Individual feeding specialisation of a naïve vs. veteran predators

Abstract – We explored the incidence of individual feeding specialisation among a naïve predator (non‐native rainbow trout postsmolts) and two native experienced predators (sea‐run Arctic charr and sea‐trout) in a subarctic Norwegian fjord. Interindividual foraging niche stability was obtained by combining information on stomach contents (recent dietary niche) with trophically transmitted parasite infestation (time‐integrated historical dietary niche) of individual predators. Individual fish showed a high degree of resource specialisation as prey items such as gammarids and small fish (both potential intermediate host of parasites) rarely co‐occurred in stomachs. In both naïve and veteran predators, positive associations between the intensity of a specific parasite species and the occurrence of their respective intermediate host (gammarids or fish) in the stomachs of individual predators demonstrated temporally interindividual feeding specialisations. Several behavioural phenotypes clearly co‐existed in both naïve and veteran predator populations, including gammaridivore (benthic feeders), piscivore (pelagic feeders) or insectivore (pleuston feeders) individuals. The likely mechanism of this observed interindividual resource specialisation in the non‐native naïve predators involves a behavioural component of which rapid learning seems to be a key factor.     

Yield Stability Parameters of Barley under Finnish Conditions

Abstract

The objective of this study was to evaluate whether it is possible to obtain reliable estimates of yield stability of barley on the basis of single year trials. The stability was analysed by using some of the most common stability parameters. The other objective was to study the influence of variation between locations and years on the yield stability of barley under growing conditions in Finland. Barley breeder's trials of the Agricultural Research Centre of Finland from the years 1987-89 were used as material in this study. In each of these years six trials from different parts of Finland and six genotypes were analysed. Four parameters were used in analysis of yield stability: b _i (Finlay & Wilkinson, 1963), s ² d _i (Eberhart & Russell, 1966), r ² _i (Pinthus, 1973) and environmental variance s ² _i. Each parameter was calculated from single- and multi-year results. The multi-year results were considered as reliable data with which to estimate yield stability. The reliability of the stability parameters was tested by Spearman's rank correlation coefficient between single- and multi-year stability values of each parameter. Although the variation between years was highly significant, there was no interaction between genotypes and years. In two experimental years genotype × location interaction was highly significant, and on the basis of this study, the genotype × location interaction seems to be a more important factor than genotype × year interaction in barley breeding for Finnish conditions. However, a series of three years may not be sufficient for indicating genotypes × years interactions. In this study two stability parameters, b _i and s ² _i, gave a reliable estimate of yield stability on the basis of single-year trials.     

MUF树脂浸注改性橡胶木初步研究

采用水溶性三聚氰胺-尿素-甲醛(MUF)共聚树脂浸注处理人工林橡胶树(Hevea brasiliensis)木材，分析树脂浓度对各项物理力学性能指标的影响。结果表明：MUF树脂对橡胶木有良好的浸注性，随着浸注树脂浓度的升高，木材的增重率逐渐增加4.51%～31.73%；气干密度明显提高3.57%～25.62%；明度指数下降7.39%～11.85%；吸湿率下降12.81%～23.68%，吸水率降低12.73%～29.51%，尺寸稳定性明显改善；抗弯弹性模量增加1.01%～18.15%，抗弯强度提高3.38%     

修正的Hoek-Brown准则在岩质边坡中的应用

通过在特定的应力水平上,利用Roclab软件,将非线性的Hoek-Brown强度包线转化为与之相匹配的Mo-hr-Coulomb强度的等效粘聚力和内摩擦角,然后采用有限差分软件对一均质岩性边坡算例进行分析,并与传统的极限平衡法相比较,结果表明:非线性的Hoek-Brown强度准则能有效地应用于工程岩体的数值模拟。     

固化的脲醛树脂水解稳定性评估方法的研究

通过一种新的已固化脲醛树脂水解稳定性评估方法的建立,研究了在较高温度下,湿度、pH值与已固化脲醛树脂水解稳定性之间的关系。揭示了湿度、pH值对固化的脲醛树脂水解稳定性有较大的影响。同时通过不同评估方法的对比,也验证了新的评估方法的可靠性。     

以纯滞后时间为参变量的根轨迹新性质

文献［1］得到一组以纯滞后时间为参变量的根轨迹性质，但在确定根轨迹穿越虚轴的方向、根轨迹的终止点和根轨迹的渐近线的过程中存在错误。本文提出计算根轨迹出射角和入射角的方法，并对文献［1］中存在的错误进行修正。利用根轨迹的性质，可以确定闭环系统的时滞稳定区间。     

Biological soil crust community types differ in key ecological functions

Soil stability, nitrogen and carbon fixation were assessed for eight biological soil crust community types within a Mojave Desert wilderness site. Cyanolichen crust outperformed all other crusts in multi-functionality whereas incipient crust had the poorest performance. A finely divided classification of biological soil crust communities improves estimation of ecosystem function and strengthens the accuracy of landscape-scale assessments.     

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Abstract

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (D_m) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in D_m of soil aggregate size distribution among tillage treatments, which suggested that D_m could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.     

Shape stability of modified engineering wood product subjected to moisture variation

Abstract

A modified softwood product would enable the utilization of softwood in new areas. Densification is an old modification method to improve wood properties such as hardness and resistance to abrasion. A major problem with densified wood is, however, its ability to retain its original dimensions under the influence of moisture. Therefore, this study investigated the influence of surface to bottom layer thickness ratio on the shape stability of a modified and three-layered cross-laminated engineering wood product (EWP) subjected to moisture variations. The study describes a simple solid wood densification technique based on compressing a clear solid piece of softwood with vertical annual rings in the radial direction by restraining the tangential expansion. Three-layered cross-laminated EWP was manufactured with the densified wood as a surface layer. The recovery of the densified wood in the surface layer was then reduced to movements in the same level as the other two layers of unmodified wood. The EWP was subjected to climatic variations in order to investigate its shape stability. The results disclosed that an appreciable degree of shape stability was obtained by an increase in the surface to bottom layer thickness ratio of the EWP.     

中国信托业的金融逻辑、功能和风险防范

对两寡头厂商2元市场用完全信息动态博弈的方法分析了实施三度价格歧视情形和统一定价情形的均衡产量，均衡价格和均衡总收益，并研究了这两种情形三个指标之间的关系.结果显示，在两个子市场的需求函数为线性需求的条件下，统一定价的市场均衡产量等于歧视定价的市场均衡产量；统一定价的均衡价格是歧视定价时两个子市场均衡价格的加权平均；统一定价的市场均衡总收益小于歧视定价的市场均衡总收益.