用TDR确定沙壤土非饱和淹灌条件下NH_4~+的硝化反应及NO_3~-的入渗迁移

对于沙壤土柱实验，用ＴＤＲ（时间域反射计）结合土壤抽提液的溶质分析，研究了在非饱和灌溉条件下的硝化和ＮＯ－３的迁移．测得的土壤体电导率与土壤抽提液的电导率之比和土壤含水量成线性关系，籍此用ＴＤＲ可以确定非饱和灌溉条件下土壤中溶质浓度的变化规律；硝化过程是在土壤表层的不连通的小孔隙中进行的，几乎不受水分运动的影响；由示踪剂Ｂｒ－的入渗及土壤表层的ＮＯ－３（相当于ＴＤＲ测得的电导率值）入渗分布得出，入渗是按活塞推移作用进行的，借此方法可以研究非饱和入渗的机理．     

An analytical model for the interpretation of pulse injection experiments performed for testing the spatial variability of clay formations

This paper presents an analytical model to describe pulse injection experiments. This model solves the advection-diffusion equation while taking into account back diffusion from the clay core to the inlet and from the outlet to the clay core. In most analytical models, back diffusion is neglected. For sufficiently high Péclet numbers, this is a good approximation. However, in experiments where the Péclet number is low, back diffusion is important and must be taken into account. An additional advantage of the present model is that both concentration and flux are conserved at the inlet and at the outlet of the clay core. This model is used to fit pulse injection experiments with iodide and tritiated water (HTO) in clay cores. The (new) model is required for fitting the experimental results since in clay layers advection is very slow leading to a low Péclet number. The experiments are performed on clay cores taken from different depths from the Boom Clay and the Ypres Clay layer under the site of the nuclear power plant of Doel (Belgium). The quality of all fits is excellent and the obtained parameter values are coherent. For HTO, the fitted value for the diffusion accessible porosity is consistent with measurements of the water content in Ypres Clay cores. In both types of clays, the apparent diffusion coefficient at zero flow is between 10(-10) and 2 x 10(-10) m(2)/s for iodide and between 2 x 10(-10) and 3 x 10(-10) m(2)/s for HTO. The dispersion length is in the order of 10(-3) m. The average value for the diffusion accessible porosity is between 0.35 and 0.4 for HTO and between 0.2 and 0.25 for iodide.     

Hydraulic constraints on the performance of a groundwater denitrification wall for nitrate removal from shallow groundwater

Denitrification walls are a practical approach for decreasing non-point source pollution of surface waters. They are constructed by digging a trench perpendicular to groundwater flow and mixing the aquifer material with organic matter, such as sawdust, which acts as a carbon source to stimulate denitrification. For efficient functioning, walls need to be permeable to groundwater flow. We examined the functioning of a denitrification wall constructed in an aquifer consisting of coarse sands. Wells were monitored for changes in nitrate concentration as groundwater passed through the wall and soil samples were taken to measure microbial parameters inside the wall. Nitrate concentrations upstream of the wall ranged from 21 to 39 g N m(-3), in the wall from 0 to 2 g N m(-3) and downstream from 19 to 44 g N m(-3). An initial groundwater flow investigation using a salt tracer dilution technique showed that the flow through the wall was less than 4% of the flow occurring in the aquifer. Natural gradient tracer tests using bromide and Rhodamine-WT confirmed groundwater bypass under the wall. Hydraulic conductivity of 0.48 m day(-1) was measured inside the wall, whereas the surrounding aquifer had a hydraulic conductivity of 65.4 m day(-1). This indicated that during construction of the wall, hydraulic conductivity of the aquifer had been greatly reduced, so that most of the groundwater flowed under rather than through the wall. Denitrification rates measured in the center of the wall ranged from 0.020 to 0.13 g N m(-3) day(-1), which did not account for the rates of nitrate removal (0.16-0.29 g N m(-3) day(-1)) calculated from monitoring of groundwater nitrate concentrations. This suggested that the rate of denitrification was greater at the upstream face of the wall than in its center where it was limited by low nitrate concentrations. While denitrification walls can be an inexpensive tool for removing nitrate from groundwater, they may not be suitable in aquifers with coarse textured subsoils where simple inexpensive construction techniques result in major decreases in hydraulic conductivity.     

MODELING PERCOLATION LOSSES FROM A PONDED FIELD UNDER VARIABLE WATER-TABLE CONDITIONS1

ABSTRACT: A numerical simulation model was developed to predict the vertical and lateral percolation losses from a ponded agricultural field. The two-dimensional steady-state unsaturated/ saturated flow equation was solved using the finite-difference technique. A constant ponding depth was maintained at the soil surface with different water table conditions in an application of the model for rice fields bordered by bunds. Field experiments were conducted for two different water table depths to collect data on the spatial distribution of volumetric soil-moisture content for model verification. The measured soil-moisture content values were found to be in close agreement with those predicted by the model. The sensitivity analysis of the model with selected hydrologic conditions shows that the model is most sensitive to the values of saturated hydraulic conductivity, but relatively less sensitive to water table depth, ponding depth, and evaporation rate from the soil surface. It implies that, in a ponded rice field condition, the lateral and vertical percolation losses are mostly governed by the hydraulic conductivity of the soil. The vertical percolation losses were almost equal to the saturated hydraulic conductivity values and, in most cases, these losses increased with deeper water table depths. The lateral percolation losses also increased with deeper water table depths; however, these losses were relatively small in comparison to the vertical percolation losses. The vertical and lateral percolation losses increased with the increase in ponding depths. The lateral percolation losses through the bund decreased when the evaporation losses increased from the soil surface. The results of this study indicate that the percolation losses from a ponded field may be predicted accurately for a wide range of soil and hydrological conditions when the values of hydraulic conductivity, evaporation rate, depth of ponding, and water table depth are accurately known.     

