Thermal degradation modeling of flexural strength of wood after exposure to elevated temperatures

Abstract

Wood is being used heavily in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. An important aspect of structural fire design is to assess postfire residual strength of existing structures. This study addresses this issue by developing models to predict strength degradation of wood after exposure to elevated temperature. The objectives were to (a) study the effect of exposure time on bending strength [Modulus of Rupture (MOR)] of wood at elevated temperatures, (b) interpret any relationships between different temperature and time of exposure using kinetics and a statistical approach, and (c) compare the two approaches. Two hundred thirty-two samples in total were tested in flexure as a function of exposure time and several temperatures. MOR of wood decreased as a function of temperature and exposure time. Rate of degradation was higher at higher temperatures. These results were fit to a simple kinetics model, based on the assumption of degradation kinetics following an Arrhenius activation energy model with apparent activation energy of 37.4 kJ/mol. A regression-based statistical model was also developed. The kinetics-based model fit the data better with one less parameter and predictions consistently matched the observed values, making the model preferred over the regression approach.     

番茄再生体系的建立

以"田园6号"番茄子叶和下胚轴为试材,研究激素的种类和浓度对愈伤组织诱导、愈伤组织继代、不定芽分化及生根的影响,并研究了各因素对番茄愈伤组织褐变的影响。结果表明:MS+IBA0.8mg/L+6-BA2.0mg/L诱导所得愈伤最好,MS+IBA1.0mg/L+6-BA0.5mg/L最适于愈伤组织的继代,MS+IAA0.5mg/L+6-BA2.0mg/L和MS+IAA0.5mg/L+6-BA1.0mg/L分别在诱导外质体直接分化不定芽和愈伤组织分化不定芽上效果最佳,MS+IAA0.5mg/L是诱导不定芽生根的理想培养基。外植体种类和光照强度均对愈伤组织的褐化有一定的影响,10mg/L的VC和0.3%的活性炭则能减缓愈伤组织的褐化。     

Effect of antioxidants in controlling enzymatic browning of minimally processed persimmon ‘Rojo Brillante’

‘Rojo Brillante’ is an important variety of persimmon that after removal of the astringency with high levels of CO₂, maintains firmness and sweetness, making possible its commercialization as a fresh-cut commodity. However, the commercial success of the product is limited mainly by enzymatic browning. This work presents the effect of a wide range of antioxidants on enzymatic browning of ‘Rojo Brillante’ persimmon combining in vitro (extracts and precipitates) and in vivo (cut tissue) studies. Preliminary screening of the antioxidants, determined by absorbance and color measurements of persimmon extracts and pellets, showed that 4-hexylresorcinol (Hexyl), citric acid (CA) and calcium chloride (CaCl₂) were effective at controlling browning at 10 mM; whereas, ascorbic acid (AA) required a higher concentration (25 mM). Peracetic acid, cyclodextrin, cysteine, and hexametaphosphate were not effective at controlling browning, even at a concentration of 50 mM. In in vivo studies, AA (1.12%) and CA (0.21%) were the most effective treatments to control enzymatic browning of fresh-cut material, reaching the limit of marketability in 5–7 days, whereas, Hexyl and CaCl₂ did not reach 1 day of storage. The results showed that optimum concentrations in cut tissue did not always correlate with the in vitro studies, indicating that antioxidants have an effect not only in browning reactions, but also in metabolic activity and cell wall changes during wound-induced reactions. The results provide relevant information for further development of minimally processed ‘Rojo Brillante’ persimmon during storage at 5 °C.     

不同温度和CO_2体积分数对丰水梨采后生理指标的影响

为明确丰水梨采后适宜的贮藏温度和CO2体积分数,从果实硬度、膜透性、乙醇质量分数、总酚质量分数、PG活性、PPO活性及果心褐变等方面研究了不同温度和CO2体积分数对丰水梨果实的防褐保鲜效果。结果表明,-1.5℃明显降低果实腐烂率,维持较高的果实硬度,但果实发生不同程度冷害;5℃适合短期贮藏(<60d)。与CK相比,3%O2+1%CO2可较好保持果实硬度和风味,明显抑制PPO活性、乙醇产生和果心褐变,延缓酚类物质降解,较好保持细胞膜完整性;2%CO2防褐保鲜效果次之;3%～5%CO2防褐保鲜效果最差。     

