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991.
风灾是北京地区玉米减产的一个重要因素,是影响玉米产量最常见的一种气象灾害,严重的风灾可造成玉米绝收。为实现对玉米风灾造成损失的定量评估,利用收集到的历史上出现的玉米风灾及产量损失数据,结合自动气象站观测资料,分析了风灾发生过程中对玉米产量损失影响显著的气象因子,最终确定选取玉米受灾过程中的最大风速的最大值、持续时间内的最大风速的平均值、最大风速持续时间和过程降水量4个气象因子,并考虑到玉米不同生育期抗风能力的不同,增加了玉米生育期影响因子,利用这5个要素,运用统计学方法建立了北京地区玉米风灾损失定量评估统计模型。通过对样本数据的拟合及剩余样本的检验,建立的定量损失评估模型具有一定的准确性和实用性,可为政策性农业保险的定损,以及生产部门确定风灾损失及保险公司理赔提供科学依据。 相似文献
992.
灌河口北部海域氮磷营养盐分布及富营养化评价 总被引:2,自引:0,他引:2
于2012年5月至2013年2月期间在灌河口北部海域取样,分析讨论了灌河口北部海域营养盐含量的时空变化及其影响因素、海域的富营养化水平和营养级类型。结果表明,整个调查期间,无机磷的含量相对较低,高N/P值显示磷可能成为该研究海域浮游植物生长的限制因子。调查海域近岸及附近海域营养指数E值大于1,处于富营养状态。营养级评价结果显示海域四个季节大多数站位处于磷中等限制潜在性富营养状态。无机氮含量较高,灌河口附近海域普遍超过第四类海水水质标准,其中夏秋季高于春冬季,是由于夏秋季陆源输送增大所致。 相似文献
993.
To achieve accurate positioning of autonomous underwater vehicles, an appropriate underwater terrain database storage format for underwater terrain-matching positioning is established using multi-beam data as underwater terrain-matching data. An underwater terrain interpolation error compensation method based on fractional Brownian motion is proposed for defects of normal terrain interpolation, and an underwater terrain-matching positioning method based on least squares estimation (LSE) is proposed for correlation analysis of topographic features. The Fisher method is introduced as a secondary criterion for pseudo localization appearing in a topographic features flat area, effectively reducing the impact of pseudo positioning points on matching accuracy and improving the positioning accuracy of terrain flat areas. Simulation experiments based on electronic chart and multi-beam sea trial data show that drift errors of an inertial navigation system can be corrected effectively using the proposed method. The positioning accuracy and practicality are high, satisfying the requirement of underwater accurate positioning. 相似文献
994.
Natural weak acidic groundwater occurs in the unconfined and confined aquifers consisting of Quaternary and Neogene unconsolidated sediments near Beihai in southern Guangxi, China. Under natural conditions the groundwater has low TDS(less than 200 mg L-1) and low concentrations of trace elements(less than 100 μg L-1) with a deceasing tend in contents of the Lanthanides(rare earth elements, less than 1 μg L-1) towards higher atomic number. The groundwater ranges in p H from 3.33 to 7.0 with an average value of 5.12(even lower than that of local rainwater, 5.88). p H values in the groundwater are a bit higher in rainy seasons than those in dry seasons and do not show significant increasing or decreasing trend with time. The average p H value in groundwater in the confined aquifers is even a bit lower than that in the unconfined aquifer. Comprehensive analyses of the groundwater environment suggest that H+ in the groundwater may be derived from dissociation of H2CO3, release of the absorbed H3O+ in clay layers and the acidity of rainwater. The H2CO3 in the groundwater may be formed by dissolution of CO2(g). Minerals in the unconsolidated sediment are predominated by quartz with small amount of clay minerals. The sediments undergoing a long-term weathering contain low levels of soluble constitutes. Lack of alkaline substances in the groundwater system is also helpful in the accumulation of acidity of the groundwater. 相似文献
995.
996.
Shirong Ye Dezhong Chen Yanyan Liu Peng Jiang Weiming Tang Pengfei Xia 《GPS Solutions》2015,19(4):545-557
997.
对13个大质量恒星形成区样本进行了SiO(2-1)、CH_3OH(2-1)和C~(34)S(2-1)热线的观测.在9个分子云核中,3条热线同时被探测到.这9个SiO探测中,有3个是新探测到的且它们强度都相对较弱.所有探测到的谱线都有较明显的线翼,这可能是外向流出现的证据.SiO谱线的线宽最宽,这也更进一步表明SiO辐射可能是来自高速的外向流,即更靠近外向流的激发源.估算了各分子谱线的旋转温度,柱密度和相对元素丰度.结果表明SiO和CH_3OH元素丰度之间有较好的相关性,相关系数R=0.77,但是SiO和C~(34)S元素丰度之间却没有任何相关性. 相似文献
998.
Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle generally induce diverse magmatism and/or associated high-temperature metamorphism. Nevertheless, the intimate coexistence of post-collisional magmatic activity and high-temperature metamorphism is rare.In this contribution, a lithological assemblage composing of diverse magmatic rocks deriving from distinct magma sources and coeval high-temperature metamorphism was identified in eastern Kunlun.Petrography, ages, mineral chemistry and whole-rock geochemistry demonstrated that those intimately coexistent diverse rocks were genetically related to post-collisional extension. The garnet-bearing mafic granulites in Jinshuikou area interior of the East Kunlun Orogenic Belt are mainly composed of garnet,orthopyroxene, and plagioclase, with peak metamorphic P–T conditions of ~ 701–756 ℃and 5.6–7.0 kbar,representing a granulite-facies metamorphism at 409.7 ± 1.7 Ma. The diverse contemporaneous magmatic rocks including hornblendites, gabbros and granites yield zircon U–Pb ages of 408.6 ± 2.5 Ma,413.4 ± 4.6 Ma, and 387–407 Ma, respectively. The hornblendites show N-MORB-like REE patterns with(La/Sm)Nvalues of 0.85–0.94. They have positive zircon εHf(t) values of 0.1–4.9 and whole-rock εNd(t) values of 3.9–4.7 but relatively high(87Sr/86Sr)ivalues of 0.7081 to 0.7088. These features demonstrate that the hornblendites derived from a depleted asthenospheric mantle source with minor continental crustal materials in source. As for the gabbros, they exhibit arc-like elemental signatures, low zircon εHf(t) values(-4.3 to 2.5) and variable whole-rock εNd(t) values(-4.9 to 1.2) as well as high(87Sr/86 Sr)ivalues(0.7068 to 0.7126), arguing for that they were originated from partial melting of heterogeneous lithospheric mantle anteriorly metasomatized by subducted-sediment released melts. Geochemistry of the granites defines their strongly peraluminous S-type signatures. Zircons from the granites yield a large range of εHf(t) values ranging from -30.8 to -5.1, while the whole-rock samples yield consistent(87Sr/86 Sr)ivalues(0.7301 to 0.7342) and negative εNd(t) values(-10.1 to -12.4). These features indicate that the S-type granites could be generated by reworking of an ancient crust. Taken together, the penecontemporaneous magmatism and metamorphic event, demonstrated the early-middle Devonian transition from crustal thickening to extensional collapse. The post-collisional mantle-derived magmas serve as an essential driving force for the high-temperature granulite-facies metamorphism and anataxis of the crust associated with formation of S-type granite. This study not only constructs a more detail Proto-Tethys evolution process of the eastern Kunlun, but also sheds new light on better understanding the intimate relationship between magmatism and metamorphism during post-collisional extensional collapse. 相似文献
999.
1000.