论影响麻花钻切削因素之间的关系

学生搞不清楚麻花钻刃磨时几何角度之间的关系,导致麻花钻头的刃磨失败,最终使学生形成了麻花钻内容太难,麻花钻刃磨起来太麻烦的结论。用图示、口诀配合文字讲解的方式讲解标准麻花钻切削部分之间的关系,学生易于接受。     

Basic handling characteristics of wood fuels: Angle of repose,friction against surfaces and tendency to bridge for different assortments

Basic handling characteristics were measured for sawdust, fuel pellets, fuel chips, hog fuel and chunkwood. The aim was to find relations between the basic handling characteristics and easily measurable fuel properties to facilitate the design of feeding systems in heating plants. The angle of repose was 25–55° and increased with the increasing ratio of particle length to thickness and with the increasing content of hooked or long particles. The angle of static friction, 10–40°, was affected more by the kind of surface than the fuel and followed the ascending order: coated plywood, urethane rubber, particle board, stainless steel, concrete and rubber belt conveyor. The tendency to bridge varied considerably and increased with greater content of hooked or long particles, a deeper fuel bed depth over the opening and a higher moisture content. The results indicate that more attention should be paid to the particle shape.     

木材表面非极性化原理的研究 Ⅱ.木材与苯乙烯接枝共聚过程中化学官能团和表面极性的变化

通过对杉木、杨木木材及其主要成分在与苯乙烯接枝共聚反应过程中化学官能团及临界表面张力变化的研究,探讨了木材各化学组成在接枝共聚过程中的反应性能和对木材表面极性的影响。研究表明:木材可与苯乙烯发生接枝共聚反应,反应只在木素和苯乙烯之间进行。木材与苯乙烯接枝共聚可降低木材临界表面张力,即降低木材表面自由能,从而有效地改善木材的极性。     

全射流喷头转折角喷管运动力学分析与试

为了扩大全射流喷头压力适用范围,提出在喷管处加转折角增加喷头固有驱动力矩.转折角喷管的重要结构因素包括转折角角度和转折角力臂长度,理论分析推导出全射流喷头步进旋转时所受总驱动力矩和旋转角方程.对不同转折角角度或转折角力臂组成的7种不同喷管进行了试验,测量性能指标包括步进角度、步进频率、射程和均匀系数.结果表明:试验值与理论分析具有较好的一致性;工作压力影响射程、均匀系数和步进频率,对步进角度影响不大;随转折角角度的增大,步进角度、均匀系数增大,步进频率减小,射程变化不大;随转折角力臂的加长,步进角度增大,射程减小,步进频率和均匀系数变化不大.     

Influence of growth ring angle,adhesive system and viscosity on the shear strength of adhesive bonds

Abstract

To investigate the influence of growth ring angle, adhesive system and viscosity on the bonding properties of adhesive bonds, shear tension tests according to DIN EN 302-1 (2004) were conducted using one-component moisture-curing polyurethane, polyvinylacetate and urea-formaldehyde. Significant differences between the systems could be detected, which were reflected in the predominant failure behaviour for each system. Specimens showing wood failure were influenced mainly by the wood factors, whereas samples which had failed in the adhesive part of the bond differed only in the adhesive properties. The growth ring angle showed the same tendencies as it does in plain wood. Therefore, to gain more information on the adhesive performance in the bond, a loading along the LT plane seems more appropriate for beech wood used in DIN EN 302-1 (2004).     

Testing Polarization Measurements with Adjusted View Zenith Angles in Varying Illumination Conditions for Detecting Leaf Orientation of Wheat Canopy

Abstract:

The previous work revealed that the polarization of light reflected from heading wheat canopies allowed the detection of changes in the canopy structure, i.e., the leaf inclination angle. Accordingly, in order to improve measurement accuracy in this study we examined the effects of the solar zenith angle (= 90º–solar elevation) and weather conditions at the time of polarization measurements for the light reflected from wheat canopies that were fertilized by different means. We measured polarization in the 660 nm spectral band from the heading canopies of wheat, which were grown in plots fertilized with a basal dressing and then top-dressed at the jointing and booting stages. The radiometric measurements were carried out at various solar zenith angles: 22º–41º on two proximal days, one overcast and the other clear. An empirical method for the adjustment of view zenith angle, based on the solar position at the time of measurement, was effective for the measurement of the degree of polarization (i.e., ratio of the polarized part of reflected light to the total reflected light energy) to eliminate interference due to the change in solar zenith angle. Although the mean values of polarization degree measured in overcast conditions were significantly lower than those measured under clear conditions, the plots top-dressed at the jointing stage could be detected via the polarized reflected light measured under both conditions of illumination.     

大型烟囱垂直度偏差的测量方法

大型烟囱一般是工业厂区的高耸建筑，经过几十年的使用，需要重新鉴定其结构可靠性，烟囱的垂直度，是一个很重要的安全指标。由于烟囱为圆形截面，不能直接测量，而且工业厂区内建筑较多，通视条件较差，给测量带来很多困难。通过测量烟囱上下两个标高处的外轮廓水平角度，换算出上下标高处的相对水平偏移角，再用角度交汇方法求出最终偏移值，经过精度分析，完全满足工程精度要求。本文以上海某大型烟囱为例，提出了对已有烟囱垂直度偏差的检测方法，以用于大型服役烟囱的监测。     

DETERMINATION OF T1 RELAXATION TIME OF NORMAL EQUINE TENDONS USING MAGIC ANGLE MAGNETIC RESONANCE IMAGING

Seven isolated equine front limbs were used to establish the normal T1 relaxation time of equine superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and suspensory ligament (SL) using magic angle magnetic resonance (MR) imaging. MR imaging of the metacarpi was performed with the limbs positioned at 55° (the magic angle) relative to the main magnetic field. Transverse spin‐echo proton density and inversion recovery images were acquired. T1 relaxation time was calculated based on ratios of signal intensity determined from the different pulse sequences. T1 relaxation times for SDFT, DDFT, and SL were 288 (±17), 244 (±14), and 349 (±16) ms, respectively. The difference in T1 values between SDFT, DDFT, and SL was statistically significant. T1 values of equine tendons can be determined with magic angle imaging on a clinical MR system using <10 min total scan time. The knowledge of the normal range of T1 values may be useful to identify horses with chronic tendinopathy, where based on the human literature, an increased T1 value may be expected.     

基于微观球体颗粒模型的土水特征曲线研究

When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.     

基于晶闸管软起动的三相异步电动机的研究

文章论述了利用改变晶闸管的触发角来调节异步电动机定子两端电压,进而改变电机的转速和定子电流的软起动的原理。这种软起动方式结构简单,性能好,调试容易,对于要求不高的风机、泵类负载非常适用。