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21.
Reliable chronological frameworks are crucial to paleoenvironmental studies, and high precision 14C dating is the foundation, but many factors, such as dating materials, surficial deposition (influenced by nuclear bomb), and the 14C age plateau, will affect the reliability of the 14C ages and chronology frameworks. In this paper, we present 87 14C dates of different peat fractions from three peat sites in Xinjiang, China. Plant macrofossils, rootlets, the fine fraction of <90 μm, the mid-size fraction of 90–250 μm and the coarse fraction of >250 μm from selected peat samples were measured to investigate the alternative suitable fraction for dating except for plant macrofossils. We discovered that the 90–250 μm component of peat can provide alternative and reliable results in case of plant macrofossils are not available. Additionally, more dating samples from surficial peat deposition were collected, and accurate surface chronological control points were produced by comparing 14C results of plant macrofossils with atmospheric 14C bomb data. Furthermore, multiple data sets with wiggle matching were used along the radiocarbon age plateau to minimize calibrated errors when dates on the 14C age plateau were shown. Finally, radiocarbon chronology frameworks in peat profiles were optimized. In conclusion, we not only focus on the reliable dating materials, but also highlight that the importance of surficial deposition (after 1950AD) and the anomalous 14C dates when establishing the dating framework in peat profiles. Furthermore, we propose that the obtaining chronological control points of surficial peat is an important part of the establishing and improving of peat chronological framework in future research. 相似文献
22.
Andrew Finlayson Emrys Phillips Ívar Örn Benediktsson Lucas K. Zoet Neal R. Iverson Jez Everest 《地球表面变化过程与地形》2019,44(1):367-380
The interaction between drumlins and overriding glacier ice is not well studied, largely due to the difficulty of identifying and accessing suitable active subglacial environments. The surge-type glacier Múlajökull, in central Iceland, overlies a known field of actively forming drumlins and therefore provides a rare opportunity to investigate the englacial structures that have developed in association with ice flow over the subglacial drumlins. In this study detailed ground-penetrating radar surveys are combined with field observations to identify clear sets of up-glacier and down-glacier dipping fractures at Múlajökull's margin. These are interpreted as conjugate shear planes or P- and R-type Reidel shears that developed and filled with saturated sediment derived from the glacier bed, during a previous surge. The fracture sets exhibit focused spatial distributions that are influenced by the subglacial topography. In particular, down-glacier dipping fractures are strongly focused over drumlin stoss slopes. These fractures, although well developed at depth, were mostly unable to transmit basal water and sediment up to the glacier surface during the surge cycle. In contrast, up-glacier dipping fractures formed over drumlin lee sides and in more gently sloping swales, and more frequently connected to the glacier surface, providing a pathway for the evacuation of basal water and water-saturated sediment. The study suggests that the subglacial drumlins under Múlajökull's margin have influenced the nature and distribution of englacial fractures, which could potentially contribute to spatial variations in basal water pressure during a surge. BGS © UKRI 2018 相似文献
23.
Karen Friese Andrzej Grzechnik Emil Makovicky Tonči Balić-Žunić Sven Karup-Møller 《Physics and Chemistry of Minerals》2008,35(8):455-465
Rietveld refinement of X-ray synchrotron data was performed for two synthetic tetrahedrite samples, with 0.61 and 1.83 Fe atoms, and two synthetic tennantite samples with 0.10 and 1.23 Fe atoms p.f.u. M12(Sb,As)4S13. Measurements were performed at 25 and 250°C. For both the phases, increased Fe substitution is reflected in the increased tetrahedral ‘Cu1’–S distance (‘Cu1’ is a site of Fe substitution) and Cu2–S distances. Cu2 was refined as a split position; the Cu2–Cu2 split about the plane of the S12S2 triangle is about 0.56 and 0.65 Å for tetrahedrite and tennantite, respectively. Cu2–Cu2 distances in the structure cavity are 2.8–2.9 Å. Between 25 and 250°C, the lattice parameter a increased by 0.02–0.04 Å and the interatomic distances by 0.01 Å on an average. Thermal expansion coefficients of little-substituted samples are similar to those of unsubstituted samples, whereas thermal expansion appears to decrease with increasing substitution by Fe. The Cu2–Cu2 split increases at 250°C by about 0.1 Å for tetrahedrite and by more than 0.15 Å for tennantite but the cage expansion is minimal so that the Cu2–Cu2 distances in the cavity decrease with temperature. Difference Fourier maps indicate that there is little residual electron density left between the two Cu2 half-sites in tetrahedrite but this inter-site density is substantially higher in tennantite. It increases with temperature, especially in the little-substituted tennantite sample. 相似文献
24.
