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In this study, we theoretically propose a surface plasmon resonance (SPR) biosensor composed of a plasmonic gold film, double negative (DNG) metamaterial, graphene-MoS2-COOH Van der Waals heterostructures and gold nanoparticles (Au NPs). We use a novel scheme of Goos-Hanchen (GH) shift to study the biosensing performances of our proposed plasmonic biosensor. The calculation results show that, both an extreme low reflectivity of 8.52x10(-10) and significantly enhanced GH sensitivity of 2.1530x10(7) mu m/RIU can be obtained, corresponding to the optimal configuration: 32 nm Au film/120 nm metamaterial/4-layer graphene/4-layer MoS2-COOH. In addition, there is a theoretically excellent linear response between the concentration of target analytes (SARS-CoV-2 and S protein) and the change in differential GH shift. Our proposed biosensor promises to be a useful tool for performing the novel coronavirus detection.
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An actively controlled Susceptible-Infected-Susceptible (actSIS) contagion model is presented for studying epidemic dynamics with continuous-time feedback control of infection rates. Our work is inspired by the observation that epidemics can be controlled through decentralized disease-control strategies such as quarantining, sheltering in place, social distancing, etc., where individuals can actively modify their contact rates in response to observations of the infection levels in the population. Accounting for a time lag in observations and categorizing individuals into distinct sub-populations based on their risk profiles, we show that the actSIS model manifests qualitatively different features as compared with the SIS model. In a homogeneous population of risk-averters, the endemic equilibrium is always reduced, although the transient infection level can overshoot or undershoot. In a homogeneous population of risk-tolerating individuals, the system exhibits bistability, which can also lead to reduced infection. For a heterogeneous population comprised of risk-tolerators and risk-averters, we prove conditions on model parameters for the existence of a Hopf bifurcation and sustained oscillations in the infected population. Copyright (C) 2020 The Authors.
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Objective: To analyze of the transmission characteristics of a cluster of COVID-19 cases in Chongqing and evaluate the infectivity of COVID-19 in the incubation period. Methods: A retrospective survey was conducted by using unified questionnaire through field and telephone interviews among 129 close contacts of COVID-19 cases. The relationship of transmission was indicated by transmission chain, and the infectivity was analyzed by the contact history. Results: This cluster of COVID-19 cases occurred after a classmate party involving members in three families and work fellows in a factory (R(0)=3.8). The infection rate during the incubation period was 17.57%. On average, it was infectious three days before onset. There was significant difference in infection rate among different contact modes (χ(2)=15.10, P<0.01), There was significant difference in infection rate among single exposureswith different time length (χ(2)=25.08, P<0.01). Conclusions: COVID-19 is highly infectious in the incubation period. The more confined the space is, the higher the risk is,and the longer the single exposure is, the higher the risk of transmission is. Indirect contact transmission still exists.