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971.
Suitable scale of Weigan River plain oasis 总被引:2,自引:0,他引:2
HU ShunJun SONG YuDong TIAN ChangYan LI YueTan LI XiuCang CHEN XiaoBing 《中国科学D辑(英文版)》2007,50(Z1):56-64
Desert coexists with oasis in long time, and the existence and development of oasis system demand better oasis vegetation ecological system. Oasis scale of arid zone plain encircling water should be determined in case of desertification caused by land over-reclamation under the circumstance of water resources shortage. Steady oasis with virtuous circle must have appropriate land use structure for agriculture, forestry and graziery. The study on the suitable scale and developmental space of oasis will provide theoretical and applicable foundation for effective construction of oases. By analyzing the hydrothermal, water and soil balance, an optimal mathematical model has been established. Based on hydrometeorology data collected for years in Weigan River plain, and by the principle of water balance, a calculation has been made of the water resources for evapotranspiration and the optimal acreage of oasis and cultivated land, which shows that the water resources for evapotranspiration in the Weigan River plain oasis is 22.32×108 m3 and the optimal oasis acreage under the condition of conventional irrigation mode is 3716.06 km2, in which the suitable cultivated land acreage is 1564.79 km2. Under the condition of water-saving irrigation, the suitable oasis acreage is 5515.49 km2, in which the suitable cultivated land acreage is 2322.31 km2. The oasis area had reached 4123 km2, and the cultivated land acreage had reached 1507 km2 after the Agriculture Irrigation Drainage Water Project of World Bank Loan in Weigan River basin was finished in 1997. The oasis and cultivated land acreage will be more suitable, and the oasis scale can be enlarged moderately by means of water saving irrigation. 相似文献
972.
973.
Taichiro Okazaki Masayoshi Nakashima Keiichiro Suita Tomohiro Matusmiya 《地震工程与结构动力学》2007,36(1):35-53
Interaction between the external wall cladding and the seismic load resisting frame was examined in a full‐scale cyclic loading test of a three‐storey steel building structure. The building specimen had Autoclaved Lightweight Concrete (ALC, also designated as Autoclaved Aerated Concrete) panels installed and anchored to the structural frame as external wall cladding, using a standard Japanese method developed following the 1995 Kobe earthquake. ALC panelling is among the most widely used material for claddings in Japan. In the test, the ALC panel cladding contributed little to the stiffness and strength of the overall structure, even under a very large storey drift of 0.04 rad. No visible damage was noted in the ALC panels other than minor cracks and spalling of the bottom of the panels in the first storey. Consequently, in a Japanese steel building with properly installed ALC panel cladding, the structural frame is likely to be little affected by its cladding, and the ALC panels are capable of accommodating the maximum storey drift generally considered in structural design without sustaining discernible damage. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
974.
975.
近50年我国持续性暴雨的统计分析及其大尺度环流背景 总被引:40,自引:3,他引:40
根据1951~2005年中国大陆730个台站的逐日降水资料和持续性暴雨发生的特点, 提出了采用局地持续性暴雨和区域持续性暴雨事件的两种客观定义来描述和统计近50年我国持续性暴雨时空特征及其变化。单站逐日降水量连续三天或三天以上均大于等于50 mm为一次局地持续性暴雨;区域持续性暴雨指在一定区域范围内连续三天降水量总和大于等于100 mm且每天降水量大于等于25 mm的面积超过某一阈值 (详细定义见正文)。根据局地持续性暴雨定义, 指出: 近50年中国局地持续性暴雨事件主要发生在江南和华南地区, 发生季节以6月为最多;根据区域持续性暴雨定义, 统计分析了四类典型的区域持续性暴雨类型, 分别是: 渤海辽西型、北方经向型、南方锋面型和华南低压型。其中南方锋面型又可根据持续性暴雨易发生的地理位置分为江淮型、江南型和华南型三种。对这六类区域持续性暴雨的历史个例进行同比分析, 研究了不同类型持续性暴雨发生的季节性和年际变化,以及它们在大尺度环流背景方面的共性特征。 相似文献
976.
The Himalayan region of north India is composed of complex mountain ranges with different altitudes and orientations, causing
prevailing weather conditions to be complex. Wintertime eastward moving synoptic weather systems `Western Disturbances' (WDs)
yield large amounts of precipitation over this region. Numerous micro/mesoscale circulations become generated along with prevailing
weather due to surface heterogeneity and land-use variability of the Himalayan region. WDs along with these circulations may
give rise to very adverse weather conditions over the region. Intraseasonal variability of surface climate over the Himalayas
is studied using regional climate model (RegCM3) with 60 km resolution. A 6-month (Oct. 1999–Mar. 2000) period, as this period
has received an enormous amount of precipitation in the form of snow, is considered to study surface climate variability in
terms of temperature, precipitation and snow amount. Model simulations show cold bias over the Himalayan region and warm bias
over the northwest India. Average monthly distribution of temperature indicates that a controlled experiment could capture
the areas of lowest temperature regime. Precipitation fields could be simulated only up to a certain degree of satisfaction
and the influence of topographic elevation and valleys needs to be seen. RegCM3 provides a representation of resolvable atmospheric
circulations that results in explaining mean variability during winter. 相似文献
977.
The ANELFA scale for hailfall intensity is proposed on the model of the 6-class Fujita scale for tornadoes. It is based on more than three thousand point hailfalls measured by hailpads over a 16-year period in France. The class number of a hailfall is determined by the integer value of the largest measured hailstone diameter in cm, or by equivalence with current objects: A0 to A5 for pea, grape, pigeon's egg, walnut, hen's egg, orange. The class number is followed by a plus or minus sign if the ground is significantly more or less than half-covered by hailstones respectively. When the scale is applied to the ANELFA data, a log-normal distribution is found for the class distribution, allowing the frequency determination of the upper class ever observed until now at the hailpad stations. 相似文献
978.
979.
通常固定增益的放大器在兼顾大的动态范围和较高的小信号精度的情况下很难满足预期的要求。本文针对增益为 2 0~ 2 3倍的可编程阶码放大器 AD5 2 6集成片 ,摆脱传统的设计方法 ,提出一种反馈式程控放大电路。该电路能够在瞬时调整信号的放大增益 ,具有很高的精度和较大的动态范围 ,能够在模数转换前端处理中发挥重要作用。 相似文献
980.