三塔自锚式悬索桥动力特性及影响参数分析

以某三塔自锚式悬索桥为工程背景,建立三维有限元模型,通过调整缆索初应变确定恒载作用下的成桥线形,基于静力平衡状态进行模态分析得到三塔自锚式悬索桥的振型及频率。结构动力特性影响参数分析表明:主缆抗拉刚度、加劲梁竖向弯曲刚度、桥面恒载集度、矢跨比等参数对结构动力特性影响较大。     

改革开放以来珠江三角洲地理研究：回顾及展望

改革开放以来,珠江三角洲经济发展取得了举世瞩目的成就,这引起了包括地理学等在内的多学科研究的热潮,地理视角的研究成果层出不穷。本文首先对珠江三角洲地理研究进行总结,核心研究主题有传统经济地理分析;城市发展与城市化;产业转移、升级与结构调整;区域合作与协调;社会空间研究;区域人口研究;区域规划与管治;土地、环境、生态与文化保护。最后,对未来珠江三角洲地理研究进行展望,归纳3个研究热点：区域协调与可持续发展研究;区域社会与文化研究;全球化背景下区域响应研究。     

A case study of long-term field performance of check-dams in mitigation of soil erosion in Jiangjia stream,China

This paper examines the long-term field performance of the check-dams in mitigation of soil erosion in the Duozhao catchment of Jiangjia stream, southwest China. Since their construction between 1979 and 1982, the check-dams have been functioning effectively. The examination is made via comparisons between the environmental conditions of the Duozhao catchment with its adjacent Menqian catchment in the stream, because no check dams were constructed in the Menqian catchment. The examination is based on recent field investigations and aerial photograph analyses, and covers four aspects: (a) bed gradients of catchment channels; (b) stability of bank slopes; (c) rates of land erosion; and (d) vegetations on bank slopes. The field data demonstrate that the check-dams have had the following good functions for mitigation of soil erosion: (1) restricting the channel depth and lateral erosions, (2) protecting the channel erosion base, (3) reducing the bed gradients of debris-flow channels, (4) fixing the channel bed, (5) stabilizing the bank slopes, as well as (6) facilitating the growth of vegetations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Crustal anisotropy in southwest Ireland from analysis of controlled source shear-wave data

Results from a travel-time analysis of three-component shear-wave (S-wave) data recorded in southwest Ireland during a controlled source seismic experiment have been used to investigate the magnitude of crustal anisotropy. The data used were recorded from 20 in-line shots on three-component short-period stations deployed at approximately 1-km spacing along two parallel profiles. Analysis of the travel-time differences between vertically and horizontally polarised S-waves recorded on vertical, radial and transverse seismometer components was undertaken using seismic phases travelling near the Earth's surface (S_g) and reflected from the Moho (S_mS). Travel-time differences between the components for both phases scatter largely within the range ± 0.2 s, which is about the uncertainty in the measurements, with no observed coherent variation with shot-receiver offset. Synthetic S-wave seismograms were also computed from 1-D S-wave velocity models with varying degrees of anisotropy in the upper and in the lower crusts. Travel-time differences of S_g and S_mS phases picked from these synthetic seismograms confirm that for anisotropies with probable symmetries of magnitude 1–2% in either the upper or lower crust should result in an observable variation of the travel-time differences between the transverse and radial, and transverse and vertical components with source–receiver offset. The study shows that crustal anisotropy does not contribute significantly to the marked anisotropy recently deduced from SKS and SKKS measurements in Ireland, which is therefore confirmed to reside at sub-crustal and deeper mantle levels.     

Two anisotropic layers in the Slave craton

Four years of recording global earthquakes using a broadband seismometer located at the Ekati diamond mine revealed variations with earthquake azimuth in the arrival of SKS phases. These variations can be modeled assuming two distinct layers of anisotropy in the lithosphere. The lower layer probably lies in the mantle, and the anisotropy aligns with both North American plate motion and the strike of mantle structures identified by previous conductivity and geochemical analyses, at ˜N50°E. The upper layer is hypothesized to result from regional structures in the uppermost mantle and the crust; these trends are distinct from the mantle trends.     

On the use of the autocorrelation method for estimating the depth to the magnetic basement

The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4.     

China's role in attaining the global 2°C target

In the recent climate change negotiations it was declared that the increase in global temperature should be kept below 2°C by 2100, relative to pre-industrial levels. China's CO₂ emissions from energy and cement processes already account for nearly 24% of global emissions, a trend that is expected to keep increasing. Thus the role of China in global GHG mitigation is crucial. A scenario analysis of China's CO₂ emissions is presented here and the feasibility of China reaching a low-carbon scenario is discussed. The results suggest that recent and continued technological progress will make it possible for China to limit its CO₂ emissions and for these emissions to peak before 2025 and therefore that the global 2°C target can be achieved.

