优化水肥与滴头间距组合对日光温室黄瓜生长及产量的影响

为探究水肥耦合+滴头间距对宁夏旱区日光温室春夏茬黄瓜生长、产量、品质和水肥利用率的影响。通过3因素3水平正交试验,利用Logistic方程模拟黄瓜株高变化规律,分析了各时期生长特点;利用极差分析和方差分析,研究了水肥耦合+滴头间距影响主次顺序、显著性及变化趋势,同时结合模糊数学隶属函数法对产量和品质指标进行综合评价,筛选最优组合。结果表明:①不同处理下黄瓜株高“S”形生长过程可分为渐增期、速生期、缓增期3个阶段,可用Logistic方程拟合,且相关系数均高达0.97;②春夏茬日光温室黄瓜在采摘期前3个月产量稳定,分别占总产30.19%、29.22%、28.58%,后1个月急剧下降,占总产12%;③3因素影响产量的顺序为灌水量>施肥浓度>滴头间距,灌水量影响显著,施肥浓度和滴头间距影响不显著,产量最高处理为TR1,达144361 kg/hm²,比最低处理TR9高44.92%。采用模糊隶属函数进行综合评价,TR2表现最好,平均隶属函数值为0.70。确定因素最优水平组合为:灌水量3040.95 m³/hm²、施肥浓度200倍液(740.55 kg/hm²)、滴头间距20 cm,产量为141077.9 kg/hm²。     

行星变速机构换挡变胞与其构态属性自动识别

针对数学表征行星变速机构换挡变胞过程及自动识别各挡位构态属性较难的问题，首先，解析了行星变速机构变胞理论，基于机构转换法定义相对转速意义下行星排构件间运动副约束函数的转换规则，构建以约束函数为元素的行星变速机构构件和关联关系的邻接矩阵；然后，根据换挡逻辑分析了操纵离合器和制动器的换挡变胞过程，基于邻接矩阵分别推导这两种换挡构态演变的变胞方程，建立包含行星排空转和整体回转等特殊构态的判别准则，结合实例分析揭示换挡变胞机理；最后，通过建立相对转速方程和行星变速机构特性参数识别，结合行星变速机构等效拓扑模型的约束条件，提出了基于构态变胞方程的行星变速机构传动比和转矩自动建模和求解方法，实现了行星变速机构各挡位构态属性的自动识别。以某拖拉机行星变速器为例进行了分析，验证了该方法的可行性和有效性。     

花期前后高温对玉米花粉发育及结实率的影响

为明确花期不同梯度高温对玉米开花特性和花粉活力的影响,以热敏感基因型玉米品种‘驻玉309’为试验材料,于花期(吐丝前8d～吐丝后8d)进行不同程度高温(31、34和37℃)处理,测定受精结实率、雄穗性状、开花时间、花粉活力及花粉超显微结构,分析生育期前后的高温对受精结实、开花特性及花粉活力的影响。结果表明,花期高温胁迫显著降低玉米受精结实率,对抽雄吐丝间隔期无显著影响,但盛花期提前;极端高温则导致玉米抽雄期显著提前、开花期和盛花期延后,抽雄吐丝间隔期延长;花期高温使花粉粒形态皱缩、萌发孔内陷,显著降低花粉活力,且温度越高,花粉活力降低幅度越大。因此,花期前后高温通过影响玉米影响雄穗开花特性、延长抽雄吐丝间隔期、影响花粉粒形态、降低花粉活力,从而降低玉米的小花受精率和籽粒结实率。     

夹茎式番茄钵苗取苗机构设计与试验

为避免取苗机构在夹取钵苗过程中对钵体与根系造成损伤，该研究针对夹茎取苗方式，提出一种基于二阶椭圆齿轮行星轮系以及凸轮摆杆机构的夹茎式番茄钵苗取苗机构。依据二阶椭圆齿轮传动特性与机构工作原理，建立机构运动学理论模型，并对凸轮轮廓曲线进行设计，结合番茄钵苗取苗作业要求及机构特点，基于MATLAB软件开发机构分析软件对机构参数进行优化，并进一步分析优化后取苗轨迹与凸轮各工作段的对应位置关系，建立了夹茎式取苗机构虚拟样机模型，利用ADAMS软件对取苗机构运动过程进行仿真分析，验证机构参数优化结果及零部件结构设计的准确性与合理性。试制取苗机构物理样机开展高速摄影试验，通过对比分析实际工作轨迹与理论分析及仿真轨迹的一致性，验证了取苗机构设计的正确性。搭建自动取苗试验台进行取苗试验。试验结果表明，取苗机构工作性能可靠、稳定，取苗频率为80株/min时，取苗成功率为92%，投苗成功率为94.2%，伤苗率为2.9%。研究结果可为番茄钵苗全自动移栽机自动取苗机构的研发提供参考。     

