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681.
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683.
Explosions are the main types of accidents causing casualties in underground coal mines. Research on the mechanisms of gas explosions is needed as a basis for the development of techniques and strategies for explosion prevention, suppression, and mitigation. The prevention of loss in explosion accidents and inquiries into their causes require understanding of the explosion process of methane in air. Because of the high cost and safety issues in full scale experiments, the experiments with small scale ducts have become a key alternative approach. Whether the experimental results at small scales agree with those at full scales needs to be investigated to validate the significance of the experimental results at small scale. Numerical simulation was used to obtain the explosion characteristics of a methane-air mixture in a gallery or duct. If the grid size is too fine in the numerical simulation for a methane-air explosion it is difficult to calculate using the present computer resource. If the grid size is too coarse, the considerable error may result. The effect of grid size on results of calculation depends on the scenario being investigated. The effect of grid sizes on simulation accuracy was analyzed in this work. The overpressure and temperature distributions and the flame propagation for the deflagration of methane-air mixtures in a gallery or duct were obtained by the AutoReaGas code at three different scales. The geometry of investigated objects and the grids in the calculation domain were similar in the three cases. The calculated overpressures vary with the scale. The calculated temperatures do not vary with the scale for the three cases. 相似文献
684.
Juárez RA Dorry LL Bello-Mendoza R Sánchez JE 《Journal of environmental management》2011,92(3):948-952
Lignocellulosic materials are used as substrate for the cultivation of the edible mushroom Pleurotus pulmonarius. After two or three flushes of mushrooms, the spent substrate is discarded although it still has an important enzymatic activity that can be used for several purposes. In this study, we sought to determine the technical feasibility of using spent substrate from P. pulmonarius to degrade chlorothalonil. Reaction mixture was prepared with 6 ml of pesticide aqueous solution (2 mg active ingredient/l) and 3 ml of enzymatic extract obtained from spent P. pulmonarius substrate. The enzymatic reaction (27 °C, pH 7.4) was conducted for 1 h with sampling at 15 min intervals. The effect of storage time and temperature (freezing or refrigerating) of spent substrate and enzymatic extract, respectively, on the activity over chlorothalonil was determined. Freshly obtained spent substrate extract was able to reduce 100% of the initial concentration of chlorothalonil (2 mg/l) after 45 min of reaction. Storage time had a negative effect on the stability of the enzymatic activity: with spent substrate stored for a week, chlorothalonil concentration was reduced in 49.5% after 1 h reaction and with substrate stored for two and three weeks, the degradation efficiency decreased to 9.15% and 0%, respectively. Cooling and freezing the spent substrate extract also had a negative effect on chlorothalonil degradation. 相似文献
685.
BOT模式被广泛地应用到各中小城市的污水处理设施建设中,用以解决当前基础设施建设融资难问题。为了探究BOT模式和传统的政府投资模式的运行效率和结果,本文采用案例分析法和对比法,分析了BOT模式下北方某市污水处理项目与政府投资模式下南方某市污水处理项目的投资、建设和运营情况,提出了在当下中国的政治、经济和法律体制下,政府投资模式在当地财政实力较强情况下应优先应用于污水处理厂建设融资中的建议。通过分析,得出了BOT模式应用于中小城市污水处理项目存在一定问题的结论,并提出了相应的风险规避措施。 相似文献
686.
Most population dynamics models explicitly track the density of a single sex. When the operational sex ratio can vary, two-sex models may be needed to understand and predict population trajectories. Various functions have been proposed to describe the relative contributions of females and males to recruitment, and these functions can differ qualitatively in the patterns that they generate. Which mating function best describes the dynamics of real populations is not known, since alternative two-sex models have not been confronted with experimental data. We conducted the first such comparison, using laboratory populations of the bean beetle Callosobruchus maculatus. Manipulations of the operational sex ratio and total density provided strong support for a demographic model in which the birth rate was proportional to the harmonic mean of female and male densities, and females, males, and their offspring made unique contributions to density dependence. We offer guidelines for transferring this approach to other, less tractable systems in which possibilities for sex ratio manipulations are more limited. We show that informative experimental designs require strong perturbations of the operational sex ratio. The functional form of density dependence (saturating vs. over-compensatory) and the relative contributions of each sex to density dependence can both determine in which direction and at which population densities such perturbations would be most informative. Our experimental results and guidelines for design strategies promote synthesis of two-sex population dynamics theory with empirical data. 相似文献
687.
