Modeling patch characteristics of farmland loss for site assessment in urban fringe of Beijing, China     

LIU Xiaona  ZHANG Weiwei  LI Hong  SUN Danfeng 《中国地理科学(英文版)》2013,23(3):365-377

Farmland protection and delimitation in the urban fringe considers not only natural factors but also the spatial characters and site factors. Taking Daxing District, Beijing in China as a case study, this paper used landscape ecology and power-law methods to analyze and evaluate farmland loss during the period of 2004-2007 based on the interpretation results of SPOT5 remote sensing images in 2004 and 2007. At the patch level, we selected four landscape indices, namely patch size, shape index, the nearest neighbor distance between farmland and construction land (including residential land and other construction land), and cropping type, to evaluate the risk of farmland loss and establish a farmland site analysis indicator system. The results showed that patch size and shape index have a significant positive correlation with farmland loss, whereas the distance to construction land has a clear negative correlation with farmland loss. As regards cropping type, fallow farmland is much easier for non-agricultural use than cultivated farmland. The relative transition ratio among vegetable land, fallow farmland and cultivated farmland is 1︰5.6︰1. The patch size of lost farmland follows a power-law distribution, indicating that not only small parcels but also large parcels can be lost. Patch size less than 4 ha or more than 15 ha is in high loss risk, between 4 ha and 10 ha in medium loss risk, and larger than 10 ha and less than 15 ha in low risk. Farmland with a more regular shape has a higher likelihood of loss. Patch shape index less than 2.0 is in high loss risk, between 2.0 and 3.0 in medium loss risk, and larger than 3.0 in low risk. Construction land has a varying impact on farmland loss, the residential land effected distance is 1000 m, and that of the other construction land is 2000 m. This analysis showed the relationships between site factors and farmland loss, and the analysis framework can provide support and reference for farmland protection and delimitation of prime farmland in China.  相似文献   

����ȫ����վ��GPS����ϵͳ��������     

田亮  段金梅  王强  赵亚平  乔亚明 《大地测量与地球动力学》2013,33(1):78-80

??????????GPS??SLR??VLBI?????????в????н??в???????????????????????????????似??????????????????????????????????????????????SLR??VLBI??????????????????????????????GPS?????????????7 mm ???????????GPS????????????????й??  相似文献   

高校信访工作探析     

钟桂安 《广东海洋大学学报》2013,(2)

近年来,高等教育各项改革不断深入,打破了原有利益格局,使旧体制下的隐性矛盾显现化,导致信访活动日益增多,增加了高校管理工作难度。基于高校信访工作的特点和现状,提出了新时期高校信访的工作目标以及实现目标的路径选择。  相似文献   

论“前乐府”的批评——兼及孔子的“删诗”问题     

王辉斌 《广东海洋大学学报》2013,(2):48-53

汉武帝"乃立乐府"前,不仅存在着"乐府"与乐府诗,而且也存在着"前乐府批评"。"前乐府"的批评,主要表现在"整理""选择""题解"三个方面,且互有关联,即"整理"之中兼有"选择","选择"之中又兼有"题解"。这种类型的批评,是文学批评在初始阶段的一种具体表现。"前乐府"的批评由先秦而唐宋,形成了乐府诗批评史上一道耀眼的风景线。  相似文献   

ZResponse to selection, heritability and genetic correlations between body weight and body size in Pacific white shrimp, Litopenaeus vannamei     

����  ��С��  ���  �ཨ�� 《中国海洋湖沼学报》2012,30(2):200-205

To quantify the response to selection,heritability and genetic correlations between weight and size of Litopenaeus vannamei,the body weight (BW),total length (TL),body length (BL),first abdominal segment depth (FASD),third abdominal segment depth (TASD),first abdominal segment width (FASW),and partial carapace length (PCL) of 5-month-old parents and of offspring were measured by calculating seven body measurings of offspring produced by a nested mating design.Seventeen half-sib families and 42 full-sib families ofL.vannamei were produced using artificial fertilization from 2-4 dams by each sire,and measured at around five months post-metamorphosis.The results show that heritabilities among various traits were high:0.515士0.030 for body weight and 0.394士0.030 for total length.After one generation of selection,the selection response was 10.70% for offspring growth.In the 5"’ month,the realized heritability for weight was 0.296 for the offspring generation.Genetic correlations between body weight and body size were highly variable.The results indicate that external morphological parameters can be applied during breeder selection for enhancing the growth without sacrificing animals for determining the body size and breed ability;and selective breeding can be improved significantly,simultaneously with increased production.  相似文献   

