Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea (SCS) were measured to make a comparison during terrestrial vegetation reconstruction from ~42 ka to ~7 ka. The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores, showing that more C4 plants developed during the Last Glacial Maximum (LGM) and C3 plants dominated in the interglacial period. However, these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols, which showed C3 plant expansion during the LGM. The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water, resulting in poor preservation of terrestrial vegetation signals. On the other hand, the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals, respectively, may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water. Nevertheless, large variations on n-alkyl lipid compositions in C3/C4 plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals, thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols. 相似文献
The floating bridge bears the dead weight and live load with buoyancy, and has wide application prospect in deep-water transportation infrastructure. The structural analysis of floating bridge is challenging due to the complicated fluid-solid coupling effects of wind and wave. In this research, a novel time domain approach combining dynamic finite element method and state-space model (SSM) is established for the refined analysis of floating bridges. The dynamic coupled effects induced by wave excitation load, radiation load and buffeting load are carefully simulated. High-precision fitted SSMs for pontoons are established to enhance the calculation efficiency of hydrodynamic radiation forces in time domain. The dispersion relation is also introduced in the analysis model to appropriately consider the phase differences of wave loads on pontoons. The proposed approach is then employed to simulate the dynamic responses of a scaled floating bridge model which has been tested under real wind and wave loads in laboratory. The numerical results are found to agree well with the test data regarding the structural responses of floating bridge under the considered environmental conditions. The proposed time domain approach is considered to be accurate and effective in simulating the structural behaviors of floating bridge under typical environmental conditions.
Urban land-use change is the result of coupling interaction between planning and environment systems. The aim of our study was to construct an effective model to show how the urban land-use changes under the planning–environment interaction system with multi-hierarchy and major function oriented zoning. Combining the Cellular automata (CA) model with logistic regression model, the proposed multi-hierarchal vector CA model (MH-VCA3) was constructed by mining multi-hierarchal land-use transition rules under the planning–environment interaction system. Taking Jiangyin City (China) as an example, we compared the simulated result of the proposed model to those of the well-accepted Logistic CA and traditional multi-level CA models to demonstrate the effectiveness of the consideration of top-down decomposition constraint and bottom-up updating. Furthermore, by simulating the land-use changes under different population regionalization scenarios, we found that in order to form the spatial pattern of “agglomeration in the north and ecology in the south,” the planned population growth at the global hierarchal level should be allocated to the district units according to the law of Central district > Chengxi district > Chengdong district > Chengnan district > Chengdongnan district. The proposed model is expected to provide scientific support for the formulation of urban planning schemes in the future. 相似文献
traditional In this paper, two drawbacks pseudo-static method (vertical of the slice method) in the slope stability evaluation have been studied. First, the sliding mass is divided into vertical slices according to this method, which is irrational to some extent in the seismic design of slope. Second, only peak ground acceleration (PGA) is considered, and the effects of shaking frequency and duration on slope stability are neglected. And then, based on the theory of elastic wave and the summarized geological model, this paper put forwards an improved method of pseudo-method by using the theory of elastic wave and Hilbert-Huang transform. The improved pseudostatic method gives reasonable considerations to the time-frequency effects of seismic wave and its rationality has been verified by the shaking table test. This method can evaluate the safety of a slope, the happening time and the scale of landslides. At the same time, this method also can improve the high accuracy of the evaluation of the safety of the slope. 相似文献
Assessing and managing the spatial variability of hydropedological properties are important in environmental,agricultural,and geological sciences.The spatial variability of soil apparent electrical conductivity(ECa) measured by electromagnetic induction(EMI) techniques has been widely used to infer the spatial variability of hydrological and pedological properties.In this study,temporal stability analysis was conducted for measuring repeatedly soil ECa in an agricultural landscape in 2008.Such temporal stability was statistically compared with the soil moisture,terrain indices(slope,topographic wetness index(TWI),and profile curvature),and soil properties(particle size distribution,depth to bedrock,Mn mottle content,and soil type).Locations with great and temporally unstable soil ECa were also associated with great and unstable soil moisture,respectively.Soil ECa were greater and more unstable in the areas with great TWI(TWI 〉 8),gentle and concave slope(slope 〈 3%; profile curvature 〉 0.2).Soil ECa exponentially increased with depth to bedrock,and soil profile silt and Mn mottle contents(R2= 0.57),quadratically(R2 = 0.47),and linearly(R 2 = 0.47),respectively.Soil ECa was greater and more unstable in Gleysol and Nitosol soils,which were distributed in areas with low elevation(〈 380 m),thick soil solum(〉 3 m),and fluctuated water table(shallow in winter and spring but deep in summer and fall).In contrast,Acrisol,Luvisol,and Cambisol soils,which are distributed in the upper slope areas,had lower and more stable soil ECa.Through these observations,we concluded that the temporal stability of soil ECa can be used to interpret the spatial and temporal variability of these hydropedological properties. 相似文献
Increasing recognition of the value of practice-based or experiential knowledge in natural resource management justifies the creation of a new category of articles in Society & Natural Resources that we are calling Practice-Based Knowledge (PBK). The rationale for focusing on PBK is due to its key role in the emergence of hybrid governance institutions across state, market, and civil society, understanding the complexity of dynamic socioecological systems, recognizing the challenges of multiple knowledge systems and context-specific practices, embracing the power of informal institutions and civic science, and engaging debates on the growing prevalence of market-oriented conservation. The goal is to provide a dedicated space within the published, peer-reviewed literature for scholars, government officials, nonprofit managers, and engaged citizens to share experiences informed by practical action. Relevant and timely practice-based insights may improve understanding and management of social and ecological processes and systems, while also offering the potential to contribute to theory. 相似文献