Gradients in fracture force and grazing resistance across canopy layers in seven tropical grass species

In reproductive swards, stems can act as a barrier that affects the grazing behaviour of ruminant livestock. The barrier effect of stems is closely associated with both the force required to fracture the stems and the density of these stems (in combination, these make up grazing resistance), and these factors need to be considered when making predictions about the forage intake of ruminants grazing reproductive pastures. Differences in grazing resistance between sward canopy layers of different grass species are thought to affect bite dimensions, but data are scarce. In this study, we assessed the grazing resistance for three canopy layers of seven tropical grass species. Species differed significantly in grazing resistance for every canopy layer, with a general ranking order for grazing resistance, in ascending order: Cenchrus ciliaris (‘American' buffel), Digitaria milanjiana (‘Jarra’ finger grass), Setaria surgens (annual pigeon grass), Setaria sphacelata (‘Narok’ setaria), Dichanthium sericeum (Queensland bluegrass), Chloris gayana (‘Callide’ Rhodes grass). In the top canopy layer, grazing resistance did not appear to create a barrier for any of the species, but in the bottom canopy layer, it did for all species. Species also differed in the relative contribution of fracture force and density to grazing resistance. The results highlight the importance of managing the grazing systems to minimize the barrier effect of the stems, which can be done by controlling the phenological stage of the pasture and the grass species and animal size used in the system.     

剑麻愈伤组织的诱导和再生体系的建立

以剑麻H.11648为材料,研究外植体类型、激素种类及其浓度对剑麻愈伤组织的诱导和植株再生的影响,并且建立剑麻茎尖愈伤组织诱导及高频再生体系.结果表明:MS基本培养基、6-BA/NAA激素组合有利于淡黄绿色愈伤组织的形成,SH基本培养基、6-BA/IBA/NAA激素组合有利于不定芽的分化;最佳愈伤组织诱导和分化培养基分别为MS+3.0 mg/L6-BA+0.2 mg/L NAA,SH+5.0 mg/L 6-BA+0.1 mg/L NAA+0.1 mg/L IBA.在该培养条件下,H.11648麻茎尖愈伤组织的诱导率为86.67％,分化率为(98.33+1.67)％,分化系数为(13.19±0.58).再生植株在不加激素的MS基本培养基上培养4周后的生根率为100％,平均生根数为(5.39±0.70)条,根长为(8.44±0.25)cm,该研究结果为剑麻转基因的研究和种质创新奠定了基础.     

智能监控在干法厌氧发酵中的应用现状及新方法研究

分析国内沼气发酵监控系统的发展现状，提出一种干法厌氧发酵过程智能监控的新方法与控制系统的框架结构。该智能监控系统以 PLC 为下位机，PC机和力控组态软件为上位机，实现对干法厌氧发酵实验研究中需要采集和处理的数据的集中管理和发酵工艺过程的实时监控。该系统具有实时自动采集数据的功能，灵活性高、控制精度高、可移植性强，为优化干法厌氧发酵的工艺过程、提高产气效率提供了一条新的可行途径。     

喀斯特区3种草篱根-土复合体抗剪性能及其影响因素

为探索喀斯特区地埂草篱根-土复合体抗剪性能的差异、变化规律及影响因素，在重庆酉阳喀斯特顺层坡分上、中、下坡位分别布设二月兰、光叶苕子和沿阶草3种草篱，测定复合体抗剪强度、根区土壤基本理化性质和复合体内根系的形态指标和化学成分指标，计算复合体黏聚力和内摩擦角。结果表明：1）在抗剪强度方面，上/中坡复合体抗剪强度表现为沿阶草显著大于二月兰、光叶苕子（P<0.05），下坡三者之间则无显著差异；在不同坡位之间，仅沿阶草复合体抗剪强度存在显著差异，表现为中坡>上坡>下坡（P<0.05）；2）各坡位复合体黏聚力和中坡内摩擦角均为沿阶草、光叶苕子显著大于二月兰（P<0.05）；沿阶草复合体黏聚力、内摩擦角和光叶苕子复合体黏聚力均表现为中坡显著大于上、下坡（P<0.05），二月兰则各坡位间无显著差异；3）相关性分析表明，光叶苕子和沿阶草复合体黏聚力与其根区土壤有机质均呈极显著正相关，相关系数分别为0.91、0.83，二月兰则无显著相关关系；这3种草篱复合体黏聚力与根系形态指标呈显著或极显著正相关，相关系数最高达0.99。综上所述，沿阶草抗剪性能最好，最优坡位为中坡。二月兰、光叶苕子和沿阶草草篱主要通过影响复合体黏聚力来影响其抗剪性能。     

