A high‐resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria,England     

Paul M. V. Coombes  Richard C. Chiverrell  Keith E. Barber 《第四纪科学杂志》2009,24(3):224-236

The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo‐Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Flood seasonality and generating conditions in the Tay catchment, Scotland from 1200 to present   总被引：1，自引：0，他引：1  

Lindsey J McEwen 《Area》2006,38(1):47-64

The new maximum recorded river flows in Scotland since 1988 have triggered widespread interest in whether floods are becoming more frequent and in the conditions that generate floods of different magnitudes and frequencies. There are questions about the longer-term variability in flood-generating characteristics, and whether there are past analogues for present hydroclimatic variability. The present paper builds on previous work reconstructing a detailed historic flood chronology for the Tay, the largest catchment in Scotland, and its tributaries over the past 800 years, extending the gauged discharge record (1952 onwards). It categorizes flood-generating factors in the Tay catchment and analyses the hydro-meteorological conditions that have generated extreme and moderate floods over a historical period. This work is placed in a broader literature context of historical 'climaxes of storminess', periods of higher storm frequency, flood patterns observed in Scotland and Europe during the Little Ice Age and longer-term rainfall and temperature patterns. The paper concludes that the variability in flood-generating characteristics is highly dependent on the timescale of observation. Inevitably the relative dominance of winter and early spring flooding can vary from year to year and within specific time-periods, but so can the level of augmentation of the flood series with summer and autumn floods to produce notable 'flood years' and flood clusters. The Tay provides a good 'all-Scotland surrogate' for historical flood patterns, reflecting its gathering areas in eastern and western Scotland. The value of a historical approach to the assessment of flood seasonality and generating characteristics is clearly demonstrated.  相似文献   

大开间小型混凝土砌块10层模型房屋抗震性能试验研究(Ⅰ)   总被引：8，自引：3，他引：8  

周抚生  郭迅  郑志华  毛国成 《地震工程与工程振动》2002,22(6):58-64

我国抗震设计规范（GB50011－2001）规定在6、7、8度区，混凝土小砌块结构分别可以建七、六、五层。由于混凝土小砌块结构的最大优势在于10－20层（与混凝土框架或框架剪力墙结构比）。本文按1／4比例制作了10层混凝土小砌块结构模型，按7度设防要求实施构造措施，通过振动台试验研究模型结构的抗震性能。结果表明，模型结构完全能够满足在7度区“小震不坏，大震不倒”的要求。圈梁、构造柱以及水平拉结筋构成的约束体系抗震作用是明显的。试验利用砌块的非注芯孔灌注铁砂来模拟墙体出平面动力效应。在本模型的构造措施下，平出面反应不对结构破坏起控制作用。  相似文献   

某中学教学楼的抗震鉴定与加固设计   总被引：1，自引：0，他引：1  

赵更歧  张冰华  张哲  王俊岭 《世界地震工程》2004,20(3):90-94

按老规范设计的砌体结构未考虑抗震，使用年代过长会出现承载力不足的问题，需对原结构按新规范进行全面检测和抗震鉴定，若鉴定结果表明该结构不符合抗震要求，则需进行加固，结合一实际工程对检测程序和加固方法做一全面论述，供工程实际中参考。  相似文献   

Pseudo‐dynamic seismic response of reinforced concrete frames infilled with non‐structural brick masonry     

F. Colangelo 《地震工程与结构动力学》2005,34(10):1219-1241

This paper presents pseudo‐dynamic test results on the in‐plane seismic behaviour of infilled frames. Thirteen single‐storey, single‐bay, half‐size‐scale, reinforced concrete‐frame specimens, most of which infilled with non‐structural masonry made of perforated bricks and cement mortar are tested. The infills are in contact with frames, without any connector; openings are not covered. The frames are different in their strength and details, reinforcement grade, and aspect ratio. Seismic input is the 1976 Tolmezzo (Friuli, Italy) ground acceleration, to which specimens are subjected two times: virgin and damaged by the previous test. The global seismic response of initially virgin infilled specimens considerably differs from that of bare specimens. This follows a dramatic change of properties: compared to a bare frame, the initial stiffness increases by one order of magnitude, and the peak strength more than doubles. The peak drift lessens; however, the displacement ductility demand does not. The energy demand is greater. Nevertheless, the influence of infill decreases as damage proceeds. Displacement time histories of damaged specimens are quite similar. At the local level, infill causes asymmetry and concentration of the frame deformation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Climate change and future flows of Rocky Mountain rivers: converging forecasts from empirical trend projection and down‐scaled global circulation modelling     

Anita Shepherd  Karen M. Gill  Stewart B. Rood 《水文研究》2010,24(26):3864-3877

To predict future river flows, empirical trend projection (ETP) analyses and extends historic trends, while hydroclimatic modelling (HCM) incorporates regional downscaling from global circulation model (GCM) outputs. We applied both approaches to the extensively allocated Oldman River Basin that drains the North American Rocky Mountains and provides an international focus for water sharing. For ETP, we analysed monthly discharges from 1912 to 2008 with non‐parametric regression, and extrapolated changes to 2055. For modelling, we refined the physical models MTCLIM and SNOPAC to provide water inputs into RIVRQ (river discharge), a model that assesses the streamflow regime as involving dynamic peaks superimposed on stable baseflow. After parameterization with 1960–1989 data, we assessed climate forecasts from six GCMs: CGCM1‐A, HadCM3, NCAR‐CCM3, ECHAM4 and 5 and GCM2. Modelling reasonably reconstructed monthly hydrographs (R² about 0·7), and averaging over three decades closely reconstructed the monthly pattern (R² = 0·94). When applied to the GCM forecasts, the model predicted that summer flows would decline considerably, while winter and early spring flows would increase, producing a slight decline in the annual discharge (?3%, 2005–2055). The ETP predicted similarly decreased summer flows but slight change in winter flows and greater annual flow reduction (?9%). The partial convergence of the seasonal flow projections increases confidence in a composite analysis and we thus predict further declines in summer (about ? 15%) and annual flows (about ? 5%). This composite projection indicates a more modest change than had been anticipated based on earlier GCM analyses or trend projections that considered only three or four decades. For other river basins, we recommend the utilization of ETP based on the longest available streamflow records, and HCM with multiple GCMs. The degree of correspondence from these two independent approaches would provide a basis for assessing the confidence in projections for future river flows and surface water supplies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

