共查询到20条相似文献，搜索用时 375 毫秒
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【目的】研究香榧假种皮开裂过程中细胞壁代谢及结构的变化，为进一步探明假种皮的开裂机制和探寻促进假种皮开裂的措施提供理论依据。【方法】在种实的不同发育时期内，测定香榧假种皮的开裂率和硬度的变化，分析细胞壁组分及相关降解酶活性的变化，结合石蜡解剖结构的观察，揭示假种皮细胞壁代谢与结构变化在开裂过程中的作用；通过测定香榧种实乙烯释放率的变化，并利用外源乙烯利/乙烯作用抑制剂（1-甲基环丙烯，1-MCP）处理分析乙烯在假种皮开裂过程中的作用，探讨乙烯与假种皮开裂的关系。【结果】1）从134～154 DASP(DASP：突破种鳞后的天数)，香榧假种皮的开裂率增加了10倍，硬度降低了61%，假种皮厚度增加了43%；假种皮开裂时（154 DASP），假种皮中靠近内表皮层的树脂道细胞群与其相邻树脂道细胞群之间的薄壁细胞降解，呈分离状态，且中间薄壁细胞层与内表皮层之间存在明显的分离层。2）从134～154 DASP，假种皮的水溶性果胶（WSP）总体上呈增加趋势，而CDTA可溶性果胶（SSP）和Na2CO3可溶性果胶（CSP）则呈降低趋势，其相关降解酶果胶甲酯酶（PME）和多聚半乳糖醛酸酶（PG）活性均呈... 相似文献
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西盟龙竹竹材的化学成分与木材相比,淀粉、糖类及蛋白质等有机物质含量较高,在贮存期间及竹产品使用过程中容易发生霉变和开裂变形等质量问题。本研究分析了西盟龙竹开裂与霉变的原因,并提出了控制西盟龙竹开裂与霉变的措施。研究表明:对竹材原料进行合理选择和干燥处理、对竹材加工过程进行技术处理和质量控制、改变竹材的内应力和含水率可以有效控制竹制品的开裂;对竹材进行高温蒸煮处理、加压除霉处理和硫磺及紫外线处理等方法可以达到对竹材的除霉和控霉效果,提高竹材制品的使用寿命。 相似文献
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混凝土内出现的裂缝按深度的不同,分为贯穿裂缝、深层裂缝及表面裂缝三种。为了保证出现最少的裂缝,就必须在混凝土施工时掌握它的基本性能,并根据实际应用情况采取有效措施,以确保施工质量。 相似文献
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The paper deals with the experimental characterisation of damage evolution within the radial (R)–tangential (T) growth plane of softwood loaded in tension perpendicular to the grain. The reported investigations comprise in-situ monitoring of crack propagation by means of Confocal Laser Scanning Microscopy (CLSM) and evaluations of crack patterns of broken specimens. Three types of notched specimens, representing different crack propagation systems, were tested; for all configurations, both, loading and crack propagation direction were located within the RT plane of wood. The CLSM pictures of broken specimens show distinct differences among the regarded configurations with respect to crack paths. Two different damage mechanisms were identified being rupture of earlywood cell walls in the case of crack propagation in tangential direction and debonding of wood fibers, i.e. rupture of the interface zone between adjacent tracheids, in case of crack progression in radial direction. In the case of an intermediate crack system with an angle of 45° between initial notch direction and radial direction the crack evolution was monitored in-situ during the tension test, whereby the combined action of both basic fracture mechanisms was observed. 相似文献
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本文对现浇混凝土楼板产生裂缝的各种原因进行了分析,并论述了产生裂缝所带来的各种危害;同时提出了一些相应的控制措施,以防止现浇板产生裂缝,保证工程质量。 相似文献
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本文论述了砌体结构裂缝产生的性质和原因 ,并针对裂缝宽度的标准问题及如何防止墙体开裂构造措施提出几点建议。 相似文献
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谈对混凝土裂缝的处理 总被引：2，自引：0，他引：2
工程结构出现裂缝是比较普遍的现象;而结构裂缝大部分是能够通过设计阶段、施工措施来避免的,本文对构件裂缝的成因、预防及处理进行了详细探讨。 相似文献
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K. Frühmann E. K. Tschegg C. Dai S. E. Stanzl-Tschegg 《Wood Science and Technology》2002,36(4):319-334
Mode I and Mode III loading experiments were performed on side grooved CT specimens of two types of Laminated Veneer Lumber
(LVL). Steady state crack propagation was maintained in order to detect complete load displacement diagrams. Fracture behaviour
and influence of fiber orientation were studied and all important fracture mechanical values (stiffness/compliance, microstructural
damage, crack initiation energy, specific fracture energy etc) were determined. Much higher crack initiation energies and
specific fracture energies resulted in mode III loading than in mode I loading for both material types. Under external mode
III loading, crack initiation occurs in mode III and crack propagation however takes place under mode I owing to crack surface
interference. The influence of fiber orientation on fracture mechanical properties of LVL was discussed.
Received 15 September 1999 相似文献
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