补偿式滴头的研制

补偿式滴头是微灌设备中最理想的灌水器,它除能保持滴水量衡定、提高灌水质量外。还具有减缓堵塞、自身清洗之功能,而且能降低工程造价。国产补偿式滴头研制成功,填补了国内空白,也为进一步开展补偿式灌水器研究积累了经验。     

基于双向渐进结构优化法的装载机动臂拓扑优化

利用双向渐进结构优化法研究了装载机动臂结构的拓扑优化问题。利用有限元软件ANSYS的APDL语言进行二次开发,实现了多工况下基于应力水平的双向渐进结构优化法(BESO)。对装载机工作装置的动臂进行多工况下的结构双向渐进拓扑优化,得到了动臂的最佳拓扑结构。结果表明了该方法的实用性和有效性,且比ESO方法具有更高的效率。     

低压射流不同喷嘴参数及压力下破碎过程实验

研究了不同低压下喷头喷嘴直径和喷嘴锥角对射流破碎的影响。采用高速摄像仪对低压圆柱射流的射流核心长度和射流破碎长度进行实验,测量了不同喷嘴结构的流量、射程和末端水滴直径。结果表明:同一压力下,当喷嘴锥角不变时,随着喷嘴直径的增大,喷头流量、射程和喷头末端水滴直径都变大,射流核心长度和破碎长度均增大;当喷嘴直径不变时,随着喷嘴锥角的增大,喷头流量逐渐减小,而喷头射程呈先增大后减小趋势,喷头末端水滴直径也变大,射流核心长度逐渐减小,射流破碎长度先减小后增大。综合考虑射程和雾化效果,直径为5 mm、锥角为45°的喷嘴为最优选择。同时通过对不同Re数和We数的实验和分析,给出了适合低压喷嘴的两种射流特征长度的拟合关联式。     

电车接触网腕臂的计算

电气化铁道的“三大元件”分为接触网、电力机车和牵引变电所。本论文论述时速200Km/h高速电气化铁路的接触网电车接触网腕臂的计算,接触网的计算精确程度就关系到接触线悬挂的可靠程度,故接触网计算是设计中基础的工作内容,其计算主要分为腕臂的计算和接触网的负载计算。文章详细分析了腕臂长度的计算方法,重点介绍了路基曲线区段腕臂长度、转换柱和中心柱腕臂长度的计算。     

Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches

Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃-N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH₄⁺-N, and greater NO₃-N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO₃-N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters.     

低压管道环状管网水力计算

本文对环状管网运行中仅开启一个出水口的水力计算方法进行了探讨。计算出了特征长度系数、平均特征长度系数和最大特征长度系数,并将其排成数表供直接查用。同时计算出了双环管网平均和最大特征长度系数的回归方程,经比较,本文提出的计算方法简单、可靠,便于设计中应用。     

多年生黑麦草叶片长度数量性状位点(QTLs)研究

选择固定有益等位基因,研究多年生黑麦草叶片长度数量性状位点,结果表明:与叶长最为相关的3个标记所表达的变异占表型总变异的50.9%(r2);在选择中如能将这3个标记最优化地组合在一起,其综合共同作用有望使叶片长度延长和缩短26 mm;鉴于供试材料在最初3个世代的群体选择中所估测到叶片长度的遗传力为0.32,这样在今后的选择工作中,即使只使用现有的两个标记,其效果亦优于传统的表型选择法.     

Ectomycorrhizal fungi identification in single and pooled root samples: terminal restriction fragment length polymorphism (TRFLP) and morphotyping compared

We describe here the results of a study conducted to evaluate a terminal restriction fragment length polymorphism (TRFLP) approach targeting rRNA genes for determination of ectomycorrhizal (ECM) communities colonizing the roots of loblolly pine (Pinus taeda L.). Root tips separated from soil cores were classified according to morphological characteristics and DNA was then extracted from each group of morphotyped tips. Labeled primers were used to generate terminal restriction fragments (TRF) for molecular fingerprinting of root colonizing fungi and to determine how well TRFLP could be used to discriminate between ectomycorrhizal types. Morphotypes generally correlated well with specific TRFs and sequence analysis confirmed that TRFs could be used to discriminate among fungal types. Sequence analysis indicated that important ECM fungi including Russulaceae, Thelephorales, and Tricholomataceae could be fingerprinted with TRFLP. In addition, a fixed proportion of the DNA extracted from each morphotype from the same core was used in a pooling experiment used to assess whether previously identified fungal species types could be distinguished from one another within reconstructed communities. Since some morphotypes share TRFs, dual analysis of ITS1 and ITS2 was necessary for accurate fingerprinting of fungal types. Approximately, 5.0±0.3 phylotypes were detected per core with TRFLP-corrected morphotyping as compared to 4.0±0.4 phylotypes using TRFLP on pooled community samples. TRFLP made on experimental sporocarp communities suggested that reduced ECM richness with TRFLP may be partly caused by differences in the amount of DNA available for PCR and primer bias. Nonetheless, TRFLP on pooled morphotypes accounted for more than 93% of colonized root tips. The method can be used to facilitate analysis of mycorrhizal communities using root tips collected from soil cores.     

Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)

It is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g cm^–3 to 1.66 g cm^–3. Rhizotrons with a soil layer 7 mm thick were used and pre‐germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30 % with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20 % and 50 % for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15 % of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots.     

Effects of decreasing soil water content on seminal lateral roots of young maize plants

Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm³ cm^–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm³ cm^–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm³ cm^–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions.