increased with increased fish size and salinity. Fish exposed to calcium-enriched, diluted seawater showed increased calcium uptake compared with fish in diluted seawater alone. Calcium uptake was unchanged in Na+- enriched, diluted seawater. Overall, [Ca2+], and not salinity/osmolarity per se, appears to be the main factor contributing to calcium uptake. By contrast, drinking was reduced by a decrease in salinity/osmolarity but was little affected by external [Ca2+]. Calculations of the maximum contribution from drinking-associated calcium uptake showed that it became almost insignificant (less than 10%) through a strong decrease in drinking rate at low salinities (0–8‰). Diluted seawater enriched in calcium to the concentration present in full-strength seawater (i.e. constant calcium, decreasing salinity) restored intestinal calcium uptake to normal. Extra-intestinal calcium uptake also benefited from calcium addition but to a lesser extent

Impurity segregation in graphene nanoribbons

The electronic properties of low-dimensional materials can be engineered by doping, but in the case of graphene nanoribbons (GNR) the proximity of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This introduces energetically favorable locations for impurities, leading to a degree of spatial segregation in the impurity concentration. We develop a simple model to calculate the change in energy of a GNR system with an arbitrary impurity as that impurity is moved across the ribbon and validate its findings by comparison with ab initio calculations. Although our results agree with previous works predicting the dominance of edge disorder in GNR, we argue that the distribution of adsorbed impurities across a ribbon may be controllable by external factors, namely an applied electric field. We propose that this control over impurity segregation may allow manipulation and fine-tuning of the magnetic and transport properties of GNRs.Comment: 5 pages, 4 figures, submitte

Guiding of Rydberg atoms in a high-gradient magnetic guide

We study the guiding of $^{87}$Rb 59D$_{5/2}$ Rydberg atoms in a linear, high-gradient, two-wire magnetic guide. Time delayed microwave ionization and ion detection are used to probe the Rydberg atom motion. We observe guiding of Rydberg atoms over a period of 5 ms following excitation. The decay time of the guided atom signal is about five times that of the initial state. We attribute the lifetime increase to an initial phase of $l$-changing collisions and thermally induced Rydberg-Rydberg transitions. Detailed simulations of Rydberg atom guiding reproduce most experimental observations and offer insight into the internal-state evolution

Rising Powers, Lowering Emissions?

The importance of ensuring that African countries can meet their rising energy needs in a low-carbon way that also benefits the poor, is widely accepted. The so-called ‘rising powers’, such as China, Brazil and India are already investing in energy infrastructure in Africa, and these countries could support transitions to low-carbon development since they are currently some of the world’s largest investors in solar, wind, hydropower and biofuels. Yet, critically, the energy needs of poorer groups are not currently shaping policy and investment decisions and so energy access considerations are not being adequately addressed where low-carbon energy transitions are emerging. Northern donors have a role to play both as knowledge and financial brokers between rising powers and African countries, and in targeting investment towards small-scale and community-managed renewable energy systems, which would directly help the poor majority that are off-grid.Department for International Development; ESRC project ES/J01270X/

(re)Structuring the agency: Agency working arrangements and social care in the era of austerity and beyond.

In Ireland, the austerity era of recent years brought (un)employment to the fore in a manner not seen since the 1980s. Within the arena of health and social care, this was epitomised by the ‘embargo’. Confined within an embargo process, recruitment agencies became a first choice response to maintaining service delivery in a deepening recessionary period. Located against this backdrop, this study explored agency-working arrangements in social care through the use of semi-structured interviews with service provider managers (n=3) and agency social care workers (n=6). Analysed using a variation of conventional content analysis; these interviews reveal a central tension between the flexibility afforded by agency working arrangements and the instability that such arrangements can foster. Although flexibility and variety in agency based employment arrangements can be beneficial for service providers, and in certain stages of career development for social care practitioners, underlying tensions arise within such working arrangements, which have a particular resonance for the social care profession. Most notably, the relationship based nature of social care practice can be disturbed by a restructuring of traditional employment pathways, especially in relation to continuity of care and practitioner support and development. Nonetheless, the findings also reveal that the extent of disruption is being dampened by adaptions to the agency process by service provider managers and social care workers through a ‘pooling’ approach to agency staffing. As such, the findings of this study both reflect common themes form literature surrounding agency working, while also observing subtle nuances. The implications of agency working for social care practice are considered, as are potential longer-term impacts given the context of impending registration of social care workers

A molecular theory for two-photon and three-photon fluorescence polarization

In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder