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121.
Rafik Absi 《Environmental Fluid Mechanics》2008,8(4):389-394
In a recent paper published in this journal, Bonakdari et al. (Environ Fluid Mech 8:1–17, 2008) presented a new formulation
of the vertical velocity profile in the central portion of steady fully developed turbulent open-channel flows which is based
on an analysis of the Navier–Stokes equations. The predicted mean streamwise velocity profiles presented by the authors represent
dip phenomenon (maximum velocity below the free surface). The discusser would like to point out some contradictions and an
error in the main demonstration. This error appears in the right-hand side term of the main Eq. 22 (Environ Fluid Mech 8:1–17,
2008) in the parameter α. Our corrected demonstration shows that α is equal to and not to as obtained by the authors (Environ Fluid Mech 8:1–17, 2008). The values of α used by the authors are under-estimated by 1, this difference has a significant effect on velocities and therefore will involve
a difference between measured and predicted velocity profiles. Finally, the assumption of at the free surface is in contradiction with predicted velocity profiles. 相似文献
122.
本文基于ASTER GDEM数据,采用简单数学函数拟合龙门山地区15条河流的河流纵剖面形态,并结合基岩水力侵蚀模型来分析龙门山不同段落的地形形态特征。初步获得以下几点认识:(1)通过对龙门山地区河流纵剖面的分析,龙门山整体上具有较强的隆升速率,导致这一地区强烈的河流侵蚀作用;(2)龙门山中段和南段的河流双对数图以上凸型为主,说明该区域未达到均衡状态,处于前均衡期;(3)龙门山北段的河流双对数图呈直线形态,说明该区域达到均衡状态,处于均衡期;(4)龙门山中段和南段具有更强的构造活动性、更高的隆升速率,控制了该地区地貌、水系演化过程,并且导致这一地区容易发生地质灾害。 相似文献
123.
Andrew O. Hughes Jon M. Olley Jacky C. Croke Ian T. Webster 《Journal of environmental radioactivity》2009,100(10):858-865
Fallout 137Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of 137Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total 137Cs inventories calculated from the detailed profile data. Information on the rates of 137Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of 137Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for 137Cs being known and without having to assume that 137Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total 137Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, 137Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites. 相似文献
124.
Anthropogenic radionuclides in seawater have been used as transient tracers of processes in the marine environment. Especially, plutonium in seawater is considered to be a valuable tracer of biogeochemical processes due to its particle-reactive properties. However, its behavior in the ocean is also affected by physical processes such as advection, mixing and diffusion. Here we introduce Pu/137Cs ratio as a proxy of biogeochemical processes and discuss its trends in the water column of the North Pacific Ocean. We observed that the 239,240Pu/137Cs ratio in seawater exponentially increased with increasing depth (depth range: 100–1000 m). This finding suggests that the profiles of the 239,240Pu/137Cs ratios in shallower waters directly reflect biogeochemical processes in the water column. A half-regeneration depth deduced from the curve fitting the observed data, showed latitudinal and longitudinal distributions, also related to biogeochemical processes in the water column. 相似文献
125.
P. B. L. Tamuno G. Howard M. D. Smith 《Environment, Development and Sustainability》2009,11(4):887-903
The Central Niger Delta is made up of a network of rivers and creeks that constitute the inland surface waters. These surface
waters have historically influenced settlement patterns and are of diverse use to residents of the Central Niger Delta. Surface
water like many ecological system are complex, whose complexity has been associated with seasonal variability. Traditional
knowledge (TK), traditional ecological knowledge (TEK) and the traditional eco-livelihood knowledge (TELK) of residents of
four rural communities in the Central Niger Delta have been explored in developing a river use profile of rural communities
of the Central Niger Delta. A questionnaire survey has been carried out in four communities, two each from the Otuoke and
Kolo Creeks. The result shows that river use varies across seasons and affected by: physico-chemical water quality and characteristics
of surface water; the hydrological characteristics; the biological/ecological characteristics; cultural use and demand; need
for development projects; and access to this vital resource. Fishing constitute one of the major livelihood source in the
Central Niger Delta and the TELK of fishers in the sample communities have specifically been explored to understanding fishing
patterns across seasons. The five seasons identified from this study are: flood season; flood recession season; dry season;
early rainy season; and rainy season. Therefore, the thesis of this paper is that there is the need to balance the current
usage of surface water in the developing world such as the Central Niger Delta with the demand for development as well as
future use if development is to meet the criteria for equitable development. The river use profile could be a promising tool
in planning for equitable development.
相似文献
M. D. SmithEmail: |
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127.
城市热环境是城市中建筑物的不断增加及人类活动、大气状况、地表热量传输等多种因素综合作用的结果,因此城市往往具有极为复杂的热表面。由于热量分配、传输具有一定的复杂性,传统的模型预测与定点观测方法在分析城市热表面空间结构及其形成机制方面存在一定的不足。随着空间信息科学的发展,卫星遥感技术为获取城市热场信息提供了可靠的手段。选用上海市2000年6月14日的Landsat ETM+热波段影像,首先反演城市地表温度,再引入剖面线分形的方法,在GIS的支持下,计算从人民广场出发的8个方向的分维数,并进一步探讨剖面线分形的意义,得到如下结论:城市热表面的剖面线具有明显的分形特征,8个方向的分维数为1.530 0~1.780 6,表征不同剖面线的复杂程度。热场表面剖面线的分维数揭示了3个方面的意义:首先不同的分维数反映热场不同方向上温度变化的复杂程度;其次,相对于城市中心,反映不同方向上城市边界形态的差异性;第三,进一步揭示不同方向上,下垫面土地利用类型空间组合变化的复杂程度。 相似文献
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130.
ITFB强化除氨及醌指纹生物群落结构分析 总被引:4,自引:0,他引:4
通过改变内循环生物流化床(internal-circulation three-phase bio-fluidized bed,ITFB)的启动水质,提高N/C组成以强化流化床后期的硝化作用.结果表明,高N/C和低进水COD是强化除氨的必要启动条件;强化启动后以模拟生活污水为研究对象,在HRT为2h时,可以实现COD和氨氮的同时高效去除,氨氮的平均去除率为74%,出水氨氮浓度小于10 m g/L.研究利用醌指纹技术对反应系统中微生物群落结构变化进行了跟踪分析,结果表明经过强化除氨启动后,内循环生物流化床生物膜中以Nitrosomonas europaea为代表的硝化细菌数量有所增加;而以Acinetobacter sp.和Pseudomonas sp.为代表的变形细菌的γ亚类数量减少.EQ值始终在0.5左右变化表明生物膜中微生物种群的分布均匀性变化较小.所有测试样品中UQ/MK的比值均大于1,说明生物膜系统中以革兰氏阴性菌为主. 相似文献