Projecting the impact of a two-dose COVID-19 vaccination campaign in Ontario,Canada

BackgroundA number of highly effective COVID-19 vaccines have been developed and approved for mass vaccination. We evaluated the impact of vaccination on COVID-19 outbreak and disease outcomes in Ontario, Canada.MethodsWe used an agent-based transmission model and parameterized it with COVID-19 characteristics, demographics of Ontario, and age-specific clinical outcomes. We implemented a two-dose vaccination program according to tested schedules in clinical trials for Pfizer-BioNTech and Moderna vaccines, prioritizing healthcare workers, individuals with comorbidities, and those aged 65 and older. Daily vaccination rate was parameterized based on vaccine administration data. Using estimates of vaccine efficacy, we projected the impact of vaccination on the overall attack rate, hospitalizations, and deaths. We further investigated the effect of increased daily contacts at different stages during vaccination campaigns on outbreak control.ResultsMaintaining non-pharmaceutical interventions (NPIs) with an average of 74% reduction in daily contacts, vaccination with Pfizer-BioNTech and Moderna vaccines was projected to reduce hospitalizations by 27.3% (95% CrI: 22.3% − 32.4%) and 27.0% (95% CrI: 21.9% − 32.6%), respectively, over a one-year time horizon. The largest benefits of vaccination were observed in preventing deaths with reductions of 31.5% (95% CrI: 22.5% − 39.7%) and 31.9% (95% CrI: 22.0% − 41.4%) for Pfizer-BioNTech and Moderna vaccines, respectively, compared to no vaccination. We found that an increase of only 10% in daily contacts at the end of lockdown, when vaccination coverage with only one dose was 6%, would trigger a surge in the outbreak. Early relaxation of population-wide measures could lead to a substantial increase in the number of infections, potentially reaching levels observed during the peak of the second wave in Ontario.ConclusionsVaccination can substantially mitigate ongoing COVID-19 outbreaks. Sustaining population-wide NPIs, to allow for a sufficient increase in population-level immunity through vaccination, is essential to prevent future outbreaks.     

神经系统轴突三维定向生长的数值模拟

目的研究轴突在三维组织中的定向生长问题,探讨轴突沿非平坦基底定向生长时基底的低起伏程度对轴突的生长速率、成束和解束速率的影响。方法根据实验观察,设轴突生长的牵引力与靶细胞分泌的可扩散吸引分子的浓度梯度成正比,轴突成束和解束的侧向力与生长锥分泌的可扩散吸引分子和排斥分子的浓度梯度成正比,并且,吸引力指向浓度高的方向,排斥力指向浓度低的方向,浓度满足扩散方程。对于非平坦基底,有效力为沿基底轮廓线的切向分量。数值计算采用三维有限差分法和改进的Euler法。结果(1)轴突在三维组织中定向生长的基本特征与在二维培养基实验中的观察是一致的,只是在形态上有三维与二维之分;(2)非平坦基底的低起伏程度影响轴突的生长,随着起伏加剧,生长锥的前进速率减小、侧向速率增加。结论(1)许多基于二维培养实验所揭示的轴突生长的基本规律在三维情况下仍然是成立的;(2)基底的几何性质是影响轴突生长速率的重要因素之一。     

人体呼吸道的二级及三级支气管内吸气流动的数值研究

呼吸系统的主要生理机能是在大气和血液之间交换氧气和二氧化碳，其生理过程与呼吸道内的气体流动和输送有密切关系。本文利用数值模拟方法对呼吸道内二级及三级支气管模型内的吸气过程进行数值研究，研究表明：二级支气管的计算结果与现有的实验值吻合很好；在三级支气管内。当人体处于正常吸气流量下，支气管内未发生任何分离现象。但流道几何形状的弯曲和分岔使支气管内出现强烈的二次流现象，主流速度出现倾斜分布及m-型分布特征。从而加大了分岔管内侧壁面及前后侧壁面上的切应力；在三级支气管的末级管内，流量分流不均匀。在计算条件下，中部支气管内的流量与侧部支气管内的流量之比为1．2。     

