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Yang S.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Zong L.,Tsinghua University | Wang Y.,Tsinghua University
Applied Mechanics and Materials | Year: 2011

Highway bridges played an important role in lifeline systems. Their seismic damage status made a direct influence on the implement plan of the earthquake relief work and the life and property security of the people. Therefore, accurate assessment and prediction for the seismic damage of highway bridges were of vital significance, based on which reasonable earthquake fortification could be implemented. This paper summarized and classified the existing seismic damage assessment methods for highway bridges, including certain index evaluation methods based on statistical results, vulnerability index evaluation methods based on probability theory and vulnerability index evaluation methods based on aggregation model. Then the capacity-spectrum method which could be used for calculating the fragility curve and the seismic assessment model of highway bridges used in HAZUS were specially explained. At last, the proposal for the development of seismic assessment systems related with highway bridges in China was put forward. Considering HAZUS's good performance in seismic assessment, a similar assessment system should be built in China as soon as possible. The first step should be classifying highway bridges in China based on their current situation and obtaining their seismic assessment model parameters roughly, which tend to be safe. The second step should be carrying out sufficient experiments and numerical analysis and revising the model parameters obtained in the first step. © (2011) Trans Tech Publications. Source


Wu Y.-S.,Beijing Normal University | Wu Y.-S.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Wu Y.-S.,Inner Mongolia Normal University | Ma W.-L.,Inner Mongolia Normal University | And 4 more authors.
Chinese Journal of Applied Ecology | Year: 2010

Sampling sites were installed in Damao Banner, Siziwang Banner, and Sunite Right Banner of Inner Mongolia, which represented lightly, moderately, and heavily degraded desert steppes, respectively, and surface (0-20 cm) soil samples were collected to analyze the quantitative charaeteristics and seasonal dynamics of soil organic carbon (SOC) and microbial biomass carbon (MBC) in these steppes. The SOC and MBC contents decreased with the increasing degradation degree of desert steppe. The total amount of soil culturable microbes in lightly and moderately degraded desert steppes was higher than that in heavily degraded desert steppe, except in summer 2006, and the MBC content and the quantity of soil culturable microbes were higher in summer and autumn than in spring and winter. Correlation analysis showed that there was a significant positive correlation between SOC and MBC (P <0. 01), suggesting that both SOC and MBC could be used as the sensitive indicators to evaluate the degradation degree of desert steppe. Source


Chen H.,Northwest University, China | Chen H.,Beijing Normal University | Tang H.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Tang H.,Beijing Normal University
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013

The Gaia hypothesis, proposed by James Lovelock in 1970s, claims that the earth is a superorganism consisting of both living organisms and a non-living environment. More specifically, the earth itself has the ability to regulate climate and chemistry, making environments on earth suitable for living organisms. The Gaia hypothesis was strongly criticized by biologists, especially Darwinists. In replying to the criticism, Lovelock and Watson developed a mathematical model called Daisyworld to test the hypothesis. The Daisyworld is a planet orbiting around the sun, which is populated by two different types of plants, black daisies and white daisies. The color of the daisies influences the albedo of the planet in a way that black daisies absorb more sunlight and warm the planet, while white daisies reflect more sunlight and cool the planet. Based on this model, we analyzed the temperature-regulating ability in the Daisyworld model under various initial conditions using the methods of system dynamics. The initial conditions that proposed in this paper included three sets of initial area distribution patterns between black and white daisies and three sets of sunlight albedo combinations of the two daisies. The software package we used here is Stella 9. 0. 2 developed by ISEE System, Inc. The simulation results showed that, although the initial conditions of the Daisyworld model were different, all temperatures, as the system settled down, eventually reached at 21.55°C, a temperature close to the optimum for daisy growth. From the results we know that the Daisyworld model is insensitive to the initial conditions such as area distribution patterns and albedo combinations. While the temperature-regulating ability is insensitive to albedo combinations of the two daisies, our results showed that albedo combinations can affect the time length that the Daisyworld model needs to reach at a stable state. That is, when the albedo difference between black daisy and white daisy is smaller, the time length will be longer. Based on the simulation process and results, we further discussed the advantages and disadvantages of the Daisyworld model. We argued that simplification and systematic analysis are the advantages of the model. Through a simple feedback relationship between organisms (i. e. black and white daisies) and environment factors (i. e. temperature), the natural selection and competition between two daisies could lead to a balance of populations that tends to favor planetary habitability, without human intervention. Because of its simplification and systematic analysis, the Daisyworld model is now applied all over the world in both system engineering and environmental science. It inspires the researchers who are not used to system thinking, and changes their thinking habits forever. But this simplification has some disadvantage in the Daisyworld model. Compared with the real complicated earth system, this model is obviously too simple, which leads to a simple result. In order to get a more scientific result, we suggests that the model should include more detailed information of the earth such as more environmental variables, biological variables, feedback relationships, and human activities. The Gaia system should eventually be integrated into the more advanced Nature-Human Coupled System. Source


