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991.
大气有机物在脱水,富集过程中的组分损失造成GC分析的系统误差。回收率测定表明,在本实验条件下,疏水性有机组分在填充碱石棉与碳酸钾的脱水预柱上的损失率分别为25%和15%左右,亲水性的乙醇的损失经高达60%左右。 相似文献
992.
993.
SAITOYoshihiro JINNOKiyokatsu 《环境化学》2003,22(3):241-245
1 IntroductionGaschromatography(GC)isoneofthemostpopularseparationmethodsfortheanalysisofvolatilecompounds,andawidevarietyofpolymericmaterialsasthestationaryphases,havebeendeveloped .Incontrasttothesuccessfulapplicationsandsubsequentcommercializationofth… 相似文献
994.
In this study numerical methods are used to investigate the relationship between chemical concentration of gas species within a cavitating bubble, equilibrium radius of the gas bubble and pressure variations in the ambient liquid. For this purpose, governing equations are developed to describe the dynamic equilibrium of a bubble in a flowing fluid and mass transfer between gas and liquid phases, where it was assumed that gases undergo isothermal compression, obey the ideal gas law, Henry law. It is further assumed that the concentration of each phase within the bubble is uniform. The resulting nonlinear equations are solved using implicit Trapezoidal method with Newton iteration. Four gas species are modeled under various initial and ambient pressure variation conditions. These conditions maybe considered to represent typical cavitation events. The numerical results obtained are presented in terms of dimensionless numbers. These results indicate that chemical damage maybe an important component of cavitation surface damage, since high concentration profiles may develop within a collapsing bubble. Proposed formulation and numerical solutions are simple and cost effective to implement. The results presented in this study maybe used to benchmark experimental investigations or other more complex solutions, which are outside the scope of this study. 相似文献
995.
中国水稻土碳循环研究进展 总被引:9,自引:1,他引:9
文章首先分析了水稻土在碳循环研究中的地位和重要性,进而对我目水稻土碳循环的研究现状作了较为详尽的阐述,对其主要研究结论进行了深入的剖析。中国大而积的水稻土自1980年以来显示出有机碳库增加现象,说明水稻田对大气CO2可能产生汇效应。水耕熟化过程足有机碳的积累过程,水稻土的碳密度是早作土碳密度的2-3倍。水稻土的同碳能力与土壤的微团聚体的粒径有关。但对于水稻土中有机碳的分布和结合状态与农业管理措施、水稻土质量变化、农业生态环境变化的关系仍不清楚。因而建议就这一问题从土壤物理学、化学和生物学的相互作朋与土壤微团聚体中矿物质、有机质和微生物的相互结合关系的层面上进行多学科研究。同时提出了今后我困水稻土碳循环的重点研究方向和领域,即从整体和系统的角度来研究碳循环和平衡,从不同的时空区域来研究碳循环的过程和强度。 相似文献
996.
Owing to its unique nutritional and immunological characteristics, human milk is the most important food source for infants. Breast milk can, however, also be a pathway of maternal excretion of toxic elements. Selected toxic elements (As, Pb, Mn,a Hg and Cd) were determined in human breast milk and blood samples obtained from 120 subjects related to an integrated steel plant environment located in central India. Samples of breast milk and blood from subjects living outside the steel plant environment were also analyzed for comparative study. Higher levels of these toxic elements were found in blood samples as compared to breast milk samples. Plant workers showed the higher presence of these metals in their breast milk and blood samples compared to the residents of the area and the subjects living outside the industrial environment, respectively. Mn, Pb and Hg have shown a higher tendency to associate with blood and breast milk than As and Cd. The order of occurrence of these metals in blood and milk samples thus found is Mn > Pb > Hg > As > Cd. 相似文献
997.
Concentrations of Potentially Toxic Metals in Urban Soils of Seville: Relationship with Different Land Uses 总被引:1,自引:0,他引:1
Ruiz-Cortés E Reinoso R Díaz-Barrientos E Madrid L 《Environmental geochemistry and health》2005,27(5-6):465-474
Fifty-two samples of surface soils were taken in the urban area of Seville, to assess the possible influence of different
land uses on their metal contents and their relationship with several soil properties. The samples corresponded to five categories
or land uses: agricultural, parks, ornamental gardens, riverbanks, and roadsides. Sequential extraction of metal according
to the procedure proposed by the former Community Bureau of Reference (BCR) was carried out, and pseudo-total (aqua regia soluble) metal contents were determined. Lower organic C, total N and available P and K contents were found in riverbank
samples, probably due to the lack of manuring of those sites, left in a natural status. In contrast, significantly higher
electrical conductivity was found in those sites, due to the tidal influence of the nearby Atlantic Ocean. Other land uses
did not show significant differences in the general properties. Concentrations of Cu, Pb and Zn, both aqua-regia soluble and sequentially extracted, were clearly higher in soils from ornamental gardens, whereas the concentrations in the
riverbank samples were slightly lower than the other categories. In contrast, other metals (Cd, Cr, Fe, Mn, Ni) were uniformly
distributed throughout all land uses. A strong statistical association is found among the concentrations of Cu, Pb, Zn and
organic C, suggesting that the larger contents of these metals in ornamental gardens are partly due to organic amendments
added to those sites more frequently than to other kinds of sites. Considering the conclusions of previous studies, heavy
traffic can also contribute to those `urban’ metals in urban soils. Periodic monitoring of the concentrations of urban metals
in busy city centres and of the quality of amendments added to soils of recreational areas are recommended. 相似文献
998.
Ahmad R. Shouman 《Journal of Loss Prevention in the Process Industries》1998,11(6):383-390
A very simple solution to the thermal explosion problem for one-dimensional solids is presented. The solution produces analytical expressions for the criticality condition. Two different solutions are used. One solution gives higher answers than those known from exact solutions and the second solution gives lower answers. This allows bracketing the expected answer with a determined tolerance. The results obtained compare quite favorably with those obtained from known exact numerical solutions. This allows the utilization of the present method for many a practical problem with an acceptable tolerances. 相似文献
999.
1000.
气相色谱法测定大气中烯烃的研究 总被引:3,自引:0,他引:3
采用硅胶-AgNO3富集样品,热解吸进样,气相色谱法分析大气中的烃一,富集过程在常温下进行。当富集样品0.1L时,乙烯,丙烯,丁二烯的最小检有度分别为0.0006mg/m^3,0.001mg/m^3、0.004mg/m^3,相对标准偏差小于6%,加标回收率97%-109%。 相似文献