With the explosive growth of Uber and other mobility service providers, their influences on urban mobility have attracted attention from both researchers and policy circles alike, yet few quantitative studies have been conducted on the topic. Using Uber pickup data in New York City in 2014, this article investigates the spatiotemporal relationship between Uber and public transit using buffer analysis and spatial cross-correlation analysis and assesses Uber’s impact on urban transportation equity with the Gini coefficient and correlation analysis. Our results confirm previous arguments that Uber both complements and competes with public transit, but competition is more prevalent in New York City. Specifically, Uber competes with public transit during most hours of the day and in areas with good public transit coverage, whereas it complements public transit at midnight and in places with insufficient public transit services. The distribution of Uber services is highly unequal, and Uber’s role in improving transport equity is insignificant. Correlation analysis shows that there tend to be fewer Uber pickups in low-income areas, which diverges from previous studies suggesting that Uber serves low-income areas well. In addition, a weak negative correlation is detected between the number of Uber pickups and the percentage of minorities. 相似文献
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26.
张倩倩 《测绘科学技术学报》2015,(5):455-459
讨论了如何提高单星座增强型接收机自主完好性监测ARAIM算法的可用性问题。借助于钟差辅助模型设计了一种能够用于垂直精密进近LPV-250服务的单星座ARAIM算法。将钟差预测值作为虚拟伪距观测值纳入到当前的定位解算中,以提高单星座ARAIM算法的可用性。设计了新的完好性风险配置方案,在计算用户保护水平时,通过直接计算故障偏差对定位误差的影响大小来解决未知故障偏差的估计问题,对于系统的可用性给出了更精确的评定。试验分析结果表明,钟差辅助对于提高单星座ARAIM算法的可用性具有显著的作用。 相似文献
27.
《The Professional geographer》2013,65(4):487-488
Book Reviewed in this article: Geographical Aspects of Health and Disease in India. Rais Akhtarand A.T.A. Learmonth, eds. Antarctic Treaty System: An Assessment. Proceedings of a Workshop at Beardmore South Field Camp, Antarctica. American Electoral Mosaics. J. Clark Archerand Fred M. Shelley. Kompas op Suidwes-Afrika/Namibie. W.S. Barnard, ed. Jerusalem in the 19th Century: The Old City. Yehoshua Ben-Arieh. The World as a Total System. Kenneth E. Boulding. A Social History of Housing 1815–1985, Second Ed. John Burnett. Human Migration. W.A.V. Clark. Regional Population Projection Models. Andrei Rogers. The State of Population Theory: Forward from Malthus. David Colemanand Roger Schofield, eds. Imagining Tomorrow: History, Technology and the American Future. Joseph C. Corn, ed. Swidden Agriculture in Indonesia: The Subsistence Strategies of the Kalimantan Kantú. Michael R. Dove. Glacial Geologic Processes. David Drewry. Physics of Desertification. Farouk El-Bazand M.H.A. Hassan, eds. Housing the Homeless. Jon Ericksonand Charles Wilhelm, eds. Settlement Patterns in Missouri: A Study of Population Origins, with a Wall Map. Russel L. Gerlach. Desert Development: Man and Technology in Sparselands. Yehuda Gradus, ed. Nuclear Winter. The Evidence and Risks. Owen Greene, Ian Percivaland Irene Ridge. The Take-off of Suburbia and the Crisis of the Central City. Günter Heinritzand Elisabeth Lichtenberger, eds. Regional Input-Output Analysis. Geoffrey J. D. Hewings. Spatial Transportation Modeling. Christian Werner. The Atlas of Georgia. Thomas W. Hodlerand Howard A. Schretter, eds. Latin America. 