Material dependence of cities and implications for regional sustainability

Cities rely on massive amounts of physical,chemical,and biological resources to support their growth and metabolism.These‘metabolic inputs’are accumulated in cities to form material stocks in buildings,infrastructures,transportation facilities,and household appliances.This study takes China’s urbanization as an example to illustrate the characteristics of material stock changes in developing countries and compare them with those in developed countries.Results show that(1)material stocks have been growing in China,but have saturated in developed countries,and(2)the major components of urban metabolism are construction and industrial materials(e.g.,steel)in developing countries but biomass(e.g.,food)in developed countries.The changes in the magnitude and types of material stocks can not only measure urban development but also directly link city and its residents,offering advantages in representing urbanization over the existing indices such as population,land use,or gross domestic product(GDP).Given the new insights provided by material stock,we recommend to embrace it as a critical index of urbanization for guiding urban planning and policy-making.

Homogenization of twin-roll cast AA8079 aluminum alloy studied by in-situ TEM

AA8079 is a commonly used stock material for manufacturing thin packaging foils.The primary alloying elements Fe and Si can form binary and tertiary intermetallics.In-situ TEM simulating homogenization annealing process of the as-cast material was used to analyze the real-time changes of the shape,type,and distribution of these particles.They affect the mechanical properties of the final product and susceptibility of the material to the formation of pinholes and other macroscopic defects.Another set of as-cast samples were annealed in a regime simulating industrial treatment in combination with measurements of resistivity to validate the results of the in-situ experiment.The results show clear temperature intervals of recovery,matrix desaturation,and phase transformations occurring in several stages:spheroidization of the original particles above 450℃,nucleation of new particles at 475℃,particles coarsening above 525℃,and an entire dissolution of the original particles above 550℃.

In-use product and steel stocks sustaining the urbanization of Xiamen, China

Introduction:In-use product and material stocks are the amount of concerned manufactured products and materials in active use,and are essential components of urban ecosystem.Methods:This study estimates the dynamic in-use stocks of steel-containing products and steel in the city of Xiamen,China,during 1980–2015 by applying a bottom-up accounting approach.We incorporate 55 categories of steel-containing products that are classified into five end-use sectors(i.e.,buildings,infrastructure,transportation equipment,machinery,and domestic appliances).Outcomes and Discussion:In-use stocks of 51%of the studied products kept increasing during 1980–2015,especially after 2000.Steel stocks have grown up to 4.9±1.4 tons per capita(t/cap)in 2015,from 0.5±0.2 t/cap in 1980.Buildings are the largest reservoirs,although its share decreased from 89%in 1980 to 68%in 2015.The dynamic spatial distribution indicates that steel stocks gradually expanded from urban core to suburban areas.Conclusion:Theresults help to explore how a city’s urbanization is sustained by the in-use stocks growth.In-use steel stocks,of which the growth is highly correlated to and probably driven by the population growth,GDP increase,and urban built-up area expansion,may serve as a supplementary indicator for urbanization.