您当前的位置:首页 > 论文浏览

按机构

1. chinaXiv:201801.00107 [pdf]

The first Stalicoolithus shifengensis discovered in a clutch from the Sanshui Basin, Guangdong Province

ZHU Xu-Feng; FANG Kai-Yong; WANG Qiang; LU Xiao-Hong; WU Wei-Qiang; DU Yan-Li; HUANG Zhi-Qing; WANG Xiao-Lin
分类: 地球科学 >> 地质学

The first clutch of Stalicoolithus shifengensis is described here. This incomplete dinosaur egg clutch in which three nearly complete eggs and two egg prints were preserved was discovered in the red deposits of the Sanshui Formation at a construction site near the sluice of North Village, Dali Town, Nanhai District, Foshan City, Guangdong Province, China. The eggs in the clutch are stacked with various ranges. Based on the characteristics of the eggshell, these eggs can be assigned to S. shifengensis. The discovery of S. shifengensis in the Sanshui Formation complements the clutch information about the oospecies as well as expands its paleogeographic distribution, and sets the foundation for discussing the diversity of dinosaur eggs in the Sanshui Basin.

提交时间: 2018-01-12 来自合作期刊:《古脊椎动物学报》 点击量83下载量59 评论 0

2. chinaXiv:201801.00114 [pdf]

国外山岳型遗产地保护发展经验及其对北京市的启示

孙威; 毛凌潇
分类: 地球科学 >> 地理学

[目的/意义] 中国是世界遗产最多的国家之一,传承保护好这些珍贵的历史文化遗产是中国人民,也是世界人民的共同责任,但是如何处理好文化遗产保护利用与城乡改造开发的关系却是一个重大的现实问题。[方法/过程] 采用实地调研、案例分析、对比研究等方法,分析了美国黑石河峡谷遗产廊道、日本纪伊山脉胜地的基本概况,总结了上述两个案例的成功经验,提出了对北京西山文化带的建设启示。[结果/结论] 研究表明,国际上山岳型遗产地保护发展有不少成功经验,可以概括为重视文化遗产保护,自然景观与人文景观相协调;因势利导发展旅游业,促进文化遗产保护与利用相结合;完善规划管理体系,政府管理与民众意愿相统一;成立专门机构,促进国家、地方、民众相联合。这启示北京应进一步凝练西山文化带的文化特色和内涵、切实保护和利用好自然和文化资源、成立专门机构进行统一管理、加强规划引导和功能定位。

提交时间: 2018-01-11 来自合作期刊:《智库理论与实践》 点击量45下载量30 评论 0

3. chinaXiv:201801.00122 [pdf]

我国土壤污染防治的挑战与战略定位

陈卫平
分类: 地球科学 >> 地理学

[目的/意义] 针对新世纪我国土壤污染凸显的严峻形势,探索能有效改善土壤质量、保护土壤环境和安全利用土地资源的战略机制,对保障农产品质量安全和公众健康、实现土地可持续利用和推动生态文明建设具有重要的现实意义和深远的战略影响。[方法/过程] 本文系统分析了我国土壤污染防治过程中面临的主要问题及挑战,并从土壤环境保护和土地安全利用的宏观视角定位土壤污染防治的关键举措。[结果/结论] 研究发现,我国土壤污染防治工作以农田和工业用地为治理重点,虽已在多方面取得重大进展,但仍存在以下主要问题:(1)针对农田污染,存在污染物空间异质性强、土壤污染与农产品超标差异大、土壤污染源头管控不到位和农田安全利用困难等问题;(2)针对工业污染地块,存在污染防治的政策法规体系不完善、技术能力建设滞后、片面强调工程修复和修复模式不持续等问题。为保护国家土壤生态安全,促进土地安全利用战略规划,应加快完善土壤污染防治顶层设计,系统开展源头治理、精准治理与综合治理,坚持“可持续修复、适度修复和绿色修复”原则,加强产业链中各利益方的密切合作,开拓多元稳定的土壤修复筹融资渠道,建立土壤环境质量预警机制。

提交时间: 2018-01-11 来自合作期刊:《智库理论与实践》 点击量9下载量7 评论 0

4. chinaXiv:201801.00103 [pdf]

New materials of Choerolophodon (Proboscidea) from Dhok Pathan Formation of Siwaliks, Pakistan

Sayyed Ghyour ABBAS; Muhammad Akbar KHAN; Muhammad Adeeb BABAR; Muhammad HANIF; Muhammad AKHTAR
分类: 地球科学 >> 地质学

