Incorporating metamorphism in geodynamic models: the mass conservation problem

Geodynamic models incorporating metamorphic phase transformations almost invariably assume the validity of the Boussinesq approximation that violates conservation of mass. In such models metamorphic density changes take place without volumetric effects. We assess the impact of the Boussinesq approximation by comparing models of orogeny accompanied by lower crustal eclogitization both with and without the approximation. Our results demonstrate that the approximation may cause errors approaching 100 per cent in characteristic measures of orogenic shape. Mass conservation errors in Boussinesq models amplify with model time. Mass conservative models of metamorphism are therefore essential to understand long-term tectonic evolution and to assess the importance of the different geodynamic processe

Development and application of 3D X-ray diffraction for the study of phase transformations in metallic materials

Many steel alloy types, both currently in use and under development, exploit a deformation-induced phase transformation to achieve a combined high strength and ductility. As deformation is applied to these alloys, a metastable retained austenite phase transforms to martensite. This process acts as a significant carrier of plasticity, increasing the work-hardening rate and therefore the ductility. The "stability", or resistance against martensitic transformation, of the austenite phase is the main parameter that governs the martensitic transformation rate and therefore the work-hardening behaviour of the steel. In the last few decades, the stability of an individual austenite grain has been shown to depend on a number of microstructural properties, such as the size of the grain, its orientation relative to the loading axis, the alloy chemistry, and the configuration of the grain's immediate crystallographic neighbourhood. A good understanding of how exactly these properties modify austenite grain stability is crucial to the development of accurate models of deformation-induced phenomena, which themselves directly contribute to the design of new and improved alloys that better exploit said phenomena. In the past, austenite grain stability has usually been evaluated for a steel sample either through phase-averaged behaviour, where the stability of the phase overall is characterised, or on an individual grain level, where typically only a few grains are considered. This is primarily due to the difficulties involved with measuring the martensitic transformation in situ at a per-grain level for a large number of grains simultaneously. The recent development of far-field Three-Dimensional X-Ray Diffraction (3DXRD) has enabled such measurements on a range of polycrystalline materials, capturing the grain-level position, orientation and strain tensor for many thousands of grains in situ. However, the 3DXRD technique poses a number of significant challenges related to data analysis and post-processing, both crucial steps that must be carefully implemented to enable detailed measurements of complicated polycrystal samples. In this study, 3DXRD was implemented at the I12 Joint Engineering, Environmental, and Processing (JEEP) Beamline at the Diamond Light Source X-ray synchrotron. Then, the capabilities of the technique were explored by examining how a microstructurally "simple" single phase ferritic steel responds to in-situ tensile deformation on a per-grain level. A number of micromechanical phenomena were investigated, including a small (but statistically significant) grain neighbourhood effect, where the stress state of a central grain was found to depend on the orientation of its immediate neighbourhood grains, a finding never before seen for large numbers of grains in a cubic polycrystal. During this 3DXRD implementation, a sophisticated automated data analysis and post-processing pipeline was developed, that enabled rapid exploration of such micromechanical effects. With 3DXRD implemented and a data analysis pipeline developed, a novel metastable stainless steel alloy system was devised that enabled the exploration of the martensitic transformation at very low applied strains, as 3DXRD is typically limited to ~2% maximum strain. This alloy system was extensively characterised non-destructively in three dimensions with laboratory electron-based and X-ray based techniques, and was used to evaluate both the performance of multi-phase laboratory-based Diffraction Contrast Tomography (DCT), as well as a novel registration algorithm that accurately located two-dimensional planes measured with Electron Back-Scatter Diffraction (EBSD) within the three-dimensional DCT dataset. Finally, the deformation response of the alloy was measured in-situ with 3DXRD at the ID11 beamline of the European Synchrotron Radiation Facility, coupled with in-situ EBSD scans using an in-chamber tensile stage. Substantial martensite transformations were found even within the ~2% maximum strain window, proving the alloy design was successful and enabling extensive in-situ analyses of austenite grain stability in the bulk material with 3DXRD. Austenite grain stability was found to be influenced by grain size, orientation, and local neighbourhood. Larger grains, grains oriented with {100} close to the loading axis, and grains with more ferrite/martensite-dense neighbourhoods were found to have reduced stability against deformation. The minimum strain work criterion model was also evaluated against the experimental data — it was found to correctly predict the orientation of martensite that formed in the majority of grains, given the parent orientation and macroscopic applied load. Grains where the model failed tended to have reduced levels of stress just before forming martensite, which was attributed to the use of the global stress state by the model as opposed to more granular measurements of the immediate stress field around a grain

Veterinary epidemiology and economics in Africa. A manual for use in the design and appraisal of livestock health policy

Discusses basic techniques involved in the planning, monitoring and evaluation of livestock disease control programmes in Africa i.e. the theory & application of epidemiology statistical analysis, economics, estimating costs and decision making

Mean Flow and Dispersion in the Western Mediterranean Sea from Drifter Observations

Currents in the ocean distribute water masses and everything floating in them. To understand how fast the water (and its flotsam) travels and how effectively it mixes, we need to study the flow statistics. There are two types of measurements of ocean currents: Eulerian measurements that look at how the ocean velocities change at a stationary point on the Earth; and Lagrangian measurements that follow a water mass. Dispersion and mixing is generally best captured by Lagrangian measurements. At the submesoscale (~10-1 – 10 km), the observational tool of choice are drifters, or floating buoys, tethered to a drogue that ensures the drifter moves with the water masses at a particular depth. Here we report on the flow statistics from a particularly rich drifter dataset collected in the Western Mediterranean Sea over 3 years, in different seasons and at different depths

