238 resultados para 148-896A


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The feasibility of biodiesel production from tung oil was investigated. The esterification reaction of the free fatty acids of tung oil was performed using Amberlyst-15. Optimal molar ratio of methanol to oil was determined to be 7.5:1, and Amberlyst-15 was 20.8wt% of oil by response surface methodology. Under these reaction conditions, the acid value of tung oil was reduced to 0.72mg KOH/g. In the range of the molar equivalents of methanol to oil under 5, the esterification was strongly affected by the amount of methanol but not the catalyst. When the molar ratio of methanol to oil was 4.1:1 and Amberlyst-15 was 29.8wt% of the oil, the acid value decreased to 0.85mg KOH/g. After the transesterification reaction of pretreated tung oil, the purity of tung biodiesel was 90.2wt%. The high viscosity of crude tung oil decreased to 9.8mm(2)/s at 40 degrees C. Because of the presence of eleostearic acid, which is a main component of tung oil, the oxidation stability as determined by the Rancimat method was very low, 0.5h, but the cold filter plugging point, -11 degrees C, was good. The distillation process did not improve the fatty acid methyl ester content and the viscosity.

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农业生态经济系统耦合指农业生态系统与农业经济系统按照其固有的互动关系,在人类适当干预和调控下所形成的有机统一体,其耦合态势可以依据农业资源与农业产业之间的循环链网结构予以表示.纸坊沟流域农业生态经济系统经历了"系统耦合→系统相悖→系统耦合→高层次上系统局部相悖"的过程,流域中农民的需求、国家宏观政策、经济手段和行政手段对农业生态经济系统耦合态势的调控和干扰是引起这一变化的主要因素.针对纸坊沟流域农业生态经济系统耦合过程中存在的问题,今后应建立以林草及其相关产业为中心的耦合体,建设农业生态经济系统优化耦合模式.

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根据米脂县1990—2007年粮食生产的相关数据,对该县耕地、人口和粮食生产动态变化以及粮食总产与其影响因素进行了灰色关联度分析。结果表明,退耕还林还草工程是耕地总面积迅速减少的主要原因;提高粮食单产保障粮食总产是实现粮食安全的最关键因子;持续增长的人口造成耕地的承载压力越来越大,并对该区实现粮食安全提出了更大的挑战。最后,根据分析结果提出了增加科技投入,提高单产,保护耕地,挖掘耕地潜力等措施以保障该区域的粮食安全,为政府部门制定相关粮食安全政策提供科学的理论依据。

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为了确定合理环保的耕作制度,2007~2008安塞田间定位试验黄土丘陵旱作农区大豆(Glycine maxL)、玉米(Zea maysL)、红小豆(Semen Phaseoli)、马铃薯(Solanum tuberosumLinn.)在翻耕化肥(CF)、翻耕有机肥(CM)、翻耕无肥(CN)、免耕化肥(NF)、免耕有机肥(NM)、免耕无肥(NN)等水平下的农田土壤脲酶、蔗糖酶活性。结果表明:在作物花期,大豆、玉米土壤脲酶活性较高,蔗糖酶活性较低,而红小豆、马铃薯则与之相反,差异极显著。到作物收获后,玉米土壤脲酶、蔗糖酶活性增高,增幅在83%以上,而马铃薯、红小豆、大豆三种作物土壤脲酶活性降低,降幅在10%以上,蔗糖酶活性增强,增幅在40%以上。从花期到收获后,免耕降低了土壤脲酶活性,提高了土壤蔗糖酶活性,在黄土丘陵沟壑旱作农区两种土壤酶活性表现较优的作物为大豆、玉米,较优的处理为NM玉米、NF大豆,其田间环保效应为:作物生长期间两种酶活性比较高,收获后两种酶活性则降低,有利于提高作物生长期土壤肥效利用率,减少作物收获后温室气体的排放。

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以延河流域为例,采用环境梯度分层采样技术,对该流域种子植被的区系成分进行调查分析。结果表明,延河流域主要的种子植物区系共涉及57个科、148属、211种,其中裸子植物3科3属3种,被子植54科145属208种。从植物区系科属的分布型看,热带亚热带成分占31.57%,温带成分占28.07%;从属的分布型看,热带亚热带成分占11.72%,温带成分占60.54%。温带成分构成了本区系的主体,本区种子植物区系属温带性质。虽然数量上较整个黄土高原的植物区系成分较少,但这些物种却是该流域种子植物群落的主要构成种,对该区的生态恢复具有更重要的意义。在此基础上,进一步借助物种空间分布与环境要素响应图,分析211个物种分布的环境梯度空间,结果表明,它们可直接满足生态恢复重建的物种选择等需求,具有较好的应用价值。