Roughness of biopores and cracks in Bt‐horizons assessed by confocal laser scanning microscopy

In structured soils, water and reactive solutes can preferentially move through larger inter‐aggregate pores, cracks, and biopores. The surface roughness of such macropores is crucial for describing microbial habitats and the exchange of water and solutes between macropores and the soil matrix together with other properties. The objective of this study was to compare the roughness of intact structural surfaces from the Bt‐horizons of five Luvisols developed on loess and glacial till and to test the applicability of confocal laser scanning microscopy. Samples of 5 to 10 cm edge length with intact structural surfaces including cracks with and without clay‐organic coatings, earthworm burrow walls, and root channels were prepared manually. The surface roughness of these structures was determined with a confocal laser scanning microscope of the type Keyence VK‐X100K. The root‐mean‐squared roughness (R_q) the curvature (R_cu) and the ratio between surface area and base area (R_A) were calculated from selected surface regions of interest of 0.342 mm² with an elevation resolution of 0.02 µm. The roughness was smaller for coated as compared to uncoated cracks and earthworm burrows of the Bt‐horizons. This reduction of roughness by the illuviation of clayey material was similar for the structural surfaces of the coarser textured till‐Bt and the finer‐textured loess‐Bt. This similarity suggested a dominant effect of pedogenesis and a minor effect of the parent material on the roughness levels of structural surfaces in the Bt‐horizons. An expected “smoothing” effect of burrow wall surfaces by earthworm activity was not reflected in the roughness values compared to those of uncoated cracks at the chosen spatial scale. However, for root channel walls from one loess‐Bt, the roughness was reduced as compared to that of other structures. These results suggest that the surface roughness of the structural surface types should separately be considered when describing preferential flow and macropore‐matrix exchange or analysing root growth, microbial habitats, and colloidal transport in structured soils. The confocal laser scanning microscopy technique was found useful for characterizing the roughness of intact structural surfaces.     

集中流作用下黄土坡面剥蚀率对侵蚀动力学参数的响应

集中流引起的细沟侵蚀是黄土高原坡耕地主要侵蚀方式之一,对坡面集中水流动力学特性研究有利于掌握坡面集中流剥蚀产沙的根本原因,但目前哪种集中流水动力学参数最能准确揭示侵蚀动力过程机理尚不明确。该文采用室内集中流放水冲刷试验,以黄土高原典型黄绵土为研究对象,研究坡面平均和瞬时剥蚀率与相应水流剪切力、水流功率、单位水流功率以及过水断面单位能量之间的关系。结果表明,除了瞬时过水断面单位能量拟合效果较差外,其他平均和瞬时水力学参数均能够较好地与坡面剥蚀率建立不同的拟合关系。所有参数中平均水流功率是描述本试验条件下的最优水力学参数。由于细沟发育过程中大量坍塌的出现,导致整个径流剪切力和水流功率与剥蚀率之间的关系曲线整体上升,出现了临界剪切力和临界水流功率为负值的情况。通过与仅考虑水流对坡面直接作用参数所得结果对比,表明坍塌等作用在细沟发育过程中具有重要影响,对剥蚀率的贡献可达90.93%。研究可为控制和预防集中流侵蚀发生提供科学依据。     

多级离心泵水力性能数值预测涡量分析法

为了研究利用CFD技术预测多级离心泵水力性能的方法,选取某一多级离心泵为研究对象.采用数值模拟方法获得了多级离心泵内部全流场信息.分别选取多级离心泵单级、二级、三级的三维模型进行全流场数值模拟,获得了3种三维模型各水力部件内部的的水力损失,通过对计算结果分析发现,多级离心泵内部各级水力损失大小基本类似,不随级数的不同而改变,这为通过对少级数的数值模拟以预测更多级数的泵性能提供了依据.通过对多级离心泵内部流场各级能量损失进行分析,分析各级能量损失特征及其流动特点,发现各级涡量分布基本一致,损失特性相同,只在最后一级导叶内部的涡结构有一定的区别.采用能量分析结合多级泵内部流场涡动力学分析方法建立了多级离心泵性能数值预测的计算方法,并建立了多级离心泵性能预测基于少级数模型数值分析的计算公式.     

