一类带有时滞的SIR模型的稳定性及分支分析

为了研究饱和发生率和时滞对传染病模型动力学性态的影响,建立了一类具有饱和发生率和指数出生且带有时滞的SIR模型,通过对模型特征方程的分析,判定了系统的地方病平衡点的稳定性,并找到了系统发生分支的临界值,通过数值模拟验证了理论分析结果的正确性。结果表明:当时滞小于临界值时,地方病平衡点是局部渐近稳定的;当时滞大于临界值时,地方病平衡点不稳定,并产生了Hopf分支。研究结果对解释传染病的周期性暴发、预防和控制传染病的传播具有借鉴作用。     

具有媒体饱和发生率的SIS时滞模型研究

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。     

具有交叉感染的2种菌株对逼近模型分析

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。     

具有异质性扩散率的传染病模型分析

为了刻画大尺度空间范围内的个体移动对疾病传播的影响,主要研究了异质集合种群网络的传染病传播过程。由于城市之间存在规模以及交通发达程度等方面的异质性,扩散率也存在一定的异质性。以城市作为节点,建立了具有异质性扩散率的传染病动力学模型,更加准确地刻画了网络结构以及人们的出行对疾病传播的影响。通过对系统进行定性及稳定性分析,发现系统存在一个无病平衡点,并得到了无病平衡点不稳定的阈值条件。当达到疾病爆发的阈值条件时,系统存在唯一的地方病平衡点,并且地方病平衡点是局部渐近稳定的。通过数值模拟验证了理论的正确性。研究表明,增大扩散率能加快疾病的流行速度,因此,通过有效控制大城市的人口出行率可以在一定程度上控制疾病的爆发。     

异质网络下含有相关系数的SIR传染病模型的建立和分析

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。     

具有季节性和接种疫苗的元胞自动机传染病模型

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。     

基于隔离和免疫的蠕虫传播模型及稳定性分析

网络蠕虫已经对网络基础设施和因特网服务造成了巨大的影响,为有效防御蠕虫病毒的入侵,提出了基于隔离和免疫的蠕虫传播SEIQV模型。利用SEIQV模型,得到了蠕虫是否灭绝的阈值,并从理论上证明了模型在无感染平衡点保持全局稳定性,在地方病平衡点保持局部稳定性,同时分析了其他参数对模型的影响,为蠕虫病毒的控制和预防提供了理论基础。     

基于T-S模型的一类时滞非线性系统模型预测控制

针对具有状态时滞特性的非线性离散系统,利用线性矩阵不等式的方法和Lyapunov稳定性理论,研究了基于状态反馈的非线性系统模型预测控制问题。基于T-S模糊模型对非线性离散系统进行描述并给出一种"min-max"预测控制算法,采用模型预测控制与模糊理论相结合的方法,利用平行分布补偿的原理,通过在每一个采样时刻优化无穷时域的性能指标,来求解在范数有界条件下相应的状态反馈控制律,讨论了预测控制器的设计问题,分析了此设计问题的可解性,给出了状态反馈控制器基于线性矩阵不等式的设计算法,保证了系统的稳定性,通过仿真实例证明了所提控制算法的有效性及系统的稳定性。该方法能够在化工、冶金、机械等具有时滞特性的工业生产过程中得到很好的应用。     

两种基因类型的丙肝传染病混合模型的动力学分析

鉴于中国丙肝患者中所含基因类型主要分为2种,且在临床上有急性和慢性之分,为了更好的研究基因类型对丙肝的影响,针对急性和慢性2种基因类型丙肝进行生物数学建模,分析讨论其相应平衡态的存在性及稳定性。结果表明,基本再生数较大的丙肝会长期存在,而基本再生数较小的丙肝会逐渐消亡,当且仅当基本再生数相等时,2种基因类型的丙肝才可能共存。数值模拟分析验证了该结果的正确性。因此,对不同基因类型的患者进行分类治疗是必要的。     

时滞超混沌系统的同步

时滞混沌系统是无穷维系统 ,由这样的系统产生的超混沌可具有多个正的L yapunov指数 ,因此系统可以产生复杂的时间序列。这个特征使它特别适用于保密通讯。本文正是根据时滞超混沌系统的这一特点 ,给出了一种同步时滞混沌系统的新方法。通过L yapunov稳定理论得到了系统同步时系统参数满足的条件。数值仿真表明了该方法的有效性。     

Comparing FTTH access networks based on P2P and PMP fibre topologies

There is an ongoing discussion in the market which Next Generation Access (NGA) architecture best suits future needs and which investment and cost differences exist. The discussion can be subsumed as P2P vs. GPON, which is somewhat misleading as this article reveals. The discussion is driven by the fact that the high capital cost and the long asset life time of fibre mean that the technology choices made today will dominate the opportunities for telecommunication business of all market players, incumbents, competitors, content providers and business and residential users for many years in the future.The paper analyzes the cost and other differences between Fibre-to-the-Home (FTTH) access network architectures and their related different wholesale approaches by using the well-known and understood steady state approach applied in other NGA analyses in the past. In addition to the steady state analysis a dynamic cost evaluation is included taking into account the different investment behaviour of the FTTH architectures over time. The results describe investment and cost differences between architectures, incumbents and wholesale based competitive operators. The analysis has been performed for different geotypes (clusters) of decreasing population density in a representative European settlement structure.     

