Emergy analysis of the urban metabolism of Beijing

Cities can be modeled as if they were superorganisms with a range of metabolic processes. Research on this urban metabolism can contribute to solving urban environmental problems by revealing details of the metabolic throughput of the system. A key issue is how to find a common basis for measuring the environmental and economic values. By providing a single unified unit, emergy theory integrates the natural and socioeconomic systems and thoroughly evaluates a system's metabolism. We analyzed Beijing's urban metabolic system using emergy synthesis to evaluate its environmental resources, economy, and environmental and economic relations with the regions outside the city during 14 years of development. We compared Beijing's emergy indices with those of five other Chinese cities and of China as a whole to assess Beijing's relative development status. These indices are the emergy self-support ratio (metabolic dependence), the environmental load ratio (metabolic loading), empower density (metabolic pressure), emergy used per person (metabolic intensity per capita), and the monetary equivalent of emergy (emdollars; metabolic intensity). Based on our emergy analysis, Beijing's socioeconomic system is not self-sufficient, and depends greatly on external environmental resources. Its GDP is supported by a high percentage of emergy purchased from outside the city. During the study period, Beijing's urban system showed an increasing dependence on external resources for its economic development. Beijing's loading and pressure on the ecological environment is continuously increasing, accompanied by continuously increasing human emergy consumption. In the future, it will become increasingly necessary to improve Beijing's metabolic efficiency.     

区域经济空间过程阻力面模型的初步研究

经济过程是各种要素流集聚和扩散的过程，在此过程中要素流的运动必然受到阻力的作用。基于此考虑，提出了经济过程阻力面模型，用以表示一个地区经济过程阻力的空间分布以及经济过程的运动趋势。空间经济过程阻力面模型对研究要素流的运动和区域发展战略规划有积极的启示意义。以浙闽赣（ZMG）边界区案例分析为例，模型计算得到的ZMG阻力面图比较客观地反映了浙闽赣交界区的物资流的阻力状况。ZMG边界区正如温台、闽南、江西经济发达区内的一个高阻力值的“岛”，从ZMG阻力面图可以看到有两个峰，一个在浙闽交界区（庆元、景宁），另一个在闽赣交界区（光泽、邵武）。在浙江境内的阻力线密度大、阻值高，说明浙江境内物资流动的地区差异明显。两峰之间为鞍（通），武夷山市处于这个“鞍”之上，同时展示了该模型在启示省域边缘带发展规划中的现实作用。     

Regeneration of Native Trees in the Presence of Invasive Saltcedar in the Colorado River Delta, Mexico

Abstract:  Many riparian zones in the Sonoran Desert have been altered by elimination of the normal flood regime; such changes to the flow regime have contributed to the spread of saltcedar ( Tamarix ramosissma Ledeb.), an exotic, salt-tolerant shrub. It has been proposed that reestablishment of a natural flow regime on these rivers might permit passive restoration of native trees, without the need for aggressive saltcedar clearing programs. We tested this proposition in the Colorado River delta in Mexico, which has received a series of large-volume water releases from U.S. dams over the past 20 years. We mapped the vegetation of the delta riparian corridor through ground and aerial surveys (1999–2002) and satellite imagery (1992–2002) and related vegetation changes to river flood flows and fire events. Although saltcedar is still the dominant plant in the delta, native cottonwood (  Populus fremontii S. Wats.) and willow ( Salix gooddingii C. Ball) trees have regenerated multiple times because of frequent flood releases from U.S. dams since 1981. Tree populations are young and dynamic (ages 5–10 years). The primary cause of tree mortality between floods is fire. Biomass in the floodplain, as measured by the normalized difference vegetation index on satellite images, responds positively even to low-volume (but long-duration) flood events. Our results support the hypothesis that restoration of a pulse flood regime will regenerate native riparian vegetation despite the presence of a dominant invasive species, but fire management will be necessary to allow mature tree stands to develop.     

Gas–Liquid Two-Phase Flow in a Mini-Channel with Water Infiltration Continuously Along the Flow Direction

Characteristics of air–water two-phase flow pattern in a square-mini-channel were investigated experimentally. One sidewall of the flow channel was made of a permeable porous media. Air was fed into the channel from its inlet, while liquid water was injected uniformly into the channel along the permeable sidewall. Based on the results of visualization, the typical flow patterns encountered in the conventional co-current gas–liquid two-phase flow were not observed in the present work. Flow patterns of this special gas–liquid two-phase flow were catalogued, and the influence of gas flow rate and liquid infiltration rate on flow patterns was also analyzed. The results also indicate that the channel differential pressure on both sides brings obvious fluctuations when the liquid is infiltrated. The frequency of this fluctuation depends not only on the amount of liquid infiltration but also relies on the gas flow rate significantly. However, the amount of liquid infiltration barely affects the fluctuation in the amplitude of the pressure differential.     

A model for the initial stages following the rupture of a natural gas transmission pipeline

Experience shows that, despite the best efforts of the pipeline industry worldwide, pipelines do fail and release their contents to the atmosphere. In the case of below-ground pipelines transmitting natural gas, there is a chance that the release will be ignited, posing a significant hazard to any people in the vicinity. Mindful of this hazard, an international group of gas companies have collaborated over a period of many years on research projects aimed at developing an understanding of how these releases may arise (failure causes), how often they might occur (failure frequency), what type of releases might be produced (failure modes) and what type of behaviour might be produced for each of these modes of release (consequence analysis). This paper has been prepared to describe the mathematical models that have been developed on behalf of this group to assess the initial transient period following the rupture of a buried natural gas transmission pipeline assuming the release ignites immediately. It gives details of the equations used by the different models and it refers to some of the experimental data that has been used in the development of the models. A comparison of the model with the experimental data is provided. This demonstrates that the early stages could have a significant impact when evaluating the harm that could be caused. This provides a justification for developing the models rather than using a simpler alternative that does not take the initial highly transient period into account.     

