午后多重极光弧观测研究          下载免费PDF全文

温艳波  杨惠根  韩德胜  T.Araki  艾勇  刘瑞源  刘勇华  胡泽骏  陈卓天  邓忠新  刘嵘  王晶 《极地研究》2005,17(4):255-263

本文利用2001-2003年南极中山站175天全天空摄像机观测,对午后多重极光弧的出现率及其与Kp指数的关系进行了统计分析,结果表明午后多重极光弧出现率呈一单峰分布,最大发生率出现在1445UT(1645MLT),其位置在1500MLT极光热点(1300-1700MLT)近夜侧的部分。与地磁活动指数Kp的相关统计分析表明,Kp值为2-3之间时多重极光弧有较大的出现率,这说明中等地磁活动情形下午后多重极光弧有较高的出现率。事件分析表明多重极光弧的强度变化与地磁Pc5脉动具有较高的相关性,并且有类似的频谱特征,这说明午后多重极光弧可能与同时出现的Pc5地磁脉动有关。  相似文献   

Using stable isotopes to understand seasonal and interannual dynamics in moisture sources and atmospheric circulation in precipitation          下载免费PDF全文

Yu Tang  Xianfang Song  Yinghua Zhang  Dongmei Han  Likun Ai  Tianbao Zhao  Yajun Wang 《水文研究》2017,31(26):4682-4692

Stable isotopes in precipitation are useful tracers to strengthen understanding of climate change and hydrological processes. In this study, the moisture sources of 190 precipitation events in Beijing were analysed using the Hybrid Single‐particle Lagrangian Integrated Trajectory model, based on which we studied the relation between variations in precipitation δ¹⁸O and dynamics in moisture sources and atmospheric circulation in seasonal and interannual timescales. Categorization of 7 groups of moisture sources was performed, among which oceanic moisture sources presented lower δ¹⁸O in precipitation than continental moisture sources. The results show that seasonal variations of precipitation δ¹⁸O were caused by changes of moisture sources. In summer, moisture from proximal oceans dominated vapour transport to Beijing due to increasing monsoon strength and resulted in a relatively small variation of precipitation δ¹⁸O. At the interannual timescale, the variations of δ¹⁸O in summer precipitation were related to dynamics in oceanic moistures, showing depleted values when the contribution of oceanic moistures, especially the proportion of long‐distance oceanic moisture, was high. Further analysis indicated that changes of oceanic moisture sources were controlled by the strength of summer monsoons. These findings address the complexity of moisture sources in midlatitude monsoon areas and suggest that isotopic signals in precipitation have the potential to deduce changes in moisture sources and atmospheric circulation and can therefore serve for palaeoclimate reconstruction.  相似文献   

A Study on the Vibration Frequency of Blasting Excavation in Highly Stressed Rock Masses     

Jianhua Yang  Wenbo Lu  Qinghui Jiang  Chi Yao  Shuihua Jiang  Lin Tian 《Rock Mechanics and Rock Engineering》2016,49(7):2825-2843

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Fourier-based multi-scale representation and progressive transmission of cartographic curves on the internet   总被引：1，自引：0，他引：1  

Pengcheng Liu  Weibo Liu  Tinghua Ai 《制图学和地理信息科学》2016,43(5):454-468

ABSTRACT

Automatic generation of multi-scale representations from the same spatial data source has been the research focus in map generalization for a long time. Based on the Fourier technique, this paper proposes a continuous, multi-scale representation model for progressive transformation of cartographic curves on the Internet. In our method, all the curves, whether closed or open, are depicted as periodical functions which are further expressed as Fourier series. The convergence degrees of the Fourier series are explored for different kinds of curves, and truncating frequencies are derived based on the similarity between the original and reconstructed curves. Using information theory and the Radical Law in cartography, the relationship between map scales and Fourier frequencies is established. Based on the proposed multi-scale model, we also introduce the principles and implementation of a progressive transmission method. Our method is evaluated using the contours from a topographic map. The results show that our model is a valid approach to multi-scale representation of cartographic curves.  相似文献   