坡质对溲疏和胡枝子根系形态及拉拔力的影响

本研究以松山地区优势乡土灌木溲疏(Deutzia scabra)和胡枝子(Lespedeza bicolor)为研究对象,采用全根系挖掘法、原位拉拔力测定法和Win-RHIZO根系扫描法,对岩石边坡和土石边坡条件下两种植物的根系形态及拉拔力进行研究,为探讨不同坡质条件下植物根系适生策略和固土护坡性能提供理论支持。结果表明:1)岩石边坡下溲疏的根长密度、根重密度和比根长均显著大于土石边坡(P<0.05),岩石边坡下胡枝子的根长密度和比根长均显著小于土石边坡(P<0.05),根重密度无显著差异(P>0.05);2)两种坡质条件下,溲疏基根数量差异显著(P<0.05),土石边坡无基根,岩石边坡下,胡枝子基根直径显著大于土石边坡(P<0.05),但基根数量无显著差异(P>0.05);3)相较于地上部,坡质对根系生物量影响更大,岩石边坡下,两种植物的根系生物量和根冠比显著大于土石边坡(P<0.05);4)坡质对植物根系的拉拔力最大值影响较大,溲疏、胡枝子分别在岩石边坡、土石边坡表现出较强的固土护坡能力。综上所述,坡质对溲疏和胡枝子根系形态结构和力学特性作用明显,根系通过改变空间造型和分布策略适应复杂的地下环境,使自身的生长效率及护坡效益最大化。     

一种新型的车辆稳定性分层控制策略

为了优化稳定性控制算法,提出并仿真分析了一种新型的车辆稳定性分层控制策略。该控制策略由上下两层组成,上层控制器基于最优控制理论的横摆力矩控制策略,下层控制器采用最优分配法,将修正横摆力矩合理分配到各车轮上。基于MATLAB/Simulink建立了八自由度非线性车辆模型,并对该模型进行了实车实验验证,然后基于该模型对该控制策略进行了仿真分析,验证了此分层控制策略的有效性。仿真结果表明,在大侧向加速度和大侧偏角的极限工况下,所设计的新型控制系统能够有效地改善车辆的操纵稳定性。     

高校要当好新时代农业科技推广体系中的"特种兵"

中国特色社会主义进入新时代以来,农业科技创新和应用推广愈发重要,农业科技推广体系中高校的作用日益凸显.文章阐述了我国农业科技推广体系的构成及特点,并分析了高校在该体系中的地位和作用,剖析了高校技术供给的局限性及主要原因,从加强学科建设、将自主创新与产学研相结合、探索和实践高校农技推广模式等方面提出了高校当好农业科技推广体系中的"特种兵"的对策建议.     

Hydrodynamic performance of a semi-submersible offshore fish farm with a single point mooring system in pure waves and current

A physical model of a semi-submersible offshore fish farm with a scale of 1:30 has been tested in a wave-current tank. The mooring force of the fish farm in waves was measured and compared for different single-point mooring arrangements, and henceforth, a safe and reliable mooring form is chosen as the mooring system for the fish farm. On this basis, the tested results for the mooring force, heave, pitch and roll of the fish farm in waves and current are presented, in which the effect of drought was discussed. The performance of blocking water flow for the fish farm in pure current was also evaluated. It has been found that increasing the anchor chain length and adding a sinker suspending from the chain could reduce the mooring force significantly despite the fluctuations in the mooring force. During the experiments, the tested value for the heave and pitch as well as the roll has been small, which indicates that the fish farm has a good stability. The mooring force has become larger, while the heave became smaller as the drought increased. Furthermore, the current velocity inside the fish farm is significantly lower than that of its outside. According to the field test results obtained in the fish farm, the farm exhibited good adaptability and it formed a suitable environment for growing cultured fish.     

基于力传感器重力补偿的机器人柔顺控制研究

基于力觉控制的机器人运动系统能够通过感知外界环境的接触力,实现机器人作业过程中对力和位置的双重控制。为了提高机器人对接触力的感知精度,实现准确的柔顺控制,提出一种基于力传感器重力补偿的机器人柔顺控制方法。首先,通过调整机器人末端姿态,采集机器人不同位姿下力传感器数据,计算机器人底座安装倾角、力传感器零点数据、末端工具重力及重心坐标等参数;然后,利用机器人姿态变换矩阵,实现对力传感器的重力补偿,为机器人柔顺控制提供准确的受力感知;最后,采用导纳控制,实现机器人对物体的抓取搬运。进行了力传感器重力补偿实验及机器人柔顺放置实验,结果表明,该方法能够提高机器人对外界环境感知的精准度,实现精准的机器人柔顺控制。     

含立方刚度滚动轴承转子系统非线性特性分析

建立了滚动轴承-转子系统非线性动力学模型,考虑了不平衡激励、轴承间隙、非线性赫兹接触力、变柔度(VC-VaryingCompliance)振动和转轴材料物理非线性的综合效应,以含立方非线性项的表达式来表征这种转轴材料的物理非线性刚度。运用Range-Kutta数值积分方法计算系统的不平衡振动响应,得到了转轴非线性刚度、轴承间隙和转子转速对系统动力学行为的影响规律。