砷污染区黄牛和水牛姐妹染色单体交换和细胞周期动力学的研究

本文以外周血淋巴细胞姐妹染色单体互换(SCE)频率和细胞周期动力学为指标,以较长期(4～13年)生活在砷污染区的黄牛和水牛为对象,对砷在动物体内慢性蓄积所诱发细胞遗传学效应进行了研究。其结果表明,砷污染区黄牛和水牛SCE频率均显著高于对照组,参照有关评价标准,可判为弱阳性,提示在当地污染水平下,黄牛和水牛都诱发了一定程度的细胞遗传学效应。对细胞周期动力学的观察结果表明,砷对黄牛和水牛没有明显的细胞毒性。本试验还报告了正常黄牛和水牛外周血液淋巴细胞SCE的自发频率以及培养72小时各期细胞的正常比率。     

土壤中积累态磷活化动力学的研究Ⅱ.沸石的影响

本文研究了NH4-沸石对潮土和红壤中积累态磷的活化动力学的影响。修正的Elovich公式和双常数速率公式对土壤中积累态磷的活化动力学拟合最好。土壤中添加了NH4-沸石后 ,土壤中积累态磷的活化释放明显增快。NH4-沸石有较强的释磷作用 ,可以促进土壤中积累态磷的活化释放。     

微生物降解动力学参数估计新算法的比较

为了有效地估计较大范围变化的微生物降解动力学参数,发展了基于瞬时精英保护策略的遗传算法(IEPGA)和简单改进遗传算法(IGA),并和多次在参数区间内获取随机初值联用Matlab的lsqnonlin搜寻的算法进行了比较.这些算法利用模拟数据和文献数据,估计了积分形式的Monod模型参数.结果表明,虽然三者均能较好解决这一问题,但考虑到实际运行规模、时间以及最终结果精度,对于较大范围变化的微生物降解参数估计问题,多次(>20次)随机初值联用lsqnonlin的方法相对两种遗传算法更为可行.     

油豆角保鲜试验研究

对油豆角的贮藏技术进行了初步研究，结果表明，油豆角在１０℃下，使用ＴＸＺ熏蒸处理后进行限气贮藏，在贮藏第３０天，商品率为８０．５％，而１０℃对照的商品率仅为３９．７％；１０℃ＴＸＺ的锈斑指数为３６．５％，而１０℃时照为５９．１％，利用ＭＡ贮藏能够有效地延缓油豆角的衰老。     

甘蔗品种抗旱性光合生理指标及其综合评价

利用相关、主成分、聚类和判别分析, 研究有关生理生化指标与甘蔗抗旱性关系. 结果表明: (1)中度水分胁迫下, MDA含量和PMP有不同程度地提高, 而Fv/Fm、 Fv/Fo、ΔFv/Fo、ΔFv/Ft和T1/2 有不同程度地降低, 变化的幅度因供试品种基因型而异. (2)PMP与MDA含量呈极显著正相关, 而与Fv/Fm、 Fv/Fo及ΔFv/Fo呈显著负相关; Fv/Fm与F     

包装对龙眼果实贮藏期间果皮失水褐变和细胞超微结构的影响

研究了(10±1)℃和50%相对湿度贮藏条件下无包装和0.015 mm厚的聚乙烯薄膜袋密封包装的“福眼”龙眼果实果皮失水、果皮褐变和细胞超微结构变化。结果表明，无包装的龙眼果实采后极易失水导致果皮迅速褐变，且褐变随贮藏时间的延长和果皮失水率的增加而升高，果皮褐变指数与果皮失水率呈极显著正相关(P<0.01)。在龙眼果皮失水褐变过程中，果皮细胞的细胞器和膜系统的完整性受到严重的破坏。而聚乙烯薄膜袋密封包装则显著减少了果皮失水和抑制果皮褐变，并保持较好的果皮细胞的细胞器和膜系统的完整性。据此认为，聚乙烯薄膜袋密封包装抑制龙眼果实失水果皮褐变与其维持细胞器和细胞膜的完整性有联系。