Steady flows driven by sources of random strength in heterogeneous aquifers with application to partially penetrating wells

Average steady source flow in heterogeneous porous formations is modelled by regarding the hydraulic conductivity K(x) as a stationary random space function (RSF). As a consequence, the flow variables become RSFs as well, and we are interested into calculating their moments. This problem has been intensively studied in the case of a Neumann type boundary condition at the source. However, there are many applications (such as well-type flows) for which the required boundary condition is that of Dirichlet. In order to fulfill such a requirement the strength of the source must be proportional to K(x), and therefore the source itself results a RSF. To solve flows driven by sources whose strength is spatially variable, we have used a perturbation procedure similar to that developed by Indelman and Abramovich (Water Resour Res 30:3385–3393, 1994) to analyze flows generated by sources of deterministic strength. Due to the linearity of the mathematical problem, we have focused on the explicit derivation of the mean head distribution G _d (x) generated by a unit pulse. Such a distribution represents the fundamental solution to the average flow equations, and it is termed as mean Green function. The function G _d (x) is derived here at the second order of approximation in the variance σ² of the fluctuation (where K _A is the mean value of K(x)), for arbitrary correlation function ρ(x), and any dimensionality d of the flow domain. We represent G _d (x) as product between the homogeneous Green function G _d ⁽⁰⁾(x) valid in a domain with constant K _A , and a distortion term Ψ _d (x) = 1 + σ²ψ _d (x) which modifies G _d ⁽⁰⁾(x) to account for the medium heterogeneity. In the case of isotropic formations ψ _d (x) is expressed via one quadrature. This quadrature can be analytically calculated after adopting specific (e.g.. exponential and Gaussian) shape for ρ(x). These general results are subsequently used to investigate flow toward a partially-penetrating well in a semi-infinite domain. Indeed, we construct a σ²-order approximation to the mean as well as variance of the head by replacing the well with a singular segment. It is shown how the well-length combined with the medium heterogeneity affects the head distribution. We have introduced the concept of equivalent conductivity K ^eq(r,z). The main result is the relationship where the characteristic function ψ^(w)(r,z) adjusts the homogeneous conductivity K _A to account for the impact of the heterogeneity. In this way, a procedure can be developed to identify the aquifer hydraulic properties by means of field-scale head measurements. Finally, in the case of a fully penetrating well we have expressed the equivalent conductivity in analytical form, and we have shown that (being the effective conductivity for mean uniform flow), in agreement with the numerical simulations of Firmani et al. (Water Resour Res 42:W03422, 2006).     

受迫摆方程的伪概周期解

利用伪概周期函数的性质和Banach压缩映像原理研究受迫摆方程的伪概周期解问题,证明伪概周期解的存在性及在条件‖y-π‖L∞<π2下的唯一性。     

中国近80年来气候变化特征及其形成机制

自 2 0世纪 2 0年代以来 ,中国地区 4 0和 90年代出现了 2个暖期及 5 0～ 6 0年代相对冷期。最近的 90年代的最暖年 (1998年 )或 5a滑动平均气温几乎已达或略高于 4 0年代的最暖年 (194 6年 )或 5a滑动平均气温。变暖最明显是北方地区 (黑龙江和新疆北部 ) ,而 35°N以南和 10 0°E以东地区自 5 0年代以来存在一个以四川盆地为中心的变冷带 ,虽然 90年代有变暖趋势 ,但基本达到 4 0年代暖期气温。中国降水则以 2 0年代为最少 (192 9年最少 ) ,5 0年代为多水年代 ,以后缓慢减少 ,70年代以后变化不大 ,但多雨带在 80年代及以后由华北南移到长江中下游。195 1～ 1990年 ,大部分地区气温和降水呈负相关 ,在东北和长江—黄河间存在 2个负相关中心 ,表明北方是变暖变旱 ,江淮间是变冷变湿。这些气候变化特征和全球气候变化相比较 ,除北方外 ,变暖期明显的滞后于全球变暖 ,并且出现变冷带等明显差异。文中还综述了用诊断和数值模拟方法对影响中国变化的气候自然变化和人类活动影响 (热岛效应和气溶胶影响 )的研究结果。我们认为 ,以上提出的 3种人类活动对中国气候变化有明显影响 ,特别是工农业发展造成的气溶胶增加是四川盆地气温变冷的主要原因。     

