Effects of Land Use Patterns on Soil Heavy Metal Contents

Through sampling in farmland and analysis in laboratory,the contents and the pollution level of Cr,Cu,As,Pb,Zn in different soils were studied. The comparative result showed that the As in all soil samples are lower than the mean value of Shaanxi and whole nation,the Cr in lower half soil samples are higher than the mean value of Shaanxi and whole nation,the Cu and Zn in majority soil samples are higher than the mean value of Shaanxi and whole nation,and the Pb in all soil samples is higher than the mean value of Shaanxi and whole nation. The single factor pollution index and multi-factor pollution index method were used to evaluate the soil pollution. According to Soil Environmental Quality Standard,the studied soils were at unpolluted degrees,the soils were clear,the quality of soil adapt to the crop growth,and not affect the quality of agricultural product.

Earth Ecosystem Theory: I Theoretical System

Earth is the place of human existence and life. Without the earth,there is no human,no nature either. To study human existence,the earth of human living is firstly studied. By the study of many natural phenomena on the earth,we firstly put forward the theory of earth ecosystem,expound its definition,structure,aim,function,content and significance,and illustrate the characteristics of earth ecosystem. So we found the theory of earth ecosystem,and unveil the variable processes and the operation mechanisms of earth ecosystem. We put forward the earth ecosystem and its theoretic system,which are different from the previous ＂ earth system science＂ and ＂ Gaia hypothesis＂. We consider that among each part of the environment,between environment and organism,there are organic,close and coalescent relationships,so that the earth ecosystem is able to have a sustainable development. Even if there is no life,the earth ecosystem also can control and regulate the earth changes,and possesses the stable state. Therefore,the foundation of the earth ecosystem theory is conducive to the studies of the global problems： the change processes and trends of resources,ecologies,environments,disasters,and so on.

Effects of Cr Content and Annealing Temperature on Microstructure and Wear Characteristics of Cast Ausferrite Nodular Iron

The effects of Cr content and annealing temperature on abrasive wear characteristics of cast ausferrite nodular iron were investigated with Suga type abrasive wear tester. The surface morphology and Vickers hardness of the tested samples were analyzed by scanning electron microscopy（SEM）, digital microscope and Vickers hardness tester. The results show that the cast ausferrite nodular iron could be obtained by alloying with Cr in the as-cast ductile cast iron and permanent mold casting, and the bainite content in the matrix increased with increasing Cr content. However, the decomposition of bainite took place during annealing at 500 °C to 800 °C; especially, at 800 °C, the bainite transformed into a mixture of fine lamellar pearlite and ferrite matrix structure. The wear loss of specimens was reduced with increasing Cr content in the cast ausferrite nodular iron. The wear loss of the sample cast ausferrite nodular iron with 0.4mass% Cr is the least. The wear loss began to increase while the Cr content is 0.6mass%. The wear loss of annealed ductile irons at different annealing temperatures was higher than that of as-cast samples. During the abrasive wear, the shear stress transformed austenite to martensite, and the hardness of specimens increased and the wear resistance of as-cast ductile cast iron was improved.