农村户用沼气慢漏气原因分析及措施

本文对农村户用沼气慢漏气现象进行探讨,对其原因进行分析,并提出解决沼气慢漏气的措施和建议。     

铁磁构件裂纹漏磁场分析及裂纹检测装置

针对铁磁材料构件裂纹损伤检测方法和仪器应用技术现状,建立了基于磁荷理论的V型裂纹漏磁场分析模型,得出了平板铁磁构件表面指定探测点的漏磁场理论表达式.采用MATLAB软件将所推导数学模型绘图,得出了漏磁场的法向分量Hy与裂纹开口宽度的关系曲线、漏磁场的法向分量Hy与裂纹深度的关系曲线、漏磁场的法向分量Hy与裂纹长度的关系曲线;得出裂纹漏磁场法向分量Hy过零点、漏磁场切向分量Hx出现最大值和漏磁场切向分量Hz出现裂纹端部过零点的漏磁场分布特性.根据理论分析得出的裂纹漏磁场特征,设计制作了阵列式的裂纹检测装置和试验平台,并对带有V型裂纹的铁磁构件进行检测.实验表明:理论分析得出的三维漏磁场与检测结果能够较好的吻合,并对分析预测裂纹的几何参数具有一定的参考意义,根据漏磁模型研制的检测装置能探测铁磁构件的裂纹缺陷.     

Late Autumn Frost Resistance of Twelve North European Provenances of Quercus Species

Twelve north European oak provenances [11 Quercus robur L. and one Quercus petraea (Matt.) Liebl] were tested for late autumn frost hardiness using visual methods and measurements of relative conductivity. Tissue from buds and twigs from 2-yr-old seedlings was used. The test was carried out in November and December. Temperatures between ?20 and ?32°C were necessary to cause serious damage to tissue, even when tissues were tested only a few weeks after leaf fall. Visual methods proved to be fast and could be applied in practical test applications. Estimation of twig viability was found to be a more reliable variable than bud assessment, which appears to be sensitive and not necessarily related to plant mortality. Relative conductivity is a more labour-intensive method and requires some technical equipment, but it provided the most consistent statistical results. Strong correlation between the visual methods and relative conductivity was demonstrated. Provenances originating from locations close to the Atlantic ocean (The Netherlands, the UK, Denmark and Norway) tended to be less frost resistant than more continental provenances (from Norway, Sweden, Finland and Poland). Frost tolerance was correlated with budset, but not with growth of the provenances. The results confirm the existence of specific ecotypes and suggest a high potential for adaptation in Q. robur.     

Preplanting indicators of survival and growth of desiccated Abies procera bareroot planting stock

Plant moisture loss during preplanting handling is considered one of the major elements in transplanting shock. The aim of the present study was to evaluate test parameters that may be suitable for assessment of the physiological condition of noble fir (Abies procera Rehd.) planting stock that has been subjected to desiccation stress. The transplanting-sensitive species was subjected to full exposure (roots and shoots) for 0, 0.5, 1.5, 3.0 and 6?h, or partial exposure (shoots) for 0, 3, 10, and 24?h before planting. The effects of desiccation on moisture content (MC), shoot water potential (ψ), root growth potential (RGP), root electrolyte leakage (REL), survival and height growth were evaluated. Desiccation effects on plant parameters and performance were generally significant after 1.5?h of full or 10?h of partial exposure to treatment. REL explained the largest percentage of performance variation in fully exposed plants, followed by MC and ψ. RGP tended to underestimate performance potential. Factors affecting the reliability of the test parameters, e.g. moisture loss rate, root rewetting and site conditions, are discussed.     

Responses of Pinus massoniana and Pinus taeda to freezing in temperate forests in central China

Abstract

Masson pine (Pinus massoniana Lamb.), a native species widely distributed in temperate forests in central China, and Loblolly pine (Pinus taeda L.), an exotic tree species introduced to China from southeastern United States, are dominant evergreen conifers that play a pivotal role in maintaining forest structure and functions for the region. We examined the effects of freezing on these species with chlorophyll fluorescence and electrolyte leakage using both field- and laboratory-based experiments in September 2009 and January 2010, respectively. We found that freezing could cause a greater impact on the Loblolly pine than the Masson pine. Although the two species showed similar values of F _v /F _m and electrolyte leakage before freezing, the Masson pine needles showed lower F _v /F _m and higher electrolyte leakage ratios than those of the Loblolly pine when treated in low temperatures (?15 to 0°C). We also found that cold-acclimation was crucial for both species to adapt to low temperatures with the F _v /F _m ratio decreased approximately by 80% in the first freezing hour for the non-acclimated needles of both species while the cold-acclimated needles showed little changes in the F _v /F _m ratio. This finding is also supported by our measurements of electrolyte leakage. These results suggest that the Loblolly pine could be more susceptible to freezing damages than the Masson pine in central China.     

