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排序方式: 共有406条查询结果,搜索用时 578 毫秒
311.
A novel microeconomic formalism for chemical processes is applied to air stripping of harmful volatile organic compounds (VOCs) from aqueous streams in a conventional packed tower. A simplified conceptual process model is combined with techno-economic aggregation rules to obtain an engineering production function, which relates process inputs (capital, material, labor, and energy) to output (stripped water flow rate). Process relationships determine column length and diameter required to achieve a specified VOC percent recovery from an aqueous stream of given composition and flow rate. Total capital is determined using a defined capital unit (1 capital unit=10 foot of 6-inch schedule 40 carbon steel welded pipe=$122, Jan. 1990) to put all installed capital equipment on the same basis and multiplying by 3.37 to account for the necessary plant infrastructure. Process labor is obtained from an empirical correlation, which relates workerhours to mass throughput. Simulations were made for four systems comprised from each of two representative random packings (i.e. 25-mm plastic Pall rings and 25-mm ceramic Raschig rings) and two model VOCs (i.e. 1,2-dichloroethane and trichloroethylene). Several examples are given, and process, technical and economic analyses of the results are presented. Two-dimensional (capital-energy) optimization was effective in determining the least cost combination of inputs for a plant to produce a specified output of stripped water. Furthermore, conventional economic models (e.g. Cobb-Douglas model) and associated methods (e.g. linear programming) were shown to be ineffective for air stripping plant design and optimization. Moreover, increasing returns to scale with economies of scale (declining long-run average cost) are prevalent. 相似文献
312.
313.
314.
Edward M. Jhee Keri L. Dandridge Arthur M. Christy Jr. A. Joseph Pollard 《Chemoecology》1999,9(2):93-95
315.
Sujay S Kaushal Peter M Groffman Paul M Mayer Elise Striz Arthur J Gold 《Ecological applications》2008,18(3):789-804
Increased delivery of nitrogen due to urbanization and stream ecosystem degradation is contributing to eutrophication in coastal regions of the eastern United States. We tested whether geomorphic restoration involving hydrologic "reconnection" of a stream to its floodplain could increase rates of denitrification at the riparian-zone-stream interface of an urban stream in Baltimore, Maryland. Rates of denitrification measured using in situ 15N tracer additions were spatially variable across sites and years and ranged from undetectable to >200 microg N x (kg sediment)(-1) x d(-1). Mean rates of denitrification were significantly greater in the restored reach of the stream at 77.4 +/- 12.6 microg N x kg(-1) x d(-1) (mean +/- SE) as compared to the unrestored reach at 34.8 +/- 8.0 microg N x kg(-1) x d(-1). Concentrations of nitrate-N in groundwater and stream water in the restored reach were also significantly lower than in the unrestored reach, but this may have also been associated with differences in sources and hydrologic flow paths. Riparian areas with low, hydrologically "connected" streambanks designed to promote flooding and dissipation of erosive force for storm water management had substantially higher rates of denitrification than restored high "nonconnected" banks and both unrestored low and high banks. Coupled measurements of hyporheic groundwater flow and in situ denitrification rates indicated that up to 1.16 mg NO3(-)-N could be removed per liter of groundwater flow through one cubic meter of sediment at the riparian-zone-stream interface over a mean residence time of 4.97 d in the unrestored reach, and estimates of mass removal of nitrate-N in the restored reach were also considerable. Mass removal of nitrate-N appeared to be strongly influenced by hydrologic residence time in unrestored and restored reaches. Our results suggest that stream restoration designed to "reconnect" stream channels with floodplains can increase denitrification rates, that there can be substantial variability in the efficacy of stream restoration designs, and that more work is necessary to elucidate which designs can be effective in conjunction with watershed strategies to reduce nitrate-N sources to streams. 相似文献
316.
Urbanization can have profound effects on the plant communities persisting in remnant habitats. That process can be explored by examining patterns of nestedness. Species composition for a set of communities exhibits a nested pattern if species present in progressively richer assemblages form a series of subsets. Nestedness can form as a result of the dynamic processes of extinction or colonization. It can also reflect a nested distribution of habitats among the sites or the differential abundance properties of species through passive sampling. This study investigated whether Sonoran Desert woody vegetation in remnant islands within metropolitan Phoenix is nested and explored which mechanisms are responsible for the pattern. It also examined whether vegetation is nested in similar habitat types across islands, and how species abundance relates to the nested pattern and hypothesized mechanisms. All data sets were significantly nested, indicating a nested pattern at the island and habitat levels. Community-level analyses did not indicate a primary mechanism leading to the nested pattern. Among species with abundances correlated with the nested rank-order of sites, abundance properties were significantly related to different variables. This suggests that individual taxa respond to divergent ecological mechanisms, leading to nestedness. Thus, nestedness in plant communities can result from a complex set of contributors and may not be attributable to a single factor. 相似文献
317.
