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51.
Mingjin Wang Nan Zheng Tong Zhu Jing Shang Ting Yu Xiaojuan Song Defeng Zhao Yong Guan Yangchao Tian 《环境科学学报(英文版)》2018,30(7):23-32
Heterogeneous reactions on the aerosol particle surface in the atmosphere play important roles in air pollution, climate change, and global biogeochemical cycles. However, the reported uptake coefficients of heterogeneous reactions usually have large variations and may not be relevant to real atmospheric conditions. One of the major reasons for this is the use of bulk samples in laboratory experiments, while particles in the atmosphere are suspended individually. A number of technologies have been developed recently to study heterogeneous reactions on the surfaces of individual particles. Precise measurements on the reactive surface area, volume, and morphology of individual particles are necessary for calculating the uptake coefficient, quantifying reactants and products, and understanding the reaction mechanism better. In this study, for the first time we used synchrotron radiation X-ray computed tomography(XCT) and micro-Raman spectrometry to measure individual CaCO_3 particle morphology, with sizes ranging from 3.5–6.5 μm. Particle surface area and volume were calculated using a reconstruction method based on software threedimensional(3-D) rendering. The XCT was first validated with high-resolution fieldemission scanning electron microscopy(FE-SEM) to acquire accurate CaCO_3 particle surface area and volume estimates. Our results showed an average difference of only 6.1% in surface area and 3.2% in volume measured either by micro-Raman spectrometry or X-ray tomography. X-ray tomography and FE-SEM can provide more morphological details of individual Ca CO3 particles than micro-Raman spectrometry. This study demonstrated that X-ray computed tomography and micro-Raman spectrometry can precisely measure the surface area, volume, and morphology of an individual particle. 相似文献
52.
瓦斯爆炸是一种复杂的链式反应,为了探求其链式反应的动力学特性,采用详细的瓦斯爆炸链式反应机理(包括53种组分,325个反应),利用软件CHEMKINⅢ中的SENKIN子程序包,利用SENKIN子程序包中的敏感性分析程序块对瓦斯爆炸的详细化学反应机理进行分析,找出对瓦斯爆炸过程反应动力学特性影响较大的反应步。通过数值计算和模拟,对瓦斯爆炸过程中反应物浓度、自由基以及致灾性气体的生成和变化做了敏感性分析,得出了影响瓦斯爆炸的关键反应步为R158,R53,R98,R57,R155,R156,R38,R32,R119。 相似文献
53.
Dimer formation was observed during ultraviolet (UV) photolysis of the anti-inflammatory drug diclofenac, and confirmed with mass spectrometry, NMR and fluorescence analysis. The dimers were combinations of the two parent molecules or of the parent and the product of photolysis, and had visible color. Radical formation during UV exposure and dissolved oxygen photosensitized reactions played a role in dimer formation. Singlet oxygen formed via photosensitization by photolysis products of diclofenac. It reacted with diclofenac to form an epoxide which is an intermediate in some dimer formation pathways. Quantum yield of photolysis for diclofenac was 0.21 ± 0.02 and 0.19 ± 0.02 for UV irradiation from medium pressure and low pressure mercury vapor lamps, respectively. Band pass filter experiments revealed that the quantum yield is constant at wavelengths >200 nm. The same dimers formed in laboratory grade water when either of the two UV sources was used. Dimers did not form in wastewater effluent matrix, and diclofenac epoxide molecules may have formed bonds with organic matter rather than each other Implications for the importance of dimer formation in NOM are discussed. 相似文献
54.
55.
Abiotic transformation of estrogens in synthetic municipal wastewater: An alternative for treatment?
Ruth Marfil-Vega Marc A. Mills 《Environmental pollution (Barking, Essex : 1987)》2010,158(11):3372-3377
The abiotic transformation of estrogens, including estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2), in the presence of model vegetable matter was confirmed in this study. Batch experiments were performed to model the catalytic conversion of E1, E2, E3 and EE2 in synthetic wastewater. Greater than 80% reduction in the parent compounds was achieved for each target chemical after 72 h with the remaining concentration distributed between aqueous and solid phases as follows: 13% and 7% for E1, 10% and 2% for E2, 6% and 2% for E3, and 8% and 3% for EE2, respectively. Testosterone, androstenedione and progesterone were also monitored in this study, and their concentrations were found to be in agreement with initially spiked amount. Data collected under laboratory conditions provided the basis for implementing new abiotic wastewater treatment technologies that use inexpensive materials. 相似文献
56.
57.
Aqueous free radical chemistry of mercury in the presence of iron oxides and ambient aerosol 总被引:1,自引:0,他引:1
Che-jen Lin Simo O. Pehkonen 《Atmospheric environment (Oxford, England : 1994)》1997,31(24):4125-4137
The effect of goethite (α-FeOOH), hematite (α-Fe203) and maghemite (γ-Fe203) on the aqueous photoreduction of divalent mercury with organic acids (oxalate, formate and acetate) is investigated. Laboratory photochemistry experiments with synthetic iron oxides and simulated sunlight were performed to assess the role of the oxides on the photoreduction. Ambient aerosol was also collected and introduced as the solid phase to compare its effect with that of synthetic oxides. It is observed that the presence of various iron oxides or aerosol particles enhances the photoreduction. It is also found that the hydroxyl radicals produced in the hematite-oxalate systems can re-oxidize the reduced mercury back to Hg(II). Based on the experimental observations, mechanisms responsible for the Hg(II) reduction are proposed. The kinetics of Hg0 oxidation by hydroxyl radicals was also studied by a steady-state kinetic technique using nitrate photolysis as the * OH radical source. The second-order rate constant is determined to be 2.0 × 109 M− s−1. The implications of the studied reactions on the atmospheric chemistry of mercury are discussed. 相似文献
58.
59.
Jing Xu Jiong Cheng Runtian He Jiaqi Lu Chunling Wang Heng Zhong Fangming Jin 《Frontiers of Environmental Science & Engineering》2023,17(10):127
60.
Catherine A. Heaney 《组织行为杂志》2014,35(2):172-193
Racial and ethnic minority employees constitute a significant proportion of the U.S. workforce. The literature on demographic similarity in the workplace suggests that the proportion of co‐workers who share the same racial/ethnic background (racial/ethnic similarity) can influence job attitudes and employee well‐being and that the reactions to racial/ethnic similarity may differ between the racially dominant and subordinate groups. This study applies status construction theory to examine the extent to which racial/ethnic similarity is associated with job satisfaction and lumbar back health among warehouse employees. We surveyed 361 warehouse workers (204 whites, 94 African‐Americans, and 63 Latino workers) in 68 jobs in nine distribution centers in the United States. Multilevel analyses indicate that white and racial/ethnic minority groups react differently to racial/ethnic similarity. For job satisfaction, white employees experience higher job satisfaction when they are highly racially/ethnically similar to their colleagues, whereas Latino employees experience higher job satisfaction when they are racially/ethnically dissimilar to others. As for lumbar back health, among Latino and African‐American employees, higher racial/ethnic similarity is associated with better lumbar back health whereas for white employees, the association is the opposite. Across all groups, moderate levels of racial/ethnic similarity were associated with the best lumbar back health. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献