The effect of glaciation on the intensity of seismic ground motion     

Samuel T. McColl  Timothy R. H. Davies  Mauri J. McSaveney 《地球表面变化过程与地形》2012,37(12):1290-1301

Seismicity is known to contribute to landscape denudation through its role in earthquake‐triggered slope failure; but little is known about how the intensity of seismic ground motions, and therefore triggering of slope failures, may change through time. Topography influences the intensity of seismic shaking – generally steep slopes amplify shaking more than flatter slopes – and because glacial erosion typically steepens and enlarges slopes, glaciation may increase the intensity of seismic shaking of some landforms. However, the effect of this may be limited until after glaciers retreat because valley ice or ice‐caps may damp seismic ground motions. Two‐dimensional numerical models (FLAC 6.0) were used to explore how edifice shape, rock stiffness and various levels of ice inundation affect edifice shaking intensity. The modelling confirmed that earthquake shaking is enhanced with steeper topography and at ridge crests but it showed for the first time that total inundation by ice may reduce shaking intensity at hill crests to about 20–50% of that experienced when no ice is present. The effect is diminished to about 80–95% if glacier ice level reduces to half of the mountain slope height. In general, ice cover reduced shaking most for the steepest‐sided edifices, for wave frequencies higher than 3 Hz, and when ice was thickest and the rock had shear stiffness well in excess of the stiffness of ice. If rock stiffness is low and shear‐wave velocity is similar to that of ice, the presence of ice may amplify the shaking of rock protruding above the ice surface. The modelling supports the idea that topographic amplification of earthquake shaking increases as a result of glacial erosion and deglaciation. It is possible that the effect of this is sufficient to have influenced the distribution of post‐glacial slope failures in glaciated seismically active areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

页岩气勘探目标层段优选   总被引：1，自引：0，他引：1  

林腊梅  张金川  刘锦霞  龙鹏宇  唐玄 《地学前缘》2012,19(3):259-263

探讨了页岩气勘探目标层段优选中含气量、埋深及有机碳含量之间的互相补偿关系,并初步提出了相应的参考特征值。Ⅰ型、Ⅱ1型、Ⅱ2和Ⅲ型有机质热进入生气主峰的成熟度门限依次递降,Ro分别为1.2%、0.9%、0.7%和0.5%,相应的深度界限依次减小;对美国页岩气产层实际资料统计分析后认为,要形成工业价值的页岩气,在1 000 m、2 000 m、3 000 m深度页岩含气量至少应达到0.5 m3/t、1.0 m3/t、1.5 m3/t;根据渝东南地区下志留统龙马溪组Ⅰ型有机质页岩研究表明,要达到一定的含气量,有机碳含量与深度应互相补偿。若要含成熟有机质的页岩吸附气含量达到1.0 m3/t,则在500 m、1 000 m、2 000 m深度处TOC值需依次达到1.4%、1.1%和0.9%以上。  相似文献   

A Bayesian palaeoenvironmental transfer function model for acidified lakes     

Philip B. Holden  Anson W. Mackay  Gavin L. Simpson 《Journal of Paleolimnology》2008,39(4):551-566

