Preconditioning for Allen-Cahn variational inequalities with non-local constraints

The solution of Allen-Cahn variational inequalities with mass constraints is of interest in many applications. This problem can be solved both in its scalar and vector-valued form as a PDE-constrained optimization problem by means of a primal-dual active set method. At the heart of this method lies the solution of linear systems in saddle point form. In this paper we propose the use of Krylov-subspace solvers and suitable preconditioners for the saddle point systems. Numerical results illustrate the competitiveness of this approach

Explicit isogeny descent on elliptic curves

In this note, we consider an l-isogeny descent on a pair of elliptic curves over Q. We assume that l > 3 is a prime. The main result expresses the relevant Selmer groups as kernels of simple explicit maps between finite- dimensional F_l-vector spaces defined in terms of the splitting fields of the kernels of the two isogenies. We give examples of proving the l-part of the Birch and Swinnerton-Dyer conjectural formula for certain curves of small conductor.Comment: 17 pages, accepted for publication in Mathematics of Computatio

Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

The potential of directional observations in the thermal infrared region for land surface studies is a largely uncharted area of research. The availability of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction. In the context of studies on heat transfer at heterogeneous land surfaces, multiangular thermal infrared (TIR) observations offer the opportunity of overcoming fundamental difficulties in modeling sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil. The first one included the use of multi-temporal field measurements at view angles of 0°, 23° and 52°. The second and third one were done with directional ATSR observations at view angles of 0° and 53° only. The first one was a contribution to the Inner-Mongolia Grassland Atmosphere Surface Study (IMGRASS) experiment in China, the second to the Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States. The IMGRASS experiment provided useful insights on the applicability of a simple linear mixture model to the analysis of observed radiance. The HEIFE case study was focused on the large oasis of Zhang-Ye and led to useful estimates of soil and vegetation temperatures. The SGP 1997 contributed a better understanding of the impact of spatial heterogeneity on the accuracy of retrieved foliage and soil temperatures. Limitations in the approach due to varying radiative and boundary layer forcing and to the difference in spatial resolution between the forward and the nadir view are evaluated through a combination of modeling studies and analysis of field data

Empirical evidence for the Birch and Swinnerton-Dyer conjectures for modular jacobians of genus 2 curves

This paper provides empirical evidence for the Birch and Swinnerton-Dyer conjectures for modular Jacobians of genus 2 curves. The second of these conjectures relates six quantities associated to a Jacobian over the rational numbers. One of these six quantities is the size of the Shafarevich-Tate group. Unable to compute that, we computed the five other quantities and solved for the last one. In all 32 cases, the result is very close to an integer that is a power of 2. In addition, this power of 2 agrees with the size of the 2-torsion of the Shafarevich-Tate group, which we could compute

Ab initio determination of excitation energies and magnetic couplings in correlated, quasi two-dimensional iridates

To determine the strength of essential electronic and magnetic interactions in the iridates Sr$_2$IrO$_4$ and Ba$_2$IrO$_4$ - potential platforms for high-temperature superconductivity - we use many-body techniques from wavefunction-based electronic-structure theory. Multiplet physics, spin-orbit interactions, and Ir-O hybridization are all treated on equal footing, fully {\it ab initio}. Our calculations put the lowest d-d excitations of Sr$_2$IrO$_4$/Ba$_2$IrO$_4$ at 0.69/0.64 eV, substantially lower than in isostructural cuprates. Charge-transfer excitations start at 3.0/1.9 eV and the magnetic nearest-neighbor exchange coupling is 51/58 meV. Available experimental results are fully consistent with these values, which strongly constrains the parametrization of effective iridate Hamiltonians

Correlation effects in ionic crystals: I. The cohesive energy of MgO

High-level quantum-chemical calculations, using the coupled-cluster approach and extended one-particle basis sets, have been performed for (Mg2+)n (O2-)m clusters embedded in a Madelung potential. The results of these calculations are used for setting up an incremental expansion for the correlation energy of bulk MgO. This way, 96% of the experimental cohesive energy of the MgO crystal is recovered. It is shown that only 60% of the correlation contribution to the cohesive energy is of intra-ionic origin, the remaining part being caused by van der Waals-like inter-ionic excitations.Comment: LaTeX, 20 pages, no figure

Gait unsteadiness and fall risk in two affective disorders: a preliminary study

BACKGROUND: In older adults, depression has been associated with increased fall risk, but the reasons for this link are not fully clear. Given parallels between major depression and Parkinson's disease, we hypothesized that major depression and related affective disorders would be associated with impairment in the ability to regulate the stride-to-stride fluctuations in gait cycle timing. METHODS: We measured stride-to-stride fluctuations of patients with two forms of mood disorders, unipolar major depressive disorder (MDD) and bipolar disorder, and compared their gait to that of a healthy control group. The primary outcomes were two measures of gait unsteadiness that have been associated with fall risk: stride time variability and swing time variability. RESULTS: Compared to the control group, the two patient groups tended to walk more slowly and with decreased swing time and increased stride time. However, none of these differences was statistically significant. Compared to the control group, swing time variability was significantly larger in the subjects with bipolar disorder (p < 0.0001) and in the subjects with MDD (p < 0.0004). CONCLUSIONS: Patients with MDD and patients with bipolar disorder display gait unsteadiness. This perturbation in gait may provide a mechanistic link connecting depression and falls. The present findings also suggest the possibility that measurement of variability of gait may provide a readily quantifiable objective approach to monitoring depression and related affective disorders

