广西苍梧马尾松林和大叶栎林的火行为比较

马尾松(Pinus massoniana)是中国南方大面积造林的树种,也是抗火能力最弱的树种。研究了广西苍梧11龄马尾松用材林和4龄大叶栎萌芽林在正常冬季和干旱夏季情景下的火行为,用behaveplus计算了火线强度、蔓延速度、树冠火可能性等参数。结果表明,两种林分在干旱夏季的火行为高于在正常冬季的火行为。无论是在正常冬季还是在干旱夏季,都没有出现马尾松可燃物模型的火行为一致高于大叶栎可燃物模型的情况;天气、地形、可燃物床结构对可燃物含水率有很大影响,而含水率是火行为的决定因素。虽然大叶栎被划分为难燃树种,大叶栎萌芽林的火行为高于成年大叶栎乔木林,苍梧大叶栎萌芽林在极端干旱的夏季情景有被火把点燃的可能性。如果将大叶栎萌芽林作为防火林带使用,需要经常清除林下枯枝落叶,割除黑莎草,减少细小可燃物。     

Energy forecasting and atmospheric CO2 perspectives: two worlds ignore each other

Macroeconomic models predict that the global primary energy demand will increase by a factor of 2–4 by the year 2050. In contrast, climate analyses made by the IPCC claim that CO₂ emissions in 2050 should not exceed the values of 1990 or even be 20% lower. By 2100 emissions should be reduced to one third of the present value. The common wisdom to deal with these opposing trends is the concept of de-carbonization, i.e., the continuous decrease of the carbon emission per unit energy utilization. De-carbonization rates needed to compensate for the growing demand while keeping the CO₂-emissions constant should at least be 2% per year compared to actual values of 0.3%. The potential of different de-carbonization rate measures is analyzed. It is argued that the goal can only be met if per capita energy utilization in the industrialized countries is significantly reduced from their typical level of 5000–10 000 W. As a realistic target we suggest 2000 Watt per capita, the present global average. This would leave expansion capacity for the developing countries which presently have per capita demand between 300 and 1000 W. Based on the example of Switzerland it is shown that the two key issues to attain this goal are the quality of buildings and the demand for mobility. It is concluded that the conversion of the present energy system into a 2000 W system is neither limited by technology nor by finances but by the acceptance of a new life style in which energy is used more efficiently and more intelligently than today. This revised version was published online in July 2006 with corrections to the Cover Date.     

Humble Opinions on the Relationship between the Percentage of Urban Residents in an Urban Region and the Economic Status in This Region in China

It is a fact that in U.S. the immigration between rural areas and city areas is free, but in China this type of immigration is restricted by HUKOU system （Hukou, namely the household registration system, was designed to control rural-urban in China）. All of those national policies in city areas are much better than those in rural areas, so those corresponding differences bring about great discrepancy of the economic status （mainly including GDP per person and income per resident） between rural and city areas in the same urban region, especially in different urban re- gions because the percentage of urban residents in those urban regions is in-equable. The present paper mainly researches the topic of relationship between the percentage of urban residents and the economic status in an urban region in China, including the relationship between the economic and the political functions of a settlement in China during the process of urbanization.     

南京市经济增长与工业“三废”污染水平计量模型研究

根据环境库兹涅茨曲线原理，选取南京市1985～2004年的经济与环境数据，运用SPSS和EXCEL软件，分析了经济因子与环境因子的相关关系，并建立了模拟经济因子与环境因子之间动态回归模型。研究结果表明，南京市工业废水排放量和人均GDP具有一般相关性，并不呈现库兹涅茨曲线倒“U”模型，而是呈三次曲线的“N”型，两个拐点分别在9 000元和29 000元，这可能与产业结构转变较快有关。工业废气排放量和固体废物产量与人均GDP存在显著相关性， 符合环境库兹涅茨曲线的倒“U”模型，拐点分别在30 000元和38 000元,均提前实现拐点。此外环境政策与科技对工业废水排放量影响也较大。经济结构是影响工业废气排放量和固体废物产量的主要因素，同时，南京市有利的环保科技政策使这两个环境指标提前实现拐点。     

煤矿百万吨死亡率动态无偏灰色马尔科夫预测

为掌握我国煤炭行业整体安全生产状况,构建动态无偏灰色马尔科夫模型,通过处理我国1999—2008年度煤矿百万吨死亡率数据,对2009—2011年度煤矿百万吨死亡率数据进行预测。用无偏灰色GM(1,1)模型代替传统灰色GM(1,1)模型,拟合得到煤矿百万吨死亡率数据的变化趋势,在此基础上应用马尔科夫模型进行预测,并在每一次预测中更新原始数据,最后对预测结果进行对比分析。计算结果表明:动态无偏灰色马尔科夫模型既能消除传统灰色GM(1,1)模型的固有偏差,又能提高预测精度尤其是中长期预测精度。其中,平均绝对误差为3.35%,平均相对误差为3.85%,均低于传统灰色GM(1,1)模型和一般灰色马尔科夫模型。动态无偏灰色马尔科夫模型对于煤矿百万吨死亡率数据的平均预测精度超过96%。     