A Bayesian approach to palaeoecological environmental reconstruction deriving from the unimodal responses generally exhibited by organisms to an environmental gradient is described. The approach uses Bayesian model selection to calculate a collection of probability-weighted, species-specific response curves (SRCs) for each taxon within a training set, with an explicit treatment for zero abundances. These SRCs are used to reconstruct the environmental variable from sub-fossilised assemblages. The approach enables a substantial increase in computational efficiency (several orders of magnitude) over existing Bayesian methodologies. The model is developed from the Surface Water Acidification Programme (SWAP) training set and is demonstrated to exhibit comparable predictive power to existing Weighted Averaging and Maximum Likelihood methodologies, though with improvements in bias; the additional explanatory power of the Bayesian approach lies in an explicit calculation of uncertainty for each individual reconstruction. The model is applied to reconstruct the Holocene acidification history of the Round Loch of Glenhead, including a reconstruction of recent recovery derived from sediment trap data. The Bayesian reconstructions display similar trends to conventional (Weighted Averaging Partial Least Squares) reconstructions but provide a better reconstruction of extreme pH and are more sensitive to small changes in diatom assemblages. The validity of the posteriors as an apparently meaningful representation of assemblage-specific uncertainty and the high computational efficiency of the approach open up the possibility of highly constrained multiproxy reconstructions.  相似文献   

淮河中游新石器时代遗址出土石器的演变所反映的人地关系——以双墩和尉迟寺遗址为例   总被引：2，自引：1，他引：1  

朱光耀  朱诚  马春梅  王吉怀  阚绪杭  马彩霞 《地理研究》2008,27(1):193-200

本文以淮河中游新石器早期的双墩遗址和中晚期的尉迟寺遗址的出土石器为主线,辅以其他遗存和遗址地层剖面的环境磁学、元素地球化学证据,探讨了石器工具的演变所反映的人地关系。研究表明:双墩古人最主要的生产活动是砍伐树木和狩猎,而尉迟寺则是谷物生产和狩猎。双墩古人使用投掷和其他多种狩猎方式,在猎物充足的全新世大暖期获取了大量的肉食资源。尉迟寺时期狩猎水平虽有所提高,但剧烈波动的气候和迅速增加的人口,使猎获量下降。双墩时期人们砍伐的树木较为细小,木料之间的结合以捆绑为主。而尉迟寺时期人们砍伐的树木比较粗大,木器和房屋已使用卯榫结构。双墩时期已有了水稻种植,但采集农业占有较大比重。尉迟寺时期的农业以种植为主,采集农业为有益的补充,该时期的出土石器和农业类型与环境演变有明显的相关性。  相似文献   

重庆中坝遗址地层Na-Ca元素含量揭示的制盐业兴衰史     

朱诚  姜逢清  马春梅  徐伟峰  黄林燕  郑朝贵  李兰  孙智彬 《地理学报(英文版)》2008,18(3):328-340

Based on dynastic period division and AMS ^14 C dating performed on the sedimentary layers at Zhongba and Yuxi sites,and also the analysis of Na,Ca and Mg of 201 sedimentary samples from Zhongba site and that of Ca and Na in 47 sedimentary samples from Yuxi by using an inductively coupled plasma-mass spectrometry（ICP）,we found that there were 35 time periods when the contents of Ca and Na were reversely correlated,i.e.whenever the content of Ca was the highest,the content of Na was the lowest,and vice versa. Among them,there were 21 time periods when the content of Ca was the highest,and Na was the lowest,indicating that there were about 21 prosperous periods of ancient salt production at Zhongba site since 3000BC.Other 14 time periods with the peak values of Na while the low values of Ca indicate 14 declined periods of salt production at Zhongba site since 3000BC.The conclusion obtained from the reverse relationship between Ca and Na contents in this paper is consistent with that＂the salt production at Zhongba site started in the new stone age,developed in the Xia and Shang dynasties,reached at the heyday in periods from the Western Zhou to the Han Dynasties,maintained stable to develop in the Tang and the Song dynasties,and gradually declined after the Song Dynasty because the sea salt were conveyed into Sichuan region,however,still had production in the 1970s-1980s＂,educed from archeological exploration.All the above mentioned results indicate that there is a reverse relationship obviously between the contents of Na and Ca in sediments at Zhongba site for ancient salt production,which can be used to reveal the process of rise and decline of ancient salt industry at Zhongba site.  相似文献