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971.
972.
近800a来内蒙古岱海湖水的盐度定量及其气候意义 总被引:6,自引:0,他引:6
在干旱半干旱地区 ,封闭湖泊的湖水盐度对气候变化反应敏感。首先通过现生介形类 (Lim nocytherecf.inopinata)壳体与湖水Sr/Ca比值的测定确定了Sr/Ca的分配系数 ;然后测试现代岱海湖水盐度与湖水Sr/Ca比值 ,建立湖水盐度与湖水Sr/Ca比值的函数关系 ;最后利用湖泊沉积剖面中介形类壳体的Sr/Ca比值定量恢复了岱海湖水近 80 0a来的盐度。通过分析岱海湖水盐度变化过程 ,揭示了研究区小冰期前期降水增加的冷湿气候 ,这明显不同于东部其它地区的冷干气候 ;研究区在小冰期中后期以偏干旱气候为主 ,这与东部其它地区干冷气候相一致 ;推测了 2 1世纪初 10~ 2 0a ,岱海地区降水将有所增加 ,干旱趋于缓和。 相似文献
973.
从地表自然生态系统发育与环境演变的一些难解之迷追索到地球内部能量的影响,对比世界各地主要地理单元的大地热流特征与生态环境特征发现,各地生态环境的优劣与区域大地热流的高低有密切的关系。典型森林生态系统的大地热流比较高,而典型荒漠生态系统的大地热流均比较低。大地热流不仅可能影响区域气候的干湿程度,而且还可能决定一个地区地表生态系统能量供给的下限,是区域生态系统发育与演变过程中一个重要的物种限制因子。大地热流低可能是导致一些盆地生态体系发育不良,进而演变成为沙漠的重要原因。研究大地热流对生态环境退化的影响和机理,了解区域生态体系和现代环境格局形成背景,以及区分环境和生态演化中自然和人文因素的作用具有重要意义,同时将为区域环境和生态建设以及管理决策提供科学依据。 相似文献
974.
用NCAR区域气候模式(RegCM2)的数值试验,研究了包络地形和地形重力波拖曳作用对1991年5、6月份中国区域内气候模拟效果的影响。通过试验结果的对比分析发现,在模式中引入地形重力波拖曳作用可在一定程度上改善模式对气候系统和要素的模拟效果,使模拟结果更符合气候实况。包络地形对模拟结果也有一定的改善,但对于细网格的区域气候模式(RCM)来说,其效果不如重力波拖曳明显。不论是地形重力波拖曳还是包络地形,在模式积分的初期,它们的作用并不明显,随着积分时间的增长,它们对模拟结果的影响程度增大。 相似文献
975.
应用NCEP/NCAR再分析资料,分析了9408号台风异常路径形成的可能原因。结果表明,环境引导流、准均匀流和偶极子流的共同作用对移向突变和移速突变有着重要影响。 相似文献
976.
977.
978.
Laurence P. Adams 《The Photogrammetric Record》2001,17(98):225-242
In the Preface to his book, The Four Faces of Fourcade, Clare Storrar (1990) wrote: "It is di.cult to appreciate the breadth and depth of Henry Georges Fourcade's intelligence and creative power. He was an intellectual giant, a phenomenon, whose theoretical and practical achievements have never received proper recognition. These were all the more remarkable because he began his original work on photogrammetry when science in South Africa was in its infancy, and he laboured alone far from libraries and other research facilities. His only higher academic training was in land surveying. He was adept in each of four sciences at various stages in his life, but, mainly because of his natural reserve, his reputation was highly compartmentalised. To foresters he was 'the most brilliant forestry officer of his time' to surveyors, he was exceptionally learned in theory and skilled in practice. Photogrammetry was a new subject, unheard of, except by a handful of scientists. In botany, which he took up seriously at the age of fifty-five, his work was highly regarded by leading botanists in South Africa and in Europe. All stood in awe of his extraordinary talent and ability. Some were frightened of him. But few were able—in fact, not even the best brains were wholly qualified—to grasp fully the tremendous intellectual stature and potential of this protean man."
This paper briefly describes the historic achievements of Henry Georges Fourcade, with the emphasis on his land surveying and, in particular, his photogrammetric contributions to science. The centenary of one of these, his proposal of a stereoscopic method of photographic surveying, occurs in October 2001. 相似文献
This paper briefly describes the historic achievements of Henry Georges Fourcade, with the emphasis on his land surveying and, in particular, his photogrammetric contributions to science. The centenary of one of these, his proposal of a stereoscopic method of photographic surveying, occurs in October 2001. 相似文献
979.
讨论了以地理信息系统作为建模与仿真过程的空间信息支持 ,在高层体系结构 (HLA)提供的RTI服务基础上 ,运用多线程技术实现地理信息系统作为仿真成员的HLA接口的设计与实现。实验表明 ,能够满足仿真的需求 相似文献
980.
Deriving rules from activity diary data: A learning algorithm and results of computer experiments 总被引:1,自引:0,他引:1
Theo A. Arentze Frank Hofman Harry J.P. Timmermans 《Journal of Geographical Systems》2001,3(4):325-346
Activity-based models consider travel as a derived demand from the activities households need to conduct in space and time.
Over the last 15 years, computational or rule-based models of activity scheduling have gained increasing interest in time-geography
and transportation research. This paper argues that a lack of techniques for deriving rules from empirical data hinders the
further development of rule-based systems in this area. To overcome this problem, this paper develops and tests an algorithm
for inductively deriving rules from activity-diary data. The decision table formalism is used to exhaustively represent the
theoretically possible decision rules that individuals may use in sequencing a given set of activities. Actual activity patterns
of individuals are supplied to the system as examples. In an incremental learning process, the system progressively improves
on the selection of rules used for reproducing the examples. Computer experiments based on simulated data are performed to
fine-tune rule selection and rule value update functions. The results suggest that the system is effective and fairly robust
for parameter settings. It is concluded, therefore, that the proposed approach opens up possibilities to derive empirically
tested rule-based models of activity scheduling. Follow-up research will be concerned with testing the system on empirical
data.
Received: 31 January 2001 / Accepted: 13 September 2001 相似文献