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61.
从地球物理反演的基本概念出发,认为地球物理反演是 对实测数据的地球物理属性的理解或解释,多方法的地球物理数据联合反演是一种多传感器 的数据融合. 本文分析了地球物理数据的模糊特性,采用基于语义的模糊化方法,使不同物 理意义和尺度的特征数据及测区的地质和地球物理背景成为一体,结合地球物理专家解释的 方法,利用基于模糊逻辑系统的神经网络实现了融合. 该方法充分利用了各种地球物理探测 数据的全部信息,避免了线性反演的复杂计算;其数据融合的观点,为解决地球物理联合反 演问题提供了新的思路. 通过模拟实验和应用实例验证,该方法是有效的. 相似文献
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The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106kn2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October,2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax).Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1pAR) >early growth period > seed maturing period > withering period (0.0098 μmolCO2 · μmol-1pAR).The Pmax did not change greatly during the first three periods, with an average of 0.433mgCO2· m-2· s-1, i.e. 9.829 μmolCO2· m-2· s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower. 相似文献
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Chemical weathering in the Upper Huang He (Yellow River) draining the eastern Qinghai-Tibet Plateau 总被引:8,自引:0,他引:8
We examined the fluvial geochemistry of the Huang He (Yellow River) in its headwaters to determine natural chemical weathering rates on the northeastern Qinghai-Tibet Plateau, where anthropogenic impact is considered small. Qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution. Most samples are supersaturated with respect to calcite, dolomite, and atmospheric CO2 with moderate (0.710-0.715) 87Sr/86Sr ratios, while six out of 21 total samples have especially high concentrations of Na, Ca, Mg, Cl, and SO4 from weathering of evaporites. We used inversion model calculations to apportion the total dissolved cations to rain-, evaporite-, carbonate-, and silicate-origin. The samples are either carbonate- or evaporite-dominated, but the relative contributions of the four sources vary widely among samples. Net CO2 consumption rates by silicate weathering (6-120 × 103 mol/km2/yr) are low and have a relative uncertainty of ∼40%. We extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide. The Ganges-Brahmaputra draining the Himalayan front has higher CO2 consumption rates (110-570 × 103 mol/km2/yr) and more radiogenic 87Sr/86Sr (0.715-1.24) than the Upper Huang He, but the rivers at higher latitudes are similar to or lower than the Upper Huang He in CO2 uptake by silicate weathering. In these orogenic zones, silicate weathering rates are only weakly coupled with temperature and become independent of runoff above ∼800 mm/yr. 相似文献
68.
Assessment of flow paths and confluences for saltwater intrusion in a deltaic river network
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Saltwater intrusion is a serious issue in estuarine deltas all over the world due to rapid urban sprawl and water shortage. Therefore, detecting the major flow paths or locations at risk of saltwater intrusion in estuarine ecosystems is important for mitigating saltwater intrusion. In this paper, we introduce a centrality index, the betweenness centrality (BC), to address this problem. Using the BC as the weighted attribute of the river network, we identify the critical confluences for saltwater intrusion and detect the preferential flow paths for saltwater intrusion through the least‐cost‐path algorithm from a graph theory approach. Moreover, we analyse the responses of the BC values of confluences calculated in the river network to salinity. Our results show that the major flow paths and critical confluences for saltwater intrusion in a deltaic river network can be represented by the least cost paths and the BC values of confluences, respectively. In addition, a significant positive correlation between the BC values of confluences and salinity is determined in the Pearl River Delta. Changes in the salinity can produce significant variation in the BC values of confluences. Therefore, freshwater can be diverted into these major flow paths and critical confluences to improve river network management under saltwater intrusion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
69.
A numerical study of mechanical behavior of a cement paste under mechanical loading and chemical leaching
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Based on relevant experimental data of a petroleum cement paste under mechanical loading and chemical leaching, an elastic‐plastic model is first proposed by taking into account plastic shearing and pore collapse. The degradation of mechanical properties induced by the chemical leaching is characterized by a chemical damage variable which is defined as the increase of porosity. Both elastic and plastic properties of the cement paste are affected by the chemical damage. The proposed model is calibrated from and applied to describe mechanical responses in triaxial compression tests respectively on sound and fully leached samples. In the second part, a phenomenological chemical model is defined to establish the relationship between porosity change and calcium dissolution process. The dissolution kinetics is governed by a diffusion law taking into account the variation of diffusion coefficient with calcium concentration. The chemical model is coupled with the mechanical model, and both are applied to describe mechanical response of cement paste samples subjected to progressive chemical leaching and compressive stresses. Comparisons between experimental data and numerical results are presented. 相似文献
70.
Hydrological cycle and water balance estimates for the megadune–lake region of the Badain Jaran Desert,China
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Yan‐Dong Ma Jing‐Bo Zhao Xiao‐Qing Luo Tian‐Jie Shao Zhi‐Bao Dong Qi Zhou 《水文研究》2017,31(18):3255-3268
The hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content, and grain size reveal 3 types of important natural phenomenon: (a) vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone; (b) seepage, wet sand deposits, and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone; (c) zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation, but it is still able to maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long‐term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts. 相似文献