Background:COVID-19 has been impacting on the whole world critically and constantly since late December 2019.Rapidly increasing infections has raised intense worldwide attention.How to model the evolution of COVID-19 ...Background:COVID-19 has been impacting on the whole world critically and constantly since late December 2019.Rapidly increasing infections has raised intense worldwide attention.How to model the evolution of COVID-19 effectively and efficiently is of great significance for prevention and control.Methods:We propose the multi-chain Fudan-CCDC model based on the original single-chain model in[Shao et al.2020]to describe the evolution of COVID-19 in Singapore.Multi-chains can be considered as the superposition of several single chains with different characteristics.We identify the parameters of models by minimizing the penalty function.Results:The numerical simulation results exhibit the multi-chain model performs well on data fitting.Though unsteady the increments are,they could still fall within the range of±30%fluctuation from simulation results.Conclusion:The multi-chain Fudan-CCDC model provides an effective way to early detect the appearance of imported infectors and super spreaders and forecast a second outbreak.It can also explain the data from those countries where the single-chain model shows deviation from the data.展开更多
Major fires and floods have enormous impacts on natural ecosystems and are predicted to increase in frequency with global warming.Land managers need to make decisions on the prioritisation of weeds for control in post...Major fires and floods have enormous impacts on natural ecosystems and are predicted to increase in frequency with global warming.Land managers need to make decisions on the prioritisation of weeds for control in post-disturbance landscapes,but little is available in the way of guidance to support timely decision making.Semi-quantitative models(e.g.,scoring systems)have been employed routinely in weed risk assessment,which considers the potential impacts posed by weeds,as well as the likelihood of these impacts being realised.Some progress has been made in the development of similar models addressing the topic of weed risk management.Under conditions prevailing after major disturbances,changes(both positive and negative)can be expected in the multiple factors that determine weed management feasibility,relative to pre-disturbance conditions.A semi-quantitative model is proposed that is based on the key factors that contribute to weed management feasibility in post-disturbance environments,along with annotated modules that could be used by land managers in both post-fire and post-flood situations.The fundamental challenge for weed management in these scenarios lies in the identification of differences between weeds and native species in relation to(1)patterns of seedling emergence;and(2)detectability relative to the growth stage.These two factors will determine the timing of control actions that are designed to address the trade-off between weed control and off-target damage during the period when both types of plants are recovering from a major disturbance event.The model is intuitively sound,but field testing is required to determine both its practical value and any necessary improvement.展开更多
作为有着重要历史渊源的国家,新加坡和中国在许多方面存在比较借鉴的基础。数学教材是数学教学系统中的重要组成部分。新加坡小学数学教材《我的朋友在这里!数学》MyPals are Here!Maths(第二版)与中国小学数学教材(人教版)有着各自不...作为有着重要历史渊源的国家,新加坡和中国在许多方面存在比较借鉴的基础。数学教材是数学教学系统中的重要组成部分。新加坡小学数学教材《我的朋友在这里!数学》MyPals are Here!Maths(第二版)与中国小学数学教材(人教版)有着各自不同的特点,新加坡小学数学教材中弥补"双基"的不足、问题解决与数学教学相融合、教材的编写以综合的数学活动为基础等做法对中国小学数学课程和教学研究有一定的启示和借鉴意义。展开更多
基金the National Natural Science Foundation of China(No.11671098)partially supported by Shanghai Science and technology research program(No.19JC1420101)+1 种基金J.C.is supported in part by the National Natural Science Foundation of China(No.11971121)Y.Y.is supported by Shanghai Sailing Program(No.20YF1412400).
文摘Background:COVID-19 has been impacting on the whole world critically and constantly since late December 2019.Rapidly increasing infections has raised intense worldwide attention.How to model the evolution of COVID-19 effectively and efficiently is of great significance for prevention and control.Methods:We propose the multi-chain Fudan-CCDC model based on the original single-chain model in[Shao et al.2020]to describe the evolution of COVID-19 in Singapore.Multi-chains can be considered as the superposition of several single chains with different characteristics.We identify the parameters of models by minimizing the penalty function.Results:The numerical simulation results exhibit the multi-chain model performs well on data fitting.Though unsteady the increments are,they could still fall within the range of±30%fluctuation from simulation results.Conclusion:The multi-chain Fudan-CCDC model provides an effective way to early detect the appearance of imported infectors and super spreaders and forecast a second outbreak.It can also explain the data from those countries where the single-chain model shows deviation from the data.
文摘Major fires and floods have enormous impacts on natural ecosystems and are predicted to increase in frequency with global warming.Land managers need to make decisions on the prioritisation of weeds for control in post-disturbance landscapes,but little is available in the way of guidance to support timely decision making.Semi-quantitative models(e.g.,scoring systems)have been employed routinely in weed risk assessment,which considers the potential impacts posed by weeds,as well as the likelihood of these impacts being realised.Some progress has been made in the development of similar models addressing the topic of weed risk management.Under conditions prevailing after major disturbances,changes(both positive and negative)can be expected in the multiple factors that determine weed management feasibility,relative to pre-disturbance conditions.A semi-quantitative model is proposed that is based on the key factors that contribute to weed management feasibility in post-disturbance environments,along with annotated modules that could be used by land managers in both post-fire and post-flood situations.The fundamental challenge for weed management in these scenarios lies in the identification of differences between weeds and native species in relation to(1)patterns of seedling emergence;and(2)detectability relative to the growth stage.These two factors will determine the timing of control actions that are designed to address the trade-off between weed control and off-target damage during the period when both types of plants are recovering from a major disturbance event.The model is intuitively sound,but field testing is required to determine both its practical value and any necessary improvement.
文摘作为有着重要历史渊源的国家,新加坡和中国在许多方面存在比较借鉴的基础。数学教材是数学教学系统中的重要组成部分。新加坡小学数学教材《我的朋友在这里!数学》MyPals are Here!Maths(第二版)与中国小学数学教材(人教版)有着各自不同的特点,新加坡小学数学教材中弥补"双基"的不足、问题解决与数学教学相融合、教材的编写以综合的数学活动为基础等做法对中国小学数学课程和教学研究有一定的启示和借鉴意义。