右肺支气管树的三维分形模拟

肺是天然的非对称不规则体。肺内的气管树呈复杂的自相似的结构。基于最小能耗思想 ,作者根据肺的解剖学数据 ,建立右肺的细分网格坐标 ,通过计算各级分块的质心 ,寻找分叉方向与确定分叉长度 ,以 Open GL 为工具 ,实现了右肺支气管树的三维分形模拟 ,并且得到各级的长度、分叉角度和管径的具体参数。所生成的图形在形态与几何参数上与现有统计数据很吻合。计算得到该模型的分形覆盖维数为 2 .19,与其他学者计算的人体肺的理想维数 2 .17[1 ] 比较接近。该模型为今后用分形思想研究肺的气体扩散传递功能奠定基础。从节省计算机存储、加快图形传输上方面来说也有一定意义     

高速线扫描OCT的可行性与光学成像特性的研究

光学相干层析成像（0cT）是一种迅速发展的非侵入式、高分辨率医学层析成像技术。由于传统时域点扫描方式的OCT系统的成像速度慢，难以用于活体的实时成像。介绍了基于线扫描方式的时域OCT系统，这种扫描方式可以无需横向扫描直接得到二维层析图像。为验证基于线扫描方式的时域OCT系统的可行性及得到其设计基本参数，借助Zemax光学设计软件模拟该系统的干涉效果，分析线扫描时域OCT的成像特性。研究表明，这种线扫描OCT在3mm的横向扫描宽度时，可以比传统点扫描方式快二百余倍。     

神经系统轴突生长的数值模拟

目的数值模拟神经系统在发育过程中轴突的生长情况。方法根据神经发育原理,建立具有一定刚性的非线性混合抛物型偏微分方程组,运用ADI差分格式和改进的欧拉法作数值分析。结果 (1)在一个正方形平面区域内有10个轴突以相等的间距围成圆形,当中心有1个靶细胞时,轴突生长路径的数值模拟结果与前人所做的有关结果一致;(2)轴突的初始位置同(1),当中央有4个两两上下并排分布的靶细胞时,数值模拟结果很好地反映了轴突生长时的趋化性;(3)在区域的近上、下边界分别有一串靶细胞和一串轴突时,数值模拟结果较好地反映了轴突结集生长时的成束和解束现象。结论本文给出的数学模型和数值主法能够较好地模拟有关实验所观测到的主要现象。     

胫骨上端外部形状及内部结构的模拟

目的，进行胫骨上端内部结构和外部形状的模拟。方法，采用高阶非线性骨再造速率方程和有限元方法相结合，引入拓扑优化的思想，选取大于模拟的胫骨上端外形的模拟域，从不固定外形出发，对正常力学环境下的胫骨上端内部结构及外部形状进行模拟。结果，模拟的胫骨上端的外部形状和内部结构与真实结构十分接近。     

基于人工视网膜神经节细胞感受野的图像边缘检测

用光电池组装一个工感受野，在一维上模拟视网膜神经节细胞的零交叉滤波特性，进一步用该工工感受野构建一个图像边缘检测系统，并成功地用系统检测到图像边缘。一与般的基于视觉原理的图像系统相比，这种以人工感受野灵基础的系统，在图像输入的同时即可并行地提取图像边缘信息，而更接近于动物视觉系统原型，此结果将为人工视觉和图像技术的发展提供新的探索。     

Natural frequency/damping coefficient relationship of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure

Using a digital simulation method, we analyzed the relationship between natural frequency (f _n ) and damping coefficient () of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure. The pulmonary artery pressure waveform was obtained with a catheter-tip transducer and it was fed into a dynamic simulator programmed on a computer. The original waveform and the output of the simulator were compared and judged visually for the fidelity. From this analysis, the combination of f _n and was obtained and was plotted on a f _n – diagram. It showed as an area, which was convex on the left side and open on the right side. The left-convex endpoint was located at a damping coefficient of about 0.7. At a lower heart rate, this area was extended to the lower frequency side, while, at a higher heart rate, this area was limited to the higher frequency side. The f _n – diagram was also constructed theoretically by calculating the relations between natural frequencies and damping coefficients of a second order system with the amplitude and phase error tolerance set at +/–5% respectively.(Kinefuchi Y, Suzuki T, Takiguchi M, et al.: Natural frequency/Damping coefficient relationship of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure. J Anesth 7: 419--426, 1993)