Parallel Chains: Improving Throughput and Latency of Blockchain Protocols via Parallel Composition

Two of the most significant challenges in the design of blockchain protocols is increasing their transaction processing throughput and minimising latency in terms of transaction settlement. In this work we put forth for the first time a formal execution model that enables to express transaction throughput while supporting formal security arguments regarding safety and liveness. We then introduce parallel-chains, a simple yet powerful non-black-box composition technique for blockchain protocols. We showcase our technique by providing two parallel-chains protocol variants, one for the PoS and one for PoW setting, that exhibit optimal throughput under adaptive fail-stop corruptions while they retain their resiliency in the face of Byzantine adversity assuming honest majority of stake or computational power, respectively. We also apply our parallel-chains composition method to improve settlement latency; combining parallel composition with a novel transaction weighing mechanism we show that it is possible to scale down the time required for a transaction to settle by any given constant while maintaining the same level of security

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AimThe SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery.MethodsThis was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin.ResultsOverall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P ConclusionOne in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease