39 research outputs found

    学校流感暴发疫情防控措施动力学模型效果分析

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    目的探讨学校流感暴发疫情的最佳控制方式,为制定停课标准提供参考。方法通过SEIAR模型对流感暴发疫情隔离和停课效果进行分析。结果本起流感暴发疫情基本再生数R0为7.6180,无干预措施下疫情会持续20天,1 169名学生和教职工(99.74%)会感染流感。第5~10天开始隔离措施,疫情持续时间介于35~44天,第10天开始隔离感染人数是第5天开始隔离的6.9倍。与单独采取隔离措施相比,停课1天、3天、5天、7天可以减少4.51%~10.92%、13.41%~29.31%、19.46%~45.40%和24.82%~57.47%的感染人数,持续时间并没有太大变化;停课14天疫情持续时间都会明显下降,感染人数下降33.43%~65.52%。结论隔离措施越早实施对疫情控制效果越好,显性感染人数达到20%以上时可以停课,出现重症或死亡病例时要将停课时间延长

    Research of Causes and Control Patterns on Land Desertification in Loess Plateau

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    土地沙漠化是一个渐进的过程,但其危害及其产生的灾害却是持久和深远的。它不仅对当代人产生影响,而且还将祸及子孙。据专家测算,中国每年因土地沙化造成的直接经济损失高达540亿元,直接或间接影响近4亿人口的生存、生产和生活。土地沙漠化不仅恶化生态环境,衰退土地生产力,威胁江河安全,而且加剧沙区贫困。本文以系统论和生态经济学为指导,在介绍了黄土高原土地沙漠化的基本概况、特征及危害的基础上,从地表沙源、气候、风沙灾害、水资源和土地利用、开发建设等方面,分析了黄土高原沙漠化的成因;结合黄土高原地区多年来沙漠化治理的经验,提出了生态建设治理、植物、工程、化学治理、沙产业主导、依托线状工程4种沙漠化治理模式。 Abstract:Though the land desertification is a gradual process, but its hazards and disasters have lasting and far reaching.Not only did it have an impact on contemporary people, but also on penalise children. According to estimating of experts,the direct economic loss reaches to $7.87 billion every year as a result of land desertification. Also, the survival,production and daily life of nearly 400 million people are all affected by land desertification, directly or indirectly. Landdesertification not only worsening the ecological environment, declining land productivity, threatening the safe of river,but also intensify poverty of the sandy areas. Using the system theory and ecological economics as a guide, on the basisof introducing a basic overview of the Loess Plateau land desertification, the characteristics as well as the harm of landdesertification, analyzing the causes of Loess Plateau desertification though the following aspects, sources of surfacesand, climates, disasters of wind and sand, water resources, land uses, developments and constructions, and combinedcontrol experience of Loess Plateau desertification over the years, the paper proposes four desertification control modes,including ecological governance, plant, engineering and chemical governance, sand industry-leading, and relying on thelinear engineering

    Soil erosion process of engineering accumulation in steep slope under

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    工程建设过程中形成的堆积体具有独特的土壤组成及复杂的下垫面条件,堆积体表面土壤结构体缺失、土质松散、植物根系及有机质缺乏等,导致其土壤抗冲性极差,径流条件下堆积体陡坡坡面的土壤侵蚀过程亦表现出不同的特点,该文通过野外放水试验,对高速公路沿线典型堆积体陡坡(36&deg;)在模拟径流冲刷条件下的土壤侵蚀过程进行了研究,结果表明,次径流过程中径流强度变化与放水强度及径流含沙量密切相关,三者之间呈多元线性相关;重力侵蚀对径流含沙量的变化具有重要影响,试验条件下重力作用的临界放水条件在20~25L/min之间;坡面产沙过程存在产沙量的突变、波动变化和稳定发展3个阶段;不同坡段产沙量的空间分布存在持续稳定减小和震荡式波动衰减2种变化形式;土壤剥蚀率与单宽流量呈线性关系,与时段产沙量及流宽呈幂函数关系;最后,时段产沙量与时段径流量呈幂函数关系,累积产沙量与累积径流量呈线性关系。 更多还原<br /