一种计算粒子电迁移率的新模型

近几年来,粒子电迁移率引起了更多学者的注意。因为它是表征带电粒子在电场中运动的重要参数之一。在这方面,人们已作了大量的研究工作,提出了一些计算粒子电迁移率的理论和半经验模型。基于前人的研究,本文提出了一种计算粒子电迁移率的新模型,并用前人的实验结果和本研究的实验结果对此模型进行了检验。计算结果和实验数据很吻合。就某种意义上讲,此模型是对以前模型的扩展和改进,它可广泛应用于溶胶的研究和工业应用。     

煤岩体导热系数试验及单因子方差分析

为研究温度和含水量对煤、岩体导热系数的影响,采用激光闪射法测得8种煤、岩样品的导热特性参数;利用单因子方差分析方法对不同温度条件下的煤岩体导热系数测定结果进行比较分析,结果表明:煤岩体的导热系数随温度升高线性降低,随含水量增大而增大;岩石的导热系数大于煤体的导热系数,岩石的导热系数为1~5W/(m·K),煤的导热系数为0.1~0.5 W/(m·K);拟合得到不同煤体导热系数和温度的关系式,其拟合函数相关度在0.93左右,最大相对误差为2.18%。因此,可利用拟合函数和测试结果预测测试矿井的煤岩体导热系数。     

基于Bayes判别模型的火场中铜导线短路熔痕 定量金相鉴定方法研究

借助计算机图像处理技术,改进了定量金相分析方法,测量了20个一次短路熔痕和20个二次短路熔痕的金相组织,对数据进行了主成分分析,提炼出了晶粒特征因子、气孔特征因子和复合因子三个主成分,基于Bayes判别法建立了火场中短路熔痕定量金相分析判别模型,经自身检验和交互检验,准确率均高于80%,充分满足鉴定要求,为更加有效地应用定量金相法鉴别短路熔痕提供了理论依据。     

氢氧爆轰电离模型研究

提出了利用氢能的脉冲爆轰波磁流体发电的设想,发电系统可以解决一般磁流体发电中的高温耐热材料问题和排渣问题.对脉冲爆轰磁流体发电中的核心参数——爆轰产物的电导率进行了理论研究.应用稳态爆轰的ZND理论和局部热力学平衡的热电离理论建立了爆轰产物电导率的计算模型,计算了不同初始压力下当量氢氧混合气体的爆轰电导率.模型计算结果与实验数据基本吻合.同时利用该模型预测了爆轰温度与氢气和氧气的混合比对爆轰产物电导率的影响.研究发现,爆轰产物的平衡电导率主要由爆轰温度决定,氢气与氧气的混合比在接近当量比的时候可以取得最大爆轰电导率,混合气体初始压力对爆轰电导率影响不大,当量氢氧混合气体的爆轰电导率在10-3～10-1 S/m范围内.     

唐古拉冬克玛底冰川流域pH值和电导率分析

2005-05-11～2005-09-27,在青藏高原唐古拉段冬克玛底冰川流域对融水径流和草地径流分别进行采样.对样品的pH值和电导率进行了分析.结果表明,研究区环境受人类活动影响很小.借助电导率水量来源模型对冬克玛底河流量进行划分,暖季径流主要以冰川冰融水补给为主,占总流量的62%以上,其次是积雪融水和降雨补给,其中,第1、3阶段的积雪融水补给分别占31%和37%,第2阶段的降雨补给占17%左右;土壤冻结水消融对径流贡献很小,占2%以下.     

崇明东滩围垦区芦苇湿地土壤盐分动态研究

2009~2013年对崇明东滩围垦区芦苇湿地10 cm和30 cm两个土层的土壤溶液电导率、水分、温度和相关微气象因子进行了为期5 a的原位同步连续监测,探讨了不同时间尺度的湿地土壤盐分动态。结果如下:(1)在年际动态方面,10 cm土层的土壤溶液电导率在5 a间逐年递减,年均降低8.10%,30 cm土层的土壤溶液电导率在前4 a逐年递减,年均降低6.06%,但2013年较2012年上升了16.34%。各个年份10 cm土层的土壤溶液电导率均值皆显著低于30 cm土层,且年均值的差异逐年递增。(2)在季节动态方面,各年份内,两个土层的土壤溶液电导率多表现为春、夏、秋升高,冬季下降的趋势,也多在秋季和冬季分别达到最大值和最小值。各年份间,10 cm土层春季和夏季以及30 cm土层春季的土壤溶液电导率呈逐年递减的趋势。(3)在日动态方面, 10 cm土层的土壤溶液电导率波动幅度大于30 cm土层,并且30 cm土层土壤溶液电导率日最大值和最小值出现的时刻较10 cm土层有一定的滞后性。综上所述,研究区在围垦后,耕层土壤每年都能以一定的速率脱盐,但在季节性气候影响下,严重的返盐现象仍可能在秋季发生,因而在秋季可以通过增加人工措施以防止土壤返盐。