5th ed. Preston E. Jamesand C.W. Minkel. Applied Remote Sensing. C.P. Lo. Localities, Class, and Gender. The Lancaster Regionalism Group. Urban Social Movements: The City after Castells. Stuart Lowe. Politics and Method. Doreen Masseyand Richard Meegan, eds. Land Use. A. S. Mather. The Kingdom of Coal. Donald L. Millerand Richard E. Sharpless. The Presidio and Militia on the Northern Frontier of New Spain, A Documentary History, Vol. 1: 1570–1700. Thomas H. Naylorand Charles W. Polzer, S.J., comps. andeds. Nuclear Power: Siting and Safety. Stan Openshaw. The Central African Republic: The Continent's Hidden Heart. Thomas O'Toole. Environmental and Dynamic Geomorphology. Márton Pécsi, ed. Remote Sensing Principles and Interpretation. Floyd F. Sabins, Jr. Acid Rain and Friendly Neighbors: The Policy Dispute between Canada and the United States. Jurgen Schmandtand Hilliard Roderick, eds. Earth's Changing Surface: An Introduction to Geomorphology. M.J. Selby. International Migration: The Female Experience. Rita J. Simonand Caroline B. Brettell, eds. On Geography and Its History. D.R. Stoddart. Transportation Networks: A Quantitative Approach. D. Teodorovic. Processes in Physical Geography. R.D. Thompson, A.M. Mannion, C.W. Mitchell, M. Parry, J.R.G. Townshend. Imaging Radar for Resources Surveys. J.W. Trevett. Dominance and Affection: The Making of Pets. Yi-Fu Tuan. Capturing the Horizon. The Historical Geography of Transportation since the Transportation Revolution of the Sixteenth Century. James E. Vance, Jr. Nations at Risk: The Impact of the Computer Revolution. Edward Yourdon. 相似文献
28.
论全国1:250000数据库的建立与更新 总被引：4，自引：0，他引：4
全国l：250000数据库是国家基础地理信息系统的重要组成部分，该数据库于1998年建成，目前已在国家许多部门得到广泛应用。它的设计和建立成功与否直接影响到数据库的使用方便程度和应用方向。同时随着时间的推移和用户使用的不断深入，数据库的更新问题变得越来越重要，国家测绘局于200l～2002年底立项并完成了对l：250000数据库的全面更新工程，使数据库主要要素的现势性达到2000～2002年。基本可以满足现阶段用户的使用需求。本文主要介绍l：250000数据库主要数据内容，数据库设计及建立；数据库更新的各种资料使用、技术流程以及更新数据库的建库等。 相似文献
29.
The concept of geodiversity, which refers to the diversity of abiotic elements of nature, is passing through a period of methodological development. The concept has a great potential of becoming an efficient territorial management tool as the physical environment is the basis in which biodiversity and human societies develop. However, this potential has not yet been achieved because the methodologies of practical application are not consistent enough. This work aimed to contribute to this issue by applying a method of quantitative mapping of geodiversity at a landscape scale and integrating it to an urban growth map in Armação dos Búzios municipality, located in Rio de Janeiro State, Brazil. On the basis of some of the most important previous proposals, a Geodiversity Index Map of Armação dos Búzios was created, which shows the richness and distribution of the elements of geodiversity (geology, geomorphology, soils, and hydrology) throughout the territory. With this product, it was possible to identify the most geodiverse areas of the municipality. After that, an Urban Growth Map of Armação dos Búzios was created by the photointerpretation of aerial photographs from 1976 to 2006, in which the urban areas in both dates were mapped, allowing the observation of how much the urban area grew during this time. By integrating these two maps, we were able to quantify the impacted areas in relation to the geodiversity. The results showed that urbanization impacted a significant portion of the areas classified with high and very high geodiversity indices, highlighting that the physical environment, and consequently the biodiversity, are under serious threat, and it must be taken into account in public policies and territorial management. In addition, this work aimed to contribute to the methodological development of the concept of geodiversity, which still needs more tests and discussions to be improved and widely applied, especially in nature conservation issues. 相似文献