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131.
132.
133.
热技术方法测算树木茎流的发展及应用 总被引:23,自引:0,他引:23
热技术方法根据其设计原理可分为热脉冲法、热平衡法、热扩散法和激光热脉冲法.回顾利用热技术方法测算树木茎流的历史,概述热技术方法的产生和发展过程,重点论述4种热技术方法的设计原理、最新研究成果和概况,及实际应用中需注意的问题.基于热技术法的特殊优点,对其拓展性应用前景进行了展望:应用热技术方法对林木耗水进行尺度扩展,扩展模型中主导环境因子的导入,不同树种群体耗水量的估测等难点问题的深入研究和解决,将推动热技术理论和研究方法的进步.对现有的研究成果和研究目标进行分析认为,热扩散方法将成为未来几年研究树木液流的重要测算方法. 相似文献
134.
论述了对大体积混凝土的原材料,通过优化配合比设计、提高混凝土设计等级、选用适当外加剂、增设导流管等技术措施和先进的施工工艺,并结合测温加强养护,可以解决大体积混凝土施工中的温度裂缝问题。 相似文献
135.
用热扩散式茎流计测定园林树木蒸腾耗水量 总被引:2,自引:0,他引:2
采用热扩散式边材液流探针和环境自动监测系统对北京3种园林树木的树干液流及主要环境因子进行了一个生长季的同步观测.结果表明,3树种树干液流的日变化呈明显的单峰曲线,晴天的液流速率大于多云天和阴天,紫叶李和悬铃木的日耗水量明显大于元宝枫;对不同天气3树种每h的液流速率与相应的环境因子进行逐步回归分析.结果显示,影响3树种液流速率的主要环境因子是空气温度、空气相对湿度、辐射强度和5 cm土层温度,在不同天气里起主导作用的因子不同,环境因子与树干液流之间的数量关系能较好地预测树木的蒸腾耗水量. 相似文献
136.
本文依据气体分子运动论与传热学的基本理论,在20~100℃温度范围内,讨论了气干材传热过程中,木材内部水分的蒸发与水蒸汽扩散的行为,研究了温度变化对气手材导热系数发生影响的规律.在理论分析与实验数据分析的基础上,推广和扩充以往关于气干材导热系数的讨论,提出了一个描述气干材导热系数温度特性的公式,计算结果与实验值比较符合 相似文献
137.
R. Lal 《Agroforestry Systems》1989,8(2):97-111
Field runoff plots, 70 x 10 m each, were established on a tropical Alifisol in southwestern Nigeria to monitor water runoff,
soil erosion and nutrient loss in water runoff. The non-agroforestry control treatment (A) was established at two levels:
plow-till and no-till systems of seedbed preparation. There were two agroforestry systems based on contour hedgerows of (B)
Leucaena leucocephala and (C) Gliricidia sepium established at 4-m and 2-m spacings. Field plots were established in 1982 and hydrological measurements were made for uniform
maize-cowpea rotation for 12 consecutive growing seasons from 1982 through 1987.
Once established hedgerows of Leucaena at 2-m spacing were extremely effective in reducing water runoff and controlling erosion. Runoff, erosion and nutrient losses
were generally more from maize grown in the first season than from cowpea grown in the second. Mean seasonal erosion from
maize was 4.3, 0.10, 0.57, 0.10, 0.64 and 0.60 t/ha for plow-till, no-till, Leucaena-4m, Leucaena-2m, Gliricidia-2m treatments, respectively. Mean runoff in the first season from treatments listed in the order above was 17.0, 1.3, 4.9,
3.3, 4.3, and 2.4 percent of the rainfall received. There were high losses of Ca and K in water runoff from the plow-till
treatment. In contrast to runoff and erosion, losses of bases in water runoff from agroforestry treatments were relatively
high, high concentration of bases in runoff was probably due to nutrient recycling by the deep-rooted perennials. 相似文献
138.
Paul Joseph Dimitri Bakirtzis Audrey Vieille 《Wood material science & engineering》2015,10(1):130-144
AbstractSaving lives and properties are of primary importance in fire disasters. Unfortunately, current fire detectors are not fast enough to allow the detection of many fires, especially, at the smouldering stages. Some preliminary studies on laevoglucosan (LG), as an important product from cellulose degradation, have shown interesting properties and could be detected by devices classified as “electronic noses” (e-noses). In the present work, the mechanisms of pyrolysis of some ligno-cellulosic materials were investigated using thermo-gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and by a tube furnace with a view to determining the major degradation products from wood, white paper and cardboard samples. Additionally, an odour sensor, made of tin oxide semiconductor thin film, was employed to evaluate its sensitivity in detecting LG. It was found that LG can be readily found among the thermal degradation products of cellulosic materials in question, and that the metal oxide sensor employed was sufficiently sensitive in detecting its presence. Therefore, the work opens up the potential of using such a sensor as an “e-nose” for the early detection of fires stemming from forest product fire loads in storage places and in other enclosures. 相似文献
139.
张家口市区环境空气质量现状及其发展对策初探 总被引:2,自引:0,他引:2
空气质量状况如何,不仅影响到人们的生活质量,同时也影响到当地经济的发展。为了更进一步探讨张家口市区环境质量状况及其发展,从市环保局监测站了解到,张家口市区空气质量污染程度严重,主要污染物是降尘、总悬浮颗粒物及燃煤、化工企业及车辆排放的有毒有害气体。因此,要达到城市环境的可持续发展,就必须加强生态建设,搞好城市绿化,从根本上改善空气质量。 相似文献
140.
Low temperature is one of the major limiting environmental factors which constitutes the growth, development,productivity and distribution of plants. Over the past several years, the proteins and genes associated with freezing resistance of plants have been widely studied. The recent progress of domestic and foreign research on plant antifreeze proteins and the identification and characterization of plant antifreeze protein genes, especially on expression regulatory mechanism of plant antifreeze proteins are reviewed in this paper. Finally, some unsolved problems and the trend of research in physiological functions and gene expression regulatory mechanism of plant antifreeze proteins are discussed. 相似文献