环境资源配置低效率及自然资本"富聚"现象剖析

根据技术效率、经济效率、自然效率、社会效率之间的关系，探讨了四个效率背离所导致的资源配置效率丧失以及由此引发的社会福利损失问题。在分析价格信号在资源配置过程中的作用的基础上，探讨了市场失效和价格背离现象。进一步指出了中国经济转型时期存在着自然资本富聚现象，并进一步分析其根源。包括：政府有效干预不足、现行经济增长方式和经济效率实现以对自然资本的低成本占用、机会导向型的资源配置方式、资本的价值取向、对经济财富以及单一行为人的效率追逐、产权缺位等。强调需要强化环境管理的公共管理属性，并对环境资源的权益主体的权利、责任和利益进行有效的界定和实施，通过制度和政策变革，干预和规范市场运作，促进资源的高效和公平配置。     

Construction and demolition waste generation in cities in India: an integrated approach

ABSTRACT

This paper quantifies construction and demolition waste (C&DW) generation rate in Indian cities using bottom-up material flow analysis approach. A dynamic model was applied to different classes of cities in India to investigate how C&DW generation rate varies across different classes of cities. The data on construction and demolition activities in different classes of cities were estimated from information reported in secondary literature. The results show that urban areas in India generated over 150 million tonnes of C&DW in 2016, and almost 50% of waste was generated in small to medium towns. The paper concludes with discussion on opportunities for recycling of C&DW and closing the material loops in Indian cities.     

Exploring regional futures,tools and methodologies

The new English regional governance framework presents fresh opportunities to direct regional development in a more sustainable direction. However, for the North West region it is yet to be seen how these aspirations can be reconciled with the strong 'pro-growth' aims of the regional economic strategy. Within this context, the nature and findings of two interlinked projects which aimed to investigate and model regional development processes are presented. The first, 4-sight, is a resource flow audit for the promotion of sustainable resource management. Focusing on mineral flows, a mass balance methodology is used to facilitate a clearer connection between the use of resources and the generation of waste. Findings from 4-sight were then used in a second project, Atlas^NW, involving the development of a digital atlas and future scenario model. Both projects make a useful contribution to the regional sustainability agenda through providing data and tools to underpin decision-making. Electronic Publication     

Explosibility of hydrogen–graphite dust hybrid mixtures

To evaluate the hazard of combined hydrogen/dust explosions under severe accident conditions in International Thermonuclear Experimental Reactor (ITER), standard method of 20-L-sphere was used to measure the explosion indices of 4-μm fine graphite dust in lean hydrogen/air mixtures. The mixtures were ignited by a weak electric spark. The tested fuel concentrations were 8–18 vol% H₂ and 25–250 g/m³ dust. If the hydrogen content is higher than 10 vol%, the dust constituent can be induced to explode by the hydrogen explosion initiated by a weak electric spark. Depending on the fuel component concentrations, the explosions proceed in either one or two stages. In two-stage explosions occurring at low hydrogen and dust concentrations, the mixture ignition initiates first a fast hydrogen explosion followed by a slower phase of the dust explosion. With increasing dust concentration, the dust explodes faster and can overlap the hydrogen-explosion stage. At higher hydrogen concentrations, the hybrid mixtures explode in one stage, with hydrogen and dust reacting at the same time scale. Maximum overpressures of hybrid explosions are higher than those observed with hydrogen alone; maximum rates of pressure rise are lower in two-phase explosions and, generally, higher in one-stage explosions, than those characteristic of the corresponding H₂/air mixtures.     

Minimum Wet‐Season Flows and Levels in Southwest Florida Rivers1

Abstract: Regulation of river flows can result in decreased stage fluctuations and alteration of inundation patterns of floodplain wetlands. However, floodplain inundation has historically not been addressed in most minimum flow determinations. Florida law requires the water management districts of the state to establish minimum flows and levels to protect water bodies from significant harm associated with water withdrawals. The Southwest Florida Water Management District utilizes a 15% reduction in habitat criterion as a threshold for defining significant harm to freshwater segments of rivers. Utilizing a multi‐parameter approach and different habitat measures for seasonal flow periods, the District has recommended minimum flow compliance standards for the Alafia, Myakka and middle Peace rivers. For the high‐flow period, the District utilized a 15% reduction in the number of days of floodplain inundation (a temporal loss) as a significant harm threshold. This approach yielded allowable flow reductions of 8% for the Alafia and Peace rivers during the high‐flow season and a 7% allowable reduction of natural flows on the Myakka River. Comparison of changes in flows associated with temporal and spatial loss thresholds indicated that flow reductions required to effect a 15% spatial loss of habitat on the Alafia, Myakka and middle Peace rivers are higher than those that would yield a 15% temporal loss. This indicates that with respect to natural flow protection, the District’s consideration of temporal reductions in habitat for establishing minimum river flows for seasonal high‐flow periods is more conservative than the use of a spatial loss criterion.