近十年海绵城市建设研究评述与展望

在全球气候变化和快速城市化的背景下,雨洪灾害的频发严重威胁现代城市的可持续发展。因此,海绵城市建设研究受到社会各界的广泛关注。本文基于对国内外近十年海绵城市建设相关文献的计量分析,梳理了这一领域的研究热点及前沿动态,并对城市雨洪成因、控制目标与指标体系、重点建设区、专项规划及技术设施五部分主要研究内容和既有的研究方法进行了系统总结。在此基础上,指出未来海绵城市建设研究应重点探索的方向。

Seismic force modification factor for ductile structures

The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDOF systems, wherein the hys-teresis models are elastic-perfectly-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped and bilinear-elastic. The latter two models are analysed for separating the effect of the ductility and the energy-dissipating capacity. Three-hundred eighty-eight earthquake records from different site conditions are used in analysis. The ductility is taken to be 2, 3, 4, 5 and 6, with the damping ratio being 0.02, 0.035 and 0.05 respectively. The post-yield stiffness ratios 0.0, 0.1 and 0.2 are used in the analysis. The R spectra are standardized by the characteristic period of the earthquake records, which leads to a much smaller scatter in averaged numerical results. It was found that the most important factor determining R is the ductility. R increases more than linearly with ductility. The energy-dissipating capacity, damping and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with short period and moderate period (0.3≤T/Tg<5.0). For EPP and ELH models, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post-yield stiffness is less than 10% of the initial stiffness. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of the system and ductility for EPP and ELH models were established for each site and soil condition.

Effect of Sc and Er additions on superplastic ductilities in Al-Mg-Mn-Zr alloy

The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr(mass fraction,%)alloys sheet was investigated,and the effect of Sc and Er was discussed.The results show that the superplastic ductilities of Al-Mg-Mn-Sc-Zr alloy was higher than that of Al-Mg-Mn-Er-Zr alloy at a wide temperature range of 400-540°C and high strain rate range of1.67×10-4-1.67×10-1 s-1.A maximum elongation 673%is obtained at 520°C and 1.67×10-3 s-1 in the Sc-containing alloy;while the Er-containing alloy only gets a maximum elongation 253%at 520°C and 1.67×10-3 s-1.Moreover,the average stress exponent of Sc-containing alloy is about 2.84,which is smaller than that of Er-containing alloy(3.64).Besides,the activation energies of the Sc-containing and Er-containing alloy are 84.8 k J/mol and 87.2 k J/mol,respectively.It is indicated that grain boundary sliding is the dominant mechanism during tensile deformation.According to microstructure examination,the better superplasticity of Sc-containing alloy may be attributed to the presence of Al3_(Sc,Zr)dispersoids,which can inhibit recrystallization and grain growth effectively.

Elastoplastic analysis of knee bracing frame

The knee bracing steel frame (KBF) is a new kind of energy dissipating frame, which combines excellent ductility and lateral stiffness. As the structural fuse of the frame, the knee element will yield first during a severe earthquake so that no damage occurs to the major structural members and the rehabilitation is easy and economical. To help fully understand the relations be- tween its seismic performance and the structural parameters, systematic elastoplastic analysis of the KBF structure with finite element method was conducted in this work. Finally, general design recommendations were made according to the results of the analysis.

Research progress of micro(nano)plastics in marine survey in China

The extensive existence of microplastics in the marine environment and the various definite and indefinite harm to the living creatures have been paid much attention.In this paper,the definition,source and pollution of micro(Nano)plastics in marine environment are reviewed.The related literatures are retrieved by using big data platform,the distribution characteristics of micro(Nano)plastics in the marine environment,control measures and so on,and the characteristics of key words making,resource distribution and contribution rate of research institutions are comprehensively analyzed.It provides the technical support for the scientific management of micro(Nano)plastics in the future.

Plastic Microbeads in Cosmetics:Regulations and Alternatives

The concept of microbeads and the use of plastic microbeads(as a form of micro plastic) in cosmetics were introduced. The legislations related to prohibition of plastic microbeads in cosmetics in different countries were reviewed. And the harzards and alternatives of plastic microbeads were described.

Analysis of Environmental Management for the Treatment of Plastic Waste in Mexico： Government Strategies

In Mexico, garbage represents a high pollution index according to national and international organizations; eighty percent of waste products stay in sanitary landfills, out of doors, where no tailings management exists. Plastic products represent 16% of this pollution （one and one-half kilos daily per person in a country with a population of 107 million people）. These sanitary landfills are methane deposits, and consequently emit gases and toxins that cause serious health problems. The object of this is to analyze governmental programs, strategies, policies and procedures which regulate both industrial sectors and society. Society and government share a responsibility since they must implement norms which include the separation, reduction, recycling and reuse of garbage. Results demonstrate that government strategies used to treat railings are complex and are directed more towards sanctions than to motivation. Furthermore these strategies discourage a cultural transformation toward industrial sustainability. Instead of reducing the garbage accumulation problem, they increase the difficulty.

EXTERNAL AND INTERNAL CONTROL IN PLANT DEVELOPMENT

Bodies of plants are modularly organized. Development proceeds by adding new modules to open endings with a potential for branching. Each module is autonomous to some extent. Development relies on the self-organized patterns that emerge from the interactions of individual modules. Interactions include both competition and cooperation,and several types of positive and negative feedback loops are involved. Development can be open to external influences, thus enabling the plant to adjust its form to the environment,for example, to the spatial distribution of ecological resources. This paper provides a review on adaptive plasticity in plants.

Exceptionally shear-stable and ultra-strong Ir-Ni-Ta high-temperature metallic glasses at micro/nano scales

Ir-Ni-Ta metallic glasses(MGs)exhibit an array of superior high-temperature properties,making them attractive for applications at high temperatures or in harsh environments.However,Ir-Ni-Ta bulk MGs are quite brittle and often fracture catastrophically even before plastic yielding,significantly undercutting their high-strength advantage.Here,we show that the Ir-Ni-Ta MGs are not intrinsically brittle,but rather malleable when the feature size is reduced to micro/nano-scales.All tested Ir-Ni-Ta MG micropillars with a diameter ranging from~500 nm to~5μm display a large plastic strain above 25%(the maximum up to 35%),together with a yield strength up to 7 GPa,well exceeding the strength recorded in most metallic materials.The intrinsic shear stability of Ir-Ni-Ta MGs,as characterized by the normalized shear displacement during a shear event,is much larger than those malleable Zr-and Cu-based MGs.Our results suggest that Ir-Ni-Ta MGs are excellent candidates for micro/nanoscale structural applications used at high-temperature or extreme conditions.