Choerolophodon corrugatus is the only species of the genus Choerolophodon found in the Siwalik Group. Its first appearance is in the Kamlial Formation (Middle Miocene) of the Lower Siwalik Subgroup and it is most abundant in the Dhok Pathan Formation of the Middle Siwalik Subgroup (Late Miocene to Early Pliocene). New remains of Choerolophodon corrugatus have been recovered from the Dhok Pathan type locality and its adjacent areas. The specimens include tusks, mandible and maxillary fragments, and deciduous premolars and permanent molars. The Siwalik species shows great affinity with the European species Ch. pentelici in dentition and differs in the cranial and mandibular characteristics.

提交时间: 2018-01-09 来自合作期刊:《古脊椎动物学报》 点击量76下载量41 评论 0

5. chinaXiv:201801.00104 [pdf]

A new species of Chilotherium (Perissodactyla, Rhinocerotidae) from the Late Miocene of Qingyang, Gansu, China

SUN Dan-Hui; LI Yu; DENG Tao
分类: 地球科学 >> 地质学

An adult skull with articulated atlas and an adult mandible, collected by Emile Licent in 1920 from the Late Miocene of Qingyang (Gansu, China), is recognized as a new species Chilotherium licenti sp. nov. These specimens possess typical characters of the genus Chilotherium, such as the strongly expanded mandibular symphysis, the huge and dagger-shaped i2s with an upturned medial flange, strongly constricted protocones, well-developed crochet and crista, and weakly developed parastyle folds and paracone ribs. Chilotherium licenti is characterized by the near absence of lingual and buccal cingula, and the medifossette on P2 to M2 forming by well-developed crochet and crista. The derived characters of the new species indicate that it is the highly specialized taxon of the genus Chilotherium, corresponding to MN12-13 of the Turolian in Europe. Based on a phylogenetic analysis of rhinocerotids, C. licenti from the Late Miocene is the most derived species in the known species of the Chilotherium lineage.

提交时间: 2018-01-09 来自合作期刊:《古脊椎动物学报》 点击量67下载量46 评论 0

6. chinaXiv:201711.02398 [pdf]

International UTC TAI comparison based on BDS PPP

Yulong Ge; Baoqi Sun; WeiJin Qin; Mingjun Ouyang; Xuhai Yang
分类: 地球科学 >> 地球科学其他学科

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.

提交时间: 2018-01-07 点击量1018下载量680 评论 0

7. chinaXiv:201712.00322 [pdf]

Decomposition characteristics of organic materials and their effects on labile and recalcitrant organic carbon fractions in a semi-arid soil under plastic mulch and drip irrigation

Wu, Jinggui
分类: 地球科学 >> 地球科学史

Labile organic carbon (LC) and recalcitrant organic carbon (RC) are two major fractions of soil organic carbon (SOC) and play a critical role in organic carbon turnover and sequestration. The aims of this study were to evaluate the variations of LC and RC in a semi-arid soil (Inner Mongolia, China) under plastic mulch and drip irrigation after the application of organic materials (OMs), and to explore the effects of OMs from various sources on LC and RC by probing the decomposition characteristics of OMs using in-situ nylon mesh bags burying method. The field experiment included seven treatments, i.e., chicken manure (CM), sheep manure (SM), mushroom residue (MR), maize straw (MS), fodder grass (FG), tree leaves (TL) and no OMs as a control (CK). Soil LC and RC were separated by Huygens D’s method (particle size-density), and the average soil mass recovery rate and carbon recovery rate were above 95%, which indicated this method was suitable for carbon pools size analysis. The LC and RC contents significantly (P<0.01) increased after the application of OMs. Moreover, LC and RC contents were 3.2%–8.6% and 5.0%–9.4% higher in 2016 than in 2015. The applications of CM and SM significantly increased (P<0.01) LC content and LC/SOC ratio, whereas they were the lowest after the application of TL. However, SOC and RC contents were significantly higher (P<0.01) after the applications of TL and MS. The correlation analysis indicated the decomposition rate of OMs was positively related with LC content and LC/SOC ratio. In addition, lignin, polyphenol, WOM (total water-soluble organic matter), WHA (water-soluble humic acid), HSL (humic-like substance) and HAL (humic acid-like) contents in initial OMs played important roles in SOC and RC. In-situ nylon mesh bags burying experiment indicated the decomposition rates of CM, SM and MS were significantly higher than those of MR, FG, and TL. Furthermore, MS could result in more lignin derivatives, WHA, and HAL polymers in shorter time during the decomposition process. In conclusion, the application of MS in the semi-arid soil under a long-term plastic mulch and drip irrigation condition could not only improve soil fertility, but also enhance soil carbon sequestration.

