用h方程计算饱和非饱和土壤水入渗问题的一种加速收敛方法

阐述了计算土壤水入渗情况下θ方程和ｈ方程的适用条件及其优缺点，讨论了用ｈ方程计算饱和非饱和土壤水入渗时的收敛问题。在计算过程中，当ｈ＜－ｈｐ时，可令ｈ＝０，即认为土壤已经饱和。这种处理方法，既满足计算精度，又加快了收敛速度。论文还通过一个实例说明ｈｐ如何确定。     

Effects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)

Abstract –  Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout ( Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage.     

云南怒江干热河谷区咖啡绿蚧周年发生规律研究

对云南怒江干热河谷区咖啡绿蚧的调查表明:咖啡绿蚧单株虫口数量变化与平均温度的变化呈显著正相关(r=0.6984),为害率的变化与单株虫口数量的变化呈极显著正相关(r=0.7651),繁殖速度与平均温度增量呈显著正相关(r=0.6984),扩散传播速度与繁殖速度呈极显著正相关(r=0.8408),周年变化曲线呈双峰曲线。     

迎面火与主地表火相互作用的实验研究

为了研究地表火卷吸作用的范围和迎面火与主火相互作用的机理 ,在大空间室内实验室进行了实验研究 .在该实验室实验可以避免环境风和环境温度变化的影响 .研究结果表明 :(1)在火头前方有明显的逆风区存在 .在逆风区下部的逆风风速要比上部的大 ,而且当高度达到某一数值时 ,逆风就不明显了 ;(2 )迎面火与主火之间即使相距较远也存在相互作用 .当它们相互接近到一定程度时 ,彼此相互吸引 .这使得火的蔓延速度显著升高 .对于火线火强度为 16 0kW·m-1地表火来说 ,蔓延速度增加2 7% .     

采用固化剂缩短酚醛胶刨花板热压时间的研究

采用添加固化剂的方法，对降低酚醛树脂胶刨花板的热压时间进行了研究。通过筛选试验，选出了加速酚醛胶固化效果比较好的固化剂Ｎ，同时探讨了固化剂Ｎ的用量与酚醛树脂胶聚合时间之间的关系，进而确定了固化剂Ｎ的合适用量。试验结果表明，当固化剂用量为２％时，１６ｍｍ厚的酚醛树脂胶刨花板的热压时间可以从１４ｍｉｎ缩短到１０ｍｉｎ，热压时间缩短了２８．５７％。     

Comparative functional anatomy of hindlimb muscles and bones with reference to aquatic adaptation of the sea otter

Although the sea otter (Enhydra lutris) is a complete aquatic species, spending its entire life in the ocean, it has been considered morphologically to be a semi-aquatic animal. This study aimed to clarify the unique hindlimb morphology and functional adaptations of E. lutris in comparison to other Mustelidae species. We compared muscle mass and bone measurements of five Mustelidae species: the sea otter, Eurasian river otter (Lutra lutra), American mink (Neovison vison), Japanese weasel (Mustela itatsi) and Siberian weasel (M. sibirica). In comparison with the other 4 species, E. lutris possessed significantly larger gluteus, popliteus and peroneus muscles, but smaller adductor and ischiopubic muscles. The popliteus muscle may act as a medial rotator of the crus, and the peroneus muscle may act as an abductor of the fifth toe and/or the pronator of the foot. The bundles of the gluteus superficialis muscle of E. lutris were fused with those of the tensor fasciae latae muscle and gluteofemoralis muscles, and they may play a role in femur abduction. These results suggest that E. lutris uses the abducted femur, medially rotated crus, eversion of the ankle and abducted fifth digit or extended interdigital web as a powerful propulsion generator. Therefore, we conclude that E. lutris is a complete aquatic animal, possessing differences in the proportions of the hindlimb muscles compared with those in other semi-aquatic and terrestrial mustelids.     

扰动下铡草机切碎辊负荷控制器设计与试验

为提高铡草机切碎作业的控制性能、作业质量及减小能耗,基于线性预测控制并结合铡草机切碎作业特点建立目标函数,由切碎运动学误差模型推导采样周期以解决控制鲁棒性,切碎动力学模型推导控制时域及预测时域以提高控制响应性,设计了铡草机切碎辊负荷控制器。Simulink仿真表明：经计算和回归优化选出的预测参数组采样周期、预测时域、控制时域为0.8、15、2 s时,其控制精度及鲁棒性最好、作业能力最大、对扰动的响应速度最快、抑制能力最强及能耗(9.27×10⁶ J)最小。现场试验结果表明：该优化预测参数组模型控制器,能够对铡草机切碎负荷有效跟踪控制,产品质量符合标准要求,同时实现了铡草机作业能力的提高,使系统控制响应更迅速,生产效率更高和单位作业能耗(1.382×10⁷ J)更小。该控制器参数模型建立方法为类属饲草作物收获机控制系统的设计提供了参考。     

曲轴摆缸式阀配流水液压马达工作特性研究

为解决盘配流和轴配流低速大扭矩水液压马达配流副存在的磨损和泄漏问题,提出一种新型阀配流结构的低速大扭矩水液压马达,柱塞配流通过配流凸轮控制配流阀的通断实现。研究柱塞运动学规律和马达输出扭矩形成,揭示配流阀推杆位移、阀芯通断、柱塞进回液间的对应关系,分析马达角排量波动随转角、结构设计参数K的变化规律,当结构设计参数K为0.13时,马达输出扭矩波动率为6.59%。在AMESim中建立了配流阀及单柱塞配流过程的仿真模型,分析配流阀的工作特性及单柱塞动态配流性能,工作中配流阀产生最大压降为0.08MPa,进/回液配流阀无高低压串液。为验证阀配流结构在水液压马达中的工作性能,建立阀配流单柱塞试验台,并研究不同工况下的配流工作特性。试验结果表明,配流阀在马达转速0~60r/min、压力0~21MPa的工况下稳定配流,进液阀口压力在柱塞腔进回液转换时存在瞬间小幅压力波动,但对配流过程基本无影响,阀配流结构能够满足曲轴摆缸式马达柱塞的配流需求,为低速大扭矩水液压马达的配流提供了思路。     

带式玉米高速导种装置旋夹纳种机理分析与参数优化

针对玉米在高速(12～16 km/h)播种时籽粒脱离种盘初速度大,与带式导种装置种腔内壁碰撞弹跳,发生碰撞异位,导致籽粒进入种腔精准度低等问题,以具有纳种机构的带式玉米高速导种装置为研究对象,建立籽粒夹取、转运和排放动力学模型,提出在拨指表面添加人字形纹路的改进方法,明确影响纳种稳定性与籽粒进入种腔精准度的主要因素。利用高速摄像与图像目标追踪技术进行单因素对比试验及多因素优化试验。单因素试验结果表明,播种速度较快时,有人字形纹路拨指轮纳种合格指数和种腔间隔变异系数均明显优于无人字形纹路拨指轮。为获得拨指轮改进后的纳种机构最佳性能参数,以轮心距、拨指轮转速及拨指长度为试验因素,以纳种合格指数与种腔间隔变异系数为评价指标,进行三因素五水平二次正交旋转组合试验,采用多目标优化方法,确定当轮心距为36.8 mm,拨指轮转速为584.97 r/min,拨指长度为10.8 mm时,纳种合格指数为98.23%,种腔间隔变异系数为0.24%。对优化结果进行验证试验,验证结果与优化结果基本一致。在相同条件下进行台架对比试验,结果表明,有带式玉米高速导种装置的作业性能远优于不安装带式玉米高速导种装置的作业...