Root exposure effects on water relations of Eucalyptus nitens nursery stock

Bare-root seedlings of Eucalyptus nitens frequently exhibit water stress after planting resulting in leaf lamina damage and reduced leaf area. Two trials examined effects of root exposure and desiccation between lifting and transplanting on post-planting water relations, leaf retention and root growth. Plants with roots exposed on a glasshouse bench initially lost water rapidly. In one trial ₁ declined to around –2.0 MPa within 2.5 h, after which there was no further change with exposure up to 7.5 h. In the second trial, the initial decline in ₁ was more rapid, reaching below –2.0 MPa in the first hour, before remaining stable with continuing exposure up to 4.5 h. A further decline then continued to –4.0 MPa after 7.5 h.Two days after transplanting into potting mix, day – time leaf water potentials in all desiccation treatments had declined to near –2.0 MPa. Hydraulic resistivity, measured as leaf specific resistivity two days after transplanting, increased following exposure for greater than 2.5 h, but there was no further increase between 4.5 and 7.5 h. The increase in resistivity corresponded with leaf water potential declining below –2.0 MPa during exposure.In the second trial, increasing root exposure time resulted in decreased leaf area due to lamina necrosis. Root growth, measured three weeks after planting, was also reduced. and there was also a positive curvilinear relationship between leaf area remaining at three weeks and new root growth. The results are discussed in terms of hardiness and the management of E. nitens seedlings from nursery to plantation.     

关于现浇箱梁预压方法--水压法的探讨

支架预压是现浇梁施工必须经过的准备工序。介绍了水压法的可行性和简单的操作过程 ,并对水压法和钢筋预压法的成本、工期进行了比较研究     

二次调节静液储能拖拉机传动系统

二次调节静液储能拖拉机传动系统是由柴油机，液压蓄能器，液压泵/马达（二次元件），差动变速器和驱动轴等组成，该系统充分利用了液压蓄能功率密度大，二次元件具有较高的控制质量，可实现四象限工作等特点；实现了柴油机和拖拉机行驶载荷的分离，工作过程中当外负载扭矩发生变化时，将引起二次元件的转速变化，从而引起二次元件排量的变化，通过调节液压马达的变量机构使其与工作负载所需转速相适应。     

装板机的机械与液压系统

介绍了装板机械与液压系统的组成，工作原理和设计特点，装板机为引进德国中密板生产线上的关键设备，对该设备的剖析于同类设备的国产化有着重要意义。     

棉花曲叶病毒对棉花造成的经济损失评估

棉花曲叶病毒(Cotton leafcurl virus)是我国进境检疫性病毒,严重危害棉花的生长,给棉花生产带来巨大经济损失。文中分析此病毒可能给棉花生产所造成的损失,包括直接经济损失、间接经济损失和防治费用。估算了棉花曲叶病毒对棉花造成的经济损失值为77.27亿元~498.61亿元。     

Effects of Vegetation Stems on Hydraulics of Overland Flow Under Varying Water Discharges

Vegetation plays an important role in soil erosion control, but few studies have been performed to quantify the effects of vegetation stems on hydraulics of overland flow. Laboratory flume experiments were conducted to investigate the potential effects of vegetation stems on Reynolds number, Froude number, flow velocity and hydraulic resistance of silt‐laden overland flow. Cylinders with diameter D of 2·0, 3·2 and 4·0 × 10⁻² m were glued onto the flume bed to simulate the vegetation stems, and a bare slope was used as control. The flow discharge varied from 0·5 to 1·5 × 10⁻³ m³ s⁻¹ and slope gradient was 9°. Results showed that Reynolds number on vegetated slope was significantly higher than that on bare slope because of the effect of vegetation stems on effective flow width. All the flows were supercritical flow, but Froude number decreased as D increased, implying a decrease in runoff ability to carry sediment. The mean flow velocity also decreased with D, while the velocity profile became steeper, and no significant differences were found in surface flow velocities among longitudinal sections on all slopes. Darcy–Weisbach friction coefficient increased with D, implying that the energy consumption of overland flow on hydraulic resistance increased. Reynolds number was not a unique predictor of hydraulic roughness on vegetated slopes. The total resistance on vegetated slopes was partitioned into grain resistance and vegetation resistance, and vegetation resistance accounted for almost 80% of the total resistance and was the dominant roughness element. Further studies are needed to extend and apply the insights obtained under controlled conditions to actual overland flow conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

