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81.
Identifying the major fluorescent components responsible for ultrafiltration membrane fouling in different water sources 总被引:1,自引:0,他引:1
Three-dimensional fluorescence excitation–emission matrix(EEM) coupled with parallel factor analysis(PARAFAC) was performed for a total of 18 water samples taken from three water sources(two lakes and one wastewater treatment plant(WWTP) secondary effluent),with the purpose of identifying the major ultrafiltration(UF) membrane foulants in different water sources. Three fluorescent components(C1, C2 and C3) were identified,which represented terrestrially derived humic-like substances(C1), microbially derived humic-like substances(C2), and protein-like substances(C3). The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components(C1, C2 and C3) made a considerable contribution to the irreversible and total fouling of the UF membrane.However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes. 相似文献
82.
相对湿度的研究对理解古气候变化有着重要的科学意义,但是目前国内利用树轮资料重建的历史时期相对湿度变化十分有限。本文利用油松树轮宽度重建了河北青龙地区1890—2012年5—7月的平均相对湿度变化,重建序列的方差解释量为39.1%(减少自由度后为38.0%)。重建序列显示出5个湿润期(1895—1899年,1906—1914年,1924—1926年,1950—1955年,1984—2000年)和5个干旱期(1900—1905年,1917—1921年,1927—1949年,1956—1973年,1975—1981年)。重建序列和观测数据均与邻近研究区的PDSI对应良好,表明该序列具有较强的空间代表性,可以反映河北北部地区的平均相对湿度变化情况。本研究表明研究区相对湿度变化不仅受局地气候控制,还可能受到ENSO影响。 相似文献
83.
根据彰武县阿尔乡北甸子硅砂矿地貌、自然条件及周边环境等特征,确定硅砂矿土地复垦的方向为林地和鱼塘。简要介绍硅砂矿土地复垦的开采流程及闭坑后土地复垦与植被恢复的技术要求,提出土地复垦和植被恢复过程具体措施及预防控制。通过开展硅砂矿土地复垦与植被恢复工作,把破坏的土地采取整治措施恢复为可利用的土地,缓解了矿区土地减少的趋势,改善了矿山生态环境,最终实现矿山生态环境保护、土地资源利用与地方经济可持续发展。 相似文献
84.
植被重建下煤矿排土场土壤熟化过程中碳储量变化 总被引:6,自引:1,他引:5
植被重建是治理因露天煤矿的开采而形成的大面积排土场行之有效的措施,了解植被重建模式对排土场土壤有机碳(SOC)储量的影响是筛选植被治理措施的重要因子.在内蒙古准格尔旗黑岱沟露天煤矿,选取15 a治理排土场中5种植被重建模式(自然恢复地、草地、灌木林、乔灌混交林、乔木林),16种植被配置类型,采集土壤剖面(0~100 cm)样品408个,研究不同重建模式下SOC储量的变化.结果表明:1治理排土场植被重建模式显著影响剖面SOC含量与分布(P<0.05),表层0~10 cm SOC呈草地>灌木>乔木>乔灌混交林>自然恢复地;全氮(TN)也呈相似的变化特征.2植被配置类型中,苜蓿地0~10 cm的SOC含量(5.71 g·kg-1)和TN含量(0.49 g·kg-1)均最高,比自然恢复地分别高166.7%和171.3%,且是沙棘、紫穗槐+油松、香花槐的两倍左右.3植被重建对SOC影响深度主要集中在0~20 cm,而对TN的影响可达40 cm.4与新建排土场相比,植被重建后,草地、灌木地和乔木地0~100 cm碳储量分别增加了15.47、6.93和6.95 t·hm-2,但仅相当于原地貌水平的2/3、1/2和1/2.植被重建表现出碳汇效应和巨大的固碳能力.从土壤固碳的角度考虑,建议植被重建模式以草地为主,植被类型优先考虑苜蓿. 相似文献
85.
Patchy distribution fields: sampling distance unit of a zigzag survey and reconstruction adequacy 总被引:1,自引:0,他引:1
Kalikhman I 《Environmental monitoring and assessment》2002,80(1):1-16
A mathematical model was used to examine the effects of choosingvarious units of sampling distance of a zigzag survey on the adequacy of reconstructing patchy distribution fields. The modelsimulates fish or plankton patches (or gaps) of different shapesand spatial orientations, and an acoustic survey by zigzag or parallel transects along which a unit of sampling distance is set. Adequacy of the reconstructed fields to those originally generated is evaluated by calculating their correlations (r). A priori information on the autocorrelation radii for the field in the directions of the survey (Rs) and perpendiculardirection (Rp) allows optimisation of the survey design andthe algorithm of data analysis. A field can be reconstructed properly (r2 > 0.70) if the distance between transects D < (1.0–1.5)Rs and the unit of sampling distance d < (1.0–1.5)Rp. A posteriori determination of patchorientation allows reconstruction of the best field attainable onthe basis of the survey data. In cases of field movement, if thedimension of patches in the direction of movement exceeds that ofa surveyed area, a survey in the opposite direction gives bestresults; in contrast, if the dimension of moving patches is smaller than that of a surveyed area, it is reasonable to carryout a survey in the same direction. The criterion remains validwhen a survey is carried out by zigzag transects and a unit ofsampling distance is set along them. The results obtained indicate that, for a fixed transect spacing and a given number of sampling points on each full transect, zigzag pattern allowsless adequate reconstruction of an original distribution field (in cases of both immovable and movable fields) than corresponding parallel pattern. 相似文献
86.
