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741.
讨论了一种新的边缘检测方法和用链码描述的线知数学模型,给出了基于不变线矩匹配的约束条件,并采用基于特征与最小二乘结合实现了精确的子像素匹配。  相似文献   
742.
聂树人  贾紫宸 《现代地质》1991,5(1):41-50,T001
本文论述了北祁连含蓝闪石岩的岩石类型、原岩类型、特征矿物组合及产态.区内含蓝闪石岩的原岩包括优地槽内发育的各类富钠火山岩、含富钠火山质的沉积岩。在含蓝闪石岩分布区,岩石的变质相有葡萄石-绿纤石相、蓝闪石—绿片岩相、绿帘石-角闪岩相、铁铝榴石—角闪岩相等,未发现高压低温矿物组合.岩石应属区域动力变质作用产物,并对其形成环境进行了探讨.  相似文献   
743.
Seagrass beds are highly productive coastal ecosystems, which provide good nursery habitat and abundant Organic Carbon Sources (OCS) as food for marine animals. Human activities have led to widespread eutrophication in coastal areas. Eutrophication may alter the composition and properties of OCS, thereby affecting the feeding process of herbivores and secondary consumer, and energy transfer efficiency in food chain. This may affect the production function of biological resource in seagrass beds. Based on the summary of the foreign and domestic researches, primary achievements were systematically reviewed in this paper in five aspects: the composition of OCS and their contribution, feeding process of herbivore, food web structure and energy transfer efficiency, and their responses to eutrophication. Future researches that should be emphasized were also prospected. With the combined application of stable isotope analysis for bulks and tissues, fatty acid biomarkers and compound-specific stable isotope analysis, the quantitative study of the contribution of OCS, food web structure, key carbon flow pathway and their seasonal change patterns should be enhanced. Meanwhile, the differences of OCS between larval and adult stages of key consumers will need to be further examined to clarify the transformation of their feeding habits. Through field investigation, in-situ mesocosm and laboratory simulation experiments, the effects of nutrient increase on the structure (seagrass and epiphyte, etc.) and chemical composition (nutritional quality and secondary compounds, etc.) of OCS, the response of feeding process of herbivore and secondary consumer to the alteration of chemical compounds in primary producers, and the response mechanism of carbon transfer efficiency of the grazing food chain and detritus food chain need to be further studied.  相似文献   
744.
贺灿飞  任卓然  王文宇 《地理学报》2022,77(6):1339-1358
京津冀地区经历了从竞争、合作到迈向高质量协同发展的过程,在“双循环”新发展格局下,京津冀协同发展面临着新挑战和新目标,亟需实现创新驱动经济转型。本文从价值链分工和要素流动等方面入手,系统梳理了京津冀在“外循环”和“国内大循环”中的价值链地位和辐射能力,以及以“京津冀小循环”为表现的京津冀协同发展现状。结果发现,京津冀在“外循环”中没有形成世界级城市群相对应的技术分工和知识生产能力,处于价值链较低附加值环节;在“国内大循环”中,京津冀占据价值链高附加值环节,并向外输出技术和资本,但吸引和辐射力有限。进一步探究发现,京津冀在“外循环”中相对边缘化的重要原因之一是“京津冀小循环”尚未打通,创新成果难以在城市群内部转化,从而未能实现“创新驱动经济增长新引擎”的城市群定位目标。下一阶段京津冀城市群应以水平知识链、梯度创新链为驱动,构建城市群垂直产业链。具体来说,“内循环”中应着力打造“北京研发—天津高端制造—河北物流服务”协同格局,“外循环”中构建以知识转移和市场突破为核心的“北京创新集聚溢出—河北综合制造—天津研发、航运”分工模式,逐步实现“内循环”反哺“外循环”。  相似文献   
745.
Changing high‐mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini ( 2012 ) general two‐phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back‐calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi‐lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision‐making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   
746.
东南极拉斯曼丘陵地区莫愁湖(69°22.3’ S,76°22.0’ E)沉积柱中的有机生物标志物记录了全新世中晚期该地区气候演变过程。不饱和长链烯酮在沉积柱111-76 cm (6450-5100 cal. yr. BP)和36-30 cm(3700-3500 cal. yr. BP)深度有检出,76 cm深度以上基本消失,表明该地区在5100 cal. yr. BP前后气候开始由冷转暖,冰川消融,陆壳抬升,相对海平面下降,同时大量的冰融水使湖泊逐渐淡化。沉积柱底部长链烯酮的检出阶段与东南极相对海平面较高时期相一致,而沉积柱36-30 cm(3700-3500 cal. yr. BP)深度不饱和长链烯酮的痕量检出则揭示了一个短暂的气候干冷,湖泊盐度升高的时期。沉积物中正构烷烃反映的当地气候变化所控制的湖生植物群落演变过程与上述过程基本一致。  相似文献   
747.
基于对中国大陆已发生的22个8级大震的研究,发现8级大震的发生有其规律性,这种规律性表现在8级大震发生的年份可组成一个矩形地震链,这种规律可用来对中国大陆8级大震进行预测。  相似文献   
748.
以系统的观点,基于可靠性理论对石河子市电力工程系统进行了震害预测。通过整体分析与局部评估讨论了电力系统的可靠性;提出未来地震发生后系统的潜在灾害率。  相似文献   
749.
地磁脉动Pc5在2000年7月15~16日磁暴期间的特征   总被引:3,自引:2,他引:3       下载免费PDF全文
采用IMAGE链22个台站的地磁脉动10 s数据,分析了2000年6月15~16日磁暴期间Pc5地磁脉动的频率、振幅、位相和极化特征:(1)磁暴初相和主相期间Pc5脉动的主频率随纬度的升高而降低,但是恢复相期间主频率随纬度的升高而升高,主相期间Pc5的主频率比初相和恢复相期间的低;(2)Pc5脉动初相期间的振幅有一个主峰在64°N附近,主相期间在66°N附近,恢复相期间在71°N附近;位相在主峰两侧随着纬度变化了大约180°, 从初相到恢复相主峰位置向高纬地区大约移动了7°;(3)Pc5地磁脉动的偏振极化椭圆初相期间在PEL站(6346°N)接近线偏振,主相期间在MAS站(6607°N)接近线偏振,恢复相期间在BJN站(7133°N)接近线偏振,并分别在这几个台站两侧的偏振椭圆的旋转方向反向.  相似文献   
750.
Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a, organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira.  相似文献   
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