Analysis of noble gases in water using a quadrupole mass spectrometer in static mode   总被引：1，自引：0，他引：1  

Jason C. Poole  Gavin W. McNeill  Stephen R. Langman  Frank Dennis 《Applied Geochemistry》1997,12(6):707-714

A quadrupole-based mass spectrometer used in static mode has been employed to determine noble gas concentrations of water samples by isotope dilution. Water samples are degassed and spiked with minor isotopes of each noble gas. After separation of the various gas components, the isotopic ratios are measured in the mass spectrometer. Because a spike is added to each sample, the recovery of each gas component does not have to be quantitative. Equilibration temperatures are calculated from the gas concentrations, based on noble gas solubility data. An accuracy of ±1°C, from the air equilibration temperature, is attainable for air-saturated water samples prepared under controlled conditions in the laboratory. The method has been applied to groundwaters from the London Basin Chalk aquifer. The noble-gas-derived temperatures are consistent with climatic conditions prevailing at the periods of recharge.  相似文献   

Isotopic and noble gas study of Chalk groundwater in the London Basin, England     

Frank Dennis  John N. Andrews  Andrew Parker  Jason Poole  Manfred Wolf 《Applied Geochemistry》1997,12(6):763-773

The chemical and isotopic composition of groundwater from 52 sites in the London (U.K.) area was determined as part of a project aimed at assessing the spatial variation in the age of Chalk groundwater, and in determining the relationship between fracture and matrix groundwater in this dual porosity system.Systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes. These processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation-reduction reactions, gypsum dissolution and saline intrusion. As a result of the above processes, Chalk groundwater follows an evolutionary path from Ca bicarbonate type to Na bicarbonate type.The age of Chalk groundwater was modelled using¹⁴C, δ¹³C,³H, δ²H and δ¹⁸0. There is a general increase in the groundwater age in a downgradient direction with the oldest water found in N central areas of the basin. Groundwater in the unconfined zones and in areas S of the Greenwich fault is almost entirely of unevolved, modem composition. Carbon-14 modelling suggests that Chalk groundwater in the S basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old. The presence of³H in concentrations of up to 7 TU in groundwater which yields ages of several 1000 a, however, indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer. Results of palaeorecharge temperature determinations using δ²H, δ¹⁸0 and noble gas analytical results suggest that significant Devensian recharge did indeed occur in the aquifer.A model of the development of the Chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system. The upper 50 m of the aquifer was flushed with fresh water during the 2–3 × 10⁶ a of the Quaternary and therefore meteoric water largely replaced the Tertiary and Cretaceous marine water that previously saturated the system. Most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high. Although fracture flow dominates the flow regime, diffusion from the matrix into the fracture porosity controls the chemistry of Chalk groundwater.  相似文献   

无锡城市制造业企业区位调整与苏南模式重组   总被引：1，自引：3，他引：1  

袁丰  魏也华  陈雯  郭垚 《地理科学》2012,(4):401-408

苏南地域广阔,区域和城市发展路径多样。较多研究关注全球化背景下国家和省级开发区发展带来的苏南模式创新,但是城市化对苏南模式重组影响同样值得关注。基于企业数据的空间分析以及企业访谈和问卷调查资料,从制造业企业进入和退出的角度,考察无锡市南长区在从乡镇企业典型发育地区(郊区)转变为城区过程中的产业升级和空间格局调整过程。研究表明:南长区制造业经历了产权重组、结构重组和空间重组三个过程,呈现出中小高新技术企业为主、空间上高度集中等城市化特征。政府表现出明显的"企业化"倾向,与传统苏南模式中直接介入企业经营不同,地方政府通过规划调控以及开发区建设、税收等金融刺激政策和措施影响企业区位行为,从而推动城市产业结构的转型升级和空间再集聚。  相似文献   

Geophysical constraints on deep weathering and water storage potential in the Southern Sierra Critical Zone Observatory   总被引：1，自引：0，他引：1       下载免费PDF全文

W. Steven Holbrook  Clifford S. Riebe  Mehrez Elwaseif  Jorden L. Hayes  Kyle Basler‐Reeder  Dennis L. Harry  Armen Malazian  Anthony Dosseto  Peter C. Hartsough  Jan W. Hopmans 《地球表面变化过程与地形》2014,39(3):366-380