涌泉灌双向流流道稳流器工作机理与水力性能分析

为了研究双向流稳流器流道结构的水力特性,以其内部双向流形成装置和结构参数为研究对象,取流道结构参数八字形分水件张角α,V字形挡水件张角β、八字形分水件中部过水孔宽度d为因素安排试验方案,利用激光精雕技术制作稳流器样机进行水力试验,测得0.05~0.21 MPa等9个不同压力对应的流量值,应用多元回归拟合其流态指数在0.476~0.501,其水力性能良好;同时采用水力学计算方法,计算当稳流器工作水头分别在5~15 m时,流道总局部损失系数为18.3~19.8,大约是1组传统流道形式局部损失系数的4~10倍,从水力学计算的角度表明双向流流道消能效果的优越性;采用Minitab软件的Gauss-Newton算法进行多元回归,迭代次数设为200次,建立流态指数与结构参数之间的回归方程,通过显著性检验和相关系数检验结论一致,均显示回归效果具有统计学意义,且各因子的系数均有意义,为其流道参数化设计、结构优化以及在农业工程中的研发与应用提供了理论依据.     

蜗壳断面形状及叶轮位置对蜗壳式轴流泵性能的影响

根据速度系数法设计了1种对称的“马蹄形”断面蜗壳和2种非对称的 “圆形”断面蜗壳与相同的轴流泵叶轮组合,并基于标准k-ε模型封闭的雷诺平均方程,应用 ANSYS CFX 14.5 软件,对设计的3个蜗壳式轴流泵内部的三维流动开展数值模拟.当采用“马蹄形”蜗壳时,设计流量点的扬程和效率最低,蜗壳内部压力分布不如非对称的圆形断面蜗壳均匀.选择水力效率相对较高的蜗壳,将4种轴向位置不同的叶轮与该蜗壳组合,并进行三维流动数值模拟,结果表明:叶轮出口与蜗壳进口中间平面距离40 mm时,轴流泵效率最高,叶轮出口与蜗壳进口中间平面距离80 mm时,轴流泵效率最低.此时,过流段和蜗壳内有明显回流和旋涡.轴流式叶轮与蜗壳的相对位置对蜗壳轴流泵的扬程-流量曲线和效率-流量曲线都有明显的影响.     

开缝叶片低比转数离心泵空化性能的数值模拟

为了进一步提高低比转数离心泵的空化性能,对离心泵叶轮叶片进口附近的开缝进行研究.考虑开缝的3个参数,设计6组水力模型探究开缝对低比转数离心泵性能的影响.针对离心泵运行过程中产生空化的流动特点,基于Rayleigh-Plesset方程来描述空泡成长和溃灭过程的空泡动力学模型,采用RNG k-ε模型对在相同工况下的离心泵中两相流动进行数值模拟与分析.模拟结果表明:在叶片进口处开缝可以提高泵空化性能,其中第二组模型的空化性能提升比较明显,空化余量由4.447 m下降到3.910 m,降低了12.1%,水力效率由71.56%上升至76.46%;在相同工况下,开缝叶轮流道内的能量分布更加均匀,而扬程在额定流量下只有很小的变化.该模拟结果对研究低比转数离心泵内部流动特性及性能的提升具有一定的参考价值.     

Linking Microbial Community Dynamics Associated with Rhizosphere Carbon Flow in a Biofuel Crop (Jatropha curcas L.)

Photosynthetically derived rhizodeposits are an important source of carbon (C) for microbes in root vicinity and can influence the microbial community dynamics. Pulse labeling of carbon dioxide (¹³CO₂) coupled with stable isotope probing techniques have potential to track recently fixed photosynthate into rhizosphere microbial taxa. Therefore, the present investigation assessed the microbial community change associated with the rhizosphere and bulk soil in Jatropha curcas L. (a biofuel crop) by combining phospholipid fatty acid (¹³C-PLFA) profiling using a stable isotope ¹³CO₂ labeling approach. The labeling (¹³C) took place after 45 days of germination, PLFAs were extracted from both soils (rhizosphere and bulk) after 1 and 20 days pulse labeling and analyzed by gas chromatography-isotope ratio mass spectrometry. There was no significant temporal effect on the PLFA profiles in the bulk soil, but significantly increased abundance of Gram positive (i15:0) and Gram negative (16:1ω7c and 16:1ω5c) biomarkers was observed in the rhizosphere soil from day 1 to day 20 after labeling. The Gram negative (16:1ω7c) decreased and fungal (18:2ω6,9c) increased significantly in rhizospheric soil compared to bulk soil after day 1 of labeling. Whereas, after 20 days of labeling, the Gram negative biomarker (16:1ω7c and 18:1ω7c) decreased and Gram positive (a15:0) increased significantly in rhizospheric soil compared to bulk soil. One day following labeling, i15:0, a15:0, i16:0, 16:1ω5c, 16:0, i17:0, a17:0, 18:2ω6,9c, 18:1ω9c, and 18:0 PLFAs were significantly more enriched in δ¹³C in the rhizosphere than in the bulk soil. Twenty days after labeling, 16:1ω5c (Gram negative) and 18:2ω6,9c (fungal) were significantly more enriched in δ¹³C in the rhizosphere than in the bulk soil. These results shows the effectives of PLFA coupled using the pulse chase labeling technique to examine the microbial community changes in response to recently fixed photosynthetic C flow in rhizodeposits.     

