叶片残留法测定植物提取物对绣线菊蚜的触杀作用

[目的]研究5种植物提取物对绣线菊蚜生物活性的影响。[方法]采用浸渍法,以95%乙醇为溶剂,对竹柏、小花八角、单瓣狗牙花、灯台树、辣蓼5种植物进行提取。将5种植物提取物分别稀释成1、5、10倍液,在室内用叶片残留法对绣线菊蚜进行触杀测定。[结果]5种植物的触杀效果为灯台树〉小花八角〉辣蓼〉竹柏〉单瓣狗牙花。不同浓度的5种植物提取物对绣线菊蚜的校正死亡率均无显著差异,竹柏、小花八角和辣蓼3种提取物的不同触杀时间的校正死亡率差异显著,单瓣狗牙花提取物不同触杀时间的校正死亡率差异极显著,灯台树提取物在不同触杀时间的校正死亡率无显著差异。[结论]5种植物提取物对绣线菊蚜的触杀效果相当。     

角度尺寸链求解新方法——回旋法

在机床设计中经常遇到角度尺寸链,角度尺寸链求解的核心是确定角度尺寸链组成环的性质即判别增、减环.判别角度尺寸链组成环的性质的方法目前有直观法、公共角顶法、角度转化法.这些方法都不同程度的存在繁琐、不易理解等问题.通过对常遇到的两例角度尺寸链的分析验证,提出了更为简单实用的角度尺寸链求解新方法--回旋法.方法简便,使角度尺寸链的解算问题既简化、又便于理解接受.     

缺氮和缺铁对平邑甜茶幼苗根系构型的影响

 研究水培条件下缺氮、缺铁对平邑甜茶幼苗根系总长度、表面积、体积、根尖数、分枝角度、分形维数等根系构型参数的影响。结果表明：缺氮或缺铁处理后，幼苗细根比例增大，根系直径变小；一级侧根与主根的夹角整体上增大，大夹角植株数量普遍增多，根系趋向于水平分布；根系分形维数降低。其中缺氮使幼苗根系总长度、根系总表面积、根系总体积以及二级侧根数显著增加，但根系活力显著下降；缺铁使根尖数和主根的长度显著增加，根系活力和根系总表面积均下降；缺铁比缺氮时根系分形维数下降更多。     

Tensile strength of softwood butt end joints. Part 1: Effect of grain angle on adhesive bond strength

Abstract

To study the effect of grain angle on the adhesive bond strength in wood, three-part Norway spruce wood specimens were bonded and tested in tension. The two axially orientated outer parts of the specimens were joined with the middle part by means of three adhesives typically used for load-bearing constructions, i.e. one-component polyurethane (PUR), melamine–urea–formaldehyde (MUF) and phenol–resorcinol–formaldehyde (PRF). The grain angle of the middle part was varied from 0° (end grain to end grain) to 90° (flat grain to end grain) in incremental steps of 10°. In general, PRF- and MUF-bonded samples exhibited highest tensile strength at end grain to end grain orientation of the three parts, while specimens bonded with PUR showed only 25% of the strength measured for PRF and MUF, respectively. At high grain angles (90°) all specimens showed similar strength values in the range of 30% of maximum strength of MUF- and PRF-bonded specimens. To explain the changing strength levels at different grain angle a composite failure criterion was applied.     

缠绕于一般曲面体上张紧力的有限元计算

欧拉创立了著名的欧拉公式,在实际中得到广泛的应用.文章据此介绍一种缠绕于一般曲面体上的广义欧拉公式,运用ANSYA WORKBENCH对其进行有限元分析计算,对分析计算的结果和公式计算所得的结果进行比较,最后得出结论.结果表明两种计算的结果有一定的相符性,缠绕于一般曲面体上的广义欧拉公式具有一定的实用意义.     

基于双向极角的植物叶凸包生成算法

为了描述和提取植物叶的形状特征,需要生成植物叶的凸包.首先,通过图像分割,获得植物叶原始图像的二值图像;其次,利用轮廓跟踪算法,获得植物叶轮廓的简单多边形;最后,利用基于双向极角的卷包裹法,生成植物叶的凸包.该算法计算复杂度为O(Nh).试验表明,算法满足图像旋转不变性要求,适用于多种不同形状的植物叶.     

Effects of contact angle on fingered flow during non-ponding infiltration into dry sand layers

Abstract

Gravity-driven fingered flow may readily occur in dry sand layers with small capillary force at the same order of magnitude as gravitational force. Capillary force is related to the contact angle. The present study examined the effects of contact angle on fingered flow development, finger size and fingertip velocity during non-ponding infiltration into dry sand layers. For contact angles of 48–87°, an induction zone always formed in the sand layer, and only one finger developed from the induction zone. Fingertip width reached a minimum value when the contact angle was approximately 70°, and the width and velocity of fingertips were negatively correlated. This finding suggests that a contact angle of approximately 70° has a physical significance for fingered flow to determine fingertip velocity and width. In addition, when the contact angle was 91°, the supplied water did not spontaneously penetrate the sand surface; instead, water drops built up on the surface and two fingers directly formed from the surface. This indicates that 90° is indeed the critical contact angle for water repellency and affects fingered flow development during non-ponding infiltration.     

Corewood in South African pine: necessity and opportunities for improvement

South Africa has made excellent progress in breeding plantation trees fulfilling the primary demands of improved volume growth, stem and branching characteristics, tolerance to pests and diseases, and general adaptability. This has had marked positive impacts on wood quality, as straight stems normally contain no or very little reaction wood, while problems associated with pith eccentricity and wandering pith are kept to a minimum. The breeding of trees with small, well-distributed branches, forming large angles with the vertical axis of the tree stem, reduced performance problems associated with knots and knot-associated features. However, tree breeding and intensive silviculture are causing the average corewood diameter to increase, creating a wood resource that is increasing in variability, especially when combined with earlier harvesting. Reducing the size and improving the properties of the corewood zone have therefore become of utmost importance to ensure that the South African pine timber resource continues to meet quality demands related to strength, stiffness and stability. Breeding programmes to date have created sound bases for further wood quality improvement of the various pine species, especially of the corewood zone. Opportunities for success are excellent as large variation in corewood properties still exists within the current breeding populations, combined with operationally important wood properties, such as wood density, microfibril angle, spiral grain and transitional age, all being under moderate to strong genetic control. Corewood properties seem to be inherited largely independently of tree and growth characteristics, making it possible to combine improvement in these characteristics with desirable wood properties. This paper discusses results from several young field trials, which have shown marked family, species and site differences in wood stiffness. This suggests that there is good opportunity to increase the dynamic modulus of elasticity of corewood by early selection and breeding, using highly reliable non-destructive acoustic technology. The results also proved that vegetative propagation through cuttings has no detrimental effect on corewood stiffness. The latter may even increase with increasing physiological age of the cutting.     

提高科技木锯材出材率的实用技术

随着技术的不断创新,利用普通木材甚至低质速生材生产各种仿天然珍贵木材颜色和纹理的科技木得到越来越广泛的应用。但是,科技木锯材出材率低是目前国内科技木生产厂家所面临的突出问题,严重制约行业发展。采用3种研究方案,即两端头锯截表面刨切后再胶合模压(A)、两端头中间夹多层单板后再胶合模压(B)和两端头直接胶合模压(C),对科技木一次锯材得到的三角形截锯端头进行再利用,以提高科技木锯材出材率。结果表明,依照3种方案制备的试样其MOR、MOE、浸渍剥离性能均高于LYT 1655—2006重组装饰材要求,同时将科技木锯材出材率提高17%左右。综合考虑试样的力学性能、出材率及经济性,A方案和C方案优于B方案。通过表面粗糙度和接触角实验,对上述结果进行了验证。     

采用H2O2溶液对落叶松表面进行活化处理的研究

为提高用水性高分子异氰酸酯胶粘剂(API)胶接的落叶松木材的胶接性能,采用H2O2溶液对落叶松表面进行活化处理.试验结果表明采用H2O2溶液处理落叶松木材表面可以提高其胶接强度,用H2O2溶液处理过的落叶松表面比未处理过的落叶松素材的常态压缩剪切强度提高15%.文中还讨论了采用H2O2溶液对落叶松表面进行活化处理可以提高其胶接强度的主要机理.通过傅立叶红外吸收光谱(FTIR)证明用H2O2溶液处理落叶松木材表面可以提高其常态压缩剪切强度的机理主要是氧化作用,即用H2O2溶液处理落叶松木材表面后,其表面或获得活性基团羰基.通过对其表面接触角的测定可以看出,H2O2溶液处理过的落叶松表面润湿性增加,这对胶接有利.