MATHEMATICAL ANALYSIS OF WEST NILE VIRUS MODEL WITH DISCRETE DELAYS

The paper presents the basic model for the transmission dynamics of West Nile virus (WNV). The model, which consists of seven mutually-exclusive compartments representing the birds and vector dynamics,...     

Mathematical Analysis of West Nile Virus Model with Discrete Delays

The paper presents the basic model for the transmission dynamics of West Nile virus (WNV). The model, which consists of seven mutually-exclusive compartments representing the birds and vector dynamics, has a locally-asymptotically stable disease-free equilibrium whenever the associated reproduction number (?₀) is less than unity. As reveal in [3, 20], the analyses of the model show the existence of the phenomenon of backward bifurcation (where the stable disease-free equilibrium of the model co-exists with a stable endemic equilibrium when the reproduction number of the disease is less than unity). It is shown, that the backward bifurcation phenomenon can be removed by substituting the associated standard incidence function with a mass action incidence. Analysis of the reproduction number of the model shows that, the disease will persist, whenever ?₀ > 1, and increase in the length of incubation period can help reduce WNV burden in the community if a certain threshold quantities, denoted by Δ_b and Δ_v are negative. On the other hand, increasing the length of the incubation period increases disease burden if Δ_b > 0 and Δ_v > 0. Furthermore, it is shown that adding time delay to the corresponding autonomous model with standard incidence (considered in [2]) does not alter the qualitative dynamics of the autonomous system (with respect to the elimination or persistence of the disease).     

西湖风景区游客逗留时间决定因素研究

随着近年来城际交通条件的改善,游客在旅游目的地的逗留时间普遍缩短,极大地影响了一个旅游城市旅游产业的赢利能力;但另一方面,热点景区的游客众多,又需要对游客的逗留时间进行控制,以利于景区环境和文物保护.本研究以杭州西湖风景区为例,运用生存分析中的Cox及Weibull模型,分析游客逗留时间的决定因素.调研数据来源于2009年夏天在西湖风景区调查的243份问卷,对象是完成西湖游览行程的来杭游客.研究发现:①家庭收入的增长、个体出行、亲友结伴、住宿开支减少等因素均能够显著增加在西湖景区的逗留时间,而随团出行、多次来杭旅行、住宿星级酒店等因素则会促使逗留时间减少.②景区的游览设施及服务质量、住宿接待的服务质量、西湖景区的整体改造、自然及文化吸引力、夜间景观及活动项目吸引力、景区门票制度的改变这几项对于增加游客逗留时间具有重要作用.③杭州整体旅游形象塑造、景区主管部门的宣传推广、亲友及网络口碑等几项对于增加游客逗留时间的效果并不明显.全文最后对西湖风景区的相关管理部门和旅游企业提出建议,以寻求景区发展面临不同影响因素时可采取的相应对策.     

西方电影对中国青少年思想道德的影响

通过问卷调查、座谈会、个别访谈调查等方法，了解西方电影对中国青少年的实证性影响。加强思想观念教育，引导青少年分辨精华糟粕，确立健康的审美观。     

东濮凹陷西部下第三系的遗迹相

本区下第三系地层中发育有大量的遗迹化石,类型多,分异度大。按其生态习性分为六大类:居住迹(Domichnia)、觅食迹(Fodichnia)停迹(Cubich-nia)、爬迹(Repichnia)、逃逸迹(Fugichnia)和牧食迹(Pascichnia),共计13个属。文中描述了类属的特征及其成因,并建立了适于本区的遗迹化石相模式,由五个相组成,即石针迹(Skolihtos)相、卷迹(Intortusichnus) 相、伸展迹(Aductusichnus)相、始网迹(Protopaleodictyon)相和古网迹(Paleodictyon)相,分别对应于滨湖、浅湖上部、浅湖下部、半深湖和深湖环境     

