可散式弹链拉断力变化规律研究

目的 确保弹箱内的弹链(抱弹状态)在库房存放一段时间后依然稳定供弹,描述可散式弹链拉断力在不同温度环境下的变化规律.方法 应用环境作用动力学理论,建立可散式弹链的拉断力变化微分方程,求解可散式弹链的拉断力变化微分方程,得到可散式弹链拉断力变化规律的微分方程通解,再通过高温加速试验数据,求得可散式弹链拉断力变化规律的微分...     

煤矿井下安全系统脆弱性的系统动力学仿真研究

为了深入探讨煤矿井下安全系统脆弱性的影响机理,针对煤矿井下安全环境的复杂性和特殊性,建立了煤矿井下安全系统脆弱性的系统动力学仿真模型,采用变异系数法确定各影响因素的权重系数,通过文献调研和问卷调查,完成了煤矿井下安全系统脆弱性仿真。结果表明:设备系统对安全系统暴露度效果最显著;环境系统对安全系统敏感度效果最显著;员工系统和管理系统对安全系统适应度效果最显著。为了有效提升煤矿井下安全系统水平,煤矿企业需要通过改进设备系统（尤其是员工安全保障品）来降低安全系统暴露度,通过完善环境管理（尤其是尘毒治理情况）来降低安全系统敏感度,通过加强员工系统和管理系统（尤其是员工违规操作和安全监督检查）来提升安全系统适应度。     

Ecological stoichiometric characteristics of carbon,nitrogen, and phosphorus in three forests in the Lüliang Mountainous Area of Shanxi Province北大核心CSCD

Using a standard plot method, the stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) in leaves, litter, and soil (0-20 cm depth) was investigated for three forest types: Populus davidiana, Larix principis-rupprechtii, and Pinus tabuliformis. The results showed that the stoichiometry of C, N, and P of the same component in the three forests were significantly different. The C and N contents in leaves, litter, and soil in P. davidiana forest were higher than those in L. principis-rupprechtii and P. tabuliformis forests were. However, P in the L. principis-rupprechtii forest was higher than that in the P. davidiana forest and P. tabuliformis forests were. The C, N, and P contents of the components in the three forests were, in order, leaves > litter > soil, and the three nutrient contents were significantly higher in leaves and litter than they were in soil. C:N and C:P in the three forests exhibited a trend of litter > leaves > soil, whereas that for N:P was leaves > soil > litter. There were highly significant positive relationships in N:P between the litter and the soil in the P. davidiana forest. Leaf C:N and litter C:P in the L. principis-rupprechtii forest were significantly negatively correlated, whereas N:P in the leaves and soil was positively correlated. There was a significant positive correlation in N:P between the leaves and the soil in the P. tabuliformis forest. In conclusion, the N contents in leaves and soil exhibited a significant positive correlation, whereas there was no significant correlation between C, N, and P in litter or soil. Environmental factors had a large influence on the stoichiometry of C, N, and P in soil. In particular, latitude and altitude had the most significant effects on C, N, P, C:N, and C:P and were significantly p ositively correlated. T hese results provide a scientific basis for f urther studies on nutrient utilization a nd t he cyclic characteristics of different forests in this area. © 2018 Science Press. All rights reserved.     

Characteristics of N2O emission from Medicago sativa stands and its response to nitrogen fertilizers in the Longdong dryland Plateau北大核心CSCD

Nitrous oxide (N2O) is one of the potent greenhouse gases (GHG) that depletes the stratospheric ozone. Nitrogen fertilizers are considered to be a major source of nitrous oxide (N2O) emissions from arable soils. To investigate the characteristics of N2O emission, its influencing factors, and its response to nitrogen application in dry grassland in the Loess Plateau, one of the most intensively used agricultural regions in China, we conducted a field trial with two treatments including N0 (0 kg hm-2) and N150 (150 kg hm-2) at the Qingyang Loess Plateau grassland agricultural research station of Lanzhou University. An LGR-N2O/CO gas analyzer was used to monitor the emissions. The results showed that the N2O fluxes of the N0 and N150 treatments during the monitoring period were -0.0036 and 0.0118 mg m-2 h-1, respectively; the flux in case of the N150 treatment was significantly higher than that for the N0 treatment. The N2O emission flux has a distinct diurnal variation characteristic, which first showed the trend of decreasing and then increasing. Regression analysis indicated a significant positive correlation between the N2O flux and the surface soil water content at a depth of 10 cm. The N2O emission flux increased by 131.3%, compared with that during the non-precipitation days. At the same time, the N2O emission flux showed a trend of decreasing with the increase of the surface soil temperature at a depth of 10 cm. The daily emission characteristics indicated that there may be a significant underestimation of the N2O flux at the daily or longer time-scale, based on the N2O flux value measured at 9:00-11:00. In summary, the N2O emissions from the sown alfalfa grassland of the eastern Gansu are strongly affected by precipitation and nitrogen application and have obvious daily dynamic characteristics. It is recommended that the accuracy and representativeness of N2O emission flux data be enhanced by continuous dynamic measurement using the instrument. © 2018 Science Press. All rights reserved.     

