Formation of carbon–carbon composite using wood as a precursor

Abstract

The use of wood as structure-giving material may be an effective approach to reduce some barriers for producing high temperature ceramic especially carbon composites. The objective of this study was to develop a simple process for producing carbon–carbon (C–C) composite through porous template result from pyrolysing of wood. Walnut, known to be relatively permeable, was being heat treated under controlled atmosphere. The carbon-template formed was infiltrated with coal tar pitch. Morphological characterization of the resulting composite was carried out by scanning electron microscopy morphology and physical properties of sample were evaluated with determination of bulk density and open porosity. In addition mechanical properties of products were analysed with three-point bending test and Vickers micro hardness. Results showed that bulk density had an uprising trend with increasing the number of densification cycles and subsequently open porosity decreased. Moreover, from mechanical property's point of view, results had a good compatibility with increase in the densification cycles.     

Occurrence of the Microcystins MC-LW and MC-LF in Dutch Surface Waters and Their Contribution to Total Microcystin Toxicity

Microcystins (MCs) are the most frequently found cyanobacterial toxins in freshwater systems. Many MC variants have been identified and variants differ in their toxicity. Recent studies showed that the variants MC-LW and MC-LF might be more toxic than MC-LR, the variant that is most abundant and mostly used for risk assessments. As little is known about the presence of these two variants in The Netherlands, we determined their occurrence by analyzing 88 water samples and 10 scum samples for eight MC variants ((dm-7-)MC-RR, MC-YR, (dm-7-)MC-LR, MC-LY, MC-LW and MC-LF) by liquid chromatography with tandem mass spectrometry detection. All analyzed MC variants were detected, and MC-LW and/or MC-LF were present in 32% of the MC containing water samples. When MC-LW and MC-LF were present, they contributed to nearly 10% of the total MC concentrations, but due to their suspected high toxicity, their average contribution to the total MC toxicity was estimated to be at least 45%. Given the frequent occurrence and possible high toxicity of MC-LW and MC-LF, it seems better to base health risk assessments on the toxicity contributions of different MC variants than on MC-LR concentrations alone.     

响应面法优化烟草游离烟碱的提取工艺研究

为研究提取因素对烟草中游离烟碱的提取得率的影响.在单因素试验基础上,选择提取溶剂中液料比、提取时间、提取温度和摇床转速,进行4因素3水平Box-Behnken试验设计,采用响应面法(RSM)分析了4个因素对响应值(游离烟碱得率)的影响.结果表明,水提取-有机溶剂萃取法提取烟草中游离烟碱的最优条件如下:液料比30∶1(V/m,mL/g),提取时间33 min,摇床转速212 r/min和提取温度34℃.在最优的条件下进行了5次验证试验,游离烟碱的平均得率为7.01 mg/g,与理论值(6.98 mg/g)的误差为0.43％,说明该优化方法可行.     

甘薯叶黄酮微波提取工艺的响应面法优化

用响应面法优化甘薯(Ipomoea batatas)叶黄酮的微波提取工艺,研究了微波功率、微波时间、乙醇体积分数、液固比4个因素对黄酮提取率的影响.并采用Box-Behnken设计对最佳提取工艺进行了优化.结果表明,最佳工艺条件为微波功率200 W、微波时间4 min、乙醇体积分数50％、液固比43∶1(V/m,mL∶g),在此条件下甘薯叶黄酮的提取率为8.082 7％,与预测值8.314 2％基本吻合.     

流苏石斛多糖理化性质·免疫活性及提取工艺研究

[目的]研究流苏石斛水溶性多糖(WDFP)、碱溶性多糖(BDFP)及酸溶性多糖(ADFP)的理化性质与免疫活性差异,并对WD-FP的提取工艺进行优化。[方法]分别以水、碱、酸提取流苏石斛获得WDFP、BDFP和ADFP,比较3者理化性质和免疫活性;并采用响应面法优化WDFP的提取工艺条件。[结果]WDFP、BDFP和ADFP的分子量分别为2.10×105、3.34×106和3.53×106Da,特性黏度分别为68.2、134.9和40.4 ml/g。WDFP主要由葡萄糖和甘露糖组成,BDFP主要由阿拉伯糖、木糖和葡萄糖组成,ADFP主要由木糖和葡萄糖组成。WDFP免疫调节活性最高,BDFP次之,ADFP最低。WDFP最佳提取条件为:提取温度82℃,提取时间51 min,料液比1∶33.3(W/V,g/ml,下同);在此条件下,提取得率为9.68%。[结论]研究结果为流苏石斛多糖的进一步研究提供基础,为其工业化生产提供参考。     

青海省海西州中东部冰雹天气时空分布特征及短临预报指标

[目的]研究海西州中东部冰雹天气时空分布特征和短临预报指标。[方法]利用1960～2010年海西中东部6个气象站的冰雹资料,分析冰雹天气的时空分布特征;基于2006～2010年30次冰雹个例的高空实况资料,利用统计学和天气学方法,分析该区冰雹天气的高空天气形势、地面天气形势和物理量场特征,归纳出冰雹天气形成的短期环流形势和短临预报特征。[结果]海西中东部冰雹天气出现在4～9月,5～8月最多,主要集中在14:00～20:00。天峻地区降雹次数最多,乌兰最少。冰雹灾害主要发生在乌兰和天峻地区。冰雹天气的500 hPa环流形势有3个类型,其中西北气流冷温槽型最多,新疆东移小槽型次之,蒙古低槽型最少。冰雹一般发生在西北气流下,且短波槽、冷中心或冷温槽、急流核三者必居其一。冰雹多产生于高层辐散、低层辐合相配置的形势下,低层充沛的水汽和水汽通量的辐合是形成冰雹的重要条件。[结论]该研究为冰雹天气预报准确率的提高提供了一定参考。     

白腐菌产漆酶培养条件的响应面法优化

[目的]采用Plackett-Burman试验设计法、响应面法,对灰盖鬼伞菌(Coprinopsis cinerea)产漆酶进行了发酵工艺条件的优化研究。[方法]首先利用Plackett Burman设计试验筛选出影响产酶的麦麸、稻草粉和酵母粉3个主要因素。在此基础上,用最陡爬坡路径逼近最大响应区域,再利用Box-Behnken试验设计、响应面分析法进行回归分析。[结果]麦麸、稻草粉和酵母粉浓度与漆酶活力存在显著的相关性,得到最佳培养基条件。当麦麸10.188 g/L、稻草粉9.379 g/L、酵母粉3.613 g/L时,漆酶活力达到729.89 U/ml。[结论]经3批培养验证,预测值与验证试验平均值接近。     

响应面法优化微波辅助提取山楂果胶工艺

[目的]用微波辅助提取山楂叶片果胶,并对提取工艺进行优化.[方法]以山楂叶片为材料,采用微波辅助提取工艺进行果胶提取.在单因素试验的基础上,得到各因素的最佳水平,再采取3因素3水平进行组合设计.[结果]单因素试验得到的3个因素的最佳水平为：pH l.5,微波处理时间2 min,料液比1∶130 g/ml.通过分析得到了山楂叶片果胶提取率与3个影响因素pH、微波处理时间、料液比的回归模型.方差分析结果显示,相关极显著,模型拟合较好.最终得到最佳提取工艺：pH为1.87,微波处理时间为2.11 min,料液比为1：124.34 g/ml,果胶提取率的预测值为6.59％.[结论]研究可为工业生产山楂果胶提供一定的参考依据.