Variation of the dynamic elastic modulus and wave velocity in the fibre direction with other properties during the drying of Eucalyptus regnans F. Muell

Dynamic elastic modulus (E_L) and wave velocity (V) were determined using resonance vibrations from initially green, 100 × 50 mm sample boards of Eucalyptus regnans F. Muell., and after several stages of drying to oven dry. E_L and V were determined from impact induced vibrations and spectral analysis. E_L and V from green wood were positively related to basic density and normal shrinkage, only V was negatively related to green density, and both E_L and V were negatively related to green moisture content and the number of internal checks after drying. The latter relationship has the potential to provide a simple method of segregating highly check prone material. No significant relationships were obtained with collapse. Outside the hygroscopic range, in low shrinkage material, E_L increased little or gradually, while in high shrinkage, collapse prone material, it increased more rapidly, but no clear breakpoint was evident. In the hygroscopic range, E_L increased rapidly in all samples. V increased curvilinearly throughout the entire moisture range, but no difference between collapse prone and non-collapse prone material was observed. Received 16 February 1998     

Variation of sapflow velocity in Eucalyptus globulus with position in sapwood and use of a correction coefficient

Sapflow sensors were used to investigate variation in sapflow velocity at different positions in the sapwood of three-year-old Eucalyptus globulus ssp. globulus Labill. trees. Sapflow velocity was measured at 5-mm intervals across the sapwood by moving two probe sets simultaneously on two opposite radii. Another probe set placed in a fixed position at right angles to the first two sets acted as a control. A sapflow velocity ratio was defined as the velocity given by each moving sensor divided by that given by the static sensor. Correlation between observations of sapflow velocity at different positions exceeded 95%, and the ratio of velocity between any pair of sensors was constant. We observed radial variation in sapflow velocity across the sapwood with the lowest velocities at the center of the tree. Variation due to sensor position was high implying the need for large numbers of sensors for accurate estimates of sap flux. To overcome this need, we used a correction coefficient, namely a simple weighted average of the sapflow ratios with depth in the sapwood, for each fixed sensor. We recommend the use of three probe sets to estimate the correction coefficient. Subsequently, two probe sets can be placed at two fixed positions for routine measurements of sap flux.     

干旱胁迫下佛甲草生理生化变化的研究

为了解佛甲草对干旱环境的适应能力,研究了干旱胁迫下佛甲草组织中MDA,脯氨酸,叶绿素含量及SOD和POD活性的变化。研究结果表明,在轻度干旱胁迫下,植物组织中SOD和POD活性呈上升趋势;在严重干旱胁迫下SOD和POD活性有所下降。MDA含量整体呈上升趋势。干旱处理使叶绿素含量呈现先上升后下降的趋势。脯氨酸含量呈现上升趋势,在严重干旱时,略有下降。     

Modeling stress wave passage times in wood utility poles

Summary The objective of this study was to develop an appropriate mathematical model to study the behavior of the stress waves in the radial-tangential plane of utility poles. It is hoped that such a study could increase the ability to use the sonic testing method in field testing procedures.A two-dimensional plane strain finite element program with dynamic capabilities was used in the study. At this point in the model development, homogeneous isotropic material properties were assumed.The pattern and duration of passage time through the pole was adequately modeled, particularly in regions on the circumference removed by more than 90 degrees from the location of impact. The model studies indicate that with more research it might be possible to develop a field testing procedure using the sonic testing method which could distinguish between large ringshake and advanced decay.This work was performed while the second author was a graduate research assistant in the Civil Engineering Department at Michigan Technological University under a fellowship provided by the Detroit Edison Company. We would also like to acknowledge the contribution by Detroit Edison of equipment and materials     

四种景天属植物高温高湿下的耐湿热性

选择4种景天属植物,研究其在高温高湿胁迫下的形态特征、生理生化变化及其适应高温高湿的机理。结果表明:随胁迫时间延长,植物叶片细胞膜透性增大,叶绿素总量有明显上升又下降趋势,可溶性蛋白含量下降,保护酶系统的平衡受到破坏,膜脂过氧化程度加重,PRO含量总体呈上升趋势。由主成分分析和隶属函数法得出耐湿热胁迫能力大小为:凹叶景天>胭脂红景天>中华景天>金叶景天。     

应力波技术在木材性质检测中的研究进展

本文简要叙述了应力波检测技术的原理以及在木材性质检测方面的研究进展，在此基础上提出用于木材性质检测的应力波技术的发展趋势。     

红树林在低温胁迫下的生态适应性

在浙江温州地区引种红树林试验,探索秋茄、桐花树、老鼠、木榄、海桑等5种红树植物在冬季低温胁迫下的生态适应性。结果表明,秋茄和桐花树的生态适应性较强,其余树种生态适应性较差,需要进行长期驯化。     