Enzymatic nitrous oxide emissions from wastewater treatment

Nitrous oxide (N₂O), a potent greenhouse gas, is emitted during nitrogen removal in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N₂O production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes’ activity is essential to minimize N₂O emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N₂O in terms of their nature, structure and catalytic mechanisms. The pathways of N₂O emission during wastewater treatment are briefly introduced. The key environmental factors influencing N₂O emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzymebased techniques for mitigating N₂O emissions directly or indirectly are proposed. Finally, areas for further research on N₂O release during wastewater treatment are discussed.

Open image in new window

     

安徽淮北矿区地表水氮的富营养化特征及来源解析

为探索淮北临涣矿区地表水体中氮的分布和来源,采集研究区河流和沉陷积水区样品,测试分析其水化学指标和氮、氧同位素特征值,并采用IsoSource模型计算不同端源氮的污染贡献率。结果表明:研究区地表水处于中度富营养化状态,矿区地表水中氮的输入源受含氮肥料、土壤有机氮和粪肥污水共同影响,所发生的硝化及反硝化作用微弱;矿区河水中氮的主要输入源为粪肥污水,贡献率达66.6%,沉陷积水区氮主要受含氮肥料输入的影响,贡献率达52.0%。     

The generative power of metaphor: long‐term action research on disaster recovery in a small Japanese village

Disaster recovery is a dynamic process of creating, maintaining, and changing the meaningful context of survivors. It is completed when they redevelop their self‐reliance and resume managing their social relations with a sense of community. This study employed action research to examine how researchers and survivors collaborated to change disaster recovery through the generative power of metaphor in a small village in Japan that experienced the Niigata–Chuetsu earthquake on 23 October 2004. It outlines long‐term collaborative practices as survivors undertook new activities owing to the power of the metaphor of ‘school’. Once ‘school’ was adopted as the metaphor for where survivors learnt new skills and passed on traditional knowledge, they created new metaphors and performed new activities independently, which is critical for recovery as it demonstrates self‐reliance. The paper assesses the reasons why generative metaphors worked effectively in this case and highlights some academic and practical implications for disaster recovery.     

Organic and nitrogen removal from landfill leachate in aerobic granular sludge sequencing batch reactors

Granule sequencing batch reactors (GSBR) were established for landfill leachate treatment, and the COD removal was analyzed kinetically using a modified model. Results showed that COD removal rate decreased as influent ammonium concentration increasing. Characteristics of nitrogen removal at different influent ammonium levels were also studied. When the ammonium concentration in the landfill leachate was 366 mg L⁻¹, the dominant nitrogen removal process in the GSBR was simultaneous nitrification and denitrification (SND). Under the ammonium concentration of 788 mg L⁻¹, nitrite accumulation occurred and the accumulated nitrite was reduced to nitrogen gas by the shortcut denitrification process. When the influent ammonium increased to a higher level of 1105 mg L⁻¹, accumulation of nitrite and nitrate lasted in the whole cycle, and the removal efficiencies of total nitrogen and ammonium decreased to only 35.0% and 39.3%, respectively. Results also showed that DO was a useful process controlling parameter for the organics and nitrogen removal at low ammonium input.     

Modelling of a downdraft gasifier fed by agricultural residues

A non-stoichiometric model for a downdraft gasifier was developed in order to simulate the overall gasification process. Mass and energy balances of the gasifier were calculated and the composition of produced syngas was predicted. The capacity of the modeled gasifier was assumed to be 0.5 MW, with an Equivalence Ratio (EQ) of 0.45. The model incorporates the chemical reactions and species involved, while it starts by selecting all species containing C, H, and O, or any other dominant elements. Olive wood, miscanthus and cardoon were tested in the formulated model for a temperature range of 800-1200 °C, in order to examine the syngas composition and the moisture impact on the supplied fuel. Model results were then used in order to design an olive wood gasification reactor.     

Assessing Public Perceptions of Computer-Based Models

Although there is a solid body of research on both collaborative decision-making and on processes using models, there is little research on general public attitudes about models and their use in making policy decisions. This project assessed opinions about computer models in general and attitudes about a specific model being used in water planning in the Middle Rio Grande Region of New Mexico, United States. More than 1000 individuals were surveyed about their perceptions of computer-based models in general. Additionally, more than 150 attendees at public meetings related to the Middle Rio Grande planning effort were surveyed about their perceptions of the specific Rio Grande-based model. The results reveal that the majority of respondents are confident in their ability to understand models and most believe that models are appropriate tools for education and for making policy decisions. Responses also reveal that trust in who develops a model is a key issue related to public support. Regarding the specific model highlighted in this project, the public revealed tremendous support for its usefulness as a public engagement tool as well as a tool to assist decision-makers in regional water planning. Although indicating broad support for models, the results do raise questions about the role of trust in using models in contentious decisions.