Grand Minima Under the Light of a Low Order Dynamo Model

In this work we use a low order dynamo model and study under which conditions can it reproduce solar grand minima. We begin by building the phase space of a proxy for the toroidal component of the solar magnetic field and we develop a model, derived from mean field dynamo theory, that gives the time evolution of the toroidal field. This model is characterized by a non-linear oscillator whose coefficients retain most of the physics behind dynamo theory. In the derivation of the model we also include stochastic oscillations in the $\alpha$ effect. We found no evidences that stochastic fluctuations in a linear $\alpha$ effect can trigger grand minima episodes in this model. In contrast, the model used points out that possible mechanism that can trigger grand minima should involve the meridional circulation, magnetic diffusivity or field intensification by buoyancy driven instabilities.Comment: 12 pages, 5 figures, Space Climate Symposium 3, Finland (in press JASTP). Version 3.0 incorporates new figures and reference

Thinking in terms of contract defences

While the terminology of defences is commonplace in other fields of private law, contract lawyers seem relatively unaccustomed to thinking in terms of defences. For example, although the leading texts in other areas of private law reserve a prominent place for defences, 1 the present edition of Chitty on Contracts does not. 2 Similarly, although Andrew Burrows dedicates Part 4 of his Restatement of the English Law of Unjust Enrichment to defences,3 he includes no equivalent section in his Restatement of the English Law of Contract. Indeed, references to \u27defences\u27 in that work are few and far between

Central issues in the law of tort defences

This book is the first part of an investigation into defences in private law. The present volume explores tort law defences. Three further volumes are planned, on unjust enrichment, contract and equity. The chapters that constitute the present volume were delivered at a workshop at All Souls College, Oxford in January 2014. In helping to bring the workshop to fruition, we are grateful, first and foremost, for the support of All Souls College, which provided both the setting for the proceedings and significant financial support. The workshop could not have gone ahead without the further financial assistance of the Oxford Law Faculty and the University of Oxford’s Fell Fund. We were also able to call on several members of the Faculty—both administrative and academic—for guidance. Discussions at the workshop were greatly enriched by the contributions of several observers, including Lord Hoffmann, Timothy Endicott and John Gardner and, on behalf of the Law Commission, Sir David Lloyd-Jones and David Hertzell. Finally, Anna Kim’s patience and efficiency helped immeasurably in the lead up to the workshop. For their assistance in helping to turn the workshop papers into the chapters that feature in this volume, we are grateful to Jodi Gardner, Elizabeth Houghton, Krishnaprasad Kizhakkevalappil, Niranjan Venkatesan and Binesh Hass. We are indebted to Hart Publishing for their editorial assistance, and in particular to Richard Hart for the characteristic enthusiasm and professionalism with which he embraced the project as a whole. Finally, we are grateful to Lord Hoffmann for generously agreeing to write the Foreword

Defences in unjust enrichment: questions and themes

This book is the second in a series of four that is concerned with defences to liability arising in private law. We felt, and still feel, that the topic has not received the attention that it deserves. 1 We are not alone in holding this view. 2 By contrast, defences have dominated the research agendas of many scholars of the criminal law.3 The asymmetry in attention to defences in these different fields is striking in part because of the apparent parallels between the two domains. For instance, the distinction in private law between causes of action and defences arguably mirrors that between offences and defences in the criminal law

A Successful Component Architecture for Interoperable and Evolvable Ground Data Systems

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) has adopted an open architecture approach for satellite control centers and is now realizing benefits beyond those originally envisioned. The Goddard Mission Services Evolution Center (GMSEC) architecture utilizes standardized interfaces and a middleware software bus to allow functional components to be easily integrated. This paper presents the GMSEC architectural goals and concepts, the capabilities enabled and the benefits realized by adopting this framework approach. NASA experiences with applying the GMSEC architecture on multiple missions are discussed. The paper concludes with a summary of lessons learned, future directions for GMSEC and the possible applications beyond NASA GSFC

The origin and dynamic interaction of solar magnetic fields

The dynamics of the solar corona are dominated by the magnetic field which creates its structure. The magnetic field in most of the corona is ‘frozen’ to the plasma very effectively. The exception is in small localised regions of intense current concentrations where the magnetic field can slip through the plasma and a restructuring of the magnetic field can occur. This process is known as magnetic reconnection and is believed to be responsible for a wide variety of phenomena in the corona, from the rapid energy release of solar flares to the heating of the high-temperature corona. The coronal field itself is three-dimensional (3D), but much of our understanding of reconnection has been developed through two-dimensional (2D) models. This thesis describes several models for fully 3D reconnection, with both kinematic and fully dynamic models presented. The reconnective behaviour is shown to be fundamentally different in many respects from the 2D case. In addition a numerical experiment is described which examines the reconnection process in coronal magnetic flux tubes whose photospheric footpoints are spun, one type of motion observed to occur on the Sun. The large-scale coronal field itself is thought to be generated by a magnetohydrodynamic dynamo operating in the solar interior. Although the dynamo effect itself is not usually associated with reconnection, since the essential element of the problem is to account for the presence of large-scale fields, reconnection is essential for the restructuring of the amplified small-scale flux. Here we examine some simple models of the solar-dynamo process, taking advantage of their simplicity to make a full exploration of their behaviour in a variety of parameter regimes. A wide variety of dynamic behaviour is found in each of the models, including aperiodic modulation of cyclic solutions and intermittency that strongly resembles the historic record of solar magnetic activity

The Dependence of Coronal Loop Heating on the Characteristics of Slow Photospheric Motions