The school as a learning organisation: a review revisiting and extending a timely concept

Purpose: Schools today have to prepare students for life and work in a fast-changing world, for jobs and for using technologies some of which have not yet been created. But the schools and school systems are not keeping up and all too often, teachers are not developing the practices and skills required to meet today’s learners’ diverse needs. Changes indicate a greater imperative but also some cautions. This review is part of the attempt to work towards a common understanding of schools as learning organisations (SLOs) today which is both solidly founded in the literature and recognisable currently by researchers, practitioners and policy makers in many countries. But this is not just a theoretical exercise. If it is to be truly relevant and have the necessary impact, the concept also needs to support those who are interested in transforming or further developing their school(s) into learning organisations (LO) at this point in time. In this paper, the authors first summarise different perspectives on the concept of the LO as used more generally across disciplines. Next, the authors describe the methodology for exploring the SLO and discuss definitional issues, before presenting a summary of the integrated model with accompanying rationale, Finally the authors discuss plans to bring the model to life, with associated issues for researchers, educators and policy makers. The paper aims to discuss these issues. / Design/methodology/approach: The search for this literature in the English language was carried out through: focussed searches of nine electronic databases – ERIC, SAGE, Google Scholar, Taylor & Francis, Emerald, JSTOR, SpringerLink, Google, Science Direct – using the search terms “SLO” and “learning school”; and contacts with leading experts in this area of work which led to identification of additional literature. The first approach led to selection of 25 most frequently found publications on the SLO and/or learning school. Through the second approach, the authors used an additional seven publications to further enrich the analysis. The interdisciplinary review was extended to include investigation of related organisational change, learning, school improvement and effectiveness literatures. / Findings: The starting hypothesis is that the seven action-oriented dimensions of the model together add up to a sustainable LO; that is, successfully realising all seven dimensions is greater than the sum of the parts. But, it is not clear how the individual dimensions relate to each other, and whether some are more important than others. Elements within dimensions are also likely to vary across country contexts. Over the next few years the authors will explore and amend the model, together with practitioners, policy makers and researchers from around the globe. / Practical implications: Despite differences in interpretation, common features emerge. First, there is general agreement that the SLO is a necessity for dealing with the rapidly changing external environment by any school organisation, regardless of context. This is exemplified by application of the concept in many countries including, for example, Australia, Canada, England and Wales, Iran, Israel, Korea, Malaysia, South-Africa and the USA. Second, the SLO is defined as “organic” and closely connected to its external environment. Third, the SLO literature strongly emphasises the importance of individual, group and organisational learning with inquiry, problem solving and experimentation as key drivers of change and innovation. Last, the literature highlights the importance of beliefs, values and norms of employees for continuous and collaborative learning, and processes, strategies and structures to create the conditions for such learning, experimentation and innovation to flourish. The review led to the design of a new action-oriented model. In its current form, the model is intended to offer a stimulus and provide practical guidance on how schools might support and use learning at all levels to improve and transform themselves into a LO and ultimately enhance outcomes. The language is deliberately action-oriented, and elements highlight both what a school aspires to and the processes it goes through in its journey of developing itself as a LO. / Originality/value: While the concept of a school LO is not new, at a time of constant and complex change, this multi-disciplinary international literature review has given it a new lease of life: drawing on previous studies, but connecting these to a wider relevant knowledge base and the current context. It offers a way forward while arguing that deeper understanding is needed on how schools can develop as LOs. It is now informing the OECD’s work on SLOs with policy makers and practitioners in different countries and the findings are being used to help assess impact at a range of levels

Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe

We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the "prompt" component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.Comment: 11 pages, 11 figures, 4 tables. Accepted for publication in ApJ on 11/02/201

Contextual cropping and scaling of TV productions

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s11042-011-0804-3. Copyright @ Springer Science+Business Media, LLC 2011.In this paper, an application is presented which automatically adapts SDTV (Standard Definition Television) sports productions to smaller displays through intelligent cropping and scaling. It crops regions of interest of sports productions based on a smart combination of production metadata and systematic video analysis methods. This approach allows a context-based composition of cropped images. It provides a differentiation between the original SD version of the production and the processed one adapted to the requirements for mobile TV. The system has been comprehensively evaluated by comparing the outcome of the proposed method with manually and statically cropped versions, as well as with non-cropped versions. Envisaged is the integration of the tool in post-production and live workflows