    Hydrodynamic process of soil erosion in steep slope of engineering

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    工程堆积体产生的新增水土流失严重威胁工程建设区及其附近区域的生态安全。该文采用野外放水冲刷试验的方法,对神木&mdash;府谷高速公路沿线典型工程堆积体陡坡坡面土壤侵蚀水动力过程进行了研究,结果表明,1)水流剪切力、水流功率及径流动能对薄层水流侵蚀土壤剥蚀率的影响皆可用线性方程描述,单位水流功率、过水断面单位能量的影响不显著;2)水流剪切力、水流功率、过水断面单位能量对细沟侵蚀土壤剥蚀率的影响皆可用线性方程描述,单位水流功率的影响可用幂函数方程描述,径流动能的影响可用对数线性方程描述;3)水流功率是与土壤剥蚀率关系最好的水动力学参数,是坡面侵蚀的动力根源;4)发生细沟侵蚀的临界水流功率为3 N/(m&middot;s),细沟可蚀性参数为8&times;10-3s2/m2。该结果可为工程堆积体陡坡坡面土壤侵蚀模型的建立奠定基础,为生产建设项目区新增水土流失治理提供科学依据</span

    Surveying and Mapping Business and Data Management System Construction in Yantai City

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    烟台市国土资源局测绘业务与数据管理系统根据管理的侧重点和需求不同,采用B/S架构实现测绘业务和日常事务管理,采用C/S架构基于ArcGIS平台和Oracle数据库的数据管理系统对单位的数据进行管理,系统采用网络技术和工作流等技术,实现各种业务的网上协同办理,领导对工作进行监控,同时系统支持流程的用户自定义,以适应业务的调整和改进,大大提高系统的灵活性和可扩展性

    Investigation and Assessment on Vegetation Restoration along the Baoniu Highway

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    &nbsp;为探讨高速公路路域植被恢复效果,以宝牛高速公路路域植被为研究对象,对比分析了路基、路堑、路肩平台、渣场和取弃土场5种不同位置的植被群落特征、多样性及草本植物地上生物量等恢复情况。结果表明:(1)宝牛高速公路路域的植物种类较为丰富,而且极大部分植物种是自然入侵的乡土植物,各位置的植物种生活型都以草本植物为主,该路域植被恢复还处于初期阶段。(2)不同路域位置的丰富度表现为自然&gt;路肩平台&gt;渣场=取弃土场&gt;路基&gt;路堑,从Shannon-Weiner指数、Simpson指数和Pielou均匀度指数来看,路域植被之间以及和自然植被之间的变化都不显著。(3)在路基护坡中,拱形骨架护坡模式的植被恢复效果较好;路堑护坡中,效果最好的是土工格室护坡。(4)对于渣场而言,建议人工种植苜蓿提高土壤肥力,并且在恢复植被前尽量覆土,从而为植被生长提供较好的物质基础。Abstract:In order to assess the effect of vegetation restoration along the highway,a case study was conducted on therevegetated land along the Baoniu highway by investigating the characteristics of vegetation communities,species diversity and aboveground biomass on the embankment,cutting,residue field,shoulders,dug field.The resultsshowed that:(1)Species diversity of Baoniu highway was abundant,and most of which were native grass species,indicating that it was still at the initial stage of vegetation restoration.(2)Plant species richness in five sitesranked as:natural>shoulders>residue field=dug field>embankment>cutting.No significant differencewas found between road area vegetation and natural vegetation on indices of Shannon-Weiner,Simpson,andPielou.(3)The framework seeding was the best model for embankment restoration while the geocel seedingis best for the cutting.(4)For the residue field,alfalfa should be planted to improve soil fertility,and toprovide the sufficient nutrients for plants,covering with soil was necessary before planting

    Soil and Water Conservation Ecological Service Function

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    &nbsp;在中国土壤侵蚀严重的情况下,运用生态服务功能的相关理论可以正确评价水土保持措施的作用,并为合理的生态建设规划提供依据。文章在梳理国内外水土保持工程措施生态服务功能物质量研究进展的基础上,运用经济外部性理论、公共产品理论、生态环境价值、土壤学、土壤地理学、水土保持学、生态经济学的理论等基本理论为依据,根据《水土保持综合治理规划通则(GBT&mdash;15772&mdash;1995)》和《水土保持综合治理效益计算方法(GB/T&mdash;15774&mdash;1995)》,借鉴蓄水拦沙指标体系经济参数,对梯田(淤地坝)蓄水与保土量、梯田(淤地坝)减洪与减沙量的生态服务功能物质量进行计算,提出符合实际的解决办法,以期实现水土保持工作的良性发展,为我国水土保持决策部门提供科学的数据支撑</span

