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Niagara is currently the fastest supercomputer accessible to academics in Canada. It was deployed at the beginning of 2018 and has been serving the research community ever since. This homogeneous 60,000-core cluster, owned by the University of Toronto and operated by SciNet, was intended to enable large parallel jobs and has a measured performance of 3.02 petaflops, debuting at #53 in the June 2018 TOP500 list. It was designed to optimize throughput of a range of scientific codes running at scale, energy efficiency, and network and storage performance and capacity. It replaced two systems that SciNet operated for over 8 years, the Tightly Coupled System (TCS) and the General Purpose Cluster (GPC) [13]. In this paper we describe the transition process from these two systems, the procurement and deployment processes, as well as the unique features that make Niagara a one-of-a-kind machine in Canada.

As part of the mitochondrial respiratory chain, cytochrome c oxidase utilizes the energy produced by the reduction of O2 to water to fuel vectorial proton transport. The mechanism coupling proton pumping to redox chemistry is unknown. Recent advances have provided evidence that each of the four observable transitions in the complex catalytic cycle consists of a similar sequence of events. However, the physico-chemical basis underlying this recurring sequence has not been identified. We identify this recurring pattern based on a comprehensive model of the catalytic cycle derived from the analysis of oxygen chemistry and available experimental evidence. The catalytic cycle involves the periodic repetition of a sequence of three states differing in the spatial distribution of charge in the active site: [0|1], [1|0], and [1|1], where the total charge of heme a and the binuclear center appears on the left and on the right, respectively. This sequence recurs four times per turnover despite differences in the redox chemistry. This model leads to a simple, robust, and reproducible sequence of electron and proton transfer steps and rationalizes the pumping mechanism in terms of electrostatic coupling of proton translocation to redox chemistry. Continuum electrostatic calculations support the proposed mechanism and suggest an electrostatic origin for the decoupled and inactive phenotypes of ionic mutants in the principal proton-uptake pathway.