Arthur P.J. Mol 《国际发展与全球生态学杂志》2013,20(4):303-318
Most globalization scholars identify negative consequences for the environment in the neo-liberal orientation in current economic globalization processes. But at the same time, we can witness constant efforts at the supra-national level to institutionalize environmental interests and considerations in new institutions, arrangements and regimes. Many of the multilateral environmental arrangements give evidence of such developments. This paper aims to analyze the nature, substance and place of institutional clashes that take place between these emerging environmental institutions and the more established economic institutions linked to liberalization of trade and investment. The paper finds that (i) current globalization processes cannot be defined as giving only leeway to capital without taking care of the environment, (ii) the clashes between the economic and environmental institutions are more than only a clash between economic priorities versus environmental interests, and (iii) the pacification of these clashes will not happen in a fortnight, as the environmental advocates especially are unlikely to move towards an integration of the two kind of institutions in the short term. 相似文献
318.
Robert D. ARTHUR Jagadish TORLAPATI Kyung-Hee SHIN Daniel K. CHA Yeomin YOON Ahjeong SON 《Frontiers of Environmental Science & Engineering》2014,8(3):386-393
Process control parameters influencing microbial perchlorate reduction via a flow-through zero-valent iron (ZVI) column reactor were investigated in order to optimize perchlorate removal from water. Mixed perchlorate reducers were obtained from a wastewater treatment plant and inoculated into the reactor without further acclimation. Examined parameters included hydraulic residence time (HRT), pH, nutrients requirement, and perchlorate reduction kinetics. The minimum HRT for the system was concluded to be 8 hr. The removal efficiency of 10 mg. L-1 influent perchlorate concentration was reduced by 20%-80% without control to the neutral pH (HRT = 8 hr). Therefore pH was determined to be an important parameter for microbial perchlorate reduction. Furthermore, a viable alternative to pH buffer was discussed. The microbial perchlorate reduction followed the first order kinetics, with a rate constant (K) of 0.761 hr-1. The results from this study will contribute to the implementation of a safe, cost effective, and efficient system for perchlorate reduction to below regulated levels. 相似文献
319.
Problem
Limited literature suggests that gasoline prices have substantial effects on reducing fatal crashes. However, the literature focuses only on fatal crashes and does not examine the effects on all traffic crashes.Methods
Mississippi traffic crash data from April 2004–December 2008 from the Mississippi Highway Patrol and regular-grade unleaded gasoline price data from the Energy Information Administration of the U.S. Department of Energy were used to investigate the effects of gasoline prices on traffic safety by age, gender, and race.Results
Gasoline prices have both short-term and intermediate-term effects on reducing total traffic crashes and crashes of females, whites, and blacks. The intermediate-term effects are generally stronger than the short-term effects. Gasoline prices also have short-term effects on reducing crashes of younger drivers and intermediate-term effects on older drivers and male drivers.Impact on Industry
Higher gasoline taxes reduce traffic crashes and may result in additional societal benefits. 相似文献320.
From Bathymetry to Bioshields: A Review of Post-Tsunami Ecological Research in India and its Implications for Policy 总被引:1,自引:0,他引:1
Nibedita Mukherjee Farid Dahdouh-Guebas Vena Kapoor Rohan Arthur Nico Koedam Aarthi Sridhar Kartik Shanker 《Environmental management》2010,46(3):329-339
More than half a decade has passed since the December 26th 2004 tsunami hit the Indian coast leaving a trail of ecological,
economic and human destruction in its wake. We reviewed the coastal ecological research carried out in India in the light
of the tsunami. In addition, we also briefly reviewed the ecological research in other tsunami affected countries in Asia
namely Sri Lanka, Indonesia, Thailand and Maldives in order to provide a broader perspective of ecological research after
tsunami. A basic search in ISI Web of Knowledge using keywords “tsunami” and “India” resulted in 127 peer reviewed journal
articles, of which 39 articles were pertaining to ecological sciences. In comparison, Sri Lanka, Indonesia, Thailand and Maldives
had, respectively, eight, four, 21 and two articles pertaining to ecology. In India, bioshields received the major share of
scientific interest (14 out of 39) while only one study (each) was dedicated to corals, seagrasses, seaweeds and meiofauna,
pointing to the paucity of research attention dedicated to these critical ecosystems. We noted that very few interdisciplinary
studies looked at linkages between pure/applied sciences and the social sciences in India. In addition, there appears to be
little correlation between the limited research that was done and its influence on policy in India. This review points to
gap areas in ecological research in India and highlights the lessons learnt from research in other tsunami-affected countries.
It also provides guidance on the links between science and policy that are required for effective coastal zone management. 相似文献