Grain-size distribution and contamination characteristics of heavy metal in street dust of Baotou,China   总被引：1，自引：0，他引：1  

Xiufeng Han  Xinwei Lu  Qinghui Zhang  Wuyuntana  Quansheng Hai  Huiyun Pan 《Environmental Earth Sciences》2016,75(6):468

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吉林红旗岭镁铁-超镁铁质岩体地球化学特征及其岩石成因意义     

李爱  王建  宋樾  刘建国  薛胜超 《地质学报》2018,92(2):263-277

红旗岭铜镍硫化物矿床位于兴-蒙造山带东部。矿区出露30多个镁铁-超镁铁质侵入体,主要由橄榄岩、辉石岩和辉(苏)长岩组成。本文通过对红旗岭含矿镁铁-超镁铁质岩体的主、微量及铂族元素(PGE)的研究,探讨了红旗岭岩体成矿母岩浆性质、PGE亏损的原因以及岩体形成的构造环境。全岩主、微量元素地球化学分析表明,红旗岭岩体具有高MgO(平均28.75%)、低TiO2(平均0.44%),富集轻稀土元素(LREE)、亏损高场强元素(HFSE),极低ΣPGE(平均2.08×10~(-9))和高Cu/Pd(平均2916×10~3)的特征。岩石样品显示相似的微量和PGE配分模式,表明其来源于相同的岩浆源区。根据橄榄石-熔体平衡及质量平衡原理估算出红旗岭母岩浆为高镁玄武质岩浆(MgO=10.74%、FeO=7.78%)。红旗岭母岩浆在早期演化过程中发生硫化物熔离作用导致了红旗岭含矿岩体PGE的极度亏损。结合中亚造山带东段构造演化历史,本文认为红旗岭岩体形成于晚三叠世碰撞后伸展环境,矿床的形成受到了古亚洲洋俯冲结束后板片断离的影响。  相似文献   

A modified mix-differenced approach for estimating multi-GNSS real-time satellite clock offsets     

Yongchang Chen  Yunbin Yuan  Baocheng Zhang  Teng Liu  Wenwu Ding  Qingsong Ai 《GPS Solutions》2018,22(3):72

A modified mixed-differenced approach for estimating multi-GNSS real-time clock offsets is presented. This approach, as compared to the earlier presented mixed-differenced approach which uses epoch-differenced and undifferenced observations, further adds a satellite-differenced process. The proposed approach, based on real-time orbit products and a mix of epoch-differenced and satellite-differenced observations to estimate only satellite clock offsets and tropospheric zenith wet delays, has fewer estimated parameters than other approaches, and thus its implementing procedure is efficient and can be performed and extended easily. To obtain high accuracy, the approach involves three steps. First, the high-accuracy tropospheric zenith wet delay of each station is estimated using mixed-differenced carrier phase observations. Second, satellite clock offset changes between adjacent epochs are estimated using also mixed-differenced carrier phase observations. Third, the satellite clock offsets at the initial epoch are estimated using satellite-differenced pseudorange observations. Finally, the initial epoch clock results and clock offset changes are concatenated to obtain the clock results of the current epoch. To validate the real-time satellite clock results, multi-GNSS post-processing clock products from IGS ACs were selected for comparison. From the comparison, the standard deviations of the GPS, GLONASS, BeiDou and Galileo systems clock results are approximately 0.1–0.4 ns, except for the BeiDou GEO satellites. The root mean squares are about 0.4–2.3 ns, which are similar to those of other international real-time products. When the clock estimates were assessed based on a pseudo-kinematic PPP procedure, the positioning accuracies in the East, North and Up components reach 5.6, 5.5 and 7.6 cm, respectively, which meet the centimeter level and are comparable to the application of other products.  相似文献   

