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131.
Spatial distribution and environmental characterization of sediment-associated metals from middle-downstream of Xiangjiang River, southern China 总被引:1,自引:0,他引:1
The contamination and environmental risk assessment of the toxic elements in sediments from the middle-downstream (Zhuzhou—Changsha
section) of the Xiangjiang River in Hunan Province of China were studied. The results show that As, Cd, Pb and Zn are major
contaminants in sediments, and average concentrations of these elements significantly exceed both the Control Standards for
Pollutants in Sludge of China (GB4284-84) for agricultural use in acidic soils and the effect range median (ERM) values. The
average concentrations of As, Cd and Pb in the river water slightly exceed the limit of Surface Water Environment Quality
Standard (GB3838—2002). The concentrations of As and Cr in depth profiles extensively change, but slight changes are observed
in Pb and Zn. Cd and Zn in most sediment samples can easily enter the food-chain and bring possible ecotoxicological risk
to organisms living in sediments according to the risk assessment code. 相似文献
132.
地震动时频分析在隧道动力响应分析中的应用 总被引:1,自引:1,他引:0
为了了解影响隧道动态内力峰值出现位置的相关因素.利用希尔伯特—黄变换,对E1 Centro等4条天然地震波和某隧道人工波(简称LBG地震波)进行了时频分析,结果表明:1)地震波各频段内所含能量的大小是影响隧道动态响应的主要因素;2)地震波中所包含的瞬时能量和总能量在时域上的分布决定了隧道内力及塑性应变最大峰值的出现时间;3)隧道内力峰值及最大塑性应变出现的位置与隧道断面形状及周围介质对衬砌的约束状态有关,与地震波的类型无关. 相似文献
133.
A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band.
Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated
as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic
representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and
then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion
for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a
finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain
compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model
works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the
experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases
around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the
pore stress flows nearly horizontally and is distributed equally far away the shear band region.
Foundation item: Project(2006G007-C) supported by the Foundation of the Science and Technology Section of Ministry of Railway of China; Project(77206)
supported by the Excellent PhD Thesis Innovation Foundation of Central South University, China 相似文献
134.
传统文化包含众多的元素,作者对传统文化元素中的色彩元素在现代视觉传达设计中的运用与影响进行了研究,分别就中国传统色彩在包装设计、标志设计以及环境设计中的运用进行了论述,并阐释了如何实现现代元素与传统文化元素在现代视觉传达设计中的完美统一,最终达到在现代视觉传达设计中传承和发展优秀传统文化的目的. 相似文献
135.
制备皮胶原纤维固载Zr(IV)吸附剂(ZLCF),并考察ZLCF对水体中苯甲酸(BA)、邻苯二甲酸(o-PA)、对苯二甲酸(p-PA)和间苯二甲酸(m-PA)的吸附特性.研究表明:这4种苯羧酸的吸附平衡同时符合Langmuir和Freundlich方程,但随着它们的羧基数量和位置的不同,其吸附容量也随之变化.总体看,ZLCF对所研究的苯羧酸均具有较大的吸附容量.当苯羧酸溶液(10 m1)的初始浓度为6 mmol/L、吸附温度为293 K时,ZLCF(0.05 g)对BA、o-PA、m-PA和p-PA的吸附容量分别达0.4616、0.5892、0.4912和0.3138 mmol/g.吸附动力学研究表明:BA的吸附符合拟一级速率方程,边界层扩散为主控步骤;而o一PA、m-PA和p-PA的吸附符合拟二级速率方程,化学吸附为主控步骤. 相似文献
136.
