To investigate the effect of ZrC on the ablative properties of C/SiC composites in a high-temperature environment, the oxidative ablation of C/SiC and C/SiC-ZrC composites at high-temperatures was ...examined through ablation tests. In this study, two ceramic matrix composites, C/SiC and C/SiC-ZrC, were prepared by chemical vapor deposition and precursor impregnation pyrolysis. The ablation properties of the materials were tested and analyzed using an oxyacetylene flame to simulate a high-temperature environment. The results revealed that the line ablation rate of C/SiC-ZrC was 8.48% and 20.81% lower than that of C/SiC at 30 s and 60 s, respectively. At the same ablation time, the depth of the crater resulting from erosion of the C/SiC material by the high-temperature airflow was deeper than that of C/SiC-ZrC. The traces of the fibers subjected to erosion were more prominent. In a longitudinal comparison, the mass ablation rate of C/SiC-ZrC material decreased with the increase in time, while the line ablation rate initially increased rapidly and then decreased. From 30 s to 90 s of ablation, the line ablation rate and mass ablation rate decreased by 55.62% and 89.5%, respectively. The overall trend for both rates was a decrease with the increase in time. Under the same ablation time, the ablation rate of C/SiC-ZrC was generally lower than that of C/SiC. This is because the generated molten ZrO2 was more viscous and denser than SiO2, effectively blocking oxidizing gases from penetrating the interior of the material. The molten ZrO2 provided better protection for the substrate in the high-temperature environment.
In the last thirty years, the Qinhuai River Basin has experienced a rapid urban development and population growth, resulting in great land use changes. The SWAT (Soil and Water Assessment Tool) model ...was applied to simulate daily runoff associated with land use changes. The spatially distributed parameters were obtained with the help of GIS (Geographic Information System) interface. The runoff calibration was conducted from 1988 to 1997, and nine years (1998 to 2006) of data were used for validation, with four land use maps, representing land use conditions of corresponding water years. Results showed that simulation of daily runoff was satisfactory, indicating SWAT had the capability of adequately simulating the effect on runoff from the temporal and spatial variability in the Qinhuai River Basin. This study was also an essential basis for further assessing the impact of land use changes on hydrology and hydrological response to different land use scenarios.
A distributed hydrological model that can simulate the hydrological processes of watershed by considering both saturation-excess and infiltration-excess runoff mechanisms is intruduced. The model is ...based on MapWinGIS platform and adopts modular programming ideas, watershed features such as river network and subbasins can be extracted automatically. In the model, the hydrological processes of watershed are divided into evapotranspiration, runoff gereration, overland flow, interflow, groundwater flow and river channel flow, and each process has a variety of calculation methods This model considers multiple runoff generation mechanisms, such as saturation-excess runoff and infiltration-excess runoff. The calibration and test of the model are performed in qinhuai river watershed, a basin in Jiangsu province, eastern China. The results show that the watershed features extracted automatically based on MapWindow GIS is reasonable, and the simulated runoff hydrograph is pretty matching the observed values.
In recent years, many studies have focused on the changes of partial or single African ecosystems and the drivers of those changes. However, focusing only on partial or single ecosystems has limited ...the understanding of the relationships between the vegetation and climate changes in all of the African ecosystems. In this study, the temporal trends of the satellite-derived annual mean leaf area index (GLASS-LAI) were analyzed, and the inter-annual relationships were developed between the annual mean LAI and the climate variables (precipitation and temperature) for the time period ranging from 1982 to 2013. Additionally, this study applied seasonal curves and step-wise multiple regression methods to investigate the relationships between intra-annual LAI and climate changes. It was found that the GLASS-LAI over half of Africa had shown general significant greening or browning trends during the period from 1982 to 2013. From the results of inter-annual analysis, with mean annual precipitation lower than 600 mm, the greening of the savannas and grasslands in the Sahel was found to highly correspond with the increased precipitation. In contrast, the evergreen broadleaf forests in the Gulf of Guinea and Congo Basin showed strongly positive responses to the annual temperature when the mean annual temperature was below 25 °C. In regard to the intra-annual responses, the precipitation with 1-month lags was found to be helpful for the vegetation growth, with the exception of the evergreen broadleaf. The results of this research study indicated that the different land-covers in Africa had displayed clear differences in their annual trends during the examined 32-year period and had responded differently to the inter- and intra-annual climate drivers. This difference was evident by the characteristics of the vegetation covers and the geographic distributions. Therefore, further examinations of these differences can potentially improve the understanding of the land surface-atmosphere interactions among the different African ecosystems.