青藏高原高寒区生物地理学研究进展     

宋艾  杨久成  丁文娜  刘佳 《冰川冻土》2021,43(3):786-797

近年来,随着DNA测序技术的发展,青藏高原及周边地区的生物地理学研究取得重大成果,从生物演化方面着手探讨了青藏高原隆升历史及其气候效应。综合近年来地质学、古生物学与生物地理学研究进展,我们发现高原及周边地区高寒生物类群的起源和分化时间以及多样性演化过程表明早在渐新世青藏高原部分地区就已经存在高寒生态系统,晚中新世以来青藏高原不同组成部分的地貌与气候格局发生重大改变,高寒生物的祖先类群不断迁入正在生长的高原或在高原上就地演化出适应高寒生境的新物种。晚上新世高寒区物种分化速率快速升高,多样性增加,可能是高原巨大山系和水系以及冰川作用造成地理隔离的结果。同时,生物地理学研究发现青藏高原及周边地区的高寒区与北半球高纬度地区存在密切联系,在第四纪冰期期间并未形成覆盖整个青藏高原的大冰盖,高原面上仍存在很多生物避难所。地质学、古生物学与生物地理学等进行的多学科交叉研究对全方位理解青藏高原隆升历史及其气候效应具有重要意义。  相似文献   

FDS-P型绳索取心钻具研制及试验研究          下载免费PDF全文

李鑫淼  胡建超  马莎莎  郑庆辉  王嘉瑞 《探矿工程》2021,48(S1):370-374

针对复杂地层绳索取心钻进时易出现的内管总成打捞失败问题,开展了FDS-P型绳索取心钻具研制。基于内管总成打捞失败原因分析,完成了FDS-P型绳索取心钻具设计,通过室内试验,初步验证了钻具结构设计的合理性。为进一步验证钻具性能,在贵州页岩气井开展了野外生产试验,先后完成16个回次取心钻进,累计进尺39.03 m,岩心采取率达到98%以上,其中有6个回次发生堵心,内管打捞全部成功,内管到位及堵心均得到了及时提示。实际应用结果表明,FDS-P型绳索取心钻具结构设计合理,具有良好的到位及堵心报信提示作用,内管总成打捞可靠性得到显著提升,有效提高了易堵心地层钻进效率及岩心采取质量。  相似文献   

Geochemistry and Tectonic History of Seamount Remnants in the Xingshuwa Subduction Accretionary Complex of the Xar Moron Area,Eastern Margin of the Central Asian Orogenic Belt     

CHENG Yang  XIAO Qinghui  LI Tingdong  LI Yan  FAN Yuxu  XU Liquan  GUO Lingju  PANG Jinli 《《地质学报》英文版》2021,95(4):1086-1098

This study focuses on the geology, geochemistry, zircon U-Pb geochronology and tectonic settings of the three types of seamount basalts from the Xingshuwa subduction accretionary complex in the Xar Moron area, eastern margin of the Central Asian Orogenic Belt(CAOB). The seamount remnants are composed of carbonate 'cap' sediments, large volumes of pillow and massive basalts, carbonate breccia slope facies and radiolarian cherts. Group 1 basalts are characterized by high contents of P2 O5 and TiO2 with alkaline affinity and LREE enrichment, indicating that they are derived from intraplate magma. Group 2 basalts display N-MORB LREE depletion patterns, indicating that they were formed at a mid-ocean ridge. Group 3 basalts have shown distinct Nb depletion and high Th/Yb ratios, indicating that they were generated in an island arc tectonic setting. The zircon U-Pb age of Group 1 basalt sample XWT18-131 is 576.4 ± 9.4 Ma, suggesting that the oceanic island seamount was the product of intraplate magmatism related to a mantle plume or 'hot spot' in the late Neoproterozoic. The zircon U-Pb age of Group 2 basalt sample XWT18-132 is 483 ± 22 Ma, indicating that the Paleo-Asian Ocean(PAO) was continuously expanding in the Early Ordovician. The zircon U-Pb age of Group 3 basalt sample XWT18-101 is 240.5 ± 8.2 Ma, suggesting that this area underwent the evolutionary path of ocean-continent transition, developing towards continentalization during the Middle Triassic. Thus, we believe that there was both mantle plume-related intraplate magmatism and intraoceanic subduction during the evolution of the PAO, the CAOB possibly being an evolutionary model of an intraoceanic subduction and mantle plume magmatism complex.  相似文献