Liu X.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Liu X.,Beijing Normal University | Zhu X.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Zhu X.,Beijing Normal University | And 7 more authors.
Acta Geographica Sinica | Year: 2014

Using the daily minimum temperature data of 121 meteorological stations in Inner Mongolia and its surrounding areas, this paper analyzed the spatiotemporal variation of cold surge and its possible influencing factors in Inner Mongolia during 1960-2012, based on piecewise regression model, Sen+Mann-Kendall model, and correlation analysis. The results show that, (1) The occurrence frequency of single-station cold surge presented a decreasing trend in Inner Mongolia during recent 53 years, with a linear tendency of -0.5 times/10a (-2.4-1.2 times/10a), of which a significant decreasing trend was detected before 1991, being -1.1 times/10a (-3.3-2.5 times/10a), while an increasing trend of 0.45 times/10a (-4.4-4.2 times/10a) was found after 1991. On the seasonal scale, the trend of spring cold surge was consistent with that of the annual value, and the most obvious change of cold surge also occurred in spring. The frequency of monthly cold surge showed a bimodal structure, and November witnessed the highest incidence of cold surge. (2) Spatially, the high incidence of cold surge is mainly observed in the northern and central parts of Inner Mongolia, and higher in the northern than the central part. The inter-decadal characteristic also detected that high frequency and low frequency regions presented a decreasing trend and an increasing trend, respectively, during 1960-1990, while high frequency regions expanded after the 1990s, regions with high frequency of cold surge were mainly distributed in Tol Gol, Xiao’ergou, and Xi Ujimqin Banner. (3) On annual scale, the cold surge was dominated by AO, NAO, CA, APVII, and CQ, while the difference in driving forces among seasons was detected. Winter cold surge was significantly correlated with AO, NAO, SHI, CA, TPI, APVII, CW, and IZ, indicating that cold surge in winter was caused multifactor. Autumn cold surge was mainly affected by CA and IM, while spring cold surge was significantly correlated with CA and APVII. Source


Zhang H.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Yuan W.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Dong W.,State Key Laboratory of Earth Surface Processes and Resource Ecology | Liu S.,U.S. Geological Survey | Liu S.,Central South University of forestry and Technology
Ecological Complexity | Year: 2014

The seasonal litterfall plays an important role in the process of forest carbon and nutrient cycles. The current dynamic vegetation models use a simplified method to simulate seasonal patterns of litterfall, and assume that litterfall inputs distributed evenly through the year for deciduous trees or occur once during the start of year for evergreen trees. In this study, we collected more than 400 litterfall measurements for different forest ecosystems from existing literature and monographs, and analyzed the seasonal patterns of litterfall over the various forest types. The results showed that the total annual litterfall varied significantly by forest types in the range of 3-11Mgha-1y-1. The seasonal litterfall patterns had diverse forms and varied obviously among the forest types. For tropical forests, the litter peaks occurred mostly in spring or winter, corresponding to the drought season; for temperate broadleaved and needle-leaved evergreen forests, litter peaks could occur at various seasons; and for temperate deciduous broadleaved and boreal evergreen needle-leaved forests, litter peaks were observed in autumn. Global analyses showed that seasonal patterns of litterfall were determined by both the physiological mechanism and environmental variables. © 2014 Elsevier B.V. Source

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