The Parker hypothesis (Parker (1972)) assumes that heating of coronal loops occurs due to reconnection, induced when photospheric motions braid field lines to the point of current sheet formation. In this contribution we address the question of how the nature of photospheric motions affects heating of braided coronal loops. We design a series of boundary drivers and quantify their properties in terms of complexity and helicity injection. We examine a series of long-duration full resistive MHD simulations in which a simulated coronal loop, consisting of initially uniform field lines, is subject to these photospheric flows. Braiding of the loop is continually driven until differences in behaviour induced by the drivers can be characterised. It is shown that heating is crucially dependent on the nature of the photospheric driver - coherent motions typically lead to fewer large energy release events, while more complex motions result in more frequent but less energetic heating events

Magnetic Quenching of Turbulent Diffusivity: Reconciling Mixing-length Theory Estimates with Kinematic Dynamo Models of the Solar Cycle

The turbulent magnetic diffusivity in the solar convection zone is one of the most poorly constrained ingredients of mean-field dynamo models. This lack of constraint has previously led to controversy regarding the most appropriate set of parameters, as different assumptions on the value of turbulent diffusivity lead to radically different solar cycle predictions. Typically, the dynamo community uses double step diffusivity profiles characterized by low values of diffusivity in the bulk of the convection zone. However, these low diffusivity values are not consistent with theoretical estimates based on mixing-length theory -- which suggest much higher values for turbulent diffusivity. To make matters worse, kinematic dynamo simulations cannot yield sustainable magnetic cycles using these theoretical estimates. In this work we show that magnetic cycles become viable if we combine the theoretically estimated diffusivity profile with magnetic quenching of the diffusivity. Furthermore, we find that the main features of this solution can be reproduced by a dynamo simulation using a prescribed (kinematic) diffusivity profile that is based on the spatiotemporal geometric-average of the dynamically quenched diffusivity. Here, we provide an analytic fit to the dynamically quenched diffusivity profile, which can be used in kinematic dynamo simulations. Having successfully reconciled the mixing-length theory estimated diffusivity profile with kinematic dynamo models, we argue that they remain a viable tool for understanding the solar magnetic cycle.Comment: Submitted to ApJ

Differences in level of confidence in diabetes care between different groups of trainees: the TOPDOC diabetes study

Background There is an increasing prevalence of diabetes. Doctors in training, irrespective of specialty, will have patients with diabetes under their care. The aim of this further evaluation of the TOPDOC Diabetes Study data was to identify if there was any variation in confidence in managing diabetes depending on the geographical location of trainees and career aspirations. Methods An online national survey using a pre-validated questionnaire was administered to trainee doctors. A 4-point confidence rating scale was used to rate confidence in managing aspects of diabetes care and a 6-point scale used to quantify how often trainees would contribute to the management of patients with diabetes. Responses were grouped depending on which UK country trainees were based and their intended career choice. Results Trainees in Northern Ireland reported being less confident in IGT diagnosis, use of IV insulin and peri-operative management and were less likely to adjust oral treatment, contact specialist, educate lifestyle, and optimise treatment. Trainees in Scotland were less likely to contact a specialist, but more likely to educate on lifestyle, change insulin, and offer follow-up advice. In Northern Ireland, Undergraduate (UG) and Postgraduate (PG) training in diagnosis was felt less adequate, PG training in emergencies less adequate, and reporting of need for further training higher. Trainees in Wales felt UG training to be inadequate. In Scotland more trainees felt UG training in diagnosis and optimising treatment was inadequate. Physicians were more likely to report confidence in managing patients with diabetes and to engage in different aspects of diabetes care. Aspiring physicians were less likely to feel the need for more training in diabetes care; however a clear majority still felt they needed more training in all aspects of care. Conclusions Doctors in training have poor confidence levels dealing with diabetes related care issues. Although there is variability between different groups of trainees according to geographical location and career aspirations, this is a UK wide issue. There should be a UK wide standardised approach to improving training for junior doctors in diabetes care with local training guided by specific needs.</p

Breaking up sitting time after stroke - How much less sitting is needed to improve blood pressure after stroke (BUST-BP-Dose): Protocol for a dose-finding study

Excessive sitting is detrimentally associated with cardiovascular disease and all-cause mortality. Frequent breaks in prolonged sitting can improve cardiometabolic responses in non-stroke populations. However, this has not been established in stroke survivors. This study will determine the most effective dose of activity breaks that (i) produce clinically meaningful improvements in mean systolic blood pressure (primary outcome), postprandial glucose, and insulin responses (secondary outcomes), and (ii) is safe and feasible. We hypothesis that systolic blood pressure, postprandial insulin, and glucose responses will improve with increasing doses of activity and be most effective at the maximum safe and feasible dose of activity. Thirty participants in the most effective dose will provide 80% power to detect a within-person, between-condition, difference of 3.5 mmHg in systolic blood pressure assuming a SD of 15 mmHg, within-person correlation of 0.9, and α = 0.05. Stroke survivors will complete 3 experimental conditions in a within-participant, dose escalation design including (i) uninterrupted sitting (8 h), (ii) Dose 1: uninterrupted sitting with bouts of light-intensity exercises while standing (initial dose involves two 5-min breaks), and (iii) Dose 2: two additional 5-min breaks above Dose 1. Ambulatory blood pressure will be collected every 30 min during experimental conditions and hourly for 24-h post-experimental conditions. Blood samples will be collected every 30 min during 2-h postprandial periods. This study will identify the most effective dose of light-intensity exercises while standing to improve cardiometabolic responses in stroke survivors