冷藏库结构温度应力的计算

作者着重的从理论上分析了冷藏库结构的内力计算方法,并结合实例加以验正。     

Effects of moisture content and temperature on acoustic velocity and dynamic MOE of radiata pine sapwood boards

The effects of moisture content from 17 to 159% MC and temperatures from −71°C to +58°C on resonance-based acoustic velocity and dynamic modulus of elasticity (DMOE) were investigated using 36 boards of radiata pine sapwood. Acoustic velocity decreased with increasing moisture content and temperature, although effects differed noticeably below and above fibre saturation point (FSP). Below FSP, acoustic velocity decreased rapidly and linearly with increasing moisture; whereas above FSP changes in velocity were rather gradual and curvilinear with marked differences in velocity patterns between temperatures below and above freezing. Acoustic velocity decreased linearly with increasing temperature but there was an abrupt discontinuity at the freezing point for wood above FSP. Changes in moisture content and temperature affecting wood density and acoustic velocity led to changes in DMOE, although this relationship was not straightforward because changes of velocity with moisture were linear or curvilinear and depended on whether wood was frozen or unfrozen, whereas changes of density with moisture content were invariably linear. For practical work, it is important to estimate the relative effect of changing moisture content or temperature with respect to standard conditions on DMOE, thus general guidelines were devised to account for significant changes.     

高温胁迫对观赏海棠形态和生长的影响

田间观测8个海棠品种的苗木形态和生长情况。结果表明:高温胁迫下,不同品种田间的形态和生长表现差异显著。耐热性强的品种始终保持较快的苗高和地茎生长速率;耐热性差的品种苗高、地茎的生长速率缓慢。海棠田间的形态表现和苗高生长速率的大小可以作为耐热性的评价指标。8个海棠品种均能在试验地安全越夏,耐热性由强到弱排列顺序为:B10>B4>B5>B7>B19>A2>B9>A4。     

基于应力波和阻抗仪技术的旱柳内部腐朽定量检测

利用应力波和阻抗仪两种仪器对旱柳行道树内部腐朽情况进行检测,应力波法每个断面采用10~12个传感器,阻抗仪法每个断面测试2~4个方向。结果表明：由应力波断层扫描得到的二维图像和由阻抗仪得到的阻力曲线均能较准确地反映活立木内部腐朽的位置、程度等状况,两者对应关系较好;阻抗仪每个测试方向的平均阻力与相应方向应力波传播速度之间呈现一定相关性,相关系数 r ﹥0.5;每个测试断面上的整体平均阻力与应力波平均传播速度之间有显著的相关性,相关系数 r ＝0.817。这为联合两种仪器的检测结果制定一个表征立木腐朽程度的量化指标奠定了基础。     

High temperature and drought stress effects on survival of Pinus ponderosa seedlings

We studied the effects of high temperature and drought on the survival, growth and water relations of seedlings of Pinus ponderosa (Dougl.) Lawson, one of few coniferous tree species that can successfully colonize drought-prone sites with high soil surface temperatures. Temperature profiles were measured with 0.07-mm thermocouples in a sparse ponderosa pine forest in northern Idaho. The soil surface and the adjacent 5 mm of air reached maximum temperatures exceeding 75 degrees C, well above the lethal temperature threshold for most plants. Air temperatures 50 mm above the soil surface (seedling needle height) rarely exceeded 45 degrees C. Pinus ponderosa seedlings that survived maintained basal stem temperatures as much as 15 degrees C lower than the surrounding air. The apparent threshold temperature at the seedling stem surface resulting in death was approximately 63 degrees C for less than 1 min. No correlation between seedling mortality and needle temperature was found, although some needles reached temperatures as high as 60 degrees C for periods of 相似文献   

高温胁迫下21个山茶种质的生理生化响应

为给山茶属植物的资源评价及进一步开发利用提供科学依据,以21个山茶种质为材料,研究了高温胁迫条件下的相对电导率、叶绿素含量、丙二醛含量和SOD活性变化情况。结果表明,随着温度的升高,21个山茶种质的相对电导率升高,且呈"S"型曲线,XSC14等5个种质的半致死高温均达60℃以上。高温胁迫促使21个山茶种质的叶绿素含量均有不同程度的下降。结合MDA含量和SOD活性测定结果,发现XSC20、XSC14耐热性较强,而XSC4耐热性较差。     

Theoretical modeling of the effects of temperature and moisture content on the acoustic velocity of Pinus resinosa wood

