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471.
472.
473.
The cyclization of ethyl 2-(aminosulfonyl)benzoate (ASB) to give saccharin was investigated in aqueous solutions at pH between 5.2 and 9.5 and in the temperature range of 296.2-334.2 K. The initial concentration of the reactant was varied between 1.45 x 10(-5) and 3.86 x 10(-4) M. Ultraviolet spectroscopy was used to obtain the kinetic data. The reaction is acid catalyzed and follows pseudo-first-order kinetics. The experimental rate constant, k(obs), increases with temperature and pH. Its dependence on the temperature and pH is well described by: k(obs) = k1 [OH-] = [(2.52 +/- 0.9) x 10(16) exp(-20.2 +/- 1 kcalmol(-1)/RT) s(-1)][OH-] A mechanism is proposed and the half-life of ethyl ASB is calculated. 相似文献
474.
Morphologies of zinc oxide particles and their effects on photocatalysis 总被引:17,自引:0,他引:17
ZnO powders with different morphologies were synthesized by alkali precipitation, organo-zinc hydrolysis, and spray pyrolysis. Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these ZnO powders. We investigated the relationship between photocatalytic activity and crystallinity, surface area, or morphology. Results indicate that the photocatalytic activity of ZnO powder depends on crystallinity rather than surface area for the same original ZnO powders prepared by equal conditions other than the difference in calcination temperature. However, no direct relationship between photocatalytic activity and crystallinity or surface area was found for the differently original ZnO powders prepared by different methods, or the same method with different conditions. Instead, we find that the particle morphology significantly affects its photocatalysis. 相似文献
475.
Optimal spatial sampling schemes for environmental surveys 总被引:4,自引:0,他引:4
Simone Di Zio Lara Fontanella Luigi Ippoliti 《Environmental and Ecological Statistics》2004,11(4):397-414
A practical problem in spatial statistics is that of constructing spatial sampling designs for environmental monitoring network. This paper presents a fractal-based criterion for the construction of coverage designs to optimize the location of sampling points. The algorithm does not depend on the covariance structure of the process and provides desirable results for situations in which a poor prior knowledge is available. The statistical characteristics of the method are explored by a simulation study while a design exercise concerning the Pescara area monitoring network is used to demonstrate potential designs under realistic assumptions. 相似文献
476.
Di Sabatino S. Kastner-Klein P. Berkowicz R. Britter R.E. Fedorovich E. 《Environmental Fluid Mechanics》2003,3(2):129-143
The modelling of pollutant dispersion at the street scale in an urban environment requires the knowledge of turbulence generated by the traffic motion in streets. In this paper, a theoretical framework to estimate mechanical turbulence induced by traffic in street canyons at low wind speed conditions is established. The standard deviation of the velocity fluctuations is adopted as a measure of traffic-produced turbulence (TPT). Based on the balance between turbulent kinetic energy production and dissipation, three different parameterisations for TPT suitable for different traffic flow conditions are derived and discussed. These formulae rely on the calculations of constants that need to be estimated on the basis of experimental data. One such estimate has been made with the help of a wind tunnel data set corresponding to intermediate traffic densities, which is the most common regime, with interacting vehicle wakes. 相似文献
477.
F. Giomi S. Raicevich A. Ferrarese F. Pranovi P. Di Muro M. Beltramini 《Marine Biology》2007,151(4):1237-1247
This work is focused on hemocyanin (Hc) heterogeneity at population level and on the biochemical characterization of the different
subunit patterns. Two different approaches have been used: we have characterized Hc subunit composition to describe the subunit
polymorphism. Then, we have measured the Hc oxygen-binding affinity to disclose the physiological implications of such heterogeneity.
In order to evaluate the intra- and inter-specific variability, different populations of Liocarcinus depurator, Liocarcinus marmoreus, Liocarcinus holsatus, Necora puber (Crustacea: Portunidae), from British Isles and Adriatic Sea, have been sampled. Results indicate that Hc polymorphism normally
occurs at both intra- and inter-specific levels and involves the protein subunit type. These evidences extend to the portunid
Hc the concept of molecular heterogeneity within species that have been previously reported for other decapod and amphipod
crustaceans. Besides, the results support the view that subunit composition of crustacean Hcs is almost species-specific,
but also that closely related species share a common pattern. Furthermore, this heterogeneity corresponds to different stability
of the native oligomers quaternary structure and different oxygen affinity. The results are discussed in relation with the
environmental regimes that characterize the different sampling areas. In addition to Hc, the hemolymph collected in specimens
from different sampling areas contained also a non-respiratory pseudo-Hc. This paper reports for the first time the occurrence
of pseudo-Hc at the level of population.
