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1. chinaXiv:201703.00485 [pdf]

快速沉积与侵蚀对地温场及天然气水合物成藏演化的影响:以南海北部陆坡为例 Impacts of fast sedimentation and erosion on the evolution of geothermal field and gas hydrate system: cases of Northern South China Sea

张毅, 何丽娟, 汪集旸
Subjects: Geosciences >> Space Physics

海洋沉积物中天然气水合物的存在与分布与地温条件紧密相关。南海北部陆坡大部分区域更、全新世沉积速率较高,同时局部地区(如神狐天然气水合物钻探区)发育有大量的海底冲蚀谷。这些快速沉积或侵蚀作用可以对地温场及天然气水合物的形成与赋存产生重要影响,然而目前注意到这些问题的研究相对较少。本文中我们结合南海北部陆坡的实际情况,建立了针对地温场发生动态变化时的水合物成藏数值模型。我们给出两个成藏模拟案例,其一是快速沉积的情形,其二是地形遭受侵蚀、产生冲蚀谷时的情形。结果表明,在这两种情形下地温场将发生不同的瞬态调整,并对天然气水合物在地层中聚集及分布产状产生重要影响。在快速沉积发生时,地温梯度将变小,天然气水合物稳定带(HSZ)将增厚;然而当其底界将随着热传递而上升,天然气水合物将不断在原稳定带底界分解,而后在新的稳定带底界处重新生成水合物。这样长时间的快速沉积作用可以造成水合物主要富集在稳定带底界处。而当快速侵蚀作用发生时,地温梯度将变大,天然气水合物稳定带的厚度将变薄,原来位于冲蚀谷处的水合物藏将被侵蚀作用破坏。而后,随着热平衡的发展,逐渐形成新的、类似于似海底反射层的稳定带底界。单纯考虑甲烷扩散作用下,高丰度水合物的形成需要较长的时间,相对而言脊下的水合物成藏较好,形成矿点的概率较大。 The occurrence and distribution of gas hydrate in marine sediments is closely related to the state of geothermal field. The sedimentation rate is relatively high during the Pleistocene and Holocene in the northern margin of the South China Sea. Moreover, there are many erosional canyons at the sea bottom in some local areas. Such fast sedimentation and erosion can greatly affect the geothermal regime and the formation and occurrence of gas hydrate deposits. However, there are few studies that consider such scenarios. In this study, considering the geological reality, we build a numerical reservoir model aimed to simulate the evaluation of the gas hydrate system upon two cases: the fast sedimentation and the development of erosional canyons. The results indicate the geothermal filed and the accumulation and distribution of gas hydrate can be adjusted dynamically when the fast sedimentation or erosion occurs. Under fast sedimentation, the geothermal gradient becomes smaller and the thickness of gas hydrate stability zone (HSZ) becomes larger. However, due to the role of heat transfer, the bottom of HSZ rises upward. This process leads to the hydrate near the previous bottom of HSZ being dissociated and depositing near the bottom of new HSZ. After a long duration, the fast sedimentation will result the formation of hydrate being mainly enriched near the bottom of HSZ. By contrast, when fast erosion occurs, the geothermal gradient increases and the HSZ turn thinner. The gas hydrate deposit system can be partially destroyed by the formation of canyons. A long time is necessary for the recovery of a gas hydrate deposit with significant abundance. Relatively, the deposits under the residual ridges are more possible to be potential “sweet spots”.

submitted time 2017-03-23 Hits38912Downloads3140 Comment 0

2. chinaXiv:201903.00239 [pdf]

An experimental study on the influences of water erosion on wind erosion in arid and semi-arid regions

YANG Huimin
Subjects: Geosciences >> Geography

Complex erosion by wind and water causes serious harm in arid and semi-arid regions. The interaction mechanisms between water erosion and wind erosion is the key to further our understanding of the complex erosion. Therefore, in-depth understandings of the influences of water erosion on wind erosion is needed. This research used a wind tunnel and two rainfall simulators to investigate the influences of water erosion on succeeding wind erosion. The wind erosion measurements before and after water erosion were run on semi-fixed aeolian sandy soil configured with three slopes (5°, 10° and 15°), six wind speeds (0, 9, 11, 13, 15 and 20 m/s), and five rainfall intensities (0, 30, 45, 60 and 75 mm/h). Results showed that water erosion generally restrained the succeeding wind erosion. At a same slope, the restraining effects decreased as rainfall intensity increased, which decreased from 70.63% to 50.20% with rainfall intensity increased from 30 to 75 mm/h. Rills shaped by water erosion could weaken the restraining effects at wind speed exceeding 15 m/s mainly by cutting through the fine grain layer, exposing the sand layer prone to wind erosion to airflow. In addition, the restraining effects varied greatly among different soil types. The restraining effects of rainfall on the succeeding wind erosion depend on the formation of a coarsening layer with a crust and a compact fine grain layer after rainfall. The findings can deepen the understanding of the complex erosion and provide scientific basis for regional soil and water conservation in arid and semi-arid regions.

