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971.
桂林毛村岩溶区与碎屑岩区不同土地利用方式对土壤水稳性团聚体特征的影响 总被引:4,自引:1,他引:3
以桂林毛村岩溶生态试验场为研究区域,通过对该地区岩溶区和碎屑岩区不同土地利用方式的土壤进行采样和分析,系统研究和比较了旱地、水田、林地和灌丛四种不同土地利用方式下土壤水稳性团聚体分布特征。结果表明:无论是岩溶区石灰土还是碎屑岩区红壤,土地利用方式对土壤水稳性团聚体分布和组成有着显著的影响(p<0.05)。与旱地和水田等传统农田相比,灌丛和林地这两种自然土壤明显提高了>5mm和>0.25mm团聚体的比例,并且团聚体稳定性增加。岩溶区灌丛的平均重量直径(MWD)和几何平均直径(GMD)较旱地分别提高了185%和179%,较水田提高了361%和481%,林地的MWD和GMD分别较旱地提高了65%和43%,较水田提高了167%和198%;而碎屑岩区灌丛的MWD和GMD分别较其旱地和水田提高了103%和134%、15%和32%,林地的MWD和GMD分别较其旱地和水田提高了117%和152%、23%和43%。这说明相比碎屑岩区红壤,岩溶区石灰土受到人类活动的频繁干扰之后退化更快,土壤团聚体稳定性下降更多,这也说明了岩溶区土壤环境的脆弱性。 相似文献
972.
2013年6~7月在广西平果县中铝广西分公司3号排泥库附近出现密集小震群活动。本文搜集本次震群中146次可用于计算尾波的ML1.0地震的近距离台站数字地震波形,利用波形高信噪比的尾波时间域信号,采用计算尾波品质因子Q_C(f)值的Sato模型,通过滤波及去除环境噪声,计算了地震波传播路径上的尾波Q_C(f)值;拟合Q_C(f)值与频率f之间的关系,分析了排泥库区域地震波衰减的时空特征。根据信噪比及计算要求,从近场7个台站的记录中挑选出273条三分向记录,计算尾波衰减参数,得到尾波Q_C(f)与频率f的关系为:Q(f)=(69.07±40.09)f~(0.90±0.23)。结果表明,本区域为低衰减区域,库区Q值相对较高,地震波衰减较慢,且Q值对频率的依赖性不强,研究区介质非均匀性程度低,介质较为稳定。 相似文献
973.
Performance of detrending models of crop yield risk assessment: evaluation on real and hypothetical yield data 总被引:2,自引:1,他引:1
Tao Ye Jianliang Nie Jun Wang Peijun Shi Zhu Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(1):109-117
Detrending is a widely used technique for obtaining stationary time series data in residual analysis and risk assessment. The technique is frequently applied in crop yield risk assessment and insurance ratings. Although several trend models have been proposed in the literature, whether these models achieve consistent detrending results and successfully extract the true yield trends is rarely discussed. In the present article, crop insurance pricing is evaluated by different trend models using real and historical yield data, and hypothetical yield data generated by Monte Carlo simulations. Applied to real historical data, the linear, loglinear, autoregressive integrated moving average trend models produce different risk assessment results. The differences among the model outputs are statistically significant. The largest deviation in the county crop assessment reaches 6–8 %, substantially larger than the present countrywide gross premium rate of 5–7 %. In performance tests on simulated yield trends, popular detrending methods based on smoothing techniques proved overall superior to linear, loglinear, and integrated autoregression models. The best performances were yielded by the moving average and robust locally weighted regression models. 相似文献
974.
975.
976.
Coalbed methane can be detected employing the amplitudevariation-with-offset technique. However, there are two issues in applying this technique to a coalbed: strong azimuthal anisotropy resulting from high-density fractures, and the seismic response being composed of many or several individual reflections within the coalbed. To overcome these difficulties, we present an exact solution for reflections in extensive dilatancy anisotropy media. First, we build a three-layer model and simulate the wave propagation in this model. Then we derive an exact P- and converted S-wave reflection coefficient equation based on boundary conditions. Finally, substituting given model parameters into the exact equation, we obtain the variation in the reflection coefficient with incidence angle. The results show that the fracture factors, wavelet frequency and thickness of the coalbed have different effects on the reflection coefficient. Furthermore, we create a synthetic seismogram by forward calculation, and the result fits well with results of the exact equation. 相似文献
977.
围绕油藏数值模拟过程中三维地质模型的建模技术进行了分析与探讨,详细介绍了基于角点网格模型的建模方法,给出了相应的实现步骤。其主要流程是:首先根据断层数据构造断层模型,在断层模型的基础上构建骨架模型;然后在骨架模型约束下采用地层恢复技术实现含断层的地层模型;最后基于结构模型插值物性参数完成属性模型。以塔河油田缝洞型油藏为例,对建模流程和技术的可行性进行验证,结果表明,其建模结果与专业地质建模软件Petrel相符。 相似文献
978.