单产提升潜力衰减模型法在河南粮食单产中长期预测中的应用研究

粮食单产水平的提高是河南粮食增产的主要原因,准确预测粮食单产水平,对科学判断河南粮食生产能力、制定粮食生产战略意义重大。论文针对目前直接以单产为变量建立的预测模型未能反映出单产增长的有限性和增速的减缓性之不足,研究提出了一种基于单产提升潜力衰减过程的单产预测方法。该方法利用河南耕地的平均单产潜力和历年实际单产数据,计算得到河南历年单产可提升潜力值;依据单产提升潜力理论上呈逐渐衰减之变化特点,可采用指数衰减函数建立单产提升潜力回归模型,以达到间接预测单产之目的。结果表明：1）单产提升潜力对数值与时间t之间具有高度负线性相关关系,适宜建立指数回归模型;2）回归模型V_q-V_t=e^{-0.009 5t+9.464 7}拟合优度R²=0.973 1,在0.01置信水平上回归显著;3）预测模型反映出了单产提升潜力的有限性和衰减性,即单产潜力对单产水平的限制性,模型理论诠释清晰;4）利用河南1978—2000年的单产数据作为样本建立预测模型,用样本以外2001—2015年的实际单产作为观测值,对预测单产进行模型预测检验,结果表明该模型预测单产绝对误差均值为129.15 kg/hm²,仅为现有方法的0.17~0.82倍,且误差平稳,适宜于单产中长期预测;5）预测得河南2020、2025、2030年的平均单产分别为6 375、6 765、7 155 kg/hm²,年均增幅为85.20~74.55 kg/hm²,增速呈逐渐减缓趋势。     

BP神经网络法预测唐山市需水量

需水量预测研究已成为当前水资源规划与管理研究中的重要课题之一.本文设定不同的神经网络运行次数,根据预测结果进行误差分析,BP神经网络在运行5 000次时,具有高度的可信度和可行性.应用5 000次运行次数的BP神经网络模型对唐山市规划水平年的需水量进行预测.最后引入人均综合用水量概念,结果表明,预测结果在理论上和实际上都具有可行性.     

18世纪中叶以来不同时段的中国水灾格局

以县域为基本统计单元。以年均水灾次为基本指标,以数字地图技术支持下,编制了一套信息来源不同、时段相对连续的中国水灾格局图。分析表明：中国水灾格局以胡焕庸线为界,呈现东西分异;水灾高值区呈现团块分布,与地貌格局关系密切;近百年来全国水灾中心呈现由黄淮海平原向东北、西部和南方转移的趋势;近50年来,华北成为水灾低值区,水灾由东向西形成4个梯度区。这些研究为揭示水灾格局对水灾过程影响机制的研究提供了科学依据。     

Explaining the resource curse, with special reference to mineral-exporting countries

Recent studies have found an inverse correlation between economic growth and natural resource abundance among developing countries. There appears to be no obvious explanation for this finding, such as an important growth variable that is common in resource-poor countries and deficient in resource-abundant countries. The resource curse hypothesis is closely related to the problem of sustainability for resource-exporting countries since periods of high growth are frequently followed by long periods of stagnation. Models are examined showing how increases in export income can affect relative prices in the trade and nontrade sectors and how the changes in relative prices affect investment and growth. It is the thesis of this article that there is nothing inherent in resource-abundance that condemns countries to either low growth or nonsustainability.     

From socioeconomic disparity to environmental injustice: the relationship between housing unit density and community green space in a medium city in Pakistan

Rapid urbanisation, lack of proactive planning and improper allocation of resources may result in socio-economic disparity among and within cities, causing social unrest and environmental injustice in the neighbourhoods. This study aims to examine whether the planning standards for housing schemes in Pakistan are able to maintain equitable access to green spaces within the cities. Ten residential sites in Sheikhupura city with different housing unit sizes and densities were selected for the study. The supply of urban green infrastructure in housing scheme has been assessed: (i) by comparing the percentage of green spaces, including community parks and open spaces and street landscape; and (ii) by calculating per dwelling unit and per capita share of green spaces. These indicators have been studied against the housing density and population density of the schemes by applying correlation and linear regression models. The results show that all the housing schemes plans provide for similar amounts of green space as a percentage of total area. The per capita share of green spaces is very low in high-density areas, but interestingly, the street landscape has a higher potential to contribute to the overall landscape in high-density neighbourhoods, compensating for low per capita green space. Housing unit density and population density must be incorporated in planning standards so planners can effectively devise a mix of community parks, street landscape and private green spaces to help maintain per capita green spaces, and hence environmental resource equality in different parts of the city.