    Variation of Soil Nutrients and Mode ofαDiversity of Plant Community

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    &nbsp;选择不同植被恢复年限的高速公路路堤边坡为研究对象,采用时空代换法,通过相关性分析及主成分分析,研究关中平原高速公路植被恢复过程中土壤养分和植被群落&alpha;多样性的变化。结果表明:路堤边坡植被恢复过程中表层土壤养分因子含量平均值变化范围分别为:有机质12.26~25.83g/kg、全氮0.60~1.25g/kg、铵态氮7.16~35.10mg/kg、硝态氮4.15~7.42mg/kg、速效磷9.30~26.68mg/kg。植被恢复过程中,土壤养分特征受恢复年限、土层、坡向的影响。随着恢复年限的增加,表土养分条件明显好转,说明植被对土壤的培肥作用与时间密切相关。0&mdash;10cm土层土壤养分含量明显高于10&mdash;20cm土层,阴面边坡土壤养分含量高于阳面边坡。在人工扰动下,群落的&alpha;多样性主要受恢复年限和土壤中硝态氮含量的影响。恢复到17a时,边坡土壤养分和群落&alpha;多样性均达到较高水平。本研究对路堤边坡土壤质量及群落多样性的提高具有重要的意义,对高速公路生态建设和水土保持具有一定的参考价值。Abstract:The embankment slope of Highways with different years of vegetation restoration in Guanzhong Plain wasselected as the study site.The dynamic changes of soil nutrient and variation mode of&alpha;diversity of plant communityof vegetation restoration were examined based on the correlation analysis and principal component analysis methods.The results indicated that:in topsoil,the change range of soil organic matter values of embankment slope of vegetation restoration was 2.26~25.83g/kg,0.60~1.25g/kg for total N,7.16~35.10mg/kg for ammonium N,4.15~7.42mg/kg nitrate N,and 9.30~26.68mg/kg for available P.In the process of vegetation restoration,the characteristic of soil nutrient was closely related with the recovery period,the depth of soil layer and the slope gradient.The content of soil nutrient obviously increased with the extension of vegetation restoration time,indicating thateffect of vegetation on soil fertilization was related to the restoration period.And the content of nutrient in 0&mdash;10cm soil layer was significantly higher than that in 10&mdash;20cm soil layer,and it was higher in the shady slopesthan that in the sunny slopes.Under artificial disturbance,variation mode of&alpha;diversity of plant communitywas mainly influenced by the vegetation restoration time and the contention of soil nitrate.The topsoil nutrient of embankment slope and the variation mode of&alpha;diversity of plant community reached to a higher levelafter 17years of vegetation restoration.This stdudy is of important significance in improving the soil qualityand the community diversity of embankment slope,and also has certain reference value on ecological construction as well as soil and water conservation of highways

    塔里木河下游绿洲荒漠过渡带群落多样性特征分析

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    结合塔里木河下游铁干里克绿洲荒漠过渡带29个植被样地的调查资料,对植物的群落结构和数量特征做了分析。结果表明:研究区群落结构较为简单,植物群落物种多样性水平较低,物种组成单一,天然植物20种,隶属12科18属。从多样性指数的数量特征来看,Simpson多样性指数的变化范围为0.517~0.830,Shannon-Wiener指数变化范围0.851~1.974;Menhinick丰富度指数的变化范围为0.977~3.784,Margalef丰富度指数的变化范围为1.517~8.496;JSW均匀度指数的变化范围为0.719~0.908,JSI指数变化范围为0.729~0.949;植被盖度的变化范围在0.035~1.001之间

    塔里木河下游绿洲荒漠过渡带土壤异质性及对植物群落的影响

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    结合塔里木河下游铁干里克绿洲荒漠过渡带9个土壤剖面的81个土样分析数据,利用非参数检验、单因素方差分析和灰色关联方法,分析了塔里木河下游铁干里克绿洲荒漠过渡带土壤特性及其对植物群落的影响。结果表明,研究区土壤除全磷外,有机质等指标存在垂直分布差异,出现显著差异的土层深度为50cm。研究区上段的土壤养分含量相对较高,下段较低;植物物种多样性指数自上段至下段的下降趋势与有机质等的变化相同,而植物群落退化则表现为从复合群落到单一群落的演变趋势,即从乔(胡杨为主)、灌(柽柳为主)、草复合群落演变到单一的柽柳灌丛群落。灰色关联分析表明,塔里木河下游铁干里克绿洲荒漠过渡带上层(0~50cm)土壤有机质、全氮、全磷、全钾含量与物种多样性的相关性较高
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