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101.
以湖北省16个副地级以上城市为研究对象,以近30 a来的改革开放阶段为研究时段(1984~2013年),构筑涵盖经济生产、社会生活与生态景观3个子系统的评价指标体系,使用AHP法为权重赋值,分别构建增长系数、协调系数与综合系数3个维度的测度模型,计算各年度各城市综合发展水平,基于Arc GIS10.0、DPS7.05与SPSS19软件,使用系统聚类、二阶段聚类、有序样本分类、非线性映射分析、Pearson相关分析、Mann-Kendall突变分析、全局莫兰指数、变异系数、局部莫兰指数等工具,模拟分析城市综合发展水平的整体时序演化(城市聚类、时段划分与演化趋势)、个体时序演化与空间格局演化(全局格局与局部格局)。结果表明,湖北省绝大多数城市的综合发展趋势正在出现积极变化,次级规模城市更具优势,总体差距仍较明显,毗邻城市差距逐渐收敛,国家发展观念、地区战略及体制机制的变化、城市发展的基础格局、城市规模的辩证作用、城市的地域特征深刻影响城市综合发展的时空格局。 相似文献
102.
不同结构网囊特性的初步研究 总被引:1,自引:0,他引:1
杨吝 《广东海洋大学学报》1998,(2)
为了测定不同拖网网囊结构对网囊的几何形状、同目张开、网目形状和拖网阻力的影响,设计和制作了4种网囊,一种是传统的菱形同目(DM)网囊,另三种是新型网囊:方形同目(SM)网囊,菱、方形网目混合二片式(DSM2)网囊和菱、方形同目混合四片式(DSM4)网囊。于1996年9月11~12日在中山大学试验水槽进行了同模试验,结果表明:1)各网囊阻力相差不大,且随拖速和渔获的增加而增大。2)新型网囊的几何形状和同目的张开及其形状均优于传统菱形网目网囊。3)空网时,各种网囊均呈圆筒状。当网囊中有了渔获后,传统菱形同目网囊的端部变为球状,除了球状部分的网目有较大张开外,其余同目张开很小,网囊使用直径也小,而新型网囊始终保持筒状,且网目充分张开,网囊使用直径也大。4)新型例翼的几何形状及使用直径和网目的张开及形状几乎不受拖速大小、有无渔获和渔获多少的影响。 相似文献
103.
FU Hongli LI Wei ZHANG Xuefeng HAN Guijun WANG Xidong WU Xinrong and ZHANG Lianxin 《中国海洋大学学报(英文版)》2014,13(2):183-190
Based on the statistics of surface drifter data of 1979–2011 and the simulation of nuclear pollutant particulate movements simulated using high quality ocean reanalysis surface current dataset, the transport pathways and impact strength of Fukushima nuclear pollutants in the North Pacific have been estimated. The particulates are used to increase the sampling size and enhance the representativeness of statistical results. The trajectories of the drifters and particulates are first examined to identify typical drifting pathways. The results show that there are three types of transport paths for nuclear pollutants at the surface: 1) most pollutant particles move eastward and are carried by the Kuroshio and Kuroshio-extension currents and reach the east side of the North Pacific after about 3.2–3.9 years; 2) some particles travel with the subtropical circulation branch and reach the east coast of China after about 1.6 years according to one drifter trajectory and about 3.6 years according to particulate trajectories; 3) a little of them travel with local, small scale circulations and reach the east coast of China after about 1.3–1.8 years. Based on the particulates, the impact strength of nuclear pollutants at these time scales can be estimated according to the temporal variations of relative concentration combined with the radioactive decay rate. For example, Cesium-137, carried by the strong North Pacific current, mainly accumulates in the eastern North Pacific and its impact strength is 4% of the initial level at the originating Fukushima area after 4 years. Due to local eddies, Cesium-137 in the western North Pacific is 1% of the initial pollutant level after 1.5 years and continuously increases to 3% after 4 years. The vertical movement of radioactive pollutants is not taken into account in the present study, and the estimation accuracy would be improved by considering three-dimensional flows. 相似文献
104.
105.
Sand/dust storms are some of the main hazards in arid and semi-arid zones. These storms also influence global environmental changes. By field observations, empirical statistics, and numerical simulations, pioneer researchers on these natural events have concluded the existence of a positive relationship between thermodynamic effects and sand/dust storms. Thermodynamic effects induce an unsteady stratified atmosphere to influence the process of these storms. However, studies on the relationship of thermodynamic effects with particles (i.e., sand and dust) are limited. In this article, wind tunnel with heating was used to simulate the quantitative relationship between thermodynamic effects and particle movement on different surfaces. Compared with the cold state, the threshold wind velocity of particles is found to be significantly decrease under the hot state. The largest decrease percentage exceedes 9% on fine and coarse sand surfaces. The wind velocity also has a three-power function in the sand transport rate under the hot state with increased sand transport. Thermodynamic effects are stronger on loose surfaces and fine particles, but weaker on compacted surfaces and coarse particles. 相似文献
106.
