Orbital forcing signal in sediments of two Amazonianlakes

Paleolimnological data from two ancient lakes at 0° latitudein Amazonia indicate that past lake level changes reflect precessional (19,000to 22,000 years) variations in insolation over the last 170,000 years. Waterlevel in Lakes Pata and Verde, Brazil, is determined by the ratio ofprecipitation:leakage. Times of low lake level are indicated in sediments byoxidized clays, evidence of algal blooms and high K⁺ concentrations.Peak K⁺ values are attributed to biogenic concentration when thelake was reduced to a shallow, productive pool. Low lake phases correlate withmaximum insolation during the dry season (June–July–August). Thusthe last glacial maximum 18,000 to 22,000 yr BP was a wet time in northernAmazonia, and the driest period of the last 170,000 years was from 35,000 to27,000 yr BP. These results from near the equator do not imply thatprecipitation changed synchronously across Amazonia, because geographiclocations throughout the vast watershed were undoubtedly influenced by localmoisture sources.     

长江经济带生态用地变化类型识别及驱动因素分析

生态用地能够为人们提供生态产品和生态服务,对于维持生态系统健康与安全有着不可替代的作用。在我国城镇化进程快速推进的过程中,生态用地被大量侵占、受损严重,许多土地生态功能丧失。本研究基于1995-2015年的土地利用数据,探究长江经济带生态用地变化时空演变规律,并使用地理探测器和地理加权回归模型对于生态用地变化的驱动机制分别开展全局效应与局部效应分析。本研究将生态用地变化划分为5个类型:严重受损、轻微受损、保持不变、轻微恢复、明显恢复。研究结果表明:1995年至2015年,长江经济带生态用地面积呈现先增加后减少的趋势,但是总体的趋势是减少的,受损面积大于恢复面积。其中,减少的面积主要来自于林地和耕地。在这20年间,从生态用地变化类型来看,保持不变类型的面积最大,其次是轻微受损和轻微恢复类型。生态用地变化是多种因素相互作用的结果,而任何两个驱动因子共同作用的解释力都大于单一的驱动因素。此外,根据地理位置的不同,不同驱动因子对于生态用地变化的影响也不同。本文研究结果有助于土地管理者和政策制定者更好地制定区域和地方的相关土地利用政策。相关经验教训也可以推广到其他地区,以更好地管理生态用地,实现可持续发展。     

上海都市区边界划分——基于手机信令数据的探索

都市区是中心城市及其主要影响范围,在区域经济发展中有重要的引领作用。国外都市区范围根据中心城市与外围地区的通勤联系划分,本质上是与中心城市具有密切经济联系的统一劳动市场区。国内由于统计数据的缺乏,通过通勤联系划分都市区的相关研究难以开展,且划分结果在内涵上与国外都市区差异较大。移动电话是目前普及率最高的移动通讯终端设备,其包含的地理位置标签可反映用户的职住地信息。利用上海移动2014年上半年某两周2G手机信令数据,识别用户的居住地和工作地,参照国外标准,根据中心与外围地区的通勤联系划分上海市都市区。在通勤联系的基础上,尝试采用消费联系作为都市区划分的辅助标准,并对划分结果进行了调整。结果表明：① 基于通勤联系的上海都市区主要包括中心城周边地区、松江新城及外围大型工业区,基于消费联系调整的上海都市区包括中心城周边地区、松江、嘉定、青浦等新城及浦东惠南地区、长兴岛,整体上呈现东西略长、南北略窄的形态;② 通勤联系和消费联系可以相互结合划分中国的都市区边界,通勤联系作为主要指标,消费联系作为辅助指标;③ 上海与国外城市都市区差异较大,国外都市区范围扩展极广,上海都市区范围未超过行政边界,局限在在中心城周围相对较小的范围内。     

Probabilistic neural networks for seismic damage mechanisms prediction

The procedure commonly employed to assess the seismic vulnerability of buildings uses simplified qualitative and quantitative observations obtained from the measured data entered into report forms. In Italy, the data sheets adopted by the National Defence Group against Earthquakes (Gruppo Nazionale per la Difesa dai Terremoti—GNDT) play a unifying and reference role. This paper proposes a method for the processing of the data contained in such report forms which is based on probabilistic neural networks producing a Bayesian classification. The final goal is to exploit the fundamental learning and generalization capabilities of neural networks to obtain an estimate of the vulnerability of structural systems. In particular, the aim is to be able to predict the damage mechanisms which may be triggered in the macro-elements of public worship buildings. Copyright © 1999 John Wiley & Sons Ltd.     