submitted time 2019-03-28 From cooperative journals:《Journal of Arid Land》 Hits14139Downloads2325 Comment 0

3. chinaXiv:201909.00085 [pdf]

基于SPEI指数的新疆天山草地近55 a干旱特征

郭燕云; 胡琦; 傅玮东; 王森; 刘艳
Subjects: Geosciences >> Other Disciplines of Geosciences

标准化降水蒸散指数(SPEI)通过标准化潜在蒸散与降水的差值,表征一个地区干湿状况偏离常年的程度,是分析干旱演变趋势的新的理想指标,目前已经广泛应用于干旱评估、水资源管理等领域。利用SPEI和1961—2015年新疆天山山区8个代表站点的月降水量及月平均气温资料,对天山山区55 a以来气温和降水的变化特征、不同时间尺度的干旱变化特征、草地生长季干旱特征及变化趋势进行了分析,结果表明:近55 a,天山山区气温呈现显著的上升趋势;降水量总体呈略微上升的趋势,但年际变化较大,变化趋势不显著;天山山区月、季、半年尺度以及年尺度的干旱事件分别为42个、25个、16个和7个;天山山区草地生长季发生轻度、中度和重度干旱的频率分别为37.5%、7.1%和1.8%;近55 a,天山山区草地生长季降水量有所增加,但由于气温升高带来的蒸散作用加强,气候仍呈变干的趋势。近55 a来,天山山区草地生长季气候存在变干的倾向,且年际间的干旱程度变化剧烈,对草地的年际间生长状况差异存在较大的影响。

submitted time 2019-09-10 From cooperative journals:《干旱区研究》 Hits2725Downloads2318 Comment 0

4. chinaXiv:201711.02398 [pdf]

International UTC TAI comparison based on BDS PPP

Yulong Ge; Baoqi Sun; WeiJin Qin; Mingjun Ouyang; Xuhai Yang
Subjects: Geosciences >> Other Disciplines of Geosciences

The BeiDou navigation satellite system (BDS) developed by China, and provided official service for Asia-pacific region freely since 2012. With development of BDS, BDS-based time transfer has become an important research direction in BDS’s application fields. At present, the main method of BDS-based time transfer is BDS Common View (BDS CV), which can reach nanoseconds magnitude. Hence, we investigate the performance time transfer based on BDS precise point positioning (PPP) toward UTC/TAI compute. In this contribution, we focus on UTC/TAI comparison based on BDS PPP by using developed quad-constellation GNSS software, which called National Time System Center’s (NTSC) Bernese. And a long-term data analysis is presented. The experiments include two parts: (1) The reliability of the software and multi-GNSS products; (2) The performance of the BDS PPP toward International UTC/TAI comparison. The experimental results reveal that the accuracy of NTSC’s Bernese GPS PPP can reach about 0.1 ns relative to BIPM TAI PPP solutions. Compared with BIPM TAI PPP solutions, the accuracy of GPS PPP solutions can achieve about 0.2 ns by using multi-GNSS precise products, such as GBM, COM. For BDS PPP solutions, the solutions of GPS PPP are regarded as reference values. It is demonstrated that the accuracy of time transfer based on BDS PPP can reach better 1 ns toward UTC/TAI comparison for the statistics of 30 days-arc solutions, while 0.1 ns magnitude can be achieved for the statistics of daily solutions due to the influence of the day boundary discontinuity. Moreover, four different processing strategies of BDS PPP which include tropospheric delay fixed, tropospheric delay and coordinates fixed, coordinates fixed, and BDS-only are tested. Results show that the comparable accuracy can be achieved for four processing strategies. Hence, one can conclude that the time transfer based on BDS-only PPP show a good performance toward UTC/TAI computation.

submitted time 2018-01-07 Hits9391Downloads2204 Comment 0

5. chinaXiv:201811.00055 [pdf]