拖拉机变速箱箱体快速设计方法与软件开发

针对目前拖拉机变速箱箱体产品开发周期长、设计与制造成本高的问题，该研究提出了一种基于知识的拖拉机变速箱箱体快速设计方法。首先，研究并建立箱体设计知识库、推理机制及参数化模型；然后，运用Visual Studio 2015的MFC编写快速设计系统的人机交互界面，联合SQL Server2012、Creo4.0完成快速设计系统与知识库、模型库的连接，建立拖拉机动力换挡变速箱箱体快速设计系统，并进行实例验证；最后，运用ANSYS workbench18.1对系统输出模型进行有限元仿真分析，箱体最大等效应力为206.19 MPa，最大变形为0.450 mm，最大间隙变化量为0.007 8 mm，最大错移量为0.026 mm，一阶固有频率为369.48 Hz，与ZF公司相同传动方案产品相比，箱体质量减少了28.8 kg。结果表明：该系统能高效、快速地完成拖拉机变速箱箱体开发，系统设计的拖拉机变速箱箱体具有良好的强度、刚度、密封性与动态特性，产品质量更轻，这对于缩短产品开发周期、降低设计与制造成本具有重要意义。     

基于直流电机与全液压转向器直联的自动转向系统研究

针对农机装备电控液压自动转向系统生产成本高及电动方向盘自动转向系统中控制力矩小、存在自由行程的问题,设计了基于直流电机与全液压转向器直联的自动转向机构及其电控系统,该系统主要包括自动转向执行机构、自动转向控制器和液压转向机构等。自动转向执行机构与原车液压转向机构连接实现自动转向功能,考虑了底盘阿克曼角的自动转向控制器实现车轮转向的精确控制,通过在转向驱动电机输出轴安装电磁离合器和转向柱扭矩传感器实现人工驾驶模式和自动驾驶模式的自动切换。试验结果表明,车轮转角响应平均稳态误差小于0.1°,最大稳态误差为0.158°,±20°阶跃信号最快响应时间达1.2 s,超调量小于1%,可以满足对各种轮式农机的自动导航辅助驾驶转向系统性能的要求。     

The effect of random and density‐dependent variation in sampling efficiency on variance of abundance estimates from fishery surveys

Abundance indices (AIs) provide information on population abundance and trends over time, while AI variance (AIV) provides information on reliability or quality of the AI. AIV is an important output from surveys and is commonly used in formal assessments of survey quality, in survey comparison studies, and in stock assessments. However, uncertainty in AIV estimates is poorly understood and studies on the precision and bias in survey AIV estimates are lacking. Typically, AIV estimates are “design based” and are derived from sampling theory under some aspect of randomized samples. Inference on population density in these cases can be confounded by unaccounted process errors such as those due to variable sampling efficiency (q). Here, we simulated fish distribution and surveys to assess the effect of q and variance in q on design‐based estimates of AIV. Simulation results show that the bias and precision of AIV depend on the mean q and variance in q. We conclude that to fully evaluate the reliability of AI, both observation error and variability in q must be accounted for when estimating AIV. A decrease in mean q and an increase in the variance in q results in increased bias and decreased precision in survey AIV estimates. These effects are likely small in surveys with mean q ≥ 1. However, for surveys where q ≤ 0.5, these effects can be large. Regardless of the survey type, AIV estimates can be improved with knowledge of q and variance in q.     

A Cross-Sectional Survey of Foaling-Related Parameters of Jennies (Equus asinus) Under Smallholder Farm Conditions in Northeast China

It is important to assess the reproductive efficiency and improve the reproductive management to promote the donkey population development. The overall foaling-related parameters of jennies under smallholder farm conditions in China were hardly under investigation. A cross-sectional survey of randomly selected 694 smallholder farms was conducted in 40 villages in the north, east, and south areas of Western Liaoning Province and Eastern Inner Mongolia Autonomous Region between March and July, 2017. Foaling-related parameters were assessed such as the mean age at first foaling, foaling rate and foaling interval during 2014–2017. Only two-thirds of the adult jennies foaled during the 3-year survey period and delivered a foal every 1.9 years. The mean age at first foaling was 45.3 months. The lowest incidence of foaling rate was in coincidence with the peak of foaling. The overall mean values for the foaling rate and foaling interval were 75% and 500.5 days, respectively. Significant changes of foaling rates before the age of 15 years and foaling intervals in the first 8 parities were not observed. The results indicate that the jennies could maintain relatively fine foaling-related parameters under smallholder farm conditions in northeast of China. However, the foaling rates hardly remained high during the whole breeding season represented a major loss to the donkey breeding.     

16份玉米自交系全生育期抗旱性鉴定与评价

以16份玉米自交系为试验材料,通过比较其在全生育期水分胁迫和正常灌溉条件下农艺性状、产量性状和光合特性的差异,以抗旱系数为基本评价指标,采用逐步回归法建立最优回归方程,同时结合相关性分析、隶属度及聚类分析方法,对玉米自交系进行抗旱性鉴定及抗旱指标筛选。结果表明：水分条件对散粉吐丝间隔期、株高、穗长等11个性状具有显著/极显著影响,单穗粒重、散粉吐丝间隔期和穗长可作为玉米自交系抗旱性鉴定的次级性状筛选指标。利用次级性状抗旱系数的平均隶属度和旱情发生时期抗旱系数的平均隶属度两种方法对自交系抗旱性进行综合评价,结果完全一致的有11份;通过聚类分析,将16份玉米自交系分成4类,其中强抗旱型5份、抗旱型6份、中抗旱型4份、弱抗旱型1份。参试材料中,抗旱性最强的自交系为Si-287,最弱的自交系为X178。