Impervious surface (here after IMP) is a typical characteristic of urban area and is one of the most important environmental indicators. A 30 year time series (1979-2009) of Landsat imagery and CBERS ...imagery for Qinhuai River basin was analyzed to estimate the IMP. A new approach was proposed to quantify impervious surface as a continuous variable by using multi-temporal and multi-source datasets. The principal component analysis (PCA) approach was performed in CBERS imagery to increase information of image. Linear Spectral Mixture Analysis (LSMA) was used to determine the fractional composition of vegetation, high- and low-albedo and soil for each pixel of the normalized data. Supervised classification technique and MNDWI (Modified Normalized Difference Water Index) method were used to extract water. IMP was then estimated by adding all of high-albedo and part of low-albedo fraction images. Temporal rule, that minimized classification error, was developed based on each pixel's classified trajectory over the time series of imagery. Overall cross-date classification accuracies for impervious vs. non-impervious surface were greater than 85%. The results indicated that the area of impervious surface in the Qinhuai River basin increased by 963% over 30 years, and impervious surface rate was from 1.70% in 1979 to 18.02% in 2009. The increase rate of IMP was 7.1% before 2003 and 12.9% after 2003. This approach demonstrated that impervious surface distribution could be derived from multi-temporal and multi-source satellite datasets with promising accuracy.
The changes of impervious surface from 1986 to 2006 and the relationship between those changes and hydrological response were studied in the Qinhuai River Basin (2631 km 2 ), which is located in the ...southwest of Jiangsu Province, P. R. China. A series of Landsat imagery during that period was employed to extract impervious area using the Linear Spectral Mixture Analysis. The results showed that impervious area increased from 2.9% in 1986 to 12.1% in 2006. The annual runoff and precipitation of the basin were collected to analyze the relationship between impervious surface area and annual runoff. Based on the regression analysis, it was found that the average annual runoff depth has increased by 26% since 2003 due to the increase of impervious area.
TOPMODEL, a semi-distributed hydrological model, has been widely used. In the process of simulation of the model, Digital Elevation Model （DEM） is used to provide the input data, such as topographic ...index and distance to the drainage outlet; thus DEM plays an important role in TOPMODEL. This study aims at examining the impacts of DEM uncertainty on the simulation results of TOPMODEL. In this paper, the effects were evaluated mainly from quantitative and qualitative aspects. Firstly, DEM uncertainty was simulated by using the Monte Carlo method, and for every DEM realization, the topographic index and distance to the drainage outlet were extracted. Secondly, the obtained topographic index and the distance to the drainage outlet were input to the TOPMODEL to simulate seven rainstorm-flood events, and four evaluation indices, such as Nash and Sutcliffe efficiency criterion （EFF）, sum of squared residuals over all time steps （SSE）, sum of squared log residuals over all time steps （SLE） and sum of absolute errors over all time steps （SAE） were recorded. Thirdly, these four evaluation indices were analyzed in statistical manner （minimum, maximum, range, standard deviation and mean value）, and effect of DEM uncertainty on TOPMODEL was quantitatively analyzed. Finally, the simulated hydrographs from TOPMODEL using the original DEM and realizations of DEM were qualitatively evaluated under each flood cases. Results show that the effect of DEM uncertainty on TOPMODEL is inconsiderable and could be ignored in the model＇s application. This can be explained by： 1） TOPMODEL is not sensitive to the distribution of topographic index and distance to the drainage outlet; 2） the distribution of topographic index and distance to the drainage outlet are slightly affected by DEM uncertainty.