开放式层次化物理实验教学体系网络管理平台建设 总被引:2,自引:0,他引:2
开放式层次化物理实验教学系统的建立和运行需要一个功能强大的网络管理平台支持和保障.介绍了开放式层次化的物理实验教学体系内涵,重点介绍其网络管理平台的设计、功能、使用效果和应用前景. 相似文献
107.
《Comptes Rendus Geoscience》2019,351(5):355-365
Located in northern Niger, the NW–SE Téfidet trough is the western branch of the Ténéré rift megasystem.Here we present a tectono-sedimentary analysis of the Téfidet trough, based on the combined use of satellite imagery, field observations and measures, and available literature. We use these data to analyse the sedimentary facies and the tectonic deformations (faults, folds, basins) in the Téfidet trough, and derive their relative chronology. Doing so, we characterize synrift and postrift deformations and their interactions with sedimentation.Altogether our analyses suggest that the Téfidet trough was affected from the Cretaceous to the Paleogene by three major tectonic periods.
- •The first period was a rifting stage with extension and transtension during the Albian–Aptian times. The mean extension was ∼N60° and dominantly produced NW–SE-trending normal faults, a few strike-slip faults locally associated with small folds with sigmoidal axis and small reverse faults, and progressive unconformities.
- •the second period was also a rifting time, which prevailed during the Upper Cretaceous. The regime was marked by transtensional to extensional tectonics, under a ∼N130° shortening and a ∼N60° trending stretching. The end of this period saw the closure of the Téfidet trough.
- •the third period was a postrift stage. It was characterized by a ∼N70° extensional to transtensional regime during the Oligocene–Pliocene. It mainly produced post-sedimentary extensional faults and fractures and alkaline volcanism. We eventually discuss these deformation phases in relation with the Cretaceous Gondwana breakup and its related rifting events in West and North Africa, and with the subsequent Africa–Europe collision.
108.
地球历史的“开”、“合”节律与古地磁变化 总被引:2,自引:0,他引:2
地球历史的节律突出表现为“开”与“合”有规律的组合。“开”、“合”节律应根据地质、地球化学、地球物理、生物等各种信息综合分析而建立,一般可分为全球性、区域性、地区性、露头和微观五个级别的“开”、“合”旋回或韵律。文中综合各方面资料编制了全球“开”、“合”旋回演化简图。古地磁场强度、古地磁场极性倒转比例、古地磁场极性倒转频率和真极移速率在地史上均呈周期变化,与开合构造关系密切,同受全球性因素制约。因此,用“开”、“合”观点研究古地磁可以揭示古地磁的本质特征。通过古地磁的研究有助于确定“开”、“合”环境,恢复“开”、“合”历史,探索“开”、“合”机制。 相似文献
109.
Variations of sea ice temperature from CHINARE 2003 and its application on sea ice model evaluation 下载免费PDF全文
Variation of vertical profiles of sea ice temperature and adjacent atmosphere and ocean temperatures were measured by ice drifting buoys deployed in the northeast Chukchi Sea as part of the 2003 Chinese Arctic Research Expedition.The buoy observations (September 2003 to February 2005) show that the cooling of the ice began in late September,propagated down through the ice,reaching the bottom of the ice in December,and continued throughout the winter.In winter 2003/04,some obvious warmings were observed in the upper portion of the ice in response to major warmings in the overlying atmosphere associated with the periodicity of storms in the northeast Chukchi Sea.It is found that the melt season at the buoy site in 2004 was about 15% longer than normal.The buoy observed vertical ice temperature profiles were used as a diagnostic for sea ice model evaluation.The results show that the simulated ice temperature profiles have large discrepancies as compared with the observations. 相似文献
110.
集沙仪是定量监测风沙活动的重要工具。设计了一种自动连续称重式集沙仪,可以根据试验需要采集不同高度沙样,每分钟收集一次质量数据,实现高频连续集沙。试验结果显示,自动连续称重式集沙仪在15、30、60 cm高度的集沙量满足随高度增加呈指数减少的规律;在15 cm高度,风速与输沙通量呈指数函数关系(y=6E-05·e0.8417x,R2=0.6042),随集沙高度升高输沙通量与风速相关性减弱。自动连续称重式集沙仪与新型平口式集沙仪所测的输沙通量具有很好的一致性(y=0.8119x+0.2645,R2=0.7481)。自动连续称重式集沙仪虽然在稳固性方面需要改良,但能够很好地捕捉高度在15 cm以下沙物质的输移信息,野外应用效果良好,是一种适合野外高精度风沙活动自动监测的新型测量工具。 相似文献