Inflation from Extra Dimensions

The radial mode of n extra compact dimensions (the radion, b) can cause inflation in theories where the fundamental gravity scale, M, is smaller than the Planck scale M_P. For radion potentials V(b) with a simple polynomial form, to get the observed density perturbations, the energy scale of V(b) must greatly exceed M ~ 1 TeV: V(b)^{1/4} = M_v ~ 10^{-4} M_P. This gives a large radion mass and reheat temperature ~ 10^9 GeV, thus avoiding the moduli problem. Such a value of M_v can be consistent with the classical treatment if the new dimensions started sufficiently small. A new possibility is that b approaches its stable value from above during inflation. The same conclusions about M_v may hold even if inflation is driven by matter fields rather than by the radion.Comment: 4 pages, 4 figures, uses epsf.te

Charge asymmetry in W + jets production at the LHC

The charge asymmetry in W + jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex

Inflation with a constant ratio of scalar and tensor perturbation amplitudes

The single scalar field inflationary models that lead to scalar and tensor perturbation spectra with amplitudes varying in direct proportion to one another are reconstructed by solving the Stewart-Lyth inverse problem to next-to-leading order in the slow-roll approximation. The potentials asymptote at high energies to an exponential form, corresponding to power law inflation, but diverge from this model at low energies, indicating that power law inflation is a repellor in this case. This feature implies that a fine-tuning of initial conditions is required if such models are to reproduce the observations. The required initial conditions might be set through the eternal inflation mechanism. If this is the case, it will imply that the spectral indices must be nearly constant, making the underlying model observationally indistinguishable from power law inflation.Comment: 20 pages, 7 figures. Major changes to the Introduction following referee's comments. One figure added. Some other minor changes. No conclusion was modifie

Epileptic multi-seizure type classification using electroencephalogram signals from the Temple University Hospital Seizure Corpus:A review

Epilepsy is one of the most paramount neurological diseases, affecting about 1% of the world's population. Seizure detection and classification are difficult tasks and are ongoing challenges in biomedical signal processing to enhance medical diagnosis. This paper presents and highlights the unique frequency and amplitude information found within multiple seizure types, including their morphologies, to aid the development of future seizure classification algorithms. Whilst many published works in the literature have reported on seizure detection using electroencephalogram (EEG), there has yet to be an exhaustive review detailing multi-seizure type classification using EEG. Therefore, this paper also includes a detailed review of multi-seizure type classification performance based on the Temple University Hospital Seizure Corpus (TUSZ) dataset for focal and generalised classification, and multi-seizure type classification. Deep learning techniques have a higher overall average performance for focal and generalised classification compared to machine learning techniques, whereas hybrid deep learning approaches have the highest overall average performance for multi-seizure type classification. Finally, this paper also highlights the limitations of the TUSZ dataset and suggests some future work, including the curation of a standardised training and testing dataset from the TUSZ that would allow a proper comparison of classification methods and spur advancement in the field.</p

Angular dependence of domain wall resistivity in SrRuO3_{{\bf 3}} films

${\rm SrRuO_3}$ is a 4d itinerant ferromagnet (T$_{c}$ $\sim$150 K) with stripe domain structure. Using high-quality thin films of SrRuO$_{3}$ we study the resistivity induced by its very narrow ($\sim 3$ nm) Bloch domain walls, $\rho_{DW}$ (DWR), at temperatures between 2 K and T$_{c}$ as a function of the angle, $\theta$, between the electric current and the ferromagnetic domains walls. We find that $\rho_{DW}(T,\theta)=\sin^2\theta \rho_{DW}(T,90)+B(\theta)\rho_{DW}(T,0)$ which provides the first experimental indication that the angular dependence of spin accumulation contribution to DWR is $\sin^2\theta$. We expect magnetic multilayers to exhibit a similar behavior.Comment: 5 pages, 5 figure

How do cities approach policy innovation and policy learning? A study of 30 policies in Northern Europe and North America

This paper reports on a study of current practice in policy transfer, and ways in which its effectiveness can be increased. A literature review identifies important factors in examining the transfer of policies. Results of interviews in eleven cities in Northern Europe and North America investigate these factors further. The principal motivations for policy transfer were strategic need and curiosity. Local officials and politicians dominated the process of initiating policy transfer, and local officials were also the leading players in transferring experience. A range of information sources are used in the search process but human interaction was the most important source of learning for two main reasons. First, there is too much information available through the Internet and the search techniques are not seen to be wholly effective in identifying the necessary information. Secondly, the information available on websites, portals and even good practice guides is not seen to be of mixed quality with risks of focussing only on successful implementation and therefore subject to some bias. Officials therefore rely on their trusted networks of peers for lessons as here they can access the ‘real implementation’ story and the unwritten lessons. Organisations which have a culture that is supportive of learning from elsewhere had strong and broad networks of external contacts and resourced their development whilst others are more insular or inward looking and reluctant to invest in policy lessons from elsewhere. Solutions to the problems identified in the evidence base are proposed