To investigate the effects of temperature and moisture content(MC) on acoustic wave velocity(AWV)in wood,the relationships between wood temperature,MC,and AWV were theoretically analyzed.According to the theoretical propagation characteristics of the acoustic waves in the wood mixture and the differences in velocity among various media(including ice,water,pure wood or oven-dried wood),theoretical relationships of temperature,MC,and AWV were established,assuming that the samples in question were composed of a simple mixture of wood and water or of wood and ice.Using the theoretical model,the phase transition of AWV in green wood near the freezing point(as derived from previous experimental results) was plausibly described.By comparative analysis between theoretical and experimental models for American red pine(Pinus resinosa) samples,it was established that the theoretically predicted AWV values matched the experiment results when the temperature of the wood was below the freezing point of water,with an averageprediction error of 1.66%.The theoretically predicted AWV increased quickly in green wood as temperature decreased and changed suddenly near 0 °C,consistent with the experimental observations.The prediction error of the model was relatively large when the temperature of the wood was above the freezing point,probably due to an overestimation of the effect of the liquid water content on the acoustic velocity and the limited variables of the model.The high correlation between the predicted and measured acoustic velocity values in frozen wood samples revealed the mechanisms of temperature,MC,and water status and how these affected the wood(particularly its acoustic velocity below freezing point of water).This result also verified the reliability of a previous experimental model used to adjust for the effect of temperature during field testing of trees.     

低温胁迫对沙棘抗寒生理指标的影响

以6个沙棘品种的1年生枝为试验材料,通过人工冷冻处理,在-15～-40℃设置6个温度梯度,以外界温度为对照,对试验材料的抗寒性进行研究。结果表明,6个品种的抗寒性具显著差异,辽阜2号抗寒能力最强,其次为李沙9号,李沙2号抗寒能力最差。抗寒顺序依次是：辽阜2号〉李沙9号〉实优2号〉实优1号〉辽阜1号〉李沙2号。低温下耐寒性强的品种能保持较高的SOD酶、POD酶活性和较低的MDA含量。因此,SOD、POD、MDA在一定程度上能反映沙棘抗寒性的大小,可作为其抗寒性评价指标。     

Using acoustic wave velocity to select fibre-managed plantation Eucalyptus nitens logs for laminated veneer lumber products

The aims and objectives of this study were to investigate the potential to predict laminated veneer lumber (LVL) stiffness from wood properties measured on trees and logs, and determine variation in log, wood and veneer properties as a function of tree height and age. Log selections were made from trees in three stands that were planned for harvesting at 14, 20 and 21 years of age. Rotary peeled veneer recovery from the logs was on average 65%. After drying, Metriguard testing showed over 50% of the veneer had an estimated dynamic modulus of elasticity (MOE_dyn) above 12 GPa, with 20% above 14 GPa, and that veneer from the second log by tree height had higher MOE_dyn values. In visual assessment to the AS/NZS 2269.0:2012 Standard, no veneer could be utilised in a panels face or subface positions and the older-age stand provided almost four times the volume of usable veneer. Standing-tree acoustic wave velocity (AWV) explained a moderate amount of variance in log MOE_dyn and Pearson correlation coefficients between the (Metriguard) veneer MOE_dyn, log AWV, log MOE_dyn and disc basic density were significant, positive and strong, with log AWV explaining most of the observed variance in log stiffness. A moderately strong and positive linear regression existed between log AWV and veneer MOE_dyn, supporting the use of log AWV tools for the ranking of stiffness in fibre-grown plantation E. nitens logs. Mechanical strength testing of LVL studs extracted from panels manufactured from the trial’s veneer indicated they equalled, and for some tested parameters exceeded, the characteristic design strength values previously published by commercial LVL manufacturers for equivalent size pine products.     

低温胁迫对海南红豆和南五味子幼苗光合特性的影响

对海南红豆和南五味子的1年生实生容器苗进行3℃的低温胁迫处理后,研究其光合特性的变化。结果表明:低温胁迫处理后,海南红豆和南五味子幼苗叶片的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和气孔限制值(Ls)均下降,而叶片细胞间隙CO2浓度(Ci)上升。低温胁迫6 d后的海南红豆各项光合指标的变化幅度均比南五味子大,说明后者比前者更耐寒。     

小径木白桦锯材不同加热方式下含水率的变化

讨论小径木白桦锯材在连续加热和间歇加热方式下含水率的变化规律.结果表明:小径木白桦锯材的干燥速率在含水率15%以后明显降低,前期干燥过程锯材的干燥速率比后期的高2～3倍;间歇加热方式有利于内部水分向外扩散,间歇时间对干燥速率的影响很小;干燥过程中锯材厚度方向上的含水率梯度呈不对称分布,这与小径木的心材占较大比例有一定关系;间歇加热减少了锯材内含水率梯度的变化值,同时减少了应力的产生,从而提高了干燥质量.