Root exposure effects on water relations of Eucalyptus nitens nursery stock

Bare-root seedlings of Eucalyptus nitens frequently exhibit water stress after planting resulting in leaf lamina damage and reduced leaf area. Two trials examined effects of root exposure and desiccation between lifting and transplanting on post-planting water relations, leaf retention and root growth. Plants with roots exposed on a glasshouse bench initially lost water rapidly. In one trial ₁ declined to around –2.0 MPa within 2.5 h, after which there was no further change with exposure up to 7.5 h. In the second trial, the initial decline in ₁ was more rapid, reaching below –2.0 MPa in the first hour, before remaining stable with continuing exposure up to 4.5 h. A further decline then continued to –4.0 MPa after 7.5 h.Two days after transplanting into potting mix, day – time leaf water potentials in all desiccation treatments had declined to near –2.0 MPa. Hydraulic resistivity, measured as leaf specific resistivity two days after transplanting, increased following exposure for greater than 2.5 h, but there was no further increase between 4.5 and 7.5 h. The increase in resistivity corresponded with leaf water potential declining below –2.0 MPa during exposure.In the second trial, increasing root exposure time resulted in decreased leaf area due to lamina necrosis. Root growth, measured three weeks after planting, was also reduced. and there was also a positive curvilinear relationship between leaf area remaining at three weeks and new root growth. The results are discussed in terms of hardiness and the management of E. nitens seedlings from nursery to plantation.     

大学生日常活动的时空特征研究——以酃湖大学城为例

以衡阳大学城的两所高校衡阳师范学院和湖南工学院为例,开展了在校大学生的日常活动调研,探讨了其日常活动的时间特征和空间特征。结果发现:在时间上,周一至周五,大学生日常活动具有时间上的重叠性和活动方式的确定性以及活动区位的固定性;周六周日或节假日,大学生的日常活动则呈现出较大的差异。在空间上,周一至周五,大学生的活动空间具有局限性;到了周末,其活动范围有所扩大,不同活动类型也会有不同的活动空间。     

紫荆光合日进程及光响应

自然条件下使用LCA-4型便携式光合测定系统研究了紫荆连体叶片的光合日变化及光响应。结果表明:(1)净光合速率的日进程曲线呈“双峰”型,胞间CO2浓度的日进程基本与净光合速率相反,中午胞间CO2浓度增高,表明净光合速率午间降低主要受非气孔限制因素的影响。暗呼吸速率日进程为单峰曲线,中午最高。气孔阻力的日变化曲线是单谷型,午间最低。(2)一天分时段光响应试验表明,饱和光强和表观量子效率上午最高,中午最低,下午有所上升。下午的光补偿点是上午的2倍,中午则是上午的近3倍。不同时段遮光都使得气孔阻力和胞间CO2浓度升高。     

梁弯曲振动边界元法仿真研究初探

简要分析了有限元法和边界元法在梁类零件振动仿真分析中的优点和缺点．梁是常用的机械结构件,在工程机械中的应用非常广泛．应用边界元法对矩形梁弯曲振动进行了仿真分析,当梁的弹性常数不变而横截面的高宽比改变时．其固有振动频率会相应地改变,为通过改变结构参数来改善梁结构的动力学性能进行理论探索．     

晚大新高梨的净光合速率变化规律初探

利用LI-6400便携式光合测定系统对晚大新高梨进行叶片净光合速率测定研究,结果表明,净光合速率日变化在4、5月份为单峰型,在6、7月份为双峰型,年变化为双峰型。净光合速率Pn在光强为18-1 476 μmol·m-2·s-1时随光强的增强而增大, 净光合速率Pn在CO2浓度为31-963 μmol·mol-1时随CO2浓度的增大而升高,叶片在展叶后23 d内,净光合速率Pn呈上升趋势,23 d后Pn值略有下降,然后趋于稳定。不同部位叶片的净光合速率Pn相比,树冠外围中部最高,下部最低。     

水分胁迫对云锦杜鹃光合特性日变化的影响

以盆栽5年生云锦杜鹃苗木为材料,分对照、轻度胁迫、中度胁迫、重度胁迫4组,研究了土壤水分胁迫对云锦杜鹃叶片光合特性日变化的影响。结果表明:随着水分胁迫的加重,云锦杜鹃的光合日变化曲线由典型的双峰型逐渐转变为峰值很小的单峰型,峰值的降低在轻度水分胁迫下由气孔限制引起,而在中度和重度水分胁迫下则由非气孔限制引起。轻度、中度和重度水分胁迫对云锦杜鹃光合特性日变化的影响差异显著。经逐步多元回归得到了净光合速率日变化的回归方程。     

毛竹林内夏季气温变化的特征比较

定位研究位于浙江省富阳市的不同结构毛竹林,2003 年夏季林内气温的日变动状况。结果表明:毛竹林内以日最低气温的变异幅度最大,日最高气温次之,日均气温最小;毛竹纯林内日均最低气温21.20℃,低于竹阔混交林1.32℃,日均最高气温为29.67℃,低于竹阔混交林1.03℃。毛竹林内最低气温主要出现在凌晨 4:00￣6:00,毛竹纯林调节林内最低气温的效应值与栎林相似约-0.3℃,竹阔混交林效应值约1.25℃。方差分析显示毛竹纯林、竹阔混交林、茶园3类林分间的日均气温差异极显著,日最低气温差异显著。     

Application of modal analysis by transfer function to nondestructive testing of wood II: modulus of elasticity evaluation of sections of differing quality in a wooden beam by the curvature of the flexural vibration wave

 The shape of the flexural vibration wave of wooden beams at the first mode was detected using the transfer function. The dynamic modulus of elasticity (MOE) of beam sections of differing quality was estimated from the ratio of the curvature of the wave shape in this section to that of a clear beam. The results were as follows: (1) If a section with a lower dynamic MOE was introduced into a clear wooden beam, the curvature of the wave shape in that section became higher. (2) The ratio of the MOE and the reciprocal of the curvature ratio were highly correlated. (3) The MOE of a defect could be estimated, and the position of the defect could be determined accurately by examining the curvature of the flexural vibration wave shapes. Received: March 22, 2002 / Accepted: May 15, 2002 Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000. This article is translated from the Japanese version, which was published in Mokuzai Gakkaishi 47(5), 2001 Correspondence to:Y. Ishimaru     

基于虚拟样机技术的双横臂独立前悬架振动仿真分析及参数优化

根据振动力学以及多刚体系统动力学原理，分析了悬架系统的振动模型，同时对双横臂独立前悬架做了合理的简化，建立了双横臂独立式前悬架力学及虚拟样机模型，并在虚拟样机软件ADAMS/VIEW模块上进行仿真，在此基础上对前悬架的各个参数进行优化设计，使得悬架振动达到一个最优值。     

河南桧柏嫩枝“全光雾”扦插育苗试验初报

河南桧柏采用嫩枝“全光雾”扦插育苗，试验表明：对难生根珍贵树种用此法育苗可大大缩短育苗周期，提高苗木产量和质量，应大力推广此种育苗方法。