东濮凹陷黄河南地区东营组沉积相研究

综合利用地质、测井和地震资料研究了东濮凹陷东南部东营组的沉积相。研究表明,研究区东营组存在着两个主要的沉积相类型,即物源来自东侧的、位于兰聊断层下降盘的冲积扇;物源来自盆地南侧的、分布广泛的河流沉积。总结了冲积扇、河流沉积物的岩性、沉积构造、电性和地震反射特征及识别标志,建立了沉积模式,并结合油气勘探实践,指出了今后的油气勘探方向。     

西部中小城市发展空间走廊的综合开发规划研究--以平凉市崆峒大道为例

目的研究西部中小城市过境公路演变为城市道路的现象,揭示其本质内涵,为编制科学合理的综合开发规划提供理论依据。方法通过平凉市崆峒大道综合开发规划实证分析,探讨城市空间走廊综合开发规划的编制。结果空间走廊的综合开发规划,包括总体布局、道路交通体系、绿地景观体系、地块控制性经济技术指标与规划设计条件、沿街建筑景观设计意向等。结论过境公路改造成城市道路必须从城市发展的角度充分关注其两侧用地的功能、结构、形态、交通和景观等诸因素,采用综合开发的手段,为城市的未来发展提供健康的空间走廊。     

川西前陆盆地须家河组沉积相及岩相古地理演化

川西前陆盆地上三叠统须家河组是油气勘探的重点层位.依据新的地层划分方案、大量钻井、露头及岩芯资料,结合区域地质特征,详细研究了须家河组沉积相、岩相古地理特征及其演化.结果表明:研究区内主要发育了冲积扇、湖相三角洲、湖泊、海相三角洲、滨岸和海湾六种主要的沉积相类型;古地理演化经历了由海相环境-海陆过渡相环境-陆相环境的转变;在须四早期,受安县运动的影响,龙门山褶皱成山,使研究区与阿坝海域完全隔绝,整个四川盆地真正进入了陆相沉积环境.     

40Ar-39Ar thermochronology of two ductile shear zones from Yiwulüshan, West Liaoning Region: Age constraints on the Mesozoic tectonic events

Two ductile shear zones trending EW and NNE respectively not only controlled the tectonic framework of the northern North China, but also constrained the geodynamic background for gold mineralization in this region. Field observations and microstructural analyses reveal that the EW trending ductile shear zones are mainly contributed to dextral compressional deformation resulting from top-to-the-southeast oblique thrust shearing, whereas the NNE trending ones are genetically related to sinistral strike-slip and extensional faulting. One sample from the former yielded an ⁴⁰Ar–³⁹Ar plateau age of (219± 4) Ma (Bi) and two samples from the latter gave ⁴⁰Ar–³⁹Ar plateau ages of (116± 2) Ma (Bi) and (127±3) Ma (Bi). These ages provide constraints on the top-to-the-southeast oblique thrusting event occurring in Late Triassic and the sinistral extensional and strike-slip faulting event which occurred in Early Cretaceous.     

40Ar-39Ar thermochronology of two ductile shear zones from Yiwulüshan, West Liaoning Region: Age constraints on the Mesozoic tectonic events

Two ductile shear zones trending EW and NNE respectively not only controlled the tectonic framework of the northern North China, but also constrained the geodynamic background for gold mineralization in this region. Field observations and microstructural analyses reveal that the EW trending ductile shear zones are mainly contributed to dextral compressional deformation resulting from top-to- the-southeast oblique thrust shearing, whereas the NNE trending ones are genetically related to sinistral strike-slip and extensional faulting. One sample from the former yielded an 40Ar-39Ar plateau age of (219±4) Ma (Bi) and two samples from the latter gave 40Ar-39Ar plateau ages of (116±2) Ma (Bi) and (127±3) Ma (Bi). These ages provide constraints on the top-to-the-southeast oblique thrusting event occurring in Late Triassic and the sinistral extensional and strike-slip faulting event which occurred in Early Cretaceous.