Policy relevance

In signing the Copenhagen Accord, China agreed to the global 2°C target. Results from this article could be used to justify low-carbon development policies and negotiations. While many still doubt the feasibility of a low-carbon pathway to support the global 2°C target, the results suggest that such a pathway can be realistically achieved. This conclusion should increase confidence and guide the policy framework further to make possible China's low-carbon development. Related policies and measures, such as renewable energy development, energy efficiency, economic structure optimization, technology innovation, low-carbon investment, and carbon capture and storage (CCS) development, should be further enhanced. Furthermore, China can play a larger role in the international negotiations process. In the global context, the 2°C target could be reaffirmed and a global regime on an emissions mitigation protocol could be framed with countries’ emissions target up to 2050.     

Abyssal geography†

Today, we are held to live in the Anthropocene, bringing to an end modern binary imaginaries, such as the separation between Human and Nature, and with them Western assumptions of progress, linear causality and human exceptionalism. Much Western critical theory, from new or vital materialism to post- and more-than-human thinking, unsurprisingly reflects this internal crisis of faith in Eurocentric or Enlightenment reasoning. At the same time, a radically different critique of modernity has gained prominence in recent years, emerging from critical Black studies, which places the Caribbean at the centre of the development of a new and distinct mode of critical thought. In attempting to grasp the ways in which Caribbean thought and practice have been seen to enable a distinctive alternative non-Eurocentric imaginary, this paper heuristically sets out a paradigmatic framing of ‘abyssal geography’. We emphasize two key points. The first is that abyssal thought is not grounded in abstract and timeless philosophical assumptions but figuratively draws upon aspects of Caribbean practices of resistance and survival, for example, from the Middle Passage, Plantation, carnival, creolization, dance forms and speculative fiction. The second is that abyssal work engages the legacies of modernity and coloniality by explicitly seeking to question the lure of ontology: seeking to disrupt, suspend and to problematize the modern project of the human and the world.     

Magnetometer array studies in India: Present status,data interpretation and assessment of numerical modelling results

Significant results from several array of magnetometers deployed in India to probe deep geoelectrical structures of the crust and the upper mantle are reviewed in this paper. Emphasis is on critical appraisal of earlier results so that the article summarizes what has been done so far and what caution is to be taken on future work. Two large-scale arrays over northwest and peninsular India during 1979–80, have been followed up with six more linear or two-dimensional arrays over different parts of the country. “Trans-Himalayan” conductor aligned along the strike of Aravalli range, delineated by arrays over northwest India, essentially represents one of the major continental induction anomalies mapped by electromagnetic methods. Efforts for quantifying the induction effects through numerical models are shown to be constrained due to the large inter-station spacing, lack of information on the regional background conductivity distribution and the non-inclusion of the frequency dependence of induction effects. A more comprehensive modelling, not biased by these factors, enables approximating the Trans-Himalayan conductor as an asymmetric domal upwarp in the middle and lower crust located between Delhi-Hardwar ridge and Moradabad fault. Numerical modelling results for southern peninsular, despite the constraints, indicate that the strong and complex induction pattern can be adequately attributed to the combination of conductors connected with triple junction between Indo-Ceylon Graben, Comorin ridge and the west coast rifting. Induction features derived from the Valsad array, operated over basalt-covered region of western India, demarcate an enhanced conducting zone beneath Plume-associated triple junction in the Gulf of Cambay, apart from characterizing the presently active seismic zone as a resistive block.     

Common features and different trajectories of land cover changes in six Western Mediterranean urban regions

Land use and land cover change (LULCC) dynamics have been particularly strong in the Mediterranean region, due to its historical development and to agro-pedoclimatic conditions favorable to human settlement. This area has undergone in the 1950s and the 1980s intense urbanization processes that has followed different trajectories. Urban expansion commonly occurs at the expense of agricultural land, leading to the fragmentation of natural areas and conflicts over access to land resources. These dynamics mainly concern the fringe between urban and agricultural land, e.g. the peri-urban areas usually included within functional urban regions. Here, to identify common features of LULCC in Western Mediterranean urban regions, we investigated two main features: direct changes due to urbanization and indirect changes affecting non-artificial land uses. We compared LULCC dynamics in 6 case studies from the north and south of the Western Mediterranean region: the urban regions of Montpellier and Avignon (France), Pisa (Italy), Madrid (Spain), Meknes (Morocco), and Constantine (Algeria), using a 30-year multitemporal spatial analysis (1980–2010). Two series of Landsat TM images were acquired for each case study and land cover data were analyzed both for dynamics and for land patterns, using landscape and class metrics. We found no significant north-south differences in LULCC dynamics between the investigated Western Mediterranean urban regions. Differences are more pronounced between small–medium cities and large metropolitan areas in type of urban diffusion, which is more sprawled in small–medium cities and more compact in large metropolitan areas. Rather, differences occur in LULCC not directly affected by urbanization, since in Northern Mediterranean urban regions afforestation and abandonment of agricultural areas are prevalent and closer to the urban areas, whereas transformation of natural areas into agricultural ones occurs mainly in Southern Mediterranean urban regions at a similar distance from urban areas than it happens for afforested or abandoned areas. In attempting for the first time to assess LULCC in these Mediterranean urban regions, we provide a preliminary comprehensive analysis that can contribute to the active LULCC research in the Mediterranean basin and that can be easily applied to other Mediterranean urban regions.