Declaration: All the experiments comply with the current laws of Italy. 相似文献
478.
城市饮用水源地水质健康风险评价 总被引:5,自引:0,他引:5
介绍饮用水水源受到基因毒物质和躯体毒物质所致的健康危害的风险度计算模型,并应用于西安市饮用水源地饮水途径健康风险评价,分别计算出了各类污染物的风险度。结果表明:(1)基因毒物质镉所致健康风险大约为10^-7a^-1,躯体毒物质所致风险在10^-12~10^-10之间。所以,基因毒物质是首先控制的污染物质。(2)对于躯体毒物质,铅的风险度是最高的,躯体毒物质所致的风险度大小排序为Pb〉NH3-N〉Hg〉挥发酚。(3)饮用水中的所有有害物质的健康危害总风险度未超过国际辐射防护委员会(ICRP)推荐的最大可接受限值5.0×10^-5a^-1,也没超过瑞典环保局、荷兰建设和环境部推荐的最大可接受水平6.0×10^-5a^-1。研究结果可直接确定该市地表水源水质的风险污染物的主次及治理的优先顺序,为该市地表水源水质风险管理提供了帮助。 相似文献
479.
为了研究高浓度磷对厌氧氨氧化效能和污泥特性的影响,采用UASB反应器进行连续试验,考察不同磷浓度时的Anammox脱氮效能,并通过扫描电镜和能谱分析技术对颗粒污泥表面形态和元素组成分析。结果表明:磷浓度达到600 mg/L时开始抑制厌氧氨氧化脱氮效能,700 mg/L对Anammox脱氮效能造成91.86%的抑制,降低磷浓度培养10 d后完全恢复;随着进水磷浓度的增加,反应器对磷的截留率减小;高浓度磷导致反应器底部颗粒污泥表面形成白色固体,为由C、O、P和Ca构成羟基磷灰石和磷酸钙等难溶化合物,能谱分析结果显示,该固体中O、P、C和Ca原子数量分别占41.89%、21.78%、14.41%和10.82%。 相似文献
480.
Xinmin Zhang Di Wang Yan Liu Yufan Cui Zhigang Xue Zhifeng Gao Jinhong Du 《环境科学学报(英文版)》2020,32(9):183-189
Coking industry is an important volatile organic compounds (VOCs) emission source in China, however, detailed information on VOCs emissions is lacking. Therefore, we selected a typical mechanized coking plant and collected air samples according to the Emission Standard of Pollutants for Coking Chemical Industry (GB16171-2012). Using gas chromatography-mass spectrometry method, we analyzed the VOCs in the air samples, and applied maximum increment reactivity (MIR) rule to estimate ozone formation potential (OFP) of the VOCs emitted from the coke production. More than 90 VOCs species were detected from the coking plant, including alkanes, alkenes, alkynes, aromatic hydrocarbons, halogenated hydrocarbons and oxygenated VOCs. The concentrations of VOCs (ρ(VOCs)) generated at different stages of the coking process are significantly different. ρ(VOCs) from coke oven chimney had the highest concentration (87.1 mg/m3), followed by coke pushing (4.0 mg/m3), coal charging (3.3 mg/m3) and coke oven tops (1.1 mg/m3). VOCs species emitted from the coke production processes were dominated by alkanes and alkenes, but the composition proportions were different at the different stages. Alkenes were the most abundant emission species in flue gases of the coke oven chimney accounting for up to 66% of the total VOCs, while the VOCs emissions from coke pushing and coal charging were dominated by alkanes (36% and 42%, respectively), and the alkanes and alkenes emitted from coke oven top were similar (31% and 29%, respectively). Based on above results, reduction of VOCs emissions from coke oven chimney flue gases is suggested to be an effective measure, especially for alkenes. 相似文献