The nature of soil erosion and possible conservation strategies in Ntabelanga area,Eastern Cape Province,South Africa

Soil erosion is a major land degradation problem in South Africa (SA) that has economic, social and environmental implications due to both on-site and off-site effects. High rates of soil erosion by water are causing rapid sedimentation of water bodies, ultimately leading to water crisis in SA. Lots of financial and human resources are channelled towards controlling of soil erosion but unfortunately with little success. The level of soil erosion in a particular area is governed by the site properties. Therefore, it is inappropriate to generalize data on soil erosion at a large-scale spatial context. The literature on soil erosion in SA classifies Eastern Cape Province as a high-erosion-potential area using data collected at a large-scale spatial context. Collecting soil erosion data at a large spatial scale ignores site-specific properties that could influence soil erosion and has resulted in failure of many traditional soil erosion control measures applied in the province. Moreover, scientific principles underlying the processes and mechanisms of soil erosion in highly erodible soils are missing in SA. This review was to find effective soil erosion control measures by having an insight on what happens during soil erosion and how soil erosion occurs in Ntabelanga. The literature suggested that erosion in Ntabelanga could be influenced by both the erosivity and erodibility factors though the erodibility factors being more influential. Soil permeability contrast between the horizons could be influencing the rate and nature of soil erosion. To mitigate the impact of soil erosion in Ntabelanga, efforts should aim to improve the vertical flow capacity in the B horizon. Clay spreading, clay delving, addition of gypsum, deep ploughing and mulching could aid the water permeability problems of the subsurface horizons. However for effective soil management and control option, detailed studies of specific site properties are needed. The generated information can assist in formulating soil erosion policies and erosion control strategies in the Ntabelanga area and SA at large.     

应用技术泥石流荷载下钢管混凝土桩林结构的抗冲击性能

[目的]分析新型拦挡坝钢管混凝土桩林结构在泥石流冲击荷载作用下的动力响应,为其结构的设计提供有效的科学依据。[方法]通过 ANSYS 有限元分析软件对3种不同泥石流荷载工况下桩林坝进行数值模拟,主要分析结构的应力、应变和位移等响应。对比3种工况的响应,得到结构的最不利荷载工况。[结果]空库桩管顶部受大石块冲击是结构的最不利荷载工况,3种工况相对比,发现大石块的冲击力是导致结构破坏的主要因素;钢管混凝土桩林具有良好的抗冲击性能,在较小的塑性变形下,结构承受较大的冲击力,且受撞击构件刚度越大,冲击力峰值越大;桩管和梁管的连接部位、桩管根部和端部受约束梁管是坝体的薄弱部位,因此设计时应采取加强措施。[结论]钢管混凝土桩林是一种节约材料稳定性较好的拦挡结构,具有良好的抗冲击性能。     

阿克苏市3种绿化乔木树干液流日变化特征

为了测算园林树木的蒸腾耗水量,应用热脉冲技术对阿克苏市3种常见绿化乔木(小叶白蜡、法国梧桐、桑树)进行树干液流的测定,并分析其日变化规律,同时运用自动气象站记录各气象参数数据,分析树干液流日变化与气象因子之间的相关性。结果显示：3种乔木树干液流速率之间有一定的差异,但其日变化过程几乎相似,均有明显的昼夜变化规律。白天的液流速率比夜间大,午间由于太阳辐射( Rs)过强出现午休现象,凌晨和晚上树干液流速率较低,夜间保持微弱的树干液流过程。小叶白蜡、法国梧桐、桑树等树干液流日变化都与太阳辐射、空气温度( Ta)、风速( Ws)呈显著正相关,而与空气湿度( H)呈显著负相关;逐步回归模型显示,影响小叶白蜡树干液流的主要气象因子是太阳辐射和空气湿度,模型拟合度为0.962,法国梧桐的是空气温度和空气湿度,拟合度为0.971,桑树的是空气温度和太阳辐射,拟合度为0.915。不同乔木的日累计液流量大小排序为小叶白蜡(57000±2400) mL﹥法国梧桐(55400±2100) mL﹥桑树(7600±1800)mL。