Diamando Vlachogiannis Spyros Andronopoulos Artemis Passamichali Nikos Gounaris John G. Bartzis 《Environmental monitoring and assessment》2000,65(1-2):41-48
This study concentrated on the effects of Biogenic Volatile Organic Compounds (BVOC) emissions on ozone (O3) in an area of the Eastern Spain on June 12, 1997, a day characterised by sea breeze. Simulation of meteorology was performed with the three-dimensional model ADREA-I. Comparisons of the model results with observations have revealed overall a good agreement in temperature and wind velocity. Two runs were performed with UAM-IV for the photochemical calculations. The first simulated the effects of the anthropogenic emissions only (run A) and the second the combined effects of anthropogenic and biogenic emissions, (run B). Comparisons of the model O3 concentrations with measurements showed a general agreement with the experimental data. Discrepancies between the calculated results and the observations during the early morning hours could be attributed to inaccuracies in nitrogen oxides (NOx) from the anthropogenic emissions inventory. Comparisons between runs A and B yielded differences up to 30% in the morning, over inland areas. It was deduced that the inclusion of BVOC in total emissions could result in an increase or decrease of tropospheric O3, depending on the available amounts of anthropogenic emissions. 相似文献
87.
88.
我国西北地区多处于干旱气候带,水资源匮乏,生态环境脆弱。为实施西北地区生态恢复与重建,必须合理开发和利用该区有限的水资源,科学地确定社会用水同生态用水的比例,积极保证生态用水,合理利用生态用水,注重生态用水的多重效益。结合西北干旱区实际情况,就这一地区生态用水的开发和利用做了分析阐述。 相似文献
89.
Computational modeling and analysis of thoracolumbar spine fractures in frontal crash reconstruction
Xin Ye James P. Gaewsky Derek A. Jones Logan E. Miller Joel D. Stitzel 《Traffic injury prevention》2018,19(8):S32-S39
AbstractObjective: This study aimed to reconstruct 11 motor vehicle crashes (6 with thoracolumbar fractures and 5 without thoracolumbar fractures) and analyze the fracture mechanism, fracture predictors, and associated parameters affecting thoracolumbar spine response.Methods: Eleven frontal crashes were reconstructed with a finite element simplified vehicle model (SVM). The SVM was tuned to each case vehicle and the Total HUman Model for Safety (THUMS) Ver. 4.01 was scaled and positioned in a baseline configuration to mimic the documented precrash driver posture. The event data recorder crash pulse was applied as a boundary condition. For the 6 thoracolumbar fracture cases, 120 simulations to quantify uncertainty and response variation were performed using a Latin hypercube design of experiments (DOE) to vary seat track position, seatback angle, steering column angle, steering column position, and D-ring height. Vertebral loads and bending moments were analyzed, and lumbar spine indices (unadjusted and age-adjusted) were developed to quantify the combined loading effect. Maximum principal strain and stress data were collected in the vertebral cortical and trabecular bone. DOE data were fit to regression models to examine occupant positioning and thoracolumbar response correlations.Results: Of the 11 cases, both the vertebral compression force and bending moment progressively increased from superior to inferior vertebrae. Two thoracic spine fracture cases had higher average compression force and bending moment across all thoracic vertebral levels, compared to 9 cases without thoracic spine fractures (force: 1,200.6 vs. 640.8 N; moment: 13.7 vs. 9.2?Nm). Though there was no apparent difference in bending moment at the L1–L2 vertebrae, lumbar fracture cases exhibited higher vertebral bending moments in L3–L4 (fracture/nonfracture: 45.7 vs. 33.8?Nm). The unadjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 9 of the 11 cases (sensitivity?=?1.0; specificity?=?0.6). The age-adjusted lumbar spine index correctly predicted thoracolumbar fracture occurrence for 10 of the 11 cases (sensitivity?=?1.0; specificity?=?0.8). The age-adjusted principal stress in the trabecular bone was an excellent indicator of fracture occurrence (sensitivity?=?1.0; specificity?=?1.0). A rearward seat track position and reclined seatback increased the thoracic spine bending moment by 111–329%. A more reclined seatback increased the lumbar force and bending moment by 16–165% and 67–172%, respectively.Conclusions: This study provided a computational framework for assessing thoracolumbar fractures and also quantified the effect of precrash driver posture on thoracolumbar response. Results aid in the evaluation of motor vehicle crash–induced vertebral fractures and the understanding of factors contributing to fracture risk. 相似文献
90.
火焰几何特性和辐射特性是刻画火灾规模及其危害的重要参量。利用三维火焰重构技术,获取了丙烷浮力扩散火焰的火焰高度、表面积、体积和火焰面元视角系数的变化规律。结果表明,三维重构的火焰能够表征真实火焰形态的动态变化。平均火焰表面积和体积均可较好地拟合为热释放速率的幂函数,火焰表面积热释放速率随火焰热释放速率的增加趋于常数。平均火焰高度、表面积和体积与火焰外部平均辐射热流之间具有较好的幂函数关系,且拟合指数随着与火源距离的增大而减小。此外,将点源、圆柱辐射模型和火焰面元积分方法得到的辐射计算值与辐射测量值进行比较,发现火焰面元积分方法能够更好地预测火焰外围的瞬时和平均辐射热流分布。 相似文献