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991.
Uranium contents and234U/238U ratios have been determined on 29 water samples from the Taiyuan area, Shanxi Province. The results show that the same artesian
aquifer has similar uranium contents and234U/238U activity ratios, and the deeper aquifers have higher A. R. values but lower uranium contents. The A. R. values increase
slightly towards groundwater flow in the artesian aquifers dominated by oxidizing ground waters.
The Lancun Spring and the famous Jinci Spring belong to two different karst groundwater systems, i.e., the east and west karst
groundwater systems. The recharge area of the Lancun Spring should cover the wide limestone outcrops of middle Ordovician
in the northeast. The Ordovician fissure-karst ground water to the Jinci Spring is extensively mixed with fissure water in
Carboniferous-Jurassic formations and seepage water from the Fenhe River. 相似文献
992.
通过对华北第四活跃期高潮期强震发生前中小地震的时、空、强分布图象的研究,发现每次七级以上强震发生前区域地震活动都经历过一个类似的阶段性变化过程,我们称为强震孕育阶段过程。华北地震活动高潮期就是由若干个这样的孕震过程所组成。华北强震孕育过程都可以划分为三个不同的时期,即预备期(A期)、激进期(B期)、逼震期(C期)。这三个时期地震活动具有的特点和某些规律性反映了华北地下介质应力应变的变化过程与现有的破裂机制概念相一致。因此认为强震的孕育不仅取块于区域应力场的作用,而且与区域内中小地震活动的变化和进程密切相关,同时提出一个简单的孕震模式——“阻导模式”。 相似文献
993.
Samples are available from 37 stony meteorites falling in China. Twenty-two chondrites are examined in terms of chemical and mineral compositions, cosmogenic nuclides, formation and exposure ages, impact effect and chondrule textures. On the basis of chemical-petrologic features these chondrites are classified asE 4 (Qingzhen),H 5 (Jilin, Changde, Shuangyang, Anlong, Xinyi and Yangjang),L 6 (Renqiu, Junan, Heze, Rugao and Nei Monggol) andLL 6 (Dongtai). E 4 is characterized by high iron and sulfur, with the former occurring mainly as Feo and FeS. FromH 5 throughH 6 toLL 6, iron and nickel decrease gradually while FeO and the ratio of Fe silicate to total iron increase gradually. indicating a general increase in the orderE-H-L-LL in the degree of oxidation at the time of formation. E 4 consists mainly of enstatite and, to much less extent, free SiO2 but olivine is hardly to be found. The olivine proportions amount to 29.07, 41.98 and 51.36 percent inH 5,L 6 andLL 6 respectively, with Fa increasing from 17 to 27 percent. Recrystallization has been noticed to different degrees inH 4,H 5,L 6 andLL 6 chondrites. The extent to which the original structure disappears and the boundaries of chondrules become indistinct decreases from type 6 through type 5 to type 4, reflecting different degrees of thermal metamorphism. Major minerals in the meteorites all exhibit signs of low to medium shock metamorphism. Specific activity, depth effect and orbit effect are also measured on some chondrites that have fallen in recent years and some new information has been obtained with respect to the orbit and source region for meteorite parent bodies in space. This results show that the environment of formation ofE group may be nearer to Mars than that ofO group. Each chemical group of chondrites has its own evolutionary history, and chondritets of different chemical groups may have originated from parent bodies of different compositions. Or owing to the differentiation caused by thermal melamorphism, various kinds of meteorites may be derived from a common parent body. From this argument it is suggested that five stages may be recognized during the formation process of chondrites. 相似文献
994.
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997.
热带太平洋海表温度年际变化对降水季节内振荡的影响 总被引:6,自引:0,他引:6
根据 1982—1992年期间的日平均 MSU(Spencer, 1993)海洋降水和 5天平均的CMAP(Xie& Arkin, 1997)降水观测资料,分析了热带太平洋大气季节内振荡(MJO)的年际变化特征。在太平洋海表温度(SST)年际变化的正常年份(1982—83年, 1986—88年, 1991—92年),均有明显的MJO信号传到日界线以东并在中、东太平洋维持数月。热带MJO活动强度的年际变化与局地SST的变化存在正相关。中、东太平洋降水的季节内振荡的年际变化与热带太平洋SST的最强正相关在Nino3区附近。以观测SST场强迫CCM3大气模式的数值试验基本上真实地再现了11年期间热带太平洋降水季节内振荡的年际变化总趋势,但模拟季节内振荡的强度较观测平均偏弱。对比分别采用周平均和月平均SST强迫场的积分结果,发现在中、东太平洋,二个积分模拟的降水季节内振荡强度的年际变化接近并且趋势与观测基本一致,而在西太平洋二个积分的模拟结果差别较大。这表明在热带中、东太平洋,SST强迫的年际变化对MJO强度的变化有强的制约。而在MJO总体活跃的热带西太平洋,SST强迫场的季节变化对模拟MJO活动也有较大影响。CCM3模拟 相似文献
998.
1901-1995年气候变化导致陆地生态系统净吸收碳 总被引:2,自引:0,他引:2
The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical model directly calculating soil respiration rate. Our model shows that during 1901-1995, about 44-89 PgC (equals to 0.5, 0.9 PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s was close to the estimated value of" missing C sink” from deconvolution analysis. Most of the total carbon sink happened during 1951-1985 with the estimated value of 33-50 PgC. Three major sinks were located in the tropics (10°S-10°N), Northern mid-latitudes (30°-60°N) and Southern subtropics (10°-40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem increased with time, and decreased after the mid-1970s. These may be due to the ch anging of climate condition, as during the 1940s-1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases in carbon sink in addition to CO2 and N fertilizer. 相似文献
999.
世界森林的数字地球监测 总被引:8,自引:0,他引:8
介绍中国风云气象卫星FY-1,FY-2对地观测数据应用于全球森林资源的分类监测。讨论中国加入WTO以后对全球森林资源再分配的新战略。以全球观点,分析贵州省的森林资源特色及其对世界的特殊贡献。评价21世纪中国森林数据库与林业管理信息系统的规划与建设。 相似文献
1000.