Achieving Efficient Strong Scaling with PETSc using Hybrid MPI/OpenMP Optimisation

The increasing number of processing elements and decreas- ing memory to core ratio in modern high-performance platforms makes efficient strong scaling a key requirement for numerical algorithms. In order to achieve efficient scalability on massively parallel systems scientific software must evolve across the entire stack to exploit the multiple levels of parallelism exposed in modern architectures. In this paper we demonstrate the use of hybrid MPI/OpenMP parallelisation to optimise parallel sparse matrix-vector multiplication in PETSc, a widely used scientific library for the scalable solution of partial differential equations. Using large matrices generated by Fluidity, an open source CFD application code which uses PETSc as its linear solver engine, we evaluate the effect of explicit communication overlap using task-based parallelism and show how to further improve performance by explicitly load balancing threads within MPI processes. We demonstrate a significant speedup over the pure-MPI mode and efficient strong scaling of sparse matrix-vector multiplication on Fujitsu PRIMEHPC FX10 and Cray XE6 systems

On the potential of linked-basin tidal power plants: An operational and coastal modelling assessment

Single-basin tidal range power plants have the advantage of predictable energy outputs, but feature non-generation periods in every tidal cycle. Linked-basin tidal power systems can reduce this variability and consistently generate power. However, as a concept the latter are under-studied with limited information on their performance relative to single-basin designs. In addressing this, we outline the basic principles of linked-basin power plant operation and report results from their numerical simulation. Tidal range energy operational models are applied to gauge their capabilities relative to conventional, single-basin tidal power plants. A coastal ocean model (Thetis) is then refined with linked-basin modelling capabilities. Simulations demonstrate that linked-basin systems can reduce non-generation periods at the expense of the extractable energy output relative to conventional tidal lagoons and barrages. As an example, a hypothetical case is considered for a site in the Severn Estuary, UK. The linked-basin system is seen to generate energy 80–100% of the time over a spring-neap cycle, but harnesses at best 30% of the energy of an equivalent-area single-basin design

Decision criteria for selecting essential medicines and their connection to guidelines:an interpretive descriptive qualitative interview study

Background and Objectives: The World Health Organization Model List of Essential Medicines has led to at least 137 national lists. Essential medicines should be grounded in evidence-based guideline recommendations and explicit decision criteria. Essential medicines should be available, accessible, affordable, and the supporting evidence should be accompanied by a rating of the certainty one can place in it. Our objectives were to identify criteria and considerations that should be addressed in moving from a guideline recommendation regarding a medicine to the decision of whether to add, maintain, or remove a medicine from an essential medicines list. We also seek to explore opportunities to improve organizational processes to support evidence-based health decision-making more broadly. Methods: We conducted a qualitative study with semistructured interviews of key informant stakeholders in the development and use of guidelines and essential medicine lists (EMLs). We used an interpretive descriptive analysis approach and thematic analysis of interview transcripts in NVIVO v12. Results: We interviewed 16 key informants working at national and global levels across all WHO regions. We identified five themes: three descriptive/explanatory themes 1) EMLs and guidelines, the same, but different; 2) EMLs can drive price reductions and improve affordability and access; 3) Time lag and disconnect between guidelines and EMLs; and two prescriptive themes 4) An “evidence pipeline” could improve coordination between guidelines and EMLs; 5) Facilitating the link between the WHO Model List of Essential Medicines (WHO EML) and national EMLs could increase alignment. Conclusion: We found significant overlap and opportunities for alignment between guideline and essential medicine decision processes. This finding presents opportunities for guideline and EML developers to enhance strategies for collaboration. Future research should assess and evaluate these strategies in practice to support the shared goal of guidelines and EMLs: improvements in health.</p