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1.
余慧容  杜鹏飞 《地理研究》2021,40(1):152-171
农业景观保护是实现农业景观可持续发展的重要举措,关系到中国粮食安全保障、农耕文明传承、乡村风貌维系、生态安全格局构建乃至社会经济稳定发展。本文借助对发达国家农业景观保护路径的长时间尺度历史回顾,总结归纳出农业景观保护路径发展的一般规律,即其在社会经济发展进程中一般经历传统保护、应对保护、管制保护、治理保护和管护保护五个发展阶段。从最初的传统保护阶段到最近的管护保护阶段,农业景观保护目标从自给生产维续逐渐转变为可持续发展,景观可持续性先降后升。在此基础上,结合中国农业景观保护状况,提炼出增强主体管护意识、提升景观功能服务、优化信息沟通渠道、完善政策弹性结构等四方面启示。  相似文献   
2.
为了探究藻胆蛋白与高等植物类囊体膜之间的光能传递规律,验证重组藻胆蛋白是否可以与高等植物类囊体膜之间的光能传递,本研究分别提取了重组藻红蛋白、重组藻蓝蛋白以及菠菜和韭菜的类囊体进行混合孵育,然后进行了全波长吸收光谱以及荧光光谱检测。结果显示:混合孵育时间为10~20 min有利于重组藻红蛋白和藻蓝蛋白与类囊体膜结合并进行光能传递,最适混合孵育时间随重组藻胆蛋白和类囊体的种类不同而稍有不同;重组藻红蛋白不能与菠菜或韭菜的类囊体膜直接发生光能传递,但是当体系中添加重组藻蓝蛋白的时候就可以;重组藻蓝蛋白可以与类囊体中的叶绿素a直接进行光能传递,使得叶绿素a的荧光发射峰值显著提升,当藻红蛋白和藻蓝蛋白的比例是1∶2时,光能传递效率较高。本研究为藻胆蛋白在构建新型光合系统中的应用提供实验依据。  相似文献   
3.
Early Cretaceous elasmobranchs still are very insufficiently known despite all progress that has been accomplished in recent years. Here, a small elasmobranch assemblage is presented from the Valanginian of Austria that contributes significantly to a better understanding of early Cretaceous elasmobranch diversity. The new assemblage comprises two new carcharhiniform sharks, Altusmirus triquetrus gen. et sp. nov. and Fornicatus austriacus gen. et sp. nov., a new orectolobiform shark, Similiteroscyllium iniquus gen. et sp. nov., and a galeomorph shark tooth of uncertain affinities. The recent identification of Similiteroscyllium gen. nov. has shown that it has strong similarities with Ornatoscyllium rugasimulatum from the Lower Cretaceous of France. Significant differences of the tooth morphology of O. rugasimulatum and the type specimen O. freemani justify full reconsideration of the systematic position of O. rugasimulatum and require it to be reassigned to Similiteroscyllium gen. nov. described in this paper. The new assemblage described here, and those from the Valanginian of France and Poland comprising 30 additional taxa, indicates that Early Cretaceous elasmobranch diversity was significantly higher than previously assumed. Consequently, the supposed diversity decline of elasmobranchs across the Jurassic-Cretaceous boundary represents a collecting bias rather than a real pattern.  相似文献   
4.
随着公众移动通信的快速发展,伪基站的泛滥不仅破坏正常电信秩序,危害公共安全,而且严重损害群众财产权益,侵犯公民个人隐私,已成为社会一大公害。如何从垃圾短信大数据中挖掘出伪基站活动的时空规律,寻找有效的防控方案,从源头上进行打击和治理成为管理部门和研究者共同关注的焦点。本文基于北京市垃圾短信数据,利用非负矩阵分解的方法分析伪基站的时空分布规律;并利用TF-IDF构建垃圾短信分类模型,对垃圾短信进行分类,结合土地利用数据,分析伪基站在发送不同类型垃圾短信时的时空分布规律。结果显示:北京市垃圾短信多分布于路网和中心城区;白天垃圾短信数量远远多于晚上;垃圾短信的分布随时间的推移沿着路网逐渐向内收缩;发送不同类型垃圾短信的伪基站的时空分布具有一定的差异;通过非负矩阵分解得到的结果,与垃圾短信分类后得到的结果有很好的匹配。研究表明,非负矩阵分解具有实现上的简便性、分解形式和分解结果上的可解释性等优点,可以有针对性的为有关部门建言打击伪基站的有效方案,对于伪基站违法行为的治理具有一定的意义。  相似文献   
5.
Many researchers have studied the influence of rainfall patterns on soil water movement processes using rainfall simulation experiments. However, less attention has been paid to the influence under natural condition. In this paper, rainfall, soil water content (SWC), and soil temperature at 10‐, 20‐, 30‐, 40‐, and 50‐cm depths were simultaneously monitored at 1‐min intervals to measure the variation in SWC (SWCv) in response to rainfall under different rainfall patterns. First, we classified rainfall events into four patterns. During the study period, the main pattern was the advanced rainfall pattern (38% of all rainfall events), whereas the delayed, central, and uniform rainfall patterns had similar frequencies of about 20%. During natural rainfall, rainwater rapidly passed through the top soil layers (10–40 cm) and was accumulated in the bottom layer (50 cm). When a high rainfall pulse occurred, the water storage balance was disturbed, resulting in the drainage of initial soil water from the top layers into the deeper layers. Therefore, the critical function of the top layers and the bottom layers was infiltration and storage, respectively. The source of water stored in the bottom layer was not only rainfall but also the initial soil water in the upper soil layers. Changes in soil temperature at each soil depth were comonitored with SWCv to determine the movement characteristics of soil water under different rainfall patterns. Under the delayed rainfall pattern, preferential flows preferred to occur. Under the other rainfall patterns, matrix flow was the main form of soil water movement. Rainfall amount was a better indicator than rainfall intensity for SWCv in the bottom layer under the delayed rainfall pattern. These results provide insights into the responses of SWCv under different rainfall patterns in northern China.  相似文献   
6.