Face stability of shallow circular tunnels driven under the water table: a numerical analysis

The stability analysis of a tunnel excavated in a water-saturated frictional soil is investigated in the light of a failure design approach. The soil strength properties being classically formulated in terms of effective stresses, it is first shown how the effect of seepage flow generated by the excavation process, may be accounted for in such an analysis by means of driving body forces derived from the gradient of an excess pore pressures distribution. The latter is obtained as the solution of a hydraulic boundary value problem, in which both water table evolution and soil deformability can be neglected. A variational formulation of this hydraulic problem in terms of filtration velocities is then presented, leading through appropriate numerical treatment, to a search for the minimum without constraints of a quadratic functional (hybrid formulation), which is formulated by a finite element method. Some numerical examples are given, which provide ample evidence of the crucial role played by seepage forces in the tunnel face stability, since the factor of stability may be divided by as much as three. The influence of such parameters as the tunnel relative depth or soil anisotropic permeability is finally discussed, thus offering a first illustration of the various capabilities of this numerical tool. Copyright © 1999 John Wiley & Sons, Ltd.     

Evaluation of CADISSE a regional storage capacity model

In this paper the validity of CADISSE, a regional storage capacity model developed to assess the sensitivity of catchment hydrology to climate variability, is examined. In CADISSE, catchment discharge sensitivity is expressed as the ratio of present maximum reservoir storage to catchment storage capacity. Present maximum storage should be interpreted as the maximum amount of water stored in a catchment at present. Catchment storage capacity is defined as the absolute amount of water that can be stored, given the catchment's dimensions and lithological characteristics. With CADISSE, catchment sensitivity can be quantified regionally using limited discharge data and topographic information. Furthermore, storage capacities can be assessed. CADISSE was successfully applied to 15 catchments in the Upper Loire Basin. However, successful application does not necessarily mean that the variables (present maximum storage and storage capacity) represent real world values. Therefore, a two‐step evaluation procedure is presented in this paper. To evaluate CADISSE, (1) the accurate assessment of regionally determined storage capacity, and (2) the importance of present maximum storage for catchment discharge sensitivity is examined with a daily discharge model by comparing observed and simulated catchment storage behaviour for dry and wet periods. The evaluation was carried out using the probability distributed daily discharge model, PDM, and a weather generator for three catchments with different storage capacities and storage behaviour. Results indicate that catchment storage capacity can be correctly quantified with CADISSE and that differences in storage behaviour are indeed important for analyses of catchment sensitivity. Hence, CADISSE has great potential as it can be used to identify flood‐ and drought‐prone catchments under present and future conditions. Copyright © 1999 John Wiley & Sons, Ltd.     

不同实验条件下GPS伪距定位精度分析

研究概括了在不同的实验条件下利用GPS伪距获得较高精度定位结果的方法。实验结果的精度表明,这些方法的定位结果都能比常规的GPS伪距定位法的结果精度高,而且定位效果稳定。同时该方法也可为后续高精度定位及定轨等研究工作打好基础。     

基于客观分析的重庆雾的BP神经元网络预报模型研究

本文利用数值预报产品、TTAA报文观测资料及重庆雾(能见度)的实况资料,采用客观分析方法将相关资料处理成二维网格资料,再运用车贝雪夫正交多项式实现二维网格图形的数学定量描述,最后建立重庆雾的BP神经网络方法预测模型,并对重庆雾进行预报试验。检验结果表明,这种方法预报效果较好,基于客观分析的BP神经网络模型进行雾的短期预报具有一定的应用前景。     

Superthermal plasma nodules and their relation to solar flares

We define superthermal plasma nodules as bright points (diameter 20), visible on high resolution X-ray heliograms. Flares appear to show a strong tendency to occur at the places of these nodules. There are indications that (part of) the hot plasma produced by consecutive flares is accumulated and confined in the superthermal plasma nodules, and that with increasing energy content of a nodule the probability for a drastic change of its magnetic structure increases, thus reducing the possibility for more flares to occur.     

中国面向遥感应用的垂直起降无人机现状和 应用前景分析

近年来,针对中国生态环境、洪涝灾害应急响应、国土安全监测等遥感观测任务,无人航空遥感手段需求越来越多。构建异构无人航空器遥感观测多任务集群系统是近几年的发展目标,为完成无人航空遥感生态建设,垂直起降无人机以其不受场地限制起降又可快速巡飞的特点,在多个领域发挥着越来越大的作用。本文主要研究内容包括国内垂直起降无人机发展现状调研、面向航空遥感应用市场的无人机分析及典型机型介绍、垂直起降无人机在遥感领域的应用场景及案例分析、垂直起降无人机在遥感领域的应用前景及发展趋势等。通过广泛调研及深入分析可知,目前垂直起降固定翼无人机正逐步取代多旋翼飞行器的主导地位;垂直起降无人机占据了遥感应用无人机80.47%的市场份额;动力多元化、系统智能化、布局多样化、尺寸小型化等是面向遥感应用的垂直起降无人机的发展方向。本文较为全面地阐述和剖析了面向遥感应用的垂直起降无人机的相关内容,为遥感航空无人机生态建设提供了参考与支撑。