针对NdFeB纳米复合永磁材料的矫顽力偏低的现状,采用熔体快淬法制备了Nd8DyxFe82Co6B4(x=0,0.4,0.8,1.2,1.6)纳米复合永磁材料,研究了Dy和Co的添加对NdFeB纳米复合永磁材料的磁性能的影响.研究结果表明,Dy的添加可提高材料的各向异性场,提高矫顽力,但是Dy元素的添加使材料的剩磁降低,结晶温度升高,因此添加量不宜过多;复合添加Co原子不仅可以提高材料的剩磁和矫顽力,而且可以弥补只添加Dy元素使材料的结晶温度升高的缺陷.在最佳的热处理条件下,Dy含量x=0.8时的样品表现出最佳的磁性能,矫顽力jHc=524kA/m,剩磁Br=1.11T,最大磁能积(BH)max=158kJ/m^3. 相似文献
137.
In order to in situ measure chemical parameters of deep-sea water and hydrothermal fluids at midocean ridge(MOR), it is necessary to use high temperature and high pressure chemical sensors.Developing new sensors is essential to measure in-situ pH and other chemical parameters(dissolved H2, dissolved H2S) of deep-sea water and hydrothermal fluids in a wide temperature range(2℃―400℃) at MOR vents.The YSZ(Yttria Stabilized Zirconia, 9%Y2O3) ceramic-based(HgO/Hg) chemical sensors possess excellent electrochemic... 相似文献
138.
方面级意见挖掘的任务通常包括从客户评论中抽取产品的特征、与产品特征相关联的观点词识别以及观点的极性判断三个方面。围绕如何实现中文评论的方面级意见挖掘问题,提出了利用条件随机场实现中文评论的方面级意见挖掘的四个主要步骤:数据预处理、训练集准备、为条件随机场模型定义学习函数、应用模型标注新的评论数据。在此基础上,通过以五种实际产品的中文评论语料为数据集,对该方法进行了数据实验。实验结果表明,该方法针对不同类型观点元素的抽取在评估性能指标上大部分达到或超过80%。为了进一步验证所提出方法的有效性,将研究结果进行了差异显著性检验。结果显示,用CRF对中文评论进行方面级意见挖掘和对英文评论的方面意见挖掘的性能差异不大。最后,比较了三种不同方法的方面抽取精度和情感分类精度,实验结果表明,CRF方法优于词典化的隐马尔可夫模型和关联规则挖掘方法。 相似文献
139.
This study reports on the elemental concentrations and vertical variation of coal seams from the Obed Mountain deposit, Alberta Foothills, Canada. Results from two sections of Seam 1 show that the major elements (i.e. Al, Fe, Mg, K, Na, Ti, and Si) have high concentrations in intervals having high ash content, with the only exception of Ca. Similarities are apparent, in both sections, in the vertical variations of Th, U, Se, and Zn; Rb, Cs, and K; Sb, Mo, and W; Mn and Sr; and Ba, Cr, Co, Hf, and Sc. These similarities are also evident among the REEs, notably between Ce and La; also between Dy, Eu, and Sm. Most elements, with the exception of Ba and Sr are slightly more concentrated in Section 2 of Seam 1, located approximately 1.5Fig. km away from Section 1. Compared to Seam 1, Seam 2 has lower mean concentrations of elements. Boron in the coal ranges from 27 to 100 ppmw, though most values are less than 50 ppmw. Boron concentrations suggest a freshwater depositional environment. The element is depleted in the sedimentary partings (12–29 ppmw only) and is enriched in the coal interval near the roof and immediately beneath the partings. This enrichment shows possible downward mobilization of boron. Vertical variations of elements are helpful in delineating the boundaries between coal and sedimentary partings in the succession. The Obed Mountain coals are “clean” by world standards and their elemental concentrations are comparable with those in coals of a lower rank from the same coal formation used for power generation in Alberta. All sedimentary partings have low concentrations of Ba, Hf, Sc, Sr, Ta, Th, U, and REEs; this, along with the absence of an Eu negative anomaly suggests a non-volcanic origin for the partings. 相似文献
140.
Rajmund S. Dybczyński Marta Pyszynska Krzysztof Kulisa Anna Bojanowska-Czajka 《分离科学与技术》2020,55(7):1364-1379
ABSTRACTNew ion interaction chromatographic (IIC) method employing Kromasil 100 C18 column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated. 相似文献