液压传动技术在烟草打顶机上的应用

针对烟草中后期田间管理阶段的打顶及喷施抑芽剂时,作业人员劳动强度大、生产效率低,严重影响烟草产量和质量的现状,研制出高地隙三轮自走式全液压烟草打顶机。该机采用T型车架及高架式机体,液压驱动行走、转向、制动系统,以及液压操纵烟草打顶、喷施药剂系统。该打顶机液压系统传递功率大、结构紧凑、布置灵活,且易于实现无级调速及过载保护,便于控制、操作简便,可高效地完成烟草打顶及喷施药剂作业。     

江苏1204拖拉机液压输出功率不足问题的解决

江苏1204拖拉机液压输出功率,在试验时,出现输出功率不足的问题。对实验数据分析,影响液压功率的两个因素流量和压力,从元件品质来看,可能是齿轮泵的容积效率以及系统低压区漏气的问题,从设计角度分析,则可能是吸油管及其管路元件结构参数的选择问题。如何确定系统元件的参数即吸油管等元件的参数,按规范设计是基本的要求;之后,才是根据实际情况,再优化设计和超越规范设计。对试验中出现的问题,查找应遵守逻辑原则,涉及到实物分解时,则是先易后难,最终找到问题的原因予以解决。     

空气罐与超压泄压阀联合水锤防护特性

提出了一种空气罐与超压泄压阀联合设置的停泵水锤防护方案,并基于瞬变流计算的特征线法建立了空气罐、液控蝶阀、超压泄压阀等边界条件的数学模型,模拟了停泵工况下系统的压力变化过程.结合工程实例,对比分析了空气罐单独防护、空气罐与两阶段关闭泵后液控蝶阀联合防护以及空气罐与超压泄压阀联合防护对停泵水锤的影响.在空气罐体型一定时,对超压泄压阀的启闭规律进行了敏感性分析.计算结果表明,空气罐与两阶段关闭泵后液控蝶阀联合防护方案对输水系统正负水锤防护均不利;而空气罐与超压泄压阀联合防护方案对输水系统正负水锤均有较好的防护效果,与空气罐单独防护方案相比,泵后高压管段最高压应力由1.343 MPa降至1.087 MPa,在满足承压标准1.2 MPa的基础上安全裕度提高了9.4%,空气罐体型也由200 m³缩减至160 m³.超压泄压阀应在5 s内开启至全开度,且开启后持续时间应接近1个相长.     

拖拉机电液耦合转向试验平台设计与硬件在环试验

针对电液耦合转向方案转向特性尚不明晰、转向数据采集和记录困难等问题，提出一种硬件在环拖拉机电液耦合转向试验平台设计方案。平台参数设计过程主要考虑功率损耗，为了满足电液耦合转向系统的性能要求，进行精度设计与量程设计。通过总体参数设计，得到电动助力、液压助力和阻力加载系统的参数计算模型，并基于AMESim建立电液耦合转向系统的控制与机械模型仿真进行了参数优化。通过基于dSPACE以及PXI的硬件在环控制方案，进行了各类转向工况试验验证，验证结果表明：阻力加载模拟系统能根据不同的地面条件、行驶工况等参数实现动态加载，响应速度和控制精度均能实现田间阻力模拟要求；电液助力转向系统能够产生较好的平滑助力，具有良好的转向路感；控制系统能与各传感器硬件协同配合，使拖拉机电液耦合转向试验平台具有良好的响应特性，能够真实还原拖拉机转向过程。