30a青海省公路可达性及县域经济联系格局演化

杨晓敏; 李玲琴
Subjects: Geosciences >> Geography

采用加权平均旅行时间、引力模型与克里金插值、XY to line、自然间断点分级法、分级符号等GIS分析方法,以1986年、1995年、2004年、2016年为时间断面,分析了青海省公路网络中43个主要节点城镇的可达性及县域经济联系格局的演化规律,结论为:1986—2016年,青海省公路网络等可达性线呈现不规则的半环状分布,影响因素主要有位置、交通、经济及其时间距离等,可达性插值表现为交通主干道指向性;青海省公路网络可达性水平均有提升,可达性值的变化呈现相似性与差异性并存的特点;1986—2016年,青海省经济联系强度与对外经济联系总量均呈现增长态势,尤其经济联系总量增长愈来愈快;前五等级的经济联系强度与前三经济联系总量的县域基本集中于西宁、海东地区,体现出青海省典型的“单核”城市空间结构,省会城市辐射带动作用明显;经济联系强度、经济联系总量与可达性均呈现正相关。

submitted time 2018-11-14 From cooperative journals:《干旱区地理》 Hits11515Downloads2162 Comment 0

6. chinaXiv:201703.01169 [pdf]

模拟海洋大气条件下直流电场作用对碳钢初期腐蚀行为的影响

林德源; 戴念维; 陈云翔; 倪清钊; 张鑫; 张俊喜
Subjects: Geosciences >> Marine Sciences

采用失重分析、极化曲线测试和SEM分析手段,研究了模拟海洋大气环境下直流电场对碳钢初期腐蚀行为的影响。结果表明,直流电场的存在加速了碳钢的初期腐蚀速率,但并没有改变其腐蚀动力学;直流电场存在有利于具有亚稳片状结构的γ-FeOOH的形成,同时抑制了γ-FeOOH向具有保护性能的α-FeOOH的转化,从而导致锈层的保护性能下降,加速了碳钢的腐蚀。

submitted time 2017-03-31 From cooperative journals:《腐蚀科学与防护技术》 Hits33650Downloads2079 Comment 0

7. chinaXiv:201703.00381 [pdf]

水圈微生物重大研究计划:聚焦水圈微生物组研究的核心科学问题

黄力,冯雪莲,杜全生,东秀珠,刘双江,温明章,戴欣
Subjects: Geosciences >> Marine Sciences

水圈包括海洋、湖沼、河流、冰川、地下水等,水圈中居住着地球上一半以上的微生物,包括细菌、古菌、真菌、藻类、病毒等,蕴含着地球上最大的微生物组。已有的研究表明,水圈微生物在重要元素生物地球化学循环中发挥关键驱动作用。但是,人们对水圈微生物组的核心科学问题,即微生物如何发挥驱动作用至今了解不多。最近,国家自然科学基金委员会“水圈微生物驱动地球元素循环的机制”重大研究计划(简称“水圈微生物计划”)正式立项。该计划拟选择典型水圈环境,解析微生物群落构建及与环境之间的相互作用、微生物物质与能量代谢机制以及微生物代谢活动的生态学意义与贡献,从而揭示水圈微生物驱动碳、氮、硫等元素生物地球化学循环的机制。文章简述了该计划提出的背景与依据,以及涉及的主要科学问题和研究设想。

submitted time 2017-03-22 From cooperative journals:《中国科学院院刊》 Hits14515Downloads2051 Comment 0

8. chinaXiv:202010.00035 [pdf]

Tree ring based drought variability in Northwest Tajikistan since 1895 AD

YANG,Meilin; YU,Yang; ZHANG,Haiyan; WANG,Qian; GAN,Miao; YU,Ruide
Subjects: Geosciences >> History of Geosciences

