活动支座摩擦力对简支梁桥地震反应的影响

本文介绍在地震作用下活动支座摩擦力简支梁桥桥墩内力和活动支座外墩,梁相对位 影响,以及水平地震系数,摩擦系数变化对固定支座水平地震荷载的影响。文中建议了考察活动以座摩擦力的简支梁桥整体分析模型。     

1961—2010年山西省极端气温年均发生频率的时空特征分析

利用山西省61个气象站点逐日最高温度、最低温度资料,采用百分位值定义法、Mann原Kendall突变检验法和Morlet小波变换等方法,分析了山西省近50 a极端温度事件年均发生频率的时空特征,结果表明：1961年以来,山西省极端高温事件年均发生频率呈显著增加趋势,趋势为6.1 d/10 a,与此同时,极端低温事件年均发生频率呈显著减少趋势,且极端气温事件的变化存在明显的区域差异;极端高温和极端低温年均发生频率均发生了突变现象,变化趋势均在20世纪90年代以来更加显著;极端高温和极端低温事件年均发生频率均呈显著波动变化,在整个研究期间极端高温存在5～6a、4～8a显著周期,极端低温存在4～5a显著周期。     

Simulating streamflow variability and aquatic states in temporary streams using a coupled groundwater-surface water model

Abstract

In order to apply the EU Water Framework Directive for temporary streams, it is important to quantify the space–time development of different aquatic states. We report on research on the development of aquatic states for temporary streams in the Evrotas basin, Greece. The SIMGRO regional hydrological model was used in a GIS framework to generate flow time series for the Evrotas River and all major tributaries. Five flow phases were distinguished: flood conditions, riffles, connected pools, isolated pools and dry bed conditions. Thresholds based on local hydraulic characteristics were identified per stream reach and flow phase, enabling the frequency of flow phases per month and the average frequencies for all streams to be derived. Three historical scenarios within the 20th century, marking periods of major changes in water management, were investigated. Additionally, a climate scenario for the 2050s was analysed. Simulations revealed that low flows are now much lower, mainly because more groundwater is abstracted for irrigation. The consequence is that stretches of the river fall dry during several months, causing the ecological status to deteriorate.

Editor Z.W. Kundzewicz Associate editor X. Chen     

Governing urban vacancy in post-crash dublin: contested property and alternative social projects

The scale and severity of property crashes following the global financial crisis has made vacancy a more visible and politically significant feature of cities. Although research has focused on urban experiments in vacant spaces, there has been less emphasis on how the contested property relations around vacancy remake urban governance. In this paper, we argue that debates about vacancy have been a central concern in post-crisis urban governance. In the first part of the paper we draw two conceptual approaches into a dialogue and apply them to an analysis of vacant space: that of Nicholas Blomley on property and Elizabeth Povinelli on “alternative social projects”. In the second part of the paper, we critically analyse how three groups discursively construct the need to “activate” and “re-use” vacant spaces in Dublin: grassroots groups, urban policy-makers, and financial actors. We argue that governing vacancy will be a key feature of post-crisis urbanisation.     

Regulating migration to Australia and back to the Philippines: Applying a ‘diaspora strategies’ framework

This paper examines circular labour migration between Australia and the Philippines by bringing Australian immigration policies and Philippine diaspora strategies under the same analytical framework. An extensive Philippine bureaucracy regulates migrants at each stage of the circular migration cycle, and as a sending state it has an interest in migrants staying temporarily in host countries such as Australia. The requirement to return home at the end of an overseas work contract compels migrants to remain attached to the sending state, their homeland, and return subsequently. However, Australia is allowing a route for temporary migrants to apply for permanent residency while in the host country. This has implications for sending states that rely on migrant ties to the homeland. The paper argues that analysing the intersections between the themes of migration, development and diaspora strategies reveals the multiple meanings of temporariness during migration and in migration studies. It questions whether associating temporariness with precariousness and marginalization is an accurate representation of the complex conditions underpinning circular labour migration.     