ABSTRACT

Crime often clusters in space and time. Near-repeat patterns improve understanding of crime communicability and their space–time interactions. Near-repeat analysis requires extensive computing resources for the assessment of statistical significance of space–time interactions. A computationally intensive Monte Carlo simulation-based approach is used to evaluate the statistical significance of the space-time patterns underlying near-repeat events. Currently available software for identifying near-repeat patterns is not scalable for large crime datasets. In this paper, we show how parallel spatial programming can help to leverage spatio-temporal simulation-based analysis in large datasets. A parallel near-repeat calculator was developed and a set of experiments were conducted to compare the newly developed software with an existing implementation, assess the performance gain due to parallel computation, test the scalability of the software to handle large crime datasets and assess the utility of the new software for real-world crime data analysis. Our experimental results suggest that, efficiently designed parallel algorithms that leverage high-performance computing along with performance optimization techniques could be used to develop software that are scalable with large datasets and could provide solutions for computationally intensive statistical simulation-based approaches in crime analysis.  相似文献   
7.
For many researchers, government agencies, and emergency responders, access to the geospatial data of US electric power infrastructure is invaluable for analysis, planning, and disaster recovery. Historically, however, access to high quality geospatial energy data has been limited to few agencies because of commercial licenses restrictions, and those resources which are widely accessible have been of poor quality, particularly with respect to reliability. Recent efforts to develop a highly reliable and publicly accessible alternative to the existing datasets were met with numerous challenges – not the least of which was filling the gaps in power transmission line voltage ratings. To address the line voltage rating problem, we developed and tested a basic methodology that fuses knowledge and techniques from power systems, geography, and machine learning domains. Specifically, we identified predictors of nominal voltage that could be extracted from aerial imagery and developed a tree-based classifier to classify nominal line voltage ratings. Overall, we found that line support height, support span, and conductor spacing are the best predictors of voltage ratings, and that the classifier built with these predictors had a reliable predictive accuracy (that is, within one voltage class for four out of the five classes sampled). We applied our approach to a study area in Minnesota.  相似文献   
8.
In concert with developments in global trade and energy resource transportation, there has been a marked increase in reliance on overseas shipping. Unimpeded marine transportation has therefore become a key issue which influences national maritime interests including the security of trade and energy resources. A strategic shipping pivot thus performs a vital controlling function for global shipping networks. In this study strategic shipping pivots are defined and subdivided into sea hubs, channels and areas. We then develop a model to identify strategic shipping pivots on a global scale. The results show that, depending on differences in location, function, and type, the concept of strategic shipping pivot permits the identification of both spatial and structural differentiation with respect to strategic hubs, corridors, and seas. Now 44 strategic hubs have formed across the globe. These hubs have become the control centers of local shipping network organization. At the same time, seven strategic corridors containing most shipping routes and transportation capacity connect important sea areas, and permit a high-degree of control over the transport of strategic materials. The strategic seas, the Caribbean, the Mediterranean, Southeast Asia, and the Pacific provide vital import and export pathways, so that the formation of strategic shipping pivots is mainly influenced by factors such as physical geographical conditions, the spatial distribution of socio-economic activities, business organization, technical progress, geopolitical patterns and geopolitical disputes. Physical geographical conditions provide the potential foundations for strategic shipping pivots, while the spatial distribution of socio-economic activities and communications determine the strategic value of these points. Finally, business organization, technical progress, and geopolitical disputes all function to strengthen the strategic mechanisms and the mutagenicity of strategic shipping pivots.  相似文献   
9.
山东地磁台网受宁东高压直流输电干扰预处理质量分析   总被引:2,自引:0,他引:2  
为进一步提高山东地磁台网受高压直流输电干扰的预处理质量,通过中国地震前兆数据处理系统中相对差值检测和预处理检测功能,对山东地磁台网多年来受宁东高压直流输电干扰预处理情况进行了总结分析。结果表明,经过数据预处理,宁东高压直流输电干扰基本被去除,但仍然存在高压直流输电干扰误判、起止时间错判、干扰幅度计量不精确等问题。针对上述问题,对数据进行复核和校对,应用"缓变台阶"功能重新处理,并加强对H、D分量干扰特征的研究。  相似文献   
10.
吴胜男  江志红 《气象科学》2019,39(5):588-598
利用欧洲中心1979—2015年夏季6—8月ERA-Interim逐日再分析资料和国家气候中心CN05.1格点化降水观测数据集,引入基于自组织映射SOM(Self-Organizing Maps)方法进行长江中下游地区夏季海平面气压空间距平场的客观分型,得到该地区25种地面天气型及其系统演变特征,发现天气型的稳定、转移与天气系统强弱有关。高低压系统越强,天气型停滞频率越高,天气型越稳定;反之,天气型越不稳定。基于SOM天气型转移概率,发现三条与局地降水联系的系统演变路径,其中1号路径暖空气势力强盛,副高北上,推动锋面北抬,产生江北降水型,多发生在7月;路径2反映冷空气势力强盛推动锋面南下的天气过程,产生沿江降水型,该天气型在6、7月均易发生;路径3表现为台风移动变化对长江下游江南地区降水的影响,为江南降水型,且集中在8月。通过引入SOM方法对逐日天气尺度环流进行分型,从气候态上捕捉与降水有关的天气系统的移动变化特征,体现SOM方法在模拟天气系统演变的优势。  相似文献   
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