Determining the mechanisms controlling the changes of wet and dry conditions will improve our understanding of climate change over the past hundred years, which is of great significance to the study of climate and environmental changes in the arid regions of Central Asia. Forest trees are ecologically significant in the local environment, and therefore the tree ring analysis can provide a clear record of regional historical climate. This study analyzed the correlation between the tree ring width chronology of Juniperus turkestanica Komarov and the standardized precipitation evapotranspiration index (SPEI) in Northwest Tajikistan, based on 56 tree ring samples collected from Shahristan in the Pamir region. Climate data including precipitation, temperature and the SPEI were downloaded from the Climate Research Unit (CRU) TS 4.00. The COFECHA program was used for cross-dating, and the ARSTAN program was used to remove the growth trend of the tree itself and the influence of non-climatic factors on the growth of the trees. A significant correlation was found between the radial growth of J. turkestanica trees and the monthly mean SPEI of February–April. The monthly mean SPEI sequence of February–April during the period of 1895–2016 was reconstructed, and the reconstruction equation explained 42.5% of the variance. During the past 122 a (1895–2016), the study area has experienced three wetter periods (precipitation above average): 1901–1919, 1945–1983 and 1995–2010, and four drier periods (precipitation below average): 1895–1900, 1920–1944, 1984–1994 and 2011–2016. The spatial correlation analysis revealed that the monthly mean SPEI reconstruction sequence of February–April could be used to characterize the large-scale dry-wet variations in Northwest Tajikistan during the period of 1895–2016. This study could provide comparative data for validating the projections of climate models and scientific basis for managing water resources in Tajikistan in the context of climate change.

submitted time 2020-10-20 From cooperative journals:《Journal of Arid Land》 Hits2084Downloads1960 Comment 0

9. chinaXiv:201709.00122 [pdf]

Introduction to terminologies of tooth enamel microstructures and a proposal for their standard Chinese translations

MAO Fang-Yuan; LI Chuan-Kui; MENG Jin; LI Qian; BAI Bin; WANG Yuan-Qing; ZHANG Zhao-Qun; ZHAO Ling-Xia; WANG Ban-Yue
Subjects: Geosciences >> Geology

Tooth enamel is composed of elongated, hexagonal crystallites of hydroxyapatite. Some crystallites are arranged into various regual structures and futher formed a composite structure in a hierarchical manner. The hierarchical system can provide a basis for analysis different levels of structural complexity from varitaiton of particular crystallite strucutes to variation of structural types throughout a individual’s dentition. The size, orientation, distribution and the packing patterns of crystallites are gene-comtrolled and have limited range of intraspecific variability. Thus, these microstructures provide considerable and reliable morphological characters that help understanding of external dental morphology in context of both phylogeny and function in vertebrates. Because teeth are highly resistant to weathering, mainly owing to their enamel covering, so that they were commonly preserved as fossils. This organic system, particularly their microstructures, has attracted more and more attention from vertebrate paleontologists and other morphologists. However, as already recognized by many previous studies, some terminologies of the enamel microstructures have been complex and used inconsistently. Although considerable effort has been made to study enamel microstructures in China during the last few decades, a standard terminology of enamel microstructures in Chinese has not be formally brought into line with that in English literatures. Here we intend to introduce and systematize the relevant terminology used in the study of enamel microstructures and translate them into Chinese, in hoping that this systematic effort will enhance researches of enamel microstructures in China. 脊椎动物牙齿釉质显微结构具丰富的形态学特征,承载着系统发育和生物力学等方面的信息。本文在前人的研究基础上,试图系统地介绍牙釉质显微结构的基本内容,提出牙釉质研究中相关术语的中文译名建议,并对一些重要术语做了简要解释,供相关研究者参考,以期促进牙釉质显微结构研究的进一步发展。

submitted time 2017-09-28 From cooperative journals:《古脊椎动物学报》 Hits5456Downloads1949 Comment 0

10. chinaXiv:202001.00050 [pdf]

基于面板门槛模型的中国旅游发展减贫效应研究

兰海霞; 赵雪雁
Subjects: Geosciences >> Geography

发展旅游业作为一种有效的减贫手段已引起政府和社会各界的广泛关注,当前急需科学评估旅游发展的减贫效应,以便为制定切实可行的旅游扶贫政策提供借鉴。基于中国2000—2015年31个省(市、自治区)的面板数据,利用熵值法评价了各地区旅游发展水平,运用面板门槛模型考察了旅游发展的减贫效应。结果表明:(1) 旅游发展存在显著的减贫效应,但因发展水平不同而存在门槛效应。(2) 减贫效应存在“东—中—西”阶梯式递增的变化特征。(3) 随旅游发展水平的提高,减贫效应具有逐步收敛的边际递减特征,其中旅游发展水平处于低区段时的减贫效应最大,中低区段的减贫效应次之,中高区段的减贫效应不显著,高区段的减贫效应进一步缩小,总体呈倒“J”型。基于此,提出了充分发挥旅游减贫效应的对策建议。

submitted time 2020-01-06 From cooperative journals:《干旱区地理》 Hits17793Downloads1942 Comment 0

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