China's Permanent and Temporary Migrants: Differentials and Changes, 1990–2000

A unique feature of migration in China is its two-track system, one consisting of permanent migration and temporary migration. This article examines whether and how hukou reforms and the maturation of migration streams since the 1980s have changed the two-track system. Using data on interprovincial migration from the 1990 and 2000 censuses, our empirical analysis focuses on the differentials between permanent migrants and temporary migrants and their changes over time. We document the size, migration reasons, and selectivity of migrants, and we evaluate the determinants of the dichotomy between permanent migrants and temporary migrants via logistic regression models. Our findings show that between 1990 and 2000 the gaps between interprovincial permanent migrants and temporary migrants did not narrow but in most aspects had widened. There is little evidence that hukou reforms have lowered the barriers to urban citizenship. At the same time, a larger spectrum of the rural population has joined the temporary migration streams. The net result is a persistence of the two-track migration system, where permanent migrants increasingly assume the position of social and economic elites and temporary migrants are the disadvantaged and disenfranchised.     

利用超导重力数据探测内核超速旋转的研究

内核存在约(0.27°~0.53°)/a的超速旋转,由此导致的全球年平均重力变化强度约为0.08~0.16μGal(0.8~1.6 nms-2)。除地震数据外,时变重力数据有可能成为探测内核超速旋转速率的重要信息源。对武汉九峰台站超导重力仪观测数据进行了潮汐改正、大气负荷改正、极移改正和日长变化改正,得到了经过各项改正后的时变重力信号;采用小波分析方法对上述时变重力信号进行了处理分析,得到了可供参考的结果;针对目前利用超导重力仪数据探测内核超速旋转所存在的困难提出了几个解决方案和建议。     

Bidirectional stream–groundwater flow in response to ephemeral and intermittent streamflow and groundwater seasonality

It is often assumed that the net groundwater flow direction is towards the channel in headwater streams in humid climates, with magnitudes dependent on flow state. However, studies that characterize stream–groundwater interactions in ephemeral and intermittent streams in humid landscapes remain sparse. Here, we examined seasonally driven stream–groundwater interactions in response to temporary streamflow on the basis of field observations of streamflow and groundwater on an adjacent hillslope. The direction of hydraulic head gradients between the stream and groundwater shifted seasonally. The stream gained water (head gradients were towards the stream) when storage state was high. During this period, streamflow was persistent. The stream lost water to the groundwater system (head gradients were away from the stream) when storage state was low. During this period, streamflow only occurred in response to precipitation events, and head gradients remained predominantly away from the stream during events. This suggested that mechanisms other than deep groundwater contributions produced run‐off when storage was low, such as surface and perched subsurface flowpaths above the water table. Analysis of the annual water balance for the study period showed that the residual between precipitation inputs and streamflow and evapotranspiration outputs, which were attributed to the loss of water to the deeper, regional groundwater system, was similar in magnitude to streamflow. This, coupled with results that showed bidirectionality in stream–groundwater head gradients, indicated that headwaters composed of temporary (e.g., ephemeral and intermittent) streams can be important focal areas for regional groundwater recharge, and both contribute to and receive water, solutes, and materials from the groundwater system.     

国家主体功能区战略背景下东北地区城市经济增长的动力与路径——基于城市暂住人口视角

经济、人口、资源与环境的协调发展是新型城市化战略的核心,也是国家主体功能区规划的重要内容。鉴于各类主体功能区在东北地区并存,考察其经济增长与城市化开发路径,可为全国提供较好借鉴。以东北地区城市暂住人口为切入点,探讨了城市暂住人口与经济增长相互影响的作用机制,进而构建暂住人口与经济增长联立方程,并使用东北地区34个地级城市的面板数据进行实证分析,考量以暂住人口吸纳与承载能力为标志的城市化潜力与经济增长的动力。研究表明:在国家主体功能区战略背景下,需充分尊重和考虑东北地区各类开发区域与城市的经济、社会、自然与生态状况,应通过中心城市产业结构调整、生态功能区人口迁出等途径进行集中均衡式的城市化开发,积极加快推进基本公共服务均等化和城市内部基础设施完善。     

海湾扇贝大水体人工育苗的高产技术

本文论述了海湾扇贝大水体人工育苗的高产技术和亲贝暂养、幼体培育,海上育成等的有关技术环节。并提出在相同的管理条件下,采用网箱暂养亲贝比网笼成活率提高14％,产卵时间提前5天,孵化率提高15％,幼体选育应及时进行。且在相同的孵化条件下下,产卵后26小时倒池比30小时后倒池成活率可提高38％,饵料投喂应坚持勤投、少投和混合投喂原则。在一定量的投饵条件下,日投10次比日投3次成活率高70％以上。但海上疏苗密度不宜过大,以每袋1000～2000个稚贝为宜。