提交时间: 2017-12-18 来自合作期刊:《Journal of Arid Land》 点击量39下载量36 评论 0

8. chinaXiv:201712.00323 [pdf]

Effects of long-term cultivation practices and nitrogen fertilization rates on carbon stock in a calcareous soil on the Chinese Loess Plateau

Chen, Zhujun
分类: 地球科学 >> 地球科学史

Soil organic carbon (SOC) and soil inorganic carbon (SIC) are important C pools in the Loess Plateau of Northwest China, however, variations of SOC and SIC stocks under different cultivation practices and nitrogen (N) fertilization rates are not clear in this area. A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices, i.e., fallow (FA), conventional cultivation (CC), straw mulch (SM), and plastic film-mulched ridge and straw-mulched furrow (RF), in combination with three N fertilization rates, i.e., 0 (N0), 120 (N120), and 240 (N240) kg N/hm2. Results indicate that the crop straw addition treatments (SM and RF) increased the contents of soil microbial biomass C (SMBC) and SOC, and the SOC stock increased by 10.1%–13.3% at the upper 20 cm soil depth in comparison to the 8-year fallow (FA) treatment. Meanwhile, SIC stock significantly increased by 19% at the entire tested soil depth range (0–100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment, particularly at the upper 60 cm soil depth. Furthermore, moderate N fertilizer application (120 kg N/hm2) increased SOC stock at the upper 40 cm soil depth, whereas SIC stock decreased as the N fertilization rate increased. We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.

提交时间: 2017-12-18 来自合作期刊:《Journal of Arid Land》 点击量39下载量36 评论 0

9. chinaXiv:201712.00324 [pdf]

Determinants and rates of land degradation: Application of stationary time-series model to data from a semi-arid environment in Kenya

Mganga, Kevin; Nyariki, Dickson
分类: 地球科学 >> 地球科学史

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.

提交时间: 2017-12-18 来自合作期刊:《Journal of Arid Land》 点击量40下载量37 评论 0

10. chinaXiv:201712.00325 [pdf]

Reconstruction of hydrological changes based on tree-ring data of the Haba River, northwestern China

Zhang, Tongwen; Yuan, Yujiang
分类: 地球科学 >> 地球科学史

Reconstructing the hydrological change based on dendrohydrological data has important implications for understanding the dynamic distribution and evolution pattern of a given river. The widespread, long-living coniferous forests on the Altay Mountains provide a good example for carrying out the dendrohydrological studies. In this study, a regional composite tree-ring width chronology developed by Larix sibirica Ledeb. and Picea obovata Ledeb. was used to reconstruct a 301-year annual (from preceding July to succeeding June) streamflow for the Haba River, which originates in the southern Altay Mountains, Xinjiang, China. Results indicated that the reconstructed streamflow series and the observations were fitting well, and explained 47.5% of the variation in the observed streamflow of 1957–2008. Moreover, floods and droughts in 1949–2000 were precisely captured by the streamflow reconstruction. Based on the frequencies of the wettest/driest years and decades, we identified the 19th century as the century with the largest occurrence of hydrological fluctuations for the last 300 years. After applying a 21-year moving average, we found five wet (1724–1758, 1780–1810, 1822–1853, 1931–1967, and 1986–2004) and four dry (1759–1779, 1811–1821, 1854–1930, and 1968–1985) periods in the streamflow reconstruction. Furthermore, four periods (1770–1796, 1816–1836, 1884–1949, and 1973–1997) identified by the streamflow series had an obvious increasing trend. The increasing trend of streamflow since the 1970s was the biggest in the last 300 years and coincided with the recent warming-wetting trend in northwestern China. A significant correlation between streamflow and precipitation in the Altay Mountains indicated that the streamflow reconstruction contained not only local, but also broad-scale, hydro-climatic signals. The 24-year, 12-year, and 2.2–4.5-year cycles of the reconstruction revealed that the streamflow variability of the Haba River may be influenced by solar activity and the atmosphere–ocean system.

提交时间: 2017-12-18 来自合作期刊:《Journal of Arid Land》 点击量35下载量32 评论 0

12345678910  尾页  转到  [42 页/ 414 条记录]