内蒙古半干旱草原土壤－植被－大气相互作用综合研究

为深化对中纬度半干旱草原气候-生态相互作用过程、机制及其对全球变化的响应与贡献的认识,一项名为“内蒙古半干旱草原土壤-植被-大气相互作用(IMGRASS)”的基金重大项目于1997~2001年在内蒙古锡林郭勒草原执行。IMGRASS计划在1998年草原生长季节在所选定的以典型草原为主,包括草甸草原、稀疏沙地草原等在内的中尺度试验区开展了多点、多要素的综合观测。观测内容包括土壤、植被、大气的相关要素和发生于地-气界面的潜热、感热通量,还包括N2O,CH4,CO2等微量气体交换量、辐射与降水分布。除1998年中尺度观测试验外,1999~2001年在代表性地点进行了微量气体收支、遥感和沙尘天气相关的专项观测,结合草原站已进行的长期监测资料,分析气候-生态长期相互作用,特别是人类活动干预的影响。在分析观测结果的基础上,对该地区的气候-生态相互作用进行了数值模拟研究。文章简要介绍IMGRASS计划目标和初步成果,包括:计划目标与实验区背景;半干旱草原不同地表陆气相互作用特征;浑善达克沙地及其沙尘气溶胶特征;半干旱草原温室气体收支与碳循环测量分析;人类活动干预下半干旱草原生态退化与恢复演替规律;半干旱草原的遥感测量。     

中新天津生态城零能耗绿色建筑的整合设计及技术集成

本项目的意义在于通过超低能耗绿色建筑的技术集成研究,因地制宜地为气候寒冷地区探索出超低能耗绿色建筑设计体系、基准建筑能耗指标体系、绿色建筑节能技术体系、超低能耗建筑运行管理体系等,实施示范项目达到建筑现场年度能耗为零,并分别申报国内外四项绿色建筑评价标识的最高奖项,为本地区绿色建筑开发建设提供技术参考,进而为城市建设的可持续发展提供积极的探讨和典型示范,为城市的开发建设提供技术、管理、政策等方面的参考。     

Response of vegetation restoration to climate change and human activities in Shaanxi-Gansu- Ningxia Region

The “Grain for Green Project” initiated by the governments since 1999 were the dominant contributors to the vegetation restoration in the agro-pastoral transitional zone of northern China. Climate change and human activities are responsible for the improvement and degradation to a certain degree. In order to monitor the vegetation variations and clarify the causes of rehabilitation in the Shaanxi-Gansu-Ningxia Region, this paper, based on the MODIS-NDVI and climate data during the period of 2000-2009, analyzes the main characteristics, spatial-temporal distribution and reasons of vegetation restoration, using methods of linear regression, the Hurst Exponent, standard deviation and other methods. Results are shown as follows. (1) From 2000 to 2009, the NDVI of the study area was improved progressively, with a linear tendency being 0.032/10a, faster than the growth of the Three-North Shelter Forest Program (0.007/10a) from 1982 to 2006. (2) The vegetation restoration is characterized by two fast-growing periods, with an “S-shaped” increasing curve. (3) The largest proportion of the contribution to vegetation restoration was observed in the slightly improved area, followed by the moderate and the significantly improved area; the degraded area is distributed sporadically over southern part of Ningxia Hui Autonomous Region as well as eastern Dingbian of Shaanxi province, Huanxian and Zhengyuan of Gansu province. (4) Climate change and human activities are two driving forces in vegetation restoration; moreover anthropogenic factors such as “Grain for Green Project” were the main causes leading to an increasing trend of NDVI on local scale. However, its influencing mechanism remains to be further investigated. (5) The Hurst Exponent of NDVI time series shows that the vegetation restoration was sustainable. It is expected that improvement in vegetation cover will expand to the most parts of the region.     