The conversion of bedrock to regolith marks the inception of critical zone processes, but the factors that regulate it remain poorly understood. Although the thickness and degree of weathering of regolith are widely thought to be important regulators of the development of regolith and its water‐storage potential, the functional relationships between regolith properties and the processes that generate it remain poorly documented. This is due in part to the fact that regolith is difficult to characterize by direct observations over the broad scales needed for process‐based understanding of the critical zone. Here we use seismic refraction and resistivity imaging techniques to estimate variations in regolith thickness and porosity across a forested slope and swampy meadow in the Southern Sierra Critical Zone Observatory (SSCZO). Inferred seismic velocities and electrical resistivities image a weathering zone ranging in thickness from 10 to 35 m (average = 23 m) along one intensively studied transect. The inferred weathering zone consists of roughly equal thicknesses of saprolite (P‐velocity < 2 km s^?1) and moderately weathered bedrock (P‐velocity = 2–4 km s^?1). A minimum‐porosity model assuming dry pore space shows porosities as high as 50% near the surface, decreasing to near zero at the base of weathered rock. Physical properties of saprolite samples from hand augering and push cores are consistent with our rock physics model when variations in pore saturation are taken into account. Our results indicate that saprolite is a crucial reservoir of water, potentially storing an average of 3 m³ m^?2 of water along a forested slope in the headwaters of the SSCZO. When coupled with published erosion rates from cosmogenic nuclides, our geophysical estimates of weathering zone thickness imply regolith residence times on the order of 10⁵ years. Thus, soils at the surface today may integrate weathering over glacial–interglacial fluctuations in climate. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Economic development,urban expansion,and sustainable development in Shanghai   总被引：2，自引：1，他引：1  

Wenze Yue  Peilei Fan  Yehua Dennis Wei  Jiaguo Qi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(4):783-799

Studies of urbanization effects in Chinese cities from the aspect of the coupled development of economy and environment are rare due to data limitations. This paper studied Shanghai’s fast urban expansion and examined the dynamic relationship between economic growth and environment consequences at the district level. We extracted data on urban built-up area and land surface temperature from remote sensing images. We analyzed the patterns of urban expansion and land use change and explained the dynamic relationship between economic development and environment conditions. We attributed the uneven economic development and environmental change in districts of Shanghai to four main institutional factors: (1) the role of the government, (2) the multi-level urban planning system, (3) land market reform, and (4) the economic restructuring.  相似文献   

Spatiotemporal dynamics of carbon intensity from energy consumption in China   总被引：6，自引：2，他引：4  

Yeqing Cheng  Zheye Wang  Xinyue Ye  Yehua Dennis Wei 《地理学报(英文版)》2014,24(4):631-650

The sustainable development has been seriously challenged by global climate change due to carbon emissions. As a developing country, China promised to reduce 40%-45% below the level of the year 2005 on its carbon intensity by 2020. The realization of this target depends on not only the substantive transition of society and economy at the national scale, but also the action and share of energy saving and emissions reduction at the provincial scale. Based on the method provided by the IPCC, this paper examines the spatiotemporal dynamics and dominating factors of China’s carbon intensity from energy consumption in 1997–2010. The aim is to provide scientific basis for policy making on energy conservation and carbon emission reduction in China. The results are shown as follows. Firstly, China’s carbon emissions increased from 4.16 Gt to 11.29 Gt from 1997 to 2010, with an annual growth rate of 7.15%, which was much lower than that of GDP (11.72%). Secondly, the trend of Moran’s I indicated that China’s carbon intensity has a growing spatial agglomeration at the provincial scale. The provinces with either high or low values appeared to be path-dependent or space-locked to some extent. Third, according to spatial panel econometric model, energy intensity, energy structure, industrial structure and urbanization rate were the dominating factors shaping the spatiotemporal patterns of China’s carbon intensity from energy consumption. Therefore, in order to realize the targets of energy conservation and emission reduction, China should improve the efficiency of energy utilization, optimize energy and industrial structure, choose the low-carbon urbanization approach and implement regional cooperation strategy of energy conservation and emissions reduction.  相似文献   

Dust ejection from planetary bodies by temperature gradients: Laboratory experiments     

