A comparison of two methods to predict the landscape-scale variation of crop yield

Landscape-scale variation is a source of information that increasingly is being taken into consideration in agricultural and environmental studies. Models that encompass and interpret this variation in fields and across contrasting management practices have the potential to improve the landscape management of agroecosystems. Our objective was to compare the results of two approaches, analysis of covariance (ANCOVA) and state-space modeling, to determine the factors affecting grain yield in three crop rotations [pea (Pisum sativum L.)–wheat (Triticum aestivum L.)–barley (Hordeum vulgare L.), canola (Brassica napus L.)–wheat–barley, and wheat–wheat–barley] at two sites in Saskatchewan, Canada. Crop rotations were established in adjacent 30 m×80 m plots arranged in a randomized complete block with five replicates. Variables that were expected to affect resource availability and pest infestations in wheat (second rotation phase) or barley (third rotation phase) were measured. Each sampling point was classified according to landscape position as either a shoulder or footslope. Landscape position was considered as a cross-classified treatment along with crop rotation, and analyzed using ANCOVA procedures. State-space modeling was conducted on a single transect connecting sampling points across all of the rotations and replicates at each site. ANCOVA frequently indicated that grain yield and other measured variables differed between landscape position across all rotations, or in a specific crop rotation. For example, grain yield, soil water content, soil N availability during the growing season, and the incidence of common root rot were higher in the footslopes than the shoulders in all of the crop rotations at one of the sites. However, the landscape position effect for grain yield was never fully explained by the landscape position effects detected for the other variables (e.g., higher soil water content in the footslopes did not correspond with higher grain yields in footslope positions at both sites). State-space modeling indicated that most of the measured variables contributed to the prediction of landscape-scale variation for grain yield in the pea–wheat rotation; whereas only leaf and root disease incidences explained landscape-scale variation in the wheat–wheat rotation. The selective omission of data indicated that state-space modeling was accounting for the varied importance of the predictors across the landscape; i.e., localized response functions. The major reason that ANCOVA did not explain landscape-scale variation of grain yield across the different crop rotations may be because it was unable to account for highly localized variation. However, there is evidence from other studies that the ANCOVA approach is appropriate when the response functions explaining grain yield do not vary significantly within the study area. This situation is most likely to occur in studies with smaller experimental areas. Future research conducted at scales reflecting ‘real world’ field conditions (i.e., study units representative of producer’s fields) should consider the use of state-space modeling or alternative statistical techniques that are designed to address and predict the complex and dynamic nature of landscape-scale processes.     

磁力泵冷却循环回路的设计及数值模拟

为避免磁力泵温升过高导致永磁体退磁及隔离套损坏,该文对磁力泵冷却循环回路的设计方法进行了探讨,采用ANSYS-APDL软件计算出了隔离套的涡流发热,根据热平衡确定冷却循环流量并设计了冷却循环回路。基于SIMPLEC算法和标准k-ε湍流模型,通过求解三维N-S方程及能量方程,对冷却循环回路内部流场及温度场进行了数值分析。从数值模拟可以看出,冷却循环回路内部流动为圆周运动和直线运动合成的螺旋运动。对比内循环、外循环2种方式表明,内循环方式隔离套底部温升最高、压力较低;外循环方式温度场分布较均匀,最高温升小于10 K,满足设计要求。在冷却循环流量相同的情况下,轴孔孔径在设计尺寸一定范围内波动对外循环方式的冷却效果影响不大,轴孔分别为3、4、5 mm,其最高温升分别为9.2、9.3、9.4 K并且分布基本相同。通过分析不同转速下冷却循环回路的流场、温度场,发现当内磁转子不转动时,流场最高温度达到了386 K,而随着转速的增加最高温度逐步降低,表明增加泵的转速能够促进不同流体层间的热量交换,改善冷却循环回路的冷却效果。该研究可为磁力泵冷却循环回路的设计提供参考。     

基于大涡模拟的轴流泵叶顶泄漏涡瞬态特性分析

为了深入掌握轴流泵叶顶区湍流特性,采用大涡模拟方法对某一模型轴流泵内部非定常流动进行了数值模拟。根据时域和频域特性图,分析间隙内压差和泄漏速度之间的关联现象,讨论了叶顶间隙内泄漏流的瞬态特性。根据三维泄漏涡结构,揭示了轴流泵叶顶区不同类型的涡系,叶顶泄漏涡带在剪切层内涡丝动力的驱动下逐渐变长,然后与射流剪切层分离;叶顶间隙内涡团的瞬态变化大于叶顶泄漏涡的周期性变化,导致剪切层内的小尺度涡的生成周期时间较短,其在主泄漏涡带上方形成了小尺度泄漏流涡带。从叶顶轴平面的涡结构可发现,随着弦长系数的增大,剪切层内的分离涡不断被分离并且被叶顶泄漏涡卷吸,在主泄漏涡向相邻叶片压力面的运动过程中,其涡量不断减小,并且在转轮室端壁面附近不断诱导各种尺度的涡产生。     

Direct and maternal genetic effects for preweaning growth in Retinta cattle estimated by a longitudinal approach throughout the calving trajectory of the cow

The direct and maternal genetic effects were estimated for the preweaning growth of Retinta calves with a multitrait model across parities, using a longitudinal approach with random regression models (RRM). The 120 (P120) and 180 days (P180) weights (5972 calves) were considered as different traits in each calving. The heritability of direct effect across parities was on average 0.37 for P120 and 0.58 for P180, slightly higher than the estimates by univariate (0.30 and 0.56) and bivariate models (0.30 and 0.51, respectively). The heritability for maternal effects was 0.16 for P120 and 0.26 for P180 and very similar by uni‐ (0.16 and 0.23) and multivariate model (0.16 and 0.22, respectively). The correlation between direct and maternal effects by RRM showed a pronounced antagonism ?0.64 for P120 and ?0.78 for P180), likewise uni‐ (?0.62 and ?0.72) and multivariate case (?0.64 and ?0.74, respectively). The preweaning weights should be considered as different traits across parities, because the genetic correlations were different from unity. The RRM also allowed us to estimate all the parameters throughout the calving trajectory of the cow. The use of multiple traits RRM across parities can provide very useful information for the breeding programmes.     