Preparation of amphiphilic composite and removal of oil and hexavalent chromium from wastewater 总被引:1,自引:0,他引:1
X. Q. Liu G. Zhang H. Q. Xing P. Huang X. L. Zhang 《Environmental Chemistry Letters》2011,9(1):127-132
A new composite for water treatment was prepared by melt blend for oil and hexavalent chromium absorption. Ethylene Propylene
Diene Monomer (EPDM) was the matrix, calcinatory Fe2O3 and anion-exchange resin 201×7 were the fillers. This composite can suspend in water–oil contact (WOC) and absorb oils and
hexavalent chromium in wastewater simultaneously. The absorbencies of composites changed greatly with various ratios of calcinatory
Fe2O3 and anion-exchange resin 201×7. The results showed that the oil absorbencies increased continuously and hexavalent chromium
absorbencies were step-down as calcinatory Fe2O3 loadings from 13 to 19%. The composite can adsorb oils and hexavalent chromium simultaneously. The optimized proportion of
calcinatory Fe2O3 and anion-exchange resin 201×7 in composite was found when the absorbencies of oils and hexavalent chromium reaching the
maximum simultaneously. This composite is an inexpensive, convenient and high efficiency material for removing oils and hexavalent
chromium from wastewater. 相似文献
688.
A preliminary study on the occurrence and behavior of carbamazepine (CBZ) in aquatic environment of Yangtze River Delta, China 总被引:4,自引:0,他引:4
X. F. Zhou C. M. Dai Y. L. Zhang R. Y. Surampalli T. C. Zhang 《Environmental monitoring and assessment》2011,173(1-4):45-53
The occurrence and behavior of carbamazepine (CBZ) was investigated in aquatic environment of Yangtze River Delta, East China. The water samples were enriched by solid-phase extraction and analyzed by high-performance liquid chromatography with diode array detector. The validation of the analytical method included linearity (0.1?C1 mg/L), recovery studies, and determination of limits of quantification. Limits of quantification of CBZ in various aquatic samples were in the range of 0.1?C0.2 ??g/L. CBZ was detected in the Tongji University Intramural River, the Huangpu River, and the Suzhou River with the highest concentration of 1,090 ng/L, but not detected in the Nanhengyin River and the Caojia River. In sewage water samples, CBZ was not detected in one of the sewage treatment plants (STPs) but was detected in the raw influents and effluents at the other three selected STPs in Shanghai, with the concentrations ranging from 230 to 1,110 ng/L. CBZ was not completely eliminated after secondary treatment (with the active sludge process). 相似文献
689.
东平湖菹草腐烂分解及其对水环境的影响 总被引:5,自引:0,他引:5
于2011年6月-7月在现场采用网袋法研究了东平湖沉水植物菹草的分解失重和营养元素的变化动态.结果表明,菹草在0~14d腐烂分解较快,40 d可分解约80%的生物量,年残留率为5.0%,与一次指数模型相比,二次指数模型Wt/W0 =0.785e-0.386t +0.215e-0.004t(R2=0.876)能更好的描述菹草分解失重动态.菹草残留物中各营养元素的损失与干重衰减不同步,C、N、S含量在1~20 d内表现为上升,20~30 d显著下降,30~40 d略有增加但变化较小;P含量在1~6 d显著下降,随后呈缓慢上升趋势.菹草各营养元素的累积释放率变化规律基本一致,均在14 d和25 d达到峰值,在腐烂初期(0~8d)表现为P>S>C>N,8d后(10~40 d)表现为P>C>S>N.各营养元素的释放主要集中在菹草腐烂分解的前期(0~ 14 d),初步估算东平湖内该期间C、N、S、P的释放量约为12510 t、1187 t、147 t和235 t,相当于水中C、N、S、P分别增加约29.9、2.84、0.35、0.56 mg·L-1,易造成水体的“二次污染”.东平湖菹草年残留量约为2090t(干重),约占东平湖沉积通量的0.6%,对湖泊的填平作用较小. 相似文献
690.
This study is aimed to determine the effect of stress corrosion with low strain rates on the electrochemical properties of alloy electrode. Stress corrosion cracking tests of Mg-Zn-In-Sn alloy in 3.5 wt.% sodium chloride solutions at 25°C were performed. The effects of the electrochemical properties under the stress corrosion with low strain rates were investigated. The microstructures of cross section were observed by optical microscope. The results showed that the ultimate tensile strengths of Mg-Zn-In-Sn alloy increased and the strain decreased as the strain rates increased. Open circuit potentials (OCP) of Mg-Zn-In-Sn alloy electrode possess stability and the loop currents (LC) were improved with the increasing of stress in the elastic zone. The variation of OCP and LC did not change with the increasing of strain-rate. The microstructure of cross section observing revealed the mechanism of OCP and LC changing 相似文献