全球地面降水月值历史数据集研制   总被引：2，自引：0，他引：2  

杨溯  徐文慧  许艳  李庆祥 《气象学报》2016,74(2):259-270

全球降水历史数据是开展气候、水循环等研究的基础。收集整理全球12个数据源降水历史月值资料,通过站号、站名甄别不同数据源中相同台站,对344个通过相关系数、一致率、均值t检验、方差F检验的台站多源资料进行拼接,尽可能多地融合各套数据产品优势,最终形成全球降水历史月值数据集(CMA Global PrecipitationV1.0, CGP)。数据集重点解决当前国际数据产品在东亚地区站点稀少、同时应用多套数据应用门槛较高等问题。数据集收录3.1万个台站共计1.87×107组月降水记录, 4152个台站序列长度达百年。与美国大气海洋局(NOAA)的全球降水数据集(GHCN-M V2.0)对比,CGP新增1万个站点、0.5×107组有效观测记录和1030条百年序列,其中141条百年序列通过多源整合技术获取。CGP的站点和数据量优势主要体现在东亚、东欧、西伯利亚等站点稀疏地区。基于CGP分析的全球降水时空特征与国际同类产品的结果较一致。新增的数据虽然没有改变全球降水分布的总体特征,但对区域性的百年降水变化检测有一定影响。基于CGP的全球降水百年序列结果显示,20世纪前半叶全球降水量偏小,近20年是1900年以来全球降水量最大的时期,各纬度带、各个国家或地区的降水长期变化趋势呈现显著的差异。   相似文献   

Multi‐proxy study of Holocene environmental change and human activity in the Central Apennine Mountains,Italy     

A. G. Brown  J. Hatton  K. A. Selby  M. J. Leng  N. Christie 《第四纪科学杂志》2013,28(1):71-82

This paper describes a multi‐proxy palaeoecological investigation undertaken in conjunction with an archaeological survey of the Upper Sangro Valley in the Abruzzo National Park, Central Italy. Despite being a biodiversity hotspot and regarded as a near‐pristine area, the pollen, spore and diatom data all show major changes in the vegetation extending to over 2000 m a.s.l. during the mid to late Holocene. Although there are changes in ecological composition earlier in the Holocene they are different in type and magnitude from the changes which began about 800 cal a BC. The pollen and diatom evidence do not correlate well with regional palaeoclimate data, or on‐site isotopic evidence, but do appear to be related to Samnite (later Iron Age) clearance and upland grazing associated with transhumance and later annexation (and centuriation) of the lower slopes by Roman surveyors. The greatest change in vegetation was during the period c. AD 500–600 and corresponds with the Byzantine–Gothic Wars, and Lombard–Carolingian settlement reorganization into nucleated hilltop settlements which managed upland grazing. This pattern of intensive land use at all altitudes persisted until the early 20th century and only changed following rural depopulation after World War II. These data illustrate how cultural factors had a profound effect on this mountainous region which, in this case, far outweighed the effects of climatic fluctuations which are known to have occurred from both this study area and the region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

新型灌浆材料在已建砌体结构抗震加固中的应用     

施养杭  余建星 《地震工程与工程振动》2005,25(2):88-92

具有悠久历史的石结构是砌体结构的重要组成部分，本文作者经广泛调研和试验分析：(1)提出以石粉为集料对石砌体进行抗震加固，寓环保与防灾于一体；(2)给出新型浆体配比和复合砂浆的强度等级，阐述加固技术和方法，建立灌浆石砌体抗震抗剪强度公式；(3)阐明抗震验算方法，提出基于模糊随机可靠理论的可靠性分析方法。  相似文献   

Towards error‐free hybrid simulation using mixed variables     

Tarek Elkhoraibi  Khalid M. Mosalam 《地震工程与结构动力学》2007,36(11):1497-1522

Two procedures are developed and implemented in a hybrid simulation system (HSS) with the aim of enhancing the accuracy and reliability of the online, i.e. pseudo‐dynamic, test results. The first procedure aims at correcting the experimental systematic error in executing the displacement command signal. The error is calculated as the difference between command and feedback signals and correlated to the actuator velocity using the least‐squares method. A feed‐forward error compensation scheme is devised leading to a more accurate execution of the test. The second procedure employs mixed variables with mode switching between displacement and force controls. The newly derived force control algorithm is evaluated using a parametric study to assess its stability and accuracy. The implementation of the mixed variables procedure is designed to adopt force control for high stiffness states of the structural response and displacement control otherwise, where the resolution of the involved instruments may favour this type of mixed control. A simple pseudo‐dynamic experiment of steel cantilever members is used to validate the HSS. Moreover, two experiments as application examples for the two developed procedures are presented. The two experiments focus on the seismic response of (a) timber shear walls and (b) reinforced concrete frames with and without unreinforced masonry infill wall. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献