Since the inception of Bitcoin, cryptocurrencies and the underlying blockchain technology have attracted an increasing interest from both academia and industry. Among various core components, consensus protocol is the defining technology behind the security and performance of blockchain. From incremental modifications of Nakamoto consensus protocol to innovative alternative consensus mechanisms, many consensus protocols have been proposed to improve the performance of the blockchain network itself or to accommodate other specific application needs.In this survey, we present a comprehensive review and analysis on the state-of-the-art blockchain consensus protocols. To facilitate the discussion of our analysis, we first introduce the key definitions and relevant results in the classic theory of fault tolerance which help to lay the foundation for further discussion. We identify five core components of a blockchain consensus protocol, namely, block proposal, block validation, information propagation, block finalization, and incentive mechanism. A wide spectrum of blockchain consensus protocols are then carefully reviewed accompanied by algorithmic abstractions and vulnerability analyses. The surveyed consensus protocols are analyzed using the five-component framework and compared with respect to different performance metrics. These analyses and comparisons provide us new insights in the fundamental differences of various proposals in terms of their suitable application scenarios, key assumptions, expected fault tolerance, scalability, drawbacks and trade-offs. We believe this survey will provide blockchain developers and researchers a comprehensive view on the state-ofthe-art consensus protocols and facilitate the process of designing future protocols.

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This is a repository copy of Survivorship of fixed vs mobile bearing unicompartmental knee replacement: A systematic review and meta-analysis of sixty-four studies and National Joint Registries.

Bacterial contamination of platelets is considered as the most frequent infectious risk of transfusion. The prevalence of bacterial contamination has been reported and varied considerably in different countries, but the data for bacterial contamination of platelets in China are rarely reported. Eight thousand apheresis platelet concentrates (PCs) were analysed by aerobic and anaerobic cultures. Ten millilitres of PCs were inoculated into aerobic and anaerobic bottles (5 mL each), followed by the incubation for a maximum of 7 days. A new sample was taken from the unit for reculturing in order to confirm the initial positive reaction. All positive culture bottles were referred for bacterial isolation and identification. Twenty one cultures (0.26%) were flagged as positive in initial culture. Five cultures (0.06%) were confirmed as true positive and nine cultures (0.11%) were confirmed as indeterminate in reculture. A bacterium from skin flora (Propionibacterium spp.) was the most prevalent contaminant. Mean time to initial positive culture from start of incubation was 22.1 h for confirmed positive units and 97.3 h for indeterminate units. Most PC units had already been issued by the time of initial positive culture with a 'negative-to-date' issued strategy. There is a risk of bacterial contamination of PCs in China. Implementing bacterial screening of platelets could reduce the risk of septic reaction and fatalities due to transfusion of bacterially contaminated platelets. However, bacterial contamination PCs can still be transfused due to the delay until a positive signal in the culture system.

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