Indigenous peoples’ nutrition transition in a right to food perspective

In indigenous communities the nutrition transition characterized by a rapid westernization of diet and lifestyle is associated with rising prevalence of chronic disease. Field work and literature reviews from two different policy environments, Argentina (Jujuy) and Canada (Nunavut), identified factors that add to indigenous peoples’ disease risk. The analytical framework was the emerging human right to adequate food approach to policies and programmes. Indigenous peoples’ chronic disease risk tends to increase as a result of government policies that infringe on indigenous peoples’ livelihoods and territories, undermining their economic system, values and solidarity networks. Policies intended to increase food security, including food aid, may also fuel the nutrition transition. There is a need to explore further the connection between well-intended policies towards indigenous peoples and the development of chronic diseases, and to broaden the understanding of the role that different forms of discrimination play in the westernization of their lifestyles, values and food habits. Food policies that take due account of indigenous peoples’ human rights, including their right to enjoy their culture, may counteract the growth of chronic disease in these communities.     

A strategic skill based model of supplier integration and its effect on supply management performance

Supplier integration is a tool to help organizations gain competitive advantage. Strategic supply management skills and the supply management function's perceived status are hypothesized as antecedents to supplier integration leading to supply management performance. The sample for this study includes 152 executive level supply management professionals. The empirical results suggest that strategic skills and perceived status are essential antecedents to supplier integration and subsequent performance. Further, the relationship between strategic skills and performance is mediated by supplier integration. Results of a dominance analysis also suggest which strategic skills are most likely to explain status integration, and performance. These findings have significant implications for supply management theory and practice.     

Cost allocation of WCDMA and wholesale pricing for mVoIP and data services

This study estimates cost-based prices for wholesale voice and data services provided to 3G (WCDMA) MVNOs according to their distinct types. For estimation, 3G MVNOs are classified into different types, and the overall cost of WCDMA facilities are separated into voice and data components based on their subscriber rates, actual traffic rates, as well as efficiency consideration of traffic rates. The study then calculates cost-based wholesale prices of voice and data services for each of the 3G MVNO types. The result of this study shows that a cost-plus pricing scheme can help achieve the policy goals of the regulator, namely, lowering telecommunications tariffs and facilitating the introduction of new convergent-type services, far more effectively than the current retail-minus pricing scheme. The findings of this study may assist firms in developing business models based on 3G networks and telecom regulators in designing policies related to interconnection, mVoIP, prepaid calls, wholesale services, and network neutrality.     

Collectivism,individualism, and outgroup cooperation in a segmented China

A consistent theme in cross-cultural management research is that collectivists are more cooperative than individualists. We use Hofstede's measure for individualism–collectivism and combine it with an experimental measure of cooperation to test this relationship in China. In contrast to the established paradigm, we find that groups with higher individualistic scores are more cooperative than those groups with higher collectivistic scores. We attribute these results to groups being composed of outgroup members. In addition, we find that subjects from the more developed coastal area are more individualistic and cooperative than are subjects from inland China.

电子产品的电磁兼容性设计

首先介绍电磁兼容性的基本概念与研究领域,然后重点阐述电子产品的电磁兼容性设计与测量。     

SPYRO在烯烃原料生产方案测算中的应用

文章对SPYRO裂解模拟软件在石化企业烯烃生产原料优化方案测算中的应用进行了比较深度的概括分析.结合该软件在上海石化的实际应用,认为在劣质化原油加工份额不断增加的趋势下,SPYRO裂解模拟软件有助于石化企业在烯烃生产原料优化选择、生产计划合理安排、原油加工生产效益比较等方面为企业相关决策者提供有效地帮助.     

施工企业工程项目部的建设浅论

工程项目的一次性决定了工程项目部的一次性，而工程项目成本中心与企业利润中心地位又辱致工程项目部的临时性，在工程项目实践过程中，项目经理部的一次性在实现其功能的过程中可能会产生很多局限和负面影响，故项目部应具有相对的稳定性，在此基础上，本对工程项目部建设实践进行了初步总结并提出了建议。     

European consumer preferences for beef with nutrition and health claims: A multi-country investigation using discrete choice experiments

The European Union (EU) nutrition labelling policy aims to facilitate consumers’ food choice, stimulate innovation and facilitate the circulation of foods bearing claims across countries. However, the beef industry has not fully taken advantage of utilizing nutrition and health claims based on the EU nutrition labelling policy to differentiate beef products in the market. This study investigates consumer preferences for nutrition and health claims on lean beef steak. Two choice experiments were conducted among 2400 beef consumers in four EU countries (Belgium, France, the Netherlands, United and United Kingdom). Multinomial logit and error component models were estimated. Our results generally suggest that consumer valuation of nutritional and health claims varies across countries. In Belgium, the Netherlands and France, nutrition and health claims on saturated fat yielded higher utilities than claims on protein and/or iron, while the opposite was found among consumers in the UK. The results imply that marketing opportunities related to nutrition and health claims on beef are promising, but that different nutritional marketing strategies are necessary within different countries.     

Social media as a useful tool in food risk and benefit communication? A strategic orientation approach

Although considerable progress has been made in understanding the determinants of risk perception and in identifying the necessary components of effective food risk and benefit communication, this has not been matched with the development of efficient and appropriate communication tools. Little work has been done examining the implications of the explosion of new media and web technologies, which may offer potential for improving food risk and benefit communication. First, this study examines the views of stakeholders (n = 38) and experts (n = 33) in the food domain on the potential use of these emerging media for food risk/benefit communication. Based on in-depth interviews in six European countries (Belgium, Ireland, Italy, Latvia, Spain and The Netherlands), strengths, weaknesses, opportunities and threats (SWOT) of social media in food risk and benefit communication were identified. Second, a Strategic Orientation Round (SOR) was used to evaluate the relative importance of the SWOT components according to stakeholders (n = 10) and experts (n = 13). Results show that both stakeholders and experts confirm a future role of social media in food risk and benefit communication. Strengths as speed, accessibility and interaction make social media an interesting tool in crisis communication or issue awareness raising. Weaknesses as the lack of a filter, low trust, the risk of information overload and a communication preference for traditional media are acknowledged.