Spin-orbit phenomena and interfacial proximity effects in magnetic multilayers

This thesis examines phenomena originating from the spin-orbit interaction in the context of interfacial effects. Four effects were studied, the anisotropic magnetoresistance, spin-orbit torques, magnetic damping and the Dzyaloshinskii-Moriya interaction. The anisotropic magnetoresistance (AMR) was studied in Ni, Ni95V5 and Ni95Cr5 thin films. The absolute resistivity change due to AMR reduced with decreasing film thickness. This was explained in terms of enhanced electron-magnon spin-flip scattering in the presence of reduced dimensionality. It was shown that the Campbell, Fert and Jaoul model could be extended to include this generalised thickness dependence. Spin-orbit torques were investigated in multilayer structures with different magnetic anisotropies. Current-induced magnetisation reversal, due to the spin-Hall efect of Pt, was observed in a symmetric Pt/Co/Pt sample with weak perpendicular magnetic anisotropy. No evidence for the Rashba effect was found in this symmetric structure. A spin Hall angle of (0.13 +- 0:06) was extracted for Pt. Using x-ray resonant magnetic reflectivity, the interfacial proximity induced magnetism (PIM) in Pt was investigated in Pt/Co/Pt multilayer structures with in-plane magnetic anisotropy and characterised as a function of Au and Ir spacer layers at the Co/Pt interface. The PIM was shown to depend strongly on interface morphology and decayed rapidly with increasing spacer layer thickness. The magnetic damping and Dzyaloshinkskii-Moriya interaction (DMI) were measured in the same samples to investigate the contribution of the PIM to these effects. It was shown that the magnetic damping was dominated by the d-d hybridisation at the Co/Pt interface which reduced as spacer layers of increasing thickness were inserted. It was not clear whether the loss of PIM plays a substantial role in this. The DMI was shown to increase as Au and Ir spacer layers were added, due to the prevention of cancellation of opposite DMI contributions from the Pt interfaces. This rise in DMI was on a different lengthscale than was found for the loss of PIM. The results suggested no correlation between the PIM and DMI

A Non-Standard String Embedding of E8

An algorithm to systematically and efficiently generate free fermionic heterotic string models was recently introduced. This algorithm has been adopted by the Free Fermionic Model Construction (FFMC) program at Baylor University. As its first application, the algorithm is being applied to systematically generate the complete set of free fermionic heterotic string models with untwisted left-moving (worldsheet supersymmetric) sectors, up to continually advancing Layer and Order. Statistical analysis of this study will be reported in the near future. However, in a series of separate notes we will be reporting some of the more interesting models that appear along the way. In this, our first such note, we reveal a different string embedding of E8 than is standard. That is, rather than realize E8 via an SO(16) embedding, 248 = 120 + 128, we realize it via an SU(9) embedding, 248 = 80 + 84 + 84-bar. This is obtained in a Layer 1, Order 6 model for which modular invariance itself dictates a gravitino sector accompany the gauge sector.Comment: Standard Latex, 7 page

Magnificent Distance: Five Site-Specific Installations Washington DC 2012

5x5, Washington DC’s inaugural public art festival, was conceived as a flagship biennial in which five curators would each be invited to curate new site-specific artworks by five artists – leading to the simultaneous installation of twenty-five artworks across Washington DC. The primary research question explored in the curation of the five Magnificent Distance artworks was the slippage between the symbolic DC of the worldwide public imagination and the ‘domestic’, human DC with its complex histories and communities. Many of the exhibition sites, selected as part of my curatorial role, were at the interstices of these two DC realities – at the meeting point between federal and community environments, in locations undergoing transformation from one use to another, and at points where differing scales of architecture meet

The growth of ‘Dry January’: promoting participation and the benefits of participation

This article explores contributors to the rapid growth of the annual UK alcohol abstinence challenge ‘Dry January’ and the benefits of registration. Evidence from four sources is presented: (i) registrations via the Dry January website, (ii) surveys of population-representative samples of drinkers, (iii) surveys of Dry January registrants and (iv) surveys of a control group of drinkers who wanted to change to their drinking behaviour but had not registered for Dry January. The data revealed that Dry January registrations increased 15-fold in 4 years. Participants reported that encouragement received from Dry January helped them to avoid drinking. Comparisons of Dry January registrants to the control group suggest that registering for Dry January reduced problematic drinking and enhanced the capacity to refuse alcohol. The four sources of data suggest that ‘social contagion’ and ‘diffusion’ have aided the growth of the awareness, appeal and practice of Dry January

Genomic architecture and prediction of censored time-to-event phenotypes with a Bayesian genome-wide analysis

While recent advancements in computation and modelling have improved the analysis of complex traits, our understanding of the genetic basis of the time at symptom onset remains limited. Here, we develop a Bayesian approach (BayesW) that provides probabilistic inference of the genetic architecture of age-at-onset phenotypes in a sampling scheme that facilitates biobank-scale time-to-event analyses. We show in extensive simulation work the benefits BayesW provides in terms of number of discoveries, model performance and genomic prediction. In the UK Biobank, we find many thousands of common genomic regions underlying the age-at-onset of high blood pressure (HBP), cardiac disease (CAD), and type-2 diabetes (T2D), and for the genetic basis of onset reflecting the underlying genetic liability to disease. Age-at-menopause and age-at-menarche are also highly polygenic, but with higher variance contributed by low frequency variants. Genomic prediction into the Estonian Biobank data shows that BayesW gives higher prediction accuracy than other approaches

