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21.
针对现有职住空间关系的研究难以在微观维度上有效促进大城市职住功能空间的均衡发展以及规划政策与现状发展存在的时序错位问题,该文以北京市为例,从房屋建筑使用用途的角度切入,运用空间自相关分析模型、热点分析模型和职住用地比三个评价方法,同时借用ArcGIS软件平台进行空间分析与可视化表达,探究北京职住空间在乡镇尺度下的组织特征。研究发现:北京市职住空间表现为聚类分布的空间格局特征,以首都功能核心区为中心,大致呈现出环状圈层分布,北京市职住空间的“热点区”在空间分布上存在差异,而“冷点区”在空间分布上基本相同,职住空间关系存在失衡,与规划目标存在一定的偏差。提出的研究方法从微观维度分析了城市职住空间的组织特征,促进了城市规划与发展时序的有效结合,可在特大城市的职住空间关系的研究中进行推广应用。 相似文献
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准确地估测植被覆盖度对于生态环境、自然资源评估有着重要的意义.本文通过无人机获取多光谱影像结合DEM,对拍摄区域植被面积进行估测;利用无人机遥感平台搭载的Sequoia多光谱相机获取影像数据,研究了常见的4种植被指数(归一化差值植被指数(NDVI)、比值植被指数(RVI)、土壤调节植被指数(SAVI)、绿度归一化植被指数(GNDVI))在植被面积估测中的适用性.实验结果表明,无人机多光谱影像结合DEM,在植被面积估测中具有可行性.其中,归一化差值植被指数(NDVI)可使植被从土壤、水体、阴影等复杂背景因素中分离出来,能较为准确地统计植被覆盖面积.通过无人机多光谱影像估测绿植覆盖面积,可为精细化作物管理、农业估产提供决策依据. 相似文献
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Ship detection using synthetic aperture radar (SAR) plays an important role in marine applications. The existing methods are capable of quickly obtaining many candidate targets, but numerous non-ship objects may be wrongly detected in complex backgrounds. These non-ship false alarms can be excluded by training discriminators, and the desired accuracy is obtained with enough verified samples. However, the reliable verification of targets in large-scene SAR images still inevitably requires manual interpretation, which is difficult and time consuming. To address this issue, a semisupervised heterogeneous ensemble ship target discrimination method based on a tri-training scheme is proposed to take advantage of the plentiful candidate targets. Specifically, various features commonly used in SAR image target discrimination are extracted, and several acknowledged classification models and their classic variants are investigated. Multiple discriminators are constructed by dividing these features into different groups and pairing them with each model. Then, the performance of all the discriminators is tested, and better discriminators are selected for implementing the semisupervised training process. These strategies enhance the diversity and reliability of the discriminators, and their heterogeneous ensemble makes more correct judgments on candidate targets, which facilitates further positive training. Experimental results demonstrate that the proposed method outperforms traditional tri-training. 相似文献
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The increasing use of pharmaceuticals has become a major environmental issue in China.The presence of antibiotics in water may have deleterious effects on non-target aquatic organisms such as microalgae.In this study,a cyanobacterium and an alga species in surface waters,Microcystis aeruginosa and Chlamydomonas microsphaera,were exposed to 0,0.1,0.5,1.0,2.0,5.0,10.0,and 20.0 mg/L of oxytetracycline dihydrate(OXY) and sulfamethoxazole(SMZ) for 96 h to determine the effects of these antibiotics on the growth and surface morphology.Moreover,the photosynthetic activity and the contents of superoxide dismutase(SOD),malondialdehyde(MDA),and protein were measured to examine the biochemical characteristics of M.aeruginosa and C.microsphaera under OXY and SMZ stress.The effects of both antibiotics on the growth of both species were concentration-dependent and characterized by low-dose stimulation and high-dose inhibition.C.microsphaera was more sensitive to both antibiotics than M.aeruginosa was.The algal cell membranes of both species disintegrated after exposure to a high concentration of OXY.All of the physiological parameters measured in this study were relatively stable at low concentrations of OXY and SMZ.After exposure to high concentrations of OXY and SMZ,photosynthetic activity decreased significantly,whereas lipid peroxidation and the abundance of SOD,MDA,and protein increased significantly.Thus,low-dose antibiotics may increase algal blooms in eutrophic waters. 相似文献
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Journal of Oceanology and Limnology - Salt stress is an abiotic stress to plants in especially saline lakes. Dunaliella, a halophilic microalga distributed throughout salt lakes and seas, can... 相似文献
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Based on X-ray diffraction, optical microscopy and scanning electron microscopy analysis of the Dachang gold ore, it is showed that the sulfide of ore is the main carrier minerals of gold. A majority of gold is embedded in pyrite and tetrahedrite as the form of inclusion and a small amount intergrowth with pyrite and gangue mineral, occasionally the presence is in form of monomer natural gold. The main factors which influence the recovery rate are sulfide mineral particle size, and the fine grained sulfide is beneficial for the dissociation and flotation of gold bearing minerals. The monomer dissociation degree of gold bearing minerals can reach 91.3% , when the grinding fineness is less than 0. 074 mm and grain level accounts as 80%. It is not conducive to the flotation of sulfide if the grinding fineness is low or high. It is difficult to completely dissociate the monomer if there is a small amount of pyrite and arsenopyrite in the ore. Therefore, before leaching the gold, it must conduct pretreatment to reach the ideal recovery rate of the gold, like roasting oxidation, pressure oxidation and biological oxidation. The fine microscopic gold has little influence on the gold recovery rate. 相似文献
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有源数字阵列雷达的波束设计非常灵活,可变的波束宽度和多波束模式不仅可以满足不同任务的观测需求,还可有效节约扫描时间,但阵列天线参数随波位改变的特性对相控阵天气雷达回波强度的精确定标提出了挑战。2013年4—6月,中国气象科学研究院与安徽四创电子股份有限公司联合研发的X波段一维有源相控阵天气雷达 (X-PAR) 进行了装配后的首次测试观测。对比该雷达与相同位置的C波段双线偏振雷达 (C-POL) 观测资料发现,X-PAR不同宽度的扫描波束均能取得较合理的观测资料。但由于各模式的雷达方程及其标定方法不尽相同,并受到阵列天线照射体积、展宽波束和发射增益的影响,造成X-PAR回波强度存在一定的测量偏差。结合天线参数分析和实际数据统计将测量偏差订正至±1 dB内,为雷达的进一步调试和改进提供了依据。 相似文献
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利用LiDAR数据进行电力设施提取与建模可以克服传统工程测量电力巡线工作量大,危险性高,效率低下等缺点,但现有的电力线提取研究主要集中在电力线的分离与提取,并且拟合的精度不高。针对此问题本文提出了一种精度较高的电力线拟合方法。首先,根据电力线两端悬挂、中间自然下垂的特点,求解电力线拟合的最佳几何模型;然后,通过电力线的走向和端点,建立电力线拟合的最佳平面坐标系;最后,采用基于二次多项式限制的最小二乘法拟合电力线,解算出最优参数,生成最终电力线模型。对真实数据的处理和精度评价表明,本文方法不仅能够实现电力线的快速3维重建,而且能够达到较高的拟合精度。 相似文献