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为了研究媒体报道对传染病动力学性态的影响,通过建立疾病发生率受媒体报道影响的SIS数学模型,确定模型的基本再生数,证明平衡点的存在性以及地方病平衡点的唯一性,并证明无病平衡点的局部渐近稳定性和全局稳定性,以及地方病平衡点的局部渐近稳定性。引入时滞因子对模型进行深入研究,通过数值模拟验证了理论结果的正确性。研究结果表明:当参数满足一定条件时,在地方病平衡点会产生Hopf分支。具有媒体饱和发生率的SIS时滞模型的研究结果,阐释了媒体报道对疾病传播的影响,丰富了饱和发生率的传染病模型结果,为有效实施疾病防控提供了理论依据。 相似文献
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为了研究基于二维元胞自动机的一类具有季节性和疫苗接种的SIR传染病模型对控制传染病的影响,利用平均场近似方法建立了非线性离散模型。对模型进行了数学分析,通过计算无病平衡点的Jacobian矩阵的谱半径,得到了无病平衡点的局部稳定性,通过数值模拟,找出了在正平衡点处染病者与元胞邻居结构δ的关系,并且考虑了不同的初始患者设置对疾病传播速度的影响,不同的接种疫苗率对疾病传播速度的影响。通过研究可知:当疾病的初始患者为中心分布时,传染病的传播速度小于初始患者为随机分布时的速度;随着接种疫苗率的增大,传染病的传播速度会减小,对初始患者为中心分布的元胞自动机影响较大。研究模型在控制传染病传播的动力学研究方面具有一定的参考价值。 相似文献
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在疾病传播过程中,染病者和易感者有多大的倾向接触是传染病是否流行的关键因素。为了研究相关系数在疾病传播过程中的动力学行为以及其对于传染病传播动力学特性的影响,将状态节点之间的相关系数作为动态变量,利用二元组的反卷积逼近方法,在异质网络上建立了含有相关系数的SIR传染病动力学模型,分析了系统平衡点的存在性,给出了染病者与易感者之间相关系数存在正值的条件。在泊松分布下,模拟出了平衡状态下相关系数的三维变化图。通过生物学意义,用概率的方法,给出了系统的最终规模。结果表明,通过分析含有相关系数的SIR传染病模型,得到SIR传染病模型复杂的动力学性态,即当染病者数量趋于零时,染病者与易感者之间的相关系数不为零。研究模型在控制传染病传播的动力学研究方面具有一定的参考价值。 相似文献
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为了研究具有一般接触率和用于治疗的SIS对逼近模型及其动力学性质,针对2种菌株是否可以独立生存,建立了一个在规则网络上2种菌株有交叉感染的SIS对逼近传染病模型。根据二项分布,利用节点的状态相关系数得到一个12维系统,计算出模型的基本再生数,得出无病平衡点的局部稳定性,进而获得了无病平衡点不稳定的阀值。通过理论分析和数值模拟得出模型的无病平衡点无条件存在,即不稳定。在研究了2种菌株独立存在以及共同生存的条件后,可以看出2种菌株可以独立生存,也可以相互感染。高维(12维)系统的引入,使得对逼近模型既能模拟疾病的传播机制又能捕捉到疾病传播所在种群的网络结构,因此将对逼近模型应用到多菌株疾病的传播中具有一定价值。 相似文献
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为了进一步研究丙型肝炎病毒的传播机理及其治疗的有效方法,针对丙型肝炎病毒潜伏期比较长,且在整个患病期内均具有传染性的特性,在已有的模型基础上引入时滞来反映丙肝潜伏期的存在。为研究时滞和药物治疗对丙肝传染病的影响,建立了具有常数输入和时滞的丙肝传染病模型,利用常微分方程定性理论知识分析其对应平衡点的存在,构造Liapunov函数讨论无病平衡点的全局稳定性,并且分析了时滞对系统的影响。通过分析可知,当时滞大于零且基本再生数小于1时,系统在无病平衡点处是全局渐近稳定的。给出了正平衡点稳定、不稳定与系统产生Hopf分支分别对应的前提条件,通过对阈值的分析给出了控制丙肝传播的措施建议。数值模拟验证了结果的正确性,其结果对具有时滞和治疗的丙肝模型的研究是有意义的,可为减少丙肝的流行提供新的思路。 相似文献
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绿色技术虽备受关注,然而在我国其创新及扩散面临着需求与扩散动力不足。本文尝试寻找影响绿色技术创新扩散程度的因素,通过构建多智能体模型来研究其扩散过程,并针对不同类型绿色技术在创新扩散过程中的影响因素进行模拟计算。根据结果得出了整个社会的创新风险对三类绿色技术扩散影响最大等系列结论,并据这些结论提出促进绿色技术创新扩散的可行建议。 相似文献
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Henrich R. Greve 《战略管理杂志》2011,32(9):949-968
Firms seek to imitate innovations that yield competitive advantage, but imitation can presage disappointment when the innovation value is below expectations. Empirical research has only rarely examined the diffusion of such disappointing innovations, and it is not known whether negative information from past adopters will halt the diffusion process. Likewise, the effect of heterogeneity in the innovation value on its spread has not been systematically investigated. Here, a unique dataset on a disappointing innovation is used to examine how adoption decisions are imitated, but actual use and subsequent abandonment can yield information that reduces the likelihood that others will adopt. The findings show imitation of the adoptions of other firms, but avoidance of the innovation once these firms start using the innovation or abandon it. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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本文使用中国31个省、直辖市和自治区2019年6月~2020年9月共16个月的月度面板数据,采用多期双重差分(DID)方法,分别就新冠肺炎疫情对服务业中的快递行业、金融行业、公路货运行业和进出口行业的影响展开分析,研究结果表明:疫情对快递行业和金融行业的影响有显著正向影响,对进出口企业和公路货运行业有显著负向影响。进一步,采用三重差分模型进行地区异质性与禀赋异质性检验后发现,疫情对东部地区的快递业影响不显著,对中西部地区的快递行业收入有显著正向影响;疫情对东部沿海地区的进出口总额有显著负向影响,对中西部进出口总额影响不显著;疫情对东部、中西部金融存贷款的影响均显著为正;疫情对东部地区公路货运量的影响显著为负,对中西部的影响显著为正。疫情与2019年卫生人员三重差分模型显示,对快递行业收入的影响显著为负;对公路货运量和进出口影响不显著;对金融存贷款影响显著为正。疫情与2019年人口资源禀赋三重差分模型显示,对快递行业收入、进出口总额和金融存贷款影响显著为正;对公路货运量影响不显著。 相似文献