Variation in HIV-1 R5 macrophage-tropism correlates with sensitivity to reagents that block envelope: CD4 interactions but not with sensitivity to other entry inhibitors

<p>Abstract</p> <p>Background</p> <p>HIV-1 R5 viruses cause most of the AIDS cases worldwide and are preferentially transmitted compared to CXCR4-using viruses. Furthermore, R5 viruses vary extensively in capacity to infect macrophages and highly macrophage-tropic variants are frequently identified in the brains of patients with dementia. Here, we investigated the sensitivity of R5 envelopes to a range of inhibitors and antibodies that block HIV entry. We studied a large panel of R5 envelopes, derived by PCR amplification without culture from brain, lymph node, blood and semen. These R5 envelopes conferred a wide range of macrophage tropism and included highly macrophage-tropic variants from brain and non-macrophage-tropic variants from lymph node.</p> <p>Results</p> <p>R5 macrophage-tropism correlated with sensitivity to inhibition by reagents that inhibited gp120:CD4 interactions. Thus, increasing macrophage-tropism was associated with increased sensitivity to soluble CD4 and to IgG-CD4 (PRO 542), but with increased resistance to the anti-CD4 monoclonal antibody (mab), Q4120. These observations were highly significant and are consistent with an increased affinity of envelope for CD4 for macrophage-tropic envelopes. No overall correlations were noted between R5 macrophage-tropism and sensitivity to CCR5 antagonists or to gp41 specific reagents. Intriguingly, there was a relationship between increasing macrophage-tropism and increased sensitivity to the CD4 binding site mab, b12, but decreased sensitivity to 2G12, a mab that binds a glycan complex on gp120.</p> <p>Conclusion</p> <p>Variation in R5 macrophage-tropism is caused by envelope variation that predominantly influences sensitivity to reagents that block gp120:CD4 interactions. Such variation has important implications for therapy using viral entry inhibitors and for the design of envelope antigens for vaccines.</p

Final report on project SP1210: Lowland peatland systems in England and Wales – evaluating greenhouse gas fluxes and carbon balances

Lowland peatlands represent one of the most carbon-rich ecosystems in the UK. As a result of widespread habitat modification and drainage to support agriculture and peat extraction, they have been converted from natural carbon sinks into major carbon sources, and are now amongst the largest sources of greenhouse gas (GHG) emissions from the UK land-use sector. Despite this, they have previously received relatively little policy attention, and measures to reduce GHG emissions either through re-wetting and restoration or improved management of agricultural land remain at a relatively early stage. In part, this has stemmed from a lack of reliable measurements on the carbon and GHG balance of UK lowland peatlands. This project aimed to address this evidence gap via an unprecedented programme of consistent, multi year field measurements at a total of 15 lowland peatland sites in England and Wales, ranging from conservation managed ‘near-natural’ ecosystems to intensively managed agricultural and extraction sites. The use of standardised measurement and data analysis protocols allowed the magnitude of GHG emissions and removals by peatlands to be quantified across this heterogeneous data set, and for controlling factors to be identified. The network of seven flux towers established during the project is believed to be unique on peatlands globally, and has provided new insights into the processes the control GHG fluxes in lowland peatlands. The work undertaken is intended to support the future development and implementation of agricultural management and restoration measures aimed at reducing the contribution of these important ecosystems to UK GHG emissions

Organic Wastes Amended with Sorbents Reduce N2O Emissions from Sugarcane Cropping

Nutrient-rich organic wastes and soil ameliorants can benefit crop performance and soil health but can also prevent crop nutrient sufficiency or increase greenhouse gas emissions. We hypothesised that nitrogen (N)-rich agricultural waste (poultry litter) amended with sorbents (bentonite clay or biochar) or compost (high C/N ratio) attenuates the concentration of inorganic nitrogen (N) in soil and reduces emissions of nitrous oxide (N2O). We tested this hypothesis with a field experiment conducted on a commercial sugarcane farm, using in vitro incubations. Treatments received 160 kg N ha−1, either from mineral fertiliser or poultry litter, with additional N (2–60 kg N ha−1) supplied by the sorbents and compost. Crop yield was similar in all N treatments, indicating N sufficiency, with the poultry litter + biochar treatment statistically matching the yield of the no-N control. Confirming our hypothesis, mineral N fertiliser resulted in the highest concentrations of soil inorganic N, followed by poultry litter and the amended poultry formulations. Reflecting the soil inorganic N concentrations, the average N2O emission factors ranked as per the following: mineral fertiliser 8.02% &gt; poultry litter 6.77% &gt; poultry litter + compost 6.75% &gt; poultry litter + bentonite 5.5% &gt; poultry litter + biochar 3.4%. All emission factors exceeded the IPCC Tier 1 default for managed soils (1%) and the Australian Government default for sugarcane soil (1.25%). Our findings reinforce concerns that current default emissions factors underestimate N2O emissions. The laboratory incubations broadly matched the field N2O emissions, indicating that in vitro testing is a cost-effective first step to guide the blending of organic wastes in a way that ensures N sufficiency for crops but minimises N losses. We conclude that suitable sorbent-waste formulations that attenuate N release will advance N efficiency and the circular nutrient economy