Spatiotemporal variation and driving forces of reference evapotranspiration in Jing River Basin,northwest China 总被引:1,自引:0,他引:1
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Lihong Xu Zhongjie Shi Shulan Zhang Xinzheng Chu Pengtao Yu Wei Xiong Haijun Zuo Yunni Wang 《水文研究》2015,29(23):4846-4862
Evapotranspiration is an important component of the hydrological cycle, which integrates atmospheric demands and surface conditions. Research on spatial and temporal variations of reference evapotranspiration (ETo) enables understanding of climate change and its effects on hydrological processes and water resources. In this study, ETo was estimated by the FAO‐56 Penman–Monteith method in the Jing River Basin in China, based on daily data from 37 meteorological stations from 1960 to 2005. ETo trends were detected by the Mann–Kendall test in annual, seasonal, and monthly timescales. Sensitivity coefficients were used to examine the contribution of important meteorological variables to ETo. The influence of agricultural activities, especially irrigation on ETo was also analyzed. We found that ETo showed a decreasing trend in most of the basin in all seasons, except for autumn, which showed an increasing trend. Mean maximum temperature was generally the most sensitive parameter for ETo, followed by relative humidity, solar radiation, mean minimum temperature, and wind speed. Wind speed was the most dominant factor for the declining trend in ETo. The more significant decrease in ETo for agricultural and irrigation stations was mainly because of the more significant decrease in wind speed and sunshine hours, a mitigation in climate warming, and more significant increase in relative humidity compared with natural stations and non‐irrigation stations. Changes in ETo and the sensitivity coefficient of meteorological variables in relation to ETo were also affected by topography. Better understanding of ETo response to climate change will enable efficient use of agricultural production and water resources, which could improve the ecological environment in Jing River Basin. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
979.
陕北黄土丘陵沟壑区农户气候变化的适应行为及影响因素分析 总被引:2,自引:0,他引:2
从农户个体微观视角,研究农业的活动主体--农户的气候变化适应行为。选择陕北黄土丘陵沟壑区,采用问卷调查和半结构式访谈相结合的方法研究农户气候变化感知与适应行为,运用二元逻辑回归模型分析影响该地区农户适应行为的因素。结果表明:农户对气候变化趋势感知比较一致,认为近5 年夏季和冬季气温升高,降水减少,但与实际观测存在一定偏差。农户应对气候变化采取适应行为的比重并不高,只有57.8% 的农户表示采取了相应的措施来应对气候变化。农户适应行为受气候变化感知的影响,此外,家庭社会经济属性对农户采取适应行为的概率影响显著,而性别、年龄、文化程度等人口属性因素与农户采取适应行为的概率关系不大。 相似文献
980.
Yong Zhang Shu–Wen Xing Chao Li Shi–Fu Liang Zheng–Tao Yu Xiao–Hui Du 《International Geology Review》2017,59(2):185-203
The Changfagou Cu deposit is a newly discovered porphyry deposit located in the southern Jilin Province of Northeastern China, on the northeastern margin of the North China Craton. To better understand the formation of the Cu deposit, we report the zircon U–Pb and molybdenite Re–Os dating, and Sr-, Nd-, and Hf- isotopic data of the granite porphyry. LA-ICP-MS dating of zircon grains from two mineral zones in the granite porphyry yield ages of 115.7 ± 0.8 and 115.3 ± 0.6 Ma, which is interpreted as the emplacement age of the granite porphyry. The molybdenite Re–Os model ages of 112.5 to 113.8 Ma, an isochron age of 113.3 ± 1.3 Ma, and a weighted mean model age of 113.0 ± 0.7 Ma, which represents the age of the Cu mineralization quite well. The Changfagou granite porphyry samples lack amphibole and muscovite, and are compositionally characterized by high SiO2, high Na2O+K2O, and low P2O5, enriched in some Rb, Th, U, and Pb, and depleted in Nb, Ta, Ti, P, and Eu. Mineralogical and geochemical features suggest that the Changfagou granite porphyry samples are slightly peraluminous and are of highly fractionated I-type granitoids. The granitic rocks also have relatively high (87Sr/86Sr)i (0.71199 to 0. 71422), and both low εNd(t) (?14.56 to ?13.19) and εHf(t) values (?14.916 to ?8.644), which suggest that Changfagou granite porphyry are derived from mixed sources of crustal and mantle, and diagenesis and mineralization were possibly related to the switch in subduction direction of the Palaeo-Pacific Plate in the late phase of Early Cretaceous. 相似文献