金华市的水资源核算与绿色利用新思路

计算表明,仅水资源一项自然资源折旧就可使金华市的GDP平均下降5.2%.指出金华市近几年GDP的快速增长是以牺牲资源和环境为代价的,也是水环境负债的一个主要原因.同时指出目前金华市的缺水不是水源型缺水,而是水质型缺水.配合金华市政府建设绿色金华的新构想,提出了金华市水资源绿色利用的新思路:采用绿色GDP;实施绿色政绩;发展绿色工业;推广绿色农业;强化绿色治理;实行绿色水价.     

基于Marchenko理论压制自由表面多次波方法研究

常规虚源点Marchenko自聚焦多次波预测方法只适用于预测不含自由表面的多次波模型,局限于压制层间多次波,该方法在构建上下行格林函数场前,必须从反射响应中去除所有与表面相关的多次波.本文对构建上下行Marchenko格林函数方程进行改进,得到了包含一次波、层间多次波和自由表面多次波的格林函数,利用改进的Marchenko自聚焦预测方法预测自由表面多次波.本文利用水平层状模型数据及SMARRT模型数据证明,改进后的Marchenko法预测海底相关的自由表面多次波效果较为理想,该方法避免了常规SRME自由表面多次波预测方法需要近道重构的缺陷,能够有效提高地震资料的信噪比和分辨率.     

“地球村”的绿色与绿色文化

本文扼要介绍近期出现的绿色变革浪潮,提出绿色文化的概念,阐述绿色的价值、绿色文化的一般原则、绿色文化与其它文化的关系,初探绿色社区建设的构想。展示绿色未来,要正视以往由于人类对地理环境的偏见和人类中心主义所招致生态危机,重新调整和确立良好的人地关系。其对地球村的发展有深远意义。     

Signature pigments of green sulfur bacteria in lower Pleistocene deposits from the Banyoles lacustrine area (Spain)

Signature pigments of photosynthetic green sulfur bacteria (GSB) were found in ancient sediments collected from an abandoned clay quarry located in the Banyoles lacustrine area (Spain). The sediments belong to the Interglacial Waalian of the lower Pleistocene (0.7–1.5 millions years old) and were deposited after a marshy event occurring during that geologic period. Reverse-phase high performance liquid chromatography (RP-HPLC) analyses of acetone:methanol sediment extracts revealed that the main pigments found were carotenoids of both eukaryotic and prokaryotic photosynthetic organisms. In particular, isorenieratene (Isr) and β-isorenieratene (β-Isr) constituted the larger bacterial fraction (35–40% of the total carotenoid content), whereas okenone, a signature pigment of purple sulfur bacteria, accounted for less than 2%. Xanthophylls from oxygenic photosynthetic organisms accounted for the remaining carotenoids. Likewise, traces of degradation products of both bacteriochlorophyll (BChl) and chlorophyll (Chl) were also detected. The low concentration of Chl degradation products made proper identification of these compounds impossible. In contrast, degradation products of BChl-e such as bacteriochlorophyllide-e and bacteriopheophorbide-e were identified in the HPLC analyses, suggesting that chemical degradation of naturally occurring BChl aggregates of GSB was slower in the clay quarry sediments. The presence of signature pigments of brown-colored species of GSB (Isr, β-Isr and degradation products of BChl-e) in the sediments suggests an ancient aquatic environment where GSB were present and where episodes of sulfide-rich anoxia reaching the photic zone could be envisaged. Similarly, the large percentage of algal xanthophylls supports that algae could be an important part of the microbial photosynthetic community in this ancient ecosystem.