Modeling Undetected Live Poliovirus Circulation After Apparent Interruption of Transmission: Pakistan and Afghanistan

Since most poliovirus infections occur with no paralytic symptoms, the possibility of silent circulation complicates the confirmation of the end of poliovirus transmission. Based on empirical field experience and theoretical modeling results, the Global Polio Eradication Initiative identified three years without observing paralytic cases from wild polioviruses with good acute flaccid paralysis surveillance as an indication of sufficient confidence that poliovirus circulation stopped. The complexities of real populations and the imperfect nature of real surveillance systems subsequently demonstrated the importance of specific modeling for areas at high risk of undetected circulation, resulting in varying periods of time required to obtain the same level of confidence about no undetected circulation. Using a poliovirus transmission model that accounts for variability in transmissibility and neurovirulence for different poliovirus serotypes and characterizes country‐specific factors (e.g., vaccination and surveillance activities, demographics) related to wild and vaccine‐derived poliovirus transmission in Pakistan and Afghanistan, we consider the probability of undetected poliovirus circulation for those countries once apparent die‐out occurs (i.e., in the absence of any epidemiological signals). We find that gaps in poliovirus surveillance or reaching elimination with borderline sufficient population immunity could significantly increase the time to reach high confidence about interruption of live poliovirus transmission, such that the path taken to achieve and maintain poliovirus elimination matters. Pakistan and Afghanistan will need to sustain high‐quality surveillance for polioviruses after apparent interruption of transmission and recognize that as efforts to identify cases or circulating live polioviruses decrease, the risks of undetected circulation increase and significantly delay the global polio endgame.     

Selecting Nonpharmaceutical Interventions for Influenza

Models of influenza transmission have focused on the ability of vaccination, antiviral therapy, and social distancing strategies to mitigate epidemics. Influenza transmission, however, may also be interrupted by hygiene interventions such as frequent hand washing and wearing masks or respirators. We apply a model of influenza disease transmission that incorporates hygiene and social distancing interventions. The model describes population mixing as a Poisson process, and the probability of infection upon contact between an infectious and susceptible person is parameterized by p. While social distancing interventions modify contact rates in the population, hygiene interventions modify p. Public health decision making involves tradeoffs, and we introduce an objective function that considers the direct costs of interventions and new infections to determine the optimum intervention type (social distancing versus hygiene intervention) and population compliance for epidemic mitigation. Significant simplifications have been made in these models. However, we demonstrate that the method is feasible, provides plausible results, and is sensitive to the selection of model parameters. Specifically, we show that the optimum combination of nonpharmaceutical interventions depends upon the probability of infection, intervention compliance, and duration of infectiousness. Means by which realism can be increased in the method are discussed.     

网络计划项目风险元传递解析模型研究

实际网络计划项目受各种风险因素的影响,为了使网络计划更能反映实际情况,本文通过对广义项目风险元传递理论的三维模型进行介绍,选取了项目应用维为网络计划,风险元传递路线维为网状型,风险元传递方法维为解析法来对网络计划项目进行解析.通过Mason公式来计算随机网络中各节点间的传递关系,利用矩母函数基本性质来计算随机网络中各工序的概率分布数字特征,从而探求随机网络项目所受风险度的大小.在此基础上,提出了基于GERT网络计划的风险元传递解析模型.最后,给出了模型的算例分析.     

类微带传輸线的准靜特性分析

本文介绍了采用有限元法和变分法分析类微带传输线的基本原理.给出了屏蔽悬置微带线和开放倒置微带线的计算曲线,与相应实验值比较基本吻合.在此基础上提出的通用程序可用于计算各式类微带传输线的准静特性.     

在立铣上加工凸轮轴的研究与实践

介绍通过改变立铣与分度头联接齿轮传动比，并进行分度，从而完成凸轮轴加工过程的一种新的工艺。     

1918年大流感在华传播路径、范围和程度新探

中国是1918年大流感的主要受灾国，但史学界对中国疫情的研究非常薄弱。既有关于中国疫情的研究，所依据资料均较单一，不能反映疫情全貌，且存在明显误判。故需要结合当时中外报道、医官报告、海关史料、日记、地方志等材料，重建疫情在华传播图景。整体上，中国经历春秋季两波流感疫情，其传播路径主要依赖铁路、航道和驿道系统，京津、沪汉等重要城市是疫情向全国扩散的中心，而其他交通沿线的主要城市则是疫情在本区域内的扩散中心。其中，第一波疫情自北向南扩散，通过南满、京奉、京汉和沪宁等铁路线迅速传播，将疫区由点串成线，同时借由内河航道和驿道将疫区由线而织成网。幸运的是，第一波疫情并未波及重庆以西地区，且程度较轻，死亡率较低，惟因症状"新""奇"而备受舆论关注。相较之下，第二波疫情则自南向北传播，疫情范围远超第一波，甚至深入云南、甘肃和新疆等内陆省份；同时，第二波疫情的疫势亦明显较第一波严重，各省均有大量死亡病例报道，且呈现乡村疫势远甚于城市的特点，两者粗死亡率相差近十倍之巨。整体上，第二波疫情导致全国死亡人数的保守估算至少在360万至450万之间。值得注意的是，考察1918年两波流感疫情在华传播亦需考虑到各种国内外因素的实际影响。事实上，此类变动的因素极大地加剧了疫情在华传播的复杂性。在国际因素上，俄国革命与黑龙江、新疆等省份的疫情传播关系密切，日本远征军的军事调动则是东三省疫情传播的关键因素，而中越、中缅间的跨国贸易网络则是云南疫情的主要源头；在国内因素上，南北交战和山东匪患加剧了政局不稳和社会动荡，并大大提升了湖南、湖北、陕西和山东等省的人口流动频率，从而增加了疫情传播的速度和范围。文章深入挖掘和全面梳理了1918年中国流感疫情的各类中外史料，详细地考辨了两波流感疫情在华传播的具体路径和范围，重估疫情严重程度，并着重考察各种变动的国内外因素对疫情在华传播的复杂影响，进而勾勒出一幅较为完整的1918年流感疫情在华传播图景。通过文章的梳理和考辨，希望能为1918年大流感的全球性比较和中国国内的区域性研究提供扎实可靠的基础。     

直齿轮副非线性振动分析中两种解法的结果比较

对直齿轮副的非线性振动进行了分析,通过轻、重载荷时直齿轮副间隙非线性振动频响曲线的分析,对两种解法的结果进行比较,并得出相应的结论.