Thorben Kelling  Gerhard Wurm  Miroslav Kocifaj  Jozef Klačka  Dennis Reiss 《Icarus》2011,212(2):935-940

Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/m² and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. This leads to the production of dust which can then be transported towards the disk edge or the outer disk regions. The generated dust might constitute a significant fraction of the warm dust observed in extrasolar protoplanetary disks. We estimate erosion rates of about 1 kg s^?1 for 100 m parent bodies. The dust might also contribute to subsequent planetary growth in different locations or on existing protoplanets which are large enough not to be susceptible to particle loss by light induced ejection. Due to the ejections, planetesimals and smaller bodies will be accelerated or decelerated and drift outward or inward, respectively. The effect might also explain the entrainment of dust in dust devils on Mars, especially at high altitudes where gas drag alone might not be sufficient.  相似文献   

Ultraviolet spectroscopy of Asteroid (4) Vesta     

Jian-Yang Li  Dennis Bodewits  Lori M. Feaga  Wayne Landsman  Michael F. A’Hearn  Max J. Mutchler  Christopher T. Russell  Lucy A. McFadden  Carol A. Raymond 《Icarus》2011,216(2):640-649

We report a comprehensive review of the UV–visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift Gamma-ray Burst Observatory with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm are derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope as measured between 240 and 320 nm in the ultraviolet displays a sharp minimum near a sub-Earth longitude of 20°, and maximum in the eastern hemisphere. This is consistent with the longitudinal distribution of the spectral slope in the visible wavelength. The photometric uncertainty in the ultraviolet is ∼20%, and in the visible wavelengths it is better than 10%. The amplitude of Vesta’s rotational lightcurves is ∼10% throughout the range of wavelengths we observed, but is smaller at 950 nm (∼6%) near the 1-μm band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/near-infrared lightcurves with respect to sub-Earth longitude. Vesta’s average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible, and near-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies a lack of global space weathering on Vesta, as previously inferred from visible–near-infrared data.  相似文献   

Trust in the fisheries scientific community     

Helen Glenn  Diana TingleySonia Sánchez Maroño  Dennis HolmGurpreet Padda  Ingi Runar EdvardssonAlexis Conides  Kostas KapirisMintewab Bezabih  Premachandra WattageSakari Kuikka 《Marine Policy》2012,36(1):54-72

This paper explores the issue of “trust” in the fisheries science community, a key corollary of effective risk communication. It presents the findings of a survey undertaken in Iceland, Greece, Spain, United Kingdom and Faroe Islands during 2008. The findings reveal differing levels of trust and mistrust in the fisheries science community between countries and between stakeholder groups, demonstrating areas for future attention in the interests of improving fisheries science and management. As this paper explores, unfortunately the “trust” necessary for effective stakeholder cooperation and participation within current fisheries science is currently somewhat lacking. The cited reasons behind this lack of trust include: a lack of soundness, credibility, responsiveness, flexibility and stakeholder involvement, flawed data and weak science, poor communications and political and lobby group interference. Notable from the results is a lack of consensus on the existence of a common language and vision. It is evident, however, that certain aspects of fisheries science are strong contributors to trust and that there are opportunities for improvement.  相似文献   

苏州市区信息通讯企业空间集聚与新企业选址   总被引：21，自引：0，他引：21  

袁丰  魏也华  陈雯  金志丰 《地理学报》2010,65(2):153-163

高科技产业是全球化背景下城市发展与区域竞争的关键,但是高科技产业发展空间极不平衡,空间要素显著影响高科技企业区位选择及空间集聚。针对现有研究主要集中在国家、省等大尺度单元,本文引入空间点模式分析方法,探讨了1996-2006年间苏州市区不同空间尺度上信息通讯企业的时空集聚特征。研究发现:在0~6km的尺度上,信息通讯企业表现出明显的集聚特征,并随着尺度的增加呈现出倒"U"型集聚趋势;随着时间的推移,企业空间集聚的"热点地区"逐渐从老城区向外围推移,但是集聚峰区依然主要分布在老城区及其外围的国家和省级开发区;同时,新企业的选址与原有企业的分布特征表现出很强的相关性。运用计数模型的计量结果也表明企业集聚特征对新企业区位选择具有显著影响,同时起作用的还有地方政府政策影响下的开发区建设、城市内外交通条件、自然环境条件等因素。  相似文献