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We study technology diffusion in the retail banking industry. Our contribution to the empirical literature is twofold: Firstly, we explore technology diffusion in the financial sector, whose relevance has often been neglected; secondly we focus on credit scoring adoption, a relevant process innovation still under-explored. Estimating a set of duration models, we analyze the patterns of diffusion of this technology among Italian banks. We find that credit scoring is firstly introduced by large banks with broad branch networks, which can fully exploit scale economies. We present robust evidence that banks with large market shares operating in more concentrated markets are early adopters, providing a direct support of the Schumpeterian hypothesis that market power enhances innovation.The views expressed here are those of the authors and do not necessarily reflect those of the Bank of Italy. 相似文献
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ALBERTO SALVO 《The Journal of industrial economics》2009,57(4):677-711
Brazil's established soft‐drink firms recently lost ground to multiple low‐price entrants, with small‐scale operations and minimal advertising. While incumbents attributed such undercutting to entrants' lower costs from non‐compliance with the law, ‘generics’ counterargued that incumbents' high prices stemmed from unilateral market power rather than cost heterogeneity. By estimating a structural model, I can single‐handedly explain established brands' high prices through low equilibrium price elasticities of demand. Tax evasion in the fringe, while plausible, appears to be offset by higher procurement costs or less efficient scale. More generally, a competitive informal sector can alleviate the allocative distortions in certain concentrated industries. 相似文献
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Anne Marie Knott 《战略管理杂志》2003,24(8):687-705
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Mingzhe Tang 《Telecommunications Policy》2011,35(11):951-969
This research provides a new perspective to investigate the broadband diffusion in eight states of the U.S. by studying the two-stage entry decisions, namely, upgrading and subsequent product decisions, by the cable television system operators, one of the early dominant players in the broadband market, and examines the role of competition, market characteristics and firm heterogeneity in the cable company's decisions in a dynamic setting. Comparing the empirical results of the decision models of both stages can give new insights into the dynamics of broadband diffusion. The empirical results show that the subsequent product decision is affected more by the demand determinants, while the upgrading decision is affected more by the cost determinants. The results also indicate that policies which aim to reduce the entry cost such as a low city fee can largely encourage firms to upgrade the network, while subsequent policies that help boost the demand can help firms diversify into new digital services early. The effectiveness of competition policy in the broadband diffusion is confirmed in both stages. Strategic responses by cable firms to the presence of RBOCs are more noticeable in the second-staged product decision than in the first-staged upgrading decision. 相似文献