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.     

The impact of land use on the credibility of dispersive clay soils in central and southern Italy

Abstract. Tracts of dispersive Plio-Pleistocene clays in central and southern Italy suffer from severe erosion, which has led to the creation of badlands characterized by 'calanchi'(unvegetated knife-edge ridges) and 'bian-cane'(cone-shaped hummocks). In recent decades, large areas of this eroded land have been reclaimed for arable cultivation by remodelling the landscape with heavy earth moving equipment. This exposes the clay to erosive rainfall. Wet aggregate strength was used to assess those physical and chemical properties that govern the erodibility of the clays. Regression analysis demonstrated that the most significant variables in predicting soil erodibility were the % organic matter and the exchangeable sodium percentage (ESP). Threshold values of 1–2% and 3–4% organic matter were obtained, dependent on the method of pre-wetting. Reclaimed land is on the borderline of these thresholds and therefore at risk of erosion. Nevertheless, the stability of reclaimed land is significantly higher than that of the badland parent material, ascribable to a lower ESP. Careful land management is required to avoid a recurrence of erosion and the reestablishment of badlands.     

Aggregate stability in organically and conventionally farmed soils

A range of factors that influence aggregate stability and soil erodibility were analysed for soils sampled from land managed under contrasting agricultural methods. These included: an organic farm; a conventional farm that incorporated organic fertilizers; a conventional farm that only used inorganic fertilizers; and a non-cultivated control site. The stability of aggregates that compose the bulk soil structure (macroaggregates), and aggregates that were mobilized from the soil by simulated rainfall and surface runoff (microaggregates), were evaluated in terms of the soil fragmentation fractal dimension, organic carbon content and ATP (adenosine 5'-triphosphate; a signature of live biomass) concentration. The results were used to interpret the existing physical condition of the soils, the (microbial) processes that contribute to that physical structure, and how both pedogenic processes and existing soil quality are influenced by agricultural methods. The soils sampled for this study were demonstrated to be multi-fractal in nature: soils with greater bulk density were composed of more stable macro-aggregates, which, in turn, fragmented into larger, more stable micro-aggregates, rendering the entire soil structure less erodible. Soil erodibility and sustainable soil management should therefore be approached at multiple scales. The primary control on both macro- and micro-aggregate stability was determined to be the organic matter input to the soil, as represented by measurements of organic carbon and ATP. Organic content was greatest for the non-cultivated soil, which reflects the degradation of organic reserves in cultivated soils. For cultivated soils, it was not possible to differentiate aggregate stability for soils managed under organic or conventional (i.e. using biological and inorganic fertilizers) farming practices, but aggregates of soils that only received artificial fertilizers consistently exhibited less stability.     

螯合物稳定性的探讨

螯合物的特殊稳定性在许多方面得到广泛应用，但其稳定性的原因未见有关资料详细报道。从原子结构和热力学两方面对其阐述之，澄清了人们对其的模糊认识。     

三种乳化剂对疫苗乳液稳定性的影响

采用正交试验L9(34),对F-188、ELP和TWEEN-80三种乳化剂的复配比例进行了研究.结果表明:F-188∶ELP∶TWEEN-80的比例为1∶3∶3时,疫苗乳液的稳定性最好,黏度较小,乳液颗粒直径皆在0.2μm以下,且粒径均匀.方差分析表明,3种乳化剂对乳液稳定性的影响差异极显著(P<0.01),且ELP、TWEEN-80的乳化效果极显著优于F-188.