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本文结合最近获得的新资料,对南洛河流域的地貌、黄土沉积和更新世环境进行综合分析。结果表明,南洛河上、中游地貌表现为河流峡谷和山间盆地相间分布的特征,盆地中河流阶地发育; 下游为平缓的山前平原和低山丘陵。黄土在全流域的山顶、河流阶地和盆地等各种地貌部位均有分布。黄土沉积受地形影响较大,上游黄土堆积速率低、颗粒细; 在下游有风道直通的地方,黄土堆积速率高、颗粒粗。在不同地貌部位,黄土开始堆积的年代不同,黄土底界的年代从早更新世到晚更新世均有所见。对埋藏旧石器的年代研究表明,南洛河流域的古人类活动从早更新世晚期(约800ka)开始,到晚更新世后期(约30ka)结束,期间有多期遗存。初步的孢粉和有机碳同位素分析表明,这里曾是森林草原景观,冰期时,乔木植被以松属为主,C4类型草本减少; 而间冰期时,乔木植被以松属-榆科占主导地位,C4类植物增多。古人类在黄土堆积期和古土壤发育期都可能在这个地方活动,但这一认识需要更多的证据支持。丰富的石制品分布和较为连续的黄土沉积,使南洛河流域成为理解更新世人类行为与环境的重要区域。 相似文献
83.
Climate change and global cycling of persistent organic pollutants: A critical review 总被引:1,自引:0,他引:1
Climate warming, one of the main features of global change, has exerted indelible impacts on the environment, among which the impact on the transport and fate of pollutants has aroused widespread concern. Persistent organic pollutants (POPs) are a class of pollutants that are transported worldwide. Determining the impact of climate warming on the global cycling of POPs is important for understanding POP cycling processes and formulating relevant environmental policies. In this review, the main research findings in this field over the past ten years are summarized and the effects of climate warming on emissions, transport, storage, degradation and toxicity of POPs are reviewed. This review also summarizes the primary POP fate models and their application. Additionally, research gaps and future research directions are identified and suggested. Under the influence of climate change, global cycling of POPs mainly shows the following responses. (1) Global warming directly promotes the secondary emission of POPs; for example, temperature rise will cause POPs to be re-released from soils and oceans, and melting glaciers and permafrost can re-release POPs into freshwater ecosystems. (2) Global extreme weather events, such as droughts and floods, result in the redistribution of POPs through intense soil erosion. (3) The changes in atmospheric circulation and ocean currents have significantly influenced the global transport of POPs. (4) Climate warming has altered marine biological productivity, which has changed the POP storage capacity of the ocean. (5) Aquatic and terrestrial food-chain structures have undergone significant changes, which could lead to amplification of POP toxicity in ecosystems. (6) Overall, warming accelerates the POP volatilization process and increases the amount of POPs in the environment, although global warming facilitates their degradation at the same time. (7) Various models have predicted the future environmental behaviors of POPs. These models are used to assist governments in comprehensively considering the impact of global warming on the environmental fate of POPs and therefore controlling POPs effectively. Future studies should focus on the synergistic effects of global changes on the cycling of POPs. Additionally, the interactions among global carbon cycling, water cycling and POP cycling will be a new research direction for better understanding the adaptation of ecosystems to climate change. 相似文献
84.
Frontal upwelling is an important phenomenon in summer in the Yellow Sea (YS) and plays an essential role in the distribution of nutrients and biological species. In this paper, a three-dimensional hydrodynamic model is applied to investigate the characteristics and influencing factors of frontal upwelling in the YS. The results show that the strength and distribution of frontal upwelling are largely dependent on the topography and bottom temperature fronts. The frontal upwelling in the YS is stronger and narrower near the eastern coast than near the western coast due to the steeper shelf slope. Moreover, external forcings, such as the meridional wind speed and air temperature in summer and the air temperature in the preceding winter and spring, have certain influences on the strength of frontal upwelling. An increase in air temperature in the previous winter and spring weakens the frontal upwelling in summer; in contrast, an increase in air temperature in summer strengthens the frontal upwelling. When the southerly wind in summer increases, the upwelling intensifies in the western YS and weakens in the eastern YS. The air temperature influences the strength of upwelling by changing the baroclinicity in the frontal region. Furthermore, the meridional wind speed in summer affects frontal upwelling via Ekman pumping. 相似文献
85.
北京时间2021年5月21日21时48分36秒,云南省大理州漾濞县发生MS 6.4地震。利用云南数字地震台网2021年5月18日至8月22日的震相报告,采用双差地震定位法,对漾濞MS 6.4地震序列进行重新定位。重新定位结果显示序列呈NW向优势分布,破裂长约20 km,宽约7 km,对重新定位结果进行误差分析,水平方向定位误差约为0.8 km,垂直方向定位误差约为1.0 km,定位结果具有较好的稳定性。依据震中分布的走向将序列划分为NW向的主断层与NNW向的分支断层,主断层存在较为明显的分段现象,分支断层呈雁列状分布。根据小震丛集性发生在大震断层面及其附近的原则,利用重新定位后的小震震源位置反演得到漾濞MS 6.4序列主断层走向约320°,倾角约89°,深度范围3~13 km。根据拟合得到的断层在地表的投影位置,推测本次地震的发震断层为维西-乔后断裂西侧的草坪断裂。基于断层滑动量分布识别出3个凹凸体,结合序列时空演化特征,分析了漾濞MS 6.4地震序列的破裂过程,结果显示断层中段的凹凸体发生初始破裂... 相似文献
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87.
LIU Fushun LI Huajun YU Guangming ZHANG Yantao WANG Weiying SUN Wanqing 《中国海洋大学学报(英文版)》2007,6(2):199-204
A new damage-locating method for bridges subjected to a moving load is presented, and a new ‘moving load damage-locating indicator' (MLDI) is introduced. A vehicle is modeled as a moving load, the bridge is simplified as an Euler-Bernoulli beam, and the damage is simulated by a reduction of stiffness properties of the elements. The curvature and MLDI values at each node of the baseline model (undamaged) and the damage model are computed respectively. Then the damage or damages can be located from a sudden change of the MLDI value. The feasibility and effectiveness of the proposed method are validated by numerical simulation. The results indicate that the method is effective, being able to not only locate a single damage accurately, but also locate multiple damages in simply-supported bridges, including multiple damages in continuous bridges. The results also indicate that the MLDI can accurately locate damages under 5% measurement noise. 相似文献
88.
The reflection coefficient and the total horizontal forces of regular waves acting on theperforated caisson are experimentally investigated. The empirical relationship between reflection coefficient and the ratio of the total horizontal forces acting on the perforated caisson to those on solid vertical walls with the relative chamber width, relative water depth and porosity of perforated wall, etc. are given. Moreover, the results of the ratio of the total horizontal forces are also compared with formulas given by Chinese Harbour Design Criteria and Takahashi, which may be useful for the practical engineering application. 相似文献
89.
From the latest Precambrian to the Early Cambrian was the most important phase throughout the evolutionary history of life on the earth. The diversification of latest Precambrian multicellular organisms was obvious and some of them began to form primary s… 相似文献
90.