颗粒体积浓度对半开式叶轮离心泵泄漏涡和磨损的影响

固液两相流条件下半开式叶轮离心泵中颗粒冲击、泄漏涡发展和颗粒轨迹之间存在紧密交互作用,导致过流部件的磨损行为复杂多变。该研究结合双向耦合欧拉-拉格朗日方法和颗粒磨损Finnie模型,对不同颗粒体积浓度下半开式叶轮离心泵固液两相流场进行求解,分析了颗粒体积浓度对泄漏涡结构特征、颗粒运移轨迹和磨损特性的影响,揭示了颗粒体积浓度、叶顶间隙泄漏涡和过流部件表面磨损规律的关联机制。结果表明：随着颗粒体积浓度的增加,颗粒的频繁撞击加剧了叶片压力面进水边和后盖板磨损程度,叶片吸力面出水边的磨损范围向进水边方向延伸;颗粒体积浓度小于1%时,颗粒的轴向运动和叶顶间隙泄漏涡的阻碍作用导致颗粒易与叶片前缘靠近叶根处和吸力面出水边靠近叶顶的区域发生撞击,诱发严重磨损,且呈现点状磨损;当颗粒体积浓度大于3%时,叶轮后盖板的整体磨损强度大于叶片,颗粒体积浓度的增加造成流入叶顶间隙层的颗粒数增加,颗粒对叶顶间隙泄漏涡的冲击导致涡流的破碎、分离、再融合,加剧不稳定流动,泵的扬程和效率均明显下降。该研究可为固液两相半开式叶轮离心泵优化设计和安全稳定运行提供理论参考。     

七叶树与马褂木抗寒性比较分析

[目的]为七叶树、马褂木在北方推广应理论依据和有益参考.[方法]以七叶树、马褂木幼树1年生休眠枝条为材料,测定了不同冷冻处理条件下枝条的相对电导率和K＋相对渗出率,利用Logistic方程计算了各树种的半致死温度（LT50）,并通过苗木生长恢复试验进行了验证.[结果]随着处理温度的下降,七叶树、马褂木枝条的相对电导率和K＋相对渗出率均随处理温度的降低而呈“S”型上升,其枝条的LT50分别为-26.1 ～-27.3℃、-14.6～-15.2℃,与生长恢复试验的结果基本吻合.[结论]马褂木抗寒能力比七叶树低,推广应用时,应适当注意.     

Current experimental models,assessment and dietary modulations of intestinal permeability in broiler chickens

Maintaining and optimising the intestinal barrier (IB) function in poultry has important implications for the health and performance of the birds. As a key aspect of the IB, intestinal permeability (IP) is mainly controlled by complex junctional proteins called tight junction proteins (TJ) that link enterocytes together. The disruption of TJ is associated with increased gut leakage with possible subsequent implications for bacterial translocation, intestinal inflammation, compromised health and performance of the birds. Despite considerable data being available for other species, research on IP in broiler chickens and in general avian species is still an understudied topic. This paper reviews the available literature with a specific focus on IP in broiler chickens with consideration given to practical factors affecting the IP, current assessment methods, markers and nutritional modulation of IP. Several experimental models to induce gut leakage are discussed including pathogens, rye-based diets, feed deprivation and stress-inducing agents such as exogenous glucocorticoids and heat stress. Although various markers including fluorescein isothiocyanate dextran, expression of TJ and bacterial translocation have been widely utilized to study IP, recent studies have identified a number of excreta biomarkers to evaluate intestinal integrity, in particular non-invasive IP. Although the research on various nutrients and feed additives to potentially modulate IP is still at an early stage, the most promising outcomes are anticipated for probiotics, prebiotics, amino acids and those feed ingredients, nutrients and additives with anti-inflammatory properties. Considerable research gaps are identified for the mechanistic mode of action of various nutrients to influence IP under different experimental models. The modulation of IP through various strategies (i.e. nutritional manipulation of diet) may be regarded as a new frontier for disease prevention and improving the health and performance of poultry particularly in an antibiotic-free production system.     

Exogenous application of humic acid and salicylic acid to alleviate seedling drought stress in two corn (Zea mays L.) hybrids

Efficacy of 1?mM humic (HA) and salicylic (SC) acids on SC 260 and SC 705 corn seedlings to alleviate drought stress via polyethylene glycol was studied via hydroponics at Shiraz University, Iran in a factorial, randomized design, with four replicates each. Under stress, SC 260 had higher electrolyte leakage compared to SC 705, and exogenous application of HA combined with SA decreased SC 705 electrolyte leakage. As a general trend, photosynthetic pigment content, relative water content, root and shoot length, mean number and diameter of central and peripheral root metaxylem, and K⁺ accumulation were higher in SC 705 treated with HA and SA compared to SC 260. Application of HA with SA could be an effective and low cost approach to ensure seedling establishment and plant growth in fields affected by soil drought in the early season, especially for the SC 705 corn hybrid in semi-arid regions.