桥梁用TMD的基本要求与电涡流TMD

总结了传统调谐质量阻尼器(TMD)在涡激振动控制中的工作性能,提出运用多重调谐质量阻尼器(MTMD)理论进行TMD设计,提高振动控制的鲁棒性;开发了电涡流阻尼器取代传统油阻尼器作为TMD的阻尼发生装置,延长TMD的疲劳寿命.利用遗传算法实现了MTMD的参数优化设计,与TMD的比较表明,MTMD在控制效率和鲁棒性方面具有更优越的综合性能.电涡流TMD在试验和实际工程中的成功应用表明电涡流TMD在桥梁振动控制领域具有广阔的应用前景.     

Visual Scorings of Drought Stress Intensity as Covariates for Improved Variety Trial Analysis

Abiotic stress can enhance the heterogeneity of fields, which leads to imprecise estimates of genotypic effects in variety trials. Our study is based on multilocation field trials of triticale (×Triticosecale Wittm.). Two of the six locations were affected by drought stress and showed increased field heterogeneity. At Willstätt, drought stress intensity was visually scored twice, and at Issoudun, overall impression of a plot was scored once. We investigated if the visual scorings can be used as covariates in an analysis of covariance (ancova ) to eliminate the influence of different drought stress intensity on plot yields. For evaluation of the ancova models, we examined if the covariates were independent from the genotypic effects and linearly associated with grain yield. In addition, ancova models were compared with baseline and spatial models based on AIC and phenotypic correlation between genotype means estimated with the model under investigation in a drought stress location with genotype means calculated across the remaining locations. We found that both scorings in Willstätt fulfilled the requirements of an ancova and led to an increase in broad‐sense heritability (h²) and efficiency. ancova with the second scoring increased h² from 0.03 for the baseline model to 0.60, whereas the best spatial model increased h² only up to 0.50. The scoring at Issoudun was not independent from the genotypic effects and reduced phenotypic correlations. We concluded that environmental factors causing spatially differing yield potential can be scored or measured and used as covariates to obtain more precise genotypic estimates.     

旋流自吸泵突台结构数值模拟及对性能的影响

基于大涡模拟方法,设定适当的边界条件,利用三维非结构四面体网格进行网格划分,采用有限体积法对控制方程进行离散,应用CFD软件Fluent对旋流自吸泵的内部三维湍流流场进行数值计算,得到泵内部流场的分布情况以及突台附近区域的流动情况.为了研究突台结构对性能的影响,对应不同突台结构,分别计算了不同工况下的流动情况,预测旋流自吸泵的宏观性能并绘制了性能曲线.通过对数值模拟结果的分析和对比,在获得旋流自吸泵宏观性能曲线的基础上,分析突台附近区域的内部微观流场与宏观外部特性之间的关系.结果表明,突台结构对扬程、效率影响较大,而对于功率影响较小.基于CFD辅助设计,通过对突台尺寸参数不同方案的性能的对比分析,获得突台尺寸参数的最佳值,从而为泵的改进设计提供参考.     

Impact of water scarcity on spruce and beech forests

One of the greatest threats posed by ongoing climate change may be regarded the drought caused by changes in precipitation distribution. The aim of presented study was to characterize reactions to dry conditions and conditions without drought stress on gross primary production (GPP) and net ecosystem production (NEP) of spruce and beech forests, as these two species dominate within the European continent. Daily courses of GPP and NEP of these two species were evaluated in relation to an expected decrease in CO2 uptake during dry days. The occurrence of CO2 uptake hysteresis in daily production was also investigated. Our study was performed at Bily Kriz(spruce) and Stitna(beech) mountain forest sites during 2010–2012 period. We applied eddy covariance technique for the estimation of carbon fluxes, vapor pressure deficit and precipitation characteristics together with the SoilClim model for the determination of drought conditions, and the inverse of the Penman–Monteith equation to compute canopy conductance. Significant differences were found in response to reduced water supply for both species. Spruce reacts by closing its stomata before noon and maintaining a reduced photosynthetic activity for the rest of the day, while beech keeps its stomata open as long as possible and slightly reduces photosynthetic activity evenly throughout the entire day. In the spruce forest, we found substantial hysteresis in the light response curve of GPP. In the beech forest, the shape of this curve was different: evening values exceeded morning values.     

风作用甘蔗的动力学仿真模型

针对目前台风作用甘蔗动力学仿真研究中,风作用甘蔗的动力学仿真研究匮乏的问题,对甘蔗进行简化研究,利用测定的几何参数和CREO三维软件建立甘蔗几何模型,测定甘蔗物理力学特性参数,并建立了甘蔗材料模型。同时,建立了流场几何模型和材料模型,采用Hyper Mesh和LS-PrePost软件分别对甘蔗和流场模型进行网格划分,并定义边界条件和流固耦合控制参数;最后,利用LS-DYNA不可压缩流ICFD求解器和强耦合计算方法,考虑大涡模拟湍流模型,实现风与甘蔗的双向流固耦合作用,并对仿真模型精度进行物理验证。结果表明:该仿真模型的构建方法合理,可用于模拟风作用甘蔗的动力学过程,